P.ANIL KUMAR 07N01A0201

CHAPTER-1

BATTERY CHARGER

1.1 INTRODUCTION:

A battery charger is a device used to put energy into a secondary cell or

(rechargeable) battery by forcing an electric current through it. The charge current depends

upon the technology and capacity of the battery being charged.

Batteries are used as a source of DC Electric power for different Applications. A

battery is a device which supplies DC power by converting the stored chemical energy into

electrical energy when it is connected to an external load. A battery set is formed by

connecting several individual cells in series or parallel according to the requirement of

Voltage and energy.

The battery charger consists of separate boost charger and Separate float charger.

The boost charger is of silicon diode type and float is of tyristor type. The booster charger is

meant for boost the battery .When it is first commissioned, when the battery is discharged

completely. Float Charger is meant for feeding regulated 220v DC supply to DC loads like

breakers, coils, memory circuits, emergency lights, pump sets Etc. Operating on DC voltage

and also to trickle charge the 220v battery both boost and Float charger work on 3-phase,

415v, 50 Hz, 4-wire AC input supply.

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CHAPTER-II

2.1 TYPES OF CHARGERS:

1. Float charger (FC)

2. Boost charger (BC)

2.1.1 FLOAT CHARGER (FC):

Float charger rectifies the input AC to DC and does the dual function of float or

trickle Charging the battery and supplying DC power to load. It senses when the battery

voltage is at the appropriate float level and temporarily ceases charging; it maintains the

charge current at zero or a very minimal level until it senses that the battery output voltage has

fallen, and then resumes charging. It is important to note that the appropriate float voltage

varies significantly with the construction of the battery and the ambient temperature. With the

appropriate voltage for the battery type and with proper temperature compensation, a float

charger may be kept connected indefinitely without damaging the battery. With a 6-cell

(nominal 12V) lead-acid battery the correct float voltage drops by about 0.1 V for a 5 °C rise

in ambient temperature. Not compensating for this will shorten battery life either by over- or

under-charging.

2.1.2 BOOST CHARGER (BC): Boost charger is required for quick recharge of a

discharged battery.

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2.2 FLOAT CUM BOOST CHARGER (FCBC):

FCBC as the name indicates is a two-in-one functional combination of a float charger

and a boost charger, under normal conditions, FCBC works as a float charger. When the

mains fail, battery takes over supply to the load. On resumption of power, FCBC switches to

the “Boost mode”, boost charges the discharged battery and return to the “Float mode”, after

the battery is restored to full charge. All along, it supplies uninterrupted DC Power to the

load.

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2.3 LOAD VOLTAGE LIMITERS (VR):

In order to protect the load against the voltage variation during the “Boost Mode”

Operation, a load voltage limiter in the form of Diode Voltage Regulator (DVR) or Chopper

Regulator (CR) is used. End cell switching which uses a divided battery, tap cell diode and

change over contactor is yet another method of protecting the load from high boost voltage.

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2.4 BATTERY DESIGN AND CONSTRUCTION:

Battery manufacturing is an intensive, heavy industrial process involving the use of

hazardous and toxic materials. Batteries are generally mass produced, combining several

Sequential and parallel processes to construct a complete battery unit. After production, initial

charge and discharge cycles are conducted on batteries before they are shipped to distributors

and consumers. Manufactures have variations in the details of their battery construction

features can be described for most all batteries. Some important components of battery

construction are described below.

2.4.1 CELL:

The cell is the basic electrochemical unit in a battery, consisting of a set of Positive

and negative plates divided by separators, immersed in an electrolytic solution and enclosed

in a case. In a typical lead-acid battery, each cell has a nominal voltage of about 2.1v, so there

are 6 series cells in a nominal 12v battery. Fig 1 shows a diagram of a basic lead-acid battery

cell.

2.4.2 Active Materials:

The active materials in a battery are the raw composition materials that form the

positive and negative plates, and are reactants in the electrochemical cell. The amount of

active materials in a battery is proportional to the capacity a battery can deliver. In lead-acid

batteries, the active materials are lead dioxide (pbo2) in the positive plates and metallic

sponge lead (Pb) in the negative plates, which react with a sulphuric acid (H2SO4) solution

during battery operation.

2.4.3 ELECTRODE:

There are generally a number of positive and negative plates in each battery cell,

typically connected in parallel at a bus bar or inter-cell connector at the top of the plates. A

pasted plate is manufactured by applying a mixture of lead oxide, sulphuric acid, fibres and

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water on to the grid. The thickness of the grid and plate affect the grid and plate affect the

deep cycle performance of a battery. In automotive starting or SLI type batteries, many thin

plates are used per cell. This results in maximum surface area for delivering high currents, but

not much thickness and mechanical durability for deep and prolonged discharges. Thick

plates are used for deep cycling applications such as for forklifts, golf carts and other electric

vehicles. The thick plates permits deep discharge over long period, while maintaining good

adhesion of the active material to the grid, resulting in longer life.

2.5 BATTERY TYPES and CLASSIFICATIONS:

Many types and classifications of batteries are manufactured today, each with

specific design and performance characteristics suited for particular applications. Each battery

type or design has its individual strengths and weaknesses. In PV systems, lead-acid batteries

are common due to their wide availability in many sizes, low cost and well understood

performance characteristics. In a few critical, low temperature applications NICKEL-

CADMIUM cells are used, but their high initial cost limits their use in most PV Systems.

There is no “perfect battery” and it is the task of PV system designer to decide which battery

type is most appropriate for each application. In general electrical storage batteries can be

divided into major categories, primary and secondary batteries.

2.5.1 PRIMARY BATTERIES:

Primary batteries can be store and deliver electrical energy, but cannot be recharged.

Typical CARBON –ZINC and LITHIUM batteries commonly used in consumers’ electronic

devices are primary batteries. Primary batteries are not used in PV systems because they

cannot be recharged.

2.5.2 SECONDARY BATTERIES:

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A secondary battery can store and deliver electrical energy and can also be recharged

by passing a current through it in an opposite direction to the discharge current. Common

LEAD-ACID batteries used in automobiles and PV systems are secondary batteries. Table 1

lists common secondary battery types and characteristics which are of importance to PV

system designers. A detailed discussion of each battery type follows.

2.6 LEAD-ACID BATTERY CLASSIFICATION:

Many types of lead-acid batteries are used in PV systems, each having specific design

and performance characteristics, while there are many variations in the design and

performance of lead-acid cells, they are often classified into one of the three categories.

