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A PRACTICAL TRAINING REPORT
132 KV G.S.S.
Submitted in partial fulfillment
for the award of the degree of
BACHELOR OF TECHNOLOGY
(Rajasthan Technical University, Kota)
SSSSUUUUBBBBMMMMIIIITTTTTTTTEEEEDDDD TTTTOOOO:::: SSSSUUUUBBBBMMMMIIIITTTTTTTTEEEEDDDD BBBBYYYY::::
Mr. Vaibhav Jain Pritam solanki
(HOD) EE&7th Sem
Electrical Department 10EPCEE092, 4th Year
DEPARTMENT OF ELECTRICAL ENGINEERING
POORNIMA COLLEGE OF ENGINEERING
ISI-6, RIICO INSTITUTIONAL AREA
DEPARTMENT OF ELECTRICAL ENGINEERING
POORNIMA COLLEGE OF ENGINEERING
This is to certify that report on “Jalore
the degree of Bachelor of Technology in 132 KV G.S.S. Jalore” has been carried out by Mr. Pritam Solanki under my guidance in partial fulfil
of Rajasthan Technical University, Kota, during the academic year 2012
the best of my knowledge and belief this work has not been submitted elsewhere for the award of any other degree. The work ha
satisfactory and is approved for submission.
Mr. Vaibhav Jain
(Asst. Prof.), E.E. (P.C.E)
Mr. Trilock Chand Sony
(Asst. Prof.), E.E. (P.C.E)
ring 2012-13 To
has been found
TABLE OF CONTENT pg.no.
LIST OF FIGURE iii
LIST OF TABLE iv
1.1 INTRODUCTION [SUB STATION] 2
2.1 SINGLE LINE DIAGRAM OF 132 KV G.S.S. 5
2.2 BUS BARS 6
2.2.1 DOUBLE BUS BAR CONTAINING MAIN BUS I
WITH MAIN BUS II
2.2.2 DOUBLE BUS BAR ARRANGEMENTS
CONTAINS MAIN BUS WITH AUXILIARY BUS
2.3 ISOLATORS 7
2.4 INSULATORS 8
2.4.1 Pin type
2.4.2 Suspension type insulator
2.4.3 Strain insulator
2.5 PROTECTIVE RELAYS 11
2.5.1 Principal of relay
2.5.2 Differential Relays
2.5.3 Buchholz Relay
2.5.4 Overcurrent Relays
2.6 CIRCUIT BREAKERS 13
2.6.1 Operating Principal
2.6.2 Arc Phenomenon
2.6.3 Classification of the Circuit Breakers
188.8.131.52 Sulphur Hexaflouride (SF6) Circuit
184.108.40.206.3 Advantages of SF6 Ckt Breaker
220.127.116.11.4 Demerits of SF6 Ckt Breaker
2.7 POWER TRANSFORMER 17
2.7.1 Principal of Transformer
2.7.2 BASIC PARTS OF TRANSFORMER
2.7.3 Description of Plant
2.7.4 Rating Datas
2.8 CURRENT TRANSFORMER 21
2.8.1 POTENTIAL TRANSFORMER
2.9 CAPACITIVE VOLTAGE TRANSFORMER 22
2.10 TRANSFORMER OIL & ITS TESTING 24
2.10.1 Breakdown Voltage
2.10.2 Flash Point
2.11 TRANSFORMER TANδ TESTING 24
2.12 LIGHTNING ARRESTORS 25
2.12.1 Thyrite Type
2.13 CONTROL ROOM 27
2.14 EARTHING OF THE SYSTEM 29
2.14.1 Procedure of Earthing
2.14.2 Neutral Earthing
2.15 POWER LINE CARRIER COMMUNICATION 30
2.16 CORONA 31
2.16.1 Factors Affecting Corona
2.16.2 Advantages and Disadvantages of Corona
LIST OF FIGURE
Figure No. Figure Name pg.no.
