power plant ppt.ppt

7/28/2019 power plant ppt.ppt

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T10A&B

POWER PLANT PRACTICE


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CONTENTS1. SECONDARY CELLS

2. BATTERY CHARGING

3. BATTERY CHARGERS

4. CONVERTERS AND INVERTERS

5. VOLTAGE STABILIZATION6. D C VOLTAGE REGULATOR


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7. UN-INTERUPTED POWER SUPPLY

SYSTEM

8. PHOTO VOLTAIC GENERATION OF

ELECTRICITY9. SAFETY PRECAUTIONS

10. POPWER SUPPLY ARRANGEMENTS

11. POWER SUPPLY LOADCALCULATIONS


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ELECTRICAL CELLS


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TOPICS COVERED1. Introduction.

2. Classification of cells.

3. Primary cells, Lead Acid Cell, construction,chemical reactions, Specifications.

4. VRLA cell/battery, Construction, uses,

Specifications.5. Capacity, Efficiency of a cell.

6. Defects in Lead Acid Cell.


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7. Routine tests, maintenance, andbattery room precautions.

8. Battery care.

9. Information to be furnished whileindenting new cell/battery.

10. Battery charging, Types, Methods.

11. Procedure of keeping a battery inunused condition.


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INTRODUCTION It deals with different types of power supply

systems like,

1. Electrical cells / Battery

2. Battery chargers3. Inverters & Converters

4. Voltage stabilizers

5. Un Interrupted Power Supplies (UPS)6. D.G. Set

7. Power supply arrangements for TelecomEquipments

etc.


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CLASSIFICATION OF CELLSCells

Primary cells Secondary cells Non conventional

Energy sources

(Solar cells, Fuel

cells)Acid type

cells

Alkaline type

cells

Eg. i) Lead Acid celli) Ni - Cd cell

ii) Lithium celliii) Ni-Iron

iv) Lithium Ion

Leclanche Dry Cell,

Lithium cell, etc.


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PRIMARY CELLS The cells which cannot be recharged

after discharge are known as Primary

cells. They cannot be kept under cyclic

operation.

Examples: Leclanche Dry Cell, Lithiumcell, etc.


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SECONDARY CELLS

The cells which can be recharged bypassing D.C. current through them and

the original condition of chemicals areregained are called as Secondarycells.

e.g. Lead Acid Cell,

Nickel Cadmium Cell,

Lithium Ion cell, etc.


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LEAD ACID CELL


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LEAD ACID CELLCONSTRUCTION


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PARTS OF LEAD ACID CELL ContainerIt is made from hard rubber or

PPCP material. It holds all the parts of cell.

Top coverIt is also made from the samematerial as above. It covers the top portion of

the cell and holds Vent plug & terminals are

comes out of the cell.

Bottom blockIt is also made from the hardrubber or PPCP material. The element of +ve

&-ve plates sits on this.


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Vent plugIt is made from the plasticmaterial or polystyrene. It provided with

holes known as vent holes which

permits gas to escape out.

FloatIt is also made from plasticmaterial. It having a Bulb & Stem

portions. On the stem markings are

provided to record the specific gravity of

the electrolyte.


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Positive platesGrids structure ismade from hard lead material & it holdsthe Lead dioxide (PbO2) materialwhich is chocolate brown in colour.

Negative platesGrid structure is madefrom hard lead material & it holds the

Spongy Lead (Pb) material which is

dark grey in colour.


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Separators These are the thin sheet ofinsulating material kept between theplates to prevent the short circuit. These

are made from PVC, glass mat, PPCP,

celluloid etc.

Electrolyte It a mixture ofConcentrated Sulphuric Acid (H2SO4)

at a give specific gravity. It act as a

medium for flow of electrons by ionicprocess.


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SPECIFICATIONS OF LEAD ACIDCELL

Voltage of a fully charged cell - 2.1V

Voltage when fully discharged1.8 V

Specific gravity when fully charged1220 Specific gravity when fully discharge1180.

Specification number of battery graded

distilled waterIS 1069. Specification number of battery graded Con.

Sulphuric acidIS 266.


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VALVE REGULAED LEAD ACIDCELL (SPECIFICATIONNO.RDSO/SPN/TC/37/2000.)


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CONSTRUCTION The construction of this cell is same as

conventional type. The grid material is

Lead Calcium alloy due to its low selfdischarge& more conductivity.

In this it is not necessary to add distilled

water periodically & it is compensatedby Gas recombination principle.


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It is completely sealed. Regulation of pressure inside the

cell is by a valve which opens and

closes automatically depending onthe pressure inside the cell.


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Glass mat separators are used. Nominal voltage2 V / cell

Mode of charging :1. Float Mode2.25 V / cell

2. Boost Mode3 V / cell


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ADVANTAGES OF VRLA CELL Maintenance free.

Safe & Reliable.

Easy to install. Compact and light in weight.

No spilling of electrolyte during

transportation. No separate room is required due to

complete sealing.


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Longer service life. Ideally suited for deep discharges. Very low self discharge of 0.5 to 1% of

capacity per week.

Can be installed in horizontal direction

without any leakage of electrolyte. No acid proof flooring is required by

virtue of their construction.

No post corrosion as there is no acid

mist.Operating temperature is wider (-40C to +55C).


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USES OF VRLA CELL /BATTERY

Back up power supply for electronicequipments.

Remote area power supplies.

Un-interrupted power supply systems.

Integrated power supply systems.

Portable power tools.


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SPECIFICATIONS1. Nominal voltage: 2V/Cell.

2. End point voltage: 1.75V/Cell.

3. Type of separators used: Glass mat.4. Mode of charging:

i) Float mode2.25V/Cell (for 16 Hours)

ii) Boost mode3V/Cell and chargingcurrent should be limited to 20% of its

AH capacity.


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5) Material used for grids: Calcium alloy.

Cycle life at 25C(77F)1200 cycles at 80% depth of discharge.

2000 cycles at 50% depth of discharge.

4000 cycles at 20% depth of discharge.6) Float life at 25C20 years design life

on full float with recommended chargingmethod.

7) Operating temperature: -20C to+55C.


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CHEMICAL REACTIONS INLEAD ACID CELL

During dischargingstate:

At positive plates,PbO2 +2H +H2So4PbSo4 +2H2O

At Negative plates,Pb + So4 Pb So4


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CHANGES DURINGDISCHARGING

Both anode & Cathode become PbSO4.

Due to formation of water specific

gravity of the electrolyte decreases.

Voltage of the cell decreases.

The cell gives out energy.


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CHEMICAL REACTIONS INLEAD ACID CELL

During charging state:

At positive plates,

PbSo4 +SO4 +2H2O PbO2+2H2So4At Negative plates,Pb So4 +H2 Pb + H2So4During gassing:H2O + So4 H2So4 + OComplete reaction;Pb(s) + Pbo2(s) + 2H2So4(aq) 2PbSo4(s) + 2H2O (l)


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CHANGES DURING CHARGING The anode becomes dark chocolate

brown in co lour (PbO2) and cathode

becomes gray metallic lead (Pb). Due to consumption of water, specific

gravity of electrolyte is increased.

There is rise in voltage.


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CAPACITY Definition: It is the ability of a fully charged battery

to deliver a specified quantity ofelectricity at a given rate (amperes)over a definite period of time. Its unit is

Ampere Hour (AH).

It is given at Hours rating.

Example: 200AH 10H.


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It depends on the following factors,

1. Discharge Rate.

2. Design and dimensions of plates.

3. Quantity and specific gravity of Electrolyte.

4. Temperature.

5. Plate spacing.

6. Active material weight.

7. Grid alloy.8. Age.


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EFFICIENCY OF A CELL The efficiency of a secondary battery is

defined as the ratio of output of a cell orbattery to the input required to restore theinitial state of charge under specified

conditions of temperature, current rate andfinal voltage.

Generally, the efficiency is expressed inthree ways:-

1. Ampere-hour efficiency.

2. Volt efficiency.

3. Watt-hour efficiency.


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AMPERE-HOUREFFICIENCY

It is the ratio of the ampere-hours output to

the ampere-hours of the recharge.

