CHAPTER- 1 INTRODUCTION 1.1 Synopsis Energy is the basic necessity for the economic development of a country. Energy exists in different form in nature but the most important for is electrical energy. The conversion of energy available in different forms of nature into electrical energy is known as generation of different forms of nature into electrical energy is known as generation of electrical energy. Various sources of energy available in nature are- 1 Solar Energy 2 Wind Energy 3 Tidal Energy 4 Nuclear energy A great demand of electrical energy is notable feature of modern civilization. The abundance of electrical energy completely changes the direction of the tempo of civilization, living standard, vast development of rural and urban areas. Electricity has become an essential commodity. The feature of electrical energy not only paralyses industries and agriculture but also upsets the lives. The whole electrical system is classified as: 1 Generation 2 Transmission 3 Distribution 4 Utilization 1
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CHAPTER- 1
INTRODUCTION
1.1 Synopsis
Energy is the basic necessity for the economic development of a country. Energy
exists in different form in nature but the most important for is electrical energy. The
conversion of energy available in different forms of nature into electrical energy is known
as generation of different forms of nature into electrical energy is known as generation of
electrical energy. Various sources of energy available in nature are-
1 Solar Energy
2 Wind Energy
3 Tidal Energy
4 Nuclear energy
A great demand of electrical energy is notable feature of modern civilization. The
abundance of electrical energy completely changes the direction of the tempo of
civilization, living standard, vast development of rural and urban areas. Electricity has
become an essential commodity. The feature of electrical energy not only paralyses
industries and agriculture but also upsets the lives.
The whole electrical system is classified as:
1 Generation
2 Transmission
3 Distribution
4 Utilization
5 Switchgear and protection
Turbines are moved with the help of different sources of energy. The generation is
coupled with turbine to generate 11KV which is further stepped up by step up
transformers to 400KV and is then distributed to various sub-stations where the voltage is
reduced to 220KV with the help of step down transformers. From these sub-stations the
energy is distributed to the consumers after reducing it to 33KV.
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1.2 Installation
The 400KV GSS Jodhpur is one of those stations, which distributes energy to the
consumers. The station was installed in 2003. Jodhpur is the second largest city of the
state Rajasthan.
1.2.1 The Incoming And Outgoing Feeder
The incoming supply is as follows:
1. 400 KV – Kankroli
2. 400 KV – Merta I
3. 400 KV – Merta II
4. 400 KV – Jaisalmer(Under Construction)
5. 400 KV – Rajwest (Under Construction)
The outgoing feeder is as follows:
1. 220 KV – Tinwari I
2. 220 KV – Tinwari II
3. 220 KV – Jodhpur I
4. 220 KV – Jodhpur II
5. 220 KV – Bilara
6. 132 KV – Banar
7. 132 KV – Mathania
8. 33 KV – Salawas
9. 33 KV – Daijar
10. 33 KV – JU Alloy
11. 33 KV – DRDO
1.2.2 Location And Coverage
The 400KV GSS is situated on near SURPURA village, about 14-15 KM from
Jodhpur Railway Station. It covers as area of 110-120 beegha of land.
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Fig. 1.1
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CHAPTER- 2
IMPORTANCE OF ELECTRICAL ENERGY
2.1 Introduction
Energy may be needed as heat, as light as motive power etc. the present day
advancement in science and technology has made it possible to convert electrical energy
into other desired form. This has given electrical energy place of pride in the modern
world. In fact the advancement of country is measured in terms of per capita consumption
of electrical energy. Electrical energy is superior to all other forms of energy due to the
following reasons
2.2 Conventional Forms And Easy Control
Electrical energy is a very convenient form of energy as it can easily converted into
any form of energy like heat, light mechanical etc.
2.3 Greater Flexibility
One important reason for preferring electrical energy is flexibility that it offers. It can
be easily transported from one place to another.
2.4 Cheapness
Electrical energy is cheaper than other forms of energy. Thus it is economical to use
this form of energy in domestic commercial and industrial purpose.
