Traning report on 220 kv gss sitapura

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A
PRACTICAL TRAINING REPORT
ON
220 kV G.S.S. SITAPURA, JAIPUR (RVPNL) SUBMITTED FOR
PARTIAL FULFILLMENT OF
BACHELOROFENGINEERING
BMIT JAIPUR
Session:2018-19
SUBMITTED TO- SUBMITTED BY-
Mr.- Rajneesh Suhalka Sumit Kumar
HOD of Electrical Department 15EBMEE049
VII SEM EE
DEPARTMENT OF ELECTRICAL ENGINEERING BALDEV RAM
MIRDHA INSTITUTE OF TECHNOLOGY,JAIPUR

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ACKNOWLEDGEMENT
I feel immense pleasure in conveying my heartiest thanks and deep sense of gratitude
to
Head of the Electrical Engineering Department of BALDEV RAM MIRDHA
INSTITUTE OF TECHNOLOGY, Jaipur for his efforts and for technical as well as
moral support.
Engineers and other technical and non technical staff, for helping in understanding the
various aspects and constructional detail of work and site in 220kV Grid-Sub Station,
Sitapura, Jaipur.
It may not be possible for me to acknowledge the support of all my friends, but I am
thankful to all my colleagues and other trainees for their valuable ideas and support
during training period.
Sumit kumar

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PREFACE
A rapid rise in the use of electricity is placing a very heavy responsibility on electrical
undertaking to maintain their electrical network in perfect condition, young engineers
is called upon to do design, system planning and construction and maintenance of
electric system before he had much experience and practice soon may be responsible
for specialize operation in an ever expending industry. Theoretical knowledge gained
in their college courses need to be supplemented with practical know-how to face this
professional challenge, so……..
As a part of our practical training we have to attempt the rule of Rajasthan Technical
University, Kota. I look my practical training at 220 kV G.S.S. Sitapura, Jaipur. Since
my training center was of Grid Sub-station hence I have included all updated
information, to the extent possible, including general introduction and brief
description of starting sub-station of 220 kV G.S.S. in this study report.
During my 60 Working days practical training, I had undertaken my training at 220
kV G.S.S. at Sitapura, Jaipur.
I had taken my first practical training at 220 kV G.S.S. Sitapura, Jaipur.
The period of training was from 07/05/2018 TO 07/07/2018.
This report dealt with the practical knowledge of general theory and technical
data/detail of equipments, which I have gained during the training period at 220 kV
GSS, Sitapura, Jaipur.
Page No.

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CONTENTS
Topic
Training Certificate ……………………………………………………………I
Acknowledgements …………………………………...…………………II
Preface ……………………………………………………………………….. III
1. Introduction………………………………………………………………...01
• 220kV G.S.S. Sitapura, Jaipur……………………………….….01
• Incoming feeders…………………………………………………….01
• Outgoing feeders…………………………………………………….02
2. Bus bars………………………………………………………………….…03
• Bus bar arrangement………………………………………………....03
3. Isolators………………………………………………………...……….….05
4. Insulators…………………………………………………………………...06
• Type of insulators…………………………………………………...06 o Pin
type……………………………………………………….06 o Suspension
type………………………………………………07 o Strain
type…………………………………………………….08
5. Protective relays………………………………………………………........09
Distance relays……………………………………………………....10
• Buchholz relay………………………………………………………11
6. Circuit Breakers………………………………………………………........12
Operating principle………………………………………………….12
• Classification of circuit breakers……………………………...…….12
• SF6 Circuit Breaker ………………………………………….……..13

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• Air Blast Circuit Breaker……………………………………..……..15
• Oil Circuit Breaker…………………………………………….……17
• Bulk Oil Circuit Breaker……………………………………………17
• Minimum Oil Circuit Breaker………………………………………18
7. Power Transformers……………………………………………………….19
• Basic parts of transformer……………………………………...…...19
8. Current transformer…………………………………………………..…...23
9. Potential transformer………………………………………………..…….24
10. Capacitive voltage transformer (CVT)……………………………………25
11. Transformer oil & its testing………………………………………………27
• Transformer Oil Testing Procedure………………………………...27
12. Lightening Arrestor……………………………………………………….29
220 kV lightening Arrestor Rating……………….………………...30
13. Control Panel…………………………………………..………………….31
14. Measuring Instruments………………………….………………………...32
15. Capacitor Bank…………………………………………………………... 33
16. Earthing of the system………………………………………………….34
Procedure of Earthing…………………………………………..…..34
• Neutral Earthing………………………………………………..…...35
17. Ratings…………………………..………………………………………....36
Transformers…………..………………………………………..…..36
• Circuit Breaker………………………………………………..…….36
• Battery Charger…………………………………………...………...37
• Current Transformer……………………………………………..…38

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• Capacitive Voltage Transformer…………………………………....38
18. Power Line Carrier Communication............................................................39
19. Conclusion………………………………………………….……………...41