For a full capacity battery, an ampere-hourefficiency between 85 and 90 is expected.

The ampere hour loss is due to gassing &local action.

ampere-hour efficiency can be increased bycontrolling the charging current.


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VOLT EFFICIENCY It is the ratio of the average voltage during

the

discharge to the average voltage during therecharge.

This will be reduced, if the rates of chargeand discharge are comparatively high.

It will also be reduced at low temperatures. Under the commercial service conditions, a

volt efficiency of about 85 may be expected.


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WATT-HOUR EFFICIENCY Watt-hour efficiency is the ratio of the watt

hours output to the watt hours of therecharge.

This is sometimes assumed to be the productof the ampere-hour efficiency and the volt

efficiency. In many cases this may be

sufficiently accurate. Under commercial service conditions, watt

hour efficiency of about 75 may beexpected.


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TEMPERATURE CORRECTION OFELECTROLYTE

The Sp. gravity of Electrolyte on thehydrometer should be corrected to read to 27deg. C.

Specific gravity is inversely proportional totemperature. Corrective factor is 0.0007 foreach degree centigrade. Hence, thecorrection should, be made as follows-

For every 1 deg C above 27 deg C subtract0.0007 to the Sp. gravity as read on thehydrometer. Similarly, for every 1 deg. Cbelow 27C, add 0.0007 from the Sp. Gr. asread on the Hydrometer.


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Example: Sp. gravity read from hydrometer is :

1.200

The temperature is 28 deg. C. The corrected Sp.Gr. is 1.200 - .0007 =

1.1993


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DEFECTS IN LEAD ACIDCELL


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DEFECTS IN LEAD ACID CELL Sulphation

Buckling

Shedding

Internal short circuit

Reverse Voltage of cells

Open Circuit

Temperature Troubles


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SULPHATION Indication:Slight white

patches will be noted onthe plates.

White patches cannotbe observed on platesas container is nottransparent, whitepatches are observed

on terminals The indication is loss of

capacity.


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Cause: Excessive discharge

Due to keeping the cell in a dischargedcondition for a long period

Due to impurities in the water or acid

Exposure of plates due to low level ofelectrolyte.


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Treatment: If slight, charge at 1/3rd of the normal rate, till

the cell deliver gas freely.

Discharge at the same rate. Repeat the cycle

till the voltage of the cell reaches 2.35 oncharge and specific gravity is as per

manufacturer's rating. If the plates are visible,

ensure that there are no white patches. If

severe, pour out the electrolyte, fill with freshelectrolyte recharge.


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BUCKLING Indication:The

plates become

saucer shape or cup

like with twisted or

bulged ends tending

to touch or touching

the sides of thecontainer or

adjacent plates.


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Cause:Excessive discharge or charge, badsulphation.

Treatment:If not very badly bent, the

plates can be removed, straightened in avice or press. If very badly bent, they

should be replaced.


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SHEDDING

Indication:Slight loss in capacity or short

circuit in the case of very severe shedding. Cause:Due to excessive gassing, thereby

dislodging peroxide paste from the grids ordue to sulphation.

Treatment:Replace cell if severe,otherwise give slight charge at low rate.


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INTERNAL SHORT CIRCUIT Indication:The cell will be warm even when

idle, specific gravity and voltage will be lowimmediately after charge. There will be nogassing.

Cause:Due to fallen pieces of hard sulphate,bending or treeing, high degree of sulphationor sludge.

Treatment:If not very badly bent, the platescan be removed, straightened in a vice orpress. If very badly bent they should bereplaced. Fallen pieces should be removed.Excess sulphation or sludge, treatment as insludge.


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REVERSE VOLTAGE OF CELLS Indication:The positive and negative

terminals will show opposite polarity.

Cause:This is due to defective cell in abattery, which got discharged already whenthe others are being discharged. As the

discharge, continues the run down cell adds

nothing to output but gets charged in thewrong direction by the main discharge current

passing through it.


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This results in the positive plate beingpartially converted into spongy lead and

the negative plate into lead peroxide.

This causes a reverse voltage and acts

in the opposite direction to the mainbattery emf.

Treatment:Remove the cause of defectand give slight charge. Remove thedischarged cell.


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OPEN CIRCUIT Indication:No EMF at the output terminal of

the cell.

Cause:Loose connections of connectingstrap or corroded terminals, or break interminals.

Treatment:Check all connections, examinefor loose joints at clamps and connectingbars. Clean terminals with sand paper and

smear Vaseline.


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TEMPERATURE TROUBLE Indication:Temperature rises even for

very slow rates of charging.

Cause:Due to bad location, proximity toany heated element, shedding, buckling

or defective separation.

Treatment:Examine for the causesgiven and remove the cause.


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PREVENTIVE MEASRES TOOVERCOME DEFECTS

1. Avoid excessive discharging,

2. Dont do excessive charging,

3. Dont keep the cells/battery in dischargedcondition not more than 2 to 3 days,

4. Dont draw more than normal current,

5. To compensate the evaporation of

electrolyte during summer, add distilledwater more frequently,

6. Observe the cell container duringmaintenance for breakage or leakage,


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7. Use only tools with insulated handles,

8. Dont place metal objects on the top of thebattery,9. Do not allow Lead pieces, coins, nuts,

washers etc. into the battery,

10 Keep flames away from battery room toavoid explosion of battery,

11. To keep battery idle, after charging put itunder trickle charging,

12. Do not the electrolyte temperature beyond50C during charging.


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ROUTINE TESTS


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THE ROUTINE TESTS There are three types

of tests to be carriedout during routinemaintenance.

They are,1. Measurement of

Specific gravity.

2. Measurement ofVoltage of each cell,.

3. Adjusting the level ofelectrolyte above theplates by addingdistilled water.


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MAINTENANCE APPLIANCES A small voltmeter preferably with two ranges,

5 Volts and 15 Volts.

An ammeter preferably with three ranges, 5,15 and 30 Amps.

Syringe type Hydrometer

Glass tubes 9" long and 1/4" dia.

Thermometer preferably graduated in F

Glass rod 1/2" dia 15" long


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Glass or porcelain trough

Glass funnel

Glass tumbler

Jar of distilled water

Jar of Sulphuric Acid


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BATTERY MAINTENANCEANDBATTERY CARE


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MAINTENANCE PRECAUTIONSOF BATTERY

1. Top-up the cells with battery graded pure

distilled water (IS 1069) once in s week or

more frequently in summer.

2. Record the specific gravity, voltage &

electrolyte temperature of pilot cells every

day and all the cells once in a week.

3. The terminals and connections should bechecked regularly, replace if required.


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4. Clean the terminals and coat withpetroleum jelly as necessary.

5. Keep electrical connections always

tight.6. Do not exceed the electrolyte

temperature beyond 50C during

charging.7. Attend the week cells without delay.


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BATTERY CARE DOS1.Unload the batteries carefully and place themupright on the floor in single tier.2.Store the batteries in a cool and dry location.3.Charge the batteries within six months if theyare under storage.4.Unpack the batteries as per the unpacking

instructions.5.Install the batteries in a cool and dry location.6.Keep the battery area clean and dry.


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7. Monitor the charge and the floatvoltages of the charger at monthly

intervals and adjust if required.

8.Check the tightness of all the electricalconnections at monthly intervals.

9.Check compatibility of the charger

before commissioning the battery.


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10. Maintain monthly service recordas per enclosed format.

11. Provide adequate ventilation and

illumination.12. Ensure the cell orientation &

connections are as per the General

arrangement Drawing.


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DONTS

1. Do not expose the packed batteries to rain.

2. Do not expose the packed batteries to

sunlight.

3. Do not exceed the storage period withoutcharging the batteries.

4. Do not install the batteries in rooms withvarying temperature pockets due to sunlight

or ventilation ducts.5. Do not short-circuit the battery or cells during

assembly.


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6. Do not charge the batteries in sealed

cubicles.

7. Do not mix batteries of different types or

makes.

8. Do not make tap connections.

9. Do not tamper with the cell vents.

10. Do not keep the batteries in discharged

condition.


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SAFETY PRECAUTIONS


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SAFETY PRECAUTIONS1. Do not touch uninsulated battery connectors

or terminals.