1.01 132 KV G.S.S. JALORE 2
2.01 single line diagram of 132 KV G.S.S. 5
2.02 132 KV BUS BARS 6
2.03 Isolator 8
2.04 Pin type insulator 9
2.05 Suspension type insulator 10
2.06 Strain insulator 10
2.07 Diagram of Relay 11
2.08 SF6 Circuit Breaker 14
2.09 Construction view of SF6 Circuit Breaker 16
2.10 Arrangement of a simple Transformer 18
2.11 Transformer 19
2.12 Ratings of Transformers 20
2.13 Current Transformers 21
2.14 Potential Transformers 22
2.15 Capacitive Voltage Transformer 23
2.16 Principal of TANδ tasting Transformers 25
2.17 Lighting Arresters 26
3.01 Control Room-1 27
3.02 Control Room-2 28
3.03 Control Room-3 28
3.04 EARTHING OF THE SYSTEM 29
3.05 POWER LINE CARRIER COMMUNICATION SYSTEM 31
LIST OF TABLE
Table No. Table Name pg.no.
1.01 Details of Circuit Breaker 3
1.02 Details of Current Transformer 4
This is opportunity to express my heartfelt words for the people who were part of this training in
numerous ways, people who gave me unending support right from beginning of the training.
I am grateful to training incharge Mr. Hari Ram Meena for giving guidelines to make the training
I want to give sincere thanks to the Campus Director, Dr. R.P. Rajoria and the principal, Dr.
Om Prakash Sharma for his valuable support.
I extend my thanks to Mr. Vaibhav Jain Head of the Department for his cooperation and
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This is training of 30 days, during these days my training place was 132 KV G.S.S. Jalore
(Rajasthan). G.S.S. is the mean of connection between generating station and
consumer by providing safety and reliability of system in case of default.
This substation step down the incoming voltage power transmission to the required valve 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.
In our substation there is two main parts 132KV and 33 KV which is a part of substation. First
we receive the power 132 KV from Leta, and then we step down the voltage at 33 KV and
distributed to the no. of feeders.
We have three main transformers which converts 132 KV to 33KV. Two transformers are rating
of 12.5 KVA (BHEL-EMCO) and the last one having rating of 25 KVA (IMP). So the total
capacity of our substation is 55 MVA.
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.
While making this training report every care has been taken to avoid any mistake. In short I hope
to provide concise sight of four weeks of my training period through this report.
I was lucky to have my training from 132 KV G.S.S., Jalore that gave me an all round
knowledge that an electrical engineer should know. During 30 days of my training Session at
G.S.S. I got knowledge about power distribution, power transmission and power line carrier
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1.1 INTRODUCTION [SUB STATION]
Electric power is generated, transmitted and distributed 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 from 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 sub-station.
Depending on the constructional feature, the high voltage sub-station may be further
a) Outdoor substation
b) Indoor substation
c) Basement or Underground substation
132 KV G.S.S. is an outdoor type station. It is primary as well as distribution substation. The
power mainly comes from JALORE-1 and JALORE-2 from Leta.
Fig (1): 132 KV G.S.S. JALORE
Table of Current Transformer
S.NO. NAME OF CT MAKE
1. 132 KV I/C JALORE-1 BHEL
2. 132 KV I/C JALORE-2 HBB
3. 132 KV Tr.(BHEL-EMCO) EASUN
4. 132 KV Tr.(IMP) TELK
5. 132 KV BUS COUPLER AMEI
6. 33 KV I/C-1(EMCO) TATA
7. 33 KV I/C-2(BHEL) AMEI
8. 33 KV I/C-3(IMP) HEI
9. 33 KV O/G FN.1 KASHWANA CG
10. 33 KV O/G FN.2 JALORE CG
11. 33 KV O/G FN.3 SAYLA AEI
12. 33 KV O/G FN.4 AHORE UNIVERSAL
13. 33 KV O/G FN.5 GODAN CG
14. 33 KV O/G FN.6 RICCO AEI
15. 33 KV CAP. BANK-1 BHEL
16. 33 KV CAP. BANK-2 BHEL
17. 33 KV CAP. BANK-3 ATE
18. 33/11 KV Tr. AEI
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Table (1.02): Details of Current Transformer
2.2 BUS BARS
Bus Bars are 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
s required. While in
case of strain type of bus bars suitable ACSR conductors are strung / tensioned by
insulator discs according to system voltages. In the widely used strain type bus bars stringing
tension is about 500-900 kg depending
effect the clearances when it swings while over tensioning may damage i
even effect the supporting structures in low temperature conditions. The clamping should be
proper, as loose clamp would s
BUS BAR ARRANGEMENT MAY BE FOLLOWING TYPES:
Which are being adopted by R.R.V.P.N.L.
