POWER SUPPLY ARRANGEMENTS - iriset

TC- 4

POWER SUPPLY ARRANGEMENTS

By

B.L.V.PRASAD

ILP 3

1IRISET-SECUNDERABADSUBJECT: TC 4

CHAPTER NO.1

CELLS AND BATTERIES

• 1. classification of cells

• 2. Primary Cells

• 3. Secondary Cells

• 4. Selecting the right battery (LA)

• 5. Types of loads

• 6. Electrical protection to the battery for SPV

• 7 Basic terminology

• 8 Battery care


• 9. Safety precautions

• 10. Standard tests on LA batteries

• 11. Troubleshooting

• 12.Indenting of LA cells

• 13.Comparison of different types of LA cells

• 14.Alkaline batteries

• 15.Comparison of various rechargeable batteries


Cell is an electrochemical device that converts chemical

energy into electricity by use of a galvanic cell or it can be

called a storage device that stores electrical energy in the

form chemical energy.

When more than one cell is connected together, it is called a

battery.

The cells which cannot be recharged after discharge are

known as “Primary cells”. Ex: Leclanche Dry Cell


• The cells in which the chemical condition as well as the

physical state of the electrodes after discharge are brought

back to the original condition by causing a current to flow in

the opposite direction (by charging ) are called Secondary

cells.

EX: a)Lead acid cell b) Alkaline cell

• Generally Lead acid secondary cells are widely used in

Indian Railways for telecom equipments as a Std/by power5IRISET-SECUNDERABADSUBJECT: TC 4

• (a) Lead Acid cell:

(b) Alkaline cell :

(i) Nickel Cadmium cell

(ii) Nickel-Metal Hydride cell (NiMh)

(iii) Nickel Iron cell


• Efficiency: The efficiency of a secondary cell is defined as the

ratio of output delivered by a cell to the input required to

restore its initial state of charge under specified conditions

of temperature, current rate and final voltage.

• Generally, the efficiency is expressed in three ways:-

a)Ampere-hour efficiency

b) Volt efficiency

c)Watt-hour efficiency7IRISET-SECUNDERABADSUBJECT: TC 4

• Ampere-hour efficiency: The ratio of the ampere-hours

output to the ampere-hours of recharge (Input).

% of Ah efficiency: Amp-hour discharge / Amp-hour charge

• Volt efficiency: The ratio of the average voltage during the

discharge to the average voltage during the recharge.

• Watt-hour efficiency: The efficiency is the ratio of the watt

hours output to the watt hours of the recharge.

• The capacity of Cell: The ability of a fully charged battery to8IRISET-SECUNDERABADSUBJECT: TC 4

deliver a specified quantity of electricity at a given rate

(amperes) over a definite period of time.

The unit for capacity is AH and it depends up on the

following factors.

a. Discharge Rate

b. Size of plates

c. Quantity and density of Electrolyte

d. Temperature

e. Age.9IRISET-SECUNDERABADSUBJECT: TC 4

• Depth of Discharge (DOD) of the cell: Secondary cell should

never be fully discharged (i.e. 100 %) due to Technical

considerations such as Increase in Internal Resistance with

increase in discharge, High Charging current for next

charging, Reduction in Life of cell etc.

Therefore, a limit is laid down on to extent of discharge

carried out on a cell is known as Depth of discharge (DOD)

and is stated as a percentage of the ampere-hour capacity.10IRISET-SECUNDERABADSUBJECT: TC 4

• Depth of Discharge permitted is as follows.

a.Flooded type of Lead Acid Cell - 70%

b.LMLA cell - 80%

c. VRLA cell - 50%.

• Self discharge of the cell: Self-discharge is a phenomenon

by which the charge of a stored cell is decreased due to

internal chemical reactions without any connection between

the electrodes (with out any load or open circuit).11IRISET-SECUNDERABADSUBJECT: TC 4

• Construction of Lead Acid Cell: The active material of the

lead acid cell is lead peroxide (Pb02) on the positive plate

and spongy lead (Pb) on the negative plate. Both the plates

are separated by an insulating material to prevent the

contact is called the separator. The plates are immersed in

an electrolyte of dilute sulphuric acid(H2SO4). The nominal

voltage of a LA cell is 2V.

• The cell is said to be discharging when it supplies current to

an external circuit or the load.12IRISET-SECUNDERABADSUBJECT: TC 4

The video below explains the construction and chemical

reactions that take place in a lead acid battery during

charging and discharging. To open the video, right click of

the mouse on the link and click the “open hyperlink”

https://www.youtube.com/watch?v=HhxtfULIO7c


https://www.youtube.com/watch?v=HhxtfULIO7c

• When current is forced through the cell from an external DC

source is called the charging.

• As the cell discharges, the density of electrolyte falls owing

to the conversion of some of the sulphuric acid (H2 So4) to

lead sulphate at the positive and negative plates and

increase in the production of water. So the specific gravity

of the electrolyte decreases which indicates the condition of

the cell.(2PbSO4 + 2 H2O). The voltage of the cell falls to 1.8 v14IRISET-SECUNDERABADSUBJECT: TC 4

and the specific gravity falls to 1.180

• During charging, the water and the sulphate on the plates

are reconverted into sulphuric acid and the specific gravity

gradually rises. (PbO2 + Pb + 2H2 SO4). If the charging current

is continued even after the plates are fully converted Pbo2

and Pb, electrolysis of water continues, the hydrogen and

oxygen are evolved freely and the cell is said to be gassing.

This condition of gassing indicates that the cell is fully

charged and further charging must be discontinued.15IRISET-SECUNDERABADSUBJECT: TC 4

• At this stage, the voltage of the cell reaches to 2.1V and the

specific gravity rises to 1.220 and gassing takes place. These

are the three indications of a fully charged LA flooded cell.

• There is a direct relationship between the state of charge of

the cell and the specific gravity of the electrolyte. In

practice, the standard way to test the condition of cell is to

measure the specific gravity of the electrolyte with a

hydrometer.


• The hydrometer is an instrument used to measure the

specific gravity (or relative density) of liquids i.e. the ratio of

the density of the liquid to the density of water.

• The routine checks to be carried out are :

1) Measurement of electrolyte level above plates.

2) Specific Gravity of electrolyte

3) Voltage.

• Types of Conventional Lead Acid Cells


• Basing on the manufacture process of the plates, the

conventional lead acid cells are broadly divided into three

categories

• Plante type or formed plates

• Tubular type

• Faure type or pasted plates

• Hence, Faure type plates are normally used as Negative

Plates and Plante or tubular type are used as Positive Plates


because of the inherent advantages and disadvantages they

possess.

• Plates:

The plates are actual electrodes holding the following active

materials.

Spongy Lead (-Ve)

Lead Peroxide (+Ve)

Electrolyte: H2 SO4 (Diluted)19IRISET-SECUNDERABADSUBJECT: TC 4

• Specific Gravity of Electrolyte:

• For a battery to work properly, it’s electrolyte (water plus

active ingredient) must contain a certain amount of active

ingredient. Since the active ingredient is dissolved in the

water, the amount of active ingredient cannot be measured

directly. An indirect way to determine whether or not the

electrolyte contains the proper amount of active ingredient

is to measure the specific gravity of electrolyte. Specific

gravity is the ratio of the weight of a certain amount of 20IRISET-SECUNDERABADSUBJECT: TC 4

Given substance compared to the weight of the same

amount of pure water.

• The SG of concentrated H2SO4 battery grade is 1.835

conforming to the specification IS:266 and added to distilled

water conforming to the specification IS: 1069. The SG of

electrolyte is measured with an instrument called

Hydrometer. The Sp. gravity of Electrolyte varies with

temperature. Any reading observed on the hydrometer

should be corrected to read at 27 deg.C.21IRISET-SECUNDERABADSUBJECT: TC 4

• Temperature Correction: Normally, if the temperature

increases, specific gravity decreases and vice versa by

0.0007 for each degree centigrade. Hence, the correction

should be made as follows-

• For every 1 deg C above 27 deg C add 0.0007 to the Sp.

gravity as read on the hydrometer.

• Similarly, for every 1 deg. C below 27 deg C, subtract 0.0007

from the Sp. Gr. as read on the Hydrometer22IRISET-SECUNDERABADSUBJECT: TC 4

• Initial charging of a new battery:

• Appliances required:

• 1.Voltmeter 2.Ammeter 3.hydrometer 4. Glass rod 5.Jar for

mixing the electrolyte 6.thermometer 7.Funnel 8.Mug 9.

Concentrated H2SO4 10. Distill water 11.battery grease

12. constant current battery charger 13. Constant voltage

charger

Tools: 1.Insulated spanners 2.Metel connector links23IRISET-SECUNDERABADSUBJECT: TC 4

• The personnel equipment: 1.gloves 2.Goggles 3.Apron

4.Gum shoes

• Stages of initial charging

• 1.Cleaning the battery

2.Preparatin of electrolyte

3.Filling of electrolyte

4. Initial Charging with a constant current battery charger

5.Discharging the battery to ascertain the capacity24IRISET-SECUNDERABADSUBJECT: TC 4

6. Recharging with constant voltage charger before

connecting to equipment.

• Initial Charging precautions:

• 1. This shall be done as per the instructions of the

Manufacturer.

• 2. For preparing electrolyte, only battery grade concentrated

Sulphuric acid (IS 266) and distilled water (IS 1069) should

be used.


• 3. Never add water to the acid as to prevent delivery

injurious fumes. During mixing, the temperature must

not be allowed to exceed 50 deg. C.

• 4. After preparation of electrolyte, allow it to cool to room

temperature before filling into the cell

• Maintenance precautions:

• 1. Keep open flames away from the battery. Smoking is

prohibited.


• A video on initial charging of LMLA batteries used in electric

locomotives in Hindi has been uploaded by camtech India

on you tube. To watch the video right click the mouse on

the below link and select “open hyperlink”.

• https://www.youtube.com/watch?v=leUkuod-v0s


https://www.youtube.com/watch?v=leUkuod-v0s

• 2. Keep surroundings clean and top of the cells dry.

• 3. Electrical connections should be kept tight. Connecting

cables should be flexible and long.

• 4. Terminals should be smeared with Vaseline (Petroleum

Jelly) to prevent corrosion.

• 5. Vent plugs should be kept in position and tight to avoid

spilling of electrolyte.

• 6.Electrolyte lost due to spillage should be replaced with


that of the same specific gravity. Acid should never be

added.

• 7.Log sheets of charging and discharging to be maintained.

• 8.Avoid undercharging or overcharging

• 9. When idle, keep batteries on trickle charge.

• 10. Give batteries an equalizing charge monthly to bring the

SG of all the cells to the same value.

• 11. Insulated metal tools should be used to prevent short


• circuit. Wear protective clothing while handling batteries.

• 12. Ensure correct polarity between the cells.

• 13. Use calibrated meters for measuring current, voltage,

specific gravity and temperature.

• 14. In case of acid burns, apply Ammonia or Baking Soda.

• 15. Batteries showing irregularities, which cannot be

corrected, should be taken out of service and report made

to proper authority.


• The defects and faults in LA battery:

• 1. Sulphation 2. Buckling 3. Internal short circuit 4. Internal

discharge 5. Loss of capacity 6. Low density of electrolyte

• 7. High density of electrolyte 8. Reverse Voltage 9. Shedding

1 0. Sludge 11. Open Circuit 12. Temperature Troubles.

• 13. Battery does not charge 14. Stratification


• 1.Sulphation: This is a common phenomenon where in the

formation of lead sulphate takes place on the surface of

both the plates whenever the battery is discharged. If the

battery is left in discharged condition for a long time, the

Lead sulphate becomes hard and will not leave the plates

even after charging leading to loss of capacity. This is

indicated by no rise in the SG of battery even after charging

continuously at prescribed charging current.

• Cause: keeping the battery in discharged condition for 32

IRISET-SECUNDERABADSUBJECT: TC 4

a long tome or exposure of plates due to low level of

electrolyte.

• Treatment: Charge at 1/3rd of the normal rate, till the cell

delivers gases freely. Discharge at the same rate. Repeat the

cycle until the voltage of the cell reaches 2.35 on charge and

specific gravity is as per manufacturer's rating.

• 2.Buckling: The plates become saucer shaped and touch

with each other or with adjacent plates.33IRISET-SECUNDERABADSUBJECT: TC 4

• Cause: if the battery subjected to high rate of discharge or

charge, and heavy sulphation.

• Treatment: Plates to be replaced

• 3. Internal short circuit:

Indication: The cell will be warm even when idle, specific

gravity and voltage will be low immediately after charge.

There will be no gassing.

Cause: Buckled or sulphated plates or formation of sludge


• Treatment: If not very badly bent, the plates can be

removed, straightened in a vice or press. If very badly bent

they should be replaced. Fallen pieces and the sludge

should be removed.

• 4. Internal Discharge:

• Indication: The cell discharges faster, warm even in idle

condition, less capacity.

• Cause: Impurities inside the cell.


Treatment: Electrolyte is to be replaced

• 5. Loss of Capacity:

• Indication: Same as of internal discharge but it may not be

warm when idle.

• Cause: May be due to slight sulphation or slight buckling or

aging or impurities.

• Treatment: Attend as in case of sulphation and buckling and

internal discharge.


• 6.Low Density of Electrolyte:

• Indication: The SG readings are lower than the rated value

after charging and do not improve by continuous charging.

• Cause: May be due to short circuit or loss of electrolyte due

to excessive gassing, spillage or sulphation.

• Treatment: Withdraw the electrolyte and make up with

fresh acid to bring the value of the specific gravity to the

rated value, half an hour after stopping the charge and


continue the cycle till the readings are correct. If after 6

cycles the specific gravity does not come up to the correct

value, treat as is done for short circuit.

• 7. High Density of electrolyte:

• Indication: Maximum and minimum values of specific

gravities will be always higher than the specified values.

• Cause: Due to topping up with acid instead of water.

• Treatment: Charge at a current equal to 1/10th of AH


capacity till gassing is observed. Remove some of the

electrolyte, and replace with distilled water. Test specific

gravity after half-an-hour and if not correct, charge again till

gassing is observed. Remove electrolyte and water and

repeat cycle until correct specific gravity is obtained.

• 8.Reverse voltage of cells:

• Indication: The positive and negative terminals will show

opposite polarity.


• Cause: This is due to defective cell in a battery, which got

discharged already when the others are being discharged.

• As the discharge continues, the rundown cell gets charged

in the wrong direction by the main discharge current

passing through it. This results in the positive plate being

partially converted into spongy lead and the negative plate

into lead peroxide. This causes a reverse voltage and acts in

the opposite direction to the main battery Emf.


• Treatment: Remove the cause of the defect and give slight

charge. Remove the discharged cell.

• 9.Shedding:

• Indication: Slight loss in capacity or short circuit in the case

of very severe shedding.

• Cause: Due to excessive gassing or due to sulphation

peroxide paste gets dislodged from the grids.

• Treatment: Replace cell if severe or charge at low rate


• 10.Sludge: This is the name given to the peroxide or

sulphate sediments collected at the bottom of the jar.

• Indication: Loss of capacity or short circuit, visible in the

case of transparent container.

• Cause: Bad maintenance, excessive gassing, shock and

vibration, excessive sulphation.

• Treatment: Wash the plates and re-charge at low rate with

fresh electrolyte in the case of slight formation. In the case42IRISET-SECUNDERABADSUBJECT: TC 4

of severe formation replace the cell.

