Unit V Electrical Installations

Components of LT Switchgear
Fuse: A short piece of metal wire, inserted in series with the circuit, which melts when predetermined valueof current
flow through it and breaks the circuit, is called a fuse.
 A fuse is connected in series as shown in below figure with the circuit to be protected and carries the load
currentwithout overheating itself under normal conditions.
 However, when abnormal condition occurs, an excessive current (more or equal to the predeterminedvalue
for which the fuse is designed) flows through it.
 This raises the temperature of fuse wire to the extent that it melts and opens the circuit. This protects thethe
machines or apparatus from damage which can be caused by the excessive current.

SWITCH FUSE UNIT (SFU): Switch fuse unit comprises of various porcelain rewireable fuses or HRC (High
Rupturing Capacity) complete with their conducting parts. The switch is fitted with sturdy side operatinghandle with
quick break type mechanism as shown in figure below.

Contacts are made of electrolytic copper silver-plated. The fixed contacts are provided with removable shield.Switch
Fuse Units are provided with rewireable fuse or HRC fuse links. All these parts are assembled in an enclosure. The
enclosure is made of sheet steel duly phosphatised and powder coated. They are provided withconduit knock-outs.
Door inter-clock is provided to prevent opening when the switch is ‘ON’ condition.
Miniature Circuit Breaker (MCB):
 MCB is a device that provides definite protection to the wiring installations and sophisticated equipmentagainst
over currents and short-circuits faults.
 Thermal operation (overload protection) is achieved with a bimetallic strip, which deflects when heatedby any
overcurrents flowing through it. In doing so, releases the latch mechanism and causes the contacts to open.
 Inverse time-current characteristics result, i.e. greater the overload or excessive current, shorter the timerequired
to operate the MCB. On the occurrence of a short circuit, the rising current energizes the solenoid, operating the
plunger to strike the trip lever causing immediate release of the latch mechanism. Rapidity of the magnetic
solenoid operation causes instantaneous opening of contacts.
 Miniature circuit breakers are available with different current ratings of 0.5, 1, 2, 2.5, 3, 4, 5, 6, 7.5, 10,16, 20, 25,
32, 35, 40, 63, 100, 125, 160 A and voltage ratings of 240/415 V ac and up to 220 V dc. Operating time is very
short (less than 5 ms.). So, they are very suitable for the protection of important and sophisticated equipment,

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such as air-conditioners, refrigerators, computer etc.

Earth-Leakage Circuit Breaker (ELCB): It is a device that provides protection against earth leakage.These are of
two types: the current operated type and the voltage operated type.
 Current operated earth-leakage circuit breaker is used when the product of the operating currentin amperes
and the earth-loop impedance in ohms does not exceed 40. Where such a circuit breaker is used, the consumer’s
earthing terminal is connected to a suitable earth electrode. A current- operated earth leakage applied to a 3-
phase;3-wire circuit is shown in figure (a). In normal conditions when there is no earth leakage the algebraic
sum of currents in the three coils of the current transformers (CTs) is zero, and no current flows through the
trip coil. In case of any earth leakage, the currents are unbalanced, and trip coil is energized and thus the circuit
breaker is tripped.
 Voltage-operated earth leakage circuit breaker is suitable for use when the earth-loop impedanceexceeds
the values applicable to fuses or excess-current circuit breaker or to current-operated earth- leakage circuit
breaker. Such an earth-leakage trip in a 2-wire circuit is shown in figure (b). When the voltage between the
earth continuity conductor (ECC) and earth electrode rises to a sufficient value,the trip coil will carry the
required current to trip the circuit breaker.

