EE403 DISTRIBUTED GENERATION AND SMARTGRIDS

EE403

DISTRIBUTED GENERATION AND

SMARTGRIDS

AISHA MEETHIAN

AP,EEE DEPT

ICET

1

Previous year questions

1.Compare Micro grid with conventional utility grid

2.What is Micro grid? List its characteristics

3.What is the function of energy management module in micro grid configuration

4.With neat sketch, explain typical micro grid configuration.

5.What is an active distribution network? Explain its relevancy in micro grid system.

6. Explain the role of central controller in stand-alone and grid connected mode of operation of microgrids.

7.Explain the control functions of micro-resource controller (MC).

8.Draw and explain the typical configuration of an AC Micro grid.

9. Draw and explain the typical configuration of a DC Micro grid.

10.Explain with diagram ,the working of energy router based interconnecting frame work for themicro grid system

2

MODULE -1

Distributed generation – Introduction - Integration of

distributed generation to Grid – Concepts of Micro Grid

- Typical Microgrid configurations - AC and DC micro

grids - Interconnection of Microgrids - Technical and

economical advantages of Microgrid - Challenges and

disadvantages of Microgrid development

Smart Grid: Evolution of Electric Grid - Definitions and

Need for Smart Grid, Opportunities, challenges and

benefits of Smart Grids

3

Background

What is electrical grid?Electric grid is network of synchronized power providers and

consumers that are connected by transmission anddistribution

lines and operated by one or more controlcenters

4

5

Context

Around the world, conventional power systemis facing

the problemsof

Gradual depletion of fossil fuelresources

Poor energy efficiency

Environmental pollution

Located at remote areas, away from

populated areas

Less overall power quality and reliability

Distributed Generation

Generating power locally at distribution voltage level.

Using non-conventional/renewable energy sources like natural gas,

biogas, wind power, solar photovoltaic cells, fuel cells, combined heat

and power (CHP) systems, micro turbines, and Stirling engines and

their integration into the utility distribution network.

This type of power generation is termed as Distributed generation

(DG) and the energy sources are termed as Distributed Energy

Resources (DERs).

The term ‘Distributed Generation’ has been devised to distinguish

this concept of generation from centralized conventional generation.

The distribution network becomes active with the integration of DG

and hence is termed as Active Distribution Network (AND).6

Common Attributes of DG

• Not centrally planned by the power utility, nor centrally dispatched.

• Normally smaller than 50 MW.

• The power sources or distributed generators are usually connected to

the distribution system, which are typically of voltages 230/415 V

up to 145 kV.

7

INTEGRATION OF DISTRIBUTED GENERATION TO

GRID

RES are projected as an alternative to depleting fossil fuel reserve

DER produce clean and ecofriendly electrical energy; hence

exploitation of RES reduces environmental pollution and global

warming.

DG s/m improves overall efficiency by enhancing tri-generation,

co-generation or CHP plants for utilizing the waste heat for industrial

/commercial /domestic applications. Utilization of thermal heat by

CHP plants reduces thermal pollution also.

T & D losses are negligible since they are located close to the load.

8

9

DER connected to utility directly or it can interconnected together to

form microgrids,which can be connected to utility grid as separate

autonomous unit.

Grid connected or stand alone operations of DERs help to improve

overall reliability and PQ.

DG systems offers fuel diversity and meets shortage of power ,which

is considerably valuable

Active Distribution Network (ADN)

• Current trend is bidirectional electricity transportation

• Distribution networks without any DG units are passive since theelectrical power is supplied by the national grid system to the customersembedded in the distribution networks.

• It becomes active when DG units are added to the distribution systemleading to bidirectional power flows in the networks.

• ADN need to incorporate flexible and intelligent control withdistributed intelligent systems.

• In order to harness clean energy from renewable DERs, activedistribution networks should also employ future network technologiesleading to smart grid or Microgrid networks.

10

Active Distribution N/w gaining growth due to

several factors such as:

Increasing desire of policy makers for accommodationof DERs with energy storage devices

Carbon commitment in reducing emissions by 50% by2050.

Provides reliable power

Motivating the distribution n/w operators towardsbetter asset utilization and management by deferral ofreplacement of age old assets etc.

11

MICROGRID

12

Its a low-voltage power distribution system integrated with

distributed energy resources (DERs) and controllable loads,

which can be operated with or without the main grid.

13

Concept of Micro Grid

Microgrids are small-scale, LV CHPsupply networks designed to supply

electrical and heat loads for asmall community, suchasavillage locality.

Microgrid is essentially an active distribution network because it is the

interconnection of DGsystems and different loads at distribution voltage

level.

The generators or microsources employed in a Microgrid are usually

renewable/non-conventional networks with bidirectional electricity

transportation.

From operational point of view, the microsources must be equipped

with power electronic interfaces (PEIs) and controls to provide the

required flexibility to maintain the specified power quality and energy

output.

14

Differences between - Microgrid and conventional power plant

• Microgrid consist of modular renewable DERs of small capacity

while conventional power plants consists of large generators

• Power generated from micro sources is directly fed to distribution

network at distribution voltage.

• Micro sources are located close to customers premises ; power

supply can be carried out with less T & D losses and satisfactory

vtg and freq.

15

Where micro grid suitable

Micro grids are suitable for supplying power

to remote areas where supply from the utility

grid s/m is either difficult to avail due to the

topology or frequently disrupted due to

severe climatic conditions or man made

disturbances.

16

ADVANTAGES

From Utility grid pt of view ,adv of MG is that it is treatedas a controlled entity within Power System. Hence MG canbe integrated into utility grid without hampering security andreliability of the power utility.

From consumer pt of view ,MG helps the to meet theirpower requirement locally with improved power quality,reliability and reduced feeder losses.

From environmental point of view ,MG reduce theemission of green house gases and carbon particulates theirby reduces environmental pollution and global warming.

17

ISSUES FACED:

A number of economic, regulatory and technical issues mustbe resolved to achieve stable operation of MG.

Problem area that need attention- Climate dependent andintermittent nature of DERs ,regulations for operating MGsin synchronism with the power utility and low energycontent of fuels and lack of standards.

Extensive real time and off line researches must be carriedout to study such issues and to solve these problems.

18

How does a micro grid connect to the grid?

A micro grid connects to the grid at a point of

common coupling that maintains voltage at the same

level as the main grid unless there is some sort of

problem on the grid or other reason to disconnect. A

switch can separate the micro grid from the main grid

automatically or manually, and it then functions as an

island.

19

Typical Microgrid configurations

20

Typical Microgrid configurations TheMicrogrid consists of three radial feeders (A, Band C)tosupply

the electrical and heat loads.

It also hastwo CHPand two non-CHPmicrosources andstoragedevices.

Microsources and storage devices are connected to feeders A and C throughmicrosource controllers (MCs).

The microsources have plug-and-play features. They are provided with PEIsto implement the control, metering and protection functions duringstand-alone and grid-connected modes of operation.

Some loads on feeders Aand Care assumed to be priority loads (i.e. requiringuninterrupted power supply), while others are non- priority loads.

FeederBcontains only non-priority electricalloads.

21

Modes of operationThe Microgrid is coupled with the main medium voltage (MV) utility grid

(denoted as ‘main grid’) through the PCC (point of common coupling)

circuit breaker CB4asper standard interfaceregulations.

TheMicrogrid isoperated in two modes:

(1) grid-connected

(2) standalone.

In grid-connected mode, the Microgrid remains connected to the main grid

either totally or partially, and imports or exports power from or to the main

grid. In case of any disturbance in the main grid, the Microgrid switches over to

stand-alone mode while still feeding power to the priority loads.

Thiscanbe achieved byeither

(i) disconnecting the entire Microgrid by opening CB4or

(ii) disconnecting feedersAand Copening CB1andCB3.

22

Operation and managementof Microgrid different modes is controlled through

local micro source controllers (MCs) and the central controller(CC):

Microsourcecontroller (MC)

The main function of MC is to independently control the power flow and

load-end voltage profile of the microsource in response to any disturbance

and load changes.

MC also participates in economic generation scheduling, load

tracking/management and demand side management by controlling the

storage devices.

It must also ensure that each microsource rapidly picks up its generation to

supply its share of load in stand-alone mode and automatically comes back to the

grid-connected mode with the help of CC.

The most significant aspect of MC is its quickness in responding to the locally

monitored voltages and currents irrespective of the data from the neighbouring

MCs.

Control feature facilitates the addition of new microsources at any point of

Microgrid without affecting the control and protection of the existing units.

MC will not interact independently with other MCs in the Microgrid and that

it will override the CC directives thatmay seem dangerous for its microsource.23

(2) Central controller – main function

• The overall control of microgridoperation

• Protection through theMCs.

Its objectives are

To maintain specified voltage and frequency at the load end throughpower-frequency (p-f ) and voltage control

To ensure energy optimization for themicrogrid.

The CC also performs protection co-ordination and provides the power dispatchand voltage set points for all the MCs. CCis designed to operate in automatic ormanualmode.

Twomain functional modules of CCare

EnergyManagementModule (EMM)

Protection Co-ordination Module(PCM).24

Energy Management Module

–EMM provides the set points for active and reactive poweroutput, voltage and frequency to each MC.

Itmust ensure(a)Microsources supply heat and electrical loads to customersatisfaction.

(b)Microgrids operate satisfactorily as per the operational apriori contracts with maingrid.

(c)Microgrids satisfy its obligatory bindings inminimising system losses and emissions of greenhousegasesand particulates.

(d)Microsources operate at their highest possibleefficiencies.25

Protection Co-ordination Module

PCMresponds to Microgrid and main grid faults and loss of grid (LOG) scenariosin away soasto ensure correct protection co-ordination ofthe Microgrid.

It also adapts to the change in fault current levels during changeover from grid-connected to stand-alonemode.

proper communication between the PCM and the MCs and upstream main gridcontrollers. For main grid fault, PCMimmediately switches over the Microgrid tostand-alone mode for supplying power to the priority loads.

Besides, if the grid fault endangers the stability of the Microgrid, then PCMmay disconnect the Microgrid fully from all main gridloads.

Under-frequency and undervoltage protection schemes with bus voltage supportare normally used for protecting thesensitive loads.

PCM also helps to re-synchronise the Microgrid to the main grid after theinitiation of switchover to the gridconnected mode of operation throughsuitable reclosingschemes.

26

The functions of the CC in the stand-alone mode

areas follows:

(1)Performing active and reactive power control of themicrosources in order to maintain stable voltage andfrequency at loadends.

(2)Adopting load interruption/load shedding strategies usingdemand side management with storage device support formaintaining power balance and busvoltage.

(3)Initiating a local black start to ensure improved reliability andcontinuity of service.

(4)Switching over the Microgrid to grid-connected mode after maingrid supply is restored without hampering thestability of either grid.

27

The functions of the CC in the grid-connected mode areas

follows:

(1)Monitoring system diagnostics by collecting information from the

microsources andloads.

(2)Performing state estimation and security assessment evaluation,

economic generation scheduling and active and reactive power

control of the microsources and demand side management

functions by using collectedinformation.

(3)Ensuring synchronised operation with the main grid

maintaining the power exchangeat prioricontract points.

28

AC and DC Microgrids

DERs - wind, tidal and hydro produces variable AC

output voltage

DERs – photovoltaic (PV) system and fuel cells

produces DC output voltage

Interconnecting them gives AC or DC microgrids

AC Microgrid systems

A small AC microgrid is formed within power system by interconnecting

loads and DG units.

DG units generating DC voltage are connected to the AC microgrid through

DC/AC converter.

DG units producing AC voltages are connected through a transformer.

During grid connected mode of operation, the two networks are

interconnected at the PCC, while the loads are supplied from microsources

and if necessary from the utility.

If power produced by DG system is more than power demand by load,

surplus power will be exported to the utility grid.

Comparing with conventional power grid, the major difference is the

emergence of storage devices and DGs.

CC

MC

DG

unit-1

AC

loads

AC/DCconverter

Sensitive

load

DC

loads

AC

loads

PEI

DC/ACconverter

MC

MC

MC

DG

unit-2

DG

unit-3

Storage

device

LVAC line

LVAC lineCB3

CB1

CB2PCC

WECS

Utility grid Micro grid

From

utility

grid

6kV/415V

Distribution

transformer

AC Mircogrid Systems

Typical AC Mircogrid configuration

Hydro-

turbine

PV

arrays

DC Microgrid systems

DC Power system have been Employed for over long distances via sea

cables, industrial power distribution systems, point-to-point transmissions,

telecommunication infrastructures and for interconnecting AC grids of

different frequencies.

Devices like fluorescent lights, mobile chargers, computers adjustable speed

drives(ASDs), radio and many business and industrial appliances need DC

power for their operation.

Available AC has to be converted to DC

In conventional grid systems the DC generated from DGs has to be converted

to AC and connected to network. Then at consumer end, it has to be

converted to DC.

Results in power loss from DC-AC-DC conversion. To avoid it DC micro

grids are formed, interconnecting loads and DC generating DGs.

DC micogrid is made attractive due to the technical advancements in HVDC

operation.

CC

MC

DG

unit-1

DC

loads

DC/ACconverter

Sensitive

load

AC

loads

AC

loads

PEI

DC/ACconverter

AC/DCconverter

MCMC

MC

DG

unit-2

DG

unit-3

Storage

device

LVDC line

LVDC lineCB3

CB1

CB2PCC

WECS

Utility grid Micro grid

From

utility

grid

6kV/415V

Distribution

transformer

DC Mircogrid Systems

Typical DC Mircogrid configuration

Fuel

cellsPV

arrays

• Currently, LVDC network are coming into existence.

• Low voltage DC links are based on bipolar configuration where loads areconnected between tow polarities or across the positive polarity and theground.

• It facilitates– More DG connections

– Guarantees higher power quality to the consumers.

• Measuring Instruments such as Demand Energy Managements (DEMs),advanced Metering Infrastructures (AMIs) and protection systems can also beincorporated into the power converters.

• Integration of these instruments

• Improve power quality

• Reduces system losses and down time

• Reduces protection malfunctions

Power from DC units or substations or storage devices can be transmittedthrough

• Monopolar link configuration (single cable)

• Bipolar link configuration (two cables)

• Homopolar link configuration (three or more cables)

Monopolar DC Link

AC

SYSTE

M

AC/DC

CONVERTER

DC/AC

CONVERTER

AC

SYSTEM

HVDC CABLE

Station 1 Station 2

MONOPOLAR DC LINK CONFIGURATION

Monopolar DC Link

• Employs one HV conductor with a sea-return or ground-return

• Economic way of power transmission

• High current returning through ground causes corrosion of pipelines

and other buried metal objects.

• Metallic return can also be employed – concerns for harmonic

interface and/or corrosion exist.

• Operated with negative polarity – as to reduce corona effects.

Bipolar DC Link

1-Ф or 3-Ф

AC supply

AC

system

AC

systemDG

unit

DC/DC

converter

DC/DC

converter

DC/DC

converter

DC/DC

converter

AC/DC

converterN 220

V220V

+LVDC

-LVDC

Industrial

supply

Station

DC load DC load

Bipolar DC Link configuration

Bipolar DC Link

• Employs two conductors operating – one at +ve polarity and other at -vepolarity

• At the ends the converters are grounded.

• Consists of two sets of power converters of equal ratings at each terminalin series on the DC side.

• Under usual operation both poles works with equal current and so groundcurrent becomes zero.

• Also facilitates for a little time, the monopolar operation with half powerrating of the devices.

Homopolar DC Link

1-Ф or 3-Ф

AC supply

AC

system

AC

systemDG

unit

DC/DC

converter

DC/DC

converter

DC/DC

converter

DC/DC

converter

AC/DC

converterN 320

V320V

+LVDC

-LVDC

Industrial

supply

Station

DC load DC load

Homopolar DC Link configuration

Homopolar DC Link

• Employs two or more conductors with same polarity.

• Usually –ve polarities with metallic return or ground return is preferred.

• Advantages – reduced insulation cost.

• Disadvantages – earth return

• Employs three-wire system due to its highest efficiency factor for DCdistribution from substation to the consumers.

• Consists of 2 outer wires and 1 neutral wire.

• Voltage is divided between two sets formed by these three wires

Comparison of AC and DC Micro grid

Types of Micro grid AC DC

Cost of converters High Low

Controllability Difficult Simple

Reliability

Difficult to guarantee Guaranteed smooth DC

power supply

Load availability High Low

Transmission efficiency Low High

Conversion efficiency Low High

Comparison of AC and DCMicrogrids

Utility

grid

Energy

router

Interconnection of micro grid

Energy router based interconnecting

framework for the micro grids system

ENERGY ROUTER

• Energy router serves as an energy hub to setup an electrical connectionbetween microgrids and the utility grid.

• Its advantages includes :

1) Resolves the problem of instantaneous energy deficiency or surplusby complementary energy exchanges between the neighboringmicrogrids.

2) Isolation guarantees that any frequency or voltage variation at one endof the energy router will have no direct impact on the systems on othersides of energy router.

3) Extensive implementation of the energy routers will encourage theshift of the power system architecture from the conventionalhierarchical framework to a more interactive and connectiveframework.

DYNAMIC INTERACTIONS OF MICROGRID WITH

UTILITY GRID

Due to small capacity stability of utility will not affected much when microgrid is connected.

With higher penetrations MG influence the security and stability of utility grid

Dynamic interactions b/w grid and MG will major issue in management and operation of both the grids.

MGs have to be designed properly to take care of their impacts on utility grid ,such that overall reliability and stability of the whole system is improved

Technical and Economical Advantages of

Microgrid

• Related to environment – Integration of DERs • Reduces no. of Thermal and nuclear power stations

• Reduces total particulate and gaseous emission and nuclear waste

• Reduces global warming and environmental pollution

• Related to Operation and Investment – Physical proximity of loads and microsource helps in

• Enhancing the voltage profile by improving reactive power support

• Reducing T&D Feeder congestion and losses by 3%

• Reducing investments for expansion of generation and transmission systems by proper asset management.

• Related to reliability and power quality

• Decentralization of power generating units

• Better match of Demand and Supply

• Reducing large-scale generation and transmission

• Enhancing restoration process and minimizing down times through black-start operation of micro sources.

• Related to economy –– Utilizes waste heat in CHP mode for heating purpose. Increases energy efficiency

above 80% as compared to conventional power system which has 40% efficiency.

– Integration of several microsources – reduces overall cost.

• Related to Energy Market

• Reduces cost of power

• Microgrids provide supplementary services

• Proper economic balance between DG utilization and network investment decreases the long-term electricity prices by about 10%.

CHALLENGES AND DISADVANTAGES OF MICROGRID

• High cost associated with DERs:

High installation cost of DERs

• Technical difficulties:

lack of technical experience in controlling a huge no ofmicrosources.

Extensive real-time and off line research on management, protectionand control aspects of Microgrids and also on the choice, sizing andplacement of microsources

lack of proper communication infrastructure in rural areas is apotential drawback in the implementation of rural Microgrids.

economic implementation of seamless switching between operatingmodes is still a major challenge

Solutions available for reclosing adaptive protection withsynchronism check are relatively expensive.

Operational and Management Issues of a Microgird

• To maintain power quality – balance between active and reactive powermust be maintained

• Operator must choose the mode of operation within the properregulatory framework

• Load demand, long term energy balance, generation, storage and supplyof energy must be properly planned.

• Control, protection and metering should be based on SCADA systems

• Economic operation must be guaranteed through generation scheduling,economic load dispatch and optimal power flow operations

• System security must be maintained through contingency analysis andemergency operations

• Suitable communication protocols and infrastructure must be employedfor overall energy management, control and protection

PYQ

1. Compare Microgrid with conventional utility grid

2. What is Microgrid? List its characteristics

3. What is the function of energy management module in micro grid configuration

4. With neat sketch ,explain typical micro grid configuration

5. What is an active distribution network? Explain its relevancy in micro grid system.

6. Explain the role of central controller in stand-alone and grid connected mode of

operation of micro grids.

7. Explain the control functions of micro-resource controller (MC).

8. Draw and explain the typical configuration of an AC Microgrid.

9. Draw and explain the typical configuration of a DC Microgrid.

10. Explain with diagram ,the working of energy router based interconnecting frame work

for the microgrid system

11. What is function of energy management module in a microgrid configuration.

52

SMART GRID

SMART GRID: Electricity supply n/w that uses digital communications

technology to detect and react to local changes in usage.

Smart Grid - Definitions

• Is a chance to utilize new communication technologies and information torevolutionize the conventional power system.

• European Technology Platform -

• Is an electricity network that can intelligently integrate the actions of all usersconnected to it – generators, consumers and those that do both-in order to efficientlydeliver sustainable, economic and secure security supplies.

• U.S. Department of Energy -

• A smart gird uses digital technology to improve reliability, security and efficiency(both energy and economic) of the electrical system from large generation, throughthe delivery systems to electricity consumers and a growing number of distributed-generation and storage resources.

Smart Grid - Definitions• IEC -

• Is a developing network of transmission lines, equipment, controls and newtechnologies working together to respond immediately to our 21st century demand forelectricity.

• IEEE -

• Is a revolutionary undertaking-entailing new communications and control capabilities,energy sources, generation models and adherence to cross jurisdictional regulatorystructures.

• In General -

• Is an advanced digital two-way power flow power system capable of self-healing,adaptive, resilient and sustainable with foresight for prediction under differentuncertainties. It is equipped for interoperability with present and future standards ofcomponents, devices and systems that are cyber-secured against malicious attack.

Need for Smart Grid

• Opportunities to take advantage of improvements in electronic

communication technology to resolve the limitations and costs of the

electrical grid have became apparent.

• Concerns over environmental damage from fossil-fired power stations.

• Rapidly falling costs of renewable based sources point to a major change

from the centralized grid topology to one that is highly distributed.

Smart Grid infrastructure will

• Improve reliability of utility grid by reducing power qualitydisturbances and reducing consequences and probability ofwidespread balckouts.

• Allows for the advancements and efficiencies yet to be envisioned.

• Reduces electricity prices by consumers by exerting downwardpressure.

• Better affordability is maintained for energy consumers.

• Greater choice of supply and information is provided to consumer.

• Integrates renewable/non-conventional DERs.

• Improves security by reducing the consequences and probability ofnatural disasters and manmade attacks.

Smart Grid infrastructure will

• Facilitate higher penetration of alternating power generation sources.

• Reduces loss of life and injuries from utility grid related events, thereby

reduces safety issues.

• Integrates electrical vehicles as generating and storing devices, thereby

revolutionize the transportation sector.

• Improves the overall efficiency by reducing losses and wastage of energy.

• Reduces environmental pollution by reducing emission of green house

gases and carbon particulates and provides cleaner power by promoting

deployment of more renewable DERs.

Characteristics of Smart Grid

• Provides better choice of supply and information and quality power

to consumers.

• Enables DSM and demand response through smart meters, micro-

generation, smart appliances, electricity storage and consumer loads.

• Provides information to consumers viz energy usage and prices.

• Allows connection and operation of all generator technologies and

sizes.

• Accommodates storage devices and intermittent generation.

• Reduces environmental effect.

Functions of Smart Grid

• Exchange data on generators, consumers and grids over the internet and process

this data by means of information technology.

• Integrate numerous new smaller electricity generation facilities.

• Balance out the fluctuations in electricity.

• Use a higher degree of network coordination to reconfigure the system to prevent

fault currents from exceeding damaging levels.

• Real-time determination of element’s ability to carry load based on electrical and

environmental conditions.

• Automatic isolation and reconfiguration of faulted segments and independently

operating portions of the T&D system.

• Online monitoring and analysis of equipment performance.

Evolution of Smart Grid

Customer load

……….….…………………....

.

…

.

L

1

L

2

L

3

L

4L

5

L

n

Distribution network

Network of substation

Transmission system

Central generation

Centralised control with

basic network

Basic operation with

no data network

Existing electricity utility grid

Evolution of Smart Grid

The evolution of Smart Grid

Electromechanical

meters

One way automated

meter reading(AMR)

Two way automated

metering infrastructure(AMI)

Smart grid(interconnected network

of micro grids with

Distributed control

Fu

nct

ion

ali

ty

Return on investments

Major components of smart grid

Nerves -AMI(network and meters)

-Advanced visualisation and grid sensing technology

Brains

-DR(via. Dynamic pricing)

-Building energy management systems(EMS)

-Data management systems (DMS)

-End – use energy efficiency

Muscle -DGs from CHP ,renewable and other sources

-Energy storage technologies (including PHEVs)

Bones -New transmission lines(superconducting and HVDC)

-new substation equipment's and transformers

Comparison Between Conventional Utility Grid

and Smart Grid

Comparison of Conventional Utility Grid and Smart Grid

Characteristics Conventional utility grid Smart grid

Active participation consumer Consumers are uninformed and they

do not participate

Consumers are involved ,informed

and participate actively

Provision of power quality for the

division of economy

Response to power quality issues are

low

Rapid resolution of power quality

issues with priority

Accommodation of all generationMany obstacles exist for integration

of DERs

Many DERs with plug-and-play

option can be integrated at any time

Optimization of assets

Little incorporation of operational

data with asset management –

business process silos

Greatly expanded data acquisition of

grid parameters ;focus on prevention

,minimizing impact to consumers


New products, service and

markets

Limited and poorly integrated wholesale

markets ; limited opportunities for

consumers

Mature and well integrated wholesale

markets ; growth of new electricity

markets for consumers

Resiliency against cyber attack

and natural disasters

Vulnerable to malicious acts of terror and

natural disasters ; slow response

Resilient to cyber attack and natural

disasters ; rapid restoration capabilities

Anticipating responses to system

disturbances(self-healing)

Responds to prevent further damage;

Focus on protecting assets following a

fault

Automatically detects and responds to

problems ; focus on prevention ;

minimizing impact to consumers

Topology Mainly radial Network

Restoration Manual Decentralized control

Reliability Based on static ,offline models and

simulations

Proactive , real-time predictions , more

actual system data

Power flow control Limited More extensive


Generation Centralized Centralized and distributed .

Substantial RES and energy storage

Operation and maintenance Manual and dispatchingDistributed monitoring , diagnostics

and predictive

Interaction with energy users Limited to large energy users Extensive two-way communications

System communications Limited to power companies Expanded and real-time

Reaction time Slow reaction time Extremely quick reaction time

Smart Grid Architecture

Opportunities of Smart Grid

• Upgrading and expanding infrastructure to improve

interconnectivity and communications.

• Build up smart tools and technologies to exploit DR, demand

load control and energy efficiency.

• Promote smart grid investment and inform regulatory

frameworks

• Build up infrastructure to guarantee cyber security and resilience.

• Regulations in communication, price and cyber security.

Local Opportunities of Smart Grid

• Integrated Communications

– Data acquisition, protection and control and allowing consumers to interact

– Connect components in real-time for control and data exchange

– Scope for improvement – Substation Automation, DR, Feeder automation,SCADA, EMSs, wireless mesh networks and other technologies, power-linecarrier communications and fiber optics.

• Sensing and measurement

– Support acquiring data for healthy and integrity of grid

– Support faster and more accurate response

• Advanced Components

• Advanced Control Methods

• Improved interfaces and decision support

Regional and National Opportunities of Smart Grid

• Provide high quality power

• Accommodate all generation and energy storage options

• Motivate consumers to actively participate in grid operations.