1. Single Bus Bar arrangement
2. Double Bus Bar arrangement
3. Double Bus Bar arrangement with auxiliary bu
2.2.1 DOUBLE BUS BAR CONTAINING MAIN BUS I WITH MAIN BUS II
1. Each load may be fed from either bus.
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heights are low and minimum clearance is
upon the size of conductor used. Loose Bus Bars would
spark under in full load condition damaging the bus bars itself.
Fig (2.2): 132 KV BUS BARS
. insulators. Clamps or
2. The load circuits may be divided in 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 and cleaning of insulators. This
arrangement has been quite frequently adopted where the loads and continuity of supply is
In such a scheme a bus coupler breaker is mostly provided as it enables on load change over
from one bus bar to other. The normal bus selection isolators cannot be used for breaking load
currents. The arrangement does not permit breaker maintenance without causing stoppage of
2.2.2 DOUBLE BUS BAR ARRANGEMENTS CONTAINS MAIN 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. Wherever maintenance is required on any
breaker the circuit is changed over to the transfer bus and is controlled through bus coupler
Isolators which are also called disconnect switches or air break switches after the assembly as
per drawings on the leveled structures the adjustment of connecting pipes, moving and fixed
contacts is done so that all the three phase of the isolator close and open simultaneously and
there is a full surface contact between moving and fixed contacts. Such switches are generally
used on both sides of equipment in order that repairs and replacement of the equipment can be
made without any danger. They should never be opened until the equipment in the same circuit
has been turned off and should always be closed before the equipment is turned on. The
adjustment of the tendon pipes leveling of post insulator, stop Holts in the fixed contacts etc. is
done for smooth operation of insulator. Following type of isolators are being used in R.S.E.B.-
a) Isolator without earth blades.
b) Isolator with earth blades.
c) Tendon isolator
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Fig (2.3): ISOLATOR
The insulators for the overhead lines provide 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 conductors 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 insulators
should have the following desirable properties: 1) High mechanical strength in order to withstand
conductor load, wind load etc. 2) High electrical resistance of insulator material in order to avoid
leakage currents to earth. 3) High relative permittivity of insulator material in order that
dielectric strength is high. 4) The insulator material should be non porous, free from impurities
and cracks otherwise the permittivity will be lowered. 5) High ratio of puncture strength to flash
over. These insulators are generally made of glazed porcelain or toughened glass. Porcelain type
8| P a g e
insulators [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.
Insulators are available in three types:
2.4.1 Pin type:- pin type insulator consists 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 33KV the pin
type insulators thus become too bulky and hence uneconomical.
Fig (2.4): pin type insulator
2.4.2 Suspension type insulator:- suspension type insulators consists 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 (2.5): suspension type insulator
2.4.3 Strain insulator:- 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 shackle
insulators are used as strain insulator.
Fig (2.6): strain insulator
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2.5 PROTECTIVE RELAYS
A protective relay is a device that detects the fault and initiates the operation of the circuit
breaker to isolator the defective element from the rest of the system. The relays detect the
abnormal condition in the electrical circuits by constantly measuring the electrical quantities i.e.
voltage, current, frequency, phase angle which are different under normal and fault conditions.
Having detected the fault, the relay operates to close the trip circuit of the breaker, which results
in opening of the breaker and disconnection of the faulty circuit. Relays circuit connections can
be divided in three parts:
1) Primary winding of C.T. that is connected in series with the line to be protected.