• 11.Open Circuit:

• Indication: No emf at the output terminal of the cell.

• Cause: Loose connections of connecting strap or corroded

terminals, or break in terminals.

• Treatment: Check all connections, examine for loose joints

at clamps and connecting bars. Clean terminals with sand

paper and smear Vaseline.43IRISET-SECUNDERABADSUBJECT: TC 4

• 12.Temperature Trouble:

• Indication: Temperature rises even for very slow rates of

charging.

• Cause: Due to bad location, proximity to any heated

element, shedding, buckling or defective separation.

• Treatment: Examine for the causes given and remove the

cause.


• 13.Battery does not charge:

• Indication: charging current is not shown by the charger

• Cause:

• (i) Disconnection in the charging circuit.

(ii) Loose connections or high resistance at terminals.

(iii) Defective charger, not feeding current.

(iv) Wrong connections.

• Treatment: above causes must be addressed


• 14.Stratification:

• Indication: on checking, SG is found to be less

• Cause: This happens to a fully charged battery when it is

kept in idle condition whenever disconnected from the load.

The electrolyte forms into two layers inside the battery i.e.

the acid being heavier settles at the bottom of the battery

and the water being lighter reaches to the top of battery

thus creating two strata or layers. As the SG of electrolyte

will be high at the bottom and low at the top of battery, the46IRISET-SECUNDERABADSUBJECT: TC 4

• bottom of the plates are eaten away by highly concentrated

acid thus leading to shedding.

• Treatment: This is prevented by giving freshening charge

every after 15 days for an idle battery for small duration.


• Sealed Lead Acid Batteries : The liquid electrolyte is

transformed into moistened separators and the enclosure is

sealed. Safety valves are added to allow venting of gas

during charge and discharge. They are the small sealed lead

acid (SLA), and the large valve regulated lead acid (VRLA).

Technically, both batteries are the same.

• Construction: These are designed to prevent electrolyte loss

through evaporation, spillage and gassing and this in turn


• prolongs the life of the battery and eases maintenance.

Instead of simple vent caps on the cells to let gas escape,

VRLA batteries have pressure valves that open only under

extreme conditions. Valve‐regulated batteries also need an

electrolyte design that reduces gassing by impeding the

release of oxygen and hydrogen into the atmosphere,

• generated by the galvanic action of the battery during

charging. This usually involves a catalyst that causes the


• hydrogen and oxygen to recombine into water and is called

gas recombinant system. Spillage of the acid electrolyte is

eliminated. Hence the SLA batteries are also safer.

• Unlike the flooded lead acid battery, both the SLA and VRLA

are designed with a low overvoltage potential to prohibit

the battery from reaching its gas-generating potential during

charge. Excess charging would cause gassing and water

depletion. Consequently , these batteries can never be50IRISET-SECUNDERABADSUBJECT: TC 4

• charged to their full potential.

• The Sealed Lead Acid batteries shall be charged with

Constant Voltage with voltage regulation. Leaving the

battery on float charge for a prolonged time does not cause

damage. The battery’s charge retention is best among

rechargeable batteries. The SLA must always be stored in a

charged state. Leaving the battery in a discharged condition

causes sulfation , a condition that makes the battery difficult

to charge.51IRISET-SECUNDERABADSUBJECT: TC 4

• Depending on the depth of discharge and operating

temperature, the SLA provides 200 to 300 discharge/ charge

cycles. The primary reason for its relatively short cycle life is

grid corrosion of the positive electrode, depletion of the

active material and expansion of the positive plates.

• These changes are most prevalent at higher operating

temperatures. The optimum operating temperature for the

SLA and VRLA battery is 27°C. As a rule of thumb, every 8°C

rise in temperature will cut the battery life to half.52IRISET-SECUNDERABADSUBJECT: TC 4

• These are also called as VRLA Batteries in the short form

because the pressure inside the cell/battery is regulated by

a special type of valve which can open and close

automatically. This is also comes under SMF LA (Sealed

Maintenance Free Lead Acid) battery because it is

completely sealed and does not require Maintenance during

its service life.


• The SLA is rated at 20 hour discharge. Longer discharge

times produce higher capacity readings.

• Valve Regulated Lead Acid batteries :

• (specification no: .IRS : S 93 / 96)

• These are also called as VRLA Batteries in the short form

because the pressure inside the cell/battery is regulated by

a special type of valve which can open and close

automatically. This is also comes under SMF LA (Sealed

Maintenance Free Lead Acid) battery because it is54IRISET-SECUNDERABADSUBJECT: TC 4

• completely sealed and does not require Maintenance during

its service life.

• VRLA batteries are two types :1.Gel type 2.AGM

• 1.GEL type : The electrolyte is suspended in either glass

fiber matting or in silica gel so makes it imobile. These

batteries can be discharged below 50% Depth of Discharge

(DOD) without danger of damaging the plates. a Gel

• battery can deliver typically 800 to 1100 cycles to 50%

Depth of Discharge (DOD)55IRISET-SECUNDERABADSUBJECT: TC 4

• Gel batteries are prone to damage if gassing is allowed to

occur. Hence, charging rates must be below 2.45 volts per

cell during boost charging and charge time is slower than

that of AGM batteries. They must be charged at a slower

rate (C/20) to prevent excess gas from damaging the cells.

They cannot be fast charged on a conventional charger as

they may be permanently damaged


• 2.AGM(Absorbed Glass Mat):Also known as Absorptive

Glass Micro‐Fiber

• In this Boron Silicate fiberglass mat acts as a separator

between the electrodes and absorbs the free electrolyte

acting like a sponge. The fiberglass matt absorbs and

immobilizes the acid in the matt but keeps it in a liquid

rather than a gel form. In this way the acid is more readily

available to the plates allowing faster reactions between the

acid and the plate material allowing higher charge/discharge57IRISET-SECUNDERABADSUBJECT: TC 4

rates as well as deep cycling. This construction is very robust

and able to withstand severe shocks and vibrations, the

cells will not leak even if the case is cracked.

• AGM's have a very low self‐discharge rate of from 1% to 3%

per month. These batteries should not be discharged below

50% Depth of Discharge (DOD) as there may be a possibility

of damaging the plates. Number of cycles is dependent on

the plate alloy used and is 300 to 500 cycles to 50% Depth

of Discharge (DOD).58IRISET-SECUNDERABADSUBJECT: TC 4

• Advantages of VRLA batteries in Railway Telecom:

1. No separate battery room is required due to compactness

and no emission of acid fumes So they can be installed by

the side of any electronic equipment.

2. Topping up with distilled water and measurement of

Specific gravity is notrequired.

3. Ideally suited for deep discharges and partial discharges

as well.59IRISET-SECUNDERABADSUBJECT: TC 4

4.Minimum grid growth for minimizing the possibility of

internal shorts.

5. Compact and light in weight

6. Very low self discharge of 0.5 to 1% of capacity per week

7. No spilling of electrolyte and can be installed in horizontal

direction without any leakage of electrolyte

8. No acid proof flooring is required as there no spillage

9. Very low self discharge of 0.5 to 1% of capacity per week.


• Specifications:

• 1. Nominal voltage: 2V/Cell

• 2. End point voltage: 1.75V/Cell

• 3. Capacities: 20 AH, 40 AH, 80 AH, 120 AH, 200 AH and

above etc

• 4. Type of separators: Glass mat

• 5. Mode of charging:

• i. Float mode-2.25V/Cell( For 16 Hours)


• ii. Boost mode- 3V/Cell and charging current should be

limited to 20 ٪of its AH capacity.

• 6. Material used for grids: Calcium alloy

• 7. Under normal operating conditions, equalizing charge is

not required. It is required when non-uniformity in voltage

has developed between the cells.

• 8. A.C. Ripple – should not exceed 3 ٪RMS

• 9. Operating temperature - -20˚C to +55˚C


• The constructional details:

• Positive plates are of PbO2 pasted to the grid made of Lead-

calcium High Tin alloy to resist corrosion and log life

• Negative plates are of Pb pasted to the grid made of lead-

calcium alloy grid for maintenance free

• Separators : These are of Low resistance, high porosity and

highly absorbent type glass mat (AGM)

• Safety valve : This is of Self resealing, pressure regulated and


explosion proof. Regulation of pressure developed inside

the cell is done by a “valve” which opens and closes

automatically as per the preset pressure there by controlling

the pressure developed inside the battery eventually

prevents the explosion of battery due to pressure.

• Container: High impact Polypropylene co-polymer, ribbed

jar design for better heat dissipation and strength.

• Electrolyte: High purity Sulphuric acid to maximize shelf life.65IRISET-SECUNDERABADSUBJECT: TC 4

Selection of a battery for a given system:

The basis information required for selection of a battery is

1. Operating voltage of the system

2. Discharge currents: Constant current discharge for telecom

applications(continueos load)

3. Backup time: Duration to be supplied by the battery to load

4. ‘K’ factor: The ratio of rated capacity at 10hr. rate to the

amperes that can be supplied for ‘t’ minutes for a given


ECV (End cell voltage).

K factor values at different ECV s & time for VRLA batteriesTime ECV

1.90 1.85 1.80 1.75

1 min 0.55 0.51 0.44 0.41

2 Min 0.60 0.54 0.52 0.50

5 Min 0.72 0.68 0.60 0.58

10 Min 0.90 0.82 0.75 0.70

15 Min 1.10 1.00 0.93 0.85

30 Min 1.42 1.30 1.15 1.10

60MIn 2.00 1.78 1.68 1.60

2 Hrs 3.25 3.00 2.87 2.75

3Hrs 4.36 4.05 3.80 3.62

4 Hrs 5.38 5.00 4.75 4.62

5 Hrs 6.75 6.18 5.85 5.70


6 Hrs 7.70 7.32 6.25 6.12

7 Hrs 8.50 8.12 7.42 7.32

8 Hrs 9.76 9.00 8.35 8.20

9 Hrs 10.80 9.90 9.20 9.05

10 Hrs 12.00 10.50 10.20 10.00

Temperature correction factors:

Ambient temperature in Correction factor

-15 1.72

-10 1.49

-5 1.32

0 1.27

10 1.14

15 1.09

20 1.04

27 1.00


5. Ageing factor: Battery be replaced when its actual capacity

drops to 80 percent of its rated capacity. Therefore, the

battery's rated capacity should be at least 1.25 times the

load expected at the end of its service life. Hence, a

correction factor of 1.25 (=1/0.8) is taken as ageing factor.

6. Design margin: A nominal 10% cushion is taken as a

standard over sizing to allow for unforeseen operating

conditions of the battery due to improper maintenance


recent discharge or ambient temperature lower than

anticipated or both.

7.Over load factor: It is a pure reserve capacity that may be

installed to take care of any future additional load. Normally

10-15 ٪ overload factor is considered.

• a) Constant current discharge (E.g. Telecom)

• Example: Selection of a battery for supplying a load of 10

amps for 5 hours to an end cell voltage of 1.75V when the

system70IRISET-SECUNDERABADSUBJECT: TC 4

voltage is 48V at an ambient temperature of 27⁰C.

The information given for battery sizing is:

1. Load current : 10 amps

2. Backup time : 5 hrs

3. System voltage : 48 volts

4. End cell voltage : 1.75 volts

5. Temperature : 27⁰C.

• Step1: No.of cells = System voltage/nominal voltage of cell71IRISET-SECUNDERABADSUBJECT: TC 4

= 48/2 = 24 cells

• Step 2:Capacity required= load current x Back up time

• Since the battery is designed for 10 hour rate, for 5 hour

backup, K- factor need to be applied.

• Step 3 :From the K-factor table, for 1.75 ECV and discharge

time of 5 hrs, the K-factor is 5.70.

• Step 4: required battery capacity: 10x5.70=57AH

• Apply aging factor 0f 1.25 capacity becomes 57x1.25=71.2572IRISET-SECUNDERABADSUBJECT: TC 4

• DOD of cell is 50% = 71.25x 2=142.5AH

• Step 6: Nearest higher available battery capacity of 150 Ah is

chosen.


• b) Constant power discharge ( E.g. UPS System ) :

• Ex 2 : Selection of a battery for supplying 40 KVA load for 30

minutes to an ECV of 1.75 with a Power factor of 0.8 and an

inverter Efficiency of 85%. The voltage window is 205 - 285V

and ambient temperature is - 1 0 C

• The information required / given for battery sizing is :

• 1. KVA/KW rating: 40 KVA (Not required when KW rating is

given for UPS )


2. Minimum Voltage: 205 volt

3. Maximum voltage: 285 volt

4. Power factor: 0.8 ( Not required when KW rating is given

for UPS )

5. Efficiency of the Inverter : 85%

6. End Cell voltage : 1.75 volts

7. Operating temperature : - 0 10 C

8. Back up time : 30 minutes


• Step 1: Choice of number of cells

• Minimum number of cells = Minimum DC voltage / End cell

voltage

• = 205 / 1.75 = 117.14

• Round this to the next higher whole number i.e. 118

numbers of cells

• Maximum number of cells = Maximum DC voltage/Float or

Boost voltage

• = 285/ 2.3 = 123.9176IRISET-SECUNDERABADSUBJECT: TC 4

• Round this to the next lower whole number i.e. 123

numbers of cells. Ensure that the rounded minimum no. of

cells is less than the rounded maximum no. of cell.

• The number of cells selected should be in between the

maximum and minimum number of cells determined above.

Let us say we had chosen 120 nos. of cell.

• Battery’s Minimum Voltage = Chosen no. of cells x 1.75 Volts

• = 120 x 1.75 = 210 volts77IRISET-SECUNDERABADSUBJECT: TC 4

• Battery’s Maximum Voltage = Chosen no. of cells x 2.30 V

= 120 x 2.30 = 276 volts

Since both the above min and max voltages are within the

UPS voltage window, proceed as below:

• Step 2: Power required for UPS in kilowatts (KVA x PF = KW)

= 40 x 0.8 = 32 KW

• Step 3: Power required from the battery

(KW/Inverter efficiency) = 32 / 0.85


= 37.647 KW = 37647 Watts

• Step 4: Power required from each cell (watts per cell)

= 37647/120 = 313.73 watts per cell

• Step 5: Applying Ageing factor of 1.25 = 313.73 x 1.25

= 392.16 watts per cell

• Step 6: Applying Temp. Correction factor at 20 C (1.04 )

392.16 x 1.04 = 407.84watts per cell


• From the performance table, the Ah capacity of the cell

capable of giving 407.84 watts to an end cell voltage of 1.75,

as a backup time of 30 minutes is 233.05

• Design margin (Cushion) =10%

Therefore, 10% of 233.05=23.3

=233.05= 256.375

• Over load factor is normally 10% to 15%

• 233.05 of 15%=34.9


• Total AH of battery=233.05+23.3+34.9= 291.25AH

• i.e. 300 Ah is chosen as it is the nearest available capacity.

• Capacity of Cell chosen is 2V 300AH

• Total Number of cells=120


• Battery Care: . Do’s & Don’ts

• Do’s

• Unload the batteries carefully and place them upright on

the floor in single tier.

• Store the batteries in a cool and dry location.

• Charge the batteries within six months if they are under

storage.

• Unpack the batteries as per the unpacking instructions.82IRISET-SECUNDERABADSUBJECT: TC 4

• Install the batteries in a cool and dry location.

• Keep the battery area clean and dry.

• Monitor the charge and float voltages of the charger at

monthly intervals and adjust if required.