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FIGURE INDEX
Figure Page No.
Figure 2.1 Bus Bars ………………………………………………………...4
Figure 4.1 Pin Type Insulator ……………...……………………………….7
Figure 4.2 Suspension type insulators ………...……………………………7
Figure 4.3 Strain Insulators ……………………...…………………………8
Figure 5.1 Relays …………………………………...………………………9
Figure 5.2 Buchholz Relay …………………………..……………………..11
Figure 6.1 SF6 Circuit Breaker ……………………….……………………13
Figure 6.2 Air Blast Circuit Breaker ………………….……………………15
Figure 7.1 Power Transformer ………………………….………………….20
Figure 7.2 Radiator with fan ………………………………………………..21
Figure 7.3 Winding and oil temperature indicator …………………………21
Figure 7.4 Silica gel Breather ………………………………………………22
Figure 8.1 Current Transformers ……………………….………………….23
Figure 10.1 CVT connection …………………………….………………...25
Figure 10.2 CVT ………………………………………….………………..26
Figure 13.1 Control Room in GSS Sitapura, Jaipur ….………………...31
Figure 15.1 Capacitor Bank ……………………………….………………..33

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1. INTRODUCTION
Electrical power is generated, transmitted in the form of alternating current. The
electric power produced at the power stations is delivered to the consumers through a
large network of transmission & distribution. The transmission network is inevitable
long and high power lines are necessary to maintain a huge block of power source of
generation to the load centers to inter connected. Power house for increased reliability
of supply greater.
The assembly of apparatus used to change some characteristics (e.g. voltage, ac to
dc, frequency, power factor etc.) of electric supply keeping the power constant is
called a substation.
Depending on the constructional feature, the high voltage substations may be further
subdivided:
(a) Outdoor substation
(b) Indoor substation
(c) Base or Underground substation
1.1. 220 kV G.S.S. Sitapura, Jaipur
1. It is an outdoor type substation.
2. It is primary as well as distribution substation.
3. One and half breaker scheme is applied.
1.2. Incoming feeders:
The power mainly comes from:
220 KV:-

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1. IG NAGAR
2. SANGANER
3. DURGAPURA(FUTURE).
1.3. Outgoing feeders:
132 KV 33 KV
1) Chambal 1) Nirman Nagar I & II
2) SMS Stadium 2) Bisalpur Pump House I & II
3) Sanganer I & II 3) Kaveri Path
4) JMRC I & II 4) Triveni
5) Adinath
6) Kiran Path
Table 1.1: Outgoing Feeder
As this substation following feeders are established:
1. Radial Feeders.
2. Tie Feeders

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2. BUS BARS
Bus Bars are the common electrical component through which a large no of feeders
operating at same voltage have to be connected.
If the bus bars are of rigid type (Aluminum types) the structure height are low and
minimum clearance is required. While in case ofstrain type of bus bars suitable ACSR
conductor are strung/tensioned by tension insulators discs according to system
voltages. In the widely used strain type bus bars stringing tension is about 500-900
Kg depending upon the size of conductor used.
Here proper clearance would be achieved only if require tension is achieved. Loose
bus bars would effect the clearances when it swings while over tensioning may
damage insulators. Clamps or even affect the supporting structures in low temperature
conditions.
The clamping should be proper, as loose clamp would spark under in full load
condition damaging the bus bars itself.
2.1. BUS BAR ARRENGEMENT MAY BE OF FOLLOWING TYPE
WHICH IS BEING ADOPTED BY R.R.V.P.N.L.:-
2.1.1) Single bus bar arrangement
2.1.2) Double bus bar arrangement
a) Main bus with transformer bus
b) Main bus-I with main bus-II
2.1.3) Double bus bar arrangement with auxiliary bus.
1. Each load may be fed from either bus.

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2.1.1. DOUBLE BUS BAR ARRANGEMENT :
2. The load circuit may be divided in to two separate groups if needed from
operational consideration. Two supplies from different sources can be put on
each bus separately.
3. Either bus bar may be taken out from maintenance of insulators.
The normal bus selection insulators can not be used for breaking load
currents. The arrangement does not permit breaker maintenance without
causing stoppage of supply.
2.1.2. DOUBLE BUS BAR ARRANGEMENTS CONTAINS MAIN BUS
WITH AUXILARY BUS :
The double bus bar arrangement provides facility to change over to either bus to carry
out maintenance on the other but provide no facility to carry over breaker
maintenance. The main and transfer bus works the other way round. It provides
facility for carrying out breaker maintenance but does not permit bus maintenance.
Whenever maintenance is required on any breaker the circuit is changed over to the
transfer bus and is controlled through bus coupler breaker.
Fig. 2.1:- Bus Bars

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3. ISOLATORS
“Isolator" is one, which can break and make an electric circuit in no load condition.
These are normally used in various circuits for the purposes of Isolation of a certain
portion when required for maintenance etc. Isolation of a certain portion when
required for maintenance etc. "Switching Isolators" are capable of
• Interrupting transformer magnetized currents
• Interrupting line charging current
• Load transfer switching
Its main application is in connection with transformer feeder as this unit makes it
possible to switch out one transformer, while the other is still on load. The most
common type of isolators is the rotating centre pots type in which each phase has three
insulator post, with the outer posts carrying fixed contacts and connections while the
centre post having contact arm which is arranged to move through 90` on its axis.
The following interlocks are provided with isolator:
a) Bus 1 and2 isolators cannot be closed simultaneously.
b) Isolator cannot operate unless the breaker is open.
c) Only one bay can be taken on bypass bus.
d) No isolator can operate when corresponding earth switch is on breaker.

