training report 400 KV GSS , Surpura Jodhpur , RRVPNL

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Dr. B.R. Ambedkar National Institute Of Technology
Jalandhar,Punjab-144011
A
Summer Training Report
On
Practical Implant training
Completed At
400 KV GSS Surpura, Jodhpur
(Rajasthan Rajya Vidyut Prasaran Nigam Limited)
Duration
29.05.2017 - 20.07.2017
Submitted by
Manish Bishnoi
14126019
Department Of Electrical Engineering
email :- manishbishnoi065@gmail.com
( NIT- Jalandhar )

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TABLE OF CONTENT
S.NO TITLE PAGE NO.
1 Acknowledgement 3
2 Abstract & Certificate 4
3 Introduction 6
4 Importance of electrical energy 9
5 Function & specification of various equipment 11
at 400 Kv gs
6 Power line carrier communication (PLCC) 37
7 Substation 39
8 Protective Relay 40
9 Earthing 46
10 Laboratory 49
11 Conclusion 50
12 Reference 52

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1:-ACKNOWLEDGMENTS
Summer training has an important role in exposing the real life situation
in an industry. It was a great experience for me to work on training at
Rajasthan Rajya Vidyut Prasaran Nigam Limited ( R.R.V.P.N.L ) through
which I could learn how to work in a professional environment.
Now, I would like to thank the people who guided me and have
been a constant source of inspiration throughout the tenure of my
summer training.
I am sincerely grateful to S.K. Vaishnav (Executive Engineer)
at 400 KV GSS Surpura , jodhpur who rendered me his valuable
assistance, constant encouragement andable guidance which made this
training actually possible . I wish my deep sense of gratitude and thanks
to Mr. Vijay prajapati (Junior Engineer) Whose affectionate guidance
has enabled me to complete this training successfully.
I also wish my deep sense of gratitude to
Dr. S.K. Pahuja (HOD, EE Department) and Training coordinators
Dr. A Mukhopadhyay & Dr. Rajeev Trehan and other faculty
members whose guidance and encouragement made my training
successful
Manish Bishnoi

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2:-ABSTRACT
Training at 400 KV GSS Surpura , Jodhpur gives the insight of the real
instruments used. There are many instruments like transformer, CT, PT,
CVT, LA, relay, PLCC, bus bars, reactors, insulator, isolators, control
room, etc. There are various problems seen in substation while handling
these instruments. There are various occasion when relay operate and
circuit breaker open, load shedding, shut down of a feeder in case of a
fault , shutdown of total system, overheating of transformer, blasting of
current transformer in case of excessive current, transformer oil
replacement, aging of transformer oil, wireless communication, insulator
classification as per current rating, conductor requirement as per rating
,2 line and 3 line transmission, how to put system on load and how to
remove the system from load, automatic resetting of relay, isolator
operation on off-load.
GSS is the mean of connection between generating station and consumer
by providing safety and reliability of system in case of fault. This sub-
station step down the incoming voltage power transmission to the
required value and then is supplied to the consumer feeder or GSS done
by connecting auto transformer operation and requirement of various
equipment have been include in detail, further in case of report is the bus
bar. Arrangement of different feeder level and switch yards included
information of bus bar arrangement of different level isolator and
growing substation also power transformer circuit breaker oil, filtration
plant, and compression protection control room and place are leveled.
The most important part of a G.S.S. is the battery room or most
commonly known as the heart of a G.S.S. without the battery system all
the control panel, metering and relay panel will not operate and therefore
it will lead to failure of substation. As the most important part of a GSS
is battery room as control panel operate on this supply it must be kept in
spare as we have 220V DC supply ,and each battery supplies 2 volt

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hence 110 batteries will be kept in parallel to supply the same ,hence
always a backup of 110 batteries are always kept in storage room
Relay system is termed as the brain of the G.S.S. as it controls the circuit
breaker operations as it is very necessary to operate the circuit break
operation in time ,we can take our time for closing on the circuit breaker
but during fault circuit breaker must be operated as soon as possible and
arc must be quenched accordingly.
To get insight of the substation, how things operate, how things are
managed inside a substation. Practical training as a whole proved to be
extremely informative and experience building and the things i learned
here would definitely help a lot in snapping the future ahead in a better
way.
CERTIFICATE

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CHAPTER-1
3:- INTRODUCTION
1.1 Synopsis
Energy is the basic necessity for the economic development of a country.
Energy exists in different form in nature but the most important for is electrical
energy. The conversion of energy available in different forms of nature into
electrical energy is known as generation of different forms of nature into electrical
energy is known as generation of electrical energy. Various sources of energy
available in nature are-
1Solar Energy
2Wind Energy
3Tidal Energy
4Nuclear energy
A great demand of electrical energy is notable feature of modern civilization.
The abundance of electrical energy completely changes the direction of the tempo
of civilization, living standard, vast development of rural and urban areas.
Electricity has become an essential commodity. The feature of electrical energy not
only paralyses industries and agriculture but also upsets the lives.
The whole electrical system is classified as:
1 Generation
2 Transmission
3 Distribution
4 Utilization
5 Switchgear and protection

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Turbines are moved with the help of different sources of energy. The generation
is coupled with turbine to generate 11KV which is further stepped up by step up
transformers to 400KV and is then distributed to various sub-stations where the
voltage is reduced to 220KV with the help of step down transformers. From these
sub-stations the energy is distributed to the consumers after reducing it to 33KV.
1.2 Installation
The 400KV GSS Jodhpur is one of those stations, which distributes energy to
the consumers. The station was installed in 2003. Jodhpur is the second largest
city of the state Rajasthan.
1.2.1 The Incoming And Outgoing Feeder
The incoming supply is as follows:
1. 400 KV – Kankroli
2. 400 KV – Merta I
3. 400 KV – Merta II
4. 400 KV – Jaisalmer(Under Construction)
5. 400 KV – Rajwest (Under Construction)
The outgoing feeder is as follows:
1. 220 KV – Tinwari I
2. 220 KV – Tinwari II
3. 220 KV – Jodhpur I

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4. 220 KV – Jodhpur II
5. 220 KV – Bilara
6. 132 KV – Banar
7. 132 KV – Mathania
8. 33 KV – Salawas
9. 33 KV – Daijar
10. 33 KV – JU Alloy
11. 33 KV – DRDO
1.2.2 Location And Coverage
The 400KV GSS is situated on near SURPURA village, about 14-15 KM from
Jodhpur Railway Station. It covers as area of 110-120 beegha of land.