Molded Case Circuit Breaker (MCCB): The main distinctions between molded-case and miniature circuitbreaker are
that the MCCB can have current ratings up to 2500 amperes, and its trip settings are normally adjustable. An additional
difference is that MCCBs tend to be much larger than MCBs. An MCCB has three main functions:

 Protection against overload: Currents above the rated value last longer than what is normal for the
application.
 Protection against electrical faults: During a fault such as a short circuit or line fault, there are
extremely high currents that must be interrupted immediately.
 Switching a circuit on and off: This is a less common function of circuit breakers, but they can be usedfor that
purpose if there isn’t an adequate manual switch.
 Operating Mechanism: At its core, the protection mechanism employed by MCCBs is based on thesame
physical principles used by all types of thermal-magnetic circuit breakers.
 Overload protection is accomplished by means of a thermal mechanism. MCCBs have a bimetallic
contact what expands and contracts in response to changes in temperature. Under normal operating
conditions, the contact allows electric current through the MCCB. However, assoon as the current
exceeds the adjustable trip value, the contact will start to heat and expand until the circuit is
interrupted. The thermal protection against overload is designed with a time delay to allow short
duration overcurrent, which is a normal part of operation for many devices. However, any
overcurrent conditions that last more than what is normally expected represent an overload, and the
MCCB is tripped to protect

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 On the other hand, fault protection is accomplished with electromagnetic induction, and the
response is instant. Fault currents should be interrupted immediately, no matter if their durationis
short or long. Whenever a fault occurs, the extremely high current induces a magnetic field ina
solenoid coil located inside the breaker – this magnetic induction trips a contact and current is
interrupted. As a complement to the magnetic protection mechanism, MCCBs have internal arc
dissipation measures to facilitate interruption.
Air Circuit Breaker and Air Blast Circuit Break
This type of circuit breakers, is those kind of circuit breaker which operates in air at atmospheric
pressure. After development of oil circuit breaker, the medium voltage air circuit
breaker (ACB) is replaced completely by oil circuit breaker in different countries. But in
countries like France and Italy, ACBs are still preferable choice up to voltage 15 KV. It is also
good choice to avoid the risk of oil fire, in case of oil circuit breaker. In America ACBs were
exclusively used for the system up to 15 KV until the development of new vacuum and
SF6 circuit breakers.
Working Principle of Air Circuit Breaker
The working principle of this breaker is rather different from those in any other types of circuit
breakers. The main aim of all kind of circuit breaker is to prevent the reestablishment of arcing
after current zero by creating a situation where in the contact gap will withstand the system
recovery voltage. The air circuit breaker does the same but in different manner. For
interrupting arc it creates an arc voltage in excess of the supply voltage. Arc voltage is defined as
the minimum voltage required maintaining the arc. This circuit breaker increases the
arc voltage by mainly three different ways,
1. It may increase the arc voltage by cooling the arc plasma. As the temperature of arc plasma
is decreased, the mobility of the particle in arc plasma is reduced, hence more voltage gradient is required to maintain the
arc.

2. It may increase the arc voltage by lengthening the arc path. As the length of arc path is
increased, the resistance of the path is increased, and hence to maintain the same
arc current more voltage is required to be applied across the arc path. That means
arc voltage is increased.
3. Splitting up the arc into a number of series arcs also increases the arc voltage.

Types of ACB

There are mainly two types of ACB are available.

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1. Plain air circuit breaker.

2. Air blast Circuit Breaker.

Types of Wires and Cables:

The wires employed for internal wiring of buildings may be divided into differentgroups according to (i) Conductor used
(ii) Number of cores used (iii) Voltage grading (iv) Types of insulation used.
 According to the conductor material used in cables, these may be divided into two classes known ascopper
conductor cables and aluminum conductor cables.
 According to the number of cores, the cable consists of, the cables may be divided into classes known assingle
core cables; twin core cables; three core cables; two core with ECC (earth continuity conductor) cables etc.
 According to voltage grading the cables may be divided into two classes: (i) 250/440 volt cables and (ii)
650/1100 volt cables.
 According to type of insulation the cables are of the following types:
1. Vulcanized Indian Rubber (VIR) insulated cables.
2. Tough rubber sheathed (TRS) or cab tyre sheathed (CTS) cables.
3. Lead sheathed cables.
4. Polyvinyl chloride (PVC) cables.
5. Weatherproof cables.
6. Flexible cords and cables.
7. XLPE cables.
8.Multi-strand cables.
1. Vulcanized Indian Rubber (VIR) Cables:
 VIR, cables are available in 240/415 volts as well as in 650/1100-volt grades.
 VIR cable consists of either tinned copper conductor covered with a layer of vulcanized Indian rubber
insulation. Over the rubber insulation cotton tap sheathed covering is provided with moisture resistant
compound bitumen wax or some other insulating material for making the cables moisture proof.
 The thickness of rubber insulation depends upon the voltage grade for which the cable is required

