various equipment used in substation and their brief introduction-copied

1. Substation equipment and its Function
Lightening Arrester
Lightening arrestors are the instrument that are used in the incoming feeders so that to prevent the high
voltage entering the main station. This high voltage is very dangerous to the instruments used in the
substation. Even the instruments are very costly, so to prevent any damage lightening arrestors are used. The
lightening arrestors do not let the lightening to fall on the station. If some lightening occurs the arrestors pull
the lightening and ground it to the earth. In any substation the main important is of protection which is firstly
done by these lightening arrestors. The lightening arrestors are grounded to the earth so that it can pull the
lightening to the ground. The lightening arrestor works with an angle of 30° to 45° making a cone.
C V T
A capacitor voltage transformer (CVT) is a transformer used in power systems to step­down extra high
voltage signals and provide low voltage signals either for measurement or to operate a protective relay. In its
most basic form the device consists of three parts: two capacitors across which the voltage signal is split, an
inductive element used to tune the device to the supply frequency and a transformer used to isolate and further
step­down the voltage for the instrumentation or protective relay. The device has at least four terminals, a
high­voltage terminal for connection to the high voltage signal, a ground terminal and at least one set of
secondary terminals for connection to the instrumentation or protective relay. CVTs are typically single­phase
devices used for measuring voltages in excess of one hundred kilovolts where the use of voltage transformers
would be uneconomical. In practice the first capacitor, C1, is often replaced by a stack of capacitors connected
in series. This results in a large voltage drop across the stack of capacitors that replaced the first capacitor and
a comparatively small voltage drop across the second capacitor, C2, and hence the secondary terminals.
Wave Trap
Wave trap is an instrument using for tripping of the wave. The function of this trap is that it traps the
unwanted waves. Its function is of trapping wave. Its shape is like a drum. It is connected to the main
incoming feeder so that it can trap the waves which may be dangerous to the instruments here in the
substation.
Instrument Transformer
Instrument transformers are used to step­down the current or voltage to measurable values. They
provide standardized, useable levels of current or voltage in a variety of power monitoring and
measurementapplications. Both current and voltage instrument transformers are designed to have predictable
characteristics on overloads. Proper operation of over­current protection relays requires that current
transformers provide a predictable transformation ratio even during a short circuit.
These are further classified into two types which are discussed below.
a. Current Transformers
b. Potential Transformers
Current Transformer
Current transformers are basically used to take the readings of the currents entering the substation. This
transformer steps down the current from 800 amps to 1 amp. This is done because we have no instrument for
measuring of such a large current. The main use of this transformer is
a. Distance Protection
SUB­STATION EQUIPMENTS & ITS FUNCTIONS

2. b. Backup Protection
c. Measurement
A current transformer is defined as an instrument transformer in which the secondary current is
substantially proportional to the primary current (under normal conditions of operation) and differs in phase
from it by an angle which is approximately zero for an appropriate direction of the connections. This
highlights the accuracy requirement of the current transformer but also important is the isolating function,
which means no matter what the system voltage the secondary circuit need to be insulated only for a low
voltage.
The current transformer works on the principle of variable flux. In the ideal current transformer,
secondary current would be exactly equal (when multiplied by the turns ratio) and opposite to the primary
current. But, as in the voltage transformer, some of the primary current or the primary ampere­turns are
utilized for magnetizing the core, thus leaving less than the actual primary ampere turns to be transformed into
the secondary ampere­turns. This naturally introduces an error in the transformation. The error is classified
into current ratio error and the phase error
Potential Transformer
There are two potential transformers used in the bus connected both side of the bus. The potential
transformer uses a bus isolator to protect itself. The main use of this transformer is to measure the voltage
through the bus. This is done so as to get the detail information of the voltage passing through the bus to the
instrument. There are two main parts in it
a. Measurement
b. Protection
The standards define a voltage transformer as one in which the secondary voltage is substantially
proportional to the primary voltage and differs in phase from it by an angle which is approximately equal to
zero for an appropriate direction of the connections. This in essence means that the voltage transformer has to
be as close as possible to the ideal transformer.
In an ideal transformer, the secondary voltage vector is exactly opposite and equal to the primary
voltage vector when multiplied by the turn’s ratio.
In a practical transformer, errors are introduced because some current is drawn for the magnetization of
the core and because of drops in the primary and secondary windings due to leakage reactance and winding
resistance. One can thus talk of a voltage error which is the amount by which the voltage is less than the
applied primary voltage and the phase error which is the phase angle by which the reversed secondary voltage
vector is displaced from the primary voltage vector.
Bus Bar
The bus is a line in which the incoming feeders come into and get into the instruments for further step
up or step down. The first bus is used for putting the incoming feeders in la single line. There may be double
line in the bus so that if any fault occurs in the one the other can still have the current and the supply will not
stop. The two lines in the bus are separated by a little distance by a conductor having a connector between
them. This is so that one can work at a time and the other works only if the first is having any fault.
A bus bar in electrical power distribution refers to thick strips of copper or aluminum that conduct
electricity within a switchboard, distribution board, substation, or other electrical apparatus. The size of the
bus bar is important in determining the maximum amount of current that can be safely carried. Bus bars are
typically either flat strips or hollow tubes as these shapes allow heat to dissipate more efficiently due to their
high surface area to cross sectional area ratio. The skin effect makes 50­60 Hz AC bus bars more than about 8
mm (1/3 in) thick inefficient, so hollow or flat shapes are prevalent in higher current applications. A hollow
section has higher stiffness than a solid rod of equivalent current carrying capacity, which allows a greater