• Check the tightness of all the electrical connections at

monthly intervals.

• Check the compatibility of the charger before

commissioning the battery.83IRISET-SECUNDERABADSUBJECT: TC 4

• Maintain monthly service record as per enclosed format

• Provide adequate ventilation and illumination.

• Ensure the cell orientation & connections are as per the

General Arrangement Drawing.

Don’ts

• Do not expose the packed batteries to rain.

• Do not expose the packed batteries to sunlight

• Do not exceed the storage period without charging the84IRISET-SECUNDERABADSUBJECT: TC 4

batteries.

• Do not install the batteries in rooms with varying

temperature pockets due to sunlight or ventilation ducts.

• Do not short-circuit the battery or cells during assembly.

• Do not charge the batteries in sealed cubicles.

• Do not mix batteries of different types or makes.

• Do not make tap connections.

• Do not keep the batteries in discharged condition.85IRISET-SECUNDERABADSUBJECT: TC 4

• Safety Precautions:

• Do not touch un insulated battery connectors or terminals.

• Isolate the battery from the charger while working on the

battery.

• All tools used for installation should be insulated to avoid

accidental shorting of connections.

• Ensure that connections are made as per general

arrangement drawing enclosed.86IRISET-SECUNDERABADSUBJECT: TC 4

• Do not attempt to move the installed battery without

removing the connectors.

• Do not expose the battery to open flame or sparks.

• Keep the battery clean and dry.

• Incase of accidental contact with acid, wash the affected

area with a continuous flow of water for 15 minutes and

consult a doctor immediately.

• Do not install batteries in a sealed cabinet or enclosure since87IRISET-SECUNDERABADSUBJECT: TC 4

• explosive gases may be released under abnormal

conditions.

• Use a suitable lifting device in handling the battery to

prevent damage.


• Comparison of different types of Lead Acid cells:

Feature Flooded Lead Acid VRLA

1. Gassing/ fuming High gassing/ fuming,

separate battery

room with exhaust

system is essential.

No gassing/fuming,

can be installed

anywhere

2. Topping up of

electrolyte

Topping up required

frequently

No topping-up

required normally

3. Charging current

level

Lowest High


4. Space

requirement

Large cell size, Large space

required.

Small cell size, Low

space requirement.

5. Stacking Vertical stacking only. Tier

stacking not practical for

large size.

Horizontal or

vertical

6. Transporta-

tion in

charged

condition

Not possible.

Transportation in

uncharged (unfilled)

condition recommended.

Easy


7. Self-discharge

during storage,

at an average

temperature of

35°C.

Self-discharge is

very high. Long

storage not

recommended.

Recovery difficult.

50% self-discharge in

6 months. Recovery

easy.

8. Cyclic Life

(to 80% DoD).

Theoretically

maximum 2000

cycles at 27°C.

1400 cycles at an

average temperature

of 35°C in normal

environmental

condition 91IRISET-SECUNDERABADSUBJECT: TC 4

9. Float life at

35°C.

Not known Good

10. High

temperature

performance

Good Average, but temperature

compensation provision

made in the Power Plants

11. Low

temperature

performance

Poor Good


12. Stratification Prominent,

requires frequent

boost charging for

prevention.

Negligible, no

boost charging

required.

13. End Cell Voltage 1.85V/cell 1.75V/cell

14. Capacity at very low

rate of discharge

Average Good

15. Deep discharge

recovery

Poor, hard

sulphation

prevents recovery.

Average, after 4 to

5 charge/discharge

cycles 93IRISET-SECUNDERABADSUBJECT: TC 4

16. Charge efficiency Poor, 12 to 14

hours for 90%

recovery.

Excellent, 6 to 8

hours for 90%

recovery.

17

Float / Boost charging

voltage per cell

2.15 to 2.2 V /

2.4 V

2.25 V / 2.3 V

18 Aging factor 1.5 1.25

19 Depth of Discharge 80 % 50-80 %

20 Cost Low Cost 2 times costlier

than FLA


• Rechargeable Alkaline batteries: Depending on the

composition of the active materials of the plates, there are

many types of rechargeable batteries and typically their

output is 1.25 Volts/Cell.

• They are as follow: 1. Nickel iron(Ni Fe). (These cells are not

as popular as Ni-Cd Cells). 2. Nickel- cadmium (NiCd).

3. Nickel-Metal Hydride (NiMh).4. Silver zinc.5. Lithium-Ion

A single Ni Cd voltaic cell has an emf of 1.30 V. 95IRISET-SECUNDERABADSUBJECT: TC 4

• Ni Cd battery packs typically contain three or more cells in

series to produce the higher emfs needed by most

electronic devices. There are drawbacks to nickel-cadmium

batteries. Cadmium is a toxic heavy metal. Its use increases

the weight of batteries and provides an environmental

hazard. Some of these problems have been alleviated by the

development of nickel-metal-hydride (NiMH) batteries. The

cathode reaction of these batteries is the same as that for

for nickel-cadmium batteries. The anode reaction of NiMH96IRISET-SECUNDERABADSUBJECT: TC 4

batteries is very different, however. The anode consists of a

metal alloy, such as ZNi2, that has the ability to absorb

hydrogen atoms. During the oxidation at the anode, the

hydrogen atoms are released as H2O, during charging. The

newest rechargeable battery to receive large use in

consumer electronic devices is the lithium-ion (Li-ion)

battery. Because lithium is a very light element, Li-ion

batteries achieve a greater energy density—the amount of

of energy stored per unit mass-than nickel-based batteries.97IRISET-SECUNDERABADSUBJECT: TC 4

• The technology of Li-ion battery is very different from that

of the other batteries we have described here, and it is

based on the ability of Li+ ions to insert themselves into

certain layered solids. For example, Li+ ions can be inserted

into layers of graphite. During discharge lithium ions migrate

between two different layered materials that serve as the

anode and cathode of the cell. The specific reactions

involved are beyond the scope of our discussion. The end

point voltage of an Alkaline Cell is normally 1.0V/Cell. 98IRISET-SECUNDERABADSUBJECT: TC 4

• Nickel-Metal Hydride Batteries (Ni MH): The NiMH has been

replacing the NiCd in systems such as wireless

communications and mobile computing. The modern NiMH

offers up to 40 percent higher energy compared to NiCd.

Nickel-metal hydride batteries employ nickel hydroxide for

the positive electrode similar to Ni-Cd batteries. The

hydrogen is stored in a hydrogen-absorbing alloy for the

negative electrode, and an aqueous solution consisting

mainly of potassium hydroxide for the electrolyte.


• Advantages and Limitations of NiMH Batteries:

• 30 – 40 percent higher capacity over a standard NiCd. The

NiMH has potential for yet higher energy densities.

• Less prone to memory than the NiCd. Periodic exercise

cycles are required less often.

• Simple storage and transportation - transportation

conditions are not subject to regulatory control.

Environmentally friendly — contains only mild toxins;

profitable for recycling100IRISET-SECUNDERABADSUBJECT: TC 4

• Limitations: Limited service life

• Limited discharge current

• More complex charge algorithm needed

• High self-discharge

• Performance degrades if stored at elevated temperatures

• High maintenance — battery requires regular full discharge

to prevent crystalline formation.

• NiMH batteries are more expensive than NiCd.101IRISET-SECUNDERABADSUBJECT: TC 4

• In Indian Railways, these Batteries are used in Walkie-Talkie

sets, Digital Clocks and Cordless Telephones.

• The Lithium Ion battery:

• A rechargeable lithium-ion battery is made of one or more

power-generating compartments called cells. Each cell has

essentially three components. The positive electrode is

typically made from a chemical compound called lithium-

cobalt oxide (LiCoO2) or, in newer batteries,from lithium

iron phosphate (LiFePO4). The negative electrode is102IRISET-SECUNDERABADSUBJECT: TC 4

• generally made from carbon (graphite) and the electrolyte

varies from one type of battery to another.

• These Batteries will be used in Mobile phones, Computers

and Laptops.

• Advantages :

• High energy density potential for yet higher capacities.

• Relatively low self-discharge

• Low Maintenance103IRISET-SECUNDERABADSUBJECT: TC 4

• Limitations:1. Requires protection circuit 2.Subject to aging

even if not in use 3.Moderate discharge current.

Comparison of various rechargeable batteries:

Lead acid Ni cd NiMh Li- ion Li-poly

1 Gravimetric EnergyDensity(Wh/kg)

30-50 45-80 60-120 110-160 100-130

2 Internal Resistance in M ohms

<100 100-200 200-300 150-250 200-300

3 Overcharge Tolerance high moderate Low very low low

4 Self-discharge / Month 5% 20% 30% 10% 10%

5 Cell Voltage(nominal 2V 1.25V 1.25V 3.6V 3.6V

6 Load Current 5c 20C 5C >2C >2C

7 Fast Charge Time in hrs 8-16 1 2-4 2-4 2-4

8 Maintenance 3-6 months 30-60 days 60-90days Not req Not req


CHAPTER - 2

BATTERY CHARGING

• BATTERY CHARGING: This is an electrochemical process of

passing a direct current (D.C) through the battery in a

direction opposite that of discharge.

• METHODS OF CHARGING:

• There are two principal methods adopted for charging

batteries: 1. Constant current 2. Constant potentialSUBJECT : TC 4 IRISET- SECUNDERABAD 105

• There are two methods of constant current charging:-

• a. Series method of charging b. Parallel method of charging

• Constant current charging system: The charging current is

maintained constant till the end of charge irrespective of

rise in voltage of battery. This method is employed for initial

charging of lead acid cells. A higher charging rate is

permissible in the initial stages till the potential rises to 2.3

volts, after which it should be reduced to avoid loss of

SUBJECT TC 4 IRISET- SECUNDERABAD 106

• electrolyte due to excessive gassing and undue rise in

temperature of the plates. In this type of charging, there is a

possibility of battery getting over charged if not monitored

properly.

• There are two methods of constant method of charging

• 1. Series method of charging 2. Parallel method of charging

• Constant voltage charging: The charger is set at a fixed

voltage per cell and the charging current depends uponSUBJECT: TC 4 IRISET- SECUNDERABAD 107

difference of potential between the charger and the battery.

The initial charging current is very high, especially if the

battery is completely discharged. Hence, it is used only for

batteries which are not discharged to a very low value.

• Charging Systems: The following different types of charging

systems are adopted as per the requirement.

• 1. Initial Charging: Constant current method

• 2. Trickle Charging: Constant potential method

SUBJECT TC 4 IRISET- SECUNDERABAD 108

• 3. Float Charging: Constant potential method.

• 4. Float Trickle Charging: Constant potential method.

• 5. Equalizing Charging: Constant potential method.

• 6. Boost Charging: Constant Current Method

• 7. Normal Charging: Constant Potential Method

• 8. Freshening Charging: Constant potential method.

SUBJECT : TC 4 IRISET- SECUNDERABAD 109

• Initial Charging: constant current charger is used. This type

of charging is done to a new cell. The voltage supplied

should be at the rate of 2.7V per cell. If manufacturer

instruction card is not available the constant current of AH

Capacity/15 may be supplied.

• Trickle Charge : A system in which battery comes into

operation, only, during emergencies. At other times the

battery is idle and maintained in charged condition by trickle

SUBJECT :TC 4 IRISET- SECUNDERABAD 110

charging at 2.25 to 2.30 volts per cell. The trickle charge

current will be approximately 1 mA per A.H. at the rated 10

Hour capacity of the battery.

• Float Charge: is a system in which the battery is connected

in parallel to the charger or DC source and load. The float

charger current is automatically controlled by maintaining

the correct float voltage across the battery terminals. The

voltage of the system is set to 2.15V to 2.20 volts per cellSUBJECT: TC 4 IRISET- SECUNDERABAD 111

• Boost Charge: Given to a battery when it is neither possible

nor practicable to give it a regular charge. This is usually a

charge of higher rate and shorter duration in order to

prevent over-discharging of the battery. It is given at rate

2.4V Cell.

• Normal Charge: Done at two rates, the Start (high) rate

being maintained till the cells reach 2.4 volts per cell after

which at the finishing (low) rate till the end of charge.


• Equalizing Charge: A periodical charge given to the battery

to correct any inequalities of Sp.Gr. among cells developed

during service. This also assures that the maximum capacity

is available when needed. The lower the floating voltage,

the more is the frequency of equalizing charge. An

equalizing charge is given at a rate of 10 Hr.Capacity/50.The

frequency of the refreshing charge is once in six months

only. This assures that the maximum capacity is available

when needed.SUBJECT: TC 4 IRISET- SECUNDERABAD 113

• Freshening Charge: Applicable to a charged battery when

kept idle at a rate of 4 ٪of the rated 10 hour capacity to

prevent stratification.

• CHARGING OF SMF (VRLA) BATTERIES:

• The battery system may require an initial charge if the

voltage per cell drops to 2.1 Volts while the battery is in

storage prior to installation. In order to give an initial charge

to the battery, the instructions below have to be observed

SUBJECT: TC 4 IRISET- SECUNDERABAD 114

• a) The battery must be kept in constant potential mode

• b) Set the voltage to 2.3 volts per cell with a current limit of

0.2C Amps max.

• c) After getting the required voltage for three consecutive

hours, (2.25V/cell) and then load is connected.

• EQUALISING CHARGE: This type of charging is to be done

for every after 6 months or if the variations in cell voltages is

more than 0.1V. SUBJECT: TC 4 IRISET- SECUNDERABAD 115

• Procedure: a. Discharge all the cells up to 1.75V/cell and

bypass the cells that have reached to 1.75V earlier.

b.Continue the discharge till all the cells reach to 1.75V

c.Charge the cells for 21 hours with a Voltage setting of

2.3V/cell in constant potential mode and the current

must be limited to 0.2 C (capacity).

d. Repeat the procedure till all the cells attain the same

voltage.


• Procedure for keeping the batteries in unused condition:

Sometimes the batteries have to be laid up for an indefinite

period. If left without attention for more than 2 months, it

will deteriorate and a period of 6 months of no attention

will definitely ruin it. Periodic freshening charge is to be

given for the batteries in such a situation.


• Various ways of connecting batteries as per requirement

1.Single battery of 12v 100ah

2. When 4 Nos. of 12V 100AH batteries are Connected in

series, the out put is 48V 100AH


12V100ah

12V100ah 12V100ah 12V100ah 12V100ah

48V 100AH

3. When four nos of batteries are connected in parallel the

out put of the bank is12V 400AH. 12V 400AH

• When batteries are connected either

in series are in parallel fashion, it

must be ensured that they are of the

Same make , voltage ,capacity and

specs.


12V100ah

12V100ah

12V100ah

12V100ah

• When 4 nos of batteries are connected in series Parallel fashion, the output will be 24V 200AH

SUBJEC: TC 4 IRISET- SECUNDERABAD 120

12V100ah

12V100ah 12V100ah

12V100ah

24V 200AH

• Do’s and Don’ts:

• 1. For normal charging constant voltage charger must be

used

• 2.Sealed maintenance free batteries must be charged with

SMPS battery chargers since these have temperature

compensating circuit s.