2. Isolate the battery from the charger whileworking on the battery.

3. All tools used for installation should be

insulated to avoid accidental shorting ofconnections.

4. Ensure that connections are made as per

general arrangement drawing enclosed.


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5. Do not attempt to move the installed batterywithout removing the connectors.

6. Do not expose the battery to open flame orsparks.

7. Keep the battery clean and dry.

8. Incase of accidental contact with acid, washthe affected area with a continuous flow ofwater for 15 min., and consult a doctorimmediately.

9. Do not install batteries in a sealed cabinet or

enclosure since explosive gases may bereleased under abnormal conditions.

10.Use a suitable lifting device in handling the

battery


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BATTERY INDENTINGPROCEDUTE


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INDENTING OF LEAD ACID CELLSor BATTERIES While indenting the cells or batteries,

applicable IS specification should be quoted.

The indent should specify batteries

manufactured by one of the reputed andRDSO approved firms.

separators made of Micro-porous PVC orsimilar materials of

adequate design, providing permanent highlyporous insulating diaphragm. The manufacturer instruction card should be

obtained with cell.


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INFORMATION TO BE FURNISHEDBY THE PURCHASERa) Nominal Voltage.

b) Capacity (in Ampere Hours at 10 Hr rate) of

the batteries.

c) Mono-block type of stackable single cell type.

d) Number of cells per battery for stackable

cells.

e) Number of identical batteries required.f) The rate of charge and discharge at which the

batteries are to work.


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g) The proposed method of working that

is,charge discharge, float working or

standby, with or without trickle charging.

h) Whether stands are required and if so details

of layout and space availablei) The proposed location of installation and

ultimate consignee.

j) Accessories and spares required, if any.

k) Special conditions, if any.


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BATTERY CHARGINGCHARGING METHODS


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METHODS OF CHARGING There are two principle methods adopted incharging batteries:

1. Constant current method: Constant currentis passed through the battery.

There are two methods of constant currentcharging:-

(i) Series method of charging

(ii) Parallel method of charging

2. Constant potential method: Keepingconstant potential across the battery till theend of charging is called as constantpotential method.


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CONSTANT CURRENTMETHOD SERIES METHOD OFCHARGING

In the series method,the current must be the

same in all parts of the

circuit. Batteries of different

types and capacities

requiring different

charging currentscannot be charged by

this method.


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PARALLEL METHOD OFCHARGING

Figureillustrates aparallel chargingarrangement.

It is superior toseries method, inthat the switchingarrangements allow

batteries of differentcapacities to becharged at correctrates.


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RATE OF CHARGE OF CURRENT ANDVOLTAGE IN CONSTANT CURRENTMETHOD


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CONSTANT POTENTIALCHARGING

In this the supply is keptat a constant voltageaveraging 2.5 to 2.6Vper cell.

The supply equipmentis designed to supply aconstant voltage of 7.5,15 or 30V supplied on

two copper bus bars asshown in figure.


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TYPES OF CHARGINGType of

charging

Method of

charging

Volt/Cell Current

1.Initial charging

Given to new cell /

Battery

Constant

current

2.7Volts/Cell As per

manufacturer or4% of capacity

2. Float charging

Given to working

cell / Battery

Constant

potential

2.15Volts/Cell Capacity / 10

3. Boost charging

Given to discharged

cell / Battery to

charge quickly

Constant

potential

2.4 Volts/Cell Capacity / 10


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4. Trickle

charging

Given to a fully

charged cell /

Battery

Constant potential 2.25-2.3 Volts /

cell

1 mA / AH

5. Equalizingcharging. Given

to correct any

inequalities of

sp.Gr amoung the

cells.

Constant potential 2.06-2.18 Volts /cell

Capacity / 50

6. Normal

charging

Constant potential 2.15 Volts / cell Capacity / 10


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INITIAL CHARGINGSTEPS DURING INITIALCHARGING:

1. Collecting of information from the

manufacturer.2. Procuring the materials and tools.

3. Preparation of required amount of

electrolyte at required specific gravity.4. Cleaning & arranging of cells.


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5. Filling of electrolyte into the cells.

6. Interconnecting the cells.

7. Installing the battery charger at

convenient place.

8. Connect the charger terminals to the

battery.

9. Switch ON the charger by keeping the

potentio meter at 0 position.


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10. Slowly adjust the current to required

value and continue charging.

11. Note down the stating time of

charging, voltage, Sp.Gr, temperature

of electrolyte at every 8 Hours.

12. Add electrolyte if level falls down

during charging.

13. Keep the current constant during

charging.


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14. If temperature goes beyond 45C

decrease the current rate or stop

charging only if 50% of charging is

over.

15. At the end of charging the cell starts

gassing freely and the voltage will

reach the final value 2.50 to 2.55 V /

cell, and the specific gravity to1.2100.005.


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16. Gassing indicates end of charging.

Stop charging only when the specificgravities of all the cells constant forthree consecutive hours.

17. Equalize the specific gravities of allthe cells to the specified value.

18. Again start charging, and continue upto three hours during which readings

should not change.19. Stop charging.


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20.Connect the battery to a load, and

discharge until any one of the cellvoltage falls to1.85 V and Sp.Gr.1.180.

21. Stop discharging and connect it

to charger again and charge at

normal rate.

22. Continue Discharging and Charging

for 2 or3 times to get full capacity.


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PRECAUTIONS DURINGINITIAL CHARGING Add only electrolyte during initial

charging.

The temperature of the cell should notgo beyond 45C during charging.

Do not stop charging until 50% of

charging is over.


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FLOAT CHARGING

It is a system in which the battery is

connected in parallel to the charger or DC sourceand load.

The correct float charger current is automaticallycontrolled by maintaining the correct float voltageacross battery terminals.

The voltage of the system is closely regulated to2.15V to 2.20 volts per cell.

The life of the battery is prolonged because it isnot subjected to any charge/discharge cycle.


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TRICKLE CHARGING This is given to batteries

used in emergencies.

The battery is

maintained in chargedcondition by trickle

charging at 2.25 to 2.30

V/Cell & approximately

1 mA per A.H. at therated 10 Hour capacity

of the battery.


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FLOAT TRICKLE WORKING

The battery is connected in parallel to theload and the source.

The voltage of the system is regulated to2.15V volts per cell as it was with trickle

charging. When A.C mains fails the batteryautomatically discharges into the load.

The battery should be given a normal chargeafter the discharge and then put to float

trickle. The method eliminates the necessity of more

frequent equalizing charges and is suitablewhere equipment itself can withstand higher

voltages without any harm.


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EQUALIZING CHARGE A periodical charge given to the battery to

correct any inequalities of Sp.Gr. among cellsdeveloped during service.

This also assures that the maximum capacityis available when needed. An equalisingcharge is given at a rate of 10 Hr.Cap/50.

However, it can also be at the finishing rateor less, done after a regular charge until theSp.Gr. of all cells stop increasing for a periodof 3 or 4 hours.


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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.


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NORMAL CHARGE Done at two rates, the Start (high) rate

being maintained till the cells reach

2.4 /volts per cell after which at thefinishing (low) rate till the end of charge.

The high rate is usually 14% and the

finishing rate is 7% of the 10 hourcapacity of the battery.


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PROCEDURE FOR KEEPING THEBATTERIES IN UNUSED CONDITION If the batteries are left idle without attention

for more than 2 months, it will deteriorateand after a period of 6 months definitely

ruin it. Two methods are given under for keeping

the batteries in unused condition for longtime.

They are:1. Periodic freshening charge.

2. Filling up with distilled water and storing.


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ALKALIN CELLS&BATTERIES


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CONTENTS1. Introduction.

2. Classification of cells.

3. Nickle-Cadmium cells.4. Chemical reactions & Types.

5. Construction & Applications.

6. Dos & Donts.

7. Precautions while handling cells.


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INTRODUCTION


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INTRODUCTION The electrolyte in Alkaline Cells is basically

an Alkali namely Potassium Hydroxide which

acts as a passage for ions.

It will not take part in chemical reaction duringcharging and discharging.