3. span between bus bar supports in outdoor switchyards. A bus bar may either be supported on insulators or else
insulation may completely surround it. Bus bars are protected from accidental contact either by a metal
enclosure or by elevation out of normal reach.
Neutral bus bars may also be insulated. Earth bus bars are typically bolted directly onto any metal
chassis of their enclosure. Bus bars may be enclosed in a metal housing, in the form of bus duct or bus way,
segregated­phase bus, or isolated­phase bus.
Circuit Breaker
The circuit breakers are used to break the circuit if any fault occurs in any of the instrument.
Thesecircuit breaker breaks for a fault which can damage other instrument in the station. For any unwanted
fault over the station we need to break the line current. This is only done automatically by the circuit breaker.
There are mainly two types of circuit breakers used for any substations. They are
a. SF6 circuit breakers
b. Spring circuit breakers.
The use of SF6 circuit breaker is mainly in the substations which are having high input kv input, say
above 220kv and more. The gas is put inside the circuit breaker by force i.e. under high pressure. When if the
gas gets decreases there is a motor connected to the circuit breaker. The motor starts operating if the gas went
lower than 20.8 bar. There is a meter connected to the breaker so that it can be manually seen if the gas goes
low. The circuit breaker uses the SF6 gas to reduce the torque produce in it due to any fault in the line. The
circuit breaker has a direct link with the instruments in the station, when any fault occur alarm bell rings.
The spring type of circuit breakers is used for small kv stations. The spring here reduces the torque
produced so that the breaker can function again. The spring type is used for step down side of 132kv to 33kv
also in 33kv to 11kv and so on. They are only used in low distribution side.
Transformer
There are three transformers in the incoming feeders so that the three lines are step down at the same
time. In case of a 220KV or more KV line station auto transformers are used. While in case of lower KV line
such as less than 132KV line double winding transformers are used.
The transformer is transported on trailor to substation site and as far as possible directly unloaded on
the plinth. Transformer tanks up to 25 MVA capacity are generally oil filled, and those of higher capacity are
transported with N2 gas filled in them +ve pressure of N2 is maintained in transformer tank to avoid the
ingress of moisture. This pressure should be maintained during storage, if necessary by filling N2 Bushings ­
generally transported in wooden cases in horizontal position and should be stored in that position. There being
more of fragile material, care should be taken while handling them. Radiators – These should be stored with
ends duly blanked with gaskets and end plates to avoid in gross of moisture, dust, and any foreign materials
inside. The care should be taken to protect the fins of radiators while unloading and storage to avoid further oil
leakages. The radiators should be stored on raised ground keeping the fins intact.
Oil Piping. The Oil piping should also be blanked at the ends with gasket and blanking plates to avoid in gross
of moisture, dust, and foreign All other accessories like temperature meters, oil flow indicators, PRVs,
buchholz relay; oil surge relays; gasket ‘ O ‘ rings etc. should be properly packed and stored indoor in store
shed. Oil is received in sealed oil barrels. The oil barrels should be stored in horizontal position with the lids
on either side in horizontal position to maintain oil pressure on them from inside and subsequently avoiding
moisture and water ingress into oil. The transformers are received on site with loose accessories hence the
materials should be checked as per bills of materials.
Isolator

