MOTORLISTRIK

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MOTOR LISTRIK


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What is an Electric Motor

70% motor pada industri adalah motor listrik

Adalah perangkat elektromekanik, yang

berfungsi untuk merubah energy listrik

menjadi energy mekanik

Energy mekanik dipakai untuk memutar

impeler pompa, kipas angin, blower.

Menggerakan kompresor

Mengangkat beban


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How Does an Electric MotorWork?


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Three types of Motor Load

Motor loads Description Examples

Constant torque

loads

Output power varies but torque

is constant

Conveyors, rotary kilns,

constant-displacement pumps

Variable torque

loads

Torque varies with square of

operation speed

Centrifugal pumps, fans

Constant power

loads

Torque changes inversely with

speed

Machine tools


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Jenis motor listrik

Motor listrik dibedakan berdasarkan:

jenis sumber tegangannya

Konstruksi mekanisnya

Prinsip kerjanya


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Jenis motor listrik

Electric Motors

Alternating Current (AC)

MotorsDirect Current (DC)

Motors

Synchronous Induction

Three-PhaseSingle-Phase

Self ExcitedSeparatelyExcited

Series ShuntCompound


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MOTOR DC

Speed control without impact power supplyquality

Changing armature voltage

Changing field current

Restricted use

Few low/medium speed applications

Clean, non-hazardous areas

Expensive compared to AC motors


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KOMPONEN MOTOR DC

Field pole North pole and south pole

Receive electricity to formmagnetic field

Armature Cylinder between the poles

Electromagnet when current goes through

Linked to drive shaft to drive the load

Commutator Overturns current direction in armature


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Motion of a current-carrying loop in a magnetic

field

N SL R

I

F

F Rotation

Commutator

(rotates with

coil)

brushes


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Motor Illustration
http://auto.howstuffworks.com/enlarge-image.htm?terms=motor&page=0


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Example of Motor
http://auto.howstuffworks.com/enlarge-image.htm?terms=motor&gallery=1&page=2


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Relationship between speed, field flux andarmature voltage

Back electromagnetic force: E = KN

Torque: T = KIa

E = electromagnetic force developed at armature terminal (volt)

= field flux which is directly proportional to field currentN = speed in RPM (revolutions per minute)T = electromagnetic torqueIa = armature currentK = an equation constant


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Type of Electric Motors

Separately excited DC motor: field currentsupplied from a separate force

Self-excited DC motor: shunt motor

Field winding parallelwith armature winding

Current = field current+ armature current

Speed constantindependent of loadup to certain torque

Speed control:insert resistancein armature or

field current

DC motors

(Rodwell Int.

Corporation, 1999)


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Self-excited DC motor: series motor

DC motors

(Rodwell Int.

Corporation, 1999)

Field winding in serieswith armature winding

Field current =armature current

Speed restricted to5000 RPM

Avoid running with

no load: speeduncontrolled

Suited for high

starting torque:cranes, hoists


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Classification of MotorsElectric Motors

Alternating Current(AC) Motors

Direct Current (DC)Motors

Synchronous Induction

Three-PhaseSingle-Phase

Self ExcitedSeparatelyExcited

Series ShuntCompound


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Electrical current reverses direction

Two parts: stator and rotor Stator: stationary electrical component

Rotor: rotates the motor shaft

Speed difficult to control

Two types Synchronous motor

Induction motor

AC Motors

(Integrated Publishing, 2003)


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UNEP 2006


Constant speed fixed by systemfrequency

DC for excitation and low startingtorque: suited for low load applications

Can improve power factor: suited for

high electricity use systems

Synchronous speed (Ns):

AC Motors Synchronous motor

Ns = 120 f / PF = supply frequency

P = number of poles


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Most common motors in industry

Advantages: Simple design

Inexpensive

High power to weight ratio

Easy to maintain

Direct connection to AC power source

AC Motors Induction motor


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Components

Rotor

Squirrel cage:conducting barsin parallel slots

Wound rotor: 3-phase, double-layer,distributed winding


Stator

Stampings with slots to carry 3-phase windings

Wound for definite number of poles

(Automated Buildings)