The electrolyte specific gravity remains

constant and it cannot be an indication for thestate of the charge.


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The electrolyte resistance remainsalmost same during discharging.

The discharged condition of the cell canonly be known by voltage.


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CLASSIFICATION OFALKALINE CELLS


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There are mainly two types of AlkalineCells:-

1. Nickle Cadmium (Ni-Cd) Cells

2. Nickle Iron (Ni-Fe) Cells

(These cells are not as popular as Ni-Cd Cells).


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NICKLE CADMIUM CELLS


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CONSTRUCTION Positive Material - Nickle Hydroxide - Ni(OH)2

Negative " - Cadmium " - Cd(OH)2

Electrolyte - Potassium Hydroxide - KOHSp.Gr. 1.17 on charge.

Separator Material - Non-woven syntheticfibre or plastic material or cloth.

Container - Steel or stainless steel as theelectrolyte used is non corrosive.


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CHEMICAL REACTIONS 2Ni(OH)2 + Cd (OH)2 2 NiO OH + Cd +

2H20

It can be observed from the aboveequation that electrolyte is not figuringin chemical reactions.

It can be observed from the above

equation that electrolyte is not figuringin chemical reactions.


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TYPES OF Ni- Cd CELLS There are basically two types of Ni-Cd

Batteries/Cells distinguished by theconstruction of the electrodes.

1) Sintered Plate type.2) Pocket Plate type.

Again the Sintered Plate type are devidedinto two types:

i) Rectangular Vented Type

ii) Sealed Cylindrical Type


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POCKET PLATE NICKEL CADMIUMCELLS (RECTANGULAR VENTED)


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In the case of Pocket Plate Ni-Cd Cells,

the basic active materials, namely chemicals of Nickel and

Cadmium are made externally. Thesepowders are then packed into pocketsof Nickel plated steel perforated strips.These strips are cut to the required sizedepending on the width of the plate and

the horizontal strips are held together bymeans of side clips to form the plates ofrequired length.


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These plates are welded or bondedtogether as in the case of sintered plate

cell to the electrodes. The separator used in this case could

be a cloth or plastic material.


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CONSTRUCTIONANDAPPLICATIONS


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SEALED CYLINDRICAL CELLS


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The sealed cylindrical cells are also sinteredplate type cells. Electrodes used in these

cells are also made in the same way as the

electrodes in the rectangular cells except thatthe electrode is made

much thinner to enable a set of positive and

negative plates separated by a separatorcloth to be wound tightly to go into the nickel

plated sealed cylindrical container.


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The positive electrode is welded to the top lid

and negative to the body of the cell with aninsulation between them. Finally the cell is

crimped at the top to avoid leakage of the

electrolyte.

Applications: In all the applications where thecells/batteries could be located outside,

The rectangular vented cells could be usedwith the only constraint that the cells should

be mounted only in vertical orientation as

otherwise the electrolyte might spill out.


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On account of the low internal

resistance and also due to the lowthickness of the plates of the sintered

plate cells compared to pocket plate

cells. 4 Ah and 1 Ah Ni-Cd Cells are now

being used in place of 6 I Cells

in S & T Installations.

RECHARGEABLE SEALED


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CYLINDRICAL NICKEL CADMIUMCELLS1) The cell has a leak proof casing with no

trouble of replenishing electrolyte, i.e.,

maintenance free.

2) The internal resistance of the Cell being verylow, it is fit for high rate of discharging.

3) The cell is hermetically sealed and can be

freely mounted in any direction.

4) The cell is mechanically rigid as thecontainer is made of steel.

5) Th ll ff t bl f DC


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5) The cell offers a stable performance as a DC

Power Source, as voltage fluctuations during

most part of its discharge is nominal.6)The cell withstands repeated cycles of

charging and discharging as many times as

500 to 2000. Hence, it is highly economical.

7) The cell comes in a Compact, Light Weightdesign.

8) The cell operates over a wide range of

temperatures i.e., -20 C to +55C.9) Quick charging facility available.


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CHARGING METHODS


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CHARGING METHODS Generally these cells are to be charged with constant

current (DC).

A typical circuit diagram of constant current charging

is indicated. Trickle charging is recommended when a fully

charged cell is kept idle for long periods in order tokeep the cell in full state of charge.

This is necessary to make up the losses due to self

discharge during storage. This is done by acontinuous charge at a very low current.


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DOS AND DONTS

Dos& Donts


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It is recommended that the battery room beprovided separately from the circuits of the

equipment.

Contact terminals of the battery holder must

be made of nickel plated steel or nickel cladcopper.

The battery room should be located awayfrom heat generating part of equipment.

Do not disassemble the cells. The electrolytewill hurt the skin and damage cloths.


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PRECAUTIONS WHILEHANDLING CHARGING: Be careful not to effect reverse charging by accident. Positive output terminal from the DC power supply

should be connected to positive terminal of thecell/battery and negative output to the negativeterminal.

Avoid parallel connection of cells. Avoid using constant voltage charging of the cells.

Do not charge the cell using charge current morethan specified. Be sure to conduct charging within a temperature

range of 0 to 45C.


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DISCHARGING: Be sure to conduct discharging within -

20 C to +55 C.

Normal cut off voltage per cell is 1.0V.Avoid discharging below this limit.

Repetition of over discharging will resultin service life reduction and cause theleakage of electrolyte.

Do not discharge the cell with currentsmore than 3 CmA continuously andmore than 5 CmA instantaneously.


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STORAGE: The cells have to be kept in non-

corrosive, gas free, dry place preferablywithin ambient temperature of -20oC to

+ 55oC It is recommended to discharge the cellbefore storing for long periods.

RDSO has specified sealed cylindricalNi-Cd Cells under fixed serialNo.IRS:TC 53-1991.


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BATTERY CHARGERS


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CONTENTS1. Introduction.

2. Simple battery charger.

3. Double circuit battery charger.4. SCR controlled battery charger.

5. Auto-Manual battery charger.

6. Technical specifications of battery charger.

7. Tests on battery chargers.


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CLASSIFICATION OFBATTERY CHARGERS


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CLASSIFICATION A system in which

D.C. voltage isdropped to the

required value or ACis converted to therequired D.C. valueto charge the

secondary battery iscalled a BatteryCharger System.

PARTS OF BATTERY


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CHARGER Mains transformerTo step down the mains

ac voltage.

Rectifier circuitTo convert AC to DC.

Filter circuitTo remove the ripplecomponent.

Regulating circuitRegulating the DCvoltage at required value.

Protective devicesTo protect from highvoltage and currents.

Other componentsLike Indicating meters,rotary switches, terminals etc.


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SIMPLE BATTERYCHARGER


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CONSTRUCTION It consists of a step

down transformer Tx.

Step down the 230VAC

to 24V AC. It is fed to the input of a

bridge rectifier through

a rotary switch.

Output of the rectifier isfed to the filter circuit.

The smoothing filter is indicated by L1C1


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The smoothing filter is indicated by L1C1,L2C2 in C1 and C2 are electrolytic

condensers the capacity of which may varyfrom 100 MFD to 3000 MFD.

Each stage may be considered as a potentialdivider for the next stage. Additionalimpedance is, therefore, introduced to reducethe change in the charging current, thisimpedance is known as 'Ballast'. RB is theballast resistance as shown in figure.

Ballast impedance can be either resistive or

choke ballast.


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DOUBLE CIRCUIT BATTERYCHARGER


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CIRCUIT DIAGRAM


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DESCRIPTION Each circuit is suitable for charging batteries from 6

to 72V at 10 amps.

Each circuit is having a voltage selector switch S1and S4, a current selector switch S2 and S5.

Both the circuits are controlled by mains OFF/L/Hswitch S3.

The charger is provided with two ammeters and amains 'ON' lamp.

Two sets of output terminals + and & Protectionfuses are on the reverse.

FOR SINGLE CIRCUIT


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OPERATION Place S3 in 'OFF'. Place S1 or S4 in

respective battery voltage position.

Switch 'ON' mains. Put S3 in low and adjustS2 or S5 till desired current is obtained (10

Amp. max).