2.6.1 SLI BATTERIES:

Starting, lighting and ignition (SLI) batteries are a type of lead –acid battery designed

Primarily for shallow cycle service, most often used to power automobile starter. These

Batteries have a no of thin positive and negative plates per cell, designed to increase the total

plate active surface area. The large no of plates per

cell allows the battery to deliver high discharged currents for short periods, while they are not

designed for long life under deep cycle service, SLI batteries are sometimes used for PV

systems in developing countries where they are the only type of battery locally manufactured.

Although not recommended for most PV applications, SLI batteries may provide up to 2 years

of useful service in small stand –alone PV systems where the average daily depth of discharge

is limited to 10-20%, and the maximum allowable depth of discharge is limited to 40-60%.

2.6.2 MOTIVE POWER or TRACTION BATTERIES:

Motive power or traction batteries are a type of lead acid battery designed for deep

discharge cycle service, typically used in electrically operated vehicles and equipments such

as golf carts, fork lifts and floor sweepers. These batteries have a fewer number of plates per

cell than SLI batteries, however the plates are much thicker and constructed more durably.

High content lead-antinomy grids are primarily used in the motive power batteries to enhance

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deep cycle performance. Traction or motive power batteries are very popular for use in PV

systems due to their deep cycle capability, long life and durability of design.

2.6.3 STATIONARY BATTERIES:

Stationary batteries are commonly used in uninterruptible power supplies (UPS) to

Provide backup power to computers, telephone equipment and other critical loads or devices.

Stationary batteries may have characteristics similar to both SLI and motive power batteries,

but are generally designed for occasional deep discharge, limited cycle service. Low water

loss lead-calcium battery designs are used for most stationary battery applications, as they are

commonly float charged continuously.

2.7 TYPES OF LEAD-ACID BATTERIES:

There are several types of lead-acid batteries manufactured. The following sections

describe the types of lead-acid batteries commonly used in PV systems. Lead-Antimony

batteries are a type of lead-acid battery which use antimony (sb) as the primary allowing

element with lead in the plate grids. The use of lead-antimony alloy in the grids has both

advantages and disadvantages. Advantages include providing greater mechanical strength

than pure lead grids, and excellent deep discharge and high discharge rate performance. Lead-

antimony grids also limit the shedding of active material and have better lifetime than lead-

calcium batteries when operated at higher temperatures.

2.8 BATTERY CHARGING:

Methods and procedure for battery charging vary considerably in a stand-alone PV

systems, the ways in which a battery is charged are generally much different from the

charging methods battery manufactures use to rate battery performance. The various methods

and considerations for battery charging in PV systems are discussed in the next section on

battery charge controllers. Battery manufactures often refer to three modes of battery

charging; normal or bulk charge, finishing or float charge and equalizing charge.

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2.8.1 BULK or NORMAL CHARGE:

Bulk or normal charging is the initial portion of a charging cycle, performed at any

charge rate which does not cause the cell voltage to exceed the gassing voltage. Bulk charging

generally occurs up to between 80 and 90% state of charge.

2.8.2 FLOAT or FINISHING CHARGE:

Once a battery is nearly fully charged, most of the active material in the battery has been

converted to its original form, and voltage or current regulation to limit the amount over

change supplied to the battery. Finish charging is usually conducted at low to medium charge

rates.

2.8.3 EQUALIZING CHARGE:

An equalizing or refreshing charge is used periodically to maintain consistency

among individual cells. An equalizing charge generally consists of a current-limited charge to

higher voltage limits then set for the finishing or float charge. For batteries deep discharged

on a daily basis, an equalizing charge is recommended every one or two weeks. For batteries

less severely discharged, equalizing may only be required every one or two months. An

equalizing charge is typically maintained until the cell voltage and specific gravities remain

consistent for a few hours.

2.9 BATTERY DISCHARGING:

2.9.1 DEPTH of DISCHARGE (DOD):

The depth of discharge (DOD) of a battery is defined as the percentage of capacity that

has been withdrawn from a battery compared to the total fully charged capacity. By

definition, the depth of discharge and state of discharge of battery add to 100 percent. The

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common qualifiers for depth of discharge in PV systems are the allowable or maximum DOD

and the average daily DOD and are described as follows.

2.9.2 ALLOWABLE DOD:

The maximum percentage of full-rated capacity that can be withdrawn from a battery is

known as its allowable depth of discharge. The allowable DOD is the maximum discharge

limit for a battery, generally dictated by the cutoff voltage and discharge rate. In stand alone

PV systems, the low voltage load disconnect (LVD) set point of the battery charge controller

dictates the allowable DOD limit at a given discharge rate. Furthermore, the allowable DOD

is generally a seasonal defect, resulting from low isolation, low temperatures and/or excessive

load usage. Depending on the type of battery used in a PV system, the design allowable depth

of discharge may be as high as 80% for deep cycle, motive power batteries, to as low as 15-

25% if SLI batteries are used. The allowable DOD is related to the autonomy, in terms of the

capacity required to operate the system loads for a given number of days without energy from

the PV array. A system design with a lower allowable DOD will result in a shorter autonomy

period. As discussed earlier, if the internal temperature of a battery reaches the freezing point

of the electrolyte, the electrolyte can freeze and expand, causing irreversible damage to the

battery. In a fully charged lead-acid battery, the electrolyte is approximately 35% by weight

and the freezing point is quite low (approximately -60c). As a lead-acid battery is discharged,

then becomes diluted, so the concentration of acid decreases and the concentration of water

increases as the freezing point.

2.9.3 AVERAGE DAILY DOD:

The average daily depth of discharge is the percentage of the full-rated capacity that is

withdrawn from a battery with the average daily load profile. If the load varies seasonally, for

example in a PV lightning system, the average daily DOD will be greater in the winter months

due to the longer nightly load operation period. For PV systems with a constant daily load, the

average daily DOD is generally in the winter due to lower battery temperature and lower rated

capacity.

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Depending on the rated capacity and the average daily load energy, the average daily DOD

may vary between only a few percent in systems designed with a lot autonomy, or as high as

50% for marginally sized battery systems. The average daily DOD is inversely related to

autonomy; meaning that systems designed for longer autonomy periods (more capacity) have

a lower average daily DOD.

BATTERY TROUBLES SUMMARIZED

A. Lack of Gassing:

Lack of gassing while on charge may indicate an internal short between plates, i.e.,

the cell discharges internally as fast as it is being charged.

B. Specific Gravity or Voltage

Specific gravity or voltage of a cell lower than other cells is an indication of

excessive internal losses and may result from consistent undercharging.

C. Color:

Color or appearance of plates or sediment different from other cells is

addressed below:

1. Patches of white lead sulfate on either the positive or negative plates:

caused by standing idle or undercharging for extended periods.