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4. INSULATOR
The insulator for the overhead lines provides insulation to the power conductors from
the ground so that currents from conductors do not flow to earth through supports.
The insulators are connected to the cross arm of supporting structure and the power
conductor passes through the clamp of the insulator. The insulators provide necessary
insulation between line conductors and supports and thus prevent any leakage current
from conductors to earth. In general, the insulator should have the following desirable
properties:
• High mechanical strength in order to withstand conductor load, wind load etc.
• High electrical resistance of insulator material in order to avoid leakage currents
to earth.
• High relative permittivity of insulator material in order that dielectric strength
is high.
• High ratio of puncture strength to flash over.
These insulators are generally made of glazed porcelain or toughened glass. Poly
come type insulator [solid core] are also being supplied in place of hast insulators if
available indigenously. The design of the insulator is such that the stress due to
contraction and expansion in any part of the insulator does not lead to any defect. It is
desirable not to allow porcelain to come in direct contact with a hard metal screw
thread.
4.1. TYPE OF INSULATORS:
4.1.1: Pin type
4.1.2: Suspension type
4.1.3: Strain insulator

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4.1.1. PIN TYPE: Pin type insulator consist of a single or multiple shells adapted
to be mounted on a spindle to be fixed to the cross arm of the supporting
structure. When the upper most shell is wet due to rain the lower shells are
dry and provide sufficient leakage resistance these are used for transmission
and distribution of electric power at voltage up to voltage 33 KV. Beyond
operating voltage of 33 KV the pin type insulators thus become too bulky
and hence uneconomical.
Fig. 4.1:- Pin Type Insulator
4.1.2. SUSPENSION TYPE: Suspension type insulators consist of a number of
porcelain disc connected in series by metal links in the form of a string. Its
working voltage is 66KV. Each disc is designed for low voltage for 11KV.

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Fig. 4.2:- Suspension type insulators
4.1.3. STRAIN TYPE INSULATOR: The strain insulators are exactly identical
in shape with the suspension insulators. These strings are placed in the
horizontal plane rather than the vertical plane. These insulators are used
where line is subjected to greater tension. For low voltage lines (< 11KV)
shackle insulator are used as strain insulator.
Fig. 4.3:- Strain Insulators

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5. PROTECTIVE RELAYS
Relays must be able to evaluate a wide variety of parameters to establish that
corrective action is required. Obviously, a relay cannot prevent the fault. Its primary
purpose is to detect the fault and take the necessary action to minimize the damage to
the equipment or to the system. The most common parameters which reflect the
presence of a fault are the voltages and currents at the terminals of the protected
apparatus or at the appropriate zone boundaries. The fundamental problem in power
system protection is to define the quantities that can differentiate between normal and
abnormal conditions.
This problem is compounded by the fact that “normal” in the present sense means
outside the zone of protection. This aspect, which is of the greatest significance in
designing a secure relaying system, dominates the design of all protection systems.

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Fig. 5.1: -Relays
5.1. Distance Relays:
Distance relays respond to the voltage and current, i.e., the impedance, at the relay
location. The impedance per mile is fairly constant so these relays respond to the
distance between the relay location and the fault location. As the power systems
become more complex and the fault current varies with changes in generation and
system configuration, directional over current relays become difficult to apply and to
set for all contingencies, whereas the distance relay setting is constant for a wide
variety of changes external to the protected line.
5.2. Types of Distance relay:-
5.2.1. Impedance Relay:
The impedance relay has a circular characteristic centred. It is non directional
and is used primarily as a fault detector.
5.2.2. Admittance Relay:
The admittance relay is the most commonly used distance relay. It is the tripping
relay in pilot schemes and as the backup relay in step distance schemes. In the
electromechanical design it is circular, and in the solid state design, it can be
shaped to correspond to the transmission line impedance.
5.2.3. Reactance Relay:
The reactance relay is a straight-line characteristic that responds only to the
reactance of the protected line. It is non directional and is used to supplement
the admittance relay as a tripping relay to make the overall protection
independent of resistance. It is particularly useful on short lines where the fault
arc resistance is the same order of magnitude as the line length.

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5.3. Buchholz Relay:
This has two Floats, one of them with surge catching baffle and gas collecting
space at top. This is mounted in the connecting pipe line between conservator
and main tank. This is the most dependable protection for a given transformer.
Gas evolution at a slow rate that is associated with minor faults inside the
transformers gives rise to the operation or top float whose contacts are wired
for alarm. There is a glass window with marking to read the volume of gas
collected in the relay. Any major fault in transformer creates a surge and the
surge element in the relay trips the transformer. Size of the relay varies with oil
volume in the transformer and the mounting angle also is specified for proper
operation of the relay.

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Fig. 5.2:-Buchholz Relay
6. CIRCUIT BREAKER
The function of relays and circuit breakers in the operation of a power system is to
prevent or limit damage during faults or overloads, and to minimize their effect on the
remainder of the system. This is accomplished by dividing the system into protective
zones separated by circuit breakers. During a fault, the zone which includes the faulted
apparatus is de-energized and disconnected from the system. In addition to its
protective function, a circuit breaker is also used for circuit switching under normal
conditions.
Each having its protective relays for determining the existence of a fault in that zone
and having circuit breakers for disconnecting that zone from the system. It is desirable
to restrict the amount of system disconnected by a given fault; as for example to a
single transformer, line section, machine, or bus section. However, economic
considerations frequently limit the number of circuit breakers to those required for
normal operation and some compromises result in the relay protection.
Some of the manufacturers are ABB, AREVA, Cutler-Hammer (Eaton), Mitsubishi
Electric, Pennsylvania Breaker, Schneider Electric, Siemens, Toshiba, Končar HVS
and others.
Circuit breaker can be classified as "live tank", where the enclosure that contains the
breaking mechanism is at line potential, or dead tank with the enclosure at earth
potential. High-voltage AC circuit breakers are routinely available with ratings up to
765,000 volts.
6.1. Various types of circuit breakers:-