2. Tough Rubber Sheathed (TRS) or Cab Tyre Sheathed (CTS) Cables:

 These cables are available in 250/440 volt and 650/1100-volt grades and used in CTS (or TRS) wiring.
 TRS cable is nothing, but a vulcanized rubber insulated conductor with an outer protective covering oftough
rubber, which provides additional insulation and protection against wear and tear.

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 These cables are waterproof, hence can be used in wet conditions. These cables are available as singlecore,
circular twin core, circular three core, flat three core, twin or three core an earth continuity conductor (ECC).
 The cores are insulated from each other and covered with a common sheathing. Different types of TRS cables
areshown in above figure.
3. Lead Sheathed Cables:
 These cables are available in 240/415-volt grade. The lead sheathed cable is vulcanized rubber insulated
conductor covered with a continuous sheath of lead.
 The lead sheath provides very good protection against the absorption of moisture and sufficient
protection against mechanical injury and so can be used without casing or conduit system.
It is available as a single core, flat twin core, flat three core and flat twin or three core with an earthcontinuity
conductor. Two-core lead sheathed cable is shown in below figure.

4. Polyvinyl Chloride (PVC) Insulated Cables:

 These cables are available in 250/440 volt and 650/1100-volt grades and are used in casing-capping,batten
and conduit wiring system.
 In this type of cable conductor is insulated with PVC insulation. Since PVC is harder than rubber, PVCcable
does not require cotton taping and braiding over it for mechanical and moisture protection.

PVC insulation is preferred over VIR insulation because of the following reasons:

(i) PVC insulation has better insulating qualities.

(ii) PVC insulation provides better flexibility.
(iii) PVC insulation has no chemical effect on metal of the wire.
(iv) Thin layer of PVC insulation will provide the desired insulation level.
(v) PVC coated wire gives smaller diameter of cable and, therefore, a greater number of wires can be
accommodated in the conduit of a given size in comparison to VIR or CTS wires.
 PVC cables are most widely used for internal wiring these days. Though the insulation resistance of PVC is
lower than that of VIR, but its effect is negligible for low and medium voltages, below 600 V.
5. Weatherproof Cables:
 These cables are used for outdoor wiring and for power supply or industrial supply. These cables are
either PVC insulated, or Vulcanized rubber insulated conductor being suitably taped (only in case of

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vulcanized rubber insulated cable) braided and then compounded with weather resisting material