• Be self-healing

• Resist attack.

Global Opportunities of Smart Grid

• Run the gird more efficiently

• Enable higher penetration of intermittent power generation sources

• Enable electricity market to flourish

Key Challenges of Smart Grid

• Strengthening of utility grid – should ensure high and efficienttransmission capacity to accommodate more energy sources

• Moving offshore – Effective and efficient connection of wind farms,tidal and wave energy

• Developing decentralized architecture – enable harmonious operationof small-scale electricity supply system with total system

• Communications – should allows the operation and trade potentially insingle market

• Advanced Demand Side – Enable consumers to play active role insystem operation

• Integrating intermittent generation – Finding best ways to integrateintermittent generation like residential micro-generation

Key Challenges of Smart Grid

• Enhanced intelligence of generations

• Advanced power monitoring and control – enable synchronizedphasor measurements and control to achieve efficientsynchronization

• Capturing the benefits of DG and Storage – Develop moreadvanced technologies for DERs.

• Ensure reliable operation of SPV-Wind, SPV-fuel cells etc.. Inremote areas.

• Preparing for electric vehicles

Previous year questions

1.Compare Micro grid with conventional utility grid

2.What is Micro grid? List its characteristics

3.What is the function of energy management module in micro grid configuration

4.With neat sketch, explain typical micro grid configuration.

5.What is an active distribution network? Explain its relevancy in micro grid system.

6. Explain the role of central controller in stand-alone and grid connected mode of operation of microgrids.


8.Draw and explain the typical configuration of an AC Micro grid.

9. Draw and explain the typical configuration of a DC Micro grid.

10.Explain with diagram ,the working of energy router based interconnecting frame work for themicro grid system

78

THANK YOU

MODULE – 2

Distributed Energy Resources

&

Control of MicrogridAISHA MEETHIAN

AP,EEE DEPT

ICET

Module Contents Hours

End.

Sem.

Exam.

Marks

II

Distributed energy resources: Introduction -

Combined heat and power (CHP) systems - Solar

photovoltaic (PV) systems – Wind energy

conversion systems (WECS) - Small-scale

hydroelectric power generation - Storage devices:

Batteries: Lead acid, nickel metal hydrate, and

lithium ion batteries, ultra-capacitors, flywheels

Control of Microgrids: Introduction to Central

Controller (CC) and Microsource Controllers

(MCs) - Control functions for microsource

controller, Active and reactive power control,

Voltage control, Storage requirement for fast load

tracking, Load sharing through power-frequency

control

6 15%

Previous year questions1.Explain the operation of a lead acid battery and mention its merits and demerits.

2.Explain the working and operation of different Wind Energy Conversion Systems. Also mention the advantages and disadvantages


4.Explain the merits and demerits of solar PV plant

5.Explain the voltage control method in Microgrid with Q-V diagram

6.Explain the load frequency control in Microgrid with p-f diagram

7.Explain how the real and reactive powers are controlled in a power inverter based energy source.

8.With the help of block diagrams, explain the classification and working micro turbines.

9.Explain the components of an Ultra capacitor. Mention its advantages and disadvantages.

10.Explain the working flywheel energy storage (FES) system.

11.Discuss the working principle and operation of ultra-capacitor with necessary diagram.

12Explain the functions of Central Controller in Microgrid.

13. Explain how active and reactive power control is performed in Microgrid.

14. Elaborate the concept of load sharing through power-frequency control in Microgrid

Distributed Energy Resources

Introduction• DERs – Distributed Energy Resources – Renewable or non-renewable electricity

generators

– Employed in microgrids or DC systems

• Microgird aims to unite all high-efficiency combined Heat Power systems and

Renewable or non-renewable DERs.

• Low carbon DERs generate clean power & reduce environmental pollution

• CHP-based, DERs utilizes heat from CHP and causes energy efficient power

generation.

• CHP-based DERs– Stirling Engines

– Micro-turbines

– Fuel cells

• Other DERs– Wind Energy Conversion Systems (WECS)

– Solar-Photovoltaic Systems (SPV)

– Small-Scale hydroelectric generation

• Choice of DERs depends on– Topology and climate of the region

– Availability

• Microgird also consist of different storage technologies viz.– Batteries

– Fly wheel

– Ultra-capacitors

– Bio-fuels

• Wide range of control is necessary for a microgird, to guarantee– Optimal operation,

– System Security

– Emission Reduction

– Seamless transfer

Combined Heat Power – CHP Systems

• CHP or cogeneration systems are most promising DERs

• Main idea is to utilize the waste heat and achieve energy-efficient

power generation.

• Heat – by product is captured and utilized by local domestic

heating applications.

• So CHPs are located very close to loads.

• Heat absorbed by absorption chillers at moderate temperatures are

used for cooling purpose.

• Tri-Generation or Poly-Generation

– Simultaneous production of electricity, heat and cooling

• CHPS offer 80% whereas conventional generation gives only 35%.

Combined Heat Power – CHP Systems• Heat transported to long distances through insulated pipes, reduces

overall %efficiency.

• When used locally, it is effective and efficient.

• Electricity transmission to large distances inquires lesser energy loss.

• So, CHPs are connected near to heat loads and at remote distance from

electrical loads.

• CHPs are employed in

– Hospitals

– Oil refineries

– Prisons

– Industrial plants

– Paper mills

Micro – CHP Systems

• Installed in small premises – small commercial buildings or homes.

• Generate heat as primary product and electricity as byproduct.

• Energy generation depends on heat demand of consumers.

• Produces more electricity frequently, than demanded

• Consists of micro-turbines coupled to high-speed single-shaft permanent magnet

synchronous machines (PMSM) with magnetic bearings or air foil.

• Electrical loads are connected to CHPS through Power Electronic Interfaces (PEIs)

• CHPs are incorporated with own heat recovery system to extract low and medium

temperature heat.

• Micro-CHPs are cheap, reliable and robust.

• Capacity – 10 kW to 100 kW

• Primary fuel – propane – liquid / natural gas – which allows complete combustion with

low particulates.

Working of Micro – CHP Systems

• Air from CHP is passed through centrifugal compressor to increase

incoming air pressure

• Temperature is then increased by passing compressed air through heat

exchanger.

• Then in combustion chamber, hot compressed air is mixed with fuel and

burnt.

• By expanding the high temperature combustion gases in the turbine,

mechanical power is produced.

• Then AC electrical power is produced though PMSM.

• Generated AC converted to DC using converters and then reconverted to

AC using inverters, when needed.

Advantages of Micro – CHP Systems

• Full utilization of waste heat

• Flexible in matching several small heat loads, as the level of heat

generation is small for individual micro-CHP systems

• Combined generation of electricity and heat can be optimized by

designing a micro-grid by mixing non-waste and waste heat

producing generators.

Challenges of Micro – CHP Systems

• For enhanced utilization of heat generated, fuel cells may be used.

• Attention must be paid to improve the flexibility of combinedly

generating heat and electricity.

Technologies of Micro – CHP Systems

• Micro-CHP systems are based on the following technologies

– Internal Combustion (IC) Engines

– Stirling Engines

–Microturbines

– Fuel Cells

Internal Combustion (IC) Engines

• Air-Fuel mixture is burnt in combustion chamber – with / or without

oxidizers.

• Combustion creates high pressure and temperature gases

• These gases are expand and acts on movable bodies viz. piston or

rotors.

• IC Engines

– Continuous combustion engines (Gas turbines, Jet engines, rockets etc.)

– Intermittent combustion engines (Bourke’s engine, Wankel engine and

reciprocating engine).

• Fuels commonly used – Gasoline, Diesel, Petroleum gas and

Propane Gas

Internal Combustion (IC) Engines

• Other fuels that can be used are – liquid and gaseous

biofuels (bio-diesel & ethanol etc.)

• Ignition – starts the fuel combustion process.

• Ignition Type - Depends on type of fuel used

–Compression Ignition

–Spark Ignition

Stirling Engines

• Heat engine with closed-cycle piston

• Working gas is contained permanently in the cylinder.

• External combustion engine – heat generated by the combustion process is used to heat a

separate working fluid which then acts on movable parts.

• Also heat can be supplied from non-combustible sources – geothermal, solar, nuclear and

chemical energy.

• Uses – external heat sink and source – but large temperature difference between them

• Working fluid used – Hydrogen or Helium (fixed quantity) + air

• Under normal operation, engine is fully sealed (closed) and gas cannot enter or leave the

engine.

• Valves are not needed like other piston engines – to control the exhaust and intake of gases.

Four main process

Cooling

Compression

Heating

Expansion

Stirling Engines

Achieved by moving working gas front and back between

cold and hot heat exchangers

Cold heat exchanger – thermal contact with external heat sink (radiator)

Hot heat exchanger – thermal contact with external heat source (fuel burner)

Temperature variation of gas causes equivalent variation in pressure, so gas expands and compress

alternately with the motion of piston.

Power Stroke

Gas expands on heating in sealed chamber and acts on piston causes power stroke

Return Stroke

Gas gets cooled Pressure drops.

To compress the gas only less power is needed in return stroke

Net Power = Work difference between Power Stoke and Return Stroke

Stirling Engines

Stirling Engines

Alpha Stirling Beta Stirling Gamma Stirling

Stirling Engines• Advantages

– Temperature difference is used for the operations

– Mechanical power generated by heat source

– Electrical power generated as byproduct

– Overall process is effective and efficient

– Energy conversion efficiency is 80%

– Quieter in operation

– Reliable and energy efficient

– Requires less maintenance

• Drawbacks

– More capital costs

• Applications

– Widely used where optimization is needed between capital cost per unit and capital cost per kW.

– Used where IC engines are incompatible – Ex: domestic refuse, agricultural waste and solar energy

(where IC engines

Microturbines

• Extensively used as energy producers in CHPs and as

generating units in DG systems

• Small and simple gas-cycle turbines

• Output range – 25 – 300 kW

• Employs performance improvement techniques viz NOx

emission technologies, recuperation and use of ceramic

materials for hot sections

• Types:

–Single-Shaft

–Split-Shaft

Single-Shaft Microturbines

Split-Shaft Microturbines

Single-Shaft Microturbines

• Turbine and compressor are mounted on same shaft of high-speed

synchronous machine

• Speed range – 50,000 to 120,000 rpm

Split-Shaft Microturbines

• Generator connected to power turbine via a gear box

• Speed range – 3,000 rpm

Microturbines

• Designed for extended period of operation

• Needs less maintenance

• Can be used for standby or demand based for cogeneration and

peak demand periods

• Uses fuels – diesel, propane, natural gas, kerosene and/or bio-

fuels

Features of Microturbines• Smaller in size compared to other DERs

• Fuel to electricity conversion – 25 to 30% efficiency

• Energy conversion efficiency – more than 80% (as waste heat can be used for

CHP applications)

• No emissions – NOs emissions are < 7 ppm

• Life – 45,000 hours minimum & 11,000 hours between major overhauls

• Operation economy

– System costs – lower

– Electricity costs – competitive compared to others

• Fuel flexibility – capable of using alternate fuels

• Less noise and reduced vibrations

• Simple installation procedures

Microturbines• Uses induction generator or permanent magnet synchronous generator

• Coupling split-shaft with generator eliminates use of power converter

• Drawbacks

– PMSM – high cost, centrifugal forces, thermal stress, rotor losses and

demagnetizing phenomenon etc.

– Induction generators – speed variation with load and cannot be connected with

grid without PEIs

–PEIs injects harmonics Reduces power quality

– Instead of PEIs, Gear boxes are recommended due to less failure

chances – but reduces efficiency, as gear box consumes fraction of

generated power.

Main part of Microturbines

• Turbine

• Alternator

• Power Electronic Interfaces

• Recuperator

• Control and communication

Turbine

• High Speed

– Single-shaft

– Split-shaft

Alternator

• Single – shaft – directly coupled with turbine

• Split-shaft – PMSM or induction generator coupled through gearbox

Power Electronic Interfaces

Recuperator• Improves energy efficiency by recovering waste heat.

• Before discharge air enters combustor chamber, heat from exhaust gas is

transferred to the discharge air by Recuperator.

• Thus reduces amount of fuel required to raise the temperature of discharge air.

• Complex design and manufacturing process – operates under high temperature

and pressure differentials.

• Exhaust heat – used for – drying processes, water heating or absorption chillers

for air conditioning.

• Single – shaft – Converts high frequency to low (1,500 to 4,000 Hz to 50Hz).

• Split-shaft – gearbox reduces PEIs.

Control and Communication

• Includes

– Turbine control mechanism

– Inverter interface

– Start-up electronics

– Signal conditioning

– Instrumentation

– User control communications

– Data logging and diagnostics

– Single-shaft

– Split-shaft

Fuel Cells

Basic Construction of Fuel Cell

Fuel Cells

• Converts chemical energy to electrical energy

• Has 2 electrodes and 1 electrolyte

• Acts similar to storage battery but the reactants and products are not

stored.

• the reactants and products are directly fed to/from the cell.

• Fuel – Hydrogen – rich & oxidant (generally air) are supplied

separately to the anode and cathodes respectively.

• Electrochemical oxidation and reduction takes place in appropriate

electrodes and generates electricity.

• Byproducts – water and heat

Fuel Cells

• Advantages

– Releases fewer CO2 and NO2 per kW of power generated

– Higher efficiency

– Lower fuel oxidation temperature

– Environment friendly energy source

– Free from noise and vibrations

– Robust and low maintenance

Fuel Cells• Features

– Doesn’t become outdated due to fuel unavailability

– 1 cell generates voltage less than 1 V

– Depending on the type and system configuration efficiency can be ranged

from 36% to 60%.

– Employing heat recovery equipment can improve efficiency to 85%.

• Employs seam reforming of liquid hydrocarbons (CnHm) – Hydrogen-rich fuel.

• seam reforming is used because storage of hydrogen is expensive and

hazardous.

• Seam reformers offer running hydrogen stream without needing hydrogen

vehicles for distribution or to use bulky pressurized hydrogen tanks.

Fuel Cells

• In the reforming process, the following endothermic reaction takes place, in

the presence of catalyst

CnHm + nH2O nCO + 0.5*(m+n)H2

CO + H2O CO2 + H2

• Carbon Monoxide and steam combines together through the water gas

shift reaction to produce more hydrogen.

Flows and Reactions in Fuel Cell

Challenges in Reformer - Fuel Cell Systems

• Reforming takes place at high temperatures, so fuel cells need costly

temperature resistant materials and have high startup time.

• Reforming fuels like biodiesel and ethanol may not be available,. This

inadequacy causes delay in supply of continuous stream of hydrogen

• Sulphur compounds might poison the catalyst and cannot be run on ordinary

gasoline systems.

• Catalysts are very expensive

• CO formation might poison the fuel cell membrane and degrade the

performance, so needs integration of CO removal system.

• Purity of hydrogen product determines thermodynamic efficiency and range is

of 70% to 85%.

Types of Fuel Cells

• Proton Exchange Membrane Fuel Cell (PEMFC)

• Phosphoric Acid Fuel Cell (PAFC)

• Molten Carbonate Fuel Cell (MCFC)

• Solid Oxide Fuel Cell (SOFC)

Proton Exchange Membrane Fuel Cell (PEMFC)• Electrolyte – solid poly membrane built-in between two porous platinum –

catalyzed electrodes

• Operating temperature determined by poly membranes– Iconic conductivity

– Thermal stability

• Iconic conductivity of proton conducting polymer electrode– Is given by liquid water

– Operating temperature kept below 100ºC

– Helps PEMFC to reach steady state operating condition quickly

• Higher power densities are achieved by operating PEMFC at high elevated

pressure (up to 8 atm)

• Fuel used – pure hydrogen-rich fuel obtained by reforming hydrocarbon

• Carbon monoxide content above 50 ppm in fuel

– is poisonous to the catalyst

– Causes severe degradation in cell performance

Proton Exchange Membrane Fuel Cell (PEMFC) Contd….

• CO should be removed from fuel by additional fuel processing scheme

• Electrical Efficiency achieved by PEMFC – 50%

• Overall efficiency – 42%

• Temperature rise from waste heat produced is too low

– Cannot be used for fuel reforming process

• PEMFC – lowest electrical efficiency and depends on type of reforming

process

• Power rating – 500 kW

• Employed for– Residential - 2 to 10 kW

– Commercial buildings – 250 to 500 kW

– Light & medium duty vehicles – 50 to 100 kW & 200 kW

– Battery replacements

– Portable or small generators

Phosphoric Acid Fuel Cell (PAFC)• Electrolyte – Concentrated Phosphoric acid

– Provides transportation medium for transfer of hydrogen ions from the cathode and conducting

the ionic charge between the two electrodes.

– Electrolyte is liquid – so migration and evaporation must be monitored carefully

• CO is reduced by 2% by the use of platinum electro-catalysts in electrodes

• Factors affecting cell performance– Corrosion of separator plate by phosphoric acid and carbon support for the catalyst layer

– Electrolyte flooding due to changes in material properties and sintering of platinum electrodes at

elevated temperatures.

• Operating conditions– Pressure – 8 atm

– Temperature 200ºC

– Provides• Steam output – 1 atm pressure

• Hot water - 60º to 120º C

• Electrical Efficiency – 37 % to 42 %

Phosphoric Acid Fuel Cell (PAFC) contd…

• Low electrical efficiency

• Life time – 40,000 hours at ambient temperature range of 32º to

49º C

• Extremely tolerant to fuel contaminants

• Have cogeneration potential

• Preferred in CHP units

• Employed in

–Schools, hospitals and commercial buildings which needs

•High quality power

•High quality heat or premium power services

Molten Carbonate Fuel Cell (MCFC)• Electrolyte – liquid form of – lithium-sodium or lithium-potassium

• Cells are arranged as flat, planar configured sacks

• CO2 is formed at anode and needed at cathode

• CO2 is transferred to cathode inlet from anode exhaust by any of two methods– Mixing air with anode exhaust

– Separating CO2 from other type of exhaust gases – Product Exchange Device

• Operating conditions– Temperature 650ºC

• Assists internal reforming of hydrocarbon fuels

– Provides• Improved efficiency and system design

• Electrical Efficiency – 44 %

• Resists CO poisoning inherently, so can be operated with different types of fuels

• High operating temperature needs– Temperature and corrosion resistant materials – steel alloys, ceramic composites and

semiconducting oxides

• Life time is lowered due to–Hardware corrosion

– Electrolyte management

–Cathode dissolution in the electrolyte

• High quality heat produced is used for– industrial processes

– Internal methane reforming

–Cogeneration

– Fuel processing

• Employed in CHP units of

–Schools, shopping malls, small to medium sized hospitals,

hotels, food, plastic, metal, paper and chemical industries

Molten Carbonate Fuel Cell (MCFC) contd…..

Solid Oxide Fuel Cell (SOFC)• Electrolyte – solid state material

• Electrolyte layer – solid yittra-stabilized zirconia ceramic material

• Operating conditions– Temperature 1000ºC

• Two phases of phase deign – Solid and Gas – for transfer at electrolyte – electrode

interface– Eliminates electrolyte management and corrosion concerns

• After reaction at cathode, generated oxygen ions migrate to anode through the

electrolyte layer where hydrogen is oxidized

• High temperature offers sufficient heat for the endothermic reforming reaction

• More tolerant to fuel impurities– CO and hydrogen fuels can operate directly at the anode

– External reformers not needed to produce hydrogen

– SOFC attracts fuels like biomass or coal gasification

• SOFC and Gas Turbine (SOFC – GT) provides efficiency of range 70 % to 75%

Solid Oxide Fuel Cell (SOFC) contd….

• Life time – 10 to 20 years– Highest among all fuel cells

• Suitable for CHP applications, DG systems and small portable

generators

• Geometrics of SOFC– Planar design – small power generation applications

– Tubular design – DG and large capacity cogeneration applications

• Drawbacks– Requirement of strict materials for critical cell components due to high operating temperature

– Increased cost of materials

• Materials used–Metal – ceramic composites, exotic ceramics and high-temperature alloys

Wind Energy Conversion System (WECS)

• WECS converts wind energy into electrical energy by employing

– wind turbine

– induction generator

– Multiple ratio gear box – couples generator and turbine

• The major parts are:-

1. ROTOR

2. NACELLE

3. TOWER

• The generators and the transmission mechanisms are housed in nacelle.

• Rotor may have two or more blades.

• The kinetic energy of wind flow is captured by rotor blades in wind turbine and then through a

gearbox it is transferred to the induction generator side.

• Mechanical power developed by the wind turbine drives the drive generator shaft to generate electric power .

• Gear box converts – slow speed of turbine to higher speed of generator

• By using supervisory control, metering and protection techniques output voltage and frequency is kept within specified range .

• Wind turbines configurations

– vertical axis

– horizontal axis

• Factors governing output power

– wind speed

– Shape

– size of the wind turbine

Wind Energy Conversion System (WECS) contd…

The power developed by WECS is given by P=(1/2Cp(V3)A)– Where P is power (W)

– Cp is power coefficient

• ρ is air density (kg/m3)

– V is wind speed (m/s)

– A is swept area of rotor blades (m2)

• The total energy extracted by rotor of the turbine is given by power coefficient Cp.

• Cp varies with rotor design and tip speed ratio (TSR).

• Cp is the relative speed of wind and the rotor, and has a maximum practical value of about 0.4.

• Fluctuation in wind speed creates dynamic variation in the torque output and caused by

– turbulence

– wind shear

– tower shadow

• Torque variation lead to a flicker in the generated voltage and dynamic perturbation in the output power.


• Voltage flicker and voltage variation in a constant speed wind

turbine cause problem in the network.

• variable speed wind turbine system produces

– stable bus voltage

– smoother output power

– lower losses

• Main problem of WECS is - net capacity is lesser than the name

plate capacity

– due to the discontinuous nature of generation of generation and energy

consumption in the generating plant


Wind Turbine Operating System

Wind turbine operating system is classified into two:-

Constant Speed Wind Turbine (CSWT)

Variable Speed Wind Turbine (VSWT)

Constant Speed Wind Turbine

• operate approximately at constant speed - prefixed by the

generator design and gear box ratio.

• The control schemes maximize the power output at high wind

speeds by regulating the pitch angle or captures energy by

controlling the rotor torque

• CSWT classified as

Pitch regulated turbine

Stall regulated turbines

• Pitch regulation is used for starting up constant speed pitch regulatedturbines.

• The turbine blades are designed to operate near the optimal TSR with a fixedpitch for a given wind speed.

• Increase in wind speed increases angle of attack

– large portion of the blade starting at the blade root enters the stall region

– limits power output and rotor efficiency

• Stall regulated wind turbines are simpler

– not able to capture wind energy efficiently at wind speed other than the designed speed

CSWT contd…….

Advantages of CSWT:

Higher Reliability - due to fewer parts

Simple and robust in construction

Electrically efficient

Less capital cost

No frequency conversion

no harmonics are injected into supply

Disadvantages of CSWT

• Aerodynamically they are less efficient

• Noisier in operation

• Prone to mechanical stress

Variable Speed Wind Turbine (VSWT)

• It controls the turbine operation by two methods

1. Blade pitch changes

2. Speed changes

• The control strategies employed are

1. Power limitation strategy

2. Power optimization strategy

• In power limitation strategy the output power is limited to the rated value by

changing the blade pitch

• Power Limitation strategy is

– employed for the wind speeds higher than the rated value

– reduces the aerodynamic efficiencies

• Power optimization strategy

– energy capturing is optimized by maintaining a constant speed related to

the optimum TSR.

– utilized when the wind speed is lower than the rated value

• If the speed is altered due to variation in load, the generator might be

overloaded for wind speeds higher than nominal value

– Controlled by generator torque control method

VSWT contd….

Variable Speed Pitch Regulated Wind Turbine

Advantages of VSWT• Low transient torque

• Aerodynamically efficient

• Subjected to less mechanical stress

• high energy capture capacity

• do not go through voltage sags or synchronization problems due to stiff electrical

control

• The electrical system provides effective damping – eliminates mechanical

damping

Electrical efficiency is on lower side

Require complex control strategies

Expensive

Disadvantages of VSWT

Solar Photovoltaic System

Out of all renewable DERs, solar energy has gained more

attention due to:

– Availability without any cost

– Cleanness

– Requirement of less maintenance & monitoring

– Inexhaustible nature & can be generated locally which in turn avoids

long transmission lines for power transfer.

• Solar energy

– radiated out from sun

– byproduct of nuclear fission reaction

• Speed of solar radiation is equal to speed of light

– eight minute is required to reach on earth surface from sun

• Terrestrial Solar Radiation - part of solar energy produced by sun

reaching the surface of earth

• Extra Terrestrial solar Irradiation - Part of solar energy which won’t

reach the earth surface

Solar Energy

• Solar Constant (Hsc) - The amount of solar irradiation reaching the

earth surface

– The maximum possible energy received over unit area in unit time which is

kept just outside the atmosphere perpendicular to incident solar irradiation at

a mean distance from earth to sun.

• Typical value of Hsc -1353W/m2.

• Solar irradiation falling on earth surface can be divided into two

components:

– Beam radiation or direct radiation

– Diffused radiation

Solar Energy contd…

• Beam Radiation or Direct Radiation:

– solar irradiation which falls on earth surface directly without undergoing any

change in the route from sun to earth.

• Diffused Radiation:

– solar radiation which falls on the earth surface after undergoing reflection &

refraction by particle present in the atmosphere.

Solar Energy contd…

Solar cell

Solar Cell

–Basic component of PV panel

–made of pure silicon wafer

–works on the principle of photovoltaic effect

• the phenomenon by which incident solar radiations are

converted into electrical energy directly.

i. Incident photons must be absorbed into the active part of semiconductormaterial & potential energy of the incident photons must be transferred tovalence shell electrons. Further with this particular energy, electrons must bedislodged from the bond & freed.

ii. The dislodged electrons having extra energy must be carried to the edge ofsemiconductor material so that it will be available for carrying to the load.This is fulfilled by creating an internal field in the material by forming p-njunction by a process known as doping.

iii. The charged particles available at the edge of material must be carried to theload through an external circuitry.

Conditions to be satisfied for obtaining useful power from solar cell:

Solar cell connected to load

Top layer of wafer is doped with n-type dopant - phosphorus.

Outermost shell of phosphorus atom contain 5 electrons, 4 combines with siliconatom and remaining one move freely in the crystal lattice.

Base layer of silicon wafer is doped with p-type dopant -boron.

Outer layer shell of boron atoms contains three free electrons, these electronscombines with the silicon atom leaving a hole, a positive charge.

Electron from the neighboring bond jumps into the hole, leaving behind a positivecharge; hence a positive charge moves freely in the crystal lattice.

Solar Cell

When p-type and n-type layers join together, electrons diffuse across the junction

and create a barrier which prevents further electron flow.

The junction formed at the point of contact of p-type and n-type material is known

as p-n junction.

An electric field is produced at p-n junction due to imbalance in electric charge.

The silicon cell is coated with anti-reflective coating to enhance the absorption of

solar irradiation.

Grid lines are drawn across the cell to collect electrons, which are released from

valance shell absorbing solar irradiation.

Solar Cell contd…..

Solar Cell contd…..

• These grid lines are then connected to metallic contacts provided at bothends of the solar cell.