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6.1.1 SF6 Circuit Breaker
6.1.2 Air Blast Circuit Breaker
6.1.3 Oil Circuit Breaker
6.1.4 Bulk Oil Circuit Breaker (MOCB)
6.1.5 Minimum Oil Circuit Breaker
6.1.1. SF6 CIRCUIT BREAKER:-
Sulphur hexafluoride has proved its-self as an excellent insulating and arc quenching
medium. It has been extensively used during the last 30 years in circuit breakers,
gasinsulated switchgear (GIS), high voltage capacitors, bushings, and gas insulated
transmission lines. In SF6 breakers the contacts are surrounded by low pressure SF6
gas. At the moment the contacts are opened, a small amount of gas is compressed and
forced through the arc to extinguish it.

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Fig. 6.1: SF6 Circuit Breaker
220 kV SF6 C.B. RATINGS:-
Manufacture: BHEL Hyderabad.
Type: DCVF (220-245 kV)
Rated voltage: 245 kV
Rated Frequency: 50 Hz
Rated power Frequency voltage: 460 kV
Rated Impulse withstands voltage: 1450 kV
Normal current Rating:
At 50 c ambient: 1120 Amp
At 40 c Ambient: 1250 Amp
Short time current rating: 20 kV for 1 sec. Rated operating duty: 0 to
o.3 sec. c-0-3min-mb Rated short circuit duration: 1 sec.

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Breaking capacity [based on specified duty cycle]:
a. Capacity at rated voltage: 14400 MVA [220 kV]
b. Symmetry current: 20 kV
c. Asymmetry current: 25 kV
Making capacity: 100kV
Rated pressure of hydraulic operating (gauge): 250-350 bars.
Rated pressure of SF6 gas at degree: 7.5 bars.
Weight of circuit breaker: 1500 Kg.
Weight of SF6 gas: 76.5 Kg.
Rated trip coil voltage: 220 V AC
Rated closing voltage: 220 V DC
Advantages of sf6 circuit breaker:
1. Due to the superior arc quenching property of SF6, such circuit breakers have
very short arching time.
2. Since the dielectric strength of SF6 gas is 2 to 3 times that of air, such breakers
can interrupt much larger currents.
3. The SF6 circuit breaker gives noiseless operation due to its closed gas circuit
and no exhaust to the atmosphere unlike the air blast circuit breaker.
6.1.2. AIR BLAST CIRCUIT BREAKER:
The principle of arc interruption in air blast circuit breakers is to direct a blast
of air, at high pressure and velocity, to the arc. Fresh and dry air of the air blast
will replace the ionized hot gases within the arc zone and the arc length is
considerably increased. Consequently the arc may be interrupted at the first
natural current zero. In this type of breaker, the contacts are surrounded by

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compressed air. When the contacts are opened the compressed air is released in
forced blast through the arc to the atmosphere extinguishing the arc in the
process.
Fig. 6.2: Air Blast Circuit Breaker
Advantages:
An air blast circuit breaker has the following advantages over an oil circuit breaker:
• The risk of fire is eliminated
• The arcing products are completely removed by the blast whereas the oil
deteriorates with successive operations; the expense of regular oil is
replacement is avoided
• The growth of dielectric strength is so rapid that final contact gap needed for
arc extinction is very small. this reduces the size of device
• The arcing time is very small due to the rapid build up of dielectric strength
between contacts. Therefore, the arc energy is only a fraction that in oil circuit
breakers, thus resulting in less burning of contacts
• Due to lesser arc energy, air blast circuit breakers are very suitable for
conditions where frequent operation is required

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• The energy supplied for arc extinction is obtained from high pressure air and is
independent of the current to be interrupted.
Disadvantages:
Air has relatively inferior arc extinguishing properties.
• Air blast circuit breakers are very sensitive to the variations in the rate of
restricting voltage.
• Considerable maintenance is required for the compressor plant which supplies
the air blast
• Air blast circuit breakers are finding wide applications in high voltage
installations. Majority of circuit breakers for voltages beyond 110 kV are of this
type.
6.1.3. OIL CIRCUIT BREAKER:
Circuit breaking in oil has been adopted since the early stages of circuit breakers
manufacture. The oil in oil-filled breakers serves the purpose of insulating the live
parts from the earthed ones and provides an excellent medium for arc interruption. Oil
circuit breakers of the various types are used in almost all voltage ranges and ratings.
However, they are commonly used at voltages below 115KV leaving the higher
voltages for air blast and SF6 breakers. The contacts of an oil breaker are submerged
in insulating oil, which helps to cool and extinguish the arc that forms when the
contacts are opened. Oil circuit breakers are classified into two main types namely:
bulk oil circuit breakers and minimum oil circuit breakers.
The advantages of using oil as an arc quenching medium are:
1. It absorbs the arc energy to decompose the oil into gases, which have
excellent cooling properties.