 These cables are available in 240/415 volt and 650/1100-volt grades. These cables are not
affected byheat or sun or rain.
6. Flexible Cords and Cables:
 The flexible cords consist of wires silk/cotton/plastic covered. Plastic cover is popular as it is availablein
different pleasing colors.
 Flexible cords have tinned copper conductors. Flexibility and strength is obtained by using conductorshaving
larger number of strands.
 These wires or cables are used as connecting wires for such purposes as from ceiling rose to lampholder,
socket outlet to portable apparatus such as radios, fans, lamps, heaters etc.
 The flexibility of such wires facilitates in handling the appliances and prevents the wires from breakage.
7. XLPE Cables:
 PVC and XLPE cables are built of insulation made of polymers. Polymers are substances consisting oflong
macromolecules built up of small molecules or groups of molecules as repeated units.
 These are divided into homopolymers and copolymers. Homopolymers are built by reactions of identical
monomers.
 Copolymers are built up of at least two different kinds of monomers.
Advantage of PVC cables Over Other Types of Cables:
1. Non-hygroscopic insulation almost unaffected by moisture.
2. Complete protection against most forms of electrolytic/chemical corrosion.
3. Tough/Resilient sheath with excellent fire resisting qualities.
4. Good ageing characteristics.
5. Not affected by vibrations
Advantage of XLPE Cables Over Both PVC and All Other Types of Cables:
1. Higher Current rating.
2. Higher short-circuit current rating.
3. Longer service life.
4. Can withstand 130 degrees Celsius (maximum) for short time is favorable to endure short-circuit
stresses.
5. It is less sensitive to the setting of network protection.
6. Because of thermosetting process taking place through cross-linking, crack resistance is increased.
7. Due to chemical cross-linking internal stresses are reduced. Consequently, material is less sensitive,during
manufacture, to the setting of the cooling gradient.
8. Multi-Strand Cables:
 Multi-strand cables have got the following advantages with respect to the single conductor and hence
preferred.
(i) The multi-strand cables are more flexible and durable and, therefore, can be handled conveniently.
(ii) The surface area of multi-strand cable is more as compared to the surface area of equivalent singlesolid

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conductor, so heat radiating capacity, being proportional to the surface area, is more.
(iii) Skin effect is better as the conductors are tubular, especially in case of high frequency.
 The number of strands in stranded cable must be 3, 7, 19, 37, 61, 91 and so on to obtain a
circularcontour.
 The section of a 3-strand cable at right angle to its length is three circles touching one another,
thecenters of which are the corners of an equilateral triangle.
 All other have a centrally disposed conductor with all the other around it. Thus a 7-strand
cable has onecentral wire with 6 wires surrounding it; the 19-strand cable has another12 wires
surrounding the 7- strands; the 37-strand cable has another 18 wires surrounding the 19-
strands and so on. It is seen that each layer of wires has always 6 more wires in it than the
layer beneath it.
Earthing:
 The connection of frame or external body of Electrical Machinery to the general mass of earth, with a conducting
material of very low resistance is called earthing.
 The earthing of electrical equipment brings the equipments to zero potential and avoid the shock to the operator,
under any fault condition.

Importance of Earthing:
i. To maintain the line voltage constant.
ii. To protect tall buildings and structures from atmospheric lightning strikes.
iii. To protect all the machines, fed from overhead lines, from atmospheric lightening.
iv. To serve as the return conductor for telephone and traction work. In such case all the complications in
laying a separate wire and the actual cost of the wire, is thus saved.
v. To protect human being from disability or death from shock in case the human body comes into the
contact with the frame of any electrical machinery, appliances, or components, which is electrically
charged due to leakage current or fault.
Methods of Earthing:
Earthing is achieved by connecting the frame or external body of electrical appliances orcomponents to earth by
employing a good conductor called “Earth Electrodes”. This Ensures very low resistance path from appliance to the
earth.
The various methods of earthing are-
Earthing Mat
Earthing mat is made by joining the number of rods through copper conductors. It reduced the overall grounding
resistance. Such type of system helps in limiting the ground potential. Earthing mat is mostly used in a placed where the
large fault current is to be experienced.

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Earthing Electrode
In this type of earthing any wire, rod, pipe, plate or a bundle of conductors, inserted in the ground horizontally or vertically.
In distributing systems, the earth electrode may consist of a rod, about 1 meter in length and driven vertically into the
ground. In generating substations, grounding mat is used rather than individual rods.

Pipe Earthing
This is the most common and best system of earthing as compared to other systems suitable for the same earth and moisture
conditions. In this method the galvanized steel and perforated pipe of approved length and diameter in place upright in a
permanently wet soil, as shown below. The size of the pipe depends upon the current to be carried and type of soil.

Plate Earthing
In Plate Earthing an earthing plate either of copper of dimension 60cm×60cm×3m of galvanized iron of dimensions 60 cm×
60 cm×6 mm is buried into the ground with its face vertical at a depth of not less than 3 meters from ground level.