2.5 Cleanliness
Electrical energy is not associated with smoke, fumes or poisonous gases. Therefore
its use ensures cleanliness and health conditions.
2.6 High Transmission Efficiency
The consumers of electrical energy are generally situated quite away from the centers
of its production. The electrical energy can be transmitted conveniently and efficiently
from the center of generation to the consumers with the help of overhead conductors
known as Transmission lines.
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CHAPTER-3
FUNCTION AND SPECIFICATIONS OF VARIOUS
EQUIPMENTS AT 400KV GSS
3.1 Metering & Indicating Instrument
There are several metering & indicating instruments e.g. Ammeters, voltmeters,
energy meters etc installed in a sub-station to keep watch on circuit quantities. The
transformer is invariably used with them for satisfactorily operation.
3.2 Bus Bars
Bus bars are the important components in a substation. There are several bus bar
arrangements the can be used in a substation. The choice of a particular arrangement
depends upon various factors such as system voltage, position of substation, degree of
reliability; cost etc. the following are the important bus bar arrangement used in sub-
stations:
a) Single bus bar systems
b) Double bus bars systems
c) Duplicate bus bars systems
In the 400KV GSS Surpura, Double bus bar substation and duplicate bus bar
system has been installed.
3.3 Control Cables
The control cable and the control system are required for officiating automatic
system. The cables employed for this purpose are multi-core cables having 10 or 37 or
61 conductors are run to the required points. The conductors used in the 400 KV GSS are
moose and conductors used in the 220 KV GSS are tarantula.
3.4 Power Transformers
A transformer consists essentially of two or more electric circuit in the form of
winding magnetically interlinked by a common magnetic circuit. An alternating voltage
applied to one of the winding produces, by electromagnetic induction, a correspondence
emf in the other windings & energy can be transferred from the ordinary circuit to the
other circuit by means of the common magnetic flux and the principle of mutual
induction. A transformer is basically a static device in which two or more stationary
electric circuits are coupled magnetically, the winding being linked by a common time
varying magnetic flux. Even though the static transformer is not an energy conversion
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device & involves only the interchange of electrical energy between two or more
electrical systems, it is an extremely important component in many conversation systems.
Fig. 3.1
3.4.1 Classification Of Power Transformer:
1. According to usages
2. Step-up transformer
3. Step –down transformer
4. According to type of construction used:
5. Core type
6. Shell type
7. According to number of winding
8. Two winding transformer
9. Three winding transformer
10. Multi winding transformer
3.4.2 Terms Related To Transformer
1 Primary Winding:
The winding that is excited or energized by connecting it to an input source is usually
referred to as the primary winding.
2 Secondary Winding:
The winding to which the electrical load is connected and forms, which the output
energy is taken, are known as the secondary winding.
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3 HV Winding:
The winding which s operated at the high voltage level is known as the HV (high
voltage) winding.
4 LV Winding:
The winding which is operated at lower voltage level is known as the LV (low voltage)
winding.
4 Regulating Winding:
It is winding, which is used to regulate the voltage at different levels y connecting tap
changers across the winding. It consists of discrete numbers of small windings with 2 or 3
terms in each ad they being connected in series.
6 Tertiary Winding:
In addition to the tradition primary and secondary windings, a transformer can also have
tertiary winding.
3.4.3 Main Parts Of Transformer Are As Follows
1. Core:
It consist terminated silicon steel in which quantity of silicon 13up to 4% thickness of
lamination is 0.35 to 0.50m. Normally the shape of core in rectangular and it has three
legs.
2. Windings: Windings of power transformer are an important part. It consists of
super enameled copper wires. The size of wire (diameter) depends on the capacity of
transformer connection of winding is r/r.