2) Secondary winding of C.T. and the relay operating coil
3) Tripping circuit (either ac or dc)
Fig (2.7): Diagram of Relay
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2.5.1 Principal of relay:-when a short circuit occurs at any point F on the transmission line
the current increases to enormous value. This results in a heavy current flow through the relay
coil, causing the relay to operate by closing its contacts. This in turn closes the trip circuit of the
breaker, making the C.B. open and isolating the family section from the rest of the system. In
this way, relay ensures the safety of the circuit equipment from damage and normal working of
the healthy portion of the system. Basic qualities that a protective relay must possess are:
Type of relays:-
2.5.2 Differential Relays:- A differential relays is one that operates when the phasor
difference of two or more similar electrical quantities exceeds a predetermined value. Thus the
current differential relay is one that compares the current entering and current leaving the
section. Under normal operating conditions, the two currents are equal but as soon as fault
occurs, this condition is no longer applied. The difference between the incoming and outgoing
currents is arranged to flow through the operating coil of the relay. If this differential current is
equal to or greater than the pickup value, the relay will operate and open the C.B. to isolate the
2.5.3 Buchholz Relay:- It is a gas-actuated relay installed in oil immersed transformers for
protection against all kinds of faults. It is used to give an alarm in case of incipient (i.e. slow
developing) faults in the transformer and to disconnect the transformer from the supply in the
event of severe internal faults. It is usually installed in the pipe connecting the conservator to
main tank. It is a universal practice to use buchholz relay on all such oil immersed transformers
having ratings in excess of 750KVA.
18.104.22.168 CONSTRUCTION:-It takes the form of a domed vessel pipe between the main
tank and the conservator. The device has two elements. The upper element consists of a mercury
type switch attached to a float. The lower element contains a mercury switch mounted on a
hinged type flap located in the direct path of the flow of oil from the transformer to the
conservator. The upper element closes an alarm circuit during incipient faults whereas the lower
element is arranged to trip the circuit breaker in case of server internal faults.
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22.214.171.124 OPERATION:-The operation of Buchholz relay is as follows: (i) In case of incipient
faults within the transformer, the heat due to fault causes the decomposition of some transformer
oil in the main tank the products of decomposition contain more than 70% of hydrogen gas. The
hydrogen gas being light tries to go into the conservator and in the process gets entrapped in the
upper part of the relay chamber. When a pre determined amount of gas gets accumulated, it
exerts sufficient pressure on the float to cause it tilt and close the contacts of the mercury switch
attached tom it. This completes the alarm circuits to sound an alarm. (ii)If a serious fault occurs
in the transformer, enormous amount of gas is generated in the main tank. The oil in the main
tank rushes to the conservator via the Buchholz relay and in doing so tilts the flap to close the
contacts of the mercury switch. This completes the trip circuit to open the circuit breaker
controlling the transformer.
(i) It is the simplest form of transformer protection.
(ii) It detects the incipient faults at a stage much earlier than possible with other forms of
(i) It can only be used with oil immersed transformers equipped with conservator tanks.
(ii) The device can detect only faults below oil level in the transformer. Therefore separate
protection is needed for connecting cables.
2.5.4 Overcurrent Relays:-
an Overcurrent relay is a relay which sense the high current. When a short ckt occurs, high
current flows if this current is equal or greater than pick up current then Overcurrent relay trip
the ckt breaker.
2.6 CIRCUIT BREAKERS
Thus circuit breakers are used for switching & protection of various parts of power system.
Circuit breaker is a piece of equipment, which can
1) Make or break a circuit either manually or automatically under normal condition.
2) Break a circuit automatically under fault condition.
3) Make a circuit either manually or by remote control under fault conditions.
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Fig (2.8): SF6 Circuit Breaker
2.6.1 OPERATING PRINCIPLES: - A C.B. consists of fixed and moving contacts
called electrodes. Under normal operating conditions, these contacts remain closed and will not
open automatically until and unless the system becomes faulty. When a fault occurs on any part
of the system, the trip coils of the circuit breaker get energized and the moving contacts are
pulled apart, thereby opening the circuit. When the contacts of the C.B. are separated under fault
conditions, an arc is struck between them. The current is thus able to continue until the discharge
ceases. The production of arc not only delays the current interruption process but it also
generates enormous heat which may cause damage to the system or to the C.B. It is thus
necessary to extinguish the arc within the shortest possible time so that the heat generated by it
may not reach a dangerous value.
2.6.2 ARC PHENOMENON:- When a short circuit occurs, a heavy current flow through
the contacts of the C.B. before they are opened by the protective system. At the instant when the
contacts begin to separate, the contact area decreases rapidly and large fault current causes
increased current density and hence rise in temperature. The heat produced in the medium
14| P a g e
between contacts is sufficient to ionize the arc or vaporize and ionize the oil. The ionized air or
vapour acts as conductor and an arc is set between the contacts. The potential difference between
the contacts is quite small and is sufficient to maintain the arc. The arc provides a low resistance
path and as a result the current in the circuit remains uninterrupted so long as the arc persists.