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Earthing Through Water Mains
In this type of earthing the GI or copper wire are connected to the water mains with the help of the steel binding wire which
is fixed on copper lead as shown below.

The water pipe is made up of metal, and it is placed below the surface of the ground, i.e. directly connected to earth. The
fault current flow through the GI or copper wire is directly get earthed through the water pipe.

Types of Batteries:
Batteries are either primary or secondary.
1) Primary batteries can be used only once because the chemical reactions that supply the current are irreversible.
 Primary batteries are the most common batteries available today because of their low cost and simplicityin use.
 Carbon-zinc dry cells and alkaline cells dominate portable consumer battery applications where currents are
low, and usage is occasional.
 Other primary batteries, such as those using mercury or lithium-based chemistries, may be used in applications
when high energy densities, small sizes, or long shelf life are especially important.
 In general, primary batteries have dominated two areas: consumer products where the initial cost of the battery
is very important and electronics products (such as watches, hearing aids and pacemakers) wheredrains are low,
or recharging is not feasible.
2) Secondary batteries, sometimes called storage batteries or accumulators, can be used, recharged, and reused. In
these batteries, the chemical reactions that provide current from the battery are readily reversed when current is
supplied to the battery.
 The process of inducing or storing energy in an accumulator is called the charging, and the process of giving
out energy in the form of an electric current, the discharging.
 Accumulator or storage batteries owe their name “secondary” since they can supply electrical energy after
they have been charged.
 Secondary batteries, which are rechargeable, have traditionally been most widely used in industrial and
automotive applications. Here users are willing to trade higher initial cost and additional handling and care
requirements for high current delivery and the economies of a rechargeable product.
 Only two rechargeable battery chemistries, lead acid and nickel-cadmium, have, to-date, achievedsignificant
commercial success, The recently introduced nickel-metal hydride couple currently shows promise of supplementing
nickel-cadmium cells in many commercial applications.

Lead- Acid Battery

Figure below shows the cut-away view of 6V commercial lead-acid battery. The following are the importantpart
of the battery.

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
 Container: It is the outer body of the battery. It is made of a hard rubber or plastic material and is sealedat the
top to prevent spilling of the electrolyte. A large space is left at the bottom of the container so that the sediments
that drop form the plates are collected here and may not short circuit the positive and negative plates.
 Plates: Generally, alloy of lead-antimony sheets covered with lead-peroxide and spongy lead forming positive
and negative plates respectively are used as electrodes. To increase the capacity of the battery, we use many
plates in each cell instead of only two plates. The number of positive and negative plates (i.e., 11, 13, 15 or 17)
of each cell are alternatively placed and sandwiched with an insulator called separator as shown in figure below.
One group of positive and negative plates forms a cell which develops an emf of 2.0 volt. A separate
compartment is provided for each cell in the container of the battery
 Separator: To reduce the internal resistance of the cell and to save the space, the plates are placed very close
to each other. To prevent the plates touching each other if they wrap or buckle, they are separated by a rubber
sheet (non-conducting material) having large number of small holes called separator.
 Electrolyte: Dilute sulphuric-acid (H2SO4) is used as an electrolyte in lead-acid batteries. Sulphuric acidis
added to water in such a proportion that with a fully charged battery, its specific gravity is about 1.28 to 1.29.
 Battery Cover: Each cell compartment is covered usually with a molded hard rubber and the joints between
covers and containers are sealed with an acid-resistance material. In each cell cover openings are provided- two
for positive and negative terminals, and third for a vent. The whole container is fitted with a leak proof cover.
 Vent caps: The vent-cap has a vent hole to allow free exit of the gases formed in the cell during charging. The
vent caps can be easily removed for adding water. The vent cap is also removed to insert the nozzle of
hydrometer for checking the specific gravity of electrolyte to check the battery charge condition.