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CHAPTER-2
4:- IMPORRTANCE OF ELECTRICAL ENERGY
2.1 Introduction
Energy may be needed as heat, as light as motive power etc. the present
day advancement in science and technology has made it possible to convert
electrical energy into other desired form. This has given electrical energy place of
pride in the modern world. In fact the advancement of country is measured in
terms of per capita consumption of electrical energy. Electrical energy is superior
to all other forms of energy due to the following reasons
2.2 Conventional Forms And Easy Control
Electrical energy is a very convenient form of energy as it can easily converted
into any form of energy like heat, light mechanical etc.
2.3 Greater Flexibility
One important reason for preferring electrical energy is flexibility that it offers.
It can be easily transported from one place to another.
2.4 Cheapness
Electrical energy is cheaper than other forms of energy. Thus it is economical
to use this form of energy in domestic commercial and industrial purpose.
2.5 Cleanliness
Electrical energy is not associated with smoke, fumes or poisonous gases.
Therefore its use ensures cleanliness and health conditions.

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2.6 High Transmission Efficiency
The consumers of electrical energy are generally situated quite away from the
centers of its production. The electrical energy can be transmitted conveniently
and efficiently from the center of generation to the consumers with the help of
overhead conductors known as Transmission lines.

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CHAPTER-3
5:- FUNCTION AND SPECIFICATIONS OF VARIOUS
EQUIPMENTS AT 400KV GSS
3.1 Metering & Indicating Instrument
There are several metering & indicating instruments e.g. Ammeters,
voltmeters, energy meters etc installed in a sub-station to keep watch on circuit
quantities. The transformer is invariably used with them for satisfactorily
operation.
3.2 Bus Bars
Bus bars are the important components in a substation. There are several
bus bar arrangements the can be used in a substation. The choice of a particular
arrangement depends upon various factors such as system voltage, position of
substation, degree of reliability; cost etc. the following are the important bus bar
arrangement used in sub-stations:
a) Single bus bar systems
b) Double bus bars systems
c) Duplicate bus bars systems
In the 400KV GSS Surpura, Double bus bar substation and duplicate bus bar
system has been installed.
3.3 Control Cables
The control cable and the control system are required for officiating
automatic system. The cables employed for this purpose are multi-core cables
having 10 or 37 or 61 conductors are run to the required points. The conductors

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used in the 400 KV GSS are moose and conductors used in the 220 KV GSS are
tarantula.
3.4 Power Transformers
A transformer consists essentially of two or more electric circuit in the form
of winding magnetically interlinked by a common magnetic circuit. An alternating
voltage applied to one of the winding produces, by electromagnetic induction, a
correspondence emf in the other windings & energy can be transferred from the
ordinary circuit to the other circuit by means of the common magnetic flux and
the principle of mutual induction. A transformer is basically a static device in
which two or more stationary electric circuits are coupled magnetically, the
winding being linked by a common time varying magnetic flux. Even though the
static transformer is not an energy conversion device & involves only the
interchange of electrical energy between two or more electrical systems, it is an
extremely important component in many conversation systems.
Fig. 3
3.4.1Classification Of Power Transformer:

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1. According to usages
2. Step-up transformer
3. Step –down transformer
4. According to type of construction used:
5. Core type
6. Shell type
7. According to number of winding
8. Two winding transformer
9. Three winding transformer
10. Multi winding transformer
3.4.2 Terms Related To Transformer
1 Primary Winding:
The winding that is excited or energized by connecting it to an input source is
usually referred to as the primary winding.
2 Secondary Winding:
The winding to which the electrical load is connected and forms, which the
output energy is taken, are known as the secondary winding.

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3 HV Winding:
The winding which s operated at the high voltage level is known as the HV (high
voltage) winding.
4 LV Winding:
The winding which is operated at lower voltage level is known as the LV (low
voltage) winding.
4 Regulating Winding:
It is winding, which is used to regulate the voltage at different levels y
connecting tap changers across the winding. It consists of discrete numbers of
small windings with 2 or 3 terms in each ad they being connected in series.
6 Tertiary Winding:
In addition to the tradition primary and secondary windings, a transformer can
also have tertiary winding.
3.4.3 Main Parts Of Transformer Are As Follows
1. Core:
It consist terminated silicon steel in which quantity of silicon 13up to 4%
thickness of lamination is 0.35 to 0.50m. Normally the shape of core in rectangular
and it has three legs.
2. Windings: Windings of power transformer are an important part. It
consists of super enameled copper wires. The size of wire (diameter) depends on
the capacity of transformer connection of winding is r/r.