If full charging current is not obtained, place

S2 or S5 in position 1, S3 on high and againadjust S2 or S5 for desired current.


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FOR PARALLEL CONNECTION Sequence of operation similar, but switches S1, S4

and S2, S5 to be so adjusted that both the ammetersread the same amount of current.

The total current is the sum of the two meter

readings. Precautions:1) Charging current should not exceed 10 amps foreach circuit.

Fuses should never be wired with higher


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2) Fuses should never be wired with highergauge of wire. 3) While switching '' always

proceed with S3 in lower battery voltagepositions i.e., for 24V battery, position shouldbe 12 to 24.

3) After completion of charge the sequence of

operation should be as shown. S1 or S4 toposition 6 to 12V, S2 or S5 in position S1 andS3 in off. Then only the charging leads mustbe disconnected.


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SCR CONTROLLEDBATTERY CHARGER


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CIRCUIT DIAGRAM

This type of Charger uses SCRs to reduce


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This type of Charger uses SCRs to reducethe rate of charge as the battery voltage rises,

until the charging current automatically

ceases when the battery reaches a pre-

determined value.

When the battery voltage is low, each halfcycle of mains input delivers current from the

secondary of the transformer to the battery

via the Silicon controlled rectifier, SCR1

because this SCR is turned 'ON' at its gatevia R1 and the Diode D3.

As charging proceeds, the battery voltage rises until


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the potential at the slider of the potentiometer, RV,exceeds the Zener Voltage of ZD, causing it toconduct.

The current through ZD into the gate of the otherSCR., SCR2, Switches that one 'ON'. SCR2 does nothave to carry heavy charging current, it can,

therefore, be a small one with a low current rating. As the battery voltage rises under charge, the point at

which the half cycle SCR2 conducts comes earlierand earlier, until eventually it takes place beforeSCR1 has had a chance to turn 'ON'.

With SCR2 conducting, the junction of R1-R2


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With SCR2 conducting, the junction of R1 R2

is only just above ground, so that SCR1 is

unable to switch 'ON' and charging ceases.

The battery voltage at which this chargelimiting occurs is set by RV.

If the battery voltage falls, charging will re-start. So making the circuit suitable for these

uses where a battery is called upon to

provide high rate intermittent, short

discharges and is left across the chargercontinuously.

AUTO/MANUAL BATTTERY


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FRONT VIEW


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CONTROLS Input double pole ON/OFF rotary

switch(SW1)

Auto/Manual Selector Switch(SW2)

Manual Mode Output voltage selectorswitch(SW3)

Total current/Battery current selector

switch(SW4) Alarm reset Switch(SW5)


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METERS & FUSES METERS:

DC Output Volt meter

DC Output Ammeter FUSES:

AC Input HRC fuse

DC Output HRC fuse SPECIAL FEATURE: charger fail condition is indicated with flasher LEDand AUDIO ALARM.

Automatic change over from float to boost mode andvice versa by sensing battery current.


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AUTO/MANUAL BATTTERY


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CHARGER. IRS.S.86/2000


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PARTS OF AUTO/MANUAL


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CHARGER The schematic circuit diagram of battery

charger consists of the following parts:

Mains transformer. A half controlled full wave rectifier.

An L.C. section filter.

Control PCB.

FUNCTIONS OF PARTS


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SW1- To switch on the AC supply to thecharger.

TR1- Mains transformer steps down the inputvoltage to the required AC output voltage .

RLY1-It is used to improve working powerfactor to above 0.7. Half controlled Bridge rectifier- Step down the

voltage to the required value.

SW2 - to select Auto/Manual mode ofoperation.

SH1- is used to sense the total chargero tp t c rrent


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output current.

SH2- is used to sense the battery current. RLY2- is used for on battery reverseconnection protection.

TR-2- is used to get low voltage AC forgenerating DC power supplies for functioningto control circuit.

TR-3 - is used to get low voltage AC used toindicate AC out of range indication and DCunder voltage indication.

SW3- is used to select the outputvoltage in manual mode.

The control circuit diagram is assembled on


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e co o c cu d ag a s asse b ed o

PCB1. It is having the following sections, +/-15V Power supplies:- The DC power

supply required for the entire circuit is

generated by it. This is regulated by IC

regulators.ICS REG1 & REG2operates ICs U2 toU7,operates on Auto Mode.

ICS REG3 - Provide +15V DC for ICs U1 &U8, Operates at Manual Mode also.


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Reverse polarity protection section:-ICU6 is used to Drop the relay RLY2which opens the +ve connection to the

battery from the charger during reverse

polarity.

Auto fail indication & Alarm:- ICU 6 is used to


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sense The Auto mode failure. ICU7 is used

to get flashing indication and Audio alarm. AC out of range and DC under voltageindication:- ICU1 is used to get AC out of

range indication and also Low DC voltage

indication and Audio alarm. Power factor improvement:- ICU6 Pin 7 is

used for giving Command signal to Relay

RLY1 whenever the working PF comes downbelow the set level.

TECHNICAL SPECIFICATIONS


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INPUT SUPPLY:1. Nominal Voltage : 230V

2. Input supply range : 160 to270V

3. Input supply frequency :50Hz +/- 2Hz

4. Phase : Single Phase

OUTPUT PARAMETERS:1. Nominal float voltage : 2.15 V/Cell

2. Adjustment range : 2.0V to 2.3V/Cell

3. Output Voltage Regulation :


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p g g

+/-2.5%(0.05V/Cell)

4. Output ripple : Less than 5% of the

output voltage

5. Boost mode output voltage : 2.4V/Cel6. Rated current : X Amps

7. Current Limit adjustment :

Continuously adjustable from 10 to100


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CHARGER PERFORMANCE1. No load current : Less than 10

2. Efficiency at rated input : Not less

than 653. Operating Input Power Factor : Better

than 0.7

4. Battery reverse leakage current whenInput fails : Less than 50 mA

PROTECTION


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1. Thyristors are protected against accidental

over voltage.

2. Charger input provided with MOVR.

3. Protection against accidental failure ofregulation.

4. DC Over voltage protection.

5. Output short circuit protection.

6. Battery reverse polarity protection.7. Soft start feature.


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Adjust the preset VR7 in the PCB for


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Adjust the preset VR7 in the PCB for

required DC output voltage in the floatmode.

Connect the battery to the battery

terminals. Depending up on the condition of the

battery, battery charger to select auto

float mode or auto boost mode.

At Auto boost mode adjust the VR12 presetin the PCB to set the battery current to the


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in the PCB to set the battery current to the

required value. If the chargers Auto Mode fails, batterycharger shows AUTO fail indication withaudible alarm, then change the spare PCBwhich is mounted inside the charger. Still

there is no output in the Battery charger,change mode selector switch SW2 tomanual mode and select the output voltageby adjusting manual selector switch SW3.

Equipment ground to be properly earthed.


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TESTS ON BATERYCHARGERS


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ACCEPTANCE TESTS


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The following shall comprise AcceptanceTests:-

a) Visual Inspection.

b) Insulation Resistance Test.c) Applied High Voltage Test.

d) Induced High Voltage Test.

e) Temperature Rise Test.

f) Performance Test.

g) Test for protective devices.

ROUTINE TESTS


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Following shall constitute routine tests to beand shall be conducted by Manufacturer on

every battery charger and test results will be

submitted during the inspection.a) Visual Inspection.

b) Insulation Resistance of main transformer.

c) Insulation resistance of complete charger.d) Performance Test.


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INTRODUCTION


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What is SMPS ?

Switch mode power supply, is an

electronic device in which the activedevice that provides regulation is

always operate in a Switched mode, ie.

It is operated either in cut-off or in

saturation for the control of outputvoltage.


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1) Efficiency over 90%.


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2) Modular construction, so the time torectify the failure is very much reduced.

3) Due to standby modular arrangement,active load sharing will be there.

4) Smaller in size when compared to linearpower supply.

5) Occupies less space and it can beaccommodated in the equipment rack

itself.6) Noise is less.

7) Stand alone rack with combined


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7) Stand alone rack with combined

distribution/switching/alarm arrangementfor small power requirements.

8) Temperature compensated battery

charging.