• Metallic contact act as the end terminal for external connection to load.

• When solar irradiation falls on the surface of panel photons with energygreater than band gap dislodge electrons from the valance band and createelectron hole pair.

• Electron hole pair diffuse across the junction and swept away in theopposite direction by electric field across the junction and are fed to theload.

Types of solar cell

• Solar Cell – made of Silicon – SiO2 – non-toxic

• Types of solar cell

–Categorized based on the Materials used for manufacturing solar cell:

• Mono crystalline silicon

• Polycrystalline silicon

• Amorphous silicon

• Copper Indium Gallium di-Selenide (CIGS)

• Cadmium Telluride (CdTe)

Efficiency of solar cell

–ratio of maximum power point (MPP) to product of solar

irradiance & area of panel

–measured under standard test conditions (STC)

Performance Measurement of Solar Cell

Mono-Crystalline Silicon Solar Cell

• More efficient

• Manufactured from pure molten silicon - thin slices

(wafer) of single crystal

• Requires high temperature for manufacturing of

silicon

– increases the production cost

• Efficiency - 15-18%

• For 1 kW output - surface area needed is 7m2mono-crystalline solar cell

Polycrystalline Silicon Solar Cell

• Thin films of molten silicon are used to manufacture

these solar cells

• not preferred for solar cell manufacturing.

• offers lower efficiency


• For 1 kW output - surface area needed is 8m2

Polycrystalline silicon solar cell

Amorphous silicon solar cell

• Non crystalline form of silicon - deposited on

different substrate as thin films at low temperatures

• Manufacturing process - easier, cheaper & simpler

• Main drawback- lower efficiency - 6-8%

• Performance under weaker irradiation condition is

much better

• Light trapping capability - increases with increase

in the amount of amorphous silicon

Amorphous silicon solar cell

Cadmium Telluride Solar Cell

• CIGS & CdTe - are commercially used solar cell


• Main drawback - shortage & toxicity of some elements

used for manufacturing purpose

• Indium used in CIGS -

– not an abundant material like silicon

– it is used to manufacture LCD

– Cost is increased the cost

• Cadmium sulphide (CdS) - interfaced with CIGS to

form p-n junction - toxic materialCadmium Telluride solar cell

Gallium Arsenide

(GaAS) Solar Cell

• Preferred in space applications

• Offers

– band gap of 1.42 eV

– greater susceptibility to intense solar irradiation in space

• Efficiency – 40 % - using solar concentrator & and triple

junction GaAs solar cell.

• Main drawback-

– need of mechanical system to track sun whole day

– Tracking system is expensive

• low temperature coefficient

• Performance is better under low irradiation condition

• manufacturing process is simple

• Cost of materials used is high

• silicon solar cell are used extensively due to

– availability,

– non toxic nature of the materials used

– efficiency

Modeling of PV Modules & Arrays

• A single PV Cell

–Generates comparatively

• Small output voltage

• High current

• PV Panel or Module

–Multiple cells are joined in series & enclosed in a common frame

–Voltage of the PV module is increased by connecting many cells in

series

–Represents the fundamental building block for large scale PV power

production

Relationship between PV Cell, Module and Array

• PV arrays

– formed by connecting multiple strings in parallel

–For better performance - all the modules must be free from

shading

• Bypass diodes - connected to avoid damage

– Increases the cost

• Power level of a

–PV string - a few hundred watts up to 5kW

–PV arrays - a few hundred watts up to hundreds megawatts

Modeling of PV Modules & Arrays contd…

Small Scale Hydro-Electric Power Generation

• Small-scale hydroelectric generators are employed to generate power effectively onsite in

microgrids

• Amount of power generated depends on

– The annual rainfall

– The topography of an area

• Output of these generators undergoes large variations due to variable water flow caused by

uneven rainfall

– Occurs in hydropower station with catchment area spread over rocky soil without vegetation

cover and which do not have storage reservoirs.

• Variable water resources - leads to varying generation with a low capacity factor

Capacity Factor:

The ratio of available annual energy to its rated annual capacity

Hydro-Electric Power Generation

• Power output can be increased by increasing

– water flow rate

– effective head

• Penstock – used to bring water to the turbine through a pipeline

• Different types of water turbines are employed depending on

– flow rate

– water heads

• Impulse Turbines –

– operate at higher heads and

– Ex: Turgo turbine and Pelton wheels

– power is extracted from kinetic energy of water jets at atmospheric pressure


• Reaction Turbines -

– operate at lower heads

– Ex: Kaplan and Francis turbines

– extract power from pressure drop

• Cross-flow impulse turbines

– employed for small hydro units

– kinetic energy is extracted from water sticking the turbine blades as a

water sheet rather than a jet.

• With suitable multiple ratio gear boxes both induction and synchronous

generators can be used for small-scale hydro power generation


Other Renewable Energy Sources

• other renewable DERs for electricity generation –

–Biomass

–municipal waste

– landfill gas

• Location of the generators is chosen based on the availability of resources

• Drawbacks

– scarcity of resource

– low energy density

– difficulty in storing them in huge quantity

• small capacity generators and operate close to the resource as load pockets

• Energy storage - important for

– utility SPV systems

– load levelling

– uninterrupted power supply

– electrical vehicles

– energy systems in remote area

• Storage options - necessary when unpredictable sources are used in

– stand alone

– islanding power systems

• Micro-grids to guarantee continuous power supply are

Storage Batteries

Flywheels

Ultra Capacitors

Storage Devices

• Importance of Energy Storage Devices

–Most of the DERs are discontinuous and generate power

when the atmospheric conditions are favorable, rather

than when energy demand is there

–Energy must be carried in the vehicle for transportation

systems

Energy Storage Devices

Parameters for selection of Storage Technology

Unit Size

Available Capacity

Self Discharge time

Efficiency

Life cycle or durability

Autonomy

Storage Capacity

Volume & Mass Densities

Cost

Feasibility

Reliability

• Unit size: Size depends based on the application

– Ex: large units support grid connected renewable DERs technology

• Storage capacity: Total energy store available after charging

• Available capacity: Average value of output power based on the Depth Of Discharge (DOD) /

State Of Charge (SOC)

• Self discharge time: Time required for a non interconnected, fully charged storage to arrive at

certain DOD

– depends on operational condition of the system

• Efficiency: Ratio of output energy from the storage device to the input energy issue of

conversation technology to storage device

• Life-cycle or durability: Number of successive charging and discharging cycles a storage device

can undergo, at the same time maintaining the installations and other specifications within the

limit


• Autonomy: Autonomy is ratio of energy capacity to maximum

discharge power.

– direct measure of total time that the storage device can continuously release

energy

• Volume and mass densities: Amount of energy stored per unit volume

or mass of storage device

• Cost:

– installation

– operation and maintenance cost of storage device throughout it's life span

• Feasibility : degree of flexibility to storage applications.

• Reliability: continuity of service


Application of Storage Devices in Electrical Power System

Time shift in electrical energy

VAR control and power factor correction

Load following

Load levelling

Spinning reserve

Black start capability

Transmission and distribution system upgrade deferral

Time of use energy cost management

Bulk energy management

Reliability in service

Power quality improvement

Time shift in renewable energy

• Time shift in electrical energy:

– Energy Arbitrage – storing energy to avoid expensive purchase

– During off-peak hours

• prices are on low side - energy is purchased

• price is higher – energy is sold

• VAR control and power factor correction:

PEIs present the capability to vary reactive as well as real power rapidly

• Load following:

– Maintains stability of utility grid - storage device responds to demand of consumer

• Load levelling:

– During

• light load periods storage units are charged using low cost energy from base load plants

• high load times discharged when the energy value is higher


• Spinning reserve:

– because of their capability to increase output quickly, storage devices with

PEIs can act as spinning reserve

• Black start capability:

– stored energy can be used to start an isolated generating unit

• Transmission and distribution system upgrade deferral:

– Addition of storage devices to a nearly overloaded transmission and

distribution system can be delay or entirely avoid extra investments

• Time of use energy cost management:

– is similar to energy arbitrage

– here consumers decrease their total electricity costs by utilizing storage

devices


• Bulk energy management:

– Bulk power transfer can be postponed by storing the energy until it is required, or

until it's value increases

• Reliability in service:

– inclusion of storage devices - improve the reliability of power supply

• Power quality improvement:

– the energy storage device are employed to offer power quality services to the

consumer

• Time shift in renewable energy:

– power output from RES depends on environment condition

– it won't produce according to the demand from consumer


Storage Batteries

• Batteries are

– energy storage devices

– consists of electrochemical cells that

convert chemical energy to electrical

energy

• Basic battery cell consist of

Anode - negative electrode

Cathode - positive electrode

Electrolyte - medium for transfer of electrode

from anode to cathode

Battery Cell Connected to Load

Nickel Metal Hydride Battery• Nickel - metal hydride battery - rechargeable type battery

• Cathode containing hydroxide acts as active material and anode is made of hydrogen absorbing alloys

• Reaction occurring at the anode of a NiMH cell is,

H2O + M + e- OH- + MH

• The charging reaction is read from left to right and the discharging reaction from right to left

• Reaction occurring at cathode of a NiMH cell is

Ni(OH)2 + OH- NiO(OH) + H2O + e-

overall reaction occurring in NIMH cell is

Ni(OH)2+M NiO(OH) + MH

• M – metal in anode - intermetallic compound - currently employed as

– AB 5

– AB 2

• AB 5

– commonly employed

– A is a rare - earth mixture of lanthanum, neodymium, cerium

– B is Cobalt, nickel, aluminium or manganese

• AB 2

– Higher- capacity anode materials

– A is vanadium or titanium

– B is nickel or zirconium, modified with manganese, iron, cobalt or chromium

Nickel Metal Hydride Battery

• NiMH cell employs

– alkaline electrolyte - potassium hydroxide

– nickel hydroxide is the positive cathode

– protons or hydrogen are anode.

• Metal - hydroxide structures stores the hydrogen ions

• Hydrophilic polyolefin nonwovens are employed as separators

• Charging voltage - 1.4 V to 1.6 V per cell

• Automatic charging cannot be done

– a constant - voltage charging method must be employed

• NiMH cells must be charged with a smart battery charger when fast -

charging to avoid overcharging which damage cells

Nickel Metal Hydride Battery

NiMH Cell construction

• Electrolyte

– Alkaline - 20% to 40 % weight of alkaline hydroxide solution with other minor

constituents

– improves battery performance

• Separator

– Isolates the electrodes

– Made of Non -woven polyolefin baseline material

– allows efficient ionic diffusion

NiMH Battery construction • The cathode and anode, insulated by the separator is sandwiched and are wound together

• Then inserted into a metallic can which is sealed after injecting electrolyte

• The can function as the negative terminal of the battery and the top function as the positive

terminal

• A plastic insulating wrapper shrunk over the can of the finished battery provides electrical

insulation between adjacent cells

• On top of NiMH battery safety vent is provided

• Over charging causes production of gases

• Design allows –

– Recombination of gases under usual operating conditions – oxygen recombination cycle

– Maintains pressure equilibrium inside the battery

• Mismatched battery / charger combination – causes excess formation of hydrogen and oxygen

than the rate of recombination

• During such case, safety vent prevents battery rupture

• Electrolyte may be carried out through the vent during gas explosion – possibly form crystals

or rust outside the can

Lead Acid Batteries • Anode - Lead dioxide

• Cathode - Metallic Lead

• Electrolyte - H2SO4

• Efficiency – 70 % to 80 %

• Drawbacks:

– Low energy density

– High maintenance

– Low life expectancy

– Environmental hazards

• Two Types:

– Recombinant

– Vented

Chemical reactions

• Reaction occurring at negative electrode

Pb + H2SO4 + (2H+) + 2e- PbSO4 + (2H+) + 2e-

• Reaction occurring at positive electrode

PbO2 + H2SO4 + (2H+) + 2e- PbSO4 + H2O

• Overall reaction

PbO2 + Pb + 2H2SO4 PbSO4 + 2H2O

• concentration of sulphuric acid

– increases with cell charging and it becomes maximum when the cell is fully charged

– decreases with cell discharging and becomes dilute when the cell is fully discharged

Lead Acid Batteries - Theory of Operation

Cell Construction

• Lead acid are constructed by placing alternative positive and negative

plates, interleaved with single or multiple layers of separator material.

• An active material is pasted onto a grid structure made of lead or lead

alloy to form plates and a mixture of water and H2SO4 forms the

electrolyte.

• Separator materials:

– microporous plastic

– cellulose fibre

– porous rubber in flooded cells

Battery Construction

• Injected - molded, plastic monoblocs which containing a group of

series connected cells are used to construct lead acid battery

• Polypropylene is used to make monoblocs

• An electrical holder will be incorporated for external connection with

plug

Charging Methods

• The constant charging method a

–2.3 to 2.4 V per cell is preferred to charge lead acid batteries

• Lead acid battery can be charged by directly connecting to the DC bus

•

• To attain acceptable battery life regulated voltage source is necessary

Temperature Effects and Limitations

• Lead acid batteries

– Operate at 25°C

– Exposure to

•high temperature shortens life

• low temperature declines the performance

Lithium Ion Batteries

• Negative electrode is

– strongly an electropositive metal - ex: like lithium

– an electronic donor group

• Positive electrode is

– strongly an electronegative material

– an electronic accepter – ex: LiMO2 ; M=Ni, Co, Mn, etc

• Reaction occurring at negative electrode

C6 + xLi+ + xe- LixC6

• Reaction occurring at positive electrode

LiCo3+O2 (xLi+) + Li1-xCo4+xCo3

(1-x)O2 + xe-

• Overall reaction

LiCoO2 + C Li(1-x)CoO2 + LixC

• During charging - Li+ ions from LiCoO2 moves to carbon through the

electrolyte and oxidizes Co3+ to Co4+

• During discharge - Li+ ions moves from carbon to LiCoO2

Lithium Ion Batteries – Theory of Operation

Key requirements for Electrolyte of Lithium Ion Batteries

Chemical compatibility with electrodes and cell components

must be stable over the operating voltage window

Should be a good Li-ion conductor and an electrolyte insulator

There should not be any charge accumulation or concentration

polarization

Must be thermally stable

Lithium Ion Batteries - Cell Construction

• Positive electrode - metal oxide - polyanion, a spinel or a layered oxide

• Negative electrode – carbon – Graphite

• Electrolyte - lithium salt in organic solvent

Lithium Ion Batteries - Battery Construction

• Li - ion batteries available in various shapes

• divided into four groups

small cylindrical with solid body and without terminals

large cylindrical with solid body and large threaded terminals

pouch with soft, flat body - employed in newer cell phones and laptops

prismatic with semi - hard plastic case with large threaded terminals

Lithium Ion Batteries - Temperature effects and limitations

• At cooler temperatures

– good charging performance

– even permit fast charging within a temperature range of 5°to 45°C

– Charging should be carried out within this temperature range.

• High temperature during charging will degrade battery performance

• At lower temperature the internal resistance of the battery increase –

causes -

– Slower charging

– Longer charging time

Ultracapacitor

• Ultra capacitor or super capacitor

– are Electrochemical Double Layer Capacitor (EDLC s)

– has high energy density

– do not have any dielectric material

– utilizes an electric double layer

– withstand low voltages

• The thickness of the dielectric material is

– exceptionally small in the double layer

– the surface area is high due to porous nature of the carbon ,which give very

high capacitance

• The charge stored at the interface by changing electric field between

cathode and anode gives high capacitance in an ELDC

• For high voltage application ultra capacitor modules may be connected

in series

• Two types of electrolyte are generally used

1) Water soluble

2) Water insoluble

• Non water soluble electrolyte

– has higher density

– withstand higher voltage per cell as compared to that of water soluble

electrolyte

Ultracapacitor contd…..

Ultracapacitor contd…..

Internal Cell Construction

• The carbon particle are

– activated and mixed with a binder,

– then it is deposited on a aluminium foil to

construct cells

• Electrodes are wound into a jellyroll

configuration

Ceq = C1*C2/C1+C2

• First order model of an ultra capacitor comprising of four ideal

components

– The series resistance Rs component - key contribute to power loss

– Parallel resistance Rp which effects self discharge

– A series inductor L

– A capacitance C that is generally small

First order equivalent circuit Ultracapacitor

• Rp is always much larger than Rs, hence it can be ignored .

• Ultra capacitor exhibits non ideal behavior due to porous nature

of electrodes

• Ladder network is used to represent ultra capacitor.

Ladder Network

First order equivalent circuit Ultracapacitor

Merits and Demerits of Ultra-Capacitor

Merits• High energy storage

– ultra capacitor posses very high energy density when compared to conventional capacitor

• Low equivalent series resistance

– internal resistance is low hence provide high power density

• Low temperature performance

– with increase in temperature performance of ultra capacitor depletes

• Fast charge/discharge

– high current charging and discharging is possible without causing any damage to the parts

Demerits

• Low voltage per cell

• Cannot be used in AC and high frequency circuits - because of their time constant

Flywheel

• Flywheel – stores energy in form of kinetic energy

• Basic components of Flywheel Energy Storage System

(FESS):

Flywheel Rotor

Electrical Machine

Bearings

Housing

Power Electronic Interface

Basic structure of a flywheel

Flywheel Rotor

• rotor energy is stored in flywheel in a rotating mass

• The amount of energy stored is a function of the moment of inertia and

angular velocity,

E = 1/2 Iw2

Where.

– I is the moment of inertia

– W is the angular velocity

• Moment of inertia of the flywheel depends on mass and shape of flywheel

I = ∫xd2dmx

• Where x is the distance from the rotational axis of the differential

mass dmx

• Energy stored in flywheel is directly proportional to moment of

inertia (I) and square of angular velocity (w)

• Large amount of energy can be stored by increasing the angular

velocity, rather than increasing moment of inertia.

• Flywheel with the shape of thin rim is considered

– infinitely thin outer rim (radius ‘r’), concentrates all mass (m) in it.

– moment of inertia (I) is

I = mr2

Flywheel Rotor

• Material with high strength and low density would be optimal choice

for flywheel rotors

• With increase in tensile strength the energy density also increases

• Specific energy is proportional to the maximum tensile stress of the

material and inversely proportional to the mass density of the

flywheel material

Flywheel Rotor

Electrical Machines for FESS• Flywheel must be coupled with an electric machine in order to charge and discharge

• Machine must

– accelerate the flywheel when it is charging – Motor action

– decelerate when discharging – Generator action

• design criterion of the machine

– must act as both motor and generator

– low rotor loss

– high power density

– low idle losses

– high efficiency

• Permanent Magnet Synchronous Machine (PMSM) is chosen in most high-speed

FESS due to better property when it comes to efficiency and power density

Bearings for FESS• The rotor has to be supported with the bearing to

– minimize the friction

– maintain rotor in position

• High speed of flywheel designs - imply broad requirements on bearing

• To run FESS efficient - the bearing losses must be low

• Mechanical bearings

– can be implemented straightforward

– low initial cost

– relatively high friction

– Requires lubrication

– Not preferred in high speed flywheel system

• Combination of mechanical and magnetic bearing is employed in several systems

Housing for Flywheel

• The aerodynamical drag losses

– contribute heavily to the total losses of the system

– these losses increases with the cube of the rotational speed

• If a high speed flywheel, works at atmospheric pressure the losses will

be significant

• In order to reduce losses, vacuum housing is build

– it reduces aerodynamically drag losses

• Housing must also withstand a potential failure if it occurs

PEIs for Flywheel

• PEIs are very important part in FESS system

• It provides an interface for the power transfer and control interface for theelectrical machines

• PEI consist of

– an Adjustable Speed Drives ASD

– a bi-directional converting/invertor

• Control of both reactive and active power is required for an FESSinterconnected with utility grid.

• Preferred attributes for the PEIs are

– high efficiency

– high power capability

– high switching frequency

How Does a Flywheel Work?

• The FESS is made up of a heavy rotating part, the flywheel, with an electric

motor/generator.

• The inbuilt motor uses electrical power to turn at high speeds to set the flywheel

turning at its operating speed. This results in the storage of kinetic energy. When

energy is required, the motor functions as a generator, because the flywheel transfers

rotational energy to it. This is converted back into electrical energy, thus completing

the cycle.

• As the flywheel spins faster, it experiences greater force and thus stores more energy.

• Flywheels are thus showing immense promise in the field of energy storage systems

designed to replace the typical lead-acid batteries.

• For a flywheel, kinetic energy is calculated as for a spinning object, as

E = ½Iω2

Advantages

• High power density

• High energy density

• Lifetime independent of charge depth

or discharge cycle

• Low maintenance

• Short recharge time

• Environmentally friendly materials and

process

Disadvantages

• Requirement for sturdy and durable

bearings with low frictional loss

• Mechanical limitations as energy storage

increases

• Short discharge time

Control of Microgrids

Control of Microgrids - Intoduction

Wide-range of control is needed to ensureoptimal operation

system security,

emission reduction

seamless transfer from one operating mode to the other without going againstregulatory requirements and system constraints.

Common Central Controllers (CC) and Microsource Controllers (MC)areused to connect individual microsources and storage devices to microgrids.

MCs perform local control function of micro sources and storage devices

CC perform the overall control function of micro grid operation andprotection through MCs.

CC major function is

– to sustain reliability and power quality through voltage (Q-V)

control, power- frequency(p-f) control and protection coordination.

–perform scheduling economic generation from micro sources and

helps to sustain power intake from utility grid at jointly agreed

contract points.

–not only coordinates the protection scheme for the whole micro grid,

but also gives the voltages and power dispatch set points for all the

MCs to meet up the requirements of the consumers.

–guarantees energy optimization for the micro grid and sustains the

specified voltages and frequency profiles for the loads.

Central Controller

• is designed to work automatic mode with a provision

of manual intervention when it is necessary.

• Monitors the functioning of MCs continuously

through two important modules i.e., the EMM and the

PCM.

MICROSOURCE CONTROLLER

It guarantees,

• Addition of new microsources without modifying the present microgrid

configuration.

• Connection/disconnection of microgrid to/from the utility grid in a

quick and seamless fashion.

• Independent control of active and reactive power.

• Correction of voltage sag and system imbalances.

• Handling faults without the loss of stability.

• Meeting the necessities of load dynamics of the power utility.

Control functions for microsource controller

• Active and reactive power control

• Voltage control

• Storage requirement for fast load tracking

• Load sharing through P-f control.

Control Features of the MCsActive and Reactive Power Control• The microsources can be

(i) DC sources like fuel cells and SPV

DC power developed is converted directly into 50 Hz AC

(ii) AC sources like wind turbines and microturbines

The variable frequency AC output is first converted to DC and then

reconverted into 50 Hz AC.

• In both DC/Ac conversion takes place through an inverter (VSI) which is

the main component of the power electronic converter.

Basic scheme for typical MC

Typical MC compressing of microsource and power electronics converter.

• VSI in the converter system controls both magnitude (V) and phase

angle (δ1) of the output voltage (V< δ1) at Bus-1(converter terminal)

• The microsource supplies controlled power to the Bus-2(microgrid

bus) at a voltage of E< δ2 via an inductor of reactance X

• V< δ1 leads E< δ2 by power angle δ,where δ= δ1 – δ2

Active and Reactive Power Control

• By controlling δ the active power flow (P) is controlled

• By controlling V the reactive power (Q) is controlled

V δ1 L E δ2

P=3VE sinδ

2X

Q=3VE (V – E cosδ)

2X

Microsources Power electronic

converter

Basic scheme for Typical MC

‖ ‖

Active and Reactive Power Control

Voltage Control

Why Voltage Control of Microgrid bus essential?

Voltage Control

• Voltage-reactive power (V-Q) droop controllers can be used to control

circulating currents.Voltage(V)

Vset point

Inductive VARCapacitive VAR

Q max Q max

Droop characteristics for V-Q droop controllers

• The droop controller decreases the local voltage set point when the

microsource reactive currents become capacitive and increases the set

point when the current become mostly inductive.

• V-Q control is performed by shunt capacitor banks installed at

substations, switching capacitor banks installed along the lines,

substation transformer load tap changers(LTCs), voltage regulators,

FACTS equipment, DERs and DG.

Voltage Control

• Centralized V-Q control: It is integrated with distribution

system which provides the information to the recording system

and determines how to proceed.

• Decentralized V-Q control: It is a stand alone system which

relies on local interaction with various devices associated with

V-Q controller.

V-Q Control

Historian

SCADA RTU

Capacitor bank Voltage regulator Volt monitor Recloser

Operation

Field

Substation

Volt/VAR

controller

Power flow

module

Centralized V-Q controller

Historian SCADA

Volt/VAR

controller

RTU

Capacitor bank Voltage regulator Volt monitor Recloser

Operation

Field

Substation

Decentralized V-Q controller

Storage Requirement for Fast Load Tracking

• Fast load tracking in stand alone is made possible with the help of

storage devices in Micro grids

• AC storage devices are directly connected to the micro grid bus

• DC storage devices are connected to the DC bus of the micro source

• The MC guarantees proper utilization of storage devices for rapid

load tracking

Load Sharing Through P-f Control

• Microgrid controllers ensure smooth and automatic change over from grid-connected mode to stand-alone mode and vice

versa as per necessity.

• Local power balance at the new loading during changeover from grid to standalone mode is achieved by changing the

operating point by exerting local P-f control through MC of each microsource.

• The controller does this autonomously after proper load tracking without waiting for any command from the CC or

neighboring MCs.

• Two modes of operation in P-f control:

(i) Isochronous mode

(ii) Droop mode

Steam

valve

Prime

mover

∫ KG -1 ∑

Steam

Speed

measurement

unit

Rotating

shaft

∆P value

[+ = open valve

- = close valve]

∆w w ref

w

Basic architecture of isochronous governor

+

-

Isochronous Mode

• Also referred as Frequency control mode .

• In Isochronous mode the machine is not affected by load and regardless of load it will

maintain the frequency.

• Systems are not connected to utility grid in this mode, hence it is necessary to run at least one

machine in this mode to take care of the load variation.

Fig. shows the basic architecture of isochronous governor.

Isochronous governor varies the input valve to a bring frequency back to nominal

value.

It cannot be used if more than one generator is electrically connected to the same system.

A droop feedback is provided additionally to run more than one generating units in parallel on

a governors are provided with a feedback signal that causes the speed error to go to zero at

different values of generator output.

By adding a feedback loop around the integrator this can be accomplished

Steam

valve

Prime

mover

∫ KG ∑

Steam

Rotating

shaft

∆P value

[+ = open valve

- = close valve]

∆w w ref

w

Basic architecture of isochronous governor in droop mode

Speed

measurement

unit

∑ KR

∑+

-

-

-

+

+

Load reference

point

Droop Mode

• A new input, the load reference is inserted to conventional

isochronous mode control.

• Slope of the droop characteristics is determined by the value of GR.

• GR is equal to pu change in frequency divided by pu change in unit

output.

• Since microgrid frequency decreases with droop regulation, the MC

must integrate control functions to re-establish the operation at rated

frequency with correct load sharing.