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2. It acts as an insulator and permits smaller clearance between live
conductors and earthed components.
The disadvantages of oil as an arc quenching medium are:
1. Its inflammable and there is risk of fire
2. It may form an explosive mixture with air.
3. The arcing products remain in the oil and it reduces the quality of oil after
several operations.
4. This necessitates periodic checking and replacement of oil.
6.1.4. BULK OIL CIRCUIT BREAKER:
Bulk oil circuit breakers are widely used in power systems from the lowest voltages
up to 115KV. However, they are still used in the systems having voltages up to
230KV. The contacts of bulk oil breakers may be of the plain-break type, where the
arc is freely interrupted in the oil, or enclose within the arc controllers.
Plain-break circuit breakers consist mainly of a large volume of oil contained in a
metallic tank. Arc interruption depends on the head of oil above the contacts and the
speed of contact separation. The head of oil above the arc should be sufficient to
cool the gases, mainly hydrogen, produced by oil decomposition. A small air
cushion at the top of the oil together with the produced gases will increase the
pressure with a subsequent decrease of the arcing time.
6.1.5. MINIMUM OIL CIRCUIT BREAKER:
Bulk oil circuit breakers have the disadvantage of using large quantity of oil. With
frequent breaking and making heavy currents the oil will deteriorate and may lead to
circuit breaker failure. This has led to the design of minimum oil circuit breakers
working on the same principles of arc control as those used in bulk oil breakers. In

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this type of breakers the interrupter chamber is separated from the other parts and
arcing is confined to a small volume of oil. The lower chamber contains the operating
mechanism and the upper one contains the moving and fixed contacts together with
the control device. Both chambers are made of an insulating material such as
porcelain. The oil in both chambers is completely separated from each other. By this
arrangement the amount of oil needed for arc interruption and the clearances to earth
are roused. However, conditioning or changing the oil in the interrupter chamber is
more frequent than in the bulk oil breakers. This is due to carbonization and slugging
from arcs interrupted chamber is equipped with a discharge vent and silica gel breather
to permit a small gas cushion on top of the oil. Single break minimum oil breakers are
available in the voltage range 13.8 to 34.5 KV.
7. POWER TRANSFORMER
Distribution transformers reduce the voltage of the primary circuit to the voltage
required by customers. This voltage varies and is usually:
 120/240 volts single phase for residential customers.
 480Y/277 or 208Y/120 for commercial or light industry customers.
Three-phase pad mounted transformers are used with an underground primary circuit
and three single-phase pole type transformers for overhead service. Network service
can be provided for areas with large concentrations of businesses. These are usually
transformers installed in an underground vault. Power is then sent via underground
cables to the separate customers.
Parts of Transformer:-

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7.1. Windings:
Winding shall be of electrolytic grade copper free from scales & burrs. Windings shall
be made in dust proof and conditioned atmosphere. Coils shall be insulated that
impulse and power frequency voltage stresses are minimum. Coils assembly shall be
suitably supported between adjacent sections by insulating spacers and barriers.
Bracing and other insulation used in assembly of the winding shall be arranged to
ensure a free circulation of the oil and to reduce the hot spot of the winding. All
windings of the transformers having voltage less than 66 kV shall be fully insulated.
Tapping shall be so arranged as to preserve the magnetic balance of the transformer
at all voltage ratio. All leads from the windings to the terminal board and bushing
shall be rigidly supported to prevent injury from vibration short circuit stresses.
Fig. 7.1: Power Transformer
7.2. Tanks and fittings:
Tank shall be of welded construction & fabricated from tested quality low carbon steel
of adequate thickness. After completion of welding, all joints shall be subjected to dye
penetration testing.

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At least two adequately sized inspection openings one at each end of the tank shall be
provided for easy access to bushing & earth connections. Turrets & other parts
surrounding the conductor of individual phase shall be non-magnetic. The main tank
body including tap changing compartment, radiators shall be capable of withstanding
full vacuum.
7.3. Cooling Equipments:
Cooling equipment shall conform to the requirement stipulated below:
(a.) Each radiator bank shall have its own cooling fans, shut off valves at the top and
bottom (80mm size) lifting lugs, top and bottom oil filling valves, air release plug at
the top, a drain and sampling valve and thermometer pocket fitted with captive screw
cap on the inlet and outlet.
(b.) Cooling fans shall not be directly mounted on radiator bank which may cause
undue vibration. These shall be located so as to prevent ingress of rain water. Each
fan shall be suitably protected by galvanized wire guard.
Fig. 7.2 Radiator with fan
7.4.2. Temperature Indicators:
Most of the transformer (small transformers have only OTI) are provided with
indicators that displace oil temperature and winding temperature. There are

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thermometers pockets provided in the tank top cover which hold the sensing bulls in
them. Oil temperature measured is that of the top oil, where as the winding
temperature measurement is indirect.
Fig. 7.3 Winding and oil temperature indicator
7.4.3. Silica Gel Breather:
Both transformer oil and cellulosic paper are highly hygroscopic. Paper being more
hygroscopic than the mineral oil The moisture, if not excluded from the oil surface in
conservator, thus will find its way finally into the paper insulation and causes
reduction insulation strength of transformer. To minimize this conservator is allowed
to breathe only through the silica gel column, which absorbs the moisture in air before
it enters the conservator air surface.
Fig. 7.4:Silica gel Breather
7.4.4. Conservator:
With the variation of temperature there is corresponding variation in the oil volume.
To account for this, an expansion vessel called conservator is added to the transformer

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with a connecting pipe to the main tank. In smaller transformers this vessel is open to
atmosphere through dehydrating breathers (to keep the air dry). In larger transformers,
an air bag is mounted inside the conservator with the inside of bag open to atmosphere
through the breathers and the outside surface of the bag in contact with the oil surface.
8. CURRENT TRANSFORMER
As you all know this is the device which provides the pre-decoded fraction of the
primary current passing through the line/bus main circuit. Such as primary current
60A, 75A, 150A, 240A, 300A, 400A, to the secondary output of 1A to 5A.
When connecting the jumpers, mostly secondary connections is taken to three unction
boxes where star delta formation is connected for three phase and final leads taken to
protection /metering scheme.