9) Low voltage battery disconnect.

10) Additional protection with MCBs on AC

as well as DC side for rectifier module.

11) Either Conventional type or VRLA typecan be used.


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MODULAR POWER SYSTEM

BLOCK DIAGRAM


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PRINCIPLE OF SMPS


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A.C.230V, 50Hz 1 is given to the inputrectifier circuit which converts AC intopulsating D.C.

This is given to a high frequency switchingcircuit. The switching element is a specialtransistor such as MOSFET. It operatesbetween 10 KHz100 KHz. The input D.C

is chopped at this high frequency in SMPS.The switching device is always operated inswitched mode, ie. It is operated either incut off or in saturation.


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The output rectifier circuit converts this


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The output rectifier circuit converts this

high frequency voltage to DC voltageby gold doped Junction Diodes or

Schottky barrier diode. The high

frequency ripples are filtered byparallel capacitors having low

equivalent series resistance.


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If the out put voltage of the SMPS decreases,th idth f th t lli l t th


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the width of the controlling pulse to the

transistor is increased. Hence it gives power

to the load for longer duration, simultaneously

increasing the output voltage.

When the output voltage of SMPS increases,the width of the controlling pulse to the

transistor is decreased. Hence it gives power

to the load for shorter duration,

simultaneously decreasing the output voltage.

SPECIAL FEATURES OF SMPS


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POWER PLANT1. Active input power factor correction &

Active input current shaper.

2. Input lightning protection as per for

tropical atmosphere.3. Input surge protection as per for noisy

& surge prone shared utility line.

4. Battery path current limiting for safecharging of VRLA batteries.


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ACTIVE INPUT POWER


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FACTOR CORRECTION Due to distortion less than 10% in

phase with the input AC, the power

factor is as high as 0.98 can be

achieved.

These feature help to save considerableenergy and reduces the running

expense.

INPUT LIGHTNING


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PROTECTION Special heavy duty & fast spark gaps are

used for lightning protection.

These arrestors have very high peak current

capability to withstand currents due to heavy& repeated lightning strikes.

These protection units when installed in theAC entry point protects the total installation.

INPUT SURGE


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PROTECTION Special high capacity surge arrestors

are used to handle the surges of high

energy content, kept inside ACDB

panel, which avoids the failure ofcharger equipment.

BATTERY PATH CURRENT


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LIMITING The charging current through the VRLA

battery limited to safe value i.e.10% of AHcapacity of the battery, by the Micro controllerin central control unit.

This feature helps to prevent heating of thebatteries & subsequent damage due to overheating.

Maximum charging current allowed in case ofVRLA battery is 20% of Capacity (AH).

REVERSE BATTERY


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PROTECTION Reverse battery protection in case of

VRLA battery is provided to get longer

life and avoid any hazardous to the unit.

This is given in MCM module.


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DIGITAL DISPLAY OF


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VOLTAGE AND CURRENT A large size digital display(12mm) on

each rectifier gives the values of rectifier

output current & voltage.

This results in better monitoring &checking of current sharing among

modules at a glance.

MENU DRIVEN MICRO CONTROLLERBASED CONTROL OF RECTIFIERS &SYSTEM


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Various charging parameters can be setor altered by entering through buttons,

provided on front panel of the charger.

LEDs have been used to indicate allalarms and status.


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BLOCK DIAGRAM OF SMPSBATTERY CHARGER

BLOCK DIAGRAM


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DIFFERENT MODULES IN


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SMPS Switch Mode power supply is a modular design of

rectifiers allow flexibility and easy replacement.

A typical power plant consists of:

a) Lightning protection Unit (LPU).

b) AC distribution panel & surge protection module.

c) Monitoring & control Module (MCM) with batteryreverse protection.

d) BI mounting panel.

e) Switch Mode Rectifier modules (SMR).f) Wired Rack.


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AC DISTRIBUTION PANELSURGE PROTECTION


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MODULE The incoming AC mains is terminated inthis panel, Circuit breakers are provided

for distribution of AC to every rectifier.

This module special very high currentSurge Suppressions devices to divert

the current to the earth in the event of

high voltage surges in AC lines.

MONITORING AND CONTROLMODULE (MCM)


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This module carries out all supervisoryand control of the power plant.

This is provided with battery reverseprotection arrangement.

BATTERY ISOLATION


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PANEL / RACK This arrangement is provided to monitor

currents flowing in or flowing out of

individual ICs. Audio &Visual alarm is

generated when any of the batteries aredisconnected from the system.

SWITCH MODE RECIFIERMODULE


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These converts AC mains voltage toregulated DC for powering Telecom

installations.

They are high efficiency converters withnear unity power factor.


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TECHNICAL SPECIFICATIONSOF SMR

TECHNICAL SPECIFICATIONS


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Input: 165 to 260 Volts phase-to-neutral AC,3 Wire,48 to 52Hz.

Output: 56 Volts at 25 Amps.

Power factor: 0.99 at full load and 230 Volts AC input.

Current harmonic distortion: Less than 10% at fullload and 230 Volts input.

Efficiency:90% at full load and 230 Volts AC input.

Ripple & noise:100mV peak-to-peak & less than 2mV

psophometric. Acoustic noise: Less than 45dBA.

Transient response: Limited to5% &recovery within 10mSec.


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y

Protections: Over voltage, Over load, Shortcircuit.

Indications; AC on, Under voltage, Over

voltage, Current limit, Float mode, Chargemode, Rectifier fail, Rectifier disable.

Environmental: As per QM-333B2 of DoT.

Cooling: Natural Convection.

POWER SYSTEMCONFIGURATION


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Sl.No Load(Equipment & BatteryBank)

(n-1)SMRmodules

1 12.5 A to 25 A (2-1)X12.5A

2 25A to 50A (2-1)X25A

3 50A to 100A (2-1)X50A

4 100 A to 150 A (3-1)X50A

5 150 A to 200A (4-1)X50A

OPERATIONALREQUIREMENTS


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A) EFFICIENCY:

1. Units working on single phase:

a) At normal input,output & full rated load better than80%.

b) For other specified input, output conditions betterthan 75%.

2. Units working on 3 phase:

a) At nominal input, output, full rated load: better than85%.

b) For other specified input, output conditions: betterthan 80%.

Purchasers should indicate whether the equipmentwork on 1 or 3.

B) POWER FACTOR:

1. At normal input and output 7 load 75% to 100% -0.95 lag & 0.98 lead.


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2. For other specified input, output conditions & loadbetween 25% to 100%: 0.90 lag & 0.90 lead.

C) OPERATING TEMPERATURE: 0-55C.

D) LIGHTNING PROTECTION:The system shall be provided with class B & C

type arrestors having thermal disconnection insideto avoid fire hazards as per specification No:VDE0675/IEC 1643. The arrestors should be in themodular form so that they can be replaced easily.

The rated voltage of arrestors should be 280V.


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H) EARTHING:

All non current carrying metal parts shall be bondedtogether and earthed.

An earth terminal suitable for taking minimum 4mm


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An earth terminal suitable for taking minimum 4mmDia wire and with suitable marking shall beprovided.

I) NAME PLATE: The name plate fix on each rackshould contain the following information:

1. Specification number.

2. Type of unit.

3. Manufacturers name and identification.

4. Model Number.

5. Unit serial Number.

6. Input voltage & Phase.7. Output voltage 7 current.Year of manufacture.

8. Suitable for battery capacity.

J) MODULAR REPLACEMENT TIME & MTBF:

The mean time to replace a faulty rectifier moduleshall be less than 20 minutes.


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The MTBF of the system shall not be less than70,000 Hours. The fan provided shall have MTBF better than

70,000 hours at 40C. In case of fan failure, the module shall have

automatic protection to switch off with extension ofsuitable alarm. It shall not cause any fire hazard.

K) ELECRTICAL REQUIREMENTS:

1. AC INPUT SUPPLY: The power plant using SMRmodules of 12.5 &25 A shall operate from 1AC

input, and SMR modules of 50 A capacity mayoperate from 1 or 3 4 wire AC input.