• For example, it is assumed that two microsources operating with

their maximum capacities P1max and P2max at common minimum

frequency wmin

• In grid-connected mode they operate at a base frequency wzero

delivering powers P01 and P02 respectively

• With variation in load demand, the microsources work at different

frequencies causing an alternation in relative power angles and the

operating frequency moves to a lower common value with different

proportions of load sharing

w0

w1

w min

P2max P1max

P02 P01

P12 P11

Frequency(Hz)

Active power (P)

Droop characteristics for P-f droop controllers

Central Controller

The CC applies its control via two modules

Energy Management Module - EMM

Protection Co-ordination Module - PCM

Energy Management Module

• It incorporates different control functions to achieve finer control, but increases design complexity.

• Basic Microsource Control Functions

-Voltage control

-Power factor control

-Prime mover speed control

-Frequency regulation

Voltage control

• By varying the magnitude and phase angle of voltage, the microsources

usually control microgrid loads and their power factors via MCs.

• There is a chance of voltage rise on the feeders on microgrid when

distribution feeders are not fully loaded. MCs monitor the local voltage

rise and give feedback to EMM.

• Main aim- to make the microgrid appear to the utility grid as an

aggregate of loads and microsources working as a controlled unit at

utility pf.

Power Factor Control

• Microsources generally do not have any inherent pf control.

• Pf being load dependent, all the MCs are incorporated with

pf control characteristics as a function of load tracking.

• Pf control feature is completely built-in MCs, so that the

control does not need any command from EMM except for

voltage set point.

Prime Mover Speed Control

• Incorporated for microsources such as wind turbines and

microturbines.

• To accommodate variation of load within the capacity of

microgrid, prime mover of microsource must change its speed

to achieve power balance for new loading. Fuel input should be

varied to achieve this which affects efficiency of prime mover.

• Prime mover speed control must guarantee power generation at

optimum efficiency for microsource.

Frequency Regulation

• With the help of power electronic devices power generated from

microsources can be converted into any desired frequency.

• In grid connected mode- do not have to exert pf control.

• In stand alone mode- MCs exert this control.

• EMM monitors microgrid frequency. If MCs do not restore the

frequency drop within a set time, the EMM performs fast load

shedding to guarantee microgrid stability.

EMM Operation in Typical Microgrid

• Number of EMM control functions is restricted to

keep the microgrid simple.

• Minimizes number of feedback signals needed by

EMM from MCs.

Grid-Connected Operation

EMM control signals are limited to the local voltage and active

power set points.

EMM does not apply extra voltage control that may hinder the

functioning of voltage regulators and shunt capacitors of the

utility grid or with the MCs in microgrid.

Slight voltage rises in microgrid due to light load distribution

feeder will be arrested by utility controllers.

Stand-alone operation

• Function of EMM

–provide voltage and active power set points for MCs.

• MCs autonomously controls frequency and reactive power

flow through V-Q and P-f drop characteristics.

• EMM- monitors the microgrid frequency and implements fast

load shedding via MCs if frequency is not re-established within

a pre-set time for ensuring system stability.

Control of Heat Loads

• Higher priority than electrical loads in CHP microsources.

• EMM integrates a priority-setting factor for heat loads in transmitting

signals to the MCs.

• Electric power output is more valuable than heat for several industrial

cogeneration systems.

• Therefore, EMM should set the priority factor as per the relative

importance of heat and electrical loads.

Energy Optimization with Maximum Efficiency

• Microgrids must be interconnected to supply a big power pool.

• EMMs should make sure that optimum number of

microsources are running near to their rated capacities during

light load conditions.

• EMM performs this control smoothly because of their prior

knowledge of weather parameters, microsource generation

schedule and process condition and fuel information.

Energy Storage Management

• EMMs control the non-priority loads by shedding them as and whenessential.

• By shedding the non-priority loads off, energy usage is reduced andconserved for long term use.

• Only the short-term power needs are supplied by storage devices,uninterrupted power supply is maintained to provide reliable supplyto prior loads.

• The power reserve for long term need is obtained by shedding thenon-priority loads without damaging the microgrid.

Optional Control Functions for Intelligent EMM

Intelligent EMMs in a microgrid are used for

1. Focussing on energy consumption

2. Giving an overview of process control systems

3. Investigating energy saving opportunities depending on

weather conditions

4. Optimize the use of microsources and storage automatically

by using real-time market

5. To monitor power consumption

Optional Control Functions for Intelligent EMM

• Intelligent EMMs must have intelligent PEIs, wide information handling

capacity and enough communication networks.

• Control algorithm on AI based techniques must be also incorporated with

EMMs.

• They must have remote monitoring and control services.

• EMMs must also provide manual intervention facilities.

• EMMs must be able to manage information, provide operation guidelines

and set points to system operator.

• Their operation should aim at maximising availability, maintaining high

quality service and minimizing downtime.

• They can also supervise and control with SCADA systems.

Protection Co-ordination Module (PCM)

Overall protection of microgrid is supervised by PCM

1. Microgrids contain both generating units and loads resulting

in bidirectional flow of power

2. Due to presence of microsources passive distribution network

turns into an active one.

3. When it transforms from grid-connected mode to stand-alone

mode, microsources go through a significant change in its

short circuit capacity.

Typical Microgrid configurations

Protection scheme for Grid-Connected Mode

• Normal Condition

• Utility Grid Fault

• Microgrid Feeder Fault

• Microgrid Bus Fault

• Re-Synchronization

Protection scheme for Grid-Connected Mode

Normal Condition

• Microgrid remains connected to the utility grid via PCC CB, CBI.

• All the CBs remain closed.

• The loads are fed jointly by the utility grid and the microsources.

Utility Grid Fault• By opening CB1, the microgrid disconnects itself from utility

grid.

• CB1 monitors the direction and magnitude of current on eachphase and sends a trip signal to CB1 if current limits go beyondspecified value within a pre-set time.

• Also guarantees that the microsources are not falsely tripped.

Protection scheme for Grid-Connected Mode Contd…

Microgrid Feeder Fault

• Fault power flow is unidirectional.

• By opening the feeder breaker, faults are cleared simply.

• The breakers have directional over current relays to detect thefaulty zone and clear fault.

• For all the relays the PCM grades relay settings such that thefaulty zone is isolated before all the microsources aredisconnected from the feeder.

• This guarantees microgrid stability and minimum loss ofgeneration.

Protection scheme for Grid-connected mode Contd….

Microgrid Bus Fault

• If fault occurs on the microgrid bus, then by opening CB1 the

microgrid would be disconnected from the utility grid.

• PCM grades the CB1 relay to co-ordinate with the upstream

protection in the utility grid in case of any fault within the microgrid.

• CB1 is also graded with respect to the protective devices for the

microsources to minimize loss of generation, spurious tripping and

supply interruption.


Re-Synchronization

• It is responsibility of PCM to synchronize and reconnect themicrogrid to the utility grid through synchronism checkschemes.

• This may need a few seconds to minutes, depending upon thenature of the loads and feeder.

• The PCM contains the control scheme to bring allmicrosources into synchronization with utility grid.

• PCM provides both options for manual and automatic re-synchronization as per requirement.


Previous year questions1.Explain the operation of a lead acid battery and mention its merits and demerits.

2.Explain the working and operation of different Wind Energy Conversion Systems. Also mention the advantages and disadvantages


4.Explain the merits and demerits of solar PV plant

5.Explain the voltage control method in Microgrid with Q-V diagram

6.Explain the load frequency control in Microgrid with p-f diagram

7.Explain how the real and reactive powers are controlled in a power inverter based energy source.

8.With the help of block diagrams, explain the classification and working micro turbines.

9.Explain the components of an Ultra capacitor. Mention its advantages and disadvantages.

10.Explain the working flywheel energy storage (FES) system.

11.Discuss the working principle and operation of ultra-capacitor with necessary diagram.

12Explain the functions of Central Controller in Microgrid.

13. Explain how active and reactive power control is performed in Microgrid.

14. Elaborate the concept of load sharing through power-frequency control in Microgrid

Thank You

Distributed Generation

&

Smart Grids

AISHA MEETHIAN

AP,EEE DEPT

ICET

MODULE – 3

Protection Issues for Microgrids

INTRODUCTIONTo guarantee the stable operation of a Microgrid during contingencies, two

major protection issues that must be dealt are:

• To find out the instance at which the Microgrid have to be islanded under a

particular contingency

• To isolate the Microgrid and give sections with sufficient coordinate fault

protection.

Performance and characteristic of majority of protection elements of a

microgrid are similar to those present in conventional utility system,

but it is not same for the inverters connected with microsources,

Reasons :

Characteristic of inverters are not similar to existing protection equipments

Different inverter designs have different characteristic and hence they do

not have any standardized characteristic that symbolize inverters as class of

equipment

Fundamental characteristic of inverter units vary clearly depending on

design and application.

Low fault current capacity in inverter units.

For Microsources with larger no. of PEIs - reduction in Microgrid fault level

during change over from grid connected to stand alone operation

Systematic understanding of Microgrid dynamics before, during and after

islanding is necessary to resolve protection issues for Microgrids properly.

Realistic evaluation on the benefits - before islanding the Microgrids

For reliable and safe operation of stand alone Microgrid, the protection system

must ensure the following:

• Stand alone Microgrid with Suitable grounding

• Coordination of Load shedding plans:-load shedding plans setup in area

by utility system must ye closely coordinated

• Fault detection devices must work in agreement with the fault detection

system of both the modes (stand alone and grid connected)Fault detection

Method - independent of large ratio between fault current and maximum

load current

• A method of fault detection must be presented to take care of fault level

after islanding.

• Avoid undesirable loss or instability of microsources with receptive

settings, current anti-islanding schemes must be examined and modified

if needed

Islanding: Separation from Utility

Islanding: Separation from Utility

• Microgrids –

– Capacity less than 10 MVA - extremely small - contrast to utility grid.

– Should have enough generation to supply major part of its load.

– Carry a part of the utility with it if islanding does not occur.

Method to minimize false separation.

Limitations on separation protection enforced by exporting microgrids

Whether re-synchronization Microgrid to utility grid will be manual or

automatic.

Whether speed of operation of the protection system want to approach

SEMI F47 specification.

Whether no fault separation would be permitted for open phase, voltage

imbalance, under-voltage conditions

Issues to be considered for proper Islanding

Different Islanding Scenarios

1. Quick Separation From Faulty FeederMicrogrid provides continuous power supply to priority loads during any

disturbance in utility.

The existing protective equipment may fail to clear the fault quickly is loads of

the Microgrid is voltage - sensitive and it requires separation times of fewer

than 50ms.

relay time required to direct and interrupt the circuit on receiving the trip

signal for an over or under voltage is up to 2 cycles and for medium voltage is

three to five cycles.

Hence, if a quick acting solid state CB is not available at PCC between

microgrid and utility grid; other methods must be employed to avoid the

voltage falling below 50 % for three cycles or longer.

MC

Non CHP

source

MC

CHP

sourceheat

load

MC

Storage

deivce

PCCCB2 SCB* Feeder A SCB

MC

Non CHP

source

MC

CHP

sourceheat

load

MC

Storage

deivce

CB1

6KV/15VDi

stribution

transformer

Fast protection

through PCM

Fast protection

through PCM

Feeder B

CB3

Feeder BCB4

Feeder C

CC

SCB Feeder D

SCB

CB5

415VMicrogrid Bus

From

utility

grid

Fig 1 Protection of typical Microgrid

Utility

grid

Microgrid

MV zoneMicrogrid LV zone

Following cases have been considered to achieve design and protection

improvements:

(i)When separation is compulsory

(ii)When separation is not compulsory

i. When separation is compulsory:

• Must be isolated from the utility grid when occurrence of fault is on its main

incoming feeder at PCC.

• As indicated in Fig. 1 the fault point is upstream to the PCC breaker CB1

• High speed separation is needed for this fault under all utility protection

requirements and technical standards, without continuing even a low under-

voltage tie to the utility

ii. When separation is not compulsory

• Such cases arise when the fault is not situated between the utility substation

breaker and the PCC.

• For example: a fault on neighbouring feeder fed from the same substation

might cause sag on substation bus.

• Installing electronics sag correctors or substituting a D-Y transformer for Y-Y

transformer at PCC and addition of a high voltage side breaker can prevent the

sag.

• Electronic sag protectors are of two types, one appropriate for longer

protection period above two cycles and other 4 shorter protection period of

about two cycles.

• The long term sag protector employs an energy storage device

• the short term sag protector doesn’t uses it.

• Sag protectors

– does not require storage device - if the under voltage condition is not less

than 50%.

– can hold up the voltage for three cycles even for zero voltage conditions.

• Hence a combination of 3 cycle breakers and instantaneous relays installed in

adjacent feeders to the main incoming feeder of the Microgrid must satisfy the

SEMI F47 necessities for fast fault clearance.

• Microgrid Separation is required

– if the utility employs instantaneous over current tripping of the feeder for

fuse saving purposes.

– Substituting D-Y transformer for Y-Y transformer is a cheaper solution, but

it is less effective.

– D-Y interconnection is effectual only for single phase to ground faults on the

D side and for loads connected between line and neutral on the Y side.

2. Prevention from False SeparationKeeping a tie between the utility grid and the Microgrid is recommended for

reliable operation

The Microgrid must be separated from the utility using fast tripping devicesin case of fault occurring on the tie.

Low cost protective devices are not safe and might cause fake trips and faultseparations.

Reliable fast tripping technique - transfer trip from utility grid substationbreaker

False tripping mainly happens from

• electromechanical relays and breakers

• from the complicated microprocessor based protection schemes.

False trips leads to serious power quality issues

Protection devices must be examined as an assurance against the loss ofpotential production

False tripping can be tolerated to some extend if backup power is supplied bythe microgrid to its own load.

The microgrid will be separated - if intolerable voltage deviation continueslonger than the permissible duration.

Relaying problem becomes

– much easier

– can be carried out without locating fault point from PCC current easier,

• Such an oversimplified approach may lead to some problems:

Permitting false separation - unnecessary outages to non priority loads ifMicrogrids shed them upon islanding.

In exporting Microgrids, it will lead to revenue loss and a period of overfrequency operation until frequency stabilizes.

In addition, the consumers might feel that such regularly interruptedgeneration will not be worthy.

3. Separation in Non Fault Conditions:

Under non –fault conditions also low voltages can occur.

Hence without the help of high speed communication between utility and

Microgrid controllers it is difficult determine whether an LV condition is

related with a fault or not.

The utility and Microgrid will also settle a trip control for balanced voltage

conditions (as in SEMI F47 specification)

The trip control will be accomplished through communication

i. With the trip restraint system

ii. With utility using balanced voltage blocking of single phase under voltage

relays at PCC when desired voltage trip levels are lesser than delayed trip

settings as specified by IEEE P1547 standards.

The criteria for fixing the under voltage tolerance limit is determined by

considering the sensitivity to voltage imbalance of microsources, loads and

other distribution equipment.

An intelligent controller function is included in the PCM at the PCC to

formulate the correct decision on whether to separate or not based on voltage

imbalance.

Open phases are normally associated with systems where fuses are located

between the PCC and the utility substation.

The Microgrid may not detect open phases as an abnormal condition, since an

open phase causes phase to phase voltage to remain at or above 50%.

If not isolated properly, excessive over voltage/over current may exist across

the open phase with three phase switching.

4. Separation of Exporting Microgrids

Simple reverse power relays won’t work with exporting Microgrids to

determine utility contingency conditions.

Impedance ratio of exporting Microgrid is much closer to that of the utility

as it contains excess generation than its maximum load - main difference

between an importing and exporting Microgrids

Hence exporting and importing Microgrids has different voltage division

during fault.

5. Re-synchronization

Re-synchronizing - conventional synchronous generator and power

electronic inverter interfaced microsources - carried out using relay

and control schemes.

Microgrids with only one microsource - choice for automatic or

manual re-synchronization depends - on the availability and skills of

operator.

Advanced control schemes - delayed re-synchronizing during storm

conditions, where disturbances may be frequent and facilities at least

with the larger microsources may be also included in PCM

Major Protection Issues of Stand-Alone Microgrid

Major Protection Issues of Stand-Alone Microgrid

The protection considerations differ for stand alone and grid connected

schemes

For proper separation of microgrid - following protection considerations must

be taken into account,

• Fault Protection of Distribution System

• Protection of Microsources

• National Electric Code (NEC) Requirements for Distribution

Transformer protection

• Neutral Grounding Requirements

Fault Protection of Distribution System

• The problems that must be properly considered as follows,

Microgrid Utility Side Protection

Low voltage Fault Clearing Requirements

Presence of Dispered DERs in a Microgrid

1. Microgrid Utility Side Protection

By tripping all the microsources the faults occurring in the utility side (I.e. MV

zone) of the Microgrid can be easily cleared.

If the fault is second contingency , it must be decided whether to keep the rest

of the Microgrid operating and go for selective isolation of MV faults.

Micro grid is a classic onsite LV active distribution system fuses on MV/LV

Assigning fault as second contingency, means the first contingency has

occurred already as a result Micro grid has occurred already, as a result of

Microgrid has be separated from the utility grid and the MV fault is a second

contingency in stand alone Micro grid

Microgrid - on site LV active distribution system

Fuses on MV/LV distribution transformer connecting Micro grid to utility

grid are the only MV protective devices employed in Micro grids.

Normally, these fuses are set to function quickly (within 0.1-0.2s) for

predefined fault current from utility grid for a utility side fault happening

during grid connected mode of operation.

On LV side fuses are set for fault currents of 10-20 times the maximum load

current and time delay within 0.5-1.5 seconds.

Drastic reduction in fault level is main problem that a protection system for

a stand alone Microgrid will face.

An MV fault – Fault Current

• = 20-50 times full load current - grid connected condition ,

• = 5 times full load current - standalone condition.

Standalone Condition:

• Distribution transformer fuses - operate very slowly to such faults with

extremely inverse time current characteristics

• Difficult to coordinate with microsource protection.

• There are only two choices under this condition

i. To accept that an MV fault will lead to a total microgrid outage

ii. To install extra protective devices to MV system for correct

coordination

• Complexities due to utility side faults in a microgrid

–Fuse will be blow rapidly if fault occurs on transformer side.

–The faulty transformer will be disconnected from the utility, but it still

connected to microgrid.

–Micro grid will be left with a an open phase condition.

• If the micro grid is having a centralized generation , then two choices are thereas discussed before:

(i) To accept outage due to second contingency.

(ii) To add properly graded additional protective devices with centralizedmicrosource.

(iii)To fit relays at proper points in LV network

• Options (ii) and (iii) are suitable choices for Microgrids with microsources atmore than one location.

• For fault within Micro grid, protection system must be sufficiently time delayedto avoid microsources generation loss due to utility disturbances

• Realize coordination through PCM

• Feeder sections employ - directional over current relay.

• The operating times of relays (if same), leads to reduced selectivity.

• Thus by employing differential protection schemes around each circuit segmentappropriate selectivity has to be achieved

• High-speed communication is necessary to and from all protective devices thattrip any faulted circuit.

2. Low Voltage Fault Clearing RequirementsConventional protective devices - time-current coordinated - fault current

levels of about 2-20 times the maximum load current.

The device nearest to fault - primary device

The devices away from the fault - backup devices.

Both devices detect the fault and maximum fault current flow through both

of them

The primary one is adjusted to operate quicker than secondary one.

When fault location moves away from the source of generation, time-graded

coordination takes the advantage of the natural falling off of the fault current.

The falling off depends upon the magnitude of impedance of

transformers/lines between the fault point and generation point.

High set instantaneous over current relays and inverse-time overcurrent

relays are used for LV and MV distribution networks.

By using this fault clearing time becomes more or less proportional to the

distance of the fault from the substation.

In fault studies the generation point is defined as infinite bus.

One main issue is that the stand-alone microgrid won’t appear as an infinite

bus on the MV side of MV/LV transformer and the apparent impedance of the

transformer may be much smaller than that of microgrid source.

So, when the fault moves from the MV zone to the LV system the fault current

change will be comparatively small.

Transition from grid-connected to stand-alone mode

• limit backup protection

• low down fault clearing in overcurrent coordinated protection schemes.

• Should not disturb the protection coordination

Inverse time characteristics of over current relays improves the time margin at

lower fault currents

Less inverse characteristics ensures proper coordination.

More distinct change will be shown by extremely inverse devices during the

transition time of operation.

Severe reduction in fault current level is caused by the transition will affected

more on high-set instantaneous over-current devices.

Fault current of both modes matched by Installing a fault limiting CB at the PCC

3. Presence of Dispersed DERs in a Microgrid

To designing a secure and reliable protection system the impact of dispersed

DERs on microgrid protection system is needed

Microgrid - in the form of a quasi network with dispersed generation, the

changes of bidirectional fault current flow in various feeders and the reduction

in fault current must also be taken into account while making changes in fault

protection scheme.

If there is a fault between the master (controller) and a slave (controlled)

DER, then the slave must be disconnected from the system as per IEEE P1547

specification.

Separation will be difficult if the protection scheme for the slave DER

is already designed in such a way that it must not trip for fault current

on the utility side of the PCC.

Hence, it will not detect whether the fault is on the master DER side

in the Microgrid or on the utility side.

Therefore, high-speed communication between all microgrid CBs and

the PCM is the only reliable way to realize selective tripping

Protection of Microsources

• The following issues should be considered while designing a reliable microsource

protection scheme,

1. Fixing frequency and voltage protection tolerances for a standalone

microgrid.

2. Evaluating the requirement for anti-islanding protection of DERs, if such

protection needed, the way to override or disable during stand-alone mode of

operation of microgrid.

3. Investigating whether the existing anti islanding methods might lead to

frequency and/or voltage instability if employed in a standalone microgrid

4. Evaluating the requirements for an under frequency load shedding scheme for

microgrid.

1. Modification of Voltage and Frequency Windows

Broadening the tolerance range is advantageous for standalone microgrids with

comparatively low generation capacity.

The tolerance range must be kept unchanged, if these windows were initially

set as protection boundaries for avoiding damage to the connected equipments.

It can be changed if they were initially set as fault and island detection levels.

This change must be only effected through the intelligent microgrid CC.

2. Anti-Islanding

It is desirable to deactivate anti-islanding protection scheme for microsources

and anti-islanding controls on their PEIs, unless the ratio of utility generation

to microsource generation is too high.

The microgrid might be left with uncontrolled islands if these controls are not

deactivated.

Majority of anti-islanding schemes cause very fast tripping, it is essential to

deactivate instantly on detection of forming an isolated Microgrid.

Transmitting a blocking signal from Microgrid CC is most reliable way for

deactivating the anti-islanding trip signal.

3. Demand Side Management and Load Shedding

For handling contingencies like equipment failures , power utilities usually

assign a group of loads as non critical loads and disconnect them to avoid

any drop in system frequency and voltage, particularly during tie lines or

Loss Of Grid (LOG).

This is carried out through DSM and load shedding scheme designed to

stabilize system frequency and voltage during disturbances.

To re-establish supply demand balance by DSM, utilities trip these loads

quickly and selectively through load shedding systems .

The LOG is characterized by system under frequency and load shedding

schemes with under frequency relays are employed by utilities to

disconnect the non – critical loads and re establish system frequency with

reduced generation .

.

Demand Side Management and Load Shedding cont..

In severe cases inertia characteristic of rest of utility is also used along

with under frequency relays based load shedding schemes to restore

normal frequency level.

General loads supplied from distribution substations are tripped in these

manner .

Consumers are neither notified prior to shedding, nor get any economic

benefit from shedding

Installation of a load shedding system in DSM always has economic ,

technical and political implications .

If load shedding is unavailable political and economic problems might

also take new direction


Tripping of non priority loads existing in the boundaries of a micro gridshould be coordinated with under frequency separation point set up forforming the micro grid

The coordination depends on the following :-

If micro grid is designed initially to supply non-priority loads partiallyor fully in grid-connected mode, premature separation will lead tofurther deterioration of the overload condition

Separating micro grid before shedding non-priority load will add extraloss of generation to the utility .

Prior to separation of micro grid, non priority load must be shed if themicro grid is not designed to supply the non-priority load in gridconnected mode .


Whether the micro grid has sufficient generation capacity to supply

this non-priority load in stand-alone mode

If surplus load has to be shed to guarantee the stable operation of

micro grid , proper studies must be carried out to be assess the effects

of load shedding on dynamic behaviour of micro grid subsequent

separation

If the grid in enforced itself to separate itself due to an equipment

failure or fault between the supply bus and PCC at the utility

substation , then it must employ its own load shedding scheme.

As the inertia constant of microgrid is less than the utility, prior to developing a load

shedding scheme following technical issues have to be resolved ,

i. It must be checked that the utility has its own load shedding set up in the

microgrid not

ii. If it has, then check whether the set points, the time delays and load blocks are in

agreement with dynamic needs of the microgrid in stand alone mode.

iii. If there is no system, verify whether the permissive under frequency trips

controlled by tripping of PCC breaker is able to act fast enough to safeguard the

micro grid.

iv. The major advantage of housing utility controlled load shedding facilities is that

if separation is caused by a fault, then fast load shedding can be received by high

speed communications directly to load shedding breakers . This will

,significantly compensate for low inertia of the microgrids.


3. National Electric Code (NEC) requirements for

Distribution Transformer Protection

Prior to designing protection scheme for the MV/LV distribution transformer, -

check whether over current protection requirements of the NEC transformer

must suit with much lower fault current capacity micro grid networks.

About 600% of transformer rating can be set as over current protection for

transformer – Article 450 of NEC.

NEC recommendation are based on the assumption that the ratio of short

circuit to maximum load current would be greater than 10.

4. Neutral Grounding Requirements

• Neutral Grounding Guarantees

– Safety under the stand alone and grid connected mode of operation

– insulation integrity

– effective fault protection

• The following issues must be taken into account while designing and developing groundsystem for micro grids

– Method to provide an effectual neutral grounding for MV and LV distribution networksystems / transformer is

(i) D-Y connected

(ii)Y-Y connected

– Method to maintain compatibility

(i)within Microgrid

(ii) between utility feeder supplying Micro grid and grounding of the MV system.

– Whether the grounding system fulfils the grounding necessities of the existing DERinstallations

1. Alternative Connection for Interconnection Transformers

On the MV side of distribution networks most power utilities employ - Y-Y connected step down distribution transformer.

Y-Y connection is better suited for supplying power to conventionalconsumer loads as it provides a common ground.

The factors that must be considered while choosing the connection of thedistribution transformer are:

Back-feed Voltage and Surge Arrester Ratings

Coordination of ground relays

Unbalanced Feeder Loads

Ground Relaying for Feeders

Need for Grounding transformers

LV Fault current Magnitude

The MV/LV distribution transformers - have D connected LV and Y

grounded MV.

The ratio X0/X1 throughout the system is less than or equal to three

Hence all along the feeder including MV system of the Microgrid, 80% of

surge arrester can be used effectively.

Due to the presence of local microsource generators grounding of micro

grids in stand alone mode becomes a little bit complicated.

When a phase to ground fault occurs on the MV zone, it will be separated

automatically from the utility substation will be disconnected completely

from the Micro grid.

But the microsources will still energize Microgrid MV system

Thus, grounding and probable overvoltage conditions will be mostly

determined by the connection of microsources, transformers and by the

microsources grounding

i. Back-feed Voltage and Surge Arrester Ratings

Back-feed Voltage and Surge Arrester Ratings contd..

A Y–D transformer (Y on MV side) with X0/X1 less than three would keep

the MV system effectively grounded, since the grounded source will

provided by transformer itself.