2. Antimony deposit dark-slate patches on negative plates (usually near the

terminal): caused by charging at too high a rate or an aged cell nearing

the end of its service life.

3. Top layer of sediment white: caused by undercharging.

4. Lumpy brown sediment: caused by overcharging.

5. All white sediment no visible layers: caused by overcharging after

prolonged low float voltage.

6. Large flaking on the interplate collector bar: caused by being on float

charge for extended periods at insufficient float voltage without

equalizing charging being performed.

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D. Plate Problems:

If any checks below are excessive, capacity tests must be run to determine if

individual cells or the entire battery should be replaced.

1. Cracks on the edges of the positive plate grids.

2. Light-colored sulfating spots on edges of plates below cracks mentioned

in check No. 1 above.

3. Excessive sediment in the bottom of the case.

4. “Mossing” or “treeing” on the tops of negative plates.

E. Water

1. Cell uses excessive water (check fig. 1 for typical water consumption):

caused by excess charging rates, high operating temperatures, or leaking

cell.

2. Cell requires very little water: caused by insufficient charging.

F. Buckling of Plates

Buckling of positive plates indicates excessive sulfation caused by

undercharging or excessive temperature.

G. Failure to Supply Rated Ampere-Hour Loads

Failure to supply rated ampere hours indicates discharged condition,

excessive sulfation, or loss of active material from positive plates. Cells may

be worn out or active material may be gone from positive plates.

H. Surface Charge Phenomenon

When a battery has been on float charge for a long time and is put under

load with the chargers off, the voltage will drop rapidly. This drop is caused

by plugging of some of the pores on the surface of the plates, which partially

blocks the transfer of ions. The voltage may drop below the low-voltage

alarm and trip settings. After this initial drop, the voltage will usually

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increase to a level above the low-voltage alarm and trip settings. The battery

will then operate normally until its capacity is exhausted.

If the battery is exercised (partially discharged) on a routine basis, the

voltage dip can be reduced or eliminated. Turning off both chargers and

allowing the battery to take the load for at least 15 minutes exercises the

battery. The first few times this procedure is performed, disconnect the low

voltage trip relay to prevent an inadvertent trip. The first time the battery is

exercised, the procedure should be performed several times in succession

until the voltage drop stays above the alarm setting. Always give the

chargers time to reduce charging current to float value before turning off the

chargers again for the next cycle.

Each battery has its own characteristics, and the frequency of exercising

should be adjusted so that the voltage drop does not cause the low voltage

alarm. Start at a monthly cycle and experiment with increasing the time

between exercises. The proper time between exercises exists when the

voltage drop is just above the alarm relay setting.

2.10 BATTERY MAINTENANCE:

The maintenance requirement for batteries varies significantly depending on the

battery design and application. Maintenance consideration may include cleaning of cases,

cables and terminals, tightening terminals, water addition, and performance checks.

Performance checks may include specific gravity recording. Conductance readings,

temperature measurements, cell voltage readings, or even a capacity test. Battery voltage and

current readings during charging can aid in determining whether the battery charge controller

is operating properly. If application, auxiliary system such as ventilation, fire extinguishers

and safety equipment may need to be inspected periodically. Generally speaking, flooded

lead-antimony batteries required the most maintenance in terms of water additions and

cleaning. Sealed lead-acid batteries including gelled and AGM types remain relatively clean

during operation and do not require water additions. Battery manufactures often provide

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maintenance recommendations for the use of their battery. Battery test equipment the ability

to measure and diagnose battery performance is an invaluable aid to users and operators of

stand-alone PV systems. Following are two of the more common instruments used to test

batteries. Hydrometer is an instrument used to measure the specific gravity of a solution

density to the density of water. While the specific gravity of the electrolyte can be estimated

from open circuit voltage readings, a hydrometer provides a much more accurate measure. As

discussed previously, the specific gravity of the electrolyte is related to the battery state of

charge I Lead-acid batteries. Hydrometers may be constructed with a float ball using

Archimedes principle, or with a prism measuring the refractive index of the solution to

determine specific gravity. In an

Archimedes hydrometer, a bulb-type syringe extracts electrolyte, a precision glass float

in the bulb is subjected to a buoyant force equivalent to the weight of the electrolyte

displaced. Graduations are marked on the sides of the glass float, calibrated to read specific

gravity directly. Hydrometer floats are only calibrated to give true readings at a specific

temperature, typically 26.7c (80F). When measurements are taken from electrolyte at other

temperature, a correction factor must be applied. Regardless of the reference temperature of

the hydrometer, a standard correction factor 0.04 specific gravity units, often referred to as

“points”, must be applied for every 5.5c (10F) change from the reference temperature. Four

“points” of specific gravity (0.004) are added to the hydrometer reading for every 5.5c (10F)

increment above the reference temperature and four points are subtracted for every 5.5c (10F)

increment below the reference temperature, when taking specific gravity measurements of

batteries.

2.11 BATTERY SAFETY CONSIDERATIONS:

Due to the hazardous materials and chemicals involved, and the amount of electrical

energy which they store, batteries are potentially dangerous and must be handled and used

with caution. Typical batteries used in stand-alone PV systems can deliver upto several

thousand amps under short-circuit conditions, requiring special precautions. Depending on the

size and location of a battery installation, certain safety precautions are be required.

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2.12 CARE, CLEANLINESS AND SAFETY OF B ATTERIES:

1. MAINTAINANCE:

Keep the battery room well ventilated.

● Keep the battery and its surroundings dry and clean.

Check and keep the electrical connections always tight.

Always keep top surface of the battery clean and dry.

Cell connections shall be kept clean and applied with Vaseline or petroleum jelly.

Remove traces of corrosion promptly by cleaning with distilled water.

Metal vessels should not be used for topping up.

Wearing of apron and rubber gloves should be taken when handling electrolyte.

● Care must be taken when doing maintenance on connectors to avoid short circuits.

● Naked lights, cigarette smoking any thing create spark should be avoided in battery room.

2. TEMPERATURE CORRECTION:

● If the temperature is different from 27degree centigrade correction to specific gravity to

be applied is +/- 0.0007 per each degree of variation above or below 27 degree c respectively.

3. TOPPING UP:

● Top up as often as necessary with distilled water (as per IS:1069) or demineralised water

to avoid the necessary of adding a large quantity of water at a time which would caused

renounce ropin he specific gravity.

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● Top up the black mark of the float is just visible above the top surface of the float guide

and level should never be allower to go slow that the red mark on the float steer comes in line

with the top surface of the plug.

