training report file on 220 kv GSS DAUSA

1. A
Seminar Report
On
“Practical Training”
Taken at
220 kV G.S.S. Dausa
And
Submitted in the partial fulfillment for award the degree of
Bachelor of Technology
In
Electrical Engineering
From
Rajasthan Technical University, Kota
Session 2012-2013
Submitted To Submitted by
Mr. Arun Sharma Rinku Kumar Meena
Head Of Department B.Tech. 4th
year (7th
Sem.)
Electrical Engineering Roll no. 10EDSEE099
S.D.I.T. Dausa Enroll. no.
Submitted to
Department of Electrical Engineering
SHREE DIGAMBER INSTITUTE OF TECHNOLOGY,
BHANDAREJ MODE, DAUSA
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2. 2

3. 3

4. ACKNOWLEDGEMENT
I feel immense pleasure in conveying my heartiest thanks and deep sense of
gratitude to Head of the Electrical Engineering Department of SHREE
DIGAMBAR INSTITUTE OF TECHNOLOGY, Dausa 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, Dausa.
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.
4

5. 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. Dausa.
Since my training centre 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 30 Working days practical training, I had undertaken my training at 220
kV G.S.S. at DAUSA.
I had taken my first practical training at 220 kV G.S.S. Dausa.
The period of training was from 17/05/2012 TO 15/06/2012.
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, Dausa.
5

6. CONTENTS
1. Introduction……………………………………………………………..02-04
• 220 kV G.S.S. Dausa………………………………………………..03
• Incoming feeders…………………………………………………….03
• Outgoing feeders…………………………………………………….04
• Radial feeders………………………………………………………..04
2. Bus bars…………………………………………………………………05-07
• Bus bar arrangement………………………………………………...05
3. Isolators…………………………………………………………………….08
4. Insulators………………………………………………………………..08-11
• Type of insulators……………………………………………………09
o Pin type……………………………………………………….10
o Suspension type………………………………………………10
o Strain type…………………………………………………….11
5. Protective relays………………………………………………………...12-16
• Differential relays…………………………………………………...14
• Buchholz relay………………………………………………………14
o Construction…………………………………………………..14
o Operation……………………………………………………..15
o Advantages…………………………………………………...15
o Disadvantages………………………………………………...16
6. Circuit breakers………………………………………………………....16-24
• Operating principle………………………………………………….16
• Arc phenomenon…………………………………………………….17
• Classification of circuit breakers…………………………………….18
• SF6 C.B……………………………………………………………...18
o Construction…………………………………………………..19
o Working………………………………………………………20
o 220 kV SF6 C.B. ratings……………………………………...21
o Advantages of SF6 C.B………………………………………22
o Demerits of SF6 C.B………………………………………….23
o Applications…………………………………………………..24
7. Power Transformers…………………………………………………….24-29
• Basic parts of transformer…………………………………………...25
• Transformer ratings………………………………………………….26
6

7. 8. Current transformer………………………………………………………...30
9. Potential transformer……………………………………………………….31
10.Capacitive voltage transformer (CVT)…………………………………31-33
• Description…………………………………………………………..31
• Applications…………………………………………………………32
• Ratings of cvt………………………………………………………..33
11.Transformer oil & its testing……………………………………………34-35
• Breakdown voltage………………………………………………….34
• Flash point…………………………………………………………...34
12.Lightening arrestor……………………………………………………...36-38
• Thyrite type………………………………………………………….36
• 220 kV lightening arrestor…………………………………………..38
13.Control panel……………………………………………………………39-41
• Reactor………………………………………………………………39
• C.B…………………………………………………………………..39
• Bus couplers…………………………………………………………40
• Disturbance reactor………………………………………………….40
• Event logger…………………………………………………………40
• On load tap changer (OLTC)………………………………………..40
• No load tap changer (NLTC)………………………………………..41
• Synchronoscope……………………………………………………..41
14.Earthing of the system………………………………………………….42-43
• Procedure of earthing………………………………………………..42
• Neutral earthing……………………………………………………...42
15.Power line carrier communication…………………………………………44
• PLCC system in Rajasthan…………………………………………..44
16.Corona effect……………………………………………………………45-47
• Factors affecting corona……………………………………………..46
• Advantages and disadvantages of corona…………………………...47
17.Conclusion………………………………………………………………….48
18.Reference…………………………………………………………………...49
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8. 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
8

9. Incoming feeders
Outgoing feeders
220 kV G.S.S. DAUSA
1. It is an outdoor type substation.
2. It is primary as well as distribution substation.
3. One and half breaker scheme is applied.
Incoming feeders:
The power mainly comes from:
220 kV G.S.S.
Dausa
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10. 220 kV:-
1. ANTA-1 & ANTA-2
2. PGCIL BASSI-1 & BASSI-2.
Out going feeders:
220 kV 132 kV 32 kV 11 kV
1) Alwar 1) Lalsot 1) Paprada 1) Hodaily
2) Bharatpur 2) Bassi 2) Bhandarej 2) Nangal
3) Hindaun 3) Toonga 3) Bapi 3) Dausa-1
4) Padasoli 4) Dausa-2
5) Dausa-3
6) Dausa-4
As this substation following feeders are established:
1. Radial Feeders.
2. Tie Feeders
RADIAL FEEDERS:
1. 220 kV DAUSA - ALWAR.
2. 220 kV DAUSA – HINDAUN.
3. 220 kV DAUSA – BHARATPUR
10