Therefore,80% of surge arresters can be used effectively

The Y-Y connected transformers are not ground sources themselves and

they present straight through paths for zero sequence current.

The X0/X1 ratio will be equal to or less than three if zero sequence

impedance exist and it is solidly grounded, so that 80% arresters can be

used safely

But if it is impedance grounded or ungrounded, then X0/X1 ratio will be

very high and voltage across the healthy phase on MV system might even

go beyond the normal phase to phase voltage.

.

Back-feed Voltage and Surge Arrester Ratings contd..

In that case fully rated surge arresters must be used

D-Y and D-D connected transformers can never be a ground sourcefor the system.

In addition to this , the effect of over voltages on other electricalapparatus in the Micro grid served by phase to neutral connectedtransformers must also be studied carefully.

If a synchronous generator is the microsources the feeder can be kepteffectively grounded by grounding it through a reactor to keep theX0/X1 ratio of the system less than or equal to three.

Even though it is easy to ground the generator neutral solidly, themagnitude of phase to ground fault current would be greater than thatfor a three phase fault as X1 of the generator is typically greater thanzero.

Fuses, relays and re-closers connected in sequences along the distribution

network must be coordinated, so that tripping time will be more for device which

is farther from the fault.

In following sequence fault tripping will take place for a microsource:

• LV breaker or contactor of the microsources Fuse of reclose just upstream

to the microsource breaker Main PCC CB of Microgrid device at MV

side of the distribution transformer CB at utility substation.

This means that the extreme upstream devices could have fairly high operating

times for certain faults.

ii. Coordination of ground relays

iii. Unbalanced Feeder Loads

Most distribution feeders operate with almost balanced loads under normal

conditions. But, feeder current may become unbalanced for some

contingencies.

In that case Y-D transformer with LV D-winding being a ground source is

mainly susceptible to the unbalanced load current.

Unbalanced feeder overload condition Overcome by Installing a reactor in the

neutral connection of the Y-winding of the transformer.

The effective zero sequence reactance of the transformer can be increased by

inserting a reactor there by helping to reduce the percentage of unbalanced

current flow.

iv. Ground Relaying for Feeders

For Feeders: In a Y-D transformer LV D-winding is a ground source itself, it will

short out a few of the zero sequence fault current from the substation ground relay.

Problems might occur if

• The microsource shorts out plenty of zero sequence fault current to avoid the

source relay from operating in anyway.

• The recloser or substation breaker does not function properly for fuse saving.

For microsources: Y-D or D-D transformers seperate the zero sequence fault current

of the microsources from the MV system successfully.

Hence any zero sequence voltage or current measured on the LV side of transformer

point out a microsource fault.

Therefore Y-D transformer with MV Y-winding, zero sequence fault current can be

measured easily by connecting current transformer (CT) in the transformer neutral.

For MV D-winding, zero sequence voltage is to be measured from the open

delta of voltage transformer connected across MV of the microsource

transformer.

v. Need for Grounding Transformers

Installing a grounding transformer - a cheaper option to present an effective

ground source for a microsource interconnected through a D-Y or D-D

transformer.

The KVA rating of microsource - decide the impedance needs of grounding

transformer.

KVA rating:

oMain distribution transformer < grounding transformer.

Installing a grounding transformer - allow to select an optimal value of X0,

independent of the impedance of the main transformer

vi. LV Fault Current Magnitude

A transformer connection doesn’t affect on the magnitude of phase-to-phase

and three phase fault currents on the LV system of a Microgrid in grid

connected mode.

The phase to ground fault current for Y-Y transformer connection =(15-25)

*full load current of transformer.

This fault current is much lower for Y-D connection

limited by neutral resistance of the microsource

D-D transformer produces the same magnitude of fault current as the Y-D

bank,

D-Y transformer produces same magnitude of fault current as the Y-Y bank .

2. Choice of Grounding SystemNo particular choice for any type of transformer connection.

Grounding system for a Microgrid must be designed to suit with its

distribution transformer interconnection scheme.

The Microgrid remains successfully grounded even after islanding, if Y-D

transformer are used.

However, if Y-Y transformer connection is Employed, then the effectiveness of

Grounding will depend on the grounding system of microsources.

Grounding system is not chosen by considering MV/LV transformer

connection only, the ground coordination necessity of the utility is also

considered.

IMPACT OF DG INTEGRATION

IMPACT OF DG INTEGRATION

Integration of DG affects the overall performance of utility grid manyways, and are explained below,

IMPACT ON POWER QUALITY AND RELIABILITY

Power quality and reliability improvements are two main impacts ofDG integration in the form of Microgrid through active distributionnetwork

For power quality and reliability improvements followingrequirements are essential,

1. Quick response: The load requires quick response of storage devices tosafeguard from momentary voltage fluctuations.

2. Synchronization: Smooth control in paralleling and synchronizationmust be there.

3. Clean power: Storage power must be converted into clean power.

4. Smooth transfer: Smooth and seamless transfer to alternate powersource must be possible.

5. Proper isolation: In case of any contingencies, integrated DG, i.e.,Microgrid must be well-organized for a quick isolation from utility.

6. Sufficient storage capability: The quantity of storage energy must beadequate to ride through any outage until restoring primary ofsecondary power.

7. Dispatch ability: DGs through Microgrid must be able of supplying

power to varying local loads.

8. Supply to priority loads: DGs through Microgrid must be able of

supplying clean power to the priority loads under any contingency.

9. Efficiency: Must operate at high efficiency.

10. Emission: DGs through Microgrid must be able to reduce emissions

drastically to minimize the environment impacts.

IMPACT ON ELECTRICITY MARKET

The cost of power and auxiliary services must vary in such a way that itwill reflect the existing system conditions. When the system is less-stressed, the price must go down and vice versa.

Microgrid CC is programmed to control heat and electricity generationaccording to the market price signals.

The market system must be more flexible by permitting expansion ofgeneration, storage and more control for loads. This will help the bidders tomake a decision about their involvement by studying the market forcesfrom time to time.

This helps the markets to optimize the power system and the individualbidder's commercial ventures, minimizing central planning and control.Microsource owners use commercial softwares to carry detailed economicassessments.

Financial analysis programs also uses detailed modelling of the economicconsiderations. Following are the economic considerations for this modeling.

1. For predicting demand database containing weather data is used

2. Cost of standby charges

3. Avoiding thermal energy price, demand charges and emissions.

4. Thermal energy utilization.

5. Evaluation of Nox, CO and ammonia emissions with the cost involvedin emission controlling.

6. Dual-fuel configurations with fuel oil and natural gas.

7. Daily demand for electrical/thermal energy in blocks of time.

8. Turbine performance under site-specific conditions.

IMPACT ON ENVIRONMENT• Emission of greenhouse gases and particulates can be effectively

reduced by CHP systems• DGs like fuel cells and microturbines have much lower NOx,

emission due to low combustion temperatures, while DGs like SPVsystem and small hydro plants doesn’t emit NOx at all. Hence , theirapplication as microsources will considerably nitrogen and carboncompounds and total hydrocarbons (THC).

• Emissions from a microturbine mainly depend on its power output,control of the combustion process and operating temperature.

• Emissions can be minimized through precise and rapid control ofcombustion process.

• The CC must be programmed to take decisions on the basis oflowest net emission to execute eco-friendly operation.

• By building in reasonable and fair emission tariff in market system(using market responsive CSs) emission of green houses gases andparticulates can be reduced by Microgrids.

IMPACT ON DISTRIBUTION SYSTEM• One of the most important aspects of integration of DGs is their

capability to provide auxiliary services to improve reliability of theexisting distribution system

• DGs are situated very close to pocket loads.

VOLTAGE AND REACTIVE POWER CONTROL• For regulation of distribution voltage within specific limits, voltage

and reactive power control are essential.

• Though conventionally, voltage regulators and capacitor bank areemployed for regulating voltages of feeders, as square of voltagethe reactive power supply from capacitor banks drops. This mightlead to voltage collapse in the feeder. But, in response to controllersettings Microgrid can carry out smooth voltage regulation locally.

• For power utilities, voltage and reactive power control is usuallyachieved at the cost of generating capacity. If DGs offer this service,it will help the utility generators to generate at their maximumpossible capacities, thus improving overall generation.

SUPPLY OF RESERVES

1. Supplemental Reserve

• DG owners can offer this service effectively by responding to thesystem operator's request, within about 10 minutes of contingency.

• After the contingency it can sustain the energy balance up to 30minutes until backup supply takes up the loads.

2. Backup supply• DG owners can offer backup supply according to prior

agreements prepared by the system operator. The systemoperator must make a plan in advance to utilize this service forsustaining supply to priority and non priority loads duringcontingency with primary consideration to priority loads.

• DG owners can make substantial profit by selling these reservesin open market mostly during high-price period.

3. Frequency responsive spinning reserve• DGs can provide spinning reserve easily because of their faster

response to deviation in system frequency. This service must beprovided within 10 seconds and must continue until it issubstituted by supplemental reserve.

• After this period the consumer should take care of its loadsthrough load shedding or own backup.

LOAD FOLLOWING AND REGULATION

Integrated DGs can effectively provide the load-following andregulation auxiliary services for addressing temporary loadvariations.

1. Load Following

• Ability of on-line generation equipment to track variations inconsumer load is defined as load following. The major differencesbetween regulation and load following are,

i. Individual load-following patterns of consumers areextremely correlated with each other unlike individualregulation patterns

ii. Load following takes place over longer periods while inregulation minute-to-minute load tracking is performed. Thus,load following can be presented by many generators.

iii. Due to the weather dependence of loads and more or less alike dailyload patterns, the load-following changes can be predicted easily. Onthe other hand, the consumers can also communicate to the controlcentre regarding any future change in their load usage pattern.

2. Regulation• DGs are employed with automatic generation controllers (AGC)

which regulate generation to sustain system frequency within the limit.This function is termed as ‘regulation’.

IMPACT ON COMMUNICATION STANDARDS AND PROTOCOLSUniversally compatible and well-structured communication process are

necessary for coordinating DG operation in a Microgrid during grid-connected and stand-alone modes. The procedures must follow theobligations and bindings imposed by the power supply authority and ISO.

Procedures employed by heat extraction equipments, local EMS, localgenerators and ISOs are all different and they cannot provide anyconnectivity among their components. Hence, a translation service fordifferent communication methods would be provided whiledeveloping the CC scheme.

Translations are executed by a device called gateway. The key role ofthe gateway 10 provide essential connectivity among various devicesby routing, formats signaling functions and message translating.

However, during information exchange gateways may also bring inunwarranted time delays and other issues in communication process.

Several problems are highlighted below,

1. The gateways are designed to pass only a restricted amount ofspecific data .Normally, they store a local copy of the polldevices passing through it. When data is requested next time,response of gateway prepared based on the stored local copy andnot based on the current data. Hence, for large complicatedsystems it might result in supplying old and misleading data.

2. Different tools are necessary to observe and interpret theprotocols side of the gateway, this makes problem solving moredifficult. Any uncertainty brought in by faulty translation maketroubleshooting even tougher.

3. Time delays are introduced due to processing time needed fortranslation, connected networks may have different rules forgaining access to the media and different transmission speeds.

ALTERNATIVE COMMUNICATION

Severe technical requirements are imposed by ISOs to avoid abovementioned problems on gateways used by generators.

The cost of gateway is proportional to the time frame of its operation.Simpler hourly type gateways are much cheaper than the fastergateways employed in critical, real-time applications.

The standardized gateway must (i) be cost-effect reliable, (ii) permitthe DGs in Microgrid to provide the on a quicker time frame. (iii) meetthe standards for a usual utility SCADA system (iv) guaranteeconnectivity between a wide range of equipments and (v) meet therequirements of Microgrid EMS and the ISO or the utility.

A widespread protocol development scheme is essential in this regardto make sure that all concepts, devices and functions are incorporatedin the standardized gateway.

OTHER AUXILIARY SERVICESA usual vertically incorporated power utility generally owns,

operates and controls the complete generation, transmission anddistribution systems.

The consumers are free to utilize this power any time in verticalsystem. Utility has to ensure consumer fulfillment withoutnegotiating power quality, irrespective of the system condition.

Main auxiliary services obtained from DGs are network stabilityand system black start, which are briefly discussed as follows,

1. Network stability

• Low-frequency oscillations in long-distance transmission lines dieslowly by natural damping, if it is not weakened by any LOG.

• If these oscillations are not naturally damped, cascade tripping ofgenerators and hence, transmission lines overloading might occur.

• Sensor network in Microgrids are able of providing adequatedamping by sensing the low frequency oscillations.

• This can be accomplished by making the DG supply power at 180out of phase from the oscillation.

• Suitable controllers must be designed for eliminating the harmfuleffects of DC inertia to improve overall grid stability.

2. System black start• The ability of power system to resume its generation subsequent to

total system collapse, without importing power from an externalsources defined as system black start.

• Without any external support power system restores major portionof the power system to normal service. System operators have avoice communication with trained operators to initiate black start incase of necessity.

• Other most likely benefits of integrating DG are,

1) Market prices for auxiliary services, heat energy and electricenergy vary significantly with time, DG owners can makemaximum profit through (i) predicting market carefully and (ii)sale energy and auxiliary services after cutting down their ownconsumption significantly during the high-price periods.

2) Allowing DG owners to sell auxiliary services in open competitivemarket will enlarge the market supplies, which will lead to bettereconomic efficiency and reduced electricity prices.

3) Joint market participation of system operators and DG owners asboth consumers and suppliers will help to improve fairness andmake possible better resource utilization.

4) If DG owners are encouraged to provide real/reactive power supportat distribution level, then the utility generators can be operated atfull capacity for generating electricity only.

5) Response time of smaller micro sources to control centre requests isless than large generators while providing the auxiliary services.This will automatically help to overcome the control andcommunication delays

6) Auxiliary services can be provided effectively and reliably byaggregate of facilities like operators and small building owners thanutility generators. Each facility supplies a small fraction of the totalsystem necessity, for each service and the failure of any singleresource is less important.

7) Through the aggregate DG resources may have common modefailures, it is much and easier to build redundancy in aggregatedDG resources than in a big generating plant.

8) The profitability and price of each service is determined by CC in aday ahead market. In case of success, the service is maintained onthe next day at the prefixed price and so on.

COMPONENTS OF SMART GRIDS

COMPONENTS OF SMART GRIDS

• Architectural framework of smart grid is partitioned into subsystems

with layers of technology, intelligence, innovations and new tools.

• It involves bulk power generation, transmission, distribution and

consumer level of electrical power system.

Generation unit

Intelligent grid

Smart consumption

Fossil renewable (SPV,

wind)

Clean energy Energy pump

portable power

Nanotech

MEMS Distributed systems

Energy economy

revolution

High level distribution and automation

New power delivery

pardigm

Intelligent interfaces

Human

Intelligence

Cyber

security

Adaptive

control

Energy

optimisation

Fig: The intelligent grid

Functions of Each Component

1. Smart device interface component• Smart device for monitoring and control forms a part of the generation

components real time information processes.

• The resources must be effortlessly included in the operation of bothDERs and centrally distributed.

2. Storage Component• Due to inconsistency of RES and mismatch between peak

consumption and peak availability, it is significant to find methods tostore energy for future use.

• Energy storage technologies include flow batteries, ultra capacitors,flywheels, pumped-hydro, super-conducting magnetic energy storageand compressed air.

3. Transmission Subsystem Component

• Connects all main substation and load centers is backbone of anintegrated power system.

• Reliability and efficiency at a reasonable cost is the ultimate aim oftransmission operators and planners.

• Transmission line should bear contingency and dynamic changes inload with no service interruption.

• To guarantee performance, quality of supply and reliability certainstandards are preferred.

• Real time monitoring based on PMU, state estimators, communicationtechnologies and sensors are transmission subsystems intelligentenabling tools for developing smart transmission functionality.

4. Monitoring and Control Technology Component• Consist of devices for self monitoring , self-healing, predictability and

adaptability of generation

• Smart intelligent network and device enough to handle reliabilityissues, instability and congestion.

• This new flexible grid has to resist shock and be dependable to realtime changes in its use.

5 Intelligent Grid Distribution Subsystem component• Last stage in transmission of power to consumers

• Primary and secondary distribution feeders supply to small industrial,commercial and residential consumers

• The automation function will be prepared with self-learning capability,including modules for automatic billing, fault detection, restorationand feeder configuration, voltage optimization and load transfer andreal time pricing

6 Demand side management component

• DSM and energy efficiency options are developed for modifying the

consumer demand to cut down operating cost by reducing the use of

expensive generators and postpone capacity addition.

• DSM options contribute to reliability of generations and reduce

emissions.

• These options have an overall impact on the utility load curve.

• Smart energy buildings, and smart homes, plug and play, clean air

requirements, demand side meters, and consumer interfaces for better

energy efficiency will be in place.

Introduction to Smart Meters

Introduction to Smart MetersSmart meter is an electricity or gas meter that has metering as well as

communication abilities.

It measures energy consumption data and permits it to read remotelyand displayed on a device within the home.

The meter can also receive information remotely, example, switchfrom credit to prepayment mode or to update tariff information

It has two key functions to perform

i. For providing data or energy usage to consumers to help controlover consumption and cost

ii. For sending data to the utility for peak load requirements, loadfactor control, and to develop pricing strategies on the basis ofconsumption information.

Key features of smart meters are

1. Automated data reading

2. Two communication between utilities and consumers

Smart meters are developed to measure electricity, gas and water

consumption datas.

Additional features of smart meters tariff options, tax credits, DR rates,

smart thermostats, prepaid metering, switching, enhanced grid

monitoring, remote connect/disconnect of users, appliance control and

monitoring and participation in voluntary rewards, programs for reduced

consumptions

Smart meter outputs can be used for voltage stability and security

assessments

Fig: Smart meter

Electric Tariff

Electric TariffThe rate at which electric energy is delivered to a consumer is defined as

tariff.

Tariff must include the following

• Recovery of electrical energy production cost

• Recovery of capital investment cost on transmission and

distribution system

• Recovery of operation and maintenance cost for supply of

electrical energy, eg; metering equipment, billing, etc.

• An appropriate profit on capital investment

Desirable charactristics of tariff includes

• Proper return: tariff should be fixed in such way that it guarantees the

correct return from all consumers

• Fairness: tariff should be reasonable so that various categories of

consumers will be contented with the rate at which electrical energy is

charged.

• Simplicity: tariff must be simple to understand so that consumers can

simply know it.

• Reasonable profit: tariff must be able to generate reasonable profit.

• Attractive: tariff should be attractive so that huge number of consumer

swill be encouraged to consume electrical energy.

One part tariff

• When there is a fixed rate per unit of energy consumed, it is called one

part tariff or simple tariff.

• The price charged per unit is constant in this type of tariff.

• It doesn’t vary with decrease or increase in number of units

consumed.

• The one-part tariff for a station must be calculated so as to recover

both the fixed cost as well as the variable cost at a definite generation

level.

Disadvantage of one-part tariff

• There is no discrimination between different types of consumers since

every consumer has to pay equitably for the fixed charges.

• The cost per unit delivered is high

• It does not enhance the use of electricity

Two-part Tariff

• When rate of electrical energy is charged based on the maximum demand

of the consumer and unit of energy consumed, it is called a two-part

tariff.

• In two-part tariff, the total charge is split into two components, running

charges and fixed charges.

• Thus the consumer is charged at a certain amount per KWh of energy

consumed plus a certain amount per KW of maximum demand.

Advantages of two-part tariff

• It is simple to understand.

Disadvantages

• Irrespective of the fact whether consumer has consumed or not

consumed the electrical energy has to pay the fixed charge

• There is always error in assessing the maximum demand of the

consumer.

Maximum demand tariff

• It is similar to two-part tariff, but in maximum demand tariff, actual

maximum demand of the consumer is measured by installing a maximum

demand meter in consumer premises.

• Eliminates the opposition of two-part tariff, where the maximum demand

is evaluated only on the basis of ratable value.

• Generally applied to large consumers but it is not appropriate for small

consumers, as it requires separate maximum demand meter.

DYNAMIC PRICING

Dynamic PricingOne of the effective motivation strategies for load shaping, particularly

in Smart Grid.

Load shaping based on dynamic pricing supported by real time

communications play a vital role in smart grid.

Dynamic pricing can be classified as :

1. Critical Peak Pricing (CPP)

2. Time Of Use Pricing (TOU)

3. Real Time Pricing

Critical Peak Pricing(CPP)CPP is an offshoot of DR in which the utilities have technology

infrastructure place to charge consumer additional for energy during

peak periods.

It allows consumer to make a decision whether or not to pay extra on

the specific critical days, rather than paying an average cost.

It helps balance risk and cost between the consumer and the utility as

well as providing an additional incentive for consumer to reduce

energy consumption.

Time Of Use Pricing (TOU)

TOU is similar to CPP, except extrapolated across every hour for everyday.

TOU permits utility charges and rates to be evaluated based on the electricity used.

A feature of TOU prices is that the prices are set well in advanced of the period, and do not regulate to reflect real conditions.

Real Time Pricing

• RTP is one of the most significant DR strategies, where the prices

declared by retailers vary usually hourly to reflect difference of the price

in the wholesale market overtime.

• Consumers are notified of RTP prices the day before or a few hours

before the delivery time.

• One of the most typical types of RTP is day ahead RTP, in which

consumers be given the prices for the next 24 hours.

Automated Meter Reading

Automated meter reading

AMR devices let utilities to read meters remotely, removing the requirement to

sent a worker to read each meter separately.

While they do represent a certain amount of two-way communication, this

functionality is limited and does not increase the efficiency or reliability of the

utility grid.

AMR in the distribution network lets utilities read the status from the consumer

premises, alarms and consumption records remotely.

Capability of AMR is restricted to reading meter data due to its one way

communication system. Based on the information received from the meters it does

not let utilities take corrective action.

READING

UNIT

COMMUNICATION

Unit

Data receiving and

processing unit

BILLING

SYSTEM

Automatic meter reading (AMR) is a technology that automatically collects

consumption data from an energy metering device. This data is used for billing

purposes, to analyze usage and manage consumption, and to identify or resolve

technical problems.

• AMR continually gathers data, and can provide this information on a real-time

basis. Usage data can be viewed, at any time, and once collected, is immediately

stored in a repository of historical consumption information for comparative or

analysis purposes.

Fig :BLOCK DIAGRAM OF AN AMR SYSTEM

Function of blocks

Reading unit

Reading unit carry out two important jobs basically. Initially, the

reading from analog meters is converted into digital. Subsequently the data

are processed to communication unit for transmission.

Communication unit

This is one of the most challenging and important part of the system.

Data is the most important part for meter reading and billing sytem, hence

this part is challenging. Data transmission should be in an efficient manner

without any loss of data.

Data receiving and processing unit

Data receiving and processing unit receives the data transmitted from

the communication unit and process it for further purpose.

Billing system

Billing system is the final stage of AMR which takes the meter reading

and can generate bill for that meter. It uses the data of the data base those

are collected from the meter reading through all the units of our system.

Analysis on electricity usage for each meter can be also carried out using

this system.

VEHICLE TO GRID (V2G)

VEHICLE TO GRID (V2G)

The incorporation of electric vehicles and plug in hybrid electric

vehicles(PHEV) is an additional part of the smart grid system.

V2G power employs electric drive vehicles to provide power to

particular electric markets.

Fuel cells, battery or hybrid of these two is employed to store energy

in vehicles.

There are 3 different versions of V2G concept

1. A hybrid or fuel cell vehicles

2. A battery is powered or plug in hybrid vehicle

3. A solar vehicle all of which involve an on battery

The major advantages of V2G are

it provides storage space for renewable energy generation

it stabilize large scale wind generation via regulation.

PHEV significantly cut down the local air pollution problems

Hybridization of electric vehicle and association to utility grid conquer the limitation of their includingbattery/size, cost and short range of application.

PHEV offers an alternative to substitute the use of petroleum based energy sources and to reduceoverall emission by using a mix of energy resources.

A V2G vehicles is capable of providing energy back to the utility grid.

Electricity flows all over the utility grid from generators to consumers where as unused energy flowsback and forth from the electric vehicle

During off peak time, battery electric vehicle can charge and during peak time,battery can dichargethrough the utility grid.

There are 2 types of V2G architecture :

Deterministic Architecture

Aggregative Architecture

1. Deterministic architecture

Services provided to PEV directly from grid operator

A direct line of communication exists between plug in vehicles and grid systems operator ,thus each vehicle can be treated as a deterministic resource.

The vehicle is permitted to bid and carry out services when it is at the charging station

2. Aggregative architecture

In aggregative architecture, an intermediate aggregator is inserted in between grid systemoperator and plug in vehicle.

The aggregator can bid to carry out services at any time, while the individual vehicles candisengage from the aggregator as they arrive at and leave from charging station

ADVANTAGES

– Peak load leveling

– Carbitrage

– Back up power solution

Plug in hybrid Electric technology

Plug in Hybrid Electric Vehicle Technology

Introduction

A Plug in Hybrid Electric Vehicle (PHEV) is basically a hybrid electric

vehicle with a larger battery pack.

It runs on electricity when its battery soc(state of charge)is high or else,

the IC engine takes over and the vehicle uses gasoline similar to a hybrid

vehicle.

The battery pack can be recharged via a plug which provides connection

to the utility grid; hence, a PHEV , compared to conventional cars , an

extra equipment to connect to an external electrical source for charging.

Aggregator 1

Aggregator 3Aggregator 2

Grid system operator Vacant

Conventional auxiliary

service providers

Fig 7:-Aggregative approach of vehicle to utility grid connection

ARCHITECTURE OF PHEV

The architecture of a PHEV is defined based on the connection between their power train components

These components are

•IC engines

•PEI

•Battery (B)

•Motor/generator (M/G)

•Transmission (T/R)

Major types of architectures are

I. Series (electrically coupling)

II. Parallel(mechanically coupling)

III. Series-parallel(mechanical and electrical coupling)

IV.Complex(mechanically and electrical coupling)

Series

Parallel Series parallel

COMPLEX

G/M PEI T/RM/GPEIB

ICE M/G T/R

PEI

ICE

B

T/RMM

PEI PEIB

ICE G/M

PEI B PEI

T/RM/G

Fig 8:-PHEV architectures

Series (eg; Chevrolet volt) and complex (eg; Toyata prius)topologies are

the most well known architectures for PHEVs.

The battery charger can be on-board or external to the vehicle.

On-board chargers are limited in capacity by their weight and size,

dedicated off-board chargers can be as large and powerful as the user can

afford, but require returning to the charger.

High speed chargers may be shared by multiple vehicle

PHEV operates in three mode

•Charge-sustaining mode

•Charge-depleting mode

• Blended mode or mixed mode

In charge-sustaining mode certain amount of charge above battery SOC is

sustained for emergency use.

Charge-depleting mode permits a fully charged PHEV to operate exclusively on electric power until its battery SOC is depleted to a predetermined level , at which time the vehicles IC engine or fuel cell will be engaged.