During the arcing period the current flowing between the contacts depends on the arc resistance.
The greater the arc resistance, the smaller the current that flows between the contacts. The arc
resistance depends upon:
(i) Degree of ionization.
(ii) Length of arc.
(iii) Cross section of arc.
2.6.3 CLASSIFICATION OF THE CIRCUIT BREAKERS
There are several ways of classifying the circuit breakers. However, the most general way of
classification is on the basis of medium used for arc extinction. The medium used for arc
extinction is usually oil, air, sulphur hexafluoride (SF6) or vacuum. Accordingly, circuit breakers
may be classified into:-They are generally classified on the basis of the medium used for arc
(i) Oil circuit breakers, which employ some insulating oil for arc extinction.
(ii) Air-blast circuit breakers in which high pressure air blast is used for extinguishing the arc.
(iii) Sulphur hexa fluroide C.B. in which SF6 gas is used for arc extinction.
(iv) Vacuum C.B. in which vacuum is used for arc extinction.
126.96.36.199 SULPHUR HEXAFLOURIDE (SF6) CIRCUIT
BREAKER In such breakers, sulphur hexa flouride (SF6) gas is used as the arc quenching
medium. The sf6 is an electro-negative gas and has a strong tendency to absorb free electrons.
The SF6 circuit breakers have been found to be very effective for high power and high voltage
The cylindrical large size steel tanks are mounted horizontally parallel to each other. Each tank
consists of SF6 under pressure. The interruption is of multibreak type & is placed along the axis
of each tank. The interruption assembly is supported inside the tank by the vertical bushing,
which are mounted near the end of each tank. Gas at high pressure is supplied to the interrupter
from a gas reservoir. The bushings are also insulated with SF6 the conductor is in the form of
copper tube supported at both end by porcelain shields. SF6 gas is supplied from the high
pressure tanks. Shields are provided with gasket seals to eliminate leakage of gas from
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Fig (2.9): Construction view of SF6 Circuit Breaker.
188.8.131.52.2 WORKING:- In the closed position of the breaker the contacts remain surrounded
by SF6 gas at a pressure of about 2.8 kg/sq cm. When the breaker operates, the moving contact is
pulled apart and an arc is struck between the contacts. The movement of the moving contact is
synchronized with the opening of a valve which permits SF6 gas at 14kg/sq cm pressure from the
reservoir to the arc interruption chamber. The high pressure flow of SF6 rapidly absorbs the free
electrons in the arc path to form immobile negative ions which are ineffective as charge carriers.
The result is that the medium between the contacts quickly builds up high dielectric strength and
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causes the extinction of the arc. After the breaker operation the valve is closed by the action of a
set of springs.
184.108.40.206.3 ADVANTAGES OF SF6 CIRCUIT BREAKER:
1. Due to the superior arc quenching property of SF6, such circuit breakers have very short
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 breakers gives noiseless operation due to its closed gas circuit and no exhaust
to the atmosphere unlike the air blast circuit breaker.
4. The closest gas enclosure keeps the interior dry so that there is no moisture problem.
5. There is on risk of fire in such breakers because SF6 gas is not inflammable. There are no
carbon deposits so that tracking and insulation problems are eliminated.
6. The SF6 breakers have low maintenance cost, light foundation requirement and minimum
7. Since SF6 breakers are totally enclosed and sealed from atmosphere they are particularly
suitable where explosion hazard exists.
220.127.116.11.4 DEMERITS OF SF6 CIRCUIT BREAKER:
1. Sealing problems arise due to the type of the construction used.
2. The presence of moisture in the system is very dangerous to SF6 circuit breaker.
3. Arced Sf6 gas is poisonous & should not be let out.
4. The double pressure SF6 CB is cost liner due to complex gas system.
5. The internal parts should be cleaned thoroughly during periodic maintenance under clean dry
6. Dust of Teflon & sulfide should be removed.
7. Special facilities are needed for transporting the gas.
2.7 POWER TRANSFORMER
2.7.1 Principal of Transformer: The transformer is a static apparatus, which receives
power/energy at it, one circuit and transmits it to other circuit without changing the frequency.