3. Tap changer:
Tap changer is switching device by which the transformation ratio can be changed by
the changing the position of tap changing the switch. Tap changing system on GSS of
power transformer on-load tap changer (OLTC): On load tap changers are employed to
change turn ratio of transformer to regulate system voltage while the transformer is
delivering normal load with the introduction of on-load tap changing the operating
efficiency of electrical system has considerably improved. Now a day, almost all the large
power transformers are fitted with on load tap changer. All forms of on load tap changing
circuit posse’s impedance. This is introduced to prevent short-circuiting of tapping
section during tap changer operation. The impedance can be either a resist of or a centre-
tapped reactor.
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4. Tanks:
It is metallic tank, which is filled of insulating oil the transformer core and winding
assembly are surrounding by the oil in this tank. It protects that the winding and core
from the external mechanical damages. Rectangular tanks are similar in fabrication.
However for large rating power transformer, shaping of tanks becomes necessary to
conform to transportable profile shaping is provided by rounded corners at the ends,
truncation of law portion of walls from considerable, of loading in well wagon grider and
on the covers to reduce the height to minimize the tank oil, the tank profile may closely
follows the electrical clearances along the coils. As is evident, shaping gives saving in
tank material and oil but increases complexity and fabrication costs.
Transformer tank may be classified as
1 Plain tanks.
2 Shaped tanks.
3 Belt shaped tanks.
4 Corrugated tanks.
5 Stub and type tank
The transformer tank used in GSS power transformer is rectangular box (plain tank) type
in shape.
5. Cooling System:
In Power transformer, the oil serves a dual purpose as an insulating medium as well as
a cooling medium. The heat generated in the transformer is removed by the transformer
oil surrounding the source and is transmitted either to atmospheric air or water. This
transforms of heat is essential to control the temperature within permissible limits for the
class of insulation, thereby ensuring longer life due to less thermal degradation.
Types of cooling used in GSS power transformer:
1 ONAN type cooling: The generated heat can be dissipated in many ways. In case of
smaller rating of transformers, its tanks may be able to dissipate the heat directly to the
atmospheric dry while bigger ratings may require additional dissipating surface in form of
tubes/ radiators connected to tank or in the term of radiator tank. In these cases, the heat
dissipation is form transformer oil at atmospheric air by natural means. This form of
cooling is known as ONAN (Oil Natural, Air Natural) types of cooling.
2 ONAF type of cooling: For further augmenting the rate of dissipating of heat, other
means such as fans blowing air on the cooling surfaces are employed. The forced air takes
away the heat at a faster rate, thereby giving better cooling rate than natural air. This type
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of cooling called ONAF (Oil Natural Air Forced) type of cooling. In this cooling
arrangement, additional raring under ONAN condition viz. after shutting off fans, is
available, which is of the order of 70-75%.
5.1 Cooling Arrangements
Depending upon the typed of cooling and rating of the transformer, the cooling
equipment can be arranged in various ways.
5.2 Arrangement with Radiators
Radiators are commonly used for ONAN and ONAF types cooling. Radiator
consists of element joined to and bottom headers, elements are made by welding two
previously rolled and pressed thin steel sheets to forms a number of channels of flutes
through which oil flow. These radiators can be either mounted directly on the transformer
tank or in a form of a bank or connected to the tank through the piper. The surface area
available for dissipation of heat is a multiple manifold by using various elements in
parallel. As oil passes downwards either due to natural circulation or force of a pump in
the cooling circuits, the surrounding atmosphere air carries heat away.
5.3 Arrangements with Fans
These fans deliver large air volume at moderate speed with minimum sound and
low power consumption. Ring mounted fans are designed to give maximum volume
under free airflow condition and resistance up to approximately 6mm WC. These fans
generally conform to IS2312 and are used for radiator cooling. Fan consists of a totally
enclosed continuously rated specially designed motor with class B insulation and IP-55
class of protection to meet fan duty, impeller constructed with four broad faced. Steel
sheet blades assembly on robust aluminum hub, four arms, pressed sheet mounting ring
and four rubber cushions.
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Fig. 3.2
6. Temperature Meters
There are two temperatures indicating metering power transformer, which indicate
the oil temperature and winding temperature. Temperature measured in degree Celsius. A
complete assembly of a transformer with details of core, wingding, tank connections and
major accessories.