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3. Tap changer:
Tap changer is switching device by which the transformation ratio can be
changed by the changing the position of tap changing the switch. Tap changing
system on GSS of power transformer on-load tap changer (OLTC): On load tap
changers are employed to change turn ratio of transformer to regulate system
voltage while the transformer is delivering normal load with the introduction of on-
load tap changing the operating efficiency of electrical system has considerably
improved. Now a day, almost all the large power transformers are fitted with on
load tap changer. All forms of on load tap changing circuit posse’s impedance.
This is introduced to prevent short-circuiting of tapping section during tap changer
operation. The impedance can be either a resist of or a centre-tapped reactor.
4. Tanks:
It is metallic tank, which is filled of insulating oil the transformer core and
winding assembly are surrounding by the oil in this tank. It protects that the
winding and core from the external mechanical damages. Rectangular tanks are
similar in fabrication. However for large rating power transformer, shaping of
tanks becomes necessary to conform to transportable profile shaping is provided by
rounded corners at the ends, truncation of law portion of walls from considerable,
of loading in well wagon grider and on the covers to reduce the height to minimize
the tank oil, the tank profile may closely follows the electrical clearances along the
coils. As is evident, shaping gives saving in tank material and oil but increases
complexity and fabrication costs.
Transformer tank may be classified as
1Plain tanks.

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2Shaped tanks.
3Belt shaped tanks.
4Corrugated tanks.
5Stub and type tank
The transformer tank used in GSS power transformer is rectangular box (plain
tank) type in shape.
5. Cooling System:
In Power transformer, the oil serves a dual purpose as an insulating medium as
well as a cooling medium. The heat generated in the transformer is removed by
the transformer oil surrounding the source and is transmitted either to
atmospheric air or water. This transforms of heat is essential to control the
temperature within permissible limits for the class of insulation, thereby ensuring
longer life due to less thermal degradation.
Types of cooling used in GSS power transformer:
1ONAN type cooling: The generated heat can be dissipated in many ways. In case
of smaller rating of transformers, its tanks may be able to dissipate the heat directly
to the atmospheric dry while bigger ratings may require additional dissipating
surface in form of tubes/ radiators connected to tank or in the term of radiator tank.
In these cases, the heat dissipation is form transformer oil at atmospheric air by
natural means. This form of cooling is known as ONAN (Oil Natural, Air Natural)
types of cooling.
2 ONAF type of cooling: For further augmenting the rate of dissipating of heat,
other means such as fans blowing air on the cooling surfaces are employed. The
forced air takes away the heat at a faster rate, thereby giving better cooling rate
than natural air. This type of cooling called ONAF (Oil Natural Air Forced) type of

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cooling. In this cooling arrangement, additional raring under ONAN condition viz.
after shutting off fans, is available, which is of the order of 70-75%.
5.1 Cooling Arrangements
Depending upon the typed of cooling and rating of the transformer, the
cooling equipment can be arranged in various ways.
5.2 Arrangement with Radiators
Radiators are commonly used for ONAN and ONAF types cooling. Radiator
consists of element joined to and bottom headers, elements are made by welding
two previously rolled and pressed thin steel sheets to forms a number of channels
of flutes through which oil flow. These radiators can be either mounted directly
on the transformer tank or in a form of a bank or connected to the tank through
the piper. The surface area available for dissipation of heat is a multiple manifold
by using various elements in parallel. As oil passes downwards either due to
natural circulation or force of a pump in the cooling circuits, the surrounding
atmosphere air carries heat away.
5.3 Arrangements with Fans
These fans deliver large air volume at moderate speed with minimum
sound and low power consumption. Ring mounted fans are designed to give
maximum volume under free airflow condition and resistance up to
approximately 6mm WC. These fans generally conform to IS2312 and are used for
radiator cooling. Fan consists of a totally enclosed continuously rated specially
designed motor with class B insulation and IP-55 class of protection to meet fan
duty, impeller constructed with four broad faced. Steel sheet blades assembly on

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robust aluminum hub, four arms, pressed sheet mounting ring and four rubber
cushions.
Fig. 3.2

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6. Temperature Meters
There are two temperatures indicating metering power transformer, which
indicate the oil temperature and winding temperature. Temperature measured in
degree Celsius. A complete assembly of a transformer with details of core,
wingding, tank connections and major accessories.
7. Conservator and Air Cell
As the temperature of oil increases or decreases during operation there is a
corresponding rise or falling volume to account for this an expansion vessel
(conservator) is connected to the transformer tank. The conservator has got a
capacity between the minimum to maximum oil level equal to 7.5 & of the oil in
transformer. The atmoseal types conservator, it is filled with oil to level
appropriate to filling temperature and in remaining portion is air cell, which is
connected to atmosphere through a breather. As the breather is through air cell no
moisture come in contact with oil, this protect the oil from deterioration or
contamination.Air cell is a flexible separator filled inside the conservator. Oil
being out of the air cell, the separator is in direct contact with the atmosphere. The
advantage of air deterioration or contamination.
1. An efficient barrier between oil and air.
2. A protection against water vapors.
3. The suppression of any gas bubbles formation in the oil.
Air cell is made from coated fabric with external coating resistance to
transformer oil and inner to coating to ozone and weather.

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8. Buchholz’s Relay
The transformer is fitted with a bubble float buchholz rely. It is fitted in the
feed pipe from conservator to tank. Any internal fault in transformer is detected by
buchholz relay the gas liberated in the transformer is divided to the buchholz relay
without being trapped anywhere.
9. Dehydration Breather
The conservator is connected outside through dehydration (Silicage filled)
breather to make sure that the air in conservation is dry.
Fig. 3.4

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10. Oil Temperature Indicator
Oil temperature indicator operates on the principal of liquid expansion. The
OTI provided with a maximum pointer and two mercury switches are adjustable
to make contact between 500
to 1200
with the fixed differential of 100
. the
temperature for alarm and trip contact setting shall be as under:- alarm 800
to
900.
11. Winding Temperature Indicator
The indicator is fitted with four mercury switches, one is used for alarm, 2nd
is
for tripe and 3rd
is for fans on and 4th
pumps control. All the switches are
adjustable.
12. Earthing
Connecting leads from core and end frame are being terminated at the top at the
top of cover. By connecting them to tank cover, core and end frames being earthed.
For Bank earthing two number studs have been provided on tank.
13. Terminal Bushings
It is used to isolate the leads that are coming from transformer. The size of
the bushing is justified according to operation voltage of particular winding. The
active part of the bushing consists of an Oil Impregnated Paper (O.I.P.) condenser
core manufactured from superior grade craft paper would on aluminum tube. This
bushing is voltage graded by suitably interposed aluminum foils forming
condenser layers. Thus the electrical stress are controlled throughout the thickness
and along the surface avoiding any highly stress concentrations. The bushing is
supplied fully assembled in a wooden packing case with the busing supported at an