With this basic conception we can use the voltages at our desired level while utilizing the power.
As, the voltage used to generate at modern power houses at 11 KV or so and afterwards we get it
step up at a level of 33 KV, 66 KV, 132 V, 220 KV or 400KV, 750 KV for transmission to
minimize the distribution losses. Again we get it step down with the help of transformer to use at
our wishes at 11 KV, 6.6 KV or even 415, 230 volts at our houses.
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Fig (2.10): Arrangement of a simple Transformer
2.7.2 BASIC PARTS OF TRANSFORMER: - The following are the inherent parts of a modern
1. Primary and secondary coils (circuit) or windings.
3. Main Tank
7. Buchholz relay
8. Explosive vent
9. Bushings (HT & LT) (Primary or secondary)
10. Cooling fans
11. Tap changer (on load and off load)
12. NGR (Neutral Grounding Resistance) to minimize the earth fault current
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Fig (2.11): Transformer
2.7.3 DESCRIPTION OF PLANT
The three transformers are oil immersed with rating of 12.5 MVA& one with 25 MVA. However
a synchronous loading of 55 MVA at 0.98 power factor. The transformer is also provided with a
separate bank of radiation, fans, and associated control equipments. The control equipments are
housed in a tank mounted miscalling.
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2.7.4 RATING DATAS
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Fig (2.12): Ratings of Transformers
2.8 CURRENT TRANSFORMER
These transformers are used with low range ammeter to measure currents in high voltage
alternating current circuits where it is not practicable to connect instruments and meters directly
to lines. In addition to insulating the instrument from the high voltage line, they step down the
current in the known ratio. The current (or series) transformers has a primary coil of 1 or more
turns of thick wires connected in series with the line whose current is to be measured. The
secondary consist of a large number of turns of fine wire and is connected across the ammeter
terminals (usually of 5 amp bracket should be removed or 1 amp range.
Fig (2.13): Current Transformers
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2.8.1 POTENTIAL TRANSFORMER
These transformers are extremely accurate ratio step down transformers and are used in
conjunction with standard low range voltmeter (usually 150 volt) whose deflection when divided
by voltage transformation ratio, gives the true voltage on the high voltage side. In general, they
are of the shell type and do not differ much from the ordinary two winding transformer, except
that their power rating is extremely small. Up to voltage of 5000 potential transformers are
usually of dry type, between 5000 and 13800 volts, they may be either dry type or oil immersed
type, although for voltage above 13800 they are oil type. Since their secondary windings are
required to operate instruments or relays or pilot lights, their ratings are usually 42 to 100 watts.
Fig (2.14): Potential Transformers
2.9 CAPACITIVE VOLTAGE TRANSFORMERS (CVT)
Capacitive voltage transformers are special kind of power transformers using capacitors to step
down the voltage. The capacitive voltage transformer comprises of a capacitor divider with its
associated electromagnetic unit. The divider provides an accurate proportioned voltage, while the
magnetic unit transforms this voltage, in both magnitude and phase to convenient levels suitable
for measuring, metering, protection etc. all WSI capacitor units has
metallic bellows to compensate the volumetric expansion of oil inside. The porcelain in multi
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Fig (2.15): CAPACITIVE VOLTAGE TRANSFORMERS
unit stack, all the potential points are electrically tied and suitably shielded to overcome the
effect of corona RIV etc.
1. Capacitive voltage transformers can be effectively as potential sources for measuring,
metering, protection, carrier communication and other vital functions of an electrical network.
2. CVT is constructed in single or multi unit porcelain housing with there associated magnetic
units. For EHV system cuts are always supplied in multi unit construction.
3. In case of EHV cuts the multi unit system has many advantage easy to transport and storing,
convenience in handling.
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2.10 TRANSFORMER OIL & ITS TESTING
The prime function of oil is to convey the heat from the core and winding to the tank where it
can be dissipated. Besides these, the oil provides additional insulation between primary and
secondary windings. So, the oil must be completely free from dirt, moisture and other un-wanted
solid matter. The oil used in the transformer is natural mineral oil and should undergo the
following tests if required:
2.10.1 BREAKDOWN VOLTAGE:-
The voltage at which the oil breaks down when subjected to an electric field.