• 3.Do not make a battery bank with batteries of different

capacities and different makes though they are of the same

voltage.SUBJECT: TC 4 IRISET- SECUNDERABAD 121

Chapter-3

Battery chargers

The battery chargers adopt the following types of Power

Supplies:

1. Linear power supply

2. Switch mode power supply

• Battery charger: Is a system in which D.C. voltage is

dropped to the required value or AC is converted to the

required D.C. value to charge the secondary battery.SUBJECT: TC 4 IRISET- SECUNDERABAD 122

• Simple Battery charger (constant voltage):

• The charging current is determined by the excess of the DC

output of the charger over the voltage of the battery rather

the difference of voltage between charger and battery.

SUBJECT:TC 4 IRISET- SECUNDERABAD 123

• The charger consists of: Step down transformer: is to step

down the input mains voltage to the selected level.

• 2. Rectifier unit: To convert the stepped down AC to DC .

• 3. A smoothing filter: is a combination of inductors and

capacitors to suppress the ripple in the output for providing

a pure DC voltage for charging the battery.

• 4.R1 (trickle resistor): is inserted into the circuit when

charger is selected to trickle mode for low rate of charging.


• R2 (ballast resistor):Introduced to reduce the change in the

charging current due to variations in input mains voltage or

variations in the load which cause fluctuations in charger

out put voltage which eventually causes change in current.

• It also provides regulation by acting as a preload there by

reducing the difference between the no load to full load.

• It provides safety to the personnel by providing a path for

stored energy of the filter capacitors to discharge through.


• Linear power supply: (Conventional regulated power supply)

• The above regulated D.C. power supply consists of four

sections as shown in the above block diagram.

• The power transformer: This converts the AC line voltage

into a higher or lower AC voltage depending on the

application and isolates the connected control equipment SUBJECT: TC 4 IRISET- SECUNDERABAD 126

Power transformer Rectifier Filter Regulator DC O/PA.C I/P

from the main power source.

• Rectifier unit: This receives transformer output and

converts the AC voltage into DC voltage. The conversion

from AC to DC is not perfect and a certain amount of AC

residue or “ripple” remains in the output of the rectifier.

• Filter unit: This receives the pulsating DC from the rectifier

and converts into pure DC.

• Regulator unit: The unregulated filtered DC is applied to an SUBJECT: TC 4 IRISET- SECUNDERABAD 127

electronic feed back or control circuit of the regulator. The

regulator circuit maintains constant DC out put during

variations in the load or variations in the I/P line voltage.

The out put AC of the transformer is always higher than the

DC out put voltage (Ex: the o/p of the transformer

approximately 18V to 20V for an O/P of 12V DC). The

difference in voltage(6Vto 8V)is dissipated as heat in the

regulating transistor as it operates in linear mode and this

causes power lossSUBJECT: TC 4 IRISET- SECUNDERABAD 128

• Limitations of linear power supply: 1.The size of the unit is

bulky because of big size power transformer and power loss

is also high during regulation. 2. The regulation response

time is low. 3. These types of power plants do not have the

scope for modular expansion due to which frequent

changing of the power plants with each expansion of the

load. These are not suitable for VRLA batteries as

temperature compensation logic is not provided.


• Switch mode power supply(SMPS): Switched-mode power

supplies (SMPS) are basically DC-to-DC converters, operating

at frequencies in the range of 20KHz to 100 KHZ.

• SMPS based power plants are compatible with conventional

flooded Lead acid as well as VRLA batteries.

• These types of power plants have the scope for modular

expansion due to which frequent changing of the power

plants is preventedSUBJECT: TC 4 IRISET- SECUNDERABAD 130

• The basic block diagram of SMPS is shown below

SUBJECT IRISET- SECUNDERABAD 131

High voltage low frequency input AC

Rectifier and filter

High frequency switch

High voltage DC

PWM oscillator

Error Amplifier

Rectifier and Filter

Out put DC

Step down

transformer

Output sensor

Feed back

Isolation

Reference

• The Ac input is fed to a high voltage rectifier and filter unit

and converted into high voltage DC. The high voltage DC is

chopped at a very high frequency in the range of 20Khz to

100Khz by the switching transistor.

• The output of the switching transistor which is a pulsating

DC is fed to the step down transformer . The stepped down

low pulsating DC is converted into pure DC by the rectifier

and filter unit and is supplied to the load.


• The out put sensor senses the output voltage and sends it

to the isolation circuit which provides physical isolation

(through an optocoupler) between the output and

controlling circuit i.e. error amplifier.

• The error amplifier is also fed with a reference voltage apart

form the sensed voltage and both the voltages are

compared and the net error voltage is fed to the PWM

oscillator by the error amplifier.


The PWM oscillator is designed to generate a very high fixed

frequency with variable pulse width. whenever there is a

change in output voltage due to input variations or load

variations, the output sensor senses it and feeds to the error

amplifier .

The error amplifier changes the width of the pulse as per

the resultant error and eventually regulates the output of

the system.

SUBJECT; TC 4 IRISET- SECUNDERABAD 134

• Since, the transistor is always in switching mode(ON or OFF),

this is called switch mode power supply system.

• The output voltage: Input voltage x D(Duty cycle)

• D =

• For example: Input voltage is 200 V and D=0.25 sec

Out put voltage= 200x0.25= 50V.


ON0.25 sec

0.75 sec OFF

On Time

On time+ off time (one cycle Duration)

If Input voltage is 200 V and D=0.5 sec

Out put voltage= 200x0.5= 100V.

• If the output voltage tends to increase (due to decrease in

load or increase in input) the comparator produces a higher

output voltage which makes the pulse that drives the base

of the switching transistor narrower. That means, the duty

cycle is reduced. Since the duty cycle is lower the output

becomes less which tries to cancel almost all the originalSUBJECT: TC 4 IRISET- SECUNDERABAD 136

ON 0.5sec

OFF 0.5 sec

increase in output voltage. Conversely, if the regulated

output voltage tries to decrease, the output of the

comparator decreases. This makes the pulse wider and the

transistor conducts for longer time and the output

increases. Finally, the output regulation is achieved by

modifying the Duty cycle. Duty cycle depends on the “on”

time of transistor, which in turn depends on the width of

the pulse applied to the base of the transistor, which is


controlled by ‘Pulse width modulator’ of the regulator

circuit.

• The power supply systems such as UPS, Computers, mobile

chargers, SMRs of battery chargers and IPS etc are all

working on the above principle.

• But different topologies areadopted as per the requirement

and design.


• 12 V power supply unit at way stations:

• Power supply unit for Telecom Installations at way Side

Stations in 25 KV Electrified areas is designed for 12 Volts/ 2

Amps switch mode with advanced circuitry techniques as

per RDSO specification No.IRS: TC-72/97. In this unit the

output load can be taken for six way station equipments

through 6 way terminal strips, through 0.2 Amps Glass or

Cartridge fuses. One number of maintenance free


Lead acid battery is fitted inside the unit having a rating of

12V/7AH. The PSU is protected against short circuit and

reverse polarity and suitable LED indications have been

provided. Protection arrangements for transients on the

input side is provided with MOVRs (320 volts rating) and

fuses with 2 ampere rating. Normally the LED on load

terminal will not glow. However, blowing of fuse on load

terminal shall be indicated by glowing of concerned 'Red'

LED. A suitable Earth terminal is provided in the PSU.SUBJECT: TC 4 IRISET- SECUNDERABAD 140

• 48 V DC SMPS POWER PLANT FOR INDIAN RAILWAYS

TELECOM EQUIPMENTS:(Rdso spec: rdso/spn/tl/23/99

version 4.0)

• This Power Plant is designed based on High Frequency

Switch Mode Techniques using switching frequencies of 20

KHz and above for the use by Indian Railways for Telecom

Equipments such as Exchanges, Multiplexing Equipments,

Microwave Radio Equips,GSM-R, TETRA and OFC equips etc.


• General description:

• This power system designed on modular basis specially for

telecom equipment and is suitable for charging VRLA or

Conventional Lead Acid Batteries.

• Main features: Local and remote (via modem) monitoring of

any alarm condition of each of the rectifiers.

• Local and remote (via modem) monitoring of output current

of each rectifier.SUBJECT: TC 4 IRISET- SECUNDERABAD 142

• Enables setting of parameters of all the rectifiers using the

CSU front panel or an optional remote PC running WINCSU

software.

• Enables monitoring of DC load current and voltage.

• A typical system comprises number of rectifiers, a

monitoring and control subsystem comprising Control

Supervisory Unit (CSU) and a Master User Interface Board

(MUIB),Mains Monitoring Interface Board (MMIB), Battery

input circuit breaker and AC input distributionSUBJECT ; TC 4 IRISET- SECUNDERABAD 143

• The system with basic blocks of monitoring and control

functions is shown in figure given below:

• The rectifier (SMR) is designed to slide and plug into a

magazine and the DC output is connected to the load and to

the battery bank.

• Low voltage disconnect switch (LVDS) is included in series

with the batteries in order to prevent deep discharge of the

battery bank in the event of an unusually long AC power

outage.SUBJECT: TC 4 IRISET- SECUNDERABAD 144

SUBJECT IRISET- SECUNDERABAD 145

• 48 V DC SMPS POWER PLANT FOR TELECOM EQUIPMENT:

LPD : Lightning protective device

SMR: Switch mode rectifier

HVD: High voltage disconnect

CSU: Control supervisory unit

MUIB: Master user interface board

LVDS: Low Voltage disconnect switch

AC Distribu

tion

HVD

SMR Rack

LPD

CSU

MUIB

LVDS

BATTERY

DCDistribution

To loads

Remote voltage free contacts

To modem or pc

• HVD (High/Low voltage disconnect switch) is installed at the

input side to provide a galvanic isolation for the modules

from abnormal AC inputs. The magazine and rack can be

configured to build different ultimate capacities of 100

Ampere and 200 ampere.

• The monitoring and control signals, such as AC input

voltage, load current, battery current, temperature, battery

switch status, LVDS control and status, system voltage are


connected to the monitoring and control module (CSU) via

master user interface board (MUIB) and mains monitoring

interface board (MMIB).

• A 4-wire cable, which carries the digital communication

signals that allow control and monitoring of the rectifier,

connects the CSU.

• A relay is provided to extend potential free contacts for

alarm condition in the MUIB. This relay operates when faultSUBJECT: TC 4 IRISET- SECUNDERABAD 147

arises. An analog AC voltmeter is provided at front panel to

monitor system AC input voltage.

• Main features of CSU as follow:

• Local and remote (via modem) monitoring of any alarm

condition of each of the rectifiers.

• Local and remote (via modem) monitoring of output current

of each rectifier.

• Enables setting of parameters of all the rectifiers using theSUBJECT: TC 4 IRISET- SECUNDERABAD 148

• CSU front panel or an optional remote PC running WINCSU

software.

• Enables monitoring of DC load current and voltage.

• The following functions are standard:

• Temperature compensation of the battery float and

equalization voltage (require temperature sensor).

• Programmable battery charging current limits (3 limits).

• Automatic equalization of the battery with selectable startSUBJECT: TC 4 IRISET- SECUNDERABAD 149

• (choose voltage/current level or discharge Ampere-hours)

and end (choose time duration or equalisation current)

parameters.

• Active current sharing.

• Installation :

• a.Initial Check up

• No damage should be observed during transportation

• Check the received material list as per the packing listSUBJECT IRISET- SECUNDERABAD 150

• All screws should be tightened once again at the site of the

rack.

• No damage should be observed in the CSU.

• Follow installation and commissioning procedure for SMR.

• Modules are individually packed and all packed modules are

supplied in one separate wooden box. Unpack the modules

and check for any transit damage Installation


• Installation & Commissioning:

• The system should be installed with sufficient space at rear

and front for easy maintenance and servicing and should be

away from heat generating equipment.

• Lightening Protection Devices (LPD) and Surge Protection

Devices (SPD) are installed in the rack side by side as these

have been tested in coordination without the need of wire or

inductor between them.SUBJECT: TC 4 IRISET- SECUNDERABAD 152

ensure that the body of the cabinet is properly earthed

before applying power to the system.

• Initial battery connection & load connection shall be done

without energizing the system.

• A minimum clearance of approximately 1.0 meter is

recommended to be provided for the power plant.

• Check and ensure that the output voltage of power plant

shown on the name plate should correspond to battery

voltage.SUBJECT : TC 4 IRISET- SECUNDERABAD 153

• The cable installed between power plant and battery must

be sized to provide minimum voltage drop.

• Installing the lightening protection devices:

• Lightening protection devices (LPD) are provided in a

separate enclosure, which is intended to be installed at the

AC mains distribution level.

• Line, neutral and earth shall b connected to the terminal

block provided inside the enclosure.SUBJECT: TC 4 IRISET- SECUNDERABAD 154

• It is advised to maintain a distance of minimum 5 meters

between the main AC distribution point and power plant. If

this distance is not physically possible, use at least 5 meter

lengths of cables to connect AC to power plant. This is

required to establish a perfect co-ordination between

lightening protection device installed near the distribution

and the surge protection device (SPD) installed in the rack.

Cable length adds some inductance in the path, which is


essential in transferring the surge energy between SPD and

LPD.

• AC input, DC output and communication cables are provided

at the rear side of the cabinet. Self locking type wago

connector is provided for AC and DC connections. Six wire

communication cable is used for communication. These

connectors have to be connected after inserting module

into the magazine.


• Telecom Integrated Power Supply System:

• 1.Consists of a Distribution-Switching-Control-Alarm

Arrangement (DSCA) and Float Rectifier-Cum-chargers (FR-

FCs) or Float Rectifier cum Boost Chargers (FR-BCs) (in N+1

configuration in hot-standby and one module in cold

standby), DC-DC converter (in N+1 configuration in hot-

standby) for 24V, 12V, 3-6V, 48V

• MPPT Battery Charger (optional) , 48V battery set of

adequate capacitySUBJECT: TC 4 IRISET- SECUNDERABAD 157

2. The Telecom Integrated Power Supply System is capable of

meeting the load requirements (equipment and battery

bank) for various telecom equipments. The system shall be

expandable at rack level itself, using the basic modules of

the same rating.

3. To cater for higher load requirements, (for modules with

more than 50 watts) the same type of modules mounted in

the same rack are capable of working in parallel load sharing

arrangementSUBJECT: TC 4 IRISET- SECUNDERABAD 158

4. The Telecom Integrated Power Supply System is suitable

for operation from AC Mains, solar power supply or from a

DG Set.

5. The Telecom Integrated Power Supply System will work

satisfactorily either with VRLA maintenance free Battery as

per IRS;S 93/96(A) or Low Maintenance Lead Acid Battery as

per IRS;S 88/2004 with latest amendment. Battery as per

requirement will be integral part of he system.SUBJECT: TC 4 IRISET- SECUNDERABAD 159

6. In case, to provide solar power as an additional source of

power supply, Solar Panel Modules of adequate capacity

has to be provided.

7. One panel consisting of status indications and critical

alarms of TIPSS will be provided in ASM’s room. The

monitoring panel is of wall mounting type. 12 core, 1.5

sq.mm signalling cable as per IRS:S 63/2007 will be used for

connecting TIPSS to Status Monitoring Panel in Station

Master’s room.SUBJECT: TC 4 IRISET- SECUNDERABAD 160

CHAPTER - 4

VOLTAGE STABILIZATION

• For telecom installations, the input supply must be

maintained reasonably constant in the face of varying load.

Since, it is not possible always with the inbuilt equipment, it

is necessary to incorporate a voltage stabilizing device as an

integral part of the equipment.