2. Nominal input frequency50Hz (48-52Hz).3. Input voltage rangeNominal 1:230V(165V-

260V)

INFORMATION SUPPLIED BYTHE PURCHASER


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1. The type of battery to be used: VRLA orConventional type Lead Acid Battery.

2. Battery Capacity.

3. Total load requirement for equipment and battery.

4. Number of SMR modules and current rating ofeach module.

5. Ultimate capacity of the system.

6. Power plant will work on 1 or 3.

7. Provision for Network Monitoring arrangement.8. Power plant to work as float mode or boost mode

or both.


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Rectifier output: Switching frequency :76KHz.


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Charging characteristic :IU in accordancewith din 41773

Float mode: 54V(adjustable from 46V to 59V).

Charge mode : 55.2V(adjustable from46 to 59V) . Nominal current in Float& charge mode :

12.5A.

Battery : 24 Pb-cells, rated voltage:48V.

Voltage change :5 Setting time :


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Regulation : Float/charge : 1 . Battery Temperature : 3mV/C/Cell. Environmental: Cooling : Natural cooling. Operating Temperature : 55C.

Specification : Meets QM333,B2. Mechanical: Height :262mm. Width : 106mm(1/4 of19).

Depth : 252mm. Weight : 5.5 Kg.


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INVERTERSANDCONVERTERS

CONTENTS


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1. Introduction. Principle of converters.2. DC to DC ConvertersDifferent types.

3. Some special features of DC-DC

converters.

4. Performance requirements.

5. Types of tests on converters.

6. 500 Watts MOSFET based inverter.


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INTRODUCTION

NESSICITY OF CONVERS &INVERTERS


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For operating communication equipmentscorrect voltage is required. So convertingequipments are necessary for converting thesupply voltage into a form suitable for being

fed to the equipment. Where only a low voltage DC supply isavailable and higher AC voltages needed DCto AC inverters are to be used.

When a higher DC voltage is needed, "DC -DC converters" must be used.


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PRINCIPLE OF CONVERTERS

BLOCK DIAGRAM


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A- Low voltage DC supply.


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B- Switches DC supply ON and OFFcontinuously at an audio frequency to

give an AC voltage.

C- Step up transformer steps uprequired AC.

D- Smoothing circuit from, which

emerges a final high voltage DC, V out.


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D.C. - D.C. CONVERTERS

Solid State Converters are built withtransistors or SCR s.


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For low power up to 100W DC, transistors arenormally used. Above 100W, SCRs take overfrom transistors.

The chopping frequency at which DC is

converted to AC is usually between 50 Hz to20 KHz.

In practice converters are used mostcommonly to step up from standard 6,12 &

24V lead acid storage batteries. SometimesDC-DC converters are used even where amains supply is available.

TWO TRANSISTORS, ONETRANSFORMER DC-DC


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CONVERTER

This is the commonest circuit used inmost of the commercial DC-DC


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converters. This self-oscillating, push-pull circuit

uses two power transistors in a

symmetrical square wave oscillator. Theoperation of the circuit depends mainly

on the square loop pattern of the BH

curve of the transformer and switchingproperties of the transistors.

DESCRIPTION


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The transistors TX1 & TX2 play the part of theswitches and are constrained by transformer-

coupled feedback to be alternately ON and

OFF, so as to connect the unidirectional inputvoltages alternately to the separate halves of

the primary windings of the output

transformer T.

This produces an alternating square waveoutput across the secondary transformer.

TWO TRANSISTORS, TWOTRANSFORMERS DC-DC


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CONVERTER

THE PRINCIPLE OFOPERATION


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Initially when the input supply is switched on,one of the transistors in the converter circuitconducts more rapidly than the other.Suppose Q2 conducts earlier than Q1 - It

tends towards saturation and takes the lowerend of the primary of 'T2' down to zero volts.

The top dot indicated end of the 'T2' primarygoes positive by an equal amount above thepositive power voltage (to which the centertap is connected).

The magnetizing current of T1 builds uplinearly until the core saturates. When


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T1 reaches its saturation, flux density,the magnetizing current increases very

rapidly and the secondary voltage

collapses and cannot hold Q2saturated.

The collector voltage of Q2 rises and

regenerative action causes Q1 and Q2to reverse states.

This carries the bottom dot, indicated end ofthe primary of T1 also positive and switchesQ2 ON and Q1 OFF.


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Q Q

As these processes repeat during each halfcycles, oscillations are sustained.

The frequency of oscillation depends on the

following:i) No. of turns of the primary windings of T1

ii) Core Cross Section and Core materialcharacteristics in T1.

iii) Value of RF (Resistor Feed Back) and RB(Resistor bias).

SCR DC-DC CONVERTERS


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SCR DC-DC CONVERTERS


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This type of converters are mostly used athigh power and high input voltages.

This converter consists of two basic units, thepower switching section and a low poweroscillator necessary for periodic triggering ofthe switching section.

It is assumed that separate oscillator isavailable to apply current pulses alternatelythrough the gates G1 and G2 of SCR to turnthem on.

FUNCTIONING The SCR1 & SCR2 are triggered alternatively


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, and the commuting voltages are applied bythe capacitor C across the primary windingof transformer. Thus generating analternating voltage wave form, which is

developed across the secondary winding oftransformer.

The function of the choke L is to limit thecurrent flow during the commutation process

i.e., while both SCRs may be conducting. Italso tends to limit the rate at which Cdischarges and so hold the SCRs reverse-biased until it.

A formula for minimum value of C is given as:


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C= 1.44n2 T off

R

T off = Turn off time of the SCRs

n = Ns/Np

R = Load resistance seen by the output of the

transformer recovers to the blocking state.


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SPECIAL FEATURES OFCONVETERS

(i) The process of starting oscillations: Most converter circuits are intrinsically self-starting

for light loading, but with higher output current,


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starting becomes difficult. The starting is generally achieved by one of the

following arrangements:

(a) Placing a large initial forward bias on the

transistor.(b) Applying an initial heavy asymmetrical pulse

to the circuit.

(c) Reducing the initial load by a series choke or by a

feedback circuit.

ii) Transient spike suppression circuit: The following de-spiking circuits may be used


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to protect the semiconductor devices,(a) Clipping diodes from collector to emitter

(b) Capacitors from collector to emitter

(c) Series capacitor-resistors across totalfeedback winding.

(d) Collector to Collector capacitor and

(e) Series capacitor-resistors across

transformer secondary.


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(iii) Regulating the output voltage of the DC-DCconverters:- In the converters the output voltage is directly

proportional to the input voltage so that theline regulation is poor. In addition, ringingchoke converters etc., works on constantoutput power basis so that output voltage forthese will vary with change in load currents

also. Very often, therefore, some form of stabilizing

circuitry is needed to keep the output voltageconstant.


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PERFORMANCEREQUIREMENTS

RDSO has specified various performancerequirements and Type Tests of DC-DC Convertersas per RDSO Specification No.123/1991.

(a) The converter shall operate from nominal inputvoltages of 120V, 50V, 48V, 24V and with output


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voltages of 5V, 10V, 12V, 18V and 24V or any othervoltage as specified by the purchaser with outputcurrent capacities, varying from 1 amp. to 15 amps.

(b) Voltage regulation shall not be worse than + 1% forall output ranges, for input supply variation from -10%

to +20% of nominal input voltage indicated in para 1above.

(c) The output shall be free from over-shoot on accountof turn 'ON/turn OFF' or power failure or when thebattery charger is switched ON/OFF.

d) It shall work in the temperature range of 00 C to 700C and relative humidity upto 95%.

(e) The unit shall be provided with over-load protection,output over voltage protection and output shortcircuit protection with feed back characteristics. Theoverload protection shall be effective at 120% of thenominal output rating.


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(f) The overall efficiency of the converter shall not beless than 50%.

(g) The switching frequency used shall not be less than20 KHz. The converter shall employ PWM techniquefor regulation of DC output.

(h) All components used such as, transistors, diodes,FETS, Integrated circuits etc., shall meet the relevantIS: Specification or JSS specification.

(i) All indications and fuses shall be provided on thefront panel.

(j) The noise spikes on the input side shall beattenuated by at least at 60 db when measured atthe output side.