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angle of 10 degree to the horizontal. The bushing should never be placed
horizontally.
14. Insulating Oil
The insulating oil has three functions:
1Provides additional insulation
2Protects the paper from dirt and moisture
3Carries away the heat generated in the core and coils.
The Insulating oil should have the following properties :
i) High Dielectric Strength.
ii) Free from inorganic acid, alkali and corrosive sulphur to prevent injury to
the conductor or insulation.
iii)Low viscosity to provide good heat transfer
iv) Free from sludge under normal operating conditions.
v) Free from sludge under normal operating conditions.
vi) Good resistance to emulsion so that the oil may throw away any moisture that
enters the apparatus.
3.5 Lighting Arresters
They are used to protect the sub-station & transmission lines arrests
is earthed . Gap is adjusted in such a way that 50% over voltage is
operators. We will use value type lighting arresters this types is called non-
linear diverter. In this spark – gap & resistance disc are used . when there is
less change in line voltage than is not flashover in gap but when there is
over voltage & rapid change in voltage then even grounding of voltage will
not possible the value of flash over voltage depends on surge currents.
Operation will start when voltage will increase 10% of rated voltage.

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1. Rod gap arresters
2. Horn gap arresters
3. Multigap arresters
4. Expulsion type arresters
5. Value type arresters
3.6 Circuit Breakers
Classification of circuit breakers
1) Are quenching (Medium Wise)
a) Air Blast CB
b) Oil CB
c) Air Blast CB
d) Vacuum CB
e) SF₆ CB
2) Application wise :
a) Generator CB
b) Transformer Line CB
c) Industrial CB
d) Distribution CB
3) Voltage Level Wise:
a) HV/EHV CB
b) MV CB
c) LV CB
4) Base on Construction:
a) Dead Tank Breaker
b) Live Tank Breaker
G.S.S has SF₆ Circuit Breaker’s which have the following mechanism.

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6.1 SF₆ Circuit Breaker: In this CB, the SF₆ gas is used as an quenching agent. The
process of extinction by the gas is shown the below block diagram
At the time of fault:
Contracts of CB open
As a result, the medium between the contacts quickly builds up high
Dielectric Strength & causes the extinction of the arc.
The Valve mechanism permits high pressure SF₆ gas from the
reservoir to flow towards the are interruption chamber from the Trip
Valve, which is now NO-normally open.
The high pressure flow of the SF₆ gas rapidly absorbs the free
electrons in the are path to form immobile negative ions, which are
ineffective are charge carriers.

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Fig. 3.5
3.6.1.1 Electrical properties of SF₆
Electron affinity: The excellent insulation properties of sulphur hexafluoride are
attributable to the strong electron affinity of the SF₆ molecule. This is based

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mainly on two mechanisms, resonance capture and dissociative attachment of
electrons in accordance with the equations:
1) SF₆ +e→ SF₆
2) SF₆ + e → SF₅ + F
The process represented by equations (1) applies to electron energies of 0.1
eV with an energy range of 0.05eV and that represented by equations (2) applies to
an energy range of 0.1 eV.
1. Are-quenching capacity: On account of its thermal properties and low
ionization temperature, sulphur hexafluoride exhibits outstanding characteristics
for the extinguishing of electric arcs. The quenching time using SF₆ is about 100
times less than that using air.
2. Dielectric Strength: The strong interaction of hi-energy electrons with the
polyatomic SF₆ reaches that of transformer oil at pressure of only 3 bars. The
breakdown strength of SF₆ is independent of frequency. It is inert gas. Chemical
inertness of this gas is advantageous in switchgear. The components do not get
oxidized or deteriorated. The life of metallic part, Contacts is longer in SF₆ gas.
Hence the maintenance requirements are reduced.
3.6.1.2 Operating Principals Of Sf₆ Circuits Breaker:
The SF6 breaker operates on what is usually referred as the puffer principle. In
puffer type SF6 circuit breaker , the entire breaker is filled with SF6 gas at single
pressure of 5 Kg/cm2
or about 7 bar. The breaker is a sealed unit . during the
opening stroke the SF6 gas is compressed released through the nozzle of
insulating material. The compressed gas flow through the nozzle at a high velocity
and takes away the heat produced by the arc the arc is quenched at a current
zero. The high dielectric strength of gas is useful in giving good with stand voltage

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SF6 circuit breaker are explosion free , can quench capacitive currents , short
circuit current etc. Early and are used for high voltage circuit breakers for voltage
above 3.3 KV During manufacture of the breaker pole it is dried internally through
pumping, the breaker pole is then to pressurized and also tested against leaks
inside the pile there is a absorption medium for the decomposition products of
the gas. The breakers pole should only be opened by trained person at the
manufacturing factory.
3.7 Isolators
Then carrying out inspection or repair in a substation installation. It is essential
to disconnect reliably the unit or the section, on which the work is to be done,
from all other live parts of the installation in order to ensure complete safety of
the working staff. To guard against mistakes it is desirable that an apparatus,
which makes a visible break in the circuit, should do this apparatus is the isolating
switch. It may be defined as a device used to pen ( or close ) a circuit in the
voltage across the terminal e.g. each pole of the isolator will result from the
operation.
Isolators are classified as:
1. Off load isolator-It is an isolator which is operated when the isolator is already
disconnected from all sources of supply or when the isolator is already
disconnected from the supply and current may be due to capacitance current of
bushings bus bar connections and very short length of cable.
2. On load isolator -It is isolator, which is operated in a circuit where there is a
parallel path of low impedance so that no significant change in the voltage across
the terminals of each pole occurs when it is operated .