• REQUIREMENTS FOR MAINS VOLTAGE STABILIZER:

• 1. To achieve accuracy of stabilization as per the specified

percentage of 1%

• 2. The second requirement for a stabilizing system is the fast

response to the sudden change in the mains voltage.

• 3. To prevent distortions in the original sinusoidal waveform

which is important for a good power supply

• 4. To achieve stabilized power with non moving elements

which is cheaper


• Ferro resonant type automatic voltage regulator:

• It consists of a primary winding , secondary winding and a

third winding called a compensating winding.

• The compensating winding is connected in series with

primary winding and added to the primary side of the

transformer. This carries the load current and opposes the

primary flux to improve voltage regulation.

• A capacitor of proper value is connected across theSUBJECT:TC 4 IRISET- SECUNDERABAD 164

secondary winding to form a parallel resonance circuit.

• A magnetic shunt is provided between the two windings. It

provides a shunting path for the secondary flux.

• Description: Primary side: Mild Steel (Unsaturated Iron),

Secondary side: Silicon Steel (Saturated Iron)

• When the voltage is applied across primary winding is gradually

increased from zero to a particular voltage, called as KNEE

VOLTAGE or point of discontinuity, the secondary gets tuned to

SUBJECT:TC 4 IRISET- SECUNDERABAD165

• parallel resonance at that point.

• Due to the resonance effect, the capacitor increases the

secondary voltage abruptly. This results in the increase of

secondary core magnetic flux due to induced current by the

capacitance in the secondary winding. This magnetic flux is

added to the flux flowing through secondary core due to the

primary voltage. Hence flux addition takes place in the

secondary core causing saturation of secondary winding.

SUBJECT:TC 4 IRISET- SECUNDERABAD167

• When the secondary magnetic circuit is saturated, much of

the secondary flux is decoupled from the primary winding

and passes through magnetic shunt.

• At primary knee voltage secondary core is saturated and

after knee voltage the increased amount of magnetic flux

passes through the magnetic shunt and does not increase

the flux in secondary. Hence secondary voltage remains

more or less constant.


• The compensating winding which is connected in series

with the primary winding carries the load current and

opposes the primary flux to give constant output voltage.

• With compensating winding short circuit protection is also

achieved. If the output is short circuited then the current

passing through the compensating winding is also very high.

This causes very high reduction in primary flux and there by

reducing the induced secondary voltage


• Features:

1. No moving parts.

2. Power handling capacity - 0.5 KVA to 10 KVA

3. It's output voltage= 230±1٪ for input voltage range of 160V

to 270 V at 50Hz,

4. Fast regulation. Response time is < 60 m.sec.

5. Complete automatic and continuous regulation

6. Watt efficiency not less than 80٪ in case of 0.5 KVA & not

less than 85٪ in case of 1 KVA to 10 KVA at full load.SUBJECT:TC 4 IRISET- SECUNDERABAD 170

7. Immune to input spikes and surges, because of high

isolation between I/P & O/P.

8. Self protection against overload

9. ‘No’ load current is not more than 30% of the rated input

current.

DRAWBACKS:

1. The harmonic distortion in the O/P voltage is maximum at

no load. Minimum 25٪ load of rated load must be provided

2. Output voltage is frequency dependentSUBJECT:TC 4 IRISET- SECUNDERABAD 171

• Servo Controlled Voltage Regulator (Stabilizer):

• Servo voltage regulator protects the appliances such as

CNC machines, electrical equipment, Battery Chargers,

motors, lab equipment etc. by correcting the voltage

fluctuations in the incoming AC voltage to the desired

voltage levels

• The principle of operating Servo Stabilizer

• It functions on comparing the output voltage with built-inSUBJECT:TC 4 IRISET- SECUNDERABAD 172

stable reference voltage source. The control circuit controls

the servo motor. The Control circuit operates the motor

whenever the output voltage falls or rises beyond the preset


voltage. The motor is mechanically attached to the arm of a

continuously variable auto transformer which feeds to the

primary of a series control buck boost transformer. The

stabilizer output voltage is compared with the reference

voltage & resultant error signal controls the Servo Motor

which corrects the voltage by bringing it to the preset

voltage.


Servo Stabilizer consists of following sub-assemblies:

a) Variable Transformers driven by the synchronous servo

motor

b) Series Transformer

c) Electronic Control

The Syn. Servo Motor driven variable Transformer feeds

the primary winding of the double wound series

Transformer secondary winding to add or subtract the

correcting voltage to the input Line voltageSUBJECT:TC 4 IRISET- SECUNDERABAD 175

The Electronic Control circuit monitors the O/P Voltage. In case

of voltage variations the control circuit drives the Servo Motor to

correct the O/P voltage within the rated limits

• Specifications & Features of 1 KVA single Phase Servo Stabilizer

• Input Voltage :: 160 – 260V, 50 Hz

• 2.Output: 230V + 1% (adjustable with + 10 V)

• 3.Capacity: 1 KVA, 1 phase

• 4.Voltage Correction Rate :20 volts/sec

• 5.Temperature Range: 0-55 CSUBJECT:TC 4 IRISET- SECUNDERABAD 176

• Mode of operation:

• The unit can be made to operate manually through the

• AUTO/MANUAL selector switch.

• Push switches INCREASE and DECREASE can increase/decrease

O/P voltage when AUTO/ MANUAL selector switch is in MANUAL

position

• Protections

• a) Output is automatically switched OFF if it is below 205 Volts or

above 245 Volts and automatically switches ON when safe

voltage returns.SUBJECT:TC 4 IRISET- SECUNDERABAD 177

• b) Built in Time-Delay for 5-6 minutes for re-start

• c) Overload protection provided through MCB

• d) Protection with auto switch off /fault signal against

single-phasing excessive input.

• Maintenance:

• The unit doesn’t require any regular maintenance, however

carbon brush of the variac should be checked occasionally.


• The unit doesn’t require any regular maintenance However

carbon brush of the variac should be checked occasionally. If

required it should be replaced by a fresh one given as spare

in moveable arm of the variable transformer

• In case, carbon gets deposited on the conducting surface of

the variac it should be cleaned up after disconnecting the

main input supply



Block diagram of Servo Voltage Regulator

Chapter 5

UNINTERRUPTED POWER SUPPLY SYSTEM (UPS)

• An uninterrupted or uninterruptible power supply (UPS) is a

device that has an alternate source of energy (battery)

that can provide power when the primary power source is

temporarily disabled. The function of an UPS is to supply

uninterrupted power to the connected load. In railways, there

are utilized in places such as PRS, UTS, EDP centers etc.

where even a short/temporary power supply failure can


cause a great inconvenience to public/ passengers and also

may lead to financial loss to the railways.

• RDSO, Lucknow has issued a technical specification for fault

tolerant Uninterrupted Power Supply (UPS) system for PRS,

EDP centers and other similar requirements of ON LINE UPS

system vide RDSO/ PE/ SPEC/ PS/ 0023-2001 (Rev. 0),

Amendment no.3 dtd.16.09.2011. As per above

specification, the UPS provided in Railways are single phase

or 3 phase system as indicated below for different ratings.SUBJECT:TC 4 IRISET- SECUNDERABAD 182

• Category A: 1 kVA to 7.5 kVA with single-phase input

and single phase output.

• Category B: 7.5 kVA to 30 kVA with three phase input

and Single phase output.

• Category C: 10 kVA and above with three phase input

and three phase output.

• Generally category ‘A’ UPS (1 kVA to 7.5 kVA with single

phase input and single phase output) are provided at

booking offices for Unreserved Ticketing System (UTS)SUBJECT:TC 4 IRISET- SECUNDERABAD 183

for continuous power backup.

UNINTERRUPTED POWER SUPPLY

In this, the rectifier accepts mains ac, converts it into dc to

feed it to the inverter as well as to charge the batteries. The

inverter converts dc power into clean, stable isolated ac

output which is given to the load connected at the output.

In the event of mains failure, the inverter works on the

battery supply and gives the uninterrupted output for a

period of backup time.SUBJECT:TC 4 IRISET- SECUNDERABAD 184

• Constant current / constant voltage (CCCV) is a combination

of the above two methods. The charger limits the amount

of current to a pre-set level until the battery reaches a pre-

set voltage level. The current then reduces as the battery

becomes fully charged. This system allows fast charging

without the risk of over-charging and is suitable for Li-ion

and other battery types.


• TYPES OF UPS: The UPS can be divided into three types

depending on the construction and change over time.

They are: 1. Online 2. Off - Line 3. Line - interactive

• Online UPS: The inverter is always in ON condition even

when the mains power supply is available. During normal

condition, the input AC is converted to DC and then fed to

Inverter circuit which in turn converts DC into AC to supply

to the load. During mains supply failure, the DC voltage from

the battery is converted to AC voltage by the inverterSUBJECT:TC 4 IRISET- SECUNDERABAD 186

circuit and stepped up to the required output voltage level. The

battery is in float mode and gets charged by the charger cum

rectifier circuit. Two transformers are used one for the charger

and another for the inverter circuit. The battery capacity decides

the backup time of UPS. The shape of the output wave form is

pure Sine Wave. since, the inverter is always in ON condition ,

this called as online UPS.

ADVANTAGE: There is no changeover time from mains to battery

mode in the case of power failure.SUBJECT:TC 4 IRISET- SECUNDERABAD 187


A C MAINS

INPUT

BATTERY

CHARGER &

RECTIFIER

B T 1

INVERTERA C OUT PUT

TO LOAD

NORMAL AND EMERGENCY POWER FLOW

T1T2

MAINS

TRANSFORMER

BATTERY

BLOCK DIAGRAM OF ON LINE UPS

USE: This type of system is mostly used supply power for

Medical and Surgical equipments, and big computer systems

where the data is most important like Banks and industries

etc.


TRICKLE

CHARGE BATTERY

CHARGER

B T 1

INVERTER

A C SWITCH

EMERGENCY

POWER FLOW

T1

T2

A C INPUT

NORMAL

BATTERY

A C SWITCH

A C OUT PUT

TO LOAD

BLOCK DIAGRAM OF OFF LINE UPS

• Off-Line UPS: The AC power is directly supplied to the load

through an AC switch and the inverter is in off condition. On

the failure of mains, the line connected to AC switch opens

and the inverter AC switch will close allowing the battery to

provide back-up power through the inverter stage. The load

is starved during switch over time.

ADVANTAGES:

1. It is very much compact due to less number of components

compared to ON-Line UPS.

2. Inverter is “On” only when the AC input is off or out of

range.

3. It is economical.SUBJECT:TC 4 IRISET- SECUNDERABAD 190


B T 1

RECTIFIER &

INVERTER

T1

A C INPUT

BATTERY

BANK

A C SWITCH

A C OUT PUT

TO LOAD

NORMAL POWER FLOW

TRICKLE

CHARGE

NORMAL

DIRECTION OF

EMERGENCY

POWER FLOW

BLOCK DIAGRAM OF LINE INTERACTIVE UPS

LINE INTERACTIVE UPS: During normal condition, the AC

power is directly supplied to the load through the AC switch

which is normally ON. Under the emergency conditions, the

AC switch opens the line and the battery comes into the circuit

to provide the backup power through the inverter stage. only

one transformer is used for charging circuit as well as for inverter

circuit. The transformer works in step down mode for charging

the battery and works in step up mode for inverter working.

• ADVANTAGES:

1. This is cheaper and less components are involved.

2. It is for only low power applications below 1KVA.


S.no ON LINE UPS OFF LINE UPS LINE INTERACTIVE UPS

1 Inverter is ON always Inverter is ON only during mains failure

Inverter is ON only during mains failure

2 Switching time is zero Switching time is < 5m secs

Switching time is <5 m secs

3 Output is Sine wave Out put is Sine/square wave

Out put is Sine/square wave

4 Cost is high

5 sealed maintenance free batteries are used

sealed maintenance free / flooded batteries are used

sealed maintenance free / flooded batteries are used

6. Used in main frame computers /medical equipments where un-interrupted power supply is required

Used with PC’s or OtherApplications Where interruption upto 5 mS is permitted

Used with PC’s or OtherApplications Where interruption upto 5 mSis permitted

7 Float performance of charger has a wide influence on battery life

Battery charging iscontrolled automatically

Battery charging iscontrolled automatically


CHAPTER 6

PHOTOVOLTAIC GENERATION OF ELECTRICITY -

SOLAR CELLS

• Electricity can be generated directly from Sunlight, by a

process called as Photovoltaic effect, which is defined as

the generation of an electromotive force as a result of the

absorption of ionizing radiation.

• Devices that use the PV effect to generate a voltage when

Sunlight is used as the source of ionizing radiation are called

Solar Cells.SUBJECT: TC4 IRISET- SECUNDERABAD 194

• Solar Cell:The heart of any PV Power System is the Solar

Cell. It is a transducer that converts the Sun's radiant energy

directly into electricity and is basically a semiconductor

diode capable of developing voltage.

• At present Silicon is the most important semiconductor

material for Photovoltaic Solar energy conversion.

• Solar Cell works on the principle of p-n semiconductor

junction. The holes in P-material and the electrons in

SUBJECT: TC4 IRISET- SECUNDERABAD 195

• N-material are are called majority carriers because they are

in excess and the majority of the current is carried by them.

Conversely the electrons in P-type material and the holes in

N-type material are called as minority carriers. The narrow

region is called as space charge region or depletion region.

• Silicon Solar Cell: In a Silicon Solar Cell layer of a typical

silicon cell is of a thickness such that light falling on the

surface penetrates far into the crystal to create electron-

hole pairs in the vicinity of the junction with the P-typeSUBJECT: TC4 IRISET- SECUNDERABAD 196

Silicon. The thickness is typically half a micron. Therefore,

when light falls on the cell electrons will collect in the N-

type layer and holes will collect in the P-type layer until

there is a voltage built up within the crystal sufficient to

push any other electron back into the P-type layer. In a

silicon Solar Cell that voltage is about 0.65 V.A current can

be drawn from the cell through a circuit that makes

electrical contact with both the front surface of the cell and

the back one. If the resistance of the external circuit is low,SUBJECT: TC4 IRISET- SECUNDERABAD 197

the current that flows through it is a measure of the rate at

which the electrons are separated from holes. That rate

depends on the intensity of the light falling on the surface of

the cell and on the rate at which electrons and holes are lost

through their recombination.

The efficiency of these Cells can be improved depending on

the fact that the output of Solar Cell of a given size is

proportional to the intensity of the radiation falling on that.


• This is achieved by concentrating sunlight onto a relatively

small area of Solar Cell, by focussing the light with a

parabolic mirror or trough shaped reflector known as

Wingston Collector.

• Solar Array Configuration: Solar Cell arrays usually consist

of Series-Parallel inter-connected Solar Cells bonded to

supporting substrate and encapsulated with transparent

materials to provide environmental protection and non-

corrosion. Most of the silicon Solar Cells employed for SUBJECT: TC4 IRISET- SECUNDERABAD 199

terrestrial applications are round wafers of 5 cm dia. and a

thickness of 0.3 to 0.5 mm. A 5 cm dia. cell with a surface

area of about 20 cm2 delivers in "Full Sun", a power about

0.3 W at less than 0.5 V, at room temperature.

• For higher power and higher voltage, a number of cells must

be assembled into Panel. If more voltage is required, the

cells should be connected in series and for more current in

parallel. By connecting a number of cells in series and

parallel, it is possible to provide any power at any voltageSUBJECT: TC4 IRISET- SECUNDERABAD 200

• The general practice is not to build a Solar Generator from

one panel but to divide the array into a number of modules

of equal voltage and power.