(k) The equipment shall withstand vibration

tests from 10 Hz to 55 Hz,0.75 mm peak to

peak displacement in all three tests for two


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hours each or at resonant frequency for twohours.

(l) Additional requirements of DC/DC converters

are to be provided for Axle Counter

installations, solid state interlocking, Data

logger and other similar equipment involving

TTL IC's, Linear IC's, Microprocessors,

CMOS devices, etc.


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5.Ripple and noise in the output shall be

less than 40 mV peak to peak with


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normal ground connection.6.The outputs, where current required is

of the order of 1 Amp. or less shall

make use of converter IC chips. In orderto increase the reliability of converter,

series-parallel combination of such IC's

shall be used.


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TESTS ON CONVERTERS

TYPE OF TESTSf


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The following shall constitute type tests andshall carried out in the given sequence:-

a) Visual inspection.

b) Applied high voltage test.c) Insulation resistance test.

d) Test for continuous operation.

e) Performance Test.

f) Test for protective devices.g) Overload and in rush current test.


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500-WATT MOSFET BASEDPWM INVERTER

BLOCK DIAGRAM


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2. A single transformer is used to cater for

inverter output and battery charger. The

h ti f th d


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charger portion of the secondarywinding is disconnected from the

charger in case of mains failure and

also when the battery tends to reach the

over-charged condition.

3.Pulse width modulation (PWM), using apopular low priced IC SG3526A, is

l d Th lt i


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employed. The error voltage isdeveloped from the AC output wheninverter is in operation.

4. Automatic shut-off of the inverter

occurs when any (one or more)conditions are present:

(a) Mains supply is available.

(b) Battery voltage is below minimumlevel.

(c) Temperature exceeds specified limit,

(d) An overload occurs.

( ) M l h t ff it h i t d


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(e) Manual shout-off switch is operated.5. Apart from the built-in electronic safe

guards additional safe guards by way of

MCCBs (modulated case circuitbreakers) have been provided in AC

output, battery charger input and battery

output to avoid any unto ward damagedue to shortages.

6. LED indications are included to indicate

the following:

(a) Whether mains is available or inverter


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is ON.

(b) Overload condition.

(c) Over temperature condition.

(d) Battery voltage level including low and

over charged condition.

(e) Battery charging in normal and trickle

charged modes.


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VOLTAGE STABILISERS

CONTENTS1 I t d ti


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1. Introduction.

2. Requirements for mains voltagestabilizer.

3. Simple voltage stabilizing circuits.4. Complex stabilizing systems.

5. Constant voltage transformer.

6. Ferro-resonant type automatic voltageregulator.

INTRODUCTIONI t f th S & T i t ll ti th


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In most of the S & T installations, thepower supply will have to be maintained

reasonably constant.

Due to variations in the A.C. supplyvoltages, it is necessary to incorporate

the

REQUIREMENTS FOR MAINSVOLAGE STABILIZER There are four main requirements for a


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mains voltage stabilizer.1. The accuracy of stabilizing action can be

within + 0.05% + 2%, but stabilization tobetter than + 0.5% can be considered as

very good.

2. The speed of response, which is defined asthe accuracy of the system divided by thetime taken to reset the voltage for a changeto bring back the accuracy (the regulatingtime). For instance, if this resetting time is 1sec, the speed of response would be 1%per sec.

3. The output waveform. In certain

applications it is important to have the

l f f di t ti f


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power supply free from distortions ofthe original sinusoidal waveform.

Stabilizing circuits using non-linear

elements, as forexample saturated inductances

introduce such distortions. They can

be removed by using low pass filters.


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SIMPLE STABILIZINGCIRCUITS

BARRETER STABILIZER


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In the case where, a stabilized source issupplying a constant load, a quite simple

stabilizing device can be designed as shown


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stabilizing device can be designed as shownin figure.

The barreter B is inserted in series with theprimary of the step up transformer T, and this

stabilizes the current drawn from the mains. With a constant load, the primary and

secondary voltages will the be stabilized and

any voltage variations will occur across the

battery.

This method works quite successfully,provided that the power required is not too

large and, as previously stated, that the

loading conditions are constant The primar


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loading conditions are constant. The primary

winding should be calculated for the actual

barreter current, otherwise, it is necessary to

shunt the primary by a resistor R to secure asufficiently high current through the battery.

In certain applications such a resistor R canbe made variable (possibly in steps) to allow

for varying loading conditions.

THERMISTER VOLTAGESTABILIZER


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Voltage stabilization can also beachieved by the use of thermistor which

are semiconductor resistors having a


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are semiconductor resistors having anegative temperature resistance co-

efficient.

Thermistor is used as non-linear devicefor stabilizing a low ac voltage. An

impedance Z connected across the

load, consists of an ordinary resistor Rand a thermistor S connected in series.


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COMPLEX STABILIZINGSYSTEMS

It involve those withmoving parts are

known as static

voltage systems of


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voltage systems of

which the constantvoltage transformeris an example.

CONSTANT VOLTAGETRANSFORMER


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BASIC OPERATION A basic static magnetic regulator circuit

making use of constant voltage transformer

principle


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principle. If Ep increases, Es and Ec also increase, Ec,

however, increase more rapidly than Es , butis smaller in magnitude.

For some range of Ep the increase in Es willbe off set by the increase in Ec since theseare connected in opposing polarity. Forreduction in Ep exactly the opposite takes

place and the total change of E out isminimised.

ADVANTAGES(1) Ultra - fast regulating action. Response time

is usually 1 5 seconds or less


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is usually 1.5 seconds or less.(2) Absence of moving or renewable parts or

manual adjustments eliminates the need forroutine maintenance and spare parts.

(3) No manual adjustments are required.

(4) Self protecting against short circuits onoutput or load circuit.

(5) Current limiting characteristic protects loadequipment from fault currents.

(6) Availability of transformer ratio for

step-up, step-down. Plate and/or

filament supply permits substitution in


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filament supply permits substitution inplace of conventional, non-regulating

transformers.

(7) Relatively compact compared to otherequipment for comparable regulation.

(8) High degree of isolation between input and

output circuits.

(9) Negligible external field.

FERRO RESONANT TYPE AUTOMATICVOLTAGE REGULATOR In this the primary side of the transformer


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In this the primary side of the transformeroperates below the saturation and secondaryside operates in the saturated region ofmagnetic curve.

Core material used: Primary side--- MILD STEEL (Unsaturated

Iron)

Secondary side---- SILICON STEEL (Saturated Iron)

WORKING


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The capacitor of the proper value isconnected across the secondary

winding to form a parallel resonance


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winding to form a parallel resonancecircuit. If the voltage is applied on

primary winding and it is gradually

increased from zero to a particularvoltage, called as KNEE VOLTAGE orpoint of discontinuity, at which

secondary is tuned to parallel

resonance.

Due to the resonance effect the capacitorsincreases the secondary voltage abruptly.

This results in the secondary core magneticfl i i d d d t it t


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This results, in the secondary core magneticflux is induced due to capacitance current

flowing in the secondary winding.

This magnetic flux is added to the magnetic

flux flowing through secondary core due tothe primary voltage.

Hence flux addition is taking place in the

secondary core causes secondary getsaturated.

BLOCK DIAGRAM


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WORKING The resonant voltage across the capacitor

bank(Vc) is not more than480 V at all inputlt & f diti t l d


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bank(Vc) is not more than480 V at all inputvoltage & frequency conditions at no load.Normally Vc =440 V no load.

Capacitors are rated for 600V AC metal-can

capacitors. A magnetic shunt is provided between thetwo windings.

When the secondary magnetic circuit issaturated, much of the secondary flux is de-coupled from the primary winding and passesthrough magnetic shunt.

At primary knee voltage secondary core issaturated and after knee voltage the

increased amount of magnetic flux passes


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increased amount of magnetic flux passesthrough the magnetic shunt and does not

increase the flux at secondary.

Hence secondary voltage remains more orless constant.

Part of the primary & secondary magnetic fluxflowing through magnetic shunt increases

magnetic isolation between the two windings.

PURPOSE OFCOMPENSATING WINDING It improves the regulation of voltage


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It improves the re

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