7. Conservator and Air Cell
As the temperature of oil increases or decreases during operation there is a
corresponding rise or falling volume to account for this an expansion vessel (conservator)
is connected to the transformer tank. The conservator has got a capacity between the
minimum to maximum oil level equal to 7.5 & of the oil in transformer. The atmoseal
types conservator, it is filled with oil to level appropriate to filling temperature and in
remaining portion is air cell, which is connected to atmosphere through a breather. As the
breather is through air cell no moisture come in contact with oil, this protect the oil from
deterioration or contamination.Air cell is a flexible separator filled inside the conservator.
Oil being out of the air cell, the separator is in direct contact with the atmosphere. The
advantage of air deterioration or contamination.
1. An efficient barrier between oil and air.
2. A protection against water vapors.
3. The suppression of any gas bubbles formation in the oil.
Air cell is made from coated fabric with external coating resistance to transformer oil
and inner to coating to ozone and weather.
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Fig. 3.3
8. Buchholz’s Relay
The transformer is fitted with a bubble float buchholz rely. It is fitted in the feed
pipe from conservator to tank. Any internal fault in transformer is detected by buchholz
relay the gas liberated in the transformer is divided to the buchholz relay without being
trapped anywhere.
9. Dehydration Breather
The conservator is connected outside through dehydration (Silicage filled)
breather to make sure that the air in conservation is dry.
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Fig. 3.4
10. Oil Temperature Indicator
Oil temperature indicator operates on the principal of liquid expansion. The OTI
provided with a maximum pointer and two mercury switches are adjustable to make
contact between 500 to 1200 with the fixed differential of 100. the temperature for alarm
and trip contact setting shall be as under:- alarm 800 to 900.
11. Winding Temperature Indicator
The indicator is fitted with four mercury switches, one is used for alarm, 2nd is for
tripe and 3rd is for fans on and 4th pumps control. All the switches are adjustable.
12. Earthing
Connecting leads from core and end frame are being terminated at the top at the top of
cover. By connecting them to tank cover, core and end frames being earthed. For Bank
earthing two number studs have been provided on tank.
13. Terminal Bushings
It is used to isolate the leads that are coming from transformer. The size of the
bushing is justified according to operation voltage of particular winding. The active part
of the bushing consists of an Oil Impregnated Paper (O.I.P.) condenser core manufactured
from superior grade craft paper would on aluminum tube. This bushing is voltage graded
by suitably interposed aluminum foils forming condenser layers. Thus the electrical stress
are controlled throughout the thickness and along the surface avoiding any highly stress
concentrations. The bushing is supplied fully assembled in a wooden packing case with
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the busing supported at an angle of 10 degree to the horizontal. The bushing should never
be placed horizontally.
14. Insulating Oil
The insulating oil has three functions:
1 Provides additional insulation
2 Protects the paper from dirt and moisture
3 Carries away the heat generated in the core and coils.
The Insulating oil should have the following properties :
i) High Dielectric Strength.
ii) Free from inorganic acid, alkali and corrosive sulphur to prevent injury to
the conductor or insulation.
iii) Low viscosity to provide good heat transfer
iv) Free from sludge under normal operating conditions.
v) Free from sludge under normal operating conditions.
vi) Good resistance to emulsion so that the oil may throw away any moisture that enters
the apparatus.
3.5 Lighting Arresters
They are used to protect the sub-station & transmission lines arrests is
earthed . Gap is adjusted in such a way that 50% over voltage is operators. We
will use value type lighting arresters this types is called non-linear diverter. In
this spark – gap & resistance disc are used . when there is less change in line
voltage than is not flashover in gap but when there is over voltage & rapid
change in voltage then even grounding of voltage will not possible the value of
flash over voltage depends on surge currents. Operation will start when voltage
will increase 10% of rated voltage.