• The present standard values are 1.5 V, 6V, 12 V, 24 V, 48V,

which are multiples of each other. Any specific power

demand can be met by connecting a suitable number of

Modules in series and in parallel

• Precautions: Careful attention must be given to matching

the electrical characteristics of the cells which are to beSUBJECT: TC4 IRISET- SECUNDERABAD 201

assembled. As a general rule, all cells to be connected in

parallel should have the same Voc and even more

important, the same max power point voltage. Cells to be

operated in series have the same ISC and the same max.

power point current. The mismatching of Solar Cell

characteristics leads to 'bad' panels, because the cells of

higher photocurrent and photo voltage dissipate their

excess power in the cells of lower electrical performance



• The terminology of solar panel is given below.

• P-V array: A typical p-v array is shown below

16 Nos. of Solar Cell Modules are connected in series

Parallel to give a peak output of 64 V and 5.8 amps. EachSUBJECT: TC4 IRISET- SECUNDERABAD 204

solar module is assembled with 34 Solar Cells in series to

give a peak output of 1.45 amps and 16V.

Power System with Photovoltaic Conversion: a typical

arrangement is shown in figure below. As the Solar Power is

not available while it is dark, a normal storage arrangement

is needed in the form of battery. In Small Scale Units, a Solar

Conversion System and Storage is sufficient to meet day and

night power demand. Where as, in large Scale units another


• charger is also provided to charge batteries during periods

of darkness and also during periods while the peak power is

not obtained by P.V. conversion.


• Main Components of Solar Photovoltaic System in Indian

Railways:

• The solar power system consists of the following

components:

I) Solar array ii) Battery Bank iii) Solar Charge Controller

iv) Field Junction Box v) Solar Module Mounting Structure

v) Earthing kit vii) Cables. These arrangement of these

components is shown below.SUBJECT: TC4 IRISET- SECUNDERABAD 207

• a) Solar array : consists of series/parallel combination of

modules, which are mounted on the metallic structure in

sunny and shadow free area at a fixed angle as

recommended by designer. All the modules will face the

South in Northern hemisphere. Cables from the array area

will come to the control and battery room through junction

boxes from panels of modules.

• b) field junction box: FJB is the interface between Solar

panels and the Charge Controller. All the incoming/outgoing SUBJECT: TC4 IRISET- SECUNDERABAD 209

cables/wires from Solar panel to Charge Controller are

terminated at FJB.

• Solar Charge Controller: this is the interface between Array

and battery bank. It protects the battery from overcharging

and ensures moderate charging at finishing end of charge of

battery bank. Therefore it enhances the life of the battery

bank. It also indicates the charging status of batteries like

battery undercharged, overcharged or deep discharged

through LEDs indications. . Some switches and MCBs areSUBJECT: TC4IRISET- SECUNDERABAD

210

provided for manual or accidental cut-off of charging. . In

some charge controllers load terminals are also provided

through a low battery charge cut-off device so that it can

protect the battery bank from deep discharge. Solar Charge

Controller units for Indian Railways are manufactured as per

RDSO Specification No.RDSO/SPN/187/2004.

. First the controller is connected to the battery bank and

then it is connected to Solar Array/Solar module for sensing

the voltage from the module. When the system is put into


operation, the SPV modules start charging the battery bank.

Care should be taken that in no case the battery

connections are removed from the controller terminals

when the system is in operation, otherwise SPV voltage may

damage the Charge controller, since the Solar voltage is

always higher than the battery voltage.

Battery bank: The Sun is not always available and it is not

regular. However, loads are to be fed any time of the day.

Therefore power should be stored in a battery bank. SUBJECT: TC4 IRISET- SECUNDERABAD 212

Low maintenance Lead acid battery as per IRS: S 88/2004 or

latest of specified capacity will be provided. The capacity of

this battery bank is given in Ampere - Hour (AH) and bus bar

voltage. The bus-bar voltage is decided by the voltage

requirement of the load.

Earthing kit: Earthing kit is provided to earth the mounting

structure. The installation shall have proper earth terminals

and shall be properly earthed. Zonal Railways shall provide

earthing arrangement as per IS:S 3043 and directions issuedSUBJECT: TC4 IRISET- SECUNDERABAD 213

by RDSO for Lighting and Surge protection for signaling

equipment vide letter No.STS/E/SPD dated 22.06.2004. The

earth resistance shall not be more than 2 ohm. Earth

provided shall preferably be maintenance free using earth

resistance improvement material.

Cables: Different types of cables to connect module to

module, modules to charge controller, charge controller to

battery, or connect battery to load as required. The cable siz


size used for interconnection of SPV module, Charge

Controller and battery shall be minimum 2 X 2.5 sq. mm Cu.

Cable. As far as some hardware is concerned the screws and

bolts/nuts are of Chrome plated, stainless steel and brass so

that rusting does not take place.

Operation: Operation of the Solar power source is very

simple. Once the system is installed, CHG.ON (Green) LED

will glow during daytime and will indicate that the power is

available for charging Battery Bank from SPV panel.SUBJECT: TC4 IRISET- SECUNDERABAD 215

Connect the equipment to be operated on solar power

to the SPV Charge Control Unit at terminals marked

‘LOAD’ position.

• Types of Solar Panels:

Solar panels are classified on the basis of the following

points:

1) Crystalline Silicon (Mono/Poly/Amorphous)

2) Different Size or Area of cells

3) Type of cells & nos. (Rectangular/Circular/Square/SUBJECT: TC4 IRISET- SECUNDERABAD 216

Pseudo-square/Semi-circular etc.)

4) Power (High/Mid/Low range

• Advantages and Disadvantages of Solar Panel:

• Advantages

• Fuel source for Solar Panel is direct and endless so no

external fuels required.

• Sunlight - free of cost.

• Unlimited life of Solar Modules, fast response and high

reliability.SUBJECT: TC4 IRISET- SECUNDERABAD 217

• Can operate under high temperature and in open.

• Inherently short circuit protected and safe under any load

condition.

• Pollution free.

• Minimum Maintenance

• Independent working

• Operation is simple and no electrochemical reaction and no

liquid medium.SUBJECT: TC4 IRISET- SECUNDERABAD 218

• No AC to DC conversion losses as DC is produced directly.

• Noise-free as there are no moving parts.

• No transmission losses as installed in the vicinity of the load.

• Suitable for remote, isolated and hilly places.

• Suitable for moving loads/objects

• Since it is in modular form, provision of future expansion of

capacity is available.

• It can generate powers from milli-watts to several

megawatts.SUBJECT: TC4 IRISET- SECUNDERABAD 219

• It can be used almost everywhere from small electronic

devices to large scale MW power generation station.

• It can be installed and mounted easily with minimum cost.

• Disadvantages

• Initial cost is high

• Dependent on sunlight

• Additional cost for storage battery.

• Climatic conditions, location, latitude, longitude, altitude, SUBJECT: TC4 IRISET- SECUNDERABAD 220

• tilt angle, ageing, dent, bird droppings, etc. affect the output.

• It has no self-storage capacity.

• Manufacturing is a very complicated process.

• To install solar panel large area is required.

• Almost all Signalling and Telecommunication gears can be run by

solar power. In Indian Railway, Signalling and Telecom system are

Solar powered in phased manner. Priorities are given to those

locations where there is no conventional power or power

transmission through cables is cost effective.SUBJECT: TC4 IRISET- SECUNDERABAD 221

• Maintenance:

• Solar panels require virtually no maintenance. However the

associated equipment such as batteries and charge

controller are to be maintained. Oncein a fortnight the

surface of the panels should be wiped clean with a wet rag

to remove dust, fallen leaves, bird dropping etc. Only, water

to be used and no other cleaning agent. With Solar Panel

Secondary battery maintenance becomes minimum. Still


• general periodical maintenance of battery should be carried

out in the usual manner and as per maintenance manual.

• Precautions and Preventive Steps:

• Ensure that:

• a) SPV Modules are connected in parallel and SPV Panel

output voltage is less than 25 Volts under normal sunshine

condition (for 12V System/Module).


• b) All connections are properly made tight and neat using

the crimped Red (for +ve) and Black (for –ve) wires supplied

by the manufacturer in order to avoid reverse connection.

• c) The rating of the fuse in the charge controller is not

changed.

• d) The SPV Panel is installed facing SOUTH and with the

correct ‘Angle of tilt’.

• e) There is no shadow on any part of the SPV Panel at any

time of the day, to get maximum power.SUBJECT: TC4 IRISET- SECUNDERABAD 224

• f)If the SPV Panel is installed on ground, it must be fenced

properly to protect it from cattle and to prevent from any

damage/theft. Fencing should be made in such a way that

no shadow should fall on SPV Panel at any time of the day.

• g) Battery Bank is placed on a rack or platform insulated

from ground and located in a well-ventilated room and also

sufficient clearance is there over the battery.

• h) FIRST the Battery Bank, then SPV Panel and then Load is


• connected to SPV Charge Control Unit and for disconnection

reverse sequence is adopted.

• i) Battery terminals are never shorted even momentarily as

shorting will result in HEAVY SPARK AND FIRE. (To avoid the

same connect the cable at Charge Controller end ‘First’ and

then Battery end.)

• Never connect the Load directly to the SPV Panel as SPV

Panel may give higher/lower voltage than required by theSUBJECT: TC4 IRISET- SECUNDERABAD 226

• Load Equipment and hence the equipment may be

DAMAGED permanently.

• k) Blocking diode is provided at the array output for

protection against reverse polarity.

• l) Make sure that the Solar PV module gets direct sunlight

throughout the day where you install it.

• m) The Green indicator on Charge controller is only an

indication for charging. It will glow even at small amount of

charging. So to ensure efficient charging, the availability SUBJECT: TC4 IRISET- SECUNDERABAD 227

• of direct sunlight over the Solar PV module for the

maximum hours of the day should be ensured.

• n) It is NOT HEAT BUT LIGHT that produces energy. So let

direct sunlight to fall on the module surface without shades.

• Troubleshooting:

• SPV Power Source is not able to drive the connected

equipment.

• The diagnosis of the problem in such situations starts with

the battery.SUBJECT: TC4 IRISET- SECUNDERABAD 228

• If the voltage of the battery bank is correct as indicated in

Charge controller, there may be a problem in the inverter or

switch between load and inverter i.e. either inverter is

tripped or switch/load MCB is tripped or load fuse is blown

off. If none of the above fault is observed then Disconnect

the load (S & T Equipment) from Charge Controller and

connect it directly to Battery Bank. If the equipment

operates, the defect may be with the Charge Controller.


• Disconnect the Charge Controller and check as per

troubleshooting instructions given in the manual supplied

with it or inform the manufacturer/supplier.

• If any of the SPV modules gives low voltage/current output

during bright sunlight.

• Sun intensity 90 mW/Sq. cm)inform the manufacturer

/Supplier with module serial number along with the

measurements taken, for necessary investigations.



CHAPTER – 7

SAFETY PRECAUTIONS, POWER SUPPLY ARRANGEMENTS

AND LOAD CALCULATIONS

Safety precautions for power supply systems:

• The fuses provided for power supply systems must be of

correct value. Rating of fuses shall be equal to 1.5 times the

current flowing through it.

• Do not bring naked flames into Battery room.

• Smoking should be prohibited inside the petrol storage

rooms and battery room.

• Dangerous growth of vegetation near the equipments or

feeder lines or masts must not be allowed.

• All power supply systems must be properly earthed.

• All electrical installations shall be provided with gas type

extinguishers. Water should not be used for extinguish

electrical fires.

• Fuses shall be removed or replaced only after the circuitSUBJECT: TC 4 IRISET- SECUNDERABAD 232

has been completely de-energized.

• Suitable protective guards and wire nets shall be provided

to prevent staff from making accidental contact at the

dangerous voltages and radio frequency high power

radiation.

• Where cables pass through metallic parts, insulating bushes

shall be provided.

• Tools which are used in S&T circuits and on any current

• carrying parts of S&T equipment are required to be


insulated to protect the staff from AC induced voltages.

• Depth of Discharge permitted as follows:

• Flooded type Lead Acid Cell - 70%, LMLA cell - 80% , VRLA

cell - 50%.

• Recommended Capacity of the battery charger = C/10 X 2.5

(as per Battery charger Spec).

• Battery Charger Capacity (Ultimate System load) consists of

Equipment load plus battery charging current at 10 hour


rate plus any other load which are to be fed from power

plant.

• Battery Charger Capacity (Ultimate System load) consists of

Equipment load plus battery charging current at 10 hour

rate plus any other load which are to be fed from power

plant.

• Ultimate load is the load of the system when it has grown to

its maximum capacity. Minimum five years growth

projection may be taken for the purpose of calculation. SUBJECT: TC 4 IRISET- SECUNDERABAD 235

• Here, the multiplying factor 2.5 is taken for SMPS chargers

on account of power factor, efficiency and future

requirement of load current.

• Total Load in VA = Voltage X Load Current/ Power Factor X

Efficiency

• = Voltage X (Charging current of battery+ Eqpt. Load)/Power

factor X Efficiency of charger.


• Power supply system arrangement in Micro wave stations:

• Charge- discharge system working:

• In this system TWO battery banks are used. If one battery

bank is under charging and the other is connected to the

equipment. Connection and disconnection of the

equipment and batteries is done by the DPDT/DPST

switches as shown in the wiring diagram. TWO generators

are provided to supply AC during the AC mains power

failure. A suitable type of battery charger is to be providedSUBJECT: TC 4 IRISET- SECUNDERABAD 237


• to charge the battery banks.

• While changing over the batteries, precautions to be taken

to prevent switching off of the equipment. For that, put

both the DPDT switches to UP side and then put the

required switch to DOWN for charging battery.


• Power supply arrangement for RE Repeater:

• RE repeater requires 24V DC for its working. It can be

provided by 12 numbers of Conventional type Lead Acid

cells connected in series to make 24V battery OF 120AH

capacity.

• The mains AC supply is given to the suitable type of battery

charger like Auto/Manual type of charger with efficient filter

circuit. The battery is connected in float fashion, so

whenever the AC mains supply goes OFF immediately


Power supply arrangement for RE Repeater:

• the battery takes care and equipment will not be

interrupted .If the AC mains voltage is not restored shortly

the battery charger can be provided with the AT (traction)

supply which will be available all the time.

• POWER SUPPLY ARRANGEMENT AT OFC HUT: The power

supply arrangement at OFC hut is shown in the above block

diagram. Single battery is floated across the output of a float

charger of required current rating.


type battery charger associated with SMRs.

• SMRs works on switch mode technique and its output is a

stabilized DC supply of 48V ±2V. Each SMR current rating is

• 25 Amps. To get 50A of current, SMR modules each 25 Amps

are working in parallel operation and the third one is in

standby mode. The output of this is given to a battery bank

of 48V comprising 24 numbers of low maintenance /SMF

type Lead Acid cells (VRLA) each 2V 200Ah capacity,


• connected in series to get 48 V 200 AH.

• Since the battery is connected in float fashion it is kept in

fully charged condition. The load current is taken from the

charger in a separate path. Whenever the AC mains supply

fails, automatically the battery takes over the load. After

resumption of AC supply, the charger gives current for

charging the battery and to the load.