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How induction motors work

Electricity supplied to stator

Magnetic field generated that moves aroundrotor

Current induced in rotorElectromagnetics

Stator

Rotor

Rotor produces secondmagnetic field thatopposes stator magneticfield

Rotor begins to rotate

(Reliance)


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Single-phase induction motor

One stator winding

Single-phase power supply

Squirrel cage rotor

Require device to start motor

3 to 4 HP applications

Household appliances: fans, washingmachines, dryers


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Three-phase induction motor

Three-phase supply produces magneticfield

Squirrel cage or wound rotor

Self-starting

High power capabilities

1/3 to hundreds HP applications: pumps,compressors, conveyor belts, grinders

70% of motors in industry!


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Speed and slip

Motor never runs at synchronousspeed but lower base speed

Difference is slip

Install slip ring to avoid this

Calculate % slip:

% Slip = Ns Nb x 100Ns

Ns = synchronous speed in RPMNb = base speed in RPM


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Relationship load, speed and torque

At start: highcurrent andlow pull-uptorque

At start: highcurrent andlow pull-uptorque

At 80% of fullspeed:highest pull-out torque

and currentdrops

At full speed:torque andstator current

are zero


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Training Agenda: Electric Motors

Introduction

Types of electric motors

Assessment of electric motors

Energy efficiency opportunities


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Assessment of Electric Motors

Motors loose energy when serving a load

Fixed loss

Rotor loss

Stator loss

Friction and rewinding

Stray load loss

Efficiency of Electric Motors

(US DOE)


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Factors that influence efficiency

Age Capacity

Speed

Type Temperature

Rewinding

Load




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Motor part load efficiency

Designed for 50-100% load

Most efficient at 75% load

Rapid drop below 50% load


(US DOE)



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Motor load is indicator of efficiency

Equation to determine load:

Motor Load

Load = Pi x HP x 0.7457

= Motor operating efficiency in %HP = Nameplate rated horse powerLoad = Output power as a % of rated powerPi = Three phase power in kW



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Three methods for individual motors

Input power measurement

Ratio input power and rate power at 100%loading

Line current measurement

Compare measured amperage with ratedamperage

Slip method

Compare slip at operation with slip at full

load

Motor Load



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Three steps for three-phase motors

Step 1. Determine the input power:

Motor Load

Pi = Three Phase power in kWV = RMS Voltage, mean line to

line of 3 PhasesI = RMS Current, mean of 3 phasesPF = Power factor as Decimal

1000

3xPFxIxVPi



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Step 2. Determine the rated power:

Step 3. Determine the percentage load:

Motor Load

r

r xhpP

7457.0

%100xP

PiLoad

r

Load = Output Power as a % of Rated PowerPi = Measured Three Phase power in kWPr = Input Power at Full Rated load in kW

Pr = Input Power at Full Rated load in kWhp = Name plate Rated Horse Powerr = Efficiency at Full Rated Load



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Result

1. Significantlyoversized andunderloaded

2. Moderatelyoversized and

underloaded

3. Properly sizedbut standardefficiency

Motor Load

Action

Replace with more efficient,properly sized models

Replace with more efficient,properly sized models whenthey fail

Replace most of these withenergy-efficient models whenthey fail



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Training Agenda: Electric Motors

Introduction

Types of electric motors

Assessment of electric motors

Energy efficiency opportunities


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1. Use energy efficient motors

2. Reduce under-loading (and avoidover-sized motors)

3. Size to variable load

4. Improve power quality

5. Rewinding

6. Power factor correction by capacitors

7. Improve maintenance

8. Speed control of induction motor

Energy Efficiency Opportunities


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38 UNEP 2006

Reduce intrinsic motor losses

Efficiency 3-7% higher

Wide range of ratings

More expensive but

rapid payback

Best to replace whenexisting motors fail

Use Energy Efficient Motors

(Bureau of Indian Standards)



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39 UNEP 2006

Power Loss Area Efficiency Improvement1. Fixed loss (iron) Use of thinner gauge, lower loss core steel reduces

eddy current losses. Longer core adds more steel tothe design, which reduces losses due to loweroperating flux densities.