Battery plates and separator

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 Inter-cell connector: The cells, placed in the same container are connected in series with a lead alloy link called
inter-cell connector.
 Cell terminals: Each cell has two terminals which are generally made of lead as it does not corrode due to the
electrolyte. The positive terminal of the battery is marked with a red color or by a large positive (+) sign.
 Capacity of a Battery
The quantity of electricity which a battery can deliver during single discharge until its terminal voltagefalls to
1.8 V per cell is called the capacity of a battery.
The capacity of a battery or cell is commercially expressed in ampere-hour and is generally denoted byA-H.
Capacity of a battery or cell = 𝐼𝑑𝑇𝑑 𝑎𝑝𝑚𝑒𝑟𝑒 − ℎ𝑜𝑢𝑟
Where, 𝐼𝑑 = 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑛 𝑎𝑚𝑝𝑒𝑟𝑒
𝑇𝑑 = 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝑡𝑖𝑚𝑒 𝑜𝑓 𝑏𝑎𝑡𝑡𝑒𝑟𝑦 𝑜𝑟 𝑐𝑒𝑙𝑙 𝑖𝑛 ℎ𝑜𝑢𝑟

Efficiency of a Battery
The efficiency of a battery (or cell) can be defined in the following two ways:
I. Quantity or A-H efficiency: The ration of output ampere-hour during discharging to the input ampere-hour
during charging of the battery is called quantity or ampere-hour efficiency of the battery.

𝐼𝑑𝑇𝑑
ɳ𝐴𝐻 =
𝐼𝑐𝑇𝑐
Where, 𝐼𝐷 = 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑛 𝑎𝑚𝑝𝑒𝑟𝑒
𝑇𝑑 = 𝑑𝑖𝑠𝑐ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝑡𝑖𝑚𝑒 𝑖𝑛 ℎ𝑜𝑢𝑟

𝐼𝑐 = 𝑐ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝑐𝑢𝑟𝑟𝑒𝑛𝑡 𝑖𝑛 𝑎𝑚𝑝𝑒𝑟𝑒

𝑇𝑐 =𝑐ℎ𝑎𝑟𝑔𝑖𝑛𝑔 𝑖𝑚𝑒 𝑖𝑛 ℎ𝑜𝑢𝑟

II. Energy or W-H efficiency: The ratio of output watt-hour during discharging to the input watt-hourduring charging
of the battery is called energy or watt-hour efficiency of the battery.
𝐼𝑑𝑇𝑑𝑉𝑑
ɳ𝑊𝐻 =
𝐼𝑐 𝑇𝑐 𝑉𝑐
Where 𝑉𝑑 = Average terminal voltage during discharging
𝑉𝑐 = Average terminal voltage during charging

Battery Back-up
The time (in hrs.) for which a battery can deliver the desired current is called battery back -up of the batterybank.
Charge Indication of a lead-acid Battery or Cell
The values of specific gravity for different condition of charge are given below

Specific gravity Condition

1.280 to 1.290 100% charged
1.230 to 1.250 75% charged
1.190 to 1.200 50% charged
1.150 to 1.160 25% charged
Below 1.130 Fully discharged
 To check the specific gravity of electrolyte (H2SO4), an instrument called hydrometer is used which works on
Archmedeies principle. In common use, the decimal point is omitted from the value of specificgravity i.e., 1.280
specific gravity is spoken as 1280 and so on.
 However, the state of battery can also be checked by checking.
(i) Voltage: When the terminal voltage of the battery on load is 2.1to 2.5 V per cell, the battery is saidto be

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fully charged. Whereas, when the voltage of the battery falls below 1.8 V per cell, the battery isconsidered
to be fully discharged and it is immediately put-on charging.
(ii) Color of plates: When lead-acid cell or battery is fully charged, its anode is PbO2 which is chocolate brown
in color and cathode is of Pb which is grey in color. However, when the battery is fully discharged, both the
plates attain PbSO4 as active material which is whitish in color.