Mixed modes describes a trip using a combination of multiple modes

Advantages of PHEV

• Operating cost

• Vehicle to grid electricity

• Fuel efficiency and petroleum displacement

Disadvantages of PHEV• Cost of batteries

• Recharging outside home garages

• Emission shifted to electric plants

• Tiered rate structure for electric bills

• Lithium availability and supply security

SMART SENSOR

Smart sensor

Smart sensors are defined as sensors that provide analog signal

processing of recorded signal , address and data transfer through a

bidirectional digital bus and manipulation and computation of the sensor-

derived data

Basic architecture of IEEE 1451 standard for

smart sensor network

XDCR ADC

XDCR

Dig,I/OXDCR

DAC

Transducers electronic

data sheet(TEDS)

Address

logic

XDCR ?

Network capable

application

processor(NCAP)

NE

T

W

OR

K1451.1 object model

Transducer

independent

interface(TII)

1451.2 interface

Basic Components of a smart sensor

SensorSignal conditioning and

digitization

Main

processor

Communication interface HMI

Measurand

DATA

GAINCONTROL

Smart sensors enable more accurate and automated collection of

environmental data with less erroneous noise amongst the accurately

recorded information.

It offers functionalities beyond conventional sensors through fusion of

embedded intelligence to predictive actions.

Smart sensors are extensively employed in monitoring and control

mechanisms in variety of fields including smart grid ,battlefield , exploration

and great number of application.

Basic structure of a local level sensor

SensorSignal conditioning and

digitization

Main

processor

Communication interface HMI

Measurand

DATA

T&D

asset

Smart sensor

Basic structure of a station/feeder level sensor

(radio topology)

Substation

computer

Smart sensorT&D

asset

Smart sensorT&D

asset

Smart sensorT&D

asset

Basic structure of a station/feeder level

sensor (meshed topology)

Smart sensorT&D

asset Smart sensorT&D

asset

Smart sensor

T&D

asset Smart sensorT&D

asset

Substation

computer

Basic structure of a centralized control room

level sensor

Asset

Monitoring system

Feeder

monitoring system

Central control

room

Transmission

Monitoring system

Substation

monitoring system

Home and Building Automation

Home and Building Automation

Home and building automation is a part of Smart Grid network

An automatic home or building is termed as a smart home.

Sources of energy and appliances are coordinated and

controlled in such a manner that the Smart Grid objectives are

met optimally

Building smarter home needs smart energy controllers which

also having smart metering capabilities.

Fig: Architecture of Smarter homes

Main Controller or the Smart Controller

The main controller is an intelligent, programmable device capable of

performing numerical processing, computations, running optimization

subroutines, metering, setting up a two-way communication with the

Smart Grid Control Centre (SGCC)

Takes decisions on the basis of specified real time constraints

It has the capability to control the electrical appliances directly

Smart Grid Control Centre (SGCC)

SGCC is the gateway of smart controller’s to the energy world; acomputer performs the function of energy database and energyexchange

Owned and functioned by a regulatory body on behalf of utilities

Information contained in the exchange consist of the following1) Past, present and the future prices of energy from various utilities

and other related costs, like discounts, offers, lock in period etc.

2) If more than one rate is valid, then the time at which the each rate isapplicable should be displayed

3) Information about trade volumes

4) Information and profiles of different connected members/users ofthe SGCC

• The main controller and optimization algorithms running in

it need a lot of inputs from SGCC

• The controller has to depend on the stored information, if

present information is not available from SGCC

• The optimization algorithms will not be capable to make the

actions on the basis of latest energy information

Fig: Typical information in SGCC

Metering Clock

Communicatio

ns interface

and reporting

Home appliances

control and

monitoring

Algorithm for supply changer

Algorithm for minimising energy

usage

Energy usage data patterns

Algorithm for minimising energy cost

Automated process

Algorithm for integrating various

energy sources

Functions of SGCC

– An SGCC must be there in every geographical area and all the

consumers and utilities in that region must be connected to the SGCC

– Every consumer must have an account in SGCC and they can access this

account to gather information associated with them. Consumers can

forecast energy consumption and through SGCC they can inform to

utility about the forecasts. The utility can choose to reward the consumer

based on the accuracy of the forecasts.

– SGCC must act as a database for storing the information about energy

system.

– It acts as a backup information storage system.

• Utilities access SGCC to place in their latest offers, to know the total number of consumers availing their service, update the present and future prices and to know about their consumer’s consumption patterns.

• SGCC keeps the consumers credit reports (only accessible to the utilities)

• Through internet connected to the controllers, consumers can access the SGCC to check the present and future energy prices to know about their present consumption patterns and to initiate the changeover to a different utility

• Information regarding the service levels of each utility will be also available in SGCC

•Acts as a gateway for the consumer complaints

•A centre of information for the consumers to inform their energy related

restoration activities, blackouts, and outages, present and future shortages

•SGCC also houses information for each utility according to the source of

energy, i.e., from the non-renewable, renewable, nuclear, etc.

•The changes in energy policy initiated by the utility or the government will

be published on SGCC and will be accessed by the consumers

Sources of Energy• Normally, sources of energy can be anyone or combination of the

following

1. Supply from utility grid

2. Supply of gas

3. Other locally offered DGs like wind energy, building integratedphotovoltaic(BIPV), small-hydro, biomass with output of fewkilowatts and storage devices

Controlled Appliances• The controlled appliance/loads are classified into

• Type-A,

• Type-B,

• Type-C

– Type-A loads are the loads which do not permit much flexibility in

switching. Their load switching operation cannot be timed according to

the requirement. Examples: domestic entertainment appliances, lighting

loads, refrigerator and appliances needed during cooking, etc.

• Type-B loads are the loads that offer switching flexibility;

their switching can be timed. Examples: Dishwashers, dryers,

washing machine, etc.

• Type-C loads are the loads which do offer flexibility in terms

of switching but need human intervention. Examples: vacuum

cleaners, electric iron, etc. Number of Type-C loads are

decreasing due to rapid growth of automation industry.

Network Interfaces

The main controller interacts with the SGCC through network

interfaces.

It can be an optical interface or electrical or combination of these.

MMI Console or the User Interface

Permits access to the information in SGCC, house owner to

interact with the controller, configure the controller, update the

software, change the settings, etc.

Controller to Appliances Interface

The interface usually consists of relays.

The relays will switch on or off the power supply to individual

appliances on the basis of commands from the controller.

Interface can be separate module or incorporated with the main

controller.

Modern day multifunction relays employed in the control and

protection appliances seamless integration of switching interface

and the controller

The Main Controller

The main controller is a computer in which the software needed

to build the intelligence related to the energy of the house is

stored.

Enormous functionalities can be build in the controller

depending upon sources of energy available in the control area,

diversity and variety o loads, etc.

Main controller receives the clocks signal from SGCC and

hence works in synchronized with it.

Features of Main controller

1. Features of controller in a simple residential area

• The main controller periodically contacts the SGCC and downloadsthe energy updates.

• Main controller downloads the newest energy prices from SGCC anduses the information to work out the energy usage changes with thepresent utility.

• On the basis of switching costs, present and future prices of energy,compulsory lock in period of present utility and the projected energyconsumption will decide whether to continue with the present utilityor initiate a switch over process.

• When the rate of energy is lowered, type-B loads which offerflexibility in switching and are not continuous, should be switched.The controller must be programmed to supply these loads only whenthe rate of energy is low.

• Records the daily, weekly and monthly energy consumption andwill provide the details to the house owner on request.

• Data related to power quality would be recorded for legal andcontractual purpose.

• Depending on the power factor in the controlled area controllercould switch on or off the reactive power equipment for pfcorrection.

• Based on availability of solar radiations the controller will alsobe programmed to switch off the lights in some parts ofcontrolled area, so that lighting loads are switched on only whenneeded.

• After some time, supply to Type-C loads must be automaticallycut off to save energy; the controller must be programmed for thesame.

2. Features of controller with BIPV in the controlled area

– Maximum power from an SPV module varies with solar radiation

and temperature. Hence, the controller must be programmed to

track peak power from the panel under all conditions irrespective of

the connected load.

– If the MPP of an SPV is higher than the total connected load of the

system, then the additional energy from the BIPV will be diverted

to the storage devices.

– BIPV employs power conditioning units(PCUs) like converter and

inverters. The equipment injects harmonics to the system. The

controller must have an algorithm to switch on the necessary filters.

3. Features of controllers with energy storage• It considers the storage system as an additional type-B load, activating

PCU and permitting energy storage devices when the energy cost is lowand it is retrieved when the cost are high.

• It also keep proof of full cycle efficiency of the storage system.

4. Features of controllers with heating systems in controlled area

• During off-peak hours, at times cost of electricity might become cheaperthan that of gas. In such cases the controller can reduce the energy bills byswitching the hating system sources between electricity and gas.

• On the basis of spot prices of electricity and gas and efficiency of heat andelectricity system, the switching over is decided.

• The controller must have the intelligence to take decisions to switch overof the source.

5. Remote access features

– One of the foremost advantage of smart controller is its ability to

permit remote access to the owner.

– Through SGCC consumer can access the controller from a remote

site on internet through a secured password based system.

– The consumer can turn on or off the main energy inputs and

appliances according to the wish.

– Helps to decrease the accidents caused by the appliance left on by

the consumer during the vacations.

– On the other hand, main controller can be programmed to turn off

new appliances i.e., type-B and type-C loads, when it detects

idleness in the house fpr certain period.

Fig: Typical information’s in a smart home controller

Energy related

information

Consumer account

numbers

Spot and future

energy prices from all

suppliers

Information on

outage work in

progress etc.

Information on users

like energy usage

pattern, credit rating

etc.

Information on

suppliers like energy

mix , service level etc.

Contractual and

financial information

backup

Latest energy

updates, news ,govt

policies, activities and

promotions

Automated Processes

Smart Grid provides the chance of setting up automatic processesthat are advantageous to all the consumers.

These processes helps the consumers to decrease the amountspent on energy by choosing cheaper source or by decreasingenergy consumption and helps to improve level of services.

Three such processes are discussed below:

1.The utility changeover processi. The utility changeover process will be initiated by the main controller

or manually by the consumer based on present and future prices ofenergy, forecasted future energy consumption and the changeovercosts

ii. The controller periodically assesses the information regarding energyprices and works out the economics in automatic changeover process.

iii. Once the controller is manually instructed by the consumer,

the controller sends message to the SGCC requesting it to

officially to make the changeover.

iv. Details of the consumer will be forwarded to the new utility

and if the new utility accepts the credentials of the

consumer, a confirmation is issued to the consumer for the

official changeover.

v. The consumer can accept or reject the contract.

vi. An acceptable letter is sent back to the utility and also one

copy is stored in the SGCC, once the contract is accepted or

deemed to be accepted.

vii.A unique number is assigned to the contract and this

number is communicated to the consumer and the utility.

viii.SGCC will debits the account of the consumer on the basis of total energy consumed until the changeover process to the changeover costs.

x. The debits made from the account of the consumer are then credited to the particular utility accounts.

xi. The changeover process will be formally completed after resetting the meter and storing new tariff in the controller which will work out the energy consumption of the consumer.

2. Complaint addressing mechanism

i. The consumer registers a complaint in SGCC. The complaint can be either quality of power supply related or billing related.

ii. An investigation is carried out based on the details of complaint in the SGCC.

iii. The investigation reports are forwarded to the consumer and necessary action is taken by the utility.

i. The consumer can be effectively compensated if the investigation proves that the utility is at fault.

ii. A database for complaint is also maintained and if the complaints are proved to be real then it is moved to the database for public review and it helps other consumers for proper selection of utility.

iii. Unsolved complaints which remain for a particular period of time will be moved to another database for public review.

3. Automated billing and collection mechanismi. The utility set up payment mode like payment when the energy

consumption goes beyond a particular amount or payment everymonth based on actual energy consumption.

ii. The consumer selects the particular payment mode from the optionsoffered by the utility.

iii. The payment conditions are decided jointly and it is stored in SGCCand controller.

i. Details of payment are also stored in main controller.

ii. Details of energy consumption are also sent to SGCC by main

controller daily, which then transfers these details to the related

utility

iii. The utility fixes the bill on the basis of payment options selected

by the consumer and sends it to the SGCC for sending to the

consumer. The bill includes the total amount and the date in which

the amount is likely to be deducted from the account.

iv. Using the data available in the controller, consumer can validate

the details.

v. Once the payment has been credited, utility sends a confirmation

to the consumer. For certain period the records will be stored in the

SGCC. Records of payment will also be stored in the main

controller.

Advantages of home and building automation

Improved energy prices due to competition in energy market

Improved services due to increased servicing monitoring

Switch over from one utility to another is easier and the

process is also faster.

For poor quality of supply the consumers will get

compensation.

Integration of home based DERs with the home energy

system become much easier.

Automated load controlling helps in distributing load over

time which is beneficial to the consumer and utility grid.

Intelligent electronic devices

INTELLIGENT ELECTRONIC DEVICES

IEDs are microprocessor based device with ability to exchange data and

control signals with another device over communication link.

IEDs can be regarded as the eyes and ears of any remote power

management systems

IEDs are installed to improving monitoring ,control, protection and data

acquisition capabilities of the power system

It capable to record various types of data

IEDs receive data from power equipment and sensors and can issue

control commands, such as tripping CBs, if they sense any abnormality

in current, voltage or frequency or lower/raise voltage levels in order to

maintain the desired level

Digital protective relays (DPR) are primarily IEDs, using a

microprocessor to perform several monitoring, control and protective

functions

A usual IED can contain around 5-8 control functions controlling

separate devices, an auto-reclose function, 5-12 protection functions,

communication functions, self monitoring function.

Common types of IEDs consist of

•CB controllers

•Capacitor bank switches

•Voltage regulators

•Protective relaying devices

•LTC controllers

Functional architecture of IED

Intelligent electronic

devices

Modern communicationSubstation server

HMI

Control

Metering

Motoring

Protection

Satellite time

synchronization

Office/home

Three types of IDEs have been considered :-1. Circuit breaker monitor(CBM)

2. Digital fault recorder(DFR)

3. Dgital protective relays(DPR)

These devices can measure internal CB control signals, relay trip signal, phase currents and voltages, internal logic operands and oscilography data.

The CBM is designed to monitor condition of CBs and control circuit signals during opening and closing process.

The DPR is designed to monitor transmission line when a fault is detected and operating conditions on trip CBs.

The DPR responds to sudden change in current, voltage, impedance, frequency and power flow and it will trip substation CBs for faults up to a certain distance away from the substation.

The DFR is a device which is primarily designed to capture andstore short duration transient events, trends of input quantities such as power harmonics, frequency, RMS and power factor and longer-term disturbances

After being triggered by a pre-set trigger value, the device records largeamount of data. Automated analysis application can be developed for each type of devices.

Data recorded by each device is converted to a standardformat using the application and reports are generated per each IED type

Those reports are small in size and can be sent easily out of substationthrough communication infrastructure (in case of multiple events)

All extracted data and information are available instantly after event occurrence

1. Circuit Breakers Monitor Analysis (CIMA)

• CIMA carries out analysis of waveform taken from the CB control

circuit using a CBM and produces an event report and suggests

repair actions

• The solution is executed using an expert system for making

decision and advanced wavelet transforms for extracting waveform

feature

• It facilitate maintenance crews, operators and protection engineers

to consistently and quickly estimate CB performance, recognize

performance shortages andoutline probable causes for formal

functioning

Circuit breaker monitor analysis architecture

Signal

Processing

unit

Expert

System

module

DFR

recording

Event

report

SP settings ES settings Rules

2. Digital Protective Relay Analysis (DPRA)

• DPRA is an expert system which automates diagnosis and validation

of relay operation .

• Different relay reports and files are taken as inputs and it generates

reports by analysing taken inputs using embedded expert system .

• Diagnosis and validation of relay operation is based on comparison

of expected and actual relay behaviour in terms of the status and

timing of logic

Digital Protective Relay Analysis architecture

Relay operation

Logic ES module

Validation and

diagnosis of ES

module

Setting file

Facts of

relay

behaviour

Analysis

report

Performance

information

Hypothesis of

relay

behaviour

Event record

report

COMTRADE

file

Performance

specifications

3. Digital fault recorder assistant(DPRA)

– DFRA carry out automated analysis and DFR event records data

integration

– It converts various DFR native file formats to COMTRADE

– Additionally , DFRA carry out signal processing to find out pre- and

post- fault analog values, statuses of the digital channels, faulted

phases and fault type

– It also checks and evaluates fault location, system protection, etc

Digital fault recorder analysis architecture

Signal

analysis

Expert

system

DFR

Comm.

DFR file

conversion

Result

processing

User

interface

Broadcast

services

Waveforms

& reports

Centralised

database

Reports

Client Server

NOTES ON DPRA AND DERA DPRA and DERA can carry out thorough disturbance event analysis

though, DERA cannot carry out complete analysis on operation of

protective relays, since the internal states of a protective relay cannot be

recorded using DFR device.

In contrast, DPRA can diagnose and validate the relay operations totally,

but disturbance information might not be complete, because DPR collects

data from single transmission line only

DERA cannot execute the CB tripping operation analysis because CB

control circuit signals are not monitored by DFR device, but CBMA

provide this information in detail.

Data incorporation across the whole substation is necessary to accomplish

full IED data utilization. To realize full eventexplanation the results of

various analyses have to be merged.

The whole idea is to collect and incorporate data automatically from all

substation IEDs , examine it and extract information needed for different type

of users such as system operators, protection engineers, maintenance staff, etc

Data can be examined at the substation level and conclusion can be sent to the

maintenance and protection group directly.

Another approach is to access data then extract and send it to the control centre

, where the information is merged with data from SCADA, processed by

centralized applications and the results prepared for various user groups.

By combining CBMA, DPRA and DFRA comprehensive reports are generated

Information for System Operators Responsibility of decision making on system operation and restoration are

with system operators.

When an event occur in the system, they are interested to know that the

fault is permanent or not, location of the fault and whether CB and relays

operated correctly.

IED devices collect more data than RTUs, hence, the extra data can be used

to verify and complementwith the SCADA reading. Normally right

conclusion are only be made by using IED data.

To improve the accuracy of the analysis data obtained from SCADA

through RTUs can be combined with data obtained from IEDs this will

provide better results to the operator

Information for Protection EngineersResponsibility on the final assessment on rightness of any system response to a

given fault condition is with protection engineers.

They have to check operation of each device using the information gathered by

IED and in case of misoperation they need to find out the cause for device

misoperation or failure.

Generally, they are involved in DPR operation during the event.

Major information needed for protection engineers, are name of substation fault

type, duration and range, affected circuit, triggered time and date event outcome

and devices operation with major focus on relay operation . If the fault was

removed within the specified time and all devices operate properly, there is no

need for any supplementary data and second level of report that have further

information will not be generated.

Second level of the report explains displays signal waveforms and internal

logic operation of relay

It lists series of the relay signals status and recommends remedial

actions

Information for Maintenance StaffMaintenance staff's are responsible for system repair and restoration.

Responsibility for monitoring CB operation is also with this group.

Report will be generated for maintenance staff which consisting of

information about signal affected by tripping operation , pre-, during and

post – fault analog signals values , waveforms display and suggestion for

remedial actions

Phasor measurement units

Phasor Measurement Unit

PMU is a device which measures the electrical waves on a

utility grid by employing a general time sources for

synchronization.

The PMUs consist of branch current phasors and bus voltage

phasors, as well as locations information and other network

parameters.

Time synchronization permits synchronized instantaneous

measurements of various remote measurement points on utility

grid.

The resulting measurement is known as a synchrophasor.

PMU is the metering device whereas a synchrophasor is the

metered value.

Basic components of a phasor measurement unit

Anti-aliasing

filter

Phasor

Micro-processor

16-bit A/D

converter

Phasor locked

oscillatorModern

GPS

receiver

• PMU can measure 50Hz Ac waveforms usually at a rate of 48

samples per cycles.

• The current and voltage signals are converted to voltages with

appropriate instrument transformers or shunts, so that they

matched with the requirements of the ADCs.

• By using an ADC for each phase the analog AC waveforms are

then digitized.

• A phase-locked oscillator along with a GPS provides the

required high-speed synchronized sampling with 1 microsecond

precision.

HIERARCHY OF PHASOR MEASUREMENT SYSTEM

Super data

concentrator

Data

concentrator

Data

concentrator

PMU PMUPMUPMUPMUPMU PMUs locted

In substation

Data storage

Application

Though, PMUs might receive in multiple time sources

including non-GPS references which is calibrated and working

synchronously.

The resultant time-stamped phasors can be transmitted to a

local or remote receiver at rates up to 120 samples per second.

Phasor measurements are taken with high accuracy from

various points of the power system at the same instant,

permitting the operator to visualize the precise angular

difference between various locations.

Microprocessor based instrumentation such as disturbance fault

recorders (DFRs) and protection relays integrate the PMU

module with other existing functionalities as an extended

feature.

When incorporated with Smart Grid communications technologies, the taken measurements will provide dynamic visibility into the power system.

Implementation of Smart Grid with real time measurement will improve every aspect of the power delivery system including generation , transmission, distribution and consumption.

It will provide dynamic visibility into the power system.

It will increase the potential of DGs integration, bringing generation closer to the pocket loads.

Additionally utility monitoring systems include electronic instrument transformers, dynamic line rating technology, cables, insulation contamination leakage current and monitors for CB and current frequency

.

• By employing phasor data concentrators (PDCs) technologies,

the phasor data is collected either at centralized locations or on-

site.

• These ISO’s will monitor phasor data from individual PMU’s

from as many as 150 PMU’s, this monitoring provides an exact

means of establishing controls for power flow from multiple

energy generation sources.

• The data is then transmitted to a regional monitoring system

which is maintained by the local ISO.

Conceptual diagram of a synchronized phasor measuring system

WIDE AREA MEASUREMENT SYSTEMS(WAMS)

WIDE AREA MEASUREMENT SYSTEMS (WAMS)

WAMS is one of the most important components in smart grid.

In comparison to the present SCADA system, measurement of the system states are carried out at a comparatively higher rate(5-60 samples per second versus one per 2-6 s).

All systems phasors are developed continuously and simultaneously, rendering real time information of power system parameters

• Thus, WAMS can improve the performance of utility grids significant by stability assessment, fault detection, remedial control action and supporting more accurate state estimation.

• Components of WAMS: PDCs for aggregating and relaying measured data. Whereas PMUs are employed widely in WAMS , the currently available dual use line relays(DULRs) introduce variability to modern WAMS construction.

Components of WAMS

• DULRs are the protection digital relays for transformers and transmission line while providing system protecting it an report synchrophasor data.

• DULR is also called “branch PMU”, since it is installed at transformers and along transmission lines.

• Even though DULR can only monitor the current phasor of the branch and the voltage phasor of its adjacent bus, it is promising due to its low construction cost.

• PMU and DULR interface WAMS with the power system and they consist of CTs, VTs, synchronous GPS clock and instrumentation cables.

• Data measured by these devices are transmitted to one or more multiple layers of PDCs located at selected location in the system, where the data are aggregated, compressed and stored in to a time stamped measurement stream.

• The data stream is then fed in to application software at the central controller for system state monitoring and control decision generation with the various control objectives.

EE403


SMART GRIDS

Module IV

Aisha MeethianAP, EEE ICET

EE403


SMART GRIDS


End.

Sem.

Exam.

Marks

IV

Smart energy efficient end use devices-

Smart distributed energy resources-

LoadCurves- Load Shaping Objectives-

Methodologies - Peak load shaving -

Energy management-Role of technology

in demand response- Demand Side

Management –Numerical Problems

7 15%

Smart energy efficient end use devices

• Devices are made smart by equipping it with 2-

way communication technology and adding

intelligence to it.

• Sensors and sensor networks are incorporated.

• Smart devices are energy aware devices capable of

communicating real-time energy consumption.

• Communication technologies- ZigBee, wi-fi,

bluetooth, ethernet..

Key features

• Information on dynamic electricity pricing

• It can respond to utility signals to improve peakmanagement capacity, energy saving by providingreminders to shift energy use while prices are lower.

• Integrity of operation

• Consumer can override all former programmedselections

• When connected to HAN, smart devices allow to develop theirown energy usage profile.

• Features to use REs by shifting power usage to anoptimal time for DGs, Eg. when the sun is shining.

Smart distributed energy resourcesSmart DERs include onsite generation techniques like SPV

and onsite storage devices like battery. Devices are

controlled dynamically to supply base load, temporary

demand reductions, peak shaving, power quality and

power export.

Smart DERs provide smart grid with

Improvement of functionality of PHEV and electric

vehicles

Utilization of vehicle battery pack

Assist power import/export with system

Remote consumption and storage of DERs

Tracking connections for billing and study

Smart distributed energy resources

• Solar

• Wind

• Bio-mass

• Small and micro-hydro

power

• Fuel cells

• Geothermal heat pumps

Load Curves

• The curve showing the variation of load on the power station

(power plant) with reference to time is known as load curve

• Time duration: 1 hr. –hourly load curve

• Time duration: 24 hrs. –daily load curve

• Time duration: 1 month– monthly load curve

• Time duration: 1 year– yearly load curve

Need for EM /

Dynamic Energy Management

(DEM)

Dynamic energy management is an innovative

approach to manage load at the demand side.

It incorporates the conventional energy use management

principles represented in DSM, demand response (DR),

and DER programs and merges them in an integrated

framework that simultaneously addresses permanent

energy savings, permanent demand reductions, and

temporary peak load reductions.

Building Blocks of

DEM

Key Features of a

Dynamic Energy Management System

1) End-user flexibility.

2) Simplicity of operation.

3) Standard IT platforms.

4) Open systems architecture and universal gateways.

5) Integration with existing building energy management

system

6) Open standards and interoperability.

7) Flat architecture for robust, low-cost systems.

Demand Response

• Demand response (DR) refers to mechanisms to manage the demand from

customers in response to supply conditions.

• For example, having electricity customers reduce their consumption at critical

times or in response to market prices.

• Demand response can broadly be of two types—

incentive-based demand response and

timebased rates

• Incentive-based demand response includes direct load control,

interruptible/curtailable rates, demand bidding/buyback programs, critical

peak rebate programs, emergency demand response programs, capacity

market programs, and ancillary services market programs.

• Time-based rates include time-of-use rates, critical-peak pricing, and

real-time pricing.

Role of technology in demand response

Demand response technology

tree

Demand side management

(DSM)

Technologies, actions and programs implemented by

utilities, governments and consumers on the demand side

of energy meters, to manage or to reduce energy

consumption through energy conservation, energy

efficiency, or onsite generation and storage to reduce total

expenditure, emission and consumer bills.

Boundaries of DSM

DSM methods

• Energy saving & load efficiency

• Pricing models

• Direct load control

• Demand side bidding

• Frequency control

• Energy storage

Benefits of DSM

Challengesi)Lack of Information, Communication and Technologyinfrastructure.

ii)Lack of awareness program about DSM and its benefits.

iii)DSM based approach increases the complexity of system whencompared with traditional approach.

iv)Improper market structure and lack if incentives.

v)DSM based approach are often less competitive.

vi) Economy associated with DSM based solutions in a long run.

vii) Rehabilitation of distribution system network is quite tedious.

1. a power station has a maximum demand of 100mw

and annual load factor of 40%,determine the total energy

generated in a year.

EE403

DISTRIBUTED

GENERATION AND SMART

GRIDS

AISHA MEETHIAN

AP,ICET

Module V


End.