• The positive of the battery shall be connected to below 1

Ohm earthing.SUBJECT: TC 4 IRISET- SECUNDERABAD 245

• SOLAR POWER SUPPLY ARRANGEMENT AT OFC HUT:

• While planning for Provision of Solar Power Supply system in

non RE area for a Telecom system load, the following

information shall be taken into consideration.

• 1. Load calculation

• 2. Sizing Solar Array

• 3. Battery capacity

• 4. Selection of Charge Controller


• OFC HUT equipment power supply designed on solar power:

• For DC Loads: Load Amps X Operating Hours per Day = Amp

Hour Per Day (AHPD)

• Total OFC hut system load = 3750 VA ( from above load

calculation)

• DC Ampere Hours per Day = Total System Load/System

Nominal Voltage

• = 3750 Watt Hours per Day/48 Volts

• = 78 Ampere Hours per DaySUBJECT: TC 4 IRISET- SECUNDERABAD 247

• Total Ampere Hours per Day with Batteries :

• Total Ampere Hours per Day/(Battery efficiency X Module

derating)

• =78/(0.9 X 0.9) = 78/0.81 = 96.29 = 100 Ampere Hours per

Day

• Total PV Array Current = Total Daily Ampere Hour

requirement / Design Insolation*

• = 100 Amp-hrs / 5.0 peak solar hours= 20 Amps

• * Insolation Based on Optimum Tilt for SeasonSUBJECT: TC 4 IRISET- SECUNDERABAD 248

• PV Module selection: For ex:- Choose PV module of 75 W

• Max Power = 75 W (@STC), Max Current = 4.41 Amps

• Max Voltage = 17 Volts

• Number of Modules in Series = System Nominal Voltage /

Module Nominal Voltage = 48 Volts / (12 Volts/module) = 4

Modules

• Total Number of Modules = Number of modules in parallel X

Number of modules in SeriesSUBJECT: TC 4 IRISET- SECUNDERABAD 249

• = 15 X 4 = 60 modules of 75 Watt each i.e. 4500W

• Minimum Battery Capacity required = [Total Daily Amp-hour

per Day with Batteries (Step 5) X Desired Reserve Time

(Days)] / Percent of Usable Battery Capacity

• = (78 Amp-hrs/Day X 3 Days) / 0.80

• = 293 Amp-hrs = 300 Amp-hrs

• Choosing of Charge Controller = No. of Parallel Modules X

Isc X 1.25SUBJECT: TC 4 IRISET- SECUNDERABAD 250

• Charge Controller Capacity = 15 x 5 x 1.25 = 93.75

• = 94 Amps (Nearest higher available Value may be selected)

• e.g. 48 Volts 100 Amps may be chosen.

• Power supply arrangement at a LC gate with solar panel:

• Solar Panel output: 18V DC (without load) / 12 VDC nominal

(with load)

• Charger consists of 12V/7 Ah SMF battery

• DTMF selective calling telephone works on 12 VDC with

100mASUBJECT: TC 4 IRISET- SECUNDERABAD 251

Power consumption.Load Calculation can be carried out as mentioned in earlier systems.


• Power supply arrangement at a LC gate with centralized

power supply at SM room:

• This Electronic LC gate Telephone system consists of a

centralized power supply unit at SM office only in a section.

This PSU consists of 2 no. of 7AH SMF batteries. This PSU

provides dual power supply of 12 & 24 V DC. Out of these,

24 V DC will be fed into line for operation of Electronic

Telephone system which is available in LC gates. Hence, the

LC gate telephone does not required at local power supplySUBJECT: TC 4 IRISET- SECUNDERABAD 253

for operation. Howe ever, the telephone available at Station

with SM works on 12V DC supply which is extended


from PSU and telephone available at LC gate also works on

12V DC which derives from Line connection unit. his system

works on simple existing line (only one pair).

• Power supply arrangement for 25w VHF set:

• 25W VHF set used at stations, cabins and important

locations for safety communication shall be provided with

battery backup. For this backup power supply arrangement,

a separate 100 Ah battery connected with SMPS based


12V/25 Amps charger shall be arranged in all the locations.

Proper earthing also has to be ensured.


• Load Calculation:

• 25 W VHF set takes a load current of 3 Amps maximum, at

12 V D.C.

• Capacity of the battery required:3 Amps X10 Hours =30 Ah.

• As per RDSO instructions the battery should be discharged

up to 50% of its capacity to make it recharge quickly,

• Therefore Actual capacity of the battery required= 30 X 2 =

60 Ah.

• Hence 100 Ah capacity battery has chosen.SUBJECT: TC 4 IRISET- SECUNDERABAD 257

• Rating of the charger required to put the battery under

charging and to supply to set= C/10 x 2.5

• = 100/10 x 2.5 = 25 Amps.

• Total Load = Voltage X Load Current: 12 X 3 = 56.25 VA =

53VA

• Power Factor X Efficiency .8 X .8


Power supply arrangement for gsm-r system at IRISET:


Item Description of equipment

Power Load (W)

1 BTS - 2 TRX 550

2 BTS – 2 TRX 550

3 eBSC 1500

4 eTRAU 1500

Total load 4100


Load Calculation as per TEC specification:

• Selection of a battery for supplying load of 4100 VA for 4

hours back up to an end point

• voltage of 1.75, when the system voltage is 48V at an

ambient temperature of 27 C.

• Total DC power consumption of all the GSM-R equipment:

4100 VA

• Operating Voltage of above GSM-R equipment: 48 V DC

• Load Current required for all the above equipment: 4100/48

= 85.42 ASUBJECT: TC 4 IRISET- SECUNDERABAD 261

• Back up time required: 4 hrs

• Capacity required = Load current x Backup time

• K-factor for 4 hours backup: 5

• Capacity of battery required: 85.42 A X 5 (K factor) = 427.1

Ah

• Applying Ageing Factor of 1.25, sized battery capacity =

427.1 x 1.25 = 533.85AH

• Hence, the nearest higher available capacity of battery:

=600 AhSUBJECT: TC 4 IRISET- SECUNDERABAD 262

• Selection of a Charger for a 600 Ah battery

• Load Current required for all the above equipment :

4100/48 = 85.42 A

• Capacity of VRLA battery: = 600 Ah

• Charging current required at 10%of 600 Ah = 60 Amps.

• Total Current (Load+ Charging Current) = 145.42 Amps

• Hence SMPS rating required = 150 Amps

• Number of SMR modules of 25 Amps required (n) = 6SUBJECT: TC 4 IRISET- SECUNDERABAD 263

• Charger with redundancy of SMR module (n+1) = 7

• Hence 600 Ah VRLA battery with 48V DC SMPS based

charger with ultimate capacity of 150 Amps consists of 7 no.

of SMRs has to be utilized.


CHAPTER - 8

DIESEL GENERATOR SET

• In Indian Railways, mostly Diesel Generators are used as

standby power supply or as main power supply where

• electrification work is not completed or in remote areas like

microwave stations/level crossing gates/IBH etc.

• Diesel Generator shall be silent genset, Single Phase, 230 V

output. Diesel Engine is as per RDSO Specification

RDSO/SPN/193/2005 with acoustic proof enclosure, panel &


• push button start assembly, remote operation panels and

anti vibration mounting of engine/ alternator along with low

maintenance battery of 12V as per IRS:S-88/93 Push button

starting arrangement is to be provided. For Railway S&T

applications based on load in RE/Non-RE area, generators of

7.5KVA, 10KVA, 12.5KVA and 15KVA are used.


• Description of DG set Working:

• The diesel engine uses diesel as fuel and converts this fuel

(chemical energy) into motion (mechanical energy) required

to drive the AC generator (alternator). The main

characteristic of diesel engine which distinguishes them

from other combustion engines is the method of igniting

fuel. This works on the principle of “Compression ignition”.

• The air is taken into the cylinder and is compressed to very


• high temperature of about 800°c. Then the diesel is injected

into it under high pressure in spray form which gets ignited

on coming into contact with hot air.

• Generally, Diesel engines ,now a days, adopt four stroke

cycle in place of 2 stroke cycle for delivering optimum power

because of inherent drawbacks in 2 stroke cycle such as

• 1. Atmospheric pollution 2. Limitation of power

• 3. Uneconomical 4. Waste of fuelSUBJECT:TC 4 IRISET- SECUNDERABAD 268

• Four- stroke cycle: A sequence of events which recur

regularly and in the same order is called a cycle. The

following events form the cycle in a diesel engine.

• 1. Filling the engine cylinder with fresh air. 2. Compression

of the fresh charge which raises its pressure and

temperature so that when the fuel is injected, it ignites

readily and burns efficiently. 3. Combustion of the fuel and

expansion of the hot gases. 4. Emptying the products of

combustion from the cylinder.SUBJECT:TC 4 IRISET- SECUNDERABAD 269

• When these four events are completed, the cycle is

repeated. When each of these four events requires a

separate stroke of the piston, the cycle is called a four stroke

cycle. Basically, a stroke is the movement of the piston in

the cylinder either from TDC (top dead center) to BDC

(bottom dead center) or from BDC to TDC. The dead center

is the maximum distance a piston can travel linearly in

either of the directions.


• 1. Intake stroke: During the intake stroke the inlet valve is

opened and the outlet valve is closed .The piston moves

downward towards BDC. The pressure drops in the cylinder

and because of the low pressure the air from the

atmosphere is sucked into the cylinder.

• 2. Compression stroke: At the beginning of the stroke the

piston is at BDC and the cylinder is at its maximum volume.

The inlet valve closes and the cylinder is filled with air. The


outlet valve remains in closed condition. Now the piston

moves upward to the TDC and compresses the air. The

pressure in the cylinder increases, the volume decreases

and the temperature increases. The temperature of

compressed air goes up to 400 °c to 700 °c .

• Power stroke: The diesel is injected or sprayed into the

cylinder in misty form under high pressure at the end of the

compression stroke. The temperature of the air inside the

cylinder is high enough to ignite the fuel and combustionSUBJECT:TC 4 IRISET- SECUNDERABAD 272


due to combustion leads to the expansion of burnt gases

takes place . The heat energy developed inside the cylinder

due to combustion leads to the expansion of burnt gases

and increase in pressure. The high pressure of the burnt

gases forces the piston to BDC. In this stroke both valves

remain in closed condition.

• Exhaust stroke: The piston which is at BDC, after completion

of power stroke, starts moving to TDC and the exhaust valve

opens. The burnt gases discharged to the atmosphere under

the upward thrust of the piston through the exhaust valve.

The inlet valve remains in closed condition during this

stroke. The piston reaches TDC and will be ready for the

next cycle of operation.SUBJECT:TC 4 IRISET- SECUNDERABAD 274


• These four strokes produce two revolutions of the

crankshaft. This process, continuously, repeats itself during

the operation of the engine.

• The diesel engine is mainly divided into four systems in

terms of regular maintenance. They are

• 1. Fuel system 2. Lubricating system.

• 3. Cooling system. 4. Starting system- hand and electric

• 1 Fuel system: The fuel system consists of the following

components.

• 1. Service tank

• 2. Fuel feed pump if fuel is not gravity fed

• 3. Fuel filter on the suction side of the fuel pump

• 4. Fuel injection pump

• 5. Injectors .


Fuel flow diagram of a DG set


• Fuel oil (diesel) from the service tank enters into the diesel

filters. The diesel gets filtered from dirt and dust in the

filters and clean fuel is supplied to the injection Pump. As

each plunger of the pump lifted in the correct sequence,

fuel under high pressure is passed through a steel tube to

the injector. The injector is located in the cylinder head and

sprays the fuel in a misty form into the cylinder.

• Governor: Some form of governor is always fitted to control

the speed of the engine. For constant speed applications, SUBJECT:TC 4 IRISET- SECUNDERABAD 278

• the governor controls the speed automatically within

specified limits under changes of load between no load and

full load. The purpose of governor is to keep the engine

running at a desired speed (RPM)regardless of changes in

the load on the engine.

• Air lock in fuel system: Air lock is the most common

problem that occurs in diesel engines. It leads to starting

trouble and erratic running of the engine. Air lock is nothing

but entry of air into the fuel system whenever the fuel filters

are opened for cleaning and for replacement or whenever SUBJECT:TC 4 IRISET- SECUNDERABAD 279

• the fuel tank gets empty or due to lose fuel delivery pipe

connections. This air enters into the fuel injection pump

(FIP) and restricts the FIP to deliver the fuel under high

pressure in misty form through injectors. This causes the

nozzles to dribble (delivery of fuel in drops) and the

combustion does not take place, as the fuel is not in spray

form. Hence, the engine does not start.

• Procedure to remove air lock:

• a. First fill the diesel tank with diesel if fuel is found less.SUBJECT:TC 4 IRISET- SECUNDERABAD 280

• b. Unscrew the fuel feed pump and operate it until the

pressure is built up.

• c. Screw out the air bleeding screws and operate the pump

till the air from the filter bowls comes out. Then close the

fuel bleeding screws and tighten the fuel feed pumps knob.

• d. Crank the engine and make sure that the air is bled out of

FIP and tighten them when the air is totally bled out of the

fuel system. E) Clean diesel at all joints and on pipes before

starting. Start the DG set and run it for some time to ensureSUBJECT:TC 4 IRISET- SECUNDERABAD 281

• that the fuel system is free from air.

• Lubricating system: - The main function of lubrication

system is to reduce the heat caused by friction, enable the

metal parts slide easily over each other and prevents wear

of engine parts. All moving parts are lubricated and those

parts, which take a heavy load such as the crankshaft,

connecting rod bearings and camshaft bearings, are

pressure lubricated.



• The lubricating system consists of the following parts: -

• a) Oil sump b) Oil pump c) Relief valve. D) Oil filter

• E) Lubricating oil.

• a)Oil pump: - The pressure is provided by a pump, which has two

gears. The oil on entering the pump is carried through the pump

between the casing and the gear teeth and thus forced into the

system. The oil pump is gear driven from the crankshaft.

• b) Oil sump: The oil sump is located underneath the engine block

and contains lubricating oil. The oil is sent to all parts under

pressure and gets back to the sump after reaching to all the

parts. The dipstick is inserted into the sump through a hole to

check the level of the lubricating oil.


• c) Relief valve: - The relief valve is provided for the

adjustment of the lubricating oil pressure delivered by

the pump within limits.

• d) Oil filter: - A coarse oil filter is fitted in front of the pump

to clean the oil before it enters the pump. A second, finer

filter cleans the oil again after it has left the pump and

before it enters the engine. The second filter to the side of

the engine and should be changed or cleaned as per

servicing schedule.SUBJECT:TC 4 IRISET- SECUNDERABAD 285

• e) Oil: Only recommended grades of oil must be used,

otherwise serious damage can be caused. Before starting

the engine, only a little oil in the bearings, but as soon as it

starts a film of oil is forced between the bearings and shafts.

If wrong grade is used the film may not be enough to stop

the shaft touching the bearings or the oil may not enter the

bearings at all. In each case rapid wear results and affects

the performance of the engine


• COOLING SYSTEM: The main purpose of the cooling system

is not only to cool the engine, but also to ensure that the

working temperature of the engine is maintained within

limits. Overheating of the engine will result in

• a) loss of fuel due to evaporation.

• b) Distortion of cylinder wall and other working parts.

• c) Overheating of lubricating oil resulting in inefficient

lubrication.