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3.8 Instrument Transformer
Is defined as a transformer intended to feed the measuring instruments,
meters, relays etc. Generally protective system are relays are connected to the
secondary of a current transformer as they cannot withstand high currents.
These IT’s help in reducing these voltages & currents to acceptable level
for operation of voltmeters & ammeters.
3.8.1 Current Transformer
A CT is an instrument transformer in which the secondary current is
substantially reduced proportional to the primary current & differs from it
by the angle which is approx. direction of current . These transformers are
different from general power transformers.
Fig. 3.6

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Shown below are the major differences that are noticeable:
Conventional Transformer Current Transformer
Driving Function: voltage. Driving Function : Current
Secondary load impedance determines
the secondary current.
CT primary current is the
determining and predominated
factor.
Corresponding to the secondary
current the primary current flows.
Secondary current follows the
primary current.
3.8.1.2 Function / Application of a CT
1. For Metering function : It transforms the high value Primary Current
substantially low value secondary current which can be fed directly to measuring
instruments for measuring the current & power in the main circuit.
2. For Protection Purpose: The secondary current can also feed Protective Relays
which operate the protective system in the main circuit in case of any abnormality
in the system.
Definition of the different terms related with current transformers :

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a) Rated Primary Current: The value of primary current on which the primary
performance of the current transformers is specified.
b) Rated Short Time Current: Its defined as r.m.s value of a.c component which
the CT can carry without damage.
c) Rated Secondary Current: The value of secondary current marked on the
rating plate.
d) Rated Exiting Current: The RMS value of current taken by the secondary
winding of a. C.T. When sinusoidal voltage of rated frequency is applied to
secondary with primary winding open.
e) Rated Burden: The burden assigned by the manufacturer at which C.T
performs with specified accuracy.
f) Current Error Ratio Error: The percentage error in the magnitude of secondary
current is defined in the terms of current error.
3.8.1.3 Burden on C.T.
Rated burden of CTS and VT’s referring to the maximum load in volt-
amperes 9 VAO which may be applied across the secondary terminals without the
ratio and phase angle error-exceeding the permissible limits. The burden depends
upon the number of relays and instruments connected and their individuals burden
typical values.
3.8.1.4 Various Types of Construction of CTs
A CT has following essential parts

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1. Insulation over the core by taps
2. Secondary winding having several turns would on the insulated core.
3. Bar primary passing through the window of the core and terminals.
4. Support porcelain or epoxy insulator.
5. Synthetic resin or oil insulation.
6. 3.8.1.5 CT’s For High Voltage Installations
Separately mounted post type CT’s are suitable for outdoor service. The
primary conductor is at high voltage with respect to the earth. Hence it is
insulated by means of insulation column filed with dielectric oil. In high voltage
CT’s the primary and secondary windings are situated at the upper end of the
unit. The primary wdg. Normally being of bar type. The top – fabricated housing is
at line potential and is supported on the porcelain insulator.
3.8.1.6 Specification Of 400 KV Current Transformers
1. Type – Dead tank, single phase out door, oil immersed & Hermetically sealed .
2. Manufacturer’s Designation – 420 kV CT.
3. Rated voltage ( KV ) – 420
4. Short time thermal rating for One second ( KA rms ). – 40
5. Rated dynamic current of primary 100 ( Kapeak).
6. Flux density at knee point voltage, 14.5 Wb/cm2
7. NO. of primary turns – single
8. No. of secondary turns – 200-1000-500
9. Core area , cum2 – 65.55
10.Core length, (Average magnetic path) cms. – 104.46
11.Type of primary winding – Hair pin type.

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12.1 Temperature rise (degree C) at rated continuous thermal current over max.
ambient temperature at site for –
i) Winding 40
ii) Oil at top 40
iii) Exposed current carrying parts 55
12.2 Temperate rise at normal rating over max. Ambient temperature site for
i) Winding 40
ii) Oil at top 40
iii) Exposed current carrying parts.
13.Total creep age distance, mm 10500
14.Protection creep age distance 5250
15.One minute power frequency with stand test voltage ( kv rms ) 630
16.250/2500 micro seconds switching impulse withstand voltage (kv peak) 1050
17.1.2/50 micro second impulse withstand test voltage (kv peak) 1425
18.Power frequency withstand test 4 kv for core IV & V and Voltage on secondary
(kv rms) 3 kv rms for core III
19.Weight of oil per C.T. kegs. 510
20.Governing standard for oil IS 335
21.Whether pressure relief device Yes Provided.
22.Total weight per CT kgs. 2150
23.Overall dimension .mm 1150 x 750 x 5200
24.Current density in primary winding at
i) Normal rating A/cm2 208

34. 34
ii) Thermal rating for 1 sec., A.cms 249
iii) Dynamic rating, A/cm2 10405
25.Visual corona extinction voltage 320 (k Vrms)
3.8.2 Potential Transformers
Potential transformers (PT) are mainly instrument transformers that are
basically used for the following purposes :
1. For stepping down the voltage for measurement
2. As line voltmeters
3. Protective relays
4. Tariff meters
3.8.2.1 Construction
The PT is mostly step down and shell type. The secondary voltage is generally
110 V potential transformers are of two types :
a. Magnetic type
The magnetic type PT work on the principles of power transformers. The design
is particularly for the system voltage of 132 K.V. and above where it becomes
increasingly more economical. Main parts of the PT are stated below :-
1. Core: The core may be shell type in its construction. Shell type core is
suitable for low voltage transformers.
2. Winding: The primary and the secondary winding are coaxial to reduce
leakage to minimum. The primary winding may be single coil but must be
subdivided.