2.10.2 FLASH POINT:-
The temperature, at which the oil gives off so many vapors, when mixed with air forms an
ignitable mixture and gives a momentary flash with small pilot flame.
2.11 TRANSFORMER TANδ TESTING:
TANδ testing is a diagnostic test conducted on the insulation of cables and windings. It is used to
measure the deterioration in the cable. It also gives an idea of the aging process in the cable and
enables us to predict the remaining life of
the cable. It is alternatively known as the loss angle test or the dissipation factor test.
The TANδ test works on the principle that any insulation in its pure state acts as a capacitor. The
test involves applying a very low frequency AC voltage. The voltage is generally double the
rated voltage of the cable or winding.
A low frequency causes a higher value of capacitive reactance which leads to lesser power
requirement during the test besides currents will be limited.
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2.12 LIGHTENING ARRESTORS
An electric discharge between cloud and earth, between cloud and the charge centers of the same
cloud is known as lightening. The earthing screens and the ground wires can well protect the
electrical system against direct lightening
strokes but they fail to provide protection against travelling waves which may reach the terminal
apparatus. The lightening arrestors or the surge diverters provide protections against such surges.
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16): Principal of TANδ tasting Transformers
Fig (2.17): LIGHTENING ARRESTORS
2.12.1 THYRITE TYPE: Ground wires run over the tower provides an adequate protection
against lighting and reduces the induced electrostatic or electromagnetic voltage but such a
shield is inadequate to protect any traveling wave, which reaches the terminal of the electrical
equipment and such wave can cause the following damage:
1. The high peak of the surge may cause a flashover in the internal wiring thus it may spoil the
insulation of the winding.
2. The steep wave front may cause internal flash over between their turns of transformer.
3. The stop wave front resulting into resonance and high voltage may cause internal or external
flashover causing building up the oscillator is the electrical operation.
Lightening arrestors are provided between the line and earth provided the protection against
traveling wave surge the thyrite lightening arrestor are provided at GSS. This type of LA has a
basic cell made of thirties, which is particular type of clay, mixed with carborendum. Thirties has
a particular property of being insulator one voltage At high voltage It will behave like a
conducting material the electrical resistance of thyrite depends upon the voltage each time the
voltage is made twice the resistance decrease in such a manner as to allow an increased current
of 12.5 times the change in current is independent of rate of application voltage and its
instantaneous value. The above law is followed by this material without any limit on the voltage
increase and after the surge has passed the thyrite again retains its original property.
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3.1 CONTROL ROOM
Fig (3.1): control Room-1
To remote control of power switch gear requires the provision of suitable control plates
located at a suitable point remote from immediate vicinity of CB’s and other
equipments. At "132 KV GSS Jalore" the separate control room provided for remote
protection of 132KV switch yards transformer incoming feeder, outing feeders. Bus bar
has their own control plant in their control rooms. The control panel carrier the appropriate
relays. Necessary meters indicating lamp control switches and fuses. There are meters for
reading purpose. A circuit concerning the panel is shown on the panel with standard co
On each panel a control switch is provided for remote operation of circuit breaker. There are
two indicators which show that weather circuit breaker is closed or open.
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Fig (3.2): Control Room-2
Fig (3.3): Control Room-2
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3.2 EARTHING OF THE SYSTEM
The provision of an earthling system for an electric system is necessary by the following reason.
1 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. 2 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 earthling system is
1. Shape and material of earth electrode used.
2. Depth in the soil
3. Specific resistance of soil surrounding in the neighborhood of system electrodes.
Fig (3.4): EARTHING OF THE SYSTEM
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3.3.1 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 below enough to prevent voltage rise between earth and neutral. The earth electrode
must be driven into 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 depths the several point of mesh then connected to
earth electrode or ground conduction. The earth electrode is metal plate copper is used for earth
3.3.2 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 points is earthed through an adjustable reactor of reactance matched with the line. The
earthling is one of the most important features of system design for switchgear protection neutral
grounding is important because:
1. The earth fault protection is based on the method of neutral earthling.
2. The neutral earthling is associated switchgear.
3. The neutral earthling is provided for the purpose of protection arcing grounds unbalanced
voltages with respect to protection from lightening and for improvement of system.