4. The use of this isolator is to protect the transformer and the other instrument in the line. The isolator
isolates the extra voltage to the ground and thus any extra voltage cannot enter the line. Thus an isolator is
used after the bus also for protection.
Control and Relay Panel
The control and relay panel is of cubical construction suitable for floor mounting. All protective,
indicating and control elements are mounted on the front panel for ease of operation and control. The hinged
rear door will provide access to all the internal components to facilitate easy inspection and maintenance.
Provision is made for terminating incoming cables at the bottom of the panels by providing separate line­up
terminal blocks. For cable entry provision is made both from top and bottom. The control and relay panel
accepts CT, PT aux 230 AC and 220V/10V DC connections at respective designated terminal points.
220V/10V DC supply is used for control supply of all internal relays and timers and also for energizing
closing and tripping coils of the breakers. 230V AC station auxiliary supply is used for internal illumination
lamp of the panel and the space heater. Protective HRC fuse are provided with in the panel for P.T secondary.
Aux AC and battery supplies. Each Capacitor Bank is controlled by breaker and provided with a line ammeter
with selector switch for 3 phase system & over current relay (2 phases and 1 Earth fault for 3 ph system).
Under voltage and over voltage relays. Neutral Current Unbalance Relays are for both Alarm and Trip
facilities breaker control switch with local/remote selector switch, master trip relay and trip alarms
acknowledge and reset facilities.
Protective Relaying
Protective relays are used to detect defective lines or apparatus and to initiate the operation of circuit
interrupting devices to isolate the defective equipment. Relays are also used to detect abnormal or undesirable
operating conditions other than those caused by defective equipment and either operate an alarm or initiate
operation of circuit interrupting devices. Protective relays protect the electrical system by causing the
defective apparatus or lines to be disconnected to minimize damage and maintain service continuity to the rest
of the system. There are different types of relays.
i. Over current relay
ii. Distance relay
iii. Differential relay
iv. Directional over current relay
i. Over Current Relay
The over current relay responds to a magnitude of current above a specified value. There are four basic
types of construction: They are plunger, rotating disc, static, and microprocessor type. In the plunger type, a
plunger is moved by magnetic attraction when the current exceeds a specified value. In the rotating induction­
disc type, which is a motor, the disc rotates by electromagnetic induction when the current exceeds a specified
value.
Static types convert the current to a proportional D.C mill volt signal and apply it to a level detector
with voltage or contact output. Such relays can be designed to have various current­versus­time operating
characteristics. In a special type of rotating induction­disc relay, called the voltage restrained over current
relay. The magnitude of voltage restrains the operation of the disc until the magnitude of the voltage drops
below a threshold value. Static over current relays are equipped with multiple curve characteristics and can
duplicate almost any shape of electromechanical relay curve. Microprocessor relays convert the current to a
digital signal. The digital signal can then be compared to the setting values input into the relay. With the
microprocessor relay, various curves or multiple time­delay settings can be input to set the relay operation.