35. 35
3. Insulation: Cotton type and varnished cambric are used or soil
construction. Hard fiber separators are used between coils. At low voltages, the
transformers are usually filled without above 700 volts been developed for use up
to 45 K.V.
b. Capacitor voltage transformers (CVT)
CVT are used for line voltmeters synchroscropes, protective relays, tariff meter
etc. The supply frequency-switching transients, magnitude of connected burden
etc, affect the performance of CVT. The CVT is more economical then an
electromagnetic voltage transformers when the nominal system voltage increase
above 66 KV. The carrier current equipment can be connected via the capacitor
voltage transformers, thereby there is no need of separated coupling capacitors.
The CVT are used for voltage above 66 KV and above. At such voltage the costs of
electromagnetic voltage transformer is too high. The capacitor connected in
series with the CVT acts like a potential divider. The burden provided by the
capacitor is negligible. The construction of CTV depends on the form if the
capacitors voltage divider. Generally HV capacitors are enclosed in porcelain
housing. Schedule of guaranteed data and technical particulars for 4400-pf-400KV
capacitor voltage transformers.
3.9 Insulators
The insulators serve two purposes. They support the conductors and confine
the current to the conductors. The most commonly used material for the
manufacture of insulator is porcelain. There are several types of insulators and
there use in the substation will depend upon the service requirement. It is

36. 36
stronger mechanically than glass gives less trouble from leakage & is less affected
by change of temperature.
Type of insulators
i) Pin type Insulator
ii) Suspension type insulator
iii)Strain Insulator
iv) Shackle Insulators
v) Post Insulators.
Their use in the substation will depend upon the service requirement.
3.9.1 Pin type Insulator
Pin type of insulator is not economical beyond 33 KV. For high voltage (>33
kV), it is a usual practice to use suspension type insulators. They consist of a
number of porcelain discs connected in series by metal links in the form of a
starting. The conductor is suspended at the bottom end of the string while the
other end of the string is secured to the cross-arm of the tower. Each unit or disc is
designed for low voltage. If working voltage is 66kv, and then six discs in series
will be provided in the string.
3.9.2 Strain Insulators
When there is a dead end of the line or there is corner or sharp curve the
line is subjected to greater tension. In order the line of excessive tension are
used. For high voltage transmission lines, strain insulators consists of an assembly
of suspension the tension in lines is exceedingly high, 2 or more strings are used
in parallel.

37. 37
CHAPTER- 4
6:- POWER LINE CARRIER COMMUNICATION (PLCC)
4.1 Introduction
For exchange of dates & transfer of message between GSS voice
communication is necessary. High frequency carrying currents audio signals is
generated, transmitted & received with the help of identical carrier current
equipment provided on each end. Carrier current equipment comprises of
following:
1. Coupling Capacitor
It acts like a filter. It blocks power frequency (50hz) while offer low reactance
to carrier frequencies as allows them to pats through because. For examples A
2000 pf capacitors offer 1.5-mega ohm to 50hz while if just offer 150 ohms to 500
kHz. Thus coupling capacitor allows carrier frequency signal to enter the carrier
equipment bus does not allow 50hz power frequency current to enter the carrier
equipments.
2. Wave Trap Unit
It is parallel turned comprising of c & I. It has low impedance to 50hz & high
impedance to carrier frequencies get passed through wave trap & carrier
frequencies passes through coupling capacitor & reaches carrier current Wave
traps are mounted in outdoor switchyard. Wave trap mounted at GSS is “under
hung”.

38. 38
3. Transmitter & Receiver Unit
Carrier current unit acts like both transmitter receiver carrier frequencies are
generated in master oscillator can be tuned to a particular frequency selected for
the application output voltage of oscillator is held constant by voltage stabilizers.
Output of oscillators is fed to amplifiers, which increases the strength of signal to
be transmitted to overcome the transmission losses. Line losses vary with length of
line frequency type of line losses in overhead lines. Receiving unit comprises of an
alternator. Band pass filter restricts the acceptance of uncounted signal & matching
transformer or matching element matches the impedance of line & receiving unit
block diagram of receiving of receiving unit.

39. 39
CHAPTER- 5
7:- SUBSTATION
5.1 Introduction:
Substations are important part of power system. The assembly of apparatus
used to change some characteristics (e.g. voltage, arc. to o.k. frequency, p.f etc) of
electrical supply is called substation.
5.2 Classification of Substation
There are several ways of classifying substations. However, the two most
important ways of classifying them are according to:
1) Service requirements and
2) Constructional features
1. According to service requirements:
a) Transformer sub-stations
b) Switching substations
c) Power factor control substation
d) Frequency changer sub stations
e) Converting substations
f) Industrial sub stations
2. According to constructional features:
a) Indoor sub-stations
b) Outdoor sub-stations
c) Underground sub-stations
d) Pole-mounted sub-stations

40. 40
CHAPTER-6
8:- PROTECTIVE RELAY
6.1 Introduction
In order to generate electric power and transmit to customers, millions of rupees
must be spent on power system equipment. This equipment is designed to work
under specified normal conditions.
However a fault may occur causing the system to collapse. This fault occurs
because of:
1) Over voltage due to switching.
2) Over voltage due to direct and indirect lighting strokes.
3) Bridging of conductors by birds.
4) Breakdown of insulation due to decrease of its dielectric strength.
5) Mechanical damage of equipment.
These short circuits may cause heavy damage to equipment and would also cause
intolerable interruption of service to customers.
6.2 Relays
Relays are the devices that detect abnormal conditions in electrical circuits
by constantly measuring electrical quantities, which are different under normal
and fault conditions. The basic electrical quantities, which may change under fault
conditions, are voltage, current, phase angle and frequency. Having detected the
faults the relays operates to competent the trip circuit which result in opening of
the circuits breaker and therefore in the disconnection of the faulty circuits.