Sem.

Exam.

Marks

V

Advanced Metering Infrastructure

(AMI), Home Area Network (HAN),

Neighborhood-Area Networks

(NANs), Sensor and Actuator

Networks (SANETs)

Smart Substations, Substation

Automation, IEC 61850

Substation Architecture,

Feeder Automation.

7 20%

Advanced Metering Infrastructure

(AMI)

• AMI is not a single technology, but rather an

integration of many technologies that provides an

intelligent connection between consumers and

system operators.

• AMI gives consumers the information they need to make

intelligent decisions, the ability to execute those

decisions and a variety of choices leading to substantial

benefits they do not currently enjoy.

• In addition, system operators are able to greatly

improve consumer service by refining utility

operating and asset management processes based

on AMI data.

Building Blocks of AMI

BPL- broadband over power line, PLC- Power line communication, RF- Radio frequency

Building Blocks of AMI

Characteristics of AMI

1. Provide the basic link between the utility grid and the consumer.

2. Generation and storage options distributed at consumer site can be

monitored and controlled via AMI technologies

3. Markets are enabled by connecting the utility grid and the consumer

through AMI

4. Smart meters are employed with power quality monitoring abilities

5. Remote connection and disconnection of individual supply

6. Automatically send the consumption data to utility at pre-defined intervals

7. Helps in self healing by detecting and locating failures

8. Improve asset management and operations

9. Accelerate the deployment of advanced distributed operations equipment

and applications

Benefits of AMI

CONSUMER BENEFITS

- more choices about price and service,

- Less intrusion and more information with which to manage consumption,

cost and other decisions.

- higher reliability, better power quality, and more prompt, more accurate

billing .

- In addition, AMI will help keep down utility costs, and therefore electricity

prices.

UTILITY BENEFITS

Utility benefits fall into two major categories, billing and operations.

Billing - AMI helps the utility avoid estimated readings, provide accurate and

timely bills, operate more efficiently and reliably, and offer significantly

better consumer service.

- AMI eliminates overhead expenses of manual meter reading.

- Consumer concerns about meter readers on their premises are eliminated.

Benefits of AMI (contd..)Operation:

• With AMI the utility knows immediately when and where an outage occurs so

it can dispatch repair crews in a more timely and efficient way.

• Using AMI, the utility can receive significant benefits from being able to

manage customer accounts more promptly and efficiently, starting with the

ability to remotely connect and disconnect service .

• Maintenance and customer service issues can be resolved more quickly

and cost-effectively through the use of remote diagnostics.

• AMI enables new programs and methods for creating and recovering

revenue such as distributed generation and prepayment programs.

• AMI also provides vast amounts of energy usage and grid status information

that can be used by consumers and utilities to make better decisions.

Benefits of AMI (contd..)SOCIETAL BENEFITS

• Improved efficiency in energy delivery and use,

producing a

Favorable environmental impact.

• It can accelerate the use of distributed generation,

which can in turn encourage the use of green energy

sources.

• It is likely that emissions trading will be enabled by AMI’S

detailed measurement and recording capabilities.

• A major benefit of AMI is its facilitation of demand

response and innovative energy tariffs.

Challenges of AMI

• High capital cost : Expenditures on all hardware and softwarecomponents, including meters, network infrastructure and networkmanagement software, along with cost associated with the installationand maintenance.

• Standards: standards are needed to ensure interoperability among theAMI Based grid system.

• Integration: AMI is a complex system of technologies, that must integrateall the information and management systems like SCADA, DMS etc.

• High capital costs• Standardization• Integration

LOCAL AREA NETWORK (LAN)

• LAN is a packet data communication system which offers high

bandwidth communication over a comparatively restricted

geographic area through an inexpensive transmission media .

• LAN is composed off two or more components of disk storage

with high capacity, which permits all computers in the network to

access a general set of rules.

• LAN has operating system software which instructs network

devices, interprets input and permits the user to communicate with

each other.

• In LAN each hardware is termed as node

• The LAN can incorporate several hundred computers within a

geographical stretch of 1-10 km

• The LAN can also interconnected together to form WAN

Advantages and special attributes of LAN

Resource sharing

Area covered

Cost and availability

High channel speed

Flexibility

Home Area Network (HAN)

A home area network is a dedicated network connectingdevices in the home such as displays, load control devices andultimately "smart appliances" seamlessly into the overall smartmetering system.

It facilitates the communication and sharing of resourcesbetween computers, mobiles and other devices over networkconnections.

It also contains software applications to monitor and controlthese networks.

HAN may be wired or wireless.

HAN is a subsystem within smart grid dedicated to DSM andincludes DR and energy efficiency

Advantages

• Asserting the utility in managing peak electric demand

• Energy optimization

• Centralized access to multiple appliances and devices

Challenges to HAN

• Major challenge is to integrate various technology solutions,

so that smart services such as comfort, automation, security,

energy management, and health can be offered seamlessly.

• Interoperability is another key concern among the technology

solutions that needs to be resolved in order for any

technology to be acceptable by the market.

• Consumer privacy and security is an issue that needs to be

address.

Neighborhood Area Network (NAN) NAN is a wireless community currently used for wireless local

distribution applications. Ideally, it will cover an area larger

than a LAN.

Some architectural structures will focus on the integration and

interoperability of the various domains within the smart grid.

Domains consist of groups of buildings, systems, individuals,

or devices which have similar communications characteristics

as shown below:

A. Bulk generation: includes market services interface, plant

control system, and generators; this domain interacts with the

market operations and transmission domains through wide area

networks, substation LANs, and the Internet.

B. Transmission : includes substation devices and controllers, data collectors,

and electric storage; this domain interacts with bulk generation and

operations through WANs and substation LANs; integrated with the

distribution domain.

C.Distribution: this domain interacts with operations and customers

through Field Area Networks.

D.Customer: includes customer equipment, metering, Energy Management

Systems (EMS), electric storage, appliances, PHEVs, and so on.

E.Service Providers: includes utility and third party providers which handle

billing customer services, and so on; this domain interacts with operations and

customers primarily through the Internet.

F.Operations : includes EMS, Web Access Management System (WAMS),

and SCADA; this domain can be sub - divided into ISO/RTO, transmission,

and distribution.

G. Market: includes /ISOs/RTOs, aggregators, and other market participants.

Sensor and Actuator Networks

(SANETs)

• A SANET is a network of nodes which sense and react

to their environment.

• Compared to traditional sensor networks, which focus

on sensing, SANET can be used for both monitoring

and control purposes.

• With SANET, closed loop control can be achieved to

support more powerful applications.

SANET actors in closed-control loop• Major actors in SANET include sensors,

actuators, controllers and communication

networks.

• Sensors are components or devices to

measure and convert physical properties

into electrical signals and/or data.

• Controllers perform calculations on the

sensed data and make control decisions.

• Actuators execute the control decisions,

convert electrical signals into physical

phenomena (e.g. displays) or actions (e.g.

switches).

• Actors in a SANET communicate with each

other through communication networks,

operating diverse kinds of protocols and

media, to enable collaboration among

nodes and interaction between nodes and

the surrounding environment.

SANET design flowSANET design is application-centric, which means the major

design requirements are determined by the specific application.

Given the application requirements, the following questions need to be

considered and answered:

(i) To realize the application, what are the required functions?

(ii) To realize the function requirements, what are the required actors?

SANET in Smartgrid

• The main application of SANET in Smartgrid is optimization

and management of energy flow by making use of

information flow.

• The facility of physical parameter sensing, physical device control

and decision making are necessary for this processing.

Applications of SANET in Smartgrid

Three major driving forces of SG are:

(i) Reducing greenhouse gas emissions to enable sustainability;

(ii) Improving security and reliability;

(iii)Enhancing energy efficiency.

Applications of SANET in 3 main areas are

(A) DER Penetration

• RE is expected to help to reduce the emissions of greenhouse gasesand other pollutants. RE sources include non-variable ones andvariable ones.

• With the help of SANET, accurate and up-todate environmentalinformation, such as wind speed, solar intensity, can be obtained topredict the characteristics of the RE generators.

• Further, based on the measurements and predictions, compensationmechanisms can be employed to adaptively control the backupgenerators

(B) Grid monitoring and control (GMC)

• Reliability is critical in the electricity network.

However, experience indicated that the traditional

electricity grid is still unreliable. GMC is essential

for reliable, secure, and high quality electricity

services.

• The core duties of SANET in GMC include

preventive and corrective functions.

• Specifically, SANET is required to monitor

equipment health, predict and detect

disturbances, prevent potential failures, respond

quickly to energy fluctuations and enable fast auto-

restoration. Eg, SCADA, PMU, WAM

(C) Generation dispatch (GD) and demand-side management

(DSM)

• An effective power grid requires a good balance between the power

supply and the power demand. GD and DSM are effective

mechanisms to maintain the required balance and thus improve

the energy efficiency.

• GD is a monitor and control mechanism to actively manage

electricity generation such that the amount of power generated

meets the demands at any time.

• With the help of SANET, Renewable Forecasting (RF) and real-time

Grid Frequency Regulation (GFR) are two effective mechanisms to

address the RE penetration problem in GD.

• DSM is an important application of SANET and imposes some

special functional requirements such as capabilities of real-time

load monitoring, two-way data exchanging between the demand

side and utilities etc.

Actors of SANET in Smart Grid

SANET is composed of sensors, controllers, actuators

andcommunication networks.

Sensors in

smartgrid

Sensor

examples

Actuators in

smartgrid

Actuator

examples

Controllers and control logic in SG• Depending on the application requirements, controllers may be complicated,

powerful, centralized control centers, or simple, less powerful, distributed

micro-controllers.

• Normally, these two kinds of controllers work collaboratively to provide the

monitor and control function in a single SANET application.

• Due to the large fluctuations in energy generation and consumption, SANET

applications in Smart Grid need more powerful controllers with powerful

computational control logics, such as AI control and fuzzy control, to handle the

dynamics.

• Additionally, SANET applications in Smart Grid might need large number of

controllers to work together. Hence, each controller must be of low cost to

facilitate a large-scale deployment.

Communication Network• To support the sophisticated features of Smart Grid, the

volume of data exchanged between different actors in SANET

unavoidably increases to a large number when compared to

conventional utility grids.

• In the mean time ,various SANET applications in Smart Grid

generally have different communication necessities, in terms

of bandwidth and transmission delay etc.

Requirements of SANET actors for different SG applications

Challenges of SANET in SG

1. Distributed operation and Heterogeneity

Heterogeneity and distributed operation and two majorcharacteristics of the information flow in SG. Since SANET relieson the information flow, the heterogeneity and distributedoperation, which render the formation of a connected andefficient information flow, become the two major challenges ofSANET in SG.

• heterogeneity -different actors may follow differentcommunication protocols, use different media and have differentcommunication capabilities.

2. Dynamics

• The dynamicity is due to the variation of supplies and demands,dynamic user behaviors, continuously changing environmentsand other random events. In an SG, increasing usage of REsources, such as wind and solar, makes the problem even morechallenging.

Challenges of SANET in SG

3. Scalability

• A typical SANET application in SG may cover hundreds of

kilometers, and involves monitoring and control of

thousands of pieces of equipment and devices. Scalability

is a major challenge.

4. Flexibility

• New technologies, policies, and user demands and SANET

is required to provide the flexibility to accommodate all the

diversities and evolving factors in smartgrid.

5. Energy-efficiency and cost-efficiency

• One of the driving forces of SG is to improve the efficiency of

the

power grid, and SANET itself must be energy-efficient.

• In addition, to lower the deployment barrier, it must be

cost effective.

SANET Applications

The service reusability and interoperability offered by SANET helps to developdiverse kinds of applications. Context aware intelligent controlContext aware intelligent system is developed to address the challenges underdynamic environment. It helps to optimize the performance of system underdifferent conditions as follows(i)Atmospheric conditions, such as humidity and temperature.(ii) Energy flow readings, such as demand level and power supply.(iii) Human behaviors, such as movement, preference on environment.(iv) Economic incentives, such as tiered electricity rates.(v) Regulation schemes, such as DERS penetration.( Compressive sensing (CS)CS is proposed to address the challenges of economy, energy efficiency andscalability. The fundamental idea of CS is to utilize data correlation in the space andtime domains to decrease the communication cost and the hardware cost.

Device Technologies

• Advanced device technologies help to improve the energy efficiency and

economy and make a SANET more flexible and scalable for Smart Grid

applications.

• SANET itself consumes certain power.

• Low power consumption design is essential to reduce the total power

consumption.

• In SANET, all the main functions, such as sensing, control, data transmission

and calculating consumes power.

• Lists of possible mechanisms to reduce power consumption are listed in Table.

• Employing a mechanism on one actor has an impact on others.

• As an example, data aggregation and data compression can reduce the power

requirement for data transmission ,but increase the consumption of power for

regenerating the data. Hence, optimization of power required to be considered

from a system point of view. The process by which energy is derived from

external sources ,captured and stored is known as power harvesting.

Smart Substation

• Conventionally a substation employs CBs, protection relays, VTs and

CTs which are wired collectively using copper cables.

• With advances in digital technology, communications and standards,

this is now changing to what is known as the smart substation in

which, the workstations, protection devices and low level transducers

are connected together on an optical fiber communications backbone.

• The substation system architecture is divided into three levels;

• (i) the station level where operations, engineering functions and

reporting take place,

• (ii) the bay level where system protection and control functions are

implemented

• (iii) the process level where signals From VTs, CTs and other

transducer are transmitted

Smart substation consists of several key components and elements

(1) Protection, monitoring and control devices (IED)

Primary devices (tap-changers, protection relays, VTs, CTs, etc.) in the smart substation

are implemented as IEDS.

IED is a key component for substation integration and automation.

These devices can communication with each other and with higher level smart

substation control via the IEC 61850 optical network. It is implemented to meet

compliance necessities and save money. EDS control CBs, voltage regulators and

capacitor bank switches.

Typical applications of IEDS in smart substation includes

DR

power fault reporting in the event of failures

low-voltage stabilization

asset management

record load curves for future planning

integrated automatic transformer monitoring

automatically reconfigure the network in case of a fault.

(2) Sensors

Sensors are used to collect data from power equipment at the substation yard such as CBs,

transformers and power lines. Conventional copper-wired analog apparatus are replaced by

optical apparatus with fiber-based sensors in smart substation for monitoring and metering.

Single sensor might serve different types of IEDS through a process bus

Advantages of fiber-based sensors includes

higher accuracy,

reduced size and weight

higher performance

high bandwidth

wide dynamic range

safe and environment friendly

No saturation

less maintenance.

(3)Station and process bus

Exchange of signals between the bay level IED and station control, the bay level IED and

transducers, devices and system equipment are carried by station bus and process bus

respectively. This provides a better reliability for main substations as compared to a single bus.

The station and process bus systems are usually implemented using Ethernet switches (external

or built into the IED), connected together in a ring configuration.

(4) Supervisory control and data acquisition

SCADA is a system or a combination of systems that gathers data from different sensors at a

station or in other remote locations and then sends these data to a central computer system,

which then manages and controls the data and controls devices in the field remotely. Control

and data acquisition equipment comprises of a system with at least one master station, a

communications system and one or more RTUS. SCADA system has operator graphical user

interface (GUI),engineering applications that act on historian software, data and other

components.

(5)GPS time clock

The accurate time keeping is an important requirement of smart substation. This guarantee

the protection functions operate within the required times and synchronizes smart substation

in different locations so that event and operation logs can be compared and trip events

analyzed. The preferred approach to achieving this is by the use of a GPS clock to transmit

time synchronization signals to the IED, using simple network time protocol (SNTP).

(6) Electronic fiber optic CTs and VTs

A growing trend in the smart substation is the use of optical current and voltage transducers

(sometimes called non-conventional instrument transformers-NCIT). These devices operate

by measuring changes in the optical performance of fibers in the presence of electric and

magnetic fields. The transducers are able to measure both current and voltage. As the signals

are generated and transmitted using optical fiber, transducer signals are not subject to voltage

drop issues and electromagnetic interference which can affect conventional equipment.

Optical transducers also tend to be smaller, have improved linearcharacteristics and more

accurately reproduce the primary signal.

7) Master stations

A master station comprises of a computer system which is responsible for

communicating with the field equipment and includes an HMI in the control room or

elsewhere.

The major components of a master station are (i) data acquisition servers that interface

with the field devices through the communications system, (ii) real-time data servers,

(iii) application server, (iv) historical server and (v) operator workstations with an HMI.

Hardware components in a master station are connected through one or more LANS.

Different types of master stations are (i) SCADA master station, (ii) SCADA master

station with AGC, (iii) EMS, (iv) DMS and (vi) FA system.

The primary functions of SCADA master station are (i) data acquisition, (ii) user

interface, (iii) remote control, (iv) report writer and historical data analysis.

The primary functions of SCADA master station with AGC are (i) economic dispatch,

(ii) AGC and (iii) interchange transaction scheduling.

The primary functions of EMS are (i) state estimation,(ii) optimal power flow, (iii)

contingency analysis, (iv) three phase balanced operator power flow, (v) dispatcher

training simulator and (vi)network configuration/topology processor.

The primary functions of DMS are (i) interface to consumer information system, (ii)

three phase unbalanced operator power flow, (iii) interface to outage management,(iv)

interface to automate mapping/facilities management and (v) map series graphics.

The primary functions of FA system are (i) two-way distribution communications, (ii)

load management, (iii) voltage reduction, (iv) fault identification/fault isolation/service

restoration,(v) short-term load forecasting and (vi) power factor control.

(8) Remote terminal unit

RTUS are microprocessor-based device that interfaces with a SCADA system which

provides data to the master station and enables the master station to issue controls to

the field equipment. RTUS have physical hardware inputs to interface with field

equipment and one or more communication ports. When compared to conventional

substations, RTUS are smaller and more flexible in smart substation. In smart

substations, one smaller RTU (capable of accepting higher level ac analog inputs)

with distributed architecture approach is employed for one or more substation

equipment. Additional functionalities include DFR and power quality monitoring

and advances in communications capabilities, with extra ports available to

communicate with IEDS.

(9) Merging units (MUs)

MUS collect signals from various equipment's and transducers. These signals are

then transmitted to other devices via the process bus. MU is the interface between

the traditional analogue signals and the bay controllers and protection relays.

10) Data types and data flowTwo types of data sets are there in smart substation,

(i) a operational or real-time data, which is for operating utility systems and

performing EMS software applications such as AGC

(ii) non operational data, which is for historical, real-time and file type data

used for analysis, maintenance, planning, and other utility applications.

Operational data and nonoperational data have independent data collection

mechanisms. Hence, two separate logical data paths must also exist to transfer

these data.

One logical data path connects the substation with the EMS and second data

path transfers nonoperational data from the substation to various utility

information technology systems.

The digital substation offers numerous advantages over a conventional

arrangement.

i)Better EMC performance and isolation of circuits

(ii) Improved measurement accuracy and recording of information.

(iii) Easy incorporation of modern electronic CT and VT sensors.

(iv) Interoperability between devices made by different manufacturers.

(v) Improved reliability. vi) Easier and simpler installation.

(vii) Improved commissioning and operations.

IEC 61850 Substation Architecture

IEC 61850 is a standard for communication network and systems

in smart substation which supports interoperability among IEDS

from different manufacturers and integrated substation

automation systems(SAS) functions for data communications

using common engineering models, communication protocols and

data formats

IEC 61850 defines an abstract object model for substations and

methods to access these objects on a network and it is identified

by NIST for field device communication and general device

object data modeling.

Typical features of IEC 61850 are listed below

(1) Interoperability: Different vendors are permitted to provide complete

incorporation of monitoring, protection and control functions within one-or

two IEDS.

(2) Free configuration: Any possible number of substation protection and

control functions can be incorporated at bay level IED

(3) Simple architecture: Ethernet based communication links are employed in

place of point-to-point copper wires. Additionally, enhanced communication

performance for time critical applications is provided by functional

hierarchy architecture.

(4) Overall cost saving: Conventional communication link using copper wiring

is replaced by high speed digital communication at process level, which

saves cost for SAS and lot of effort..

Substation operation is divided into three distinct levels in the IEC 61850

standard,

(1) Process level: The process level consists of devices such as CBs and data

acquisition equipment employed to measure the voltage, current and other

parameters in various parts of substation.

(2) Bay level: The bay level consists of IEDS that gather the measurements

provided by process level. The IEDS can transmit the data to other IEDS,

make local control decisions or send the data for further monitoring and

processing to the substation SCADA system

(3) Station level: The station level comprises of HMIS and SCADA servers, as

well as the human operators who monitor the substation and station bus. The

process bus handles the communication between the process level and the

bay level and the station bus handles communication between the bay level

and station level.

The real communication between IEDS is handled via common

1EC61850 protocols such as sampled measured values (SMV),

manufacturing message specification (MMS) and generic object oriented

substation event(GOOSE).

(1) MMS: Information regarding substation status used for monitoring

is sent using the MMS protocol.

(2) GOOSE: Critical data such as warmings and control signals are

sent using the GOOSE protocol.

(3) SMV: Power line voltage and current measurements are sent using

the SMV protocol.

Transmission protocol of IEC 61850 substation architecture

IEC Substation Model

Data from electronic/optical current and voltage sensors and status information will be

collected and digitized by the MUS at the process layer. MUS must be physically situated

either in the control house or in the field. Through redundant 10OMB fiber optic Ethernet

connections data from the MUS will be collected. Redundant Ethernet switches with 1GB

uplinks and 1GBinternal data buses that support Ethernet virtual LAN (VLAN) and Ethernet

priority will be the collection points. VLAN permits the Ethernet switch to deliver datasets

only to those IEDS/switch ports that have subscribed to the data. For process bus

implementations, manufacturers must provide the ability to incorporate data from the newer

optical/electronic sensors with the data from existing CTs and VTs. In this architecture, upon

detection of failure of Clock 1, Clock 2 will have to automatically come on line and continue

providing sampling synchronization. At substation level a station bus exists. Again, this bus

is 10MB Ethernet with a clear migration path to 100MB Ethernet. The primary

communications between the various LNs will provided by the station bus, which provide the

various station monitoring, control, protection and logging functions. Communications will

function on either a connection-less basis (GOOSE) or a connection oriented basis (e.g.

request of configuration, information, etc.)

Since application of IED to IED data transmission puts the communication system

on the critical path in case of a failure, redundant communication architecture is

recommended. Finally, this architecture supports remote network access for all

types of data reads and writes. Since all communication is network enabled,

numerous remote "clients" will try to access the broad information available.

Typical clients would include local HMI, planning, engineering, operations and

maintenance. The remote access point is one logical location to implement security

functions such as authentication and encryption. These realizations relieves the

individual IEDS from performing encryption on internal data transfers but still

provide security on all external transactions.

IEC 61850 substation architecture is shown in Fig

conceptual SAS based on the IEC 61850 standard is shown in Fig. In the

conceptual scheme, the station level equipment comprises of the operator's

workplace, station computer with a database, interfaces for remote communication,

etc. Bay level equipment comprises of monitoring, control and protection units per

bay. Process level equipment comprises of conventional and electronic CTs and

VTs, transducers, CBs and MUS. The station level equipment's communicate with

bay level equipment through station bus. Further, bay level equipment

communicate with process level equipment's through process bus. Station bus and

process bus are generally realized using LAN. HMI enables the operator to monitor

and operate the switching elements in the substation through GUI at substation

level. The engineering station provides computer aided control decision, which can

be implemented at primary equipment level through local HMI. MU acts like a

switch and provides the appropriate path to messages. Eventually, the function will

be performed by the process level devices.

The major focus of IEC-61850 standard is to support the

substation functions through the communication of

(1)Sampled values for CTs and VTs.

(2) I/O data for control and protection.

(3) Trip and control signals.

(4) Configuration and engineering data.

(5) Supervision and monitoring signals.

(6) Data to control-center.

(7)Time-synchronization signals, etc.

The advantages of implementing the IEC 61850 standard are

(1) Simplified architecture: In a modern substation, localized intelligence is used by

thousands of IEDS to handle many of the decision making necessary at the local

site and via Ethernet switch they communicate with other devices, which

themselves are connected to the substation's Ethernet network.

(2) Greater reliability: The IEC 61850 standard places enormous importance on

reliability by design.

(3) Future proof design: When the requirement arises, it is simple to expand an

Ethernet network. Additionally, any new products that connect to an existing IEC

61850 substations are needed to be completely compatible with what's there

already.

(4) Vendor independence: IEC 61850 products developed by different companies are

all compulsory to speak the same language provides substation system integrators

a huge advantage, since they can pick and choose the best products from different

vendors.

Substation Automation (SA)

Substation is a focal point of electricity generation, transmission and

distribution, where voltages is transformed from low to high or reverse using

transformers.

There are different types of substations, such as transmission substations,

distribution substation, collector substations and switching substations

The general functions of a substation are

(i) Voltage transformation,

(ii) monitoring point for control center,

(iii) switch yard for electrical transmission and/or distribution system

configuration,

(iv) communication with other substation and other regional control center

(v) monitoring point for control center

Substations and feeders are source of critical real-time data for efficient and

safe operation of utility network. Real time data's are time critical and are

used to protect the of power system field equipment's.

Various Substation Automation ArchitecturesIn cascade architecture each switch is connected to the next switch or previous switch via one of

its ports. The simple cascading architecture is cost effective as this structure permits for shorter

wiring instead of bringing all connections to a central point. But, connections to all down-stream

IEDS will be lost if one of the cascáde connections is lost

Fig. 5.15 shows a typical simple cascading architecture of a substation

Fig. shows a typical redundant cascading architecture of a substation. When

compared to simple cascading architecture this architecture provides a higher

level of availability.

Typical ring architecture of a substation is shown in Fig. It identical to the

simple cascading architecture except that the loop is close If any of the ring

connections fail, the closed loop structure provides evel of redundancy. This

type of architecture is also cost effective and itoffer redundancy in the form

of immunity to physical breaks in the network.

Fig. shows a typical star architecture of a substation. This type of

arrangement offers the least amount of delay. The star architecture has the

lowest delay time when compared to the other architectures. Though, this

category of configuration has no redundancy. All switches are isolated if the

backbone switch fails.

Fig. shows typical hybrid architecture, which is a combination of ring and star

architectures. This architecture provides a high level of availability and is immune to

numerous types of faults.

Functional Architecture

The information from transducers/sensors in the substation is extracted by

process level function and it is send to upper level device, called bay level

device. Other main assignment of process level function is to receive the

control command from bay level device and perform it at the proper switch

level. Bay level functions obtain the data from bay and then mostly act on the

primary equipment of the bay.

Fig. shows different conceptual subparts of a substation (encircled by dotted

line); these subparts are called bays and designated by Bayl to Bay7.

For example, a transformer with its related switchgear between the two bus

bars representing the two voltage levels forms one bay, designated by Bay3.

The CT and VT are an integral part ofBay3 for monitoring, control and

protection of the transformer. The actuator ,CT and VT are connected to control

and protection unit via MU. MU is a device used to gather the instantaneous

values of current and voltage from CT and VT, sample it and send to the control

and protection unit. Control land protection units are bay level devices. Bay

level devices collect data from the different bays and/or same bay from and

perform actions on the primary equipment in its own bay. At the bay level, the

IED must provide all bay level functions regarding control, monitoring and

protection, inputsBay1

Feeder Automation (FA)

• FA is the ability to monitor and control the distribution network

remotely, to collect and provide information to consumers in a

useful manner.