5. Some relays allow the user to define the curve with points or calculations to determine the output
characteristics.
ii. Distance Relay
The distance relay responds to a combination of both voltage and current. The voltage restrains
operation, and the fault current causes operation that has the overall effect of measuring impedance. The relay
operates instantaneously (within a few cycles) on a 60­cycle basis for values of impedance below the set
value. When time delay is required, the relays energizes a separate time­delay relay or function with the
contacts or output of this time­delay relay or function performing the desired output functions. The relay
operates on the magnitude of impedance measured by the combination of restraint voltage and the operating
current passing through it according to the settings applied to the relay. When the impedance is such that the
impedance point is within the impedance characteristic circle, the relay will trip. The relay is inherently
directional. The line impedance typically corresponds to the diameter of the circle with the reach of the relay
being the diameter of the circle.
iii. Differential Relay
The differential relay is a current­operated relay that responds to the difference between two or more
device currents above a set value. The relay works on the basis of the differential principle that what goes into
the device has to come out .If the current does not add to zero, the error current flows to cause the relay to
operate and trip the circuit.
The differential relay is used to provide internal fault protection to equipment such as transformers,
generators, and buses. Relays are designed to permit differences in the input currents as a result of current
transformer mismatch and applications where the input currents come from different system voltages, such as
transformers. A current differential relay provides restraint coils on the incoming current circuits. The restraint
coils in combination with the operating coil provide an operation curve, above which the relay will operate.
Differential relays are often used with a lockout relay to trip all power sources to the device and prevent the
device from being automatically or remotely reenergized. These relays are very sensitive. The operation of the
device usually means major problems with the protected equipment and the likely failure in re­energizing the
equipment.
iv. Directional Over current Relay
A directional over current relay operates only for excessive current flow in a given direction.
Directional over current relays are available in electromechanical, static, and microprocessor constructions.
An electromechanical overcorrect relay is made directional by adding a directional unit that prevents the over
current relay from operating until the directional unit has operated. The directional unit responds to the
product of the magnitude of current, voltage, and the phase angle between them or to the product of two
currents and the phase angle between them. The value of this product necessary to provide operation of the
directional unit is small, so that it will not limit the sensitivity of the relay (such as an over current relay that it
controls). In most cases, the directional element is mounted inside the same case as the relay it controls. For
example, an over current relay and a directional element are mounted in the same case, and the combination is
called a directional over current relay. Microprocessor relays often provide a choice as to the polarizing
method that can be used in providing the direction of fault, such as applying residual current or voltage or
negative sequence current or voltage polarizing functions to the relay.
DC Power Supply
I . DC Battery and Charger
All but the smallest substations include auxiliary power supplies. AC power is required for substation
building small power, lighting, heating and ventilation, some communications equipment, switchgear
operating mechanisms, anti­condensation heaters and motors. DC power is used to feed essential services such
as circuit breaker trip coils and associated relays, supervisory control and data acquisition (SCADA) and

6. communications equipment. This describes how these auxiliary supplies are derived and explains how to
specify such equipment. It has Single 100% battery and 100% charger, Low capital cost, No standby DC
System outage for maintenance. Need to isolate battery/charger combination from load under boost charge
conditions in order to prevent high boost voltages.
I I . Battery and Charger configurations
Capital cost and reliability objectives must first be considered before defining the battery and battery
charger combination to be used for a specific installation. The comparison given in Table 5.1 describes the
advantages and disadvantages of three such combinations.
Capital cost and reliability objectives must first be considered before defining the battery/battery
charger combination to be used for a specific installation. The comparison given describes the advantages and
disadvantages of three such combinations
III . 400V DC Battery
Make: Exide
Capacity: 300 AH at 27°
No. of Cells: 110 No.
Date of installation: 06/2001
Make: Universal,
Sr. No. : BC 1020/82
Date of manufacturing: 4/2000
Input Rating: Voltage: 415 V + 10 %
Output Rating : Float: 220 V, 10 Amp
Boost: 180 V, 30Amp
Functions of Associated System in Substation
Functions of Associated System in Substation is as shown below in table­4.1
Table­4.1 Functions of Associated System in Substation
Sr. System Function
1. Substation Earthing system
­ Earth mat
­ Earthing spikes
­ Earthing risers
To provide an earth mat for connecting neutral points,
equipment body, support structures to earth. For safety
of personnel and for enabling earth fault protection. To
provide the path for discharging the earth currents from
neutrals, faults, Surge Arresters, overheads shielding
wires etc. with safe step­potential and touch potential.
2. Overhead earth wire
shielding or Lightning masts.
To protect the outdoor substation equipment from
lightning strokes.
3. Illumination system (lighting)
­ for switchyard
­ buildings
­ roads etc.
To provide proper illumination to substation yard.
4. Protection system
­ protection relay panels
­ control cables
­ circuit breakers
­ CTs, VTs etc.
To provide alarm or automatic tripping of faulty part
from healthy part and also to minimize damage to
faulty equipment and associated system.
5. Control cable For Protective circuits, control circuits, metering
circuits, communication circuits

7. 6. Power cable To provide supply path to various auxiliary equipment
and machines.
7. PLCC system
power line carrier
communication system
For communication, telemetry, tele­control, power line
carrier protection etc.
8. Telephone, telex, microwave,
OPF
For internal and external communication
9. Auxiliary standby power
system
For supplying starting power, standby power for
auxiliaries.
10. Fire Fighting system
­ Sensors, detection system
­ water spray system
­ fire port, panels, alarm
System.
­ water tank and spray system
To sense the occurrence of fire by sensors and to
initiate water spray, to disconnect power supply to
affected region to pinpoint location of fire by indication
in control room.