41. 41
Basic requirements of protective relaying:
A well designed and protective relaying should have
i) Speed
ii) Selectivity
iii)Sensitivity
iv) Reliability
v) Simplicity
vi)Economy
6.3 Types of Protection
There are two types of protection known as primary and back up. The
primary protection is the first line to defense and primary relays clear faults in the
protected system as fast as possible. The reliability, not only if the protected
scheme but also of the associated C.T.’s, P.T.’s and the C.B.’s cannot be
guaranteed. Therefore some sort of back up protection must be provided. The
backup relay operates if the primary relays fails and covers not only the local
primary relays to operate. Protective relays are classified depending upon their
construction and principles of operation such as:-Ordinary electromagnetic relays
consisting of moving plunger, moving iron, attracted armature hinged and
balanced beams types of relays are various examples, D.C. actuated such replays.
Electromagnetic induction or simply induction relays use the principles of
induction motors (whereby torque is developed by induction in rotor) in their

42. 42
operation. Such relays are actuated by A.C. quantities only. Electro thermal relays
(thermal overload protection using bimetallic strip) Physic-electrical relays:
Bucholy’s relays are examples of this type. Static relays employing thermionic
valves, transistors or magnetic amplifiers to obtain the operating characteristics.
Electro-dynamic relays operate on the same principles as moving coil instrument.
The various types of relays installed at 400 KV GSS are: -
1) Over current relays
2) Distance relays
3) Differential relays
4) Earth fault relays
1) Over Current Relays:
Directional type over current relays works on the induction principles and
initiates corrective measures when current in the circuit. Exceed the pre-
determined value. The actuating source is a current in the circuit supplied to the
relay from a current transformer. These relays are used on a.c. circuits and can
operate for fault flow in either direction. But their relays are unsuitable for use as a
directional protective relay under short circuit conditions. When a short circuit
occurs, the system value falls to a low value and there may be insufficient torque
developed in the in the relays to cause its operation. This difficulty is over come in
the directional over current relays, which is designed to be almost independent of
system voltage and power factor.
Operation:
Under normal operating conditions, powers flows in the normal direction in the
circuit protected by the relays. Therefore, directional power relays (upper element)

43. 43
does not operate, thereby keeping the over current element (lower element)
energized. However when a short circuit occurs, there is tendency for the current or
power to flow in the reverse direction. Should this happen, the disc of the upper
elements rotates to bridge the fixed contact 1 and 2. This completes the circuits for
over current elements. The disc of this element rotates and the moving contact
attached to it closes and the trip circuit. This operates this circuits breaker which
isolates final tripping of the current by them is not made till the following
conditions are satisfied: -
(a) Current flows in a direction such as to operate the directional element.
(b) Current in the reverse direction exceed the pre-set value.
Grading of the time lags of the relays, which controls a number of switches in a
feeder. These relays automatically adjust their time of operation depending upon
their distance from fault.
There are four main elements in any distance protection as follows: -
(i) Operating elements “O”: The element brings protection into action whenever
a fault occurs within the protected zone.
(ii) Directional elements “S”: This gives directional features to the operation of
the system and is useful in network having duplicate feeder. As soon as the fault
current into the bus bar from the line this element operates.
(iii) Distance element “Z”: This is sensitive to the ratio of the operating voltage
to the fault current i.e. V/ if or upon fictitious impedance when looking into the
system from the fault.
Zf=V/1f

44. 44
The value of Zf is dependent upon the distance of the fault from the relays. The
principle of this element is more or less like ohmmeter.
(iv) Time delay element “T”: This element creates a time lag, the importance of
which has already been discussed above. This time lag depends upon the distance
of the fault point from the relay.
2) Distance Relay:
Distance protection is the name given to the protection, whose action depends
upon the distance of the feeding point to the fault. The time of operation of such a
protection is a function of the ratio of voltage and current, i.e. impedance. This
impedance between the relay and the fault is dependent upon the electrical distance
between them. An impedance relay has an operating force proportional to the fault
current and restraining force proportional to the line voltage at the relay. As soon
as the ratio of this voltage to the fault current change i.e. falls below a certain
value, the relay operates. This value is dependent upon the distance of the fault,
which is predetermined. Hence for this reason the relay is discriminative and it
does not operate for any fault occurring outside this distance. As it is very
important to localize the fault, a relay of the above type is given a controlled time
lag, so that the relay nearest to the fault operates first. This time lag is made
proportional to the distance of the fault by so designing the relay that it has a time
lag characterizes, which is dependent upon the line voltage at the relay directly.
Again, the time lag characteristic is inversely proportional to the fault current that
is passing through the relay. In case of a fault, there is a steady fall of voltage along
the line from the feeding point to the fault. This voltage gradient can be utilized for
longer be in balance. This voltage difference will cause a current to flow through
the operating coil of relay, which closes the trip circuit.