● It is advisable, if necessary to top up cells during early part of charging

4. WEAK CELLS:

● Cells which do not pick up specific gravity in spite of repeated charging are

called weak cells. The weak cells must be removed from battery and charged separately at

normal charging rate until gassing point is reached and then reduced to half the normal rate

● When the cells appear to be in fully charged condition i.e.., specific gravity of the acid

seems to be stationary, the charging should be stopped for an hour and then be resumed as

half the normal rate until free gassings again takes place. Again after another one hour stop,

charging should be resumed at half the normal rate. These stops of one hour duration

alternated by charging should be repeated until gassing starts instantaneously with switching

on the charging current.

5. RECOMMENDED ACTIONS

If any cells seem to be in trouble, the whole battery should be given an

equalizing charge and then specific gravity readings should be taken on all

cells. If all cells gas evenly and specific gravity of every cell is normal, all the

battery needed was the charge. Otherwise, all low gravities should be

recorded, and an extra thorough charge, should be given. The temperature of all cells should

be compared by thermometer or IR camera with the rest of the cells. Sulfated cells will run

hot enough tocause damage if not corrected. Any cells that still will not gas with the extra

charging should be investigated for impurities and inspected for internal short circuits.

If this standard does not help solve a problem, record the voltage of each cell and the

specific gravity of 10 percent of all the cells. Also, record the electrolyte temperature and the

ambient temperature, then contact the battery

manufacturer for assistance.

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6. CAUTION:

● While preparing the acid solution, it is very much important to note that always acid is

added to the water and never add water to the acid.

CHAPTER-3

3.1 GENERAL DESCRIPTION:

The system basically consists of one float charger, one boost charger, interlocking

contractor with float/boost selector switch, tap cell diode and dc distribution board. Both the

float and booster are similar in nature and works on the same principle. Each charger

consisting of one three phase double wound charger input transformer, rectifier power bridge,

LCA filter circuit and charger control circuit.

The system can be operated to supply load at float voltage and simultaneously to

charge the batteries in charge mode. Naturally float charger is made on, supplying both load

and battery trickle charging current. Naturally float charger is made on, supplying both load

and battery trickle charging current. Whenever battery requires boost charging, the same can

be achieved manually by throwing FLOAT/BOOST selector switch (SW 502) cin to boost

position. During this operation, the interlocking contactor is opened separating load path and

battery charging path. The boost charger is provided with charge and extended charge modes

to charge the battery. The charge and ext charge modes can be selected using the charge/ext

charge selector switch (SW 501).

The battery charger works on 415v AC, 3 phase, 50hz supply. The chargers are capable

of supplying the full rated current at the specified voltage at its output terminals. This voltage

is maintained for AC input variation of +/- 10% and load current variation from 10-100% full

load.The float charger and booster charger are housed in a single cabinet and the DC

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distribution is provided in another cabinet of steel construction. All the meters and meter

selector switches are provided on the top meter panel. All the incoming and outgoing breakers

are provided on the breaker panels which are provided on the middle of the cabinet. By

opening the middle panel door one can reach the breakers easily. All the indications are

provided on the top panel of the cabinet. By opening the middle panel door can reach the

breakers easily. All the indications are provided on the top panel of the cabinet. The input,

output and batter input terminals are provided at the front bottom of the cubicle. The outgoing

feeder switches are provided on the DCDB panel and all the output. Output feeders

terminations are provided on the DCDB side panel of the cabinet.

3.2 TECHNICAL SPECIFICATIONS:

TYPE :FLOAT AND BOOST CHARGER AND DCDB

FULL WAVE HALF CONTROLLED TYPE

RATINGS :220V/45A FC and 220V/50A BC.

1. AC INPUT: a. Voltage : 415V AC (+/-) 10%

b. Frequency : 50hz, (+/-) 5%

c. Phase : 3 phase, 4 wire

2. DC OUTPUT:

a. Float charger:

1. Voltage : 237V DC

2. Regulation : (+/-) 1% of set value

3. ripple : 2% rms

4. Current : 45A

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b. Boost charger:

1.Voltage:

1.Charge mode : 258V Dc

2. Extended charge mode : 297V Dc

2.Regulation : (+/-) 1% of set value 3. Ripple : 2% rms

4. Current : 50A

C.System Output : Max. 237vDC

3. METERS : Following the analog type meters of 1444*144 with 90

Deg. Deflection are provided in the system for Measuring

the respective parameters

1. DC Voltmeter with selector switch

2. DC Ammeter for both FC&BC

3. Battery Charge/Discharge Ammeter

4. A Voltmeter with selector switch

5. Earth leakage ammeter

4. INDICATIONS: 1. Neon lamps are provided at AC input

2. Long life LED indications are provided for the

Following condition with audio alarm for abnormal

Condition

1. In both FC&BC

a. AC input fuse fail

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b. DC output fuse fail

c. Charger fuse fail

d. AC over load trip/phase fail

e. Charger fail

f. AC contact ON

g. Filter cap fuse f

2.Common:

a. AC mains

b. DC over voltage

c .DC under voltage

d. DC earth fault

e. DC contractor ON

5. PROTECTION: Following protections are provided in the system

1. AC input fuses for both FC & BC

2. DC output fuses for both FC & BC

3. Fast semiconductor fuses for both FC & BC

4. over voltage cutback protection

5. Charger over load protection

6. Thermal over load relay with single phasing protection

At AC input of both FC&FCBC

7. Battery input fuses

8. Filter cap fuses

9.DC MCCB at battery input

6. CONTROLS & SWITCHES :

1. AC input MCB for both FC & FCBC

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2.AC input contractor ON/OFF switch for Both FC&FCBC

3. DC output MCB for both FC & FCBC

4. Float voltage variable potentiometer for FC

5. Charge & extend charge voltage variable Potentiometers

6. Lamp test push button

7. Alarm silence push button

8. Heater power supply switch

9. Door lamp power supply switch

10. AC output power supply switch

11. Battery input MCCB

12. charger/EX. Charger mode selector switch

7.SPECIAL FEATURES : The following features are provided in the

system

1. Soft start on DC side

2. Class-F insulation for all magnetics.

8. DC DISTRIBUTION BOARD:

Incoming: 200A, 2pole ON/OFF switch-1 No.

200A, fuse with fuse base -2 No.s

Outgoing : 10A, 2poles ON/OFF switch -16NO.s

10A, fuse with fuse base -32No.s

20A, 2pole ON/OFF switch -8No.s

20A, fuse with fuse base -16No.s

Indication: All the incoming outgoing feeders are provided With ON indication

9. GENERAL:

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1. Cabinet: 2 No’s individual cabinets for charger and DCCB

Free standing cabinet, floor mounting type, and

sheet Steel construction, easy access for

installation And maintenance

2. Paint: light gray of IS 5-631 Shade

3. Dimensions ( in mm ) :

a) Charger : 1800(H) X 1225 (W) X 850 (D)

d) DCCB : 1800 (H) X 875 (W) X 880 (D)

4. Protection : IP-42

5. Ambient temperature :0-50c

Range of operation.