• D) If the lubrication between the piston and cylinder wall

breaks down, it will result in scuffing of the piston and

sticking of the piston rings. e) Burning of valves and valve

seats. Hence, the function of the cooling system is to

maintain the proper temperature of the engine under

varying operating conditions. The cooling system used in DG

sets is water cooling system. It consists of Radiator, Coolant,

Thermostat, water pump and a reservoir for coolant. The

coolant is a mixture of distill water and colored chemical.SUBJECT:TC 4 IRISET- SECUNDERABAD 288

Water cooling system in DG set


• Let’s assume that the engine just started and is cold. Water

pump inlet and outlet is connected to the engine with help

of rubber hoses. We have thermostat mounted in path of

outlet to the engine. So Water is pumped by this radial

pump through thermostat into the engine water vents.

Thermostat does not allow the water to go into radiator

circuit until engine is at low temperature and water comes

back to pump through outlet hose. Coolant temperature

sensor is mounted just near the thermostat.SUBJECT:TC 4 IRISET- SECUNDERABAD 290

• As water keeps on circulating it extracts heat from the engine

and its temperature rises. As it reaches a temperature between

160 to 190 Fahrenheit, it melts the paraffin wax in thermostat

and opens it up. So now this hot water is circulated through

radiator circuit. Water enters the radiator through inlet port and

exchange it’s heat with air as it flows through number of small

radiator pipes and with help of fins attached to these pipes. But

as engine operates at higher rpm, engine’s temperature goes up,

so does the coolant’s temperature. This coolant gets heated up


• to such a high temperature that it would create a high

pressure situation in radiator. If such a high pressure keeps

on increasing it would burst out the radiator pipes, which

we don’t want in any case. So to deal with this pressure we

have pressure cap and a radiator overflow tank. When

pressure in radiator reaches up-to 15 psi of pressure it lifts

up the spring in the pressure cap, thus opening a port for

coolant to be transfer to the radiator overflow tank, thus

keeping pressure in control.SUBJECT:TC 4 IRISET- SECUNDERABAD 292

• When coolant flowing into the overflow tank exceeds its

volume limits it flows out of tank through overflow hose.

When pressure drops in the radiator, it creates a vacuum in

the radiator, thus sucking coolant back to radiator from

overflow tank. That’s why we fill the radiator overflow tank

before going out for a ride. If the level of coolant falls below

minimum limit.

• In engine cooling system, radiator fan starts its operation

when temperature exceeds a particular temperature value.

It helps in lowering the coolant temperature by blowing airSUBJECT:TC 4 IRISET- SECUNDERABAD 293

• through radiator fins thus removing heat at a faster rate

from the coolant. It is regulated by the data from the

coolant temperature sensor.

• Coolant temperature sensor is a multi-purpose sensor as it’s

data is required in optimizing the performance of modern

ECU equipped engines.


ELECTRICAL STARTING

• The engine is started by DC starter motor electrically. The

electrical starting system consists of a) Starter motor b) Battery

(usually of 12 V). c) 12v alternator.

• a) Starter motor: - The starter motor is mounted near the

flywheel and its shaft is provided with a small gear (pinion).

When the starter motor is operated, this small gear slides into

the teeth of the flywheel and turns it. When the flywheel turns,

the crankshaft, connecting rod and all operative parts of the

engine begin to move and the engine starts.SUBJECT:TC 4 IRISET- SECUNDERABAD 295

• b) Battery: - The purpose of the battery is to supply required

DC power to the starter motor for starting the engine. It also

supplies power to the control panel for to monitor the

engine parameters. This is usually a 12 volt lead acid battery.

The battery gets charged by the engine driven d.c.

alternator when the engine is running.

• 12v alternator: This is driven by the engine through a pulley

mechanism. It produces 12 V three phase AC and is rectified

and regulated for charging the battery.SUBJECT:TC 4 IRISET- SECUNDERABAD 296

• Main Alternator:

• An Alternator works on Faraday's law of Electromagnetic

Induction. Its main function is to convert the kinetic energy

into electrical energy. It has the following salient parts.

• a) Rotor b) Stator (c) Exciter

• ROTOR

• Rotors are of two types:

• a. Salient pole type

• b. Smooth cylindrical type.SUBJECT:TC 4 IRISET- SECUNDERABAD 297

• STATOR:

• The stator motor is equipped with seal type bearing and

requires no lubrication. stator is insulated on one side with

paper or varnish and house in a frame.

• EXCITER

• The exciter is generally a DC shunt motor or compound

generator whose voltage is 250V. In small alternator, the

exciter is mounted on the same shaft of the alternator.


• INSTALLATION:

• The procedure for installation of DG set is recommended as

follows:

• (a) The foundation of Diesel Engine must perform three

functions:

• (i) Support the weight of the Engine.

• (ii) Maintain the Engine in proper alignment with the driven

machinery.

• (iii) Absorb vibrations produced by unbalanced forces.SUBJECT:TC 4 IRISET- SECUNDERABAD 299

• (b) DG sets shall be installed in a separate room of adequate

size with proper ventilation.

• (c) The diesel generator set shall be mounted on anti-

vibration pads.

• (d) The exhaust pipe shall be extended outside the

generator room and the silencer fixed away from the

premises. Exhaust pipe shall be appropriately insulated.

• (e) DG sets shall be installed in a separate room of

adequate size with proper ventilation.


• (f) The diesel generator set shall be mounted on anti-vibration

pads.

• (g) The exhaust pipe shall be extended outside the generator

room and the silencer fixed away from the premises. Exhaust

pipe shall be appropriately insulated.

• (h)Where automatic start has been provided, the generator once

started should stop only with a time delay after Main supply is

resumed.

• (i) The connection between the battery and the DG Set shall


• be through sufficiently thick wire to avoid drop in voltage.

• SPECIAL ATTENTION ON FOUNDATION:

• (a) DG set foundation should be separated from foundations

of adjoining structures.

• (b) Ground water level should be as low as possible and

should be deeper at least one fourth of foundation below

base plane. This reduces vibrations.

• (c) Any hot piping if embedded in the foundation should

be properly isolatedSUBJECT:TC 4 IRISET- SECUNDERABAD 302

• (d) Foundation must be protected from engine oil by

means of acid resisting coating

• To achieve the above object the engine should always be

installed on a good cement concrete foundation. The

composition for concrete is one part cement, two parts

clean sharp sand and four to five parts of washed ballast.

After pouring, the concrete should be allowed to set for at

least 48 hours. Before engine is bolted down, in very hot.

• and dry climate the block should be moistened with water

during this period.SUBJECT:TC 4 IRISET- SECUNDERABAD 303

• ERECTION:

• The Engine should be leveled up on the foundation block

where the Engine is mounted on superstructures, there

should be rigid construction leveled, before the engine is

bolted down. In case of a direct coupled set, the driven

unit must be lined up with the Engine and joined through a

flexible coupling. In case of a trolley mounted Engine, the

trolley should be parked on the horizontal ground.


• MAINTENANCE:

• DAILY:

• (a) Check the lubricating oil level in the sump. Top up if

necessary.

• (b) Keep fuel tank full. The tank should be full completely

with clean fuel oil at the end of day’s work.

• (c) Clean the engine at the end of day’s work. If there are

any leakages, dust will collect at the leaky spots during the


• next day’s work. Such leakages should be attended

promptly.

• (d) In case of tank or radiator cooled engines, check the

water level and top up if necessary, before starting the

Engine.

• (e) Run the Engine 5 minutes daily, check working properly

or not.


• WEEKLY MAINTENANCE:

• (a)Clean the air cleaner completely

• (b) Clean fuel filter blows.

• (c) Check the electrolyte level in the battery. If required top up

with distilled water.

• (d) Check the cable connection at starter and dynamo.

• (e) Check the belt tension of dynamo/Alternator. It should be 8

to 10 mm, if required adjust it with the help of Tension adjusting


• lever.

• (f) The brushes should be examined after every 100/150 hrs.

running to see that they are bedding properly.

• (g) Make sure that the vent hole in fuel tank cap is clear.

• (h) Check nut and bolts tighten if found loose.

• (i) Check the cooling system is perfect or not, if water

cooling, radiator should be full of water. If air cooling, check

belt it should not loose.SUBJECT:TC 4 IRISET- SECUNDERABAD 308

• MONTHLY MAINTENANCE

• (a) Drain the sump, flush out with approved brand or

flushing oil and refill with new oil.

• (b) Thoroughly clean out the fuel tank.

• (c) Clean filter oil bowl.

• (d) Change lubricating oil in the air cleaner after 250 hrs.

Operation.

• (e) Know out spot from the exhaust silencer.

• (f) Clean inlet and exhaust valves, grind valves - decarboniseSUBJECT:TC 4 IRISET- SECUNDERABAD 309

• Cylinder

• (g) After 200 hr. of operation examine bearing.

• (h) Wash out lubrication oil pipes.

• (i) Clean out water spaces in cylinder head and radiator.al

the servicing should be carried out as per periodicity

mentioned in service manual supplied with the DG set.


• TROUBLESHOOTING:

• ENGINE FAIL TO START: Possible reason may be:

• a) Dirty clogged air cleaner – clean it.

• b) Check fuel tank, if empty – refill it.

• c) Check air in injection pump – Bleed (as procedure given).

• d) Check pressure valve spring – replace if broken.

• e) Check leakage of fuel in external and internal

connections.

• Check nozzle - if jammed clean or replace it.SUBJECT:TC 4 IRISET- SECUNDERABAD 311


• Check fuel filter - clean or replace it.

• ENGINE STARTS BUT STOPS AFTER SOME TIME: Check

• (a) Air cleaner is clogged – clean it.

• (b) No fuel – refuel it.

• (c) Air in fuel line – bleed it.

• (d) Fuel line is choked – clean it.

• (e) Fuel filter is choked – clean it.

• (f) Faulty fuel pump – replace it.

• (g) Water mixed with fuel – change it.

• ENGINE NOT GAINING FULL SPEED

• Possible reasons may be:

• (a) Fuel tank may empty – refuel it.

• (b) Governor spring is broken – replace it

• (c) Dirty choked fuel filter – clean it.


• ENGINE NOT GAINING FULL SPEED: Reasons may be:

• (a) Fuel tank may empty – refuel it.

• (b) Governor spring is broken – replace it

• (c) Dirty choked fuel filter – clean it.

ENGINE MISSES DURING OPERATION: Causes may be:

• (a) Air in fuel line – bleed.

• (b) Choked fuel injection holes – clean them.

• (c) Damaged or dribbling nozzle – replace it.

• (d) Faulty fuel pump-replace it.SUBJECT:TC 4 IRISET- SECUNDERABAD 314

• (e) Water mixed with fuel – change it.

• EXCESSIVE SMOKE AT NO LOAD:

• Possible reasons may be:

• (a) Dirty clogged air cleaner – clean it.

• (b) Choked fuel injection holes – clean it.

• (c) Faulty fuel pump – change it.

• EXCESSIVE SMOKE AT FULL LOAD:


• (b) Poor quality of fuel – use proper grade of fuel.SUBJECT:TC 4 IRISET- SECUNDERABAD 315

• d) Nozzle damaged – replace it.

• Choked fuel injector holes – clear it.

• (f) Faulty fuel pump– replace it.

• (g) Engine overloaded – adjust the load.

• (h) Broken seized/worn-out piston rings – replace them.

• (i) One or more cylinder not working – check and repair it.

• (j) Engine needs overhauling – send for overhauling.

• (k) Choke fuel injector holes – clear it


• ENGINE GIVES OUT BLUE SMOKE:

• Possible reason may be:

• (a) Worn-out liner or piston – replace it.

• (b) Wrong grade lubricating oil used.

• (c) Engine used after a long time – ensure weekly starting.

• 8.9.9 ENGINE GIVES OUT WHITE SMOKE

• This is due to: (a) Water mixed with fuel.


• ENGINE OVERHEATS:

• (a) Faulty fuel pump – replace it.

• (b) High exhaust back pressure – release the pressure.

• (c) Wrong grade of lubricating oil used. – use fresh.

• (d) Clogged oil passage – clear the passage.

• (e) Faulty relief valve setting – adjust it.

• (f) Loose fan belt – adjust it.

• (g) Air leakage through cowling – repair it.

• (h) Engine oil not changed – change oil.SUBJECT:TC 4 IRISET- SECUNDERABAD 318

• (i) Engine overloaded – adjust the load.

• (j) Broken/worn-out piston rings – replace them.

• (k) Damaged main or connecting bearings – replace them.

• 8.9.11 EXCESSIVE VIBRATIONS:

• (a) Engine needs overhauling – Manufacturer representative

or skilled mechanic should carry out O/H.

• Loose flywheel - tighten it

• (c) Battery run down – Battery to be charge in boost mode

or replace if defectiveSUBJECT:TC 4 IRISET- SECUNDERABAD 319

• EXCESSIVE FUEL CONSUMPTION Possible reasons may be:


• (b) Poor quality of fuel – use proper grade oil.

• (c) External/internal fuel leakage – checks it and prevent.

• (d) Faulty fuel pump – replace it.

• (e) Engine overloaded – adjust the load.

• (f) Broken worn-out piston rings – replace them.

• Damaged main or connecting bearing – replace them.

• Injector need adjustment – adjust it.SUBJECT:TC 4 IRISET- SECUNDERABAD 320

• VOLTAGE REGULATION IS UNSATISFACTORY

• Possible causes may be:

• (a) Incorrect speed of prime mover – Adjust the speed of

prime mover to correct Value on no load or full load. The

speed should be between 1560-1570 RPM on No Load and

1500 RPM at full load.

• OVERHEATING OF ALTERNATOR::

• Excessive room temp/Improper ventilation-Machine should

be installed in good ventilated room with exhaust fan.SUBJECT:TC 4 IRISET- SECUNDERABAD 321

• (a) Misalignment – Check alignment and adjust.

• (b) Faulty foundation – Reconstruct the foundations and

properly level it.

• (c) Overloading of machine – Check the load Current, if

more than reduce the load.

• (d) Block of ventilation holes – Clean the inlet and outlet

holes.


• DO’S AND DON’TS

• DO’S:

• (a) Ensure proper cleaning of air cleaner and fuel filter.

• (b) Before starting ensure full tank of diesel in the tank.

• (c) Connect the load only when generator voltage regulation

is normal.

• (d) Before starting the DG open the door and windows for

proper ventilation.

• (e) Check that engine running without load for few minutes

before stopping.SUBJECT:TC 4 IRISET- SECUNDERABAD 323

• f) After every 100 hrs. running, check brush are bedding

properly and having correct

• pressure.

• (g) Change the lubricating oil periodically or after every 120

hours of running.

• (h) Check the load current is within limit as prescribed in the

machine plate.

• (i) Clean the inlets and outlets ventilation weekly.


• DON’TS:

• (a) Don’t mix water into fuel.

• (b) Don’t mix different grades of grease.

• (c) Don’t pour diesel when engine is running.

• (d) Don’t start the engine without checking the level of

lubricating oil.

• (e) Don’t start the engine without opening fuel taps.

• (f) Don’t start the engine with load, first start the engine and

allow it to gain full speed then put the load.SUBJECT:TC 4 IRISET- SECUNDERABAD 325

• (g) Don’t smoke in the Generator room and also don’t keep

inflammable goods in Generator room.

• (h) Don’t forget to clean silencer after every three-six

months positively.

• DUTY CYCLE

• The generating sets should be run for a period of 18 to 20

hours maximum in 24 hours. Codal life of the DG set is 10

Years.


POWER SUPPLY ARRANGEMENTS - iriset

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