11. 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 of strain 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.
3.1) BUS BAR ARRENGEMENT MAY BE OF FOLLOWING TYPE
WHICH IS BEING ADOPTED BY R.R.V.P.N.L.:-
3.1.1) Single bus bar arrangement
3.1.2) Double bus bar arrangement
a) Main bus with transformer bus
b) Main bus-I with main bus-II
3.1.3) Double bus bar arrangement with auxiliary bus.
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12. 3.1.1) DOUBLE BUS BAR ARRANGEMENT :
1. Each load may be fed from either bus.
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.
3.1.2) 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.
12

13. Fig.:- Bus Bars
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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14. 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
14

15. 4.1.2: Suspension type
4.1.3: Strain insulator
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.:- 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.
15

16. Fig.:- 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.:- Strain Insulators
16

17. 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.
17

18. Fig.: -Relays
7.1) 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.
7.2) Types of Distance relay:-
7.2.1) Impedance Relay:
The impedance relay has a circular characteristic centred. It is non
directional and is used primarily as a fault detector.
7.2.2) Admittance Relay:
18

19. 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.
7.2.3) 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.
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.
19

20. Fig.:-Buchholz Relay
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.
20

21. 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:-
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, gas-insulated 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
21

22. opened, a small amount of gas is compressed and forced through the arc to
extinguish it.
Fig. 8-SF6 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 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.
22

23. Fig. 9-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
23

24. • Due to lesser arc energy, air blast circuit breakers are very suitable for
conditions where frequent operation is required
• 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:
24

25. 1. It absorbs the arc energy to decompose the oil into gases, which have
excellent cooling properties.
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
25

26. 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.
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:
Lightning: 1450 kV
Switching: 1050 kV
Normal current Rating:
26

27. 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.
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.
27

28. 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.
POWER TRANSFORMER
Distribution transformers reduce the voltage of the primary circuit to the voltage
required by customers. This voltage varies and is usually:
28

29.  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:-
8.1) 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.
29

30. Fig. 11-Power Transformer
8.2) 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.
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.
8.3) 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.
30

31. (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. 12-Radiator with fan
8.4.2) Temperature Indicators:
Most of the transformer (small transformers have only OTI) are provided with
indicators that displace oil temperature and winding temperature. There are
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. 14-Winding and oil temperature indicator
8.4.3) Silica Gel Breather:
31

32. 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.:-Silica gel Breather
8.4.4) 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 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.
CURRENT TRANSFORMER
32

33. 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.
Fig.:-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.
POTENTIAL TRANSFORMER
33

34. 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.
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.
CAPACITIVE VOLTAGE TRANSFORMERS (CVT)
A capacitor voltage transformer (CVT) is a transformer used in power systems to
step-down 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 high voltage signal, a ground terminal and at
34

35. 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.:- 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.
Capacitive voltage transformer is being used more and more for voltage
measurement in high voltage transmission network, particularly for systems
35

36. 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.
The capacitance type voltage transformers are of twp type:
• Coupling Capacitor type
• Pushing Type
TRANSFORMER OIL & ITS TESTING
36

37. 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.
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
standard-compliant 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.
37

38.  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)
 As a result the breakdown voltage is calculated as mean value of the
individual measurements.
LIGHTNING ARRESTOR
38

39. 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 high-voltage 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.
Lightning-produced extreme voltage spikes in incoming power lines can damage
electrical home appliances.
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 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
39

40. 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 varistors 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
40

41. No. of phase: One
Rated voltage: 360 kV
Nominal discharge current: (8×20µs) 10 kA
High current impulse: (4× 100µs) 100 kA
Long distribution rating: (200µs) 500 kA
CONTROL PANEL
41

42. 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.
Fig.:-Control Room in GSS Dausa
12.1) MEASURING INSTRUMENT USED:
42

43. 12.1.1) 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.
12.1.2) WATTMETERS: It is attached to each feeder to record the power
exported from GSS.
12.1.3) FREQUENCY METER: To measure the frequency at each feeder
there is the provision of analog or digital frequency meter.
12.1.4) VOLTMETER: It is provided to measure the phase to phase voltage
.It is also available in both the analog and digital frequency meter.
12.1.5) AMETER: It is provided to measure the line current. It is also
available in both the forms analogue as well as digital.
12.1.6) MAXIMUM DEMAND INDICATOR: There are also mounted the
control panel to record the average power over successive predetermined
period.
12.1.7) MVAR METER: It is to measure the reactive power of the circuit.
Capacitor Bank:-
The capacitor bank provides reactive power at grid substation. The voltage
regulation problem frequently reduces so of circulation of reactive power.
43

44. 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. 20-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
3. Increase power factor of loading current
44

45. 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.
15.1) 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.
15.2) NEUTRAL EARTHING:
45

46. 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.
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
46

47. 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
SF6 CB
BREAKER SERIAL NO. 030228
RATED VOLTAGE 145KV
NORMAL CURRENT 1250A
FREQUENCY 5OHz
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 8.7Kg
17.3) BATTERY CHARGER:
Battery Charger – 220AH VDC HBL NIFE LTD.
47

48. 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:
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 110/1.732 110/1.732
RATED BURDON 220Va 110Va
FREQUENCY 49.5-50.5Hz
48

49. 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 2nd
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 220 kV GSS has
broadened my knowledge and widened my thinking as a professional.
49

50. REFERENCE:-
Principles of Power System-by V.K. MEHTA
Electrical Power System-by C.L. WADHWA
50