Characteristics of Lead-acid Battery

(i) The emf of a fully charged lead-acid cell is 2.2 V decreases to 2.0 V rapidly. However the averageemf
of the cell is 2.0 V which decreases to 1.8 V when fully discharged.
(ii) The internal resistance of this cell is quite low.
 The A-H efficiency of this cell is nearly 80% whereas; the W-H efficiency is 60%.
 The specific gravity of electrolyte is 1.280 to 1.290 but to 1.150 when the battery is fully discharged.
Charging and discharging curves

 When the cell is charged, the voltage of the

cell increases from 1.8V to 2.2V during first
two hours, then increases very slowly, rather
remains almost costant for sufficient time and
finally rises to 2.5 to 2.7V.
 When a charged storage cell has just been
disconnected from a charge source, its
terminal voltage falls rapidly to 2.2V. On
discharge, the voltage of the cell drops to
2.0V in the beginning; remains constant for
sufficient time and falls to 1.8V finally. 

Care and Maintenance of lead-acid Batteries

The average life of lead-acid battery is two to four years depending upon its manufacturing qualities and technique.
However, to obtain longer life and efficient service, the following points must be kept in view:
1. The battery should not be allowed to use when the emf of the battery falls to 1.8 V per cell. Otherwise, the lead
sulphate of the plates partly changes to non-active lead sulphate and reduces he life of the battery.
2. The specific gravity to the electrolyte should not be allowed to fall below 1.15.
3. The battery should never be left standing in a discharged condition, otherwise sulphation will occur and the
battery cells are permanently damaged.
4. When not in use, the battery must be fully charged and stored in a cool and dry place.
5. Great care should be taken that the acid used as electrolyte should not contain any substantial impurity.It should
be colorless when viewed through a 12 cm column.
6. The electrodes must remain completely immersed in the electrolyte, preferably the level of electrolyteshould
always be about 10 mm above the electrodes.
7. Whenever the level of the electrolyte decreases due to evaporation or gassing, distilled water should beadded
so as to keep the same concentration of electrolyte
Types of bus-bar
A bus-bar is a metallic bar in a switchgear panel used to carry electric power from incoming feeders and distributes to the
outgoing feeders. In simple terms, bus-bar is a electrical junction where incoming and outgoing currents exchange.
Based on the construction of the bus bar, they are divided as follows.

 Single bus-bar system.

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 Double bus-bar system.
 Ring bus-bar system.

Single Bus-Bar Arrangement

The arrangement of such type of system is very simple and easy. The system has only one bus bar along with the switch.
All the substation equipment like the transformer, generator, the feeder is connected to this bus bar only. The advantages
of single bus bar arrangements are

Advantage

 It has low initial cost.

 It requires less maintenance
 It is simple in operation

Drawbacks of Single Bus-Bars Arrangement

 The only disadvantage of such type of arrangement is that the complete supply is disturbed on the occurrence of
the fault.
 The arrangement provides the less flexibility and hence used in the small substation where continuity of supply is
not essential.

Double Bus Double Breaker Arrangement

This type of arrangement requires two bus bar and two circuit breakers. It does not require any additional equipment like
bus coupler and switch.

Advantages of Double Bus Double Breaker

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 Unit V Electrical Installations
 This type of arrangement provides the maximum reliability and flexibility in the supply. Because the fault and
maintenance would not disturb their continuity.
 The continuity of the supply remains same because the load is transferrable from one bus to another on the
occurrence of the fault.

Disadvantages of double bus Double breaker

 In such type of arrangement two buses and two circuit breakers are used which increases the cost of the system.
 Their maintenance cost is very high.

Ring Bus-bar System

 In this type of arrangement, two circuit breakers serve on one line. For example CB1 and CB2 on one
line, where are CB3, CB4 on another line.
 This ring bus-bar system has the advantage that there are always two parallel paths to the circuit and
failure of one path does not interrupt the service completely.

Advantages of Ring Bus-bar System

 This ring bus-bar system has redundant path to the circuit and failure of one section does not interrupt the service
completely.
 Maintenance of any circuit breaker is possible, without interruption of power.
Disadvantages of Ring Bus-bar System

 It may be difficult in adding new circuit line.

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