6. Relative humidity : 0-95% non condensing

3.3 SYSTEM THEORY OF OPERATION:

The system consists of one Float charger, one Boost charger, interlocking circuit and

DCDB. Both the chargers are similar in nature and works on the same principle. The Chargers

are designed using SCR/Diode full wave half controlled bridge of constant Potential type,

these charges are rated to meet the requirement offload and Battery. Each Charger consists of

common interlocking circuit. For clear understanding of system Description refers schematic

Drawing.

Both the chargers are connected to the common AC input through AC input contactor,

Thermal overload relay and input MCBs CB401/501. The input transformer T 401/501 is

having two secondaries namely power secondary and control secondary. The transformer

Steps down the incoming AC into required level and feeds it the rectifier bridge through

power secondary. The control secondary which feeds power supply to the charger control

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Board PC 401/501, which provides regulation and current limit to the charger. In addition it

supplies gate pulses to the power SCRs SCR 401-403/501-503. The filter circuit boards PC

402,502 are capacitive filter boards which protects the system from surges and Transients at

AC input.

Proper operation of the charger is a matter of carefully determining the precise

moment to fire the SCRs by supplying the proper gate pulses to SCRs. This function is

accomplished by the charger control board PC 401/501. The control board PC 401/501

Detects the zero cross overs (-ve to +ve) of these coltage wave forms and send the gate Pulses

to SCRs at appropriate timings.

The output voltage feed back is given to the charger control board PC 401/501, which

Changes the firing angles to the SCRs in such a way that the output DC voltage should be

maintained at set value. This regulated DC output DC voltage can be set by using the

Float/Boost voltage adjustment potentiometers R 401/501/502.

The shun SH401/501 provides the current feed back to the charger control board PC

401/501 which causes the unit to go into current limit beyond the set value. This

characteristics causes the unit to go into current limit beyond the set value. This

characteristics causes the output to the reduced when the battery is run down, so as to

maintain a constant level of charging current.

The meters M401/501 monitors the DC output current through DC shunts SH401/501.

The center zero ammeter M 2 monitors the battery charging discharging currents respectively.

The voltmeter M 1 with selector switch SW1 measures the FC,BC, load and Battery voltages

respectively. The battery earth leakage Ammeter M 1 monitors the battery +ve Earth leakage

milliamps respectively. The AC input voltmeter M402 measures AC input line to line and line

to neutral voltage based on switch position.

23

The 408/508 is an alarm indication board, this circuit consists trigger pulse is also

generated and this actuates the alarm. The fault is reset using the front panel alarm reset push

button. The 12v DC is generated within the board.

The battery bank is connected to the DC bus through battery input circuit breaker and

contactor CON1. Also 105 cells are connected to positive DC bus through diodes D-1.

3.4 INTER LOCKING CONTACTOR (CON-1) OPERATION:

Provision is made to close the CON-1 for various conditions of operation. The

contractor operates on battery through potential free contacts of BC and FC input contractors.

The precautions are taken for the following conditions.

1. If both FC and BC AC input failed, the contactor energizes through the float/boost

selector switch SW 502 and connects the total battery bank to load through the

interlocking contactor CON-1.

2. When BC is supplying Battery charging requirement, if FC falls, the load will be

connected to tap cell (105th cell) of the Battery Bank.

3. When both the charges are ON, if Boost charger fails the Float charger will be

automatically connected to Battery bus and Float charges the battery through

interlocking contactor CON-1.

3.5 PRINCIPLE OF OPERATION:

During normal operation, the Float/Boost selector switch SW 502 is in Float position.

The Float charger supplies load current as well as trickle (float) current to the battery. At this

stage the Boost charger is made OFF and no boost charger output will be available. The

switch SW 501 in BC is kept in charge/ext. charge mode to select the battery charging mode

24

manually based on battery condition. The battery is connected to the DC bus through

contactor CON-1.

When the Battery needs charge/ex. Charge charging the same can be achieved by

throwing the Float/Boost selector switch to boost position. When the Battery is fully charged

and the charging current comes down in meter M1 the Boost charger should be switched OFF

by switching back the float/boost selector switch to float position.

3.6 PROTECTIONS:

3.6.1 DC OVER LOAD/ SHORT CIRCUIT PROTECTION:

Both the chargers (FC & BC) are current limited at 105% The meters M401/501

provides the current feedback to the control board PC 401/501 which causes the unit to go

into current limit beyond the set value. Whenever the current exceeds the set point the control

board PC 401/501 senses this over load and reduces the output DC voltage. So that the output

current does not exceed the limited value.

3.6.2 OVER VOLTAGE PROTECTION:

The charger control board PC 401/501 is having built in over voltage protection for

any failure in regulating circuit. In this the operational amplifier compares the output voltage

over a reference voltage. If the output voltage is more than the set one, the OP,AMP. Inhibits

the firing pulses to the charger SCRs. Thus avoiding over voltage at Charger output. Thus the

output voltage never goes beyond a set value. The reference voltage is set at factory.

3.6.3 SOFT START:

25

The equipment is provided with soft start feature and this makes the DC output

voltage to rise gradually to its rated value over duration of 6-10seconds. Whenever the

charger is powered or at the time of restoration of mains failure. This avoids the sudden

application of full voltage to the drained battery and DC capacitors.

3.6.4 AC OVER LOAD PROTECTION:

The system is provided with Thermal over Load relay at its AC input which is interfaced

with the AC input contactor. Normally the over Load Relay is in OFF condition. Whenever

the system AC input is over loaded this AC input over Load Relay operates which in turn

deenergises the AC input contactor and thus no AC input is available to system input. Thus

the system is protected from AC input over load.

3.7 GENERAL PROTECTIONS:

The following components are provided for different protections.

3.8 MAINTAINENCE:

Battery charger units ordinarily require very little routine maintenance occasionally

the customer may give the unit a visual inspection every six months or so to locate

components which may be over heating.

Components located for use in charges are of very high quantity and are

conservatively applied so they should last a very long time is no needs for periodic

replacement of any component since the problem associated with infant mortality failures are

likely to be greater than the failures of components due to again.

26

The system operating conditions are brought out on the front panel for continuous

monitoring whenever fault conditions occur the corrective steps should be followed

immediately to bring the system back to normal operation.