3.4 POWER LINE CARRIER COMMUNICATION
As electronics plays a vital role in the industrial growth, communication is also a backbone of
any power station, communication between various generating and receiving station is very
essential for proper operation of power system. This is more so in case of a large interconnected
system where a control load dispatch station has to coordinate the working of various units to see
that the system is maintained in the optimum working condition, power line communication is
the most economical and reliable method of communication for medium and long distance in a
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Fig (3.5): POWER LINE CARRIER COMMUNICATION SYSTEM
3.5 CORONA EFFECT
When an alternating potential difference is applied across two conductors whose spacing is as
large as compared to their diameters, there is no apparent change in the condition of atmospheric
air surrounding the wires if the applied voltage is low. However when the applied voltage
exceeds a certain value called critical disruptive voltage, the conductors are surrounded by a faint
violet glow called corona. The phenomenon of corona is accompanied by a hissing sound,
production of ozone, and power loss and radio interference. The higher the voltage is raised the
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larger and higher the luminous envelope becomes, and greater are the sound, the power loss and
the radio noise. If the applied voltage is increased to breakdown value, a flash over will occur
between the conductors due to the breakdown of air insulation. The phenomenon of violet glow,
hissing noise and production of ozone gas in an overhead transmission line is known as corona.
If the conductors are polished and smooth, the corona glow will be uniform throughout the
length of the conductors; otherwise the rough points will appear brighter. The positive wire has
uniform glow about it, while the negative conductors has spotty glow.
3.5.1 FACTORS AFFECTING CORONA:-The phenomenon of corona is affected by
the physical state of the atmosphere as well as by the conditions of the line. The following are
the factors on which corona depends:
1. Atmosphere. In the stormy weather, the number of ions is more than normal and as such
corona occurs at much less voltage as compared with fair weather.
2. Conductor size. The rough and irregular surface will give rise to more corona because
unevenness of the surface decreases the value of breakdown voltage.
3. Spacing between conductors. Larger space between conductors reduces the electro-static
stresses at the conductor surface, thus avoiding corona formation. 4. Line voltage. If the line
voltage is low, there is no chance in the condition of air surrounding the conductors and hence no
corona is formed.
3.5.2 ADVANTAGES AND DISADVANTAGES OF CORONA:-Corona has
many advantages and disadvantages. In the correct design of a high voltage overhead line, a
balance should be struck between the advantages and disadvantages.
1. Due to corona formation, the air surrounding the conductor becomes conducting and hence
virtual diameter of the conductor is increased. The increased diameter reduces the electro-static
stresses between the conductors.
2. Corona reduces the effect of the transients produced by surges.
1. Corona is accompanied by a loss of energy. This affects the transmission efficiency of the line.
2. Ozone is produced by corona and may cause corrosion of the conductor due to chemical
3. The current drawn by the line due to corona is non-sinusoidal and hence non-sinusoidal
voltage drop occurs in the line. This may cause inductive interference with neighboring
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CONCLUSION & FUTURE SCOPE
A technician needs to have not just theoretical but practical as well and so every student is
supposed to undergo a practical training session after III year where I have imbibed the
knowledge about transmission, distribution, generation and maintenance with economical issues
related to it. During our 30 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 132KV GSS has broadened my knowledge and
has widened my thinking as a professional.
After our technical summer training we gained more knowledge. While making this training
report every care has been taken to avoid any mistake. In short I hope to provide concise sight of
four weeks of my training period through this report.
I was lucky to have my training from 132 KV G.S.S., Jalore that gave me an all round
knowledge that an electrical engineer should know. During 30 days of my training Session at
G.S.S. I got knowledge about power distribution, power transmission and power line carrier
At last, I would like to say that practical training taken at Jalore has broadened my knowledge
and has widened my thinking as a professional.
Future scope of G.S.S. for PLCC system by which we connect other G.S.S. without any
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· Principles of Power System-by V.K.MEHTA
· Electrical Power System-by C.L.WADHWA
· REPORT BY- PRITAM SOLANKI (PCE), JAIPUR
· ““Electrical technology- by B.L. Thareja
· Generation of Electrical power- by B.R.Gupta.
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