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Fig. 8.1: Current Transformers
It can be used to supply information for measuring power flows and the electrical
inputs for the operation of protective relays associated with the transmission and
distribution circuit or for power transformer. These current transformers have the
primary winding connected in series with the conductor carrying the current to be
measured or controlled. The secondary winding is thus insulated from the high voltage
and can then be connected to low voltage metering circuits.
9. POTENTIAL TRANSFORMER
A potential transformer (PT) is used to transform the high voltage of a power line to
a lower value, which is in the range of an ac voltmeter or the potential coil of an ac
voltmeter.
The voltage transformers are classified as under:
Capacitive voltage transformer or capacitive type
Electromagnetic type.

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Capacitive voltage transformer is being used more and more for voltage measurement
in high voltage transmission network, particularly for systems voltage of 132KV and
above where it becomes increasingly more economical. It enables measurement of the
line to earth voltage to be made with simultaneous provision for carrier frequency
coupling, which has reached wide application in modern high voltage network for
tele-metering remote control and telephone communication purpose.
10. CAPACITIVE VOLTAGE TRANSFORMERS (CVT)
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 step-down the voltage for the instrumentation or protective relay.
The device has at least four terminals, a high-voltage terminal for connection to the

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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 single-phase
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.
Fig. 10.1: CVT connection
The porcelain in multi unit stack, all the potentials points are electrically tied and
suitably shielded to overcome the effect of corona RIV etc. Capacitive voltage
transformers are available for system voltage.
CVT is affected by the supply frequency switching transient and magnitude of
connected Burdon. The CVT is more economical than an electromagnetic voltage
transformer when the nominal supply voltage increases above 66KV.
The carrier current equipment can be connected via the capacitor of the CVT. There
by there is no need of separate coupling capacitor. The capacitor connected in series
act like potential dividers, provided, the current taken by burden is negligible
compared with current passing through the series connected capacitor.

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Capacitive voltage transformer is being used more and more for voltage measurement
in high voltage transmission network, particularly for systems voltage of 132KV and
above where it becomes increasingly more economical. It enables measurement of the
line to earth voltage to be made with simultaneous provision for carrier frequency
coupling, which has reached wide application in modern high voltage network for
telemetering remote control and telephone communication purpose.
The capacitance type voltage transformers are of two type:
• Coupling Capacitor type
• Pushing Type
Fig. 10.2:
11. TRANSFORMER OIL & ITS TESTING
The insulation oil of voltage- and current-transformers fulfills the purpose of
insulating as well as cooling. Thus, the dielectric quality of transformer is a matter of
secure operation of a transformer.
Since transformer oil deteriorates in its isolation and cooling behavior due to ageing
and pollution by dust particles or humidity, and due to its vital role, transformer oil
must be subject to oil tests on a regular basis.

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In most countries such tests are even mandatory. Transformer oil testing sequences
and procedures are defined by various international standards.
Periodic execution of transformer oil testing is as well in the very interest of energy
supplying companies, as potential damage to the transformer insulation can be
avoided by well timed substitution of the transformer oil. Lifetime of plant can be
substantially increased and the requirement for new investment may be delayed.
Transformer Oil Testing Procedure
To assess the insulating property of dielectric transformer oil, a sample of the
transformer oil is taken and its breakdown voltage is measured.
 The transformer oil is filled in the vessel of the testing device. Two
standardcompliant test electrodes with a typical clearance of 2.5 mm are
surrounded by the dielectric oil.
 A test voltage is applied to the electrodes and is continuously increased up to the
breakdown voltage with a constant, standard-compliant slew rate of e.g. 2 kV/s.
 At a certain voltage level breakdown occurs in an electric arc, leading to a collapse
of the test voltage.
 An instant after ignition of the arc, the test voltage is switched off automatically
by the testing device. Ultra fast switch off is highly desirable, as the carbonization
due to the electric arc must be limited to keep the additional pollution as low as
possible.
 The transformer oil testing device measures and reports the root mean square value
of the breakdown voltage.
 After the transformer oil test is completed, the insultaion oil is stirred automatically
and the test sequence is performed repeatedly. (Typically 5 Repetitions, depending
on the standard)

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 As a result the breakdown voltage is calculated as mean value of the individual
measurements.
12. LIGHTNING ARRESTOR
A lightning arrester (in Europe: surge arrester) is a device used on power systems
and telecommunications systems to protect the insulation and conductors of the
system from the damaging effects of lightning. The typical lightning arrester has a
highvoltage terminal and a ground terminal. When a lightning surge (or switching
surge, which is very similar) travels along the power line to the arrester, the current
from the surge is diverted through the arrestor, in most cases to earth.
In telegraphy and telephony, a lightning arrestor is placed where wires enter a
structure, preventing damage to electronic instruments within and ensuring the safety
of individuals near them. Smaller versions of lightning arresters, also called surge
protectors, are devices that are connected between each electrical conductor in power
and communications systems and the Earth. These prevent the flow of the normal
power or signal currents to ground, but provide a path over which high-voltage
lightning current flows, bypassing the connected equipment. Their purpose is to limit
the rise in voltage when a communications or power line is struck by lightning or is
near to a lightning strike.
If protection fails or is absent, lightning that strikes the electrical system introduces
thousands of kilovolts that may damage the transmission lines, and can also cause
severe damage to transformers and other electrical or electronic devices.
Potential target for a lightning strike, such as a television antenna, is attached to the
terminal labeled A in the photograph. Terminal E is attached to a long rod buried in
the ground. Ordinarily no current will flow between the antenna and the ground
because there is extremely high resistance between B and C, and also between C and