However, the following general checks may be carried out once in three months for

smooth running of the system.

Measuring the charge level

A hydrometer can be used to test the specific gravity of each cell as a measure

of its state of charge.

Because the electrolyte takes part in the charge-discharge reaction, this battery

has one major advantage over other chemistries. It is relatively simple to determine the state

of charge by merely measuring the specific gravity (S.G.) of the electrolyte, the S.G. falling as

the battery discharges. Some battery designs include a simple hydrometer using colored

floating balls of differing density. When used in diesel-electric submarines, the S.G. was

regularly measured and written on a blackboard in the control room to indicate how much

longer the boat could remain submerged.

27

BATTERY SAFETY EXPLOSIVE HAZARD All storage batteries give off a highly explosive mixture of hydrogen and

Oxygen when gassing. Therefore, never permit sparks, open flame, or lighted

cigarettes near a storage battery. Post "No Smoking" signs where they are clearly

visible to anyone entering the battery room area. A nonmetallic flashlight is

desirable for battery inspection. Use only alcohol thermometers when

taking electrolyte temperatures. Keep all battery connections tight to avoid

sparking. Never lay any metallic object on top of a battery.

A class C 10pound fire extinguisher should be mounted just inside the battery room

door. Carbon dioxide (CO2) is not recommended because of the potential

for thermal shock to the batteries.

ELECTROLYTE HAZARD

When handling electrolyte, wear face shields (face shields should not have

metal reinforcing rims, which could cause a battery short if dropped), rubber

aprons, and rubber gloves; avoid splashes. The electrolyte is injurious to

skin and clothing and must therefore always be handled carefully. The eyes

in particular should be guarded. If acid is splashed into the eyes or

anywhere on the skin, flood with water for at least 15 minutes and get

medical attention. Do not use bicarbonate of soda on the skin, which may

aggravate the burn. For neutralization of acid electrolyte spilled on the floor

or rack, a bicarbonate of soda solution—1 pound per gallon of water—is

28

recommended.

For neutralization of ni-cad battery electrolyte (potassium hydroxide), keep

a concentrated solution of 20 ounces of boric acid powder per gallon of

water available for neutralizing spills on skin or clothing. Use plain water to

wash up spills of potassium hydroxide on the cells or racks. Care must be

taken to prevent the solution from getting into the cells.

A combination eye-wash, face, and body spray unit must be located within

25 feet of each battery room or battery system. These units can be

permanently mounted and connected to the facility's potable water system

or can be of a portable pressurized type.

FLAME ARRESTERS PURPOSE AND CLEANING

Article 480-9 of the National Electric Code requires each vented battery cell

to be equipped with a flame arrester designed to prevent destruction of the

cell attributable to an ignition of gases outside the cell.

The diffuser material of flame arresters can become partially clogged from

electrolyte spray if cells are overfilled with water or have been excessively

overcharged. Flame arresters should therefore be inspected annually, and all

arresters having clogged pores should be replaced or cleaned as follows:

Immerse the flame arrester several times in fresh water in a plastic

bucket.

Eject the water after each immersion by vigorous shaking or an air blast.

Dump and refill the bucket with clean water for every 15 flame arresters

that are cleaned.

Do not use any cleaning or neutralizing agents in the water because any

dry residue may clog the pores of the diffuser materials.

29

VENTILATION A determination must be made for each battery area as to whether sufficient

ventilation is being provided to ensure adequate diffusion of hydrogen gas

during maximum gas generating conditions. Such determination can be

made from the following data:

1) When the battery is fully charged, each charging ampere supplied to the

cell produces about 0.016 cubic feet of hydrogen per hour from each cell.

2) This rate of production applies at sea level, when the ambient

temperature is about 77 EF, and when the electrolyte is "gassing or

bubbling."

3) Number of battery cells and maximum charging rate (not float rate) can

be obtained from specifications or field inspection.

4) Hydrogen gas lower explosive limit is 4 percent by volume. Good practice

dictates a safety factor of 5, which reduces the critical concentration to

0.8 percent by volume. This large safety factor is to allow for hydrogen

production variations with changes in temperature, battery room

elevation, and barometric pressure and also allows for deterioration in

ventilation systems.

ELIMINATION OF OVER SULFATION

A battery or cell that is "over sulfated" should be charged fully in the regular

way until specific gravity stops rising. Then one of the weakest cells should

be discharged through a load resistor at the normal 8-hour discharge rate to

30

a final voltage of 1.75 volts. The battery is not over sulfated if the

representative cell gives normal capacity, that is, about 100 percent rated

capacity for a fairly new battery or down to 80 percent of initial rated

capacity for a battery nearing the end of its expected life.

If the above capacity is not obtained, possible over sulfation should be

treated as follows:

In cases where one or more individual cells have become "over sulfated"

and the rest of the battery is in good condition, these cells should be

treated separately after removing them from the circuit.

Recharge the removed cells at half the 8-hour discharge rate. Record

Hydrometer readings and temperature at regular intervals (3 to 5 hours)

during the charge to determine if rising specific gravity has peaked.

Maintain constant electrolyte level by adding water after each reading.

Do not add water before taking readings.

Continue the charge, recording the readings until no further specific

gravity rise has occurred in any cell for 10 hours. If the temperature

reaches 100 °F, reduce the current or temporarily interrupt the charge so

as not to exceed this temperature. When the specific gravity has reached

maximum, terminate the charge and record the hydrometer reading of

each cell.

The cells must be replaced if they again fail the capacity

31

32

CHAPTER-IV

4.1 STORAGE CELLS-DEFINITION:

The function of ‘storage’ cells is to convert electrical energy into chemical energy

during the process known as ‘charging’ and the reverse of it when ‘discharging’.

During charging of the cell, when current is passed through it, certain chemical

changes take place in the active materials of the cell. Such chemical changes absorb energy

during their formation. When these chemical reactions are completed and the electric current

produces no further chemical changes, the cell is said to be fully charged.

When the cell is next connected to an external circuit, the active materials of the cell

revert to their original condition, thereby reversing the changes which occurred during

charging. In this process of undoing the chemical changes, absorbed energy is released in the

form of electric current, the process being known as discharging.

It should be noted that the cell does not ‘store’ electricity as such but absorbs electric

energy in the form of chemical energy, the whole process being reversible.

We will discuss two types of storage cells or accumulators or secondary cells i.e.

Lead-acid cell and Edison alkali cell.

4.2 CHEMICAL CHANGES:

Following chemical changes take place during the charging and discharging of a lead-

acid cell.