2. Stator I2R Use of more copper & larger conductors increasescross sectional area of stator windings. This lowerresistance (R) of the windings & reduces losses due tocurrent flow (I)

3 Rotor I2R Use of larger rotor conductor bars increases size of

cross section, lowering conductor resistance (R) &losses due to current flow (I)

4 Friction &Winding

Use of low loss fan design reduces losses due to airmovement

5. Stray Load Loss Use of optimized design & strict quality controlprocedures minimizes stray load losses

(BEE India, 2004)

Use Energy Efficient Motors



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Reasons for under-loading Large safety factor when selecting motor

Under-utilization of equipment

Maintain outputs at desired level even at lowinput voltages

High starting torque is required

Consequences of under-loading Increased motor losses

Reduced motor efficiency

Reduced power factor

2. Reduce Under-loading


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41 UNEP 2006


Replace with smaller motor If motor operates at


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Motor selection based on

Highest anticipated load: expensive and riskof under-loading

Slightly lower than highest load: occasionaloverloading for short periods

But avoid risk of overheating due to Extreme load changes

Frequent / long periods of overloading

Inability of motor to cool down

3. Sizing to Variable Load

X

Motors haveservice factor

of 15% aboverated load


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43 UNEP 2006


Motor performance affected by

Poor power quality: too high fluctuations involtage and frequency

Voltage unbalance: unequal voltages to threephases of motor

4. Improve Power Quality

Example 1 Example 2 Example 3

Voltage unbalance (%) 0.30 2.30 5.40

Unbalance in current (%) 0.4 17.7 40.0

Temperature increase (oC) 0 30 40


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Keep voltage unbalance within 1%

Balance single phase loads equallyamong three phases

Segregate single phase loads andfeed them into separateline/transformer

4. Improve Power Quality


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Rewinding: sometimes 50% of motors

Can reduce motor efficiency

Maintain efficiency after rewinding by

Using qualified/certified firm

Maintain original motor design

Replace 40HP, >15 year old motors instead ofrewinding

Buy new motor if costs are less than 50-65%

of rewinding costs

5. Rewinding


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46 UNEP 2006


Use capacitors for induction motors

Benefits of improved PF Reduced kVA

Reduced losses

Improved voltage regulation Increased efficiency of plant electrical system

Capacitor size not >90% of no-load

kVAR of motor

6. Improve Power Factor (PF)


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47 UNEP 2006


Checklist to maintain motor efficiency

Inspect motors regularly for wear, dirt/dust

Checking motor loads for over/under loading

Lubricate appropriately

Check alignment of motor and equipment

Ensure supply wiring and terminal box andproperly sized and installed

Provide adequate ventilation

7. Maintenance


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48 UNEP 2006


Multi-speed motors

Limited speed control: 2 4 fixed speeds

Wound rotor motor drives

Specifically constructed motor

Variable resistors to control torqueperformance

>300 HP most common

8. Speed Control of Induction Motor


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Variable speed drives (VSDs)

Also called inverters

Several kW to 750 kW

Change speed of induction motors

Can be installed in existing system

Reduce electricity by >50% in fans and pumps

Convert 50Hz incoming power to variablefrequency and voltage: change speed

Three types



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Direct Current Drives

Oldest form of electrical speed control

Consists of

DC motor: field windings and armature

Controller: regulates DC voltage to armaturethat controls motor speed

Tacho-generator: gives feedback signal tocontrolled


T i i S i E


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Training Session on EnergyEquipment

Electric Motors

THANK YOU

FOR YOUR ATTENTION

UNEP 2006


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Disclaimer and References

This PowerPoint training session was prepared as part ofthe project Greenhouse Gas Emission Reduction from

Industry in Asia and the Pacific (GERIAP). While reasonable

efforts have been made to ensure that the contents of this

publication are factually correct and properly referenced,

UNEP does not accept responsibility for the accuracy or

completeness of the contents, and shall not be liable for any

loss or damage that may be occasioned directly or indirectly

through the use of, or reliance on, the contents of this

publication. UNEP, 2006. The GERIAP project was funded by the Swedish

International Development Cooperation Agency (Sida)

Full references are included in the textbook chapter that is

MOTORLISTRIK

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