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D. The voltage of a lightning strike, however, is many times higher than that needed
to move electrons through the two air gaps. The result is that electrons go through the
lightning arrester rather than traveling on to the television set and destroying it.
A lightning arrester may be a spark gap or may have a block of a semi conducting
material such as silicon carbide or zinc oxide. Some spark gaps are open to the air,
but most modern varieties are filled with a precision gas mixture, and have a small
amount of radioactive material to encourage the gas to ionize when the voltage across
the gap reaches a specified level. Other designs of lightning arresters use a glow
discharge tube (essentially like a neon glow lamp) connected between the protected
conductor and ground, or voltage-activated solid-state switches called visitors or
MOVs.
Lightning arresters built for power substation use are impressive devices, consisting
of a porcelain tube several feet long and several inches in diameter, typically filled
with disks of zinc oxide. A safety port on the side of the device vents the occasional
internal explosion without shattering the porcelain cylinder.
Lightning arresters are rated by the peak current they can withstand, the amount of
energy they can absorb, and the break over voltage that they require to begin
conduction. They are applied as part of a lightning protection system, in combination
with air terminals and bonding.
220 kV LIGHTNENING ARRESTOR:
Manufacture: English electric company
No. of phase: One
Rated voltage: 360 kV
Nominal discharge current: (8×20µs) 10 kA
High current impulse: (4× 100µs) 100 kA

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Long distribution rating: (200µs) 500 kA
13. CONTROL PANEL
Control panel contain meters, control switches and recorders located in the control
building, also called the dog house. These are used to control the substation equipment
to send power from one circuit to another or to open or to shut down circuits when
needed.

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Fig. 13.1: Control Room in GSS Sitapura, Jaipur
14. MEASURING INSTRUMENT
14.1. ENERGY METER: To measure the energy transmitted energy meters are fitted
to the panel to different feeders the energy transmitted is recorded after one hour
regularly for it MWHr, meter is provided.
14.2. WATTMETERS: It is attached to each feeder to record the power exported from
GSS.
14.3. FREQUENCY METER: To measure the frequency at each feeder there is the
provision of analog or digital frequency meter.
14.4. VOLTMETER: It is provided to measure the phase to phase voltage .It is also
available in both the analog and digital frequency meter.
14.5. AMMETER: It is provided to measure the line current. It is also available in
both the forms analogue as well as digital.
14.6. MAXIMUM DEMAND INDICATOR: There are also mounted the control
panel to record the average power over successive predetermined period.
14.7. MVAR METER: It is to measure the reactive power of the circuit.

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15. CAPACITOR BANK
The capacitor bank provides reactive power at grid substation. The voltage regulation
problem frequently reduces so of circulation of reactive power.
Unlike the active power, reactive power can be produced, transmitted and absorbed
of course with in the certain limit, which have always to be workout. At any point in
the system shunt capacitor are commonly used in all voltage and in all size.
Fig. 15.1: Capacitor Bank
Benefits of using the capacitor bank are many and the reason is that capacitor reduces
the reactive current flowing in the whole system from generator to the point of
installation.
1 .Increased voltage level at the load
2. Reduced system losses

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3. Increase power factor of loading current
16. EARTHING OF THE SYSTEM
The provision of an earthing system for an electric system is necessary by the
following reason.
• In the event of over voltage on the system due to lightening discharge or other
system fault. These parts of equipment, which are normally dead, as for as
voltage, are concerned do not attain dangerously high potential.
• In a three phase, circuit the neutral of the system is earthed in order to stabilize
the potential of circuit with respect to earth. The resistance of earthing system
is depending on:
• Shape and material of earth electrode used.
• Depth in the soil.
Specific resistance of soil surrounding in the neighbourhood of system electrodes.
16.1. PROCEDURE OF EARTHING:
Technical consideration the current carrying path should have enough capacity to deal
with more faults current. The resistance of earth and current path should be low
enough to prevent voltage rise between earth and neutral. The earth electrode must be
driven in to the ground to a sufficient depth to as to obtain lower value of earth
resistance. To sufficient lowered earth resistance a number of electrodes are inserted
in the earth to a depth, they are connected together to form a mesh. The resistance of
earth should be for the mesh in generally inserted in the earth at 0.5m depth the several
point of mesh then connected to earth electrode or ground conduction. The earth
electrode is metal plate copper is used for earth plate.

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16.2. NEUTRAL EARTHING:
Neutral earthing of power transformer all power system operates with grounded
neutral. Grounding of neutral offers several advantages the neutral point of generator
transformer is connected to earth directly or through a reactance in some cases the
neutral point is earthed through an adjustable reactor of reactance matched with the
line.
The earth fault protection is based on the method of neutral earthing.