When the cell is fully charged, its positive plate or anode is PbO2 (dark chocolate

brown) and the negative plate or cathode is Pb (slate grey). When the cell discharges i.e. it

sends current through the external load, then H2SO4 is dissociated into positive H2 ions and

negative SO4 ions. As the current within the cell is flowing from cathode to anode, H2 ions

move to anode and SO4 ions move to the cathode.

33

At anode (PbO2), H2 combines with the oxygen of PbO2 and H2SO4 attacks lead to

form PbSO4

PbO2 + H2 + H2SO4 PbSO4 + 2H2O

At the cathode (Pb), SO4 combines with it to form PbSO4

Pb+SO4 PbSO4

It will be noted that during discharging,

1. Both anode and cathode become PbSO4 which is somewhat whitish in colour

2. Due to formation of water, specific gravity of the acid decreases.

3. Voltage of the cell decreases.

4. The cell gives out energy.

4.3 TWO EFFICIENCIES OF THE CELL:

The efficiency of a cell be considered in two ways:

1. The quantity or ampere-hour (Ah) efficiency

2. The energy or watt-hour (Wh) efficiency.

The Ah efficiency does not take into account the varying voltages of charge and

discharge. The Wh efficiency does so and is always less Ah efficiency because

average p.d.during discharging is less than that during charging. Usually, during

discharge, the e.m.f.falls from about 2.1V to 1.8V whereas during charges, it rises

from 1.8 volts to about 2.6V.

• Ah.eff. = ampere – hours on discharge /Ampere – hours on charge

34

The Ah efficiency of a lead-acid cell is normally between 90 to 95% meaning

that about 100 Ah must be put back into the cell for every 90 – 95 taken out of it.

If Ah efficiency is given, Wh efficiency can be found from the following relation:

Wh efficiency = Ah efficiency X average volts on discharge / Average volts on charge

The Wh efficiency varies between 72-80%

From the above, it is clear that anything that increases the charge volts or reduces the

discharge volts will decrease Wh efficiency. Because high charge and discharge rates will do

this, it is advisable to avoid these.

4.4 ELECTRICAL CHARACTERISTICS OF THE LEAD-ACID CELL:

The three important features of an accumulator, of interest to an engineer, are (i)

voltage, (ii) capacity and (iii) efficiency.

4.4.1 Voltage.

The open-circuit voltage of a fully-charged cell is approximately 2.1 volts. This value

is not fixed but depends on (a) length of time since it was last charged (b) specific

gravity-voltage increasing with increase in specific gravity and vice-versa. If specific

gravity comes near to density of water i.e. 1.00, then voltage of the cell will disappear

altogether (c) temperature-voltage increases (through not much) with increase in

temperature.

35

CHARGE AND DISCHARGE VOLTAGE CURVES:

The variation in the terminal p.d. of a cell on charge and discharge are shown in

Fig. The voltage fall depends on the rate of discharge. Rates of discharge are

generally specified by the number of hours during which the cell will sustain the rate

in question before falling to 1.8V. The voltage falls rapidly in the beginning (rate of

fall in the beginning on the rate of discharge), then very slowly up to 1.85 V and

again suddenly to 1.8 V. The voltage should not be allowed to fall to lower than 1.8 V,

other wise hard insoluble lead sulphate is formed on the plates which increases the

internal resistance of the cell.

The general form of the voltage-time curves corresponding to 1-,3-,5- and 10-

hour rates of discharge, are shown in Fig. corresponding to the steady currents which

would discharge the cell in the above mentioned times (in hours). It will be seen that

both the terminal voltage and the rate at which the voltage falls depends on the rate of

discharge. The more rapid fall in voltage at higher rates of discharge is due to rapid

increase in the internal resistance of the cell.

During charging, the p.d. increases (Fig. ). The curve is similar to the discharge

curve reversed but is every where higher due to the increased density of H2SO4 in the

pores of the positive plates.

36

4.4.2 Capacity :

It is measured in ampere-hours (Ah). One ampere-hour (Ah) is the amount of

electricity conveyed by one ampere in one hour.

The capacity is always given at a specified rate of discharge (10-hour

discharge in U.K., 8-hour discharge in U.S.A.). The capacity of a cell depends on the

amount of the active material on its plates. In other words, it depends on the size and

thickness of the plates However, for a given battery , the capacity is affected by the

following factors:

(1)_Rate of Discharge. The capacity of a cell, as measured in Ah, depends on

the discharge rate. It decreases with increased rate of discharge. Rapid rate of

discharge means greater fall in p.d. of the cell due to internal resistance of the

cell. Moreover, with rapid discharge, the weakening of the acid in the pores of

the plates is also greater. Hence, the chemical change produced at the plates by

1 amperes for 10 hours is not the same as produced by 2 amperes for 5 hours of

4 amperes for 2.5 hours. It is found that a cell having a 100 Ah capacity at 10-

hour discharge rate, has its capacity reduced to 82.5 Ah at 5-hour rate and

50Ah at 1-hour rate. The variation of capacity with discharge rate is shown in

Fig.

37

(2) TEMPERATURE:

Capacity increases with increase in temperature, the increase in capacity being more

marked at higher rates of discharge. This is due to the fact that at higher temperatures

Chemical action is more vigorous, (b) the résistance of the acid decrease and (c) there is better

diffusion of the electrolyte.

With decrease in temperature, available voltage and capacity decrease until at

freezing point, the capacity is zero even when the cell is fully charged.

(3) DENSITY OF ELECTROLYTE:

As the density of electrolyte affects the internal resistance and the vigor of chemical

reaction, it has important effect on the capacity. Capacity increase with the density

4.5 INDICATIONS OF A FULLY – CHARGED CELL:

The indication of a fully-charged cell is:

1. Gassing

2. Voltage

38

3. Specific gravity

4. color of plates.

4.5.1 Gassing

When the cell is fully charged, it freely gives off hydrogen at cathode and oxygen

at the anode, the process being known as ‘gassing’. Gassing at both plates indicates

that the current is no longer doing any useful work and hence should be stopped.

4.5.2 Voltage

The voltage ceases to rise when the cell becomes fully charged. The value of

the voltage of a fully-charged cell is a variable quantity being affected by the rate of

charging, the temperature and specific gravity of the electrolyte etc. The approximate

value of the e.m.f. is 2.1 V or so.

4.5.3 Specific Gravity of the Electrolyte

A third indication of the state of charge of a battery is given by the specific

gravity of the electrolyte. We have seen from the chemical equations of that during

discharging, the density of electrolyte decreases due to the production of water,

whereas it increases during charging due to the absorption of water. The value of

density when the cell is fully charged is 1.21 and 1.18 when discharged up to1.8 V.