• Feeder automation includes data acquisition and supervisory

control of line equipment, reclosers, regulators, capacitors,

sectionlizers and switches. Remote monitoring of the status of

fault indicators and analyzers can also be included.

• Feeder Automation minimizes feeder down time by quickly

and automatically restoring operation to serviceable feeder

sections, while isolating those requiring repair.

• This results in minimal outage time, fewer service calls, and

reduced monitoring and management demands.

Duties of FA

1) Fault Isolation and Sectionalizing:

Remote monitoring of the recloser operation to the melting of a

fuse link, utilities can detect the fault very fast and can take quick

action to clear that fault.

By correlating the last voltage or current measured before an

outage, an indication of the nature of the fault and fault location

can be obtained.

2) Remote Interconnect Switching:

DA systems can be deployed to drive remotely interconnected

switches that separate different portion of the utility distribution

feeders and to restore power.

Duties of FA (contd..)

3) Capacitor Bank Switching:

to install a number of one-way receivers at the capacitor

locations for positive control and to monitor the aggregate

effects of the capacitor switching at the substation low voltage

level bus. Utilities with capacitor bank switching facilities can

operate with reduced losses and as a result with higher

efficiency.

4) Voltage Monitoring:

By monitoring the feeder voltage remotely utility personal gets

advance notification about the line voltage drop due to high

usage. Also recorded data of feeder voltages will give snapshot

of the actual usage patterns.

Main Components of FA1) Remote fault indicators

• Remote fault indicators are sensors that detect current and

voltage levels on feeders outside usual operating boundaries.

• Operators can utilize this information to determine the location

of a fault rapidly or distinguish between temporary high loads

and a fault, such as high motor starting current.

• Visual displays are equipped with fault indicators to assist field

crews and connected to communications networks that are

incorporated with SCADA or distribution management system

(DMS)for providing greater accuracy in locating and identifying

faults.

2) Smart relays

• smart relays apply sophisticated software to accurately detect,

isolate and diagnose the cause of faults.

• They may be installed on devices in automated switching schemes

or in utility substations for feeder protection,

• Device controls are activated according to algorithms and

equipment settings. (The relays also store and process data to send

back to grid operators and back office systems for further analysis

• Advances in relay and sensor technologies have enhanced the

detection of high impedance faults difficult to detect with

conventional relays, that occur when energized power lines contact

a foreign object, but such contact only produces a low-fault current.

3) Automated feeder switches and recloses

• Automated feeder switches open and close to isolate faults and

reconfigure faulted segments of the distribution feeder to restore

power to consumers on line segments without a fault) They are

normally configured to work with smart relays to operate in response

to signals from utilities, distribution management systems or control

commands from autonomous control packages. Switches can be also

configured to open and close at programmed sequences and intervals

when fault currents are detected. This action, known as reclosing, is

used to stop power flow to a feeder that has been impacted by a

hindrance and re-energize after the obstruction has cleared itself from

the line. Reclosing reduces the probability of continuous outages

when trees and other objects temporarily contact power lines during

high wind sand storms.

(4) Automated capacitors

Utilities employ capacitors for reactive power compensation

requirements caused by inductive loads from overhead lines, consume

equipment or transformers. Reactive power compensation reduces the

total amount of power that need to be provided by power plants,

resulting in a flatter voltage profile along the feeder and less energy

wasted from electrical losses in the feeder.

A distribution capacitor bank consists of a group of capacitors

connected together. The capacity of the banks installed on distribution

feeders depends on the number of capacitors, and usually ranges from

300 to 1,800 kilovolt-ampere reactive (KVAR), Capacitor banks are

mounted on substation structures, distribution poles or "pad-mounted"

in enclosures.

(5) Automated voltage regulators and LTCS

Transformers that make small adjustments to voltage levels in

response to changes in load are termed as voltage regulators. They are

installed along distribution feeders and in substations to regulate down

stream voltage. Multiple "raise" and "lower" positions are available

with voltage regulators and can automatically adjust according to

loads ,feeder configurations and device settings.

6) Automated feeder monitors

Feeder monitors measure load on distribution lines and equipment and can trigger

alarms when equipment or line loadings reach potentially damaging levels.

Monitors deliver data-in near-real time to office systems and analysis tools so that

grid operators can successfully assess loading trends and take corrective switching

actions, such as repairing equipment when necessary, transferring load or taking

equipment offline. These field devices are employed in coordination with

information and control systems to avoid outages from occurring due to overload

conditions or equipment failure.

(7) Transformer monitors

Transformer monitors are equipment health sensors for measuring parameters,

such as insulation oil temperatures of power transformer, which can reveal

possibilities for abnormal operating conditions and premature failures. To measure

various parameters of different types of devices these devices can be configured.

Usually, these devices are applied on substation transformers and other equipment

whose breakdown would result in considerable cost and reliability impacts for

utilities and consumers.

Performance of FA technology in four main areas are

(1) Reliability and outage management

FA technologies provided highly developed ability for operators to locate, detect

and diagnose faults. In particular (fault location, isolation and service restoration

(FLISR) technologies can automate power restoration within seconds by isolating

faults automatically and switching a few consumers to adjacent feeders) FLISR can

decrease the number of affected consumers and consumer minutes of disruption by

half during a feeder outage for certain feeders. Fully automated validation and

switching normally improves reliability than operator initiated switching with

manual validation. Accurate fault location allows the operators to send repair crews

precisely and inform consumers on outage status, which in turn reduces repair costs

and outage length, reduces the load on consumers to report outages and guarantees

satisfaction of consumer.

(2) Voltage and reactive power management

Automated power factor correction and voltage regulation enables utilities to reduce

peak demands; more efficiently utilize existing assets ,improve power quality and

defer capital investments for the growing digital economy.)Utilities use CVR to

reduce energy consumption ,reduce feeder voltage levels and improve the

distribution system efficiency particularly during peak demand times. Automated

power factor correction provides new ability to utilities for boosting power quality

and managing reactive power flows.

3) Equipment health monitoring

Installing sensors on main components (e.g., transformer banks and power

lines) to assess equipment health parameters can provide real-time alerts

for abnormal conditions of equipment as well as analytics that help utilities

to plan preventative equipment maintenance, repair and replacement.

(4) Integration of DERS Grid integration of DERS needs highly developed

tools to monitor and dispatch DERS, and to address new control and power

flow issues, such as reactive power management, voltage fluctuations,

harmonic injection and low-voltage ride through. Few Smart Grid network

shave been tested distributed energy resource management

systems(DERMS) and integrated automated dispatch systems (IADS) on

small DER installments.

Benefits of FA1. Reduced line loss

A close coordination between the substation equipment, distribution

feeders and associated equipment is necessary to increase system

reliability.

Volt/VAR control is addressed through expert algorithms which monitors and

controls substation voltage devices in coordination with down-line voltage

devices to reduce line loss and increase line throughout.

2. Power quality

The substation RTU in conjunction with power monitoring equipment on

the feeders monitors, detects, and corrects power-related problems before they

occur, providing a greater level of customer satisfaction.

3. Deferred capital expenses

A preventive maintenance algorithm may be integrated into the system.

The resulting ability to schedule maintenance, reduces labour

costs, optimizes equipment use and extends equipment life.

https://electrical-engineering-portal.com/maintenance-management-of-electrical-equipment-condition-monitoring-based-part-2

4. Energy cost reduction

Real-time monitoring of power usage throughout the distributionfeeder provides data allowing the end user to track his energyconsumption patterns, allocate usage and assign accountability toreduce overall costs.

5. Optimal energy use

Real-time control, as part of a fully-integrated, automated powermanagement system, provides the ability to perform calculations toreduce demand charges.

6. Economic benefits

Investment related benefits came from a more effective use of thesystem by operating the system closer to the physical limits. FA makesthis possible by providing better data for planning, engineering andmaintenance.

FA provides benefits in the areas of interruption and customer serviceby automatically locating feeder faults, decreasing the time required torestore service to unfaulted feeder sections, and reducing costsassociated with customer complaints.

7. Improved reliability

On the qualitative side, improved reliability adds perceived value for

customer and reduce the number of complaints. Distribution

automation features that provide interruption and customer service

related benefits include load shedding and other automatic control

functions.

In addition, data acquisition and processing and remote metering

functions reduce operating costs.

8. Compatibility

Distribution automation spans many functional and product areas

including computer systems, application software, RTUs,

communication systems and metering products. No single vendor

provides all the pieces. Therefore, in order to be able to supply a utility

with a complete and integrated system, it is important for the supplier to

have alliances and agreements with other vendors.

EE403

DISTRIBUTED GENERATION AND SMART GRIDS Module VI

AISHA MEETHIAN AP EEE ICET

Module

Contents

Hours

End.

Sem.

Exam.

Marks

VI

Cloud computing in smart grid: Private, public and Hybrid cloud. Cloud architecture of smart grid. Power quality: Introduction - Types of power quality disturbances - Voltage sag (or dip), transients, short duration voltage variation, Long duration voltage variation, voltage imbalance, waveform distortion, and voltage flicker - Harmonic sources: SMPS, Three phase power converters, arcing devices, saturable devices, fluorescent lamps, harmonic indices (THD, TIF, DIN, C – message weights) Power quality aspects with smart grids.

8

20%

Cloud Computing in Smart grid

• Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, servers, storage, applications, and services) that can be rapidly provisioned and released with minimal management effort or service provider interaction.

• This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models.

Definition of Cloud Computing

https://www.nist.gov/sites/default/files/documents/itl/cloud/cloud-def-v15.pdf

Essential Characteristics 1. On-demand self-service. • A consumer can unilaterally provision computing capabilities, such

as server time and network storage, as needed automatically without requiring human interaction with each service’s provider.

2. Broad network access. • Capabilities are available over the network and accessed through

standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, laptops, and PDAs).

3. Resource pooling. • The provider’s computing resources are pooled to serve multiple

consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to consumer demand. The customer generally has no control or knowledge over the exact location of the provided resources but may be able to specify location at a higher level of abstraction (e.g., country, state, or datacenter). Examples of resources include storage, processing, memory, network bandwidth, and virtual machines.

Essential Characteristics (contd..) 4. Rapid elasticity.

• Capabilities can be rapidly and elastically provisioned, in some cases automatically, to quickly scale out and rapidly released to quickly scale in. To the consumer, the capabilities available for provisioning often appear to be unlimited and can be purchased in any quantity at any time.

5. Measured Service.

• Cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts). Resource usage can be monitored, controlled, and reported providing transparency for both the provider and consumer of the utilized service.

Service Models

1. Cloud Software as a Service (SaaS)

2. Cloud Platform as a Service (PaaS)

3. Cloud Infrastructure as a Service (IaaS)

Service Models (contd..)

1. Cloud Software as a Service (SaaS) The capability provided to the consumer is to use the

provider’s applications running on a cloud infrastructure.

The applications are accessible from various client devices through a thin client interface such as a web browser (e.g., web-based email).

The consumer does not manage or control the underlying cloud infrastructure including network, servers, operating systems, storage, or even individual application capabilities, with the possible exception of limited user-specific application configuration settings.


2. Cloud Platform as a Service (PaaS)

The capability provided to the consumer is to deploy onto the cloud infrastructure consumer-created or acquired applications created using programming languages and tools supported by the provider.

The consumer does not manage or control the underlying cloud infrastructure including network, servers, operating systems, or storage, but has control over the deployed applications and possibly application hosting environment configurations.


3. Cloud Infrastructure as a Service (IaaS)

The capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications.

The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, deployed applications, and possibly limited control of select networking components (e.g., host firewalls).

Service Model at a glance

Ref: https://samj.net/2009/04/20/introducing-the-cloud-computing-stack-2009-edition/

Deployment Models

1. Private cloud.

The cloud infrastructure is operated solely for an organization. It may be managed by the organization or a third party and may exist on premise or off premise.

2. Community cloud.

The cloud infrastructure is shared by several organizations and supports a specific community that has shared concerns (e.g., mission, security requirements, policy, and compliance considerations). It may be managed by the organizations or a third party and may exist on premise or off premise.

Deployment Models (contd..)

3. Public cloud.

The cloud infrastructure is made available to the general public or a large industry group and is owned by an organization selling cloud services.

4. Hybrid cloud.

The cloud infrastructure is a composition of two or more clouds (private, community, or public) that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for load-balancing between clouds).

Benefits of Cloud Computing 1. Minimum downtime and optimized life cycle costs through online monitoring and control of all grid assets.

2. It provides necessary software‘s applications to the users just paying according to their usage.

3. Reduction in CO2 emissions through grid access of large wind, hydro, and solar power plants.

4. Significant improvement of customer processes and services.

5. Active management of power generat ion and load profiles of buildings.

6. It provides unlimited data storage for storing User‘s data.

7. Users can access the data from the cloud

8 . Provider via internet anywhere in the world

Power Quality (PQ)

Any power problem manifested in voltage, current, or frequency deviations that results in failure or mis-operation of customer equipment.

Definition

Ref: R. C. Durgan, M. F. Me Granaghen, H. W. Beaty, “Electrical Power System Quality”, McGraw-Hill

Reasons for the increased concern about Power Quality

1. Newer-generation load equipment, with microprocessor-based controls and power electronic devices, is more sensitive to power quality variations than was equipment used in the past.

2. The increasing emphasis on overall power system efficiency has resulted in continued growth in the application of devices such as high-efficiency, adjustable-speed motor drives and shunt capacitors for power factor correction to reduce losses. This is resulting in increasing harmonic levels on power systems and has many people concerned about the future impact on system capabilities.

Reasons for the increased concern about Power Quality (contd..)

3. End users have an increased awareness of power quality issues. Utility customers are becoming better informed about such issues as interruptions, sags, and switching transients and are challenging the utilities to improve the quality of power delivered.

4. Many things are now interconnected in a network. Integrated processes mean that the failure of any component has much more important consequences.

Types of Power Quality Disturbances

Voltage sag (or dip)

Transients

Short duration voltage variation

Long duration voltage variation

Voltage imbalance

Waveform distortion

Voltage flicker

Transcient • An undesirable and momentary variation in voltage or current

or both is termed as transient.

• Transients can be classified into two categories, impulsive and oscillatory. These terms reflect the waveshape of a current or voltage transient.

An impulsive transient is a sudden, non–power frequency change in the steady-state condition of voltage, current, or both that is unidirectional in polarity (primarily either positive or negative).

Impulsive transients are normally characterized by their rise and decay times, which can also be revealed by their spectral content.

An oscillatory transient is a sudden, non–power frequency change in the steady-state condition of voltage, current, or both, that includes both positive and negative polarity values.

An oscillatory transient consists of a voltage or current whose instantaneous value changes polarity rapidly. It is described by its spectral content (predominate frequency), duration, and magnitude.

Oscillatory transients with a primary frequency component – greater than 500 kHz and a typical duration measured in

microseconds are considered high-frequency transients. between 5 and 500 kHz with duration measured in the tens

of microseconds are termed a medium-frequency transient. less than 5 kHz, and a duration from 0.3 to 50 ms are

considered a low-frequency transient.

Lightning stroke current impulsive transient

Oscillatory transient current caused by back-to-back capacitor switching

Long-Duration Voltage Variations • Long-duration variations encompass root-mean-square (rms)

deviations at power frequencies for longer than 1 min.

• Voltage variation is considered to be long duration when the ANSI limits (steadystate voltage limits)are exceeded for greater than 1 min.

• Long-duration variations can be either overvoltages or undervoltages.

• An overvoltage is an increase in the rms ac voltage greater than 110 percent at the power frequency for a duration longer than 1 min.

• An undervoltage is a decrease in the rms ac voltage to less than 90 percent at the power frequency for a duration longer than 1 min.

Short-Duration Voltage Variations

• This category encompasses the IEC category of voltage dips and short interruptions.

• Each type of variation can be designated as instantaneous, momentary, or temporary, depending on its duration.

Interruption An interruption occurs when the supply voltage or load current decreases to less than 0.1 pu for a period of time not exceeding 1 min.

Voltage sag (or dip)

• A sag is a decrease to between 0.1 and 0.9 pu in rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min.

• Voltage sags are usually associated with system faults but can also be caused by energization of heavy loads or starting of large motors.

Voltage sag caused by an SLG fault

(a) RMS waveform for voltage sag event. (b) Voltage sag waveform.

Swell • A swell is defined as an increase to between 1.1 and 1.8 pu

in rms voltage or current at the power frequency for durations from 0.5 cycle to 1 min.

• As with sags, swells are usually associated with system fault conditions, but they are not as common as voltage sags.

• One way that a swell can occur is from the temporary voltage rise on the unfaulted phases during an SLG fault.

• Swells can also be caused by switching off a large load or energizing a large capacitor bank.

• Swells are characterized by their magnitude (rms value) and duration.

• The severity of a voltage swell during a fault condition is a function of the fault location, system impedance, and grounding.

Instantaneous voltage swell caused by an SLG fault

Voltage Imbalance

• Voltage imbalance (voltage unbalance) is defined as the maximum deviation from the average of the three-phase voltages or currents, divided by the average of the three-phase voltages or currents, expressed in percent.

• The ratio of either the negative- or zero sequence component to the positive-sequence component can be used to specify the percent unbalance.

• The primary source of voltage unbalances of less than 1% is single-phase loads on a three-phase circuit.

• Voltage unbalance can also be the result of blown fuses in one phase of a three-phase capacitor bank.

• Severe voltage unbalance (greater than 5 %) can result from single-phasing conditions.

Waveform Distortion

Waveform distortion is defined as a steady-state deviation from an ideal sine wave of power frequency principally characterized by the spectral content of the deviation.

There are five primary types of waveform distortion: ■ DC offset ■ Harmonics ■ Inter-harmonics ■ Notching ■ Noise

• The presence of a dc voltage or current in an ac power system is termed dc offset.

• This can occur as the result of a geomagnetic disturbance or asymmetry of electronic power converters.

sinusoidal voltages or currents having frequencies that are integer multiples of the fundamental frequency, usually 50 Hz.

Periodically distorted waveforms can be decomposed into a sum of the fundamental frequency and the harmonics.

Harmonic distortion originates in the nonlinear characteristics of devices and loads on the power system.

DC offset

Harmonics

• Harmonic distortion levels are described by the complete harmonic spectrum with magnitudes and phase angles of each individual harmonic component.

• It is also common to use a single quantity, the total harmonic distortion (THD), as a measure of the effective value of harmonic distortion.

• But misleading, as many adjustable-speed drives will exhibit high THD values for the input current while operating at very light loads.

• This is not a significant concern because the magnitude of harmonic current is low, even though its relative distortion is high.

• To handle this concern for characterizing harmonic currents in a consistent fashion, IEEE Standard 519-1992 defines another term, the total demand distortion (TDD).

• TDD is same as THD except that the distortion is expressed as a percent of some rated load current rather than as a percent of the fundamental current magnitude at the instant of measurement.

Current waveform and harmonic spectrum for an ASD input current.

• Voltages or currents having frequency components that are not integer multiples of the fundamental frequency (eg. 50 Hz) are called interharmonics.

• They can appear as discrete frequencies or as a wideband spectrum.

• Main sources of interharmonic waveform distortion are static frequency converters, cycloconverters, induction furnaces, and arcing devices.

• Power line carrier signals can also be considered as interharmonics.

• Interharmonics affect power-line-carrier signaling and induce visual flicker in fluorescent and other arc lighting as well as in computer display devices.

Interharmonics.

voltage notching caused by a three-phase converter

Notching is a periodic voltage disturbance caused by the normal operation of power electronic devices when current is commutated from one phase to another. During this period, there is a momentary short circuit between two phases, pulling the voltage as close to zero as permitted by system impedances.

Notching

• Noise is defined as unwanted electrical signals with broadband spectral content lower than 200 kHz superimposed upon the power system voltage or current in phase conductors, or found on neutral conductors or signal lines.

• Noise in power systems can be caused by power electronic devices, control circuits, arcing equipment, loads with solid-state rectifiers, and switching power supplies.

• Noise problems are often exacerbated by improper grounding that fails to conduct noise away from the power system.

• Noise disturbs electronic devices such as microcomputer and programmable controllers.

• The problem can be mitigated by using filters, isolation transformers, and line conditioners.

Noise

Voltage Flicker (Voltage Fluctuation)

• Voltage fluctuations are systematic variations of the voltage envelope or a series of random voltage changes, the magnitude of which does not normally exceed the voltage ranges of 0.9 pu to 1.1 pu.

• Arc furnace is one of the most common causes of voltage fluctuations on utility transmission and distribution systems.

• The flicker signal is defined by its rms magnitude expressed as a percent of the fundamental.

• Voltage flicker is measured with respect to the sensitivity of the human eye.

Voltage fluctuations caused by arc furnace operation

Harmonic Sources Commercial facilities such as office complexes, department stores,

hospitals, and Internet data centers are dominated with high-efficiency fluorescent lighting with electronic ballasts, adjustable-speed drives for the heating, ventilation, and air conditioning (HVAC) loads, elevator drives, and sensitive electronic equipment supplied by single-phase switch-mode power supplies.

Commercial loads are characterized by a large number of small harmonic-producing loads.

Single-phase power supplies

Older technologies use ac-side voltage control methods, such as transformers, to reduce voltages to the level required for the dc bus.

Newer-technology switch-mode power supplies use dc-to-dc conversion techniques to achieve a smooth dc output with small, lightweight components.

A. Switch-mode power supply (SMPS)

• The input diode bridge is directly connected to the ac line, eliminating the transformer.

• This results in a coarsely regulated dc voltage on the capacitor. This direct current is then converted back to alternating current at a very high frequency by the switcher and subsequently rectified again.

SMPS • Personal computers, printers, copiers, and most other single-phase

electronic equipment now almost universally employ switch-mode power supplies.

• The key advantages are the light weight, compact size, efficient operation, and lack of need for a transformer.

• Switch-mode power supplies can usually tolerate large variations in input voltage.

• Because there is no large ac-side inductance, the input current to the power supply comes in very short pulses as the capacitor C1 regains its charge on each half cycle.

• A distinctive characteristic of switch-mode power supplies is a very high third-harmonic content in the current. Since third-harmonic current components are additive in the neutral of a three-phase system, the increasing application of switch-mode power supplies causes concern for overloading of neutral conductors.

SMPS current and harmonic spectrum

Fluorescent lighting • Lighting typically accounts for 40 % to 60 % of a commercial

building load and fluorescent lighting was used on 77 % of commercial floor spaces.

• Fluorescent lights are discharge lamps; thus they require a ballast to provide a high initial voltage to initiate the discharge for the electric current to flow between two electrodes in the fluorescent tube.

• Once the discharge is established, the voltage decreases as the arc current increases.

• It is essentially a short circuit between the two electrodes, and the ballast has to quickly reduce the current to a level to maintain the specified lumen output.

• Thus, a ballast is also a current-limiting device in lighting applications.

Fluorescent lighting

• There are two types of ballasts, magnetic and electronic. A standard magnetic ballast is simply made up of an iron-core transformer with a capacitor encased in an insulating material.

• An electronic ballast employs a switch-mode–type power supply to convert the incoming fundamental frequency voltage to a much higher frequency voltage typically in the range of 25 to 40 kHz.

• With a delta-connected supply transformer, the amount of triplen harmonic currents flowing onto the power supply system reduces.

Fluorescent lamp with (a) magnetic ballast current

waveform and (b) its harmonic spectrum.

Fluorescent lamp with (a) electronic ballast current

waveform and (b) its harmonic spectrum.

Three-phase power converters

• Three-phase electronic power converters differ from single-phase converters mainly because they do not generate third-harmonic currents.

• This is a great advantage because the third-harmonic current is the largest component of harmonics.

Current and harmonic spectrum for CSI-type Adjustable Speed Drives (ASD)

CSI- Current Source Inverter

Current and harmonic spectrum for PWM-type ASD

6-pulsed DC ASD

PWM ASD

Arcing devices Includes arc furnaces, arc welders, and discharge-type lighting (fluorescent, sodium vapor, mercury vapor) with magnetic (rather than electronic) ballasts.

The arc is basically a voltage clamp in series with a reactance that limits current to a reasonable value.

Equivalent circuit for an arcing device

• The voltage-current characteristics of electric arcs are nonlinear.

• Following arc ignition, the voltage decreases as the arc current increases, limited only by the impedance of the power system.

• This gives the arc the appearance of having a negative resistance for a portion of its operating cycle such as in fluorescent lighting applications.

• The electric arc itself is actually best represented as a source of voltageharmonics.

• If a probe were to be placed directly across the arc, one would observe a somewhat trapezoidal waveform.

• Threephase arcing devices can be arranged to cancel the triplen harmonics through the transformer connection. But not so effective due to unbalancing during melting phase.

Saturable devices

• Equipment in this category includes transformers and other electromagnetic devices with a steel core, including motors. Harmonics are generated due to the nonlinear magnetizing characteristics of the steel.

• Transformers are not as much of a concern as electronic power converters and arcing devices which can produce harmonic currents of 20 percent of their rating, or higher.

• However, their effect will be noticeable, particularly on utility distribution systems, which have hundreds of transformers.

• Power transformers are designed to normally operate just below the “knee” point of the magnetizing saturation characteristic.

• The operating flux density of a transformer is selected based on a complicated optimization of steel cost, no-load losses, noise, and numerous other factors.

Harmonic Indices 1. THD (Total harmonic distortion)

• THD is a measure of the effective value of the harmonic components (voltage/ current) of a distorted waveform.

• DPF (displacement power factor)

- cosine of the phase angle between fundamental voltage and fundamental current.

• DF- Distortion factor = Is1/Is

• PF=DF*DPF

2. TDD (total demand distortion) TDD is same as THD except that the distortion is expressed as a percent of some rated load current rather than as a percent of the fundamental current magnitude at the instant of measurement.

Harmonic Indices 3. TIF (Telephone influence factor)

TIF is used to describe the interference of a power transmission line on a telephone line.

TIF = (𝑉𝑛𝑊𝑛)

2∞𝑛=1

𝑉𝑛2∞

𝑛=1

Where Vn=single frequency rms voltage at harmonic frequency,n; denominator=total rms voltage, Wn= single frequency TIF weighting factor at harmonic,n

4. DIN (Distortion Index)

DIN= 𝑉𝑛

2∞𝑛=2

𝑉𝑛2∞

𝑛=1

= 𝑇𝐻𝐷

(1+𝑇𝐻𝐷2)

Harmonic Indices 5. C-message weights:

Similar to TIF except that the weights cn are used in place of Wn. cn are related to the frequency response of human ear.

C = (𝑉𝑛𝑐𝑛)

2∞𝑛=1

𝑉𝑛2∞

𝑛=1

Where cn= C-message weighting factor at harmonic,n

Ref: Power Quality in Power Systems and Electrical Machines By Ewald Fuchs,

Mohammad A. S. Masoum, Academic press

PQ issues with Smartgrid

The major power quality issues affected by DG are:

Sustained interruptions

Voltage regulation

Harmonics

Voltage sags

Operating conflicts

EE403 DISTRIBUTED GENERATION AND SMARTGRIDS

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