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17. RATINGS
17.1. TRANSFORMER:
Total No. of transformers = 6 No. of transformers
220/132 KV------------------------------------ 100MVA 2
132/33 KV--------------------------------------20/25MVA 2
132/33KV---------------------------------------40/50MVA 1
132/11 KV---------------------------------------10/12.5 MVA 1
MAKE Company
220/133 KV, 100MVA X-Mer 1----------------------------------- TELK
220/133KV, 100 MVA X-Mer 2---------------------------------- ALSTOM
132/33 KV, 20/25 MVA X-Mer 1---------------------------------- TELK
132/33 KV, 20/25 MVA X-Mer 2-----------------------------------BBL
132/33 KV, 40/50 MVA X-Mer 3-----------------------------------T&R
132/33 KV, 10/12.5 MVA X-Mer 1---------------------------------EMCO
17.2. CIRCUIT BREAKER:
No. of 220KV breaker - 6
No. of 132KV breaker - 13
No. of 33KV breaker - 12
No. of Capacitor Bank (33kv) - 4
No. of 11KV breaker - 7

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SF6 CB
BREAKER SERIAL NO. 030228
RATED VOLTAGE 145KV
NORMAL CURRENT 1250A
FREQUENCY 50Hz
LIGHTNING IMPULSE WITHSTAND 650KV (Peak)
FIRST POLE TO CLEAR TO CLEAR FACTOR 1-2
SHORT TIME WITHSTAND CURRENT 31.5KA
DURATION OF SHORT CIRCUIT 3 Sec.
(SHORT CIRCUIT SYM. 31.5KA
BREAKING CURRENT) ASYM. 37.5KA
SHORT TIME MAKING CURRENT 8.0KA
OUT OF PHASE BREAKING CURRENT 7.9KA
OPERATING SEQUENCE 0-0.3-CO-3min-CO
SF6 GAS PRESSURE AT 20C 6.3 Bar
TOTAL MASS OF CB 1300Kg
MASS OF SF6 GAS
17.3. BATTERY CHARGER:
8.7Kg
Battery Charger – 220AH VDC HBL NIFE LTD.
440AH VDC HBL NIFE LTD.
Capacitor BankNo.-1 BHEL 38KV 6.6MVAR
Capacitor BankNo.-2 BHEL 38KV 7.2MVAR
Capacitor BankNo.-1 ABB 38KV 7.2MVAR
Capacitor BankNo.-1 WS 38KV 7.2MVAR
17.4. CURRENT TRANSFORMER:

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FREQUENCY 50Hz
HIGHEST SYSTEM VOLTAGE 245KV
SHORT TIME CURRENT 40KA/15
RATED CURRENT 600A
CURRENT RATIO 600-300-150/1
MIN. KNEE POTENTIAL VOLTAGE 850V at 150/1
MAX. EXCITING CURRENT 100MA at 150/1
MAX. SEC. WINDING RESISTANCE 2.5OHM at 150/1
17.5. CAPACITIVE VOLTAGE TRANSFORMER:
SERIAL NO. 0173537
INSULATION LEVEL 460KV
RATED VOLTAGE FACTOR 1.2/cont
TIME 1.5/30sec.
HIGHEST SYSTEM VOLTAGE 245KV
PRIMARY VOLTAGE 22OKV/1.732
TYPE OUTDOOR Wgt. 850Kg
PHASE SINGLE TBONP.CAT 50C
SECONDARY VOLTAGE 110/1.732
RATED BURDON 220Va-110Va
FREQUENCY 49.5-50.5Hz
18. POWER LINE CARRIER COMMUNICATION

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Power Line Carrier Communication (PLCC) provides for signal transmission down
transmission line conductors or insulated ground wires. Protection signaling, speech
and data transmission for system operation and control, management information
systems etc. are the main needs which are met by PLCC.
PLCC is the most economical and reliable method of communication because of the
higher mechanical strength and insulation level of high voltage power line which
contribute to the increased reliability of communication and lower attenuation over
the larger distances involves.
High frequency signals in the range of 50 KHZ to 400 KHZ commonly known as the
carrier signal and to result it with the protected section of line suitable coupling
apparatus and line traps are employed at both ends of the protected section. Here in
Sanganer and also in other sub-station this system is used. The main application of
power line carrier has been from the purpose of supervisory control telephone
communication, telemetering and relaying.
18.1. PLCC Equipment
The essential units of power line carrier equipment consists of :-
a. Wave trap
b. Coupling Capacitor
c. LMU and protective equipments.

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18.2. Merits
The severity that a power line can withstand is much more than that odd
communication line due to higher mechanical strength of transmission line power
lines generally provide the shortest route between the Power Station and the Receiving
Larger spacing between conductors reduces the capacitances which results in lesser
attenuation of higher frequencies. Large spacing also reduces the cross talk to a certain
extent. The construction of a separate communication line is avoided.
18.3. Demerits
Utmost care is required to safeguard the carrier equipment and persons using them
against high voltage and currents on the line. Noise introduced by power line is far
more than in the case of communication line. This is due to the discharge across
insulators and corona etc.
Induced voltage surges in the power line may affect the connected carrier
equipment.

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19. CONCLUSION
A technician needs to have not just theoretical but practical as well and so every
student is supposed to undergo practical training session after 3rd year where I have
imbibed the knowledge about transmission, distribution, generation and maintenance
with economical issues related to it.
During our 60 days training session we were acquainted with the repairing of the
transformers and also the testing of oil which is a major component of transformer.
At last I would like to say that practical training taken at 220 kV GSS has broadened
my knowledge and widened my thinking as a professional.