Specific gravity can be measured with a suitable hydrometer.

4.5.4 Color

The color of plates, on full charge, is deep chocolate brown for positive plates

and slate grey for negative plates and the cell looks quite brisk and alive.

39

4.6 APPLICATIONS OF LEAD-ACID BATTERIES:

Storage batteries are, these days, used for a great variety and range of purposes, some

of which are summarized below:

1. In central stations for supplying the whole load during light load periods, also to

assist the generating plant during peak load periods for providing reserve

emergency supply during periods of plant breakdown and finally, to store energy

at times when load is light for use at times when load is at its peak value.

2. In private generating plants both for industrial and domestic use, for much the

same purpose as in Central Stations.

3. In sub-stations, they assist in maintaining the declared voltage by meeting a part

of the demand and so reducing the load on and the voltage drop in the feeder

during peak-load periods.

4. As a power source for industrial and mining battery locomotives and for road

vehicles like cars and trucks.

5. As a power source for submarines when submerged.

6. For petrol motor-car starting and ignition etc.

7. As a low-voltage supply for operating purpose in many different ways such as

high-tension switchgear, automatic telephone exchange and repeater stations,

broadcasting stations and for wireless receiving sets.

8. Semi-sealed portable lead-acid batteries find many applications such as in

electronic cash registers, alarm systems, cordless TV sets, mini-computers and

terminals, electronically-controlled petrol pumps, portable instruments and tools

etc.

40

4.7 COMMON BATTERY TERMS:

4.7.1 Cell:

A cell is a device that transforms chemical energy into electrical energy. The simplest

cell is a voltaic cell shown in Fig. 3.5. It consists of a carbon strip and a zinc strip suspended

in a jar containing a solution of water (H2 O) and sulphuric acid (H2SO4).

A cell is fundamental unit of a battery. The cell shown in fig consists of two strips or electrodes placed in the jar which also contains the electrolyte. The electrolyte in a battery can be in the form of either a liquid or a paste.

4.7.2 ELECTRODES:

Electrodes are conductors through which current leaves or returns to the electrolyte.

In a simple cell they are copper and zinc strips that are immersed in the electrolyte, where as

in a dry cell they are a carbon strip in the centre and a zinc container in which the cell is

assembled.

41

4.7.3 ELECTROLYTE:

The electrolyte is the solution in which the chemical action called electrolysis

occurs. The electrolyte be a salt (example: sodium chloride), an acid (example: Sulphuric acid

or an alkaline solution. In the simple voltaic cell and in the battery, the electrolyte is in liquid

form, whereas in dry cell, the electrolyte is a paste.

4.8 SERIES AND PARLLEL COMBINATION OF CELLS:

In many cases, a battery operated device may require energy more then what one

cell can provide. The device may require either a higher voltage or higher current or in some

cases both. Under such conditions, it is necessary to connect more cells to meet the

requirement. If a higher is needed, cells are connected in series. They are connected in parallel

42

if higher current is desired. To supply both higher voltage and current, they are connected in

combinations of series – parallel networks.

4.8.1 Series connection of cells:

In a series connection, the cathode of the first cell is connected to the anode of the

second cell, the cathode of the second cell to the anode of the third cell and so on

Fig (a)

43

Fig (a) pictorial view of series connected cells

(b) Schematic diagram of the series connection

Let n be the number of cells connected in series,

E be the emf of one cell.

r be the internal resistance of one cell, and

R be the load resistance.

Then,

the total emf of the battery of n cells = nE volts

The total internal resistance of n cells = nr ohms

Therefore ,

total resistance of the circuit = R + nr ohms

Hence,

the current in the circuit I = nE / (R + nr) amperes

44

In this type of a circuit, the maximum current flow depends on the internal resistance

of the battery.

When the internal resistance is minimum, the current will be maximum.

4.8.2 PARALLEL CONNECTION OF CELLS:

In a parallel connection of cells, all cathodes are connected are connected to one line

and all the nodes to another line, as shown in fig.. Therefore, the emf of the combination is

the same as the emf of one cell. The equivalent internal resistance of the battery is r/n, which

comes in series with the load resistance(R).

45

Figure (a) pictorial view of parallel connected cells.

(b) Schematic diagram of the parallel connection

Therefore, the total resistance = R + (r/n) ohms

Hence, the current in circuit I = nE/(nr + r ) A

4.8.3 SERIES – PARLLEL CONNECTION OF CELLS:

Generally, in series – parallel combination of cells, first a certain number of cells

are connected in series and a few such series combinations are then connected in parallel as

shown in fig(a)

46

SERIES-PARALLE CONNECTION OF CELLS fig (a)

If n cells are connected in a series circuit, and if m such series circuits are connected in

parallel, then

The internal resistance of each series circuit = nr ohms

The total internal resistance of parallel circuit = nr/m ohms

Therefore

The total resistance of the circuit = (R + nr/ m) ohms

the emf across the circuit = mf of the series circuit

= nE volts

Therefore the current in the circuit = I = nE/(R + nr/m) amperes

i.e. I = mnE/(mR+nr) amperes

from this equation it can be seen that the numerator is a constant . therefore, the

current in the circuit will be maxim only if the denominator is minimum . The denominator

47

will have a minimum value if mR=nr or R=nr/m, i.e., when the load resistance is equal to the

internal resistance of the battery

]

48

CONCLUSION The battery system is heart of system any electrical control system because the

supply is fed from batteries for protection purpose for emergency ledio pumps etc, during

critical condition i.e., total grid failure.

If the battery system is failed, then the damage in the electrical system will be very

very high so there are to be maintains very carefully. It is also learnt various maintenance free

type battery system available however in power plant only lead-acid maintenance type is

preferred because its reliability, short term rating and rugged construction.

49

BIBLIOGRAPHY:

1. Baldsing, et.al.”Lead-Acid Batteries for Remote Area Energy Storage”, CSIRO

Australia, January 1991.

2. Institute of Electrical and Electronics Engineers, ”IEEE Recommended practice for

installation and operation of Lead-Acid Batteries for photovoltaic(pv) systems” ,

ANSI/IEEE Std. 937-1987, New York, NY, 1987.

3. Linden, “Handbook of Batteries and Fuel cells”,Mc Graw Hill, Inc., 1984

4. Vinal,”storage Batteries”, John Wiley & sons, inc., Fourth Edition, 1954.

5. IEEE 485-1983—Recommended Practice for Sizing Large Lead Storage Batteries for

Generating Stations and Substations

6. *IEEE 450-1995—Recommended Practice for Maintenance,Testing,and

Vented Lead-Acid Batteries for Stationary Applications

50