45. 45
3) Differential Relays:
A differential relay is one that operates when the difference of two or more
electrical quantities exceeds a predetermined value. Almost any type of relay
connected, in a certain way, can be made to operate as differential relays. There
are two fundamental system of differential protection viz.
1) Current balance protection
2) Voltage balance protection
A current balance differential relay is one that compares the current entering a
section of the system of the system with the current leaving the section. Under
normal operating condition no longer applies. If this differential current is equal
to or greater than the pick-up value, the relay will operate & open the circuit
breaker to isolate the faulty section. Under healthy condition equal current flows
in both primary windings. Therefore the secondary voltages are balanced against
each other & no current will through the relay-operating coil.
4) Earth Fault Relays:
Directional type over current relays work on the induction principle and
initiates the char-active measures. When current in the circuit exceeds the
predetermined values. The actuating source is a current in the circuit supplied to
the relay from a CT. these relays are unsuitable for use as directional protective
relays under short-circuit conditions. When a short circuit occurs, the system
values falls to a low value and there may be insufficient torque developed in the
relay to cause its operation. This difficult is overcome in the directional over
current relay, which is designed to be almost independent of system voltage an

46. 46
CHAPTER- 7
9 :- EARTHING
7.1 Introduction
Connecting of an electrical equipment or apparatus to the earth with the help
of a connecting wire of negligible resistance is called as “Earthling or
grounding”. The provision of earth electrode for an electrical system is necessity
by following reasons.
1. All the parts of an electrical equipments like casings of machines circuit
breaker, lead sheathing & armoring of cables, tanks of transformer etc, which have
to be the at earth potential, must be connected to an earth electrodes. This current
operates the proactive device & thus the faulty circuits is halted in case occur.
2. The electrode ensures that in the event of over voltage of an the system due to
lighting discharge or other system faults which are normally “dead” as for as
voltage are concerned do not attain dangerously high potentials.
3. In a 3-phase circuit the neutral of the system is earthed in order to stabilize the
potentials of the circuit with respect to earth. In electrical installations the
following components must be earthed: -
a) The flames, tanks & enclosed of electric machines transformers and apparatus,
lighting fitting.
b) The operating mechanism of the switchboards control boards individual panel
boards, cubicles.
c) The structural steel work of sub-stations, metal cable jointing boxes, the metal
sheaths of the cable s the rigid metal conduct runs & similar metal work.
There are 2 methods of earthing:
1- Pipe earthing.

47. 47
2- Plate earthing.
7.2 Earthing Arrangements 400 KV GSS
In a GSS or any magnitude various non current carrier equipment
to be earthed namely substation structures , shielding g wires or masts
,equipments tanks spread over large areas therefore it becomes necessary to
lay a grounding bus connect the various items to be earthed to be ground
bus through suitable connection to heave duplicate earthing is broken the
sub - station may remains safe under all conditions . It generally, therefore
becomes desirables to form a ring of the earthing electrodes. Another way of
looking into the sub - station earthing problem is that a very low
Earthing problem is that a very low earthing resistance value is
required resistance in a very large low earthing value is required in a large
areas occupied but the sub - station such can only be obtained by using a
number of rod & joining them in parallel .In a sub -station the earthing
system invariably takes the shape of grounding meet with necessary or
additional rounding rods accepts in the case of very small sub stations.
Common earth electrodes should be use for both system earths & equipments
earth. Here also it is recommended to have common earth bus for high voltage
system. Where there are manual operating handle to the system .A typical earthing
arrangements for a GSS .
7.3 Plate Earthing
In plate earthing plate either of copper of dimensions 600cm * 60cm
*3.15mm or of galvanized iron of dimensions 60cm * 60cm * 6.30cm s
burled into the ground with its face vertical at a depth of not less that 3mt
from ground levels .A small masonry brick wall enclosure with a cast iron

48. 48
cover or top an RCC pipe round the earth plate is provided to facilitate its
identification & for carrying out periodical inspection & tests. The earth wire
GI wire of GI plate earthing is securely. Bolted to an earth place with the help of a
bolt nut & washer made of material & of galvanized iron in case of GI plate
earthing.

49. 49
Chapter-8
10:- LABORATORY
8.1 Introduction:
The Laboratory at 400 KV GSS substation is equipped with various
instruments to test the transformer oil. It is very important to test the oil at regular
intervals. It also used to test the oil in failure conditions to find out the reason of
failure.
8.2 Importance of Transformer Oil
1. The Oil serves dual purpose of insulating medium & coolant.
2. Heat generated inside a Transformer is dissipated to the Atmosphere
through Insulating Medium.
3. This ensures Longer Life & Less Thermal Degradation of Insulation.
4. Provide Arc Quenching Medium.
8.3 Deterioration of Transformer Oil
1. Accidental Leakage of Water
2. Chemical Decomposition
3. Contamination by Gases
4. Electrical Stresses
5. Thermal Stresses
6. Effect of Oxidation Products
7. Physical Contamination

50. 50
11 Conclusion
Now from this report we can conclude that electricity plays an important role in
our life. We are made aware of how the transmission of electricity is done. We
too came to know about the various parts of the Substation system.
The Rajasthan Rajya Vidyut Prasharan Nigam Limited (RRVPNL) has
got radio communication in microwave range in order to transmit and receive
data with various Substations in Uttar Pradesh to get reliable transmission and
distribution of electricity.

51. 51
Some Full Forms Related To Substations
S.No. Short Forms Full Forms
1. PLCC Power Line Carrier Communication
2. LA Lightning Arresters
3. CBT Capacitor Bank Transformer
4. CT Current Transformer
5. PT Potential Transformer
6. CVT Capacitive Voltage Transformer
7. LV Low Voltage
8. HV High Voltage
9. DCDB Direct Current Distribution Board
10. CTR Current Transfer Ratio
11. VTR Voltage Transfer Ratio
12. LSI Line Side Isolator
13. BSI Bus Side Isolator
14. CB Circuit Breaker
15. TI Tendom Isolator
16. BCT Base Current Transformer
17. MRI Meter Reading Instrument
18. OTI All Temp. Indicator
19. WTI Winding Temp. Indicator
20. kV Kilo Voltage

52. 52
12 Reference
1. www.wikipedia.com
2. www.yahooanswers.com
3. www.britannica.com
4. www.webopedia.com
5. www.encyclopedia.com
6. www.worldbook.com
7. www.encyclopediadramatica.com/