1. Rod gap arresters
2. Horn gap arresters
3. Multigap arresters
4. Expulsion type arresters
5. Value type arresters
3.6 Circuit Breakers
Classification of circuit breakers
1) Are quenching (Medium Wise)
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a) Air Blast CB
b) Oil CB
c) Air Blast CB
d) Vacuum CB
e) SF₆ CB
2) Application wise :
a) Generator CB
b) Transformer Line CB
c) Industrial CB
d) Distribution CB
3) Voltage Level Wise:
a) HV/EHV CB
b) MV CB
c) LV CB
4) Base on Construction:
a) Dead Tank Breaker
b) Live Tank Breaker
G.S.S has SF₆ Circuit Breaker’s which have the following mechanism.
6.1 SF₆ Circuit Breaker: In this CB, the SF₆ gas is used as an quenching agent. The
process of extinction by the gas is shown the below block diagram
At the time of fault:
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Contracts of CB open
The Valve mechanism permits high pressure SF₆ gas from the reservoir to flow towards the are interruption chamber from the
Trip Valve, which is now NO-normally open.
The high pressure flow of the SF₆ gas rapidly absorbs the free electrons in the are path to form immobile negative ions, which
are ineffective are charge carriers.
As a result, the medium between the contacts quickly builds up high Dielectric Strength & causes the extinction of the arc.
Fig. 3.5
3.6.1.1 Electrical properties of SF₆
Electron affinity: The excellent insulation properties of sulphur hexafluoride are
attributable to the strong electron affinity of the SF ₆ molecule. This is based mainly on
two mechanisms, resonance capture and dissociative attachment of electrons in
accordance with the equations:
1) SF₆ +e→ SF₆
2) SF₆ + e → SF₅ + F
The process represented by equations (1) applies to electron energies of 0.1 eV
with an energy range of 0.05eV and that represented by equations (2) applies to an energy
range of 0.1 eV.
1. Are-quenching capacity: On account of its thermal properties and low
ionization temperature, sulphur hexafluoride exhibits outstanding characteristics for the
extinguishing of electric arcs. The quenching time using SF₆ is about 100 times less than
that using air.
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2. Dielectric Strength: The strong interaction of hi-energy electrons with the
polyatomic SF₆ reaches that of transformer oil at pressure of only 3 bars. The breakdown
strength of SF₆ is independent of frequency. It is inert gas. Chemical inertness of this gas
is advantageous in switchgear. The components do not get oxidized or deteriorated. The
life of metallic part, Contacts is longer in SF₆ gas. Hence the maintenance requirements
are reduced.
3.6.1.2 Operating Principals Of Sf₆ Circuits Breaker:
The SF6 breaker operates on what is usually referred as the puffer principle. In puffer
type SF6 circuit breaker , the entire breaker is filled with SF6 gas at single pressure of 5
Kg/cm2 or about 7 bar. The breaker is a sealed unit . during the opening stroke the SF6 gas
is compressed released through the nozzle of insulating material. The compressed gas
flow through the nozzle at a high velocity and takes away the heat produced by the arc the
arc is quenched at a current zero. The high dielectric strength of gas is useful in giving
good with stand voltage SF6 circuit breaker are explosion free , can quench capacitive
currents , short circuit current etc. Early and are used for high voltage circuit breakers for
voltage above 3.3 KV During manufacture of the breaker pole it is dried internally
through pumping, the breaker pole is then to pressurized and also tested against leaks
inside the pile there is a absorption medium for the decomposition products of the gas.
The breakers pole should only be opened by trained person at the manufacturing factory.
3.7 Isolators
Then carrying out inspection or repair in a substation installation. It is essential to
disconnect reliably the unit or the section, on which the work is to be done, from all other
live parts of the installation in order to ensure complete safety of the working staff. To
guard against mistakes it is desirable that an apparatus, which makes a visible break in the
circuit, should do this apparatus is the isolating switch. It may be defined as a device used
to pen ( or close ) a circuit in the voltage across the terminal e.g. each pole of the isolator
will result from the operation.
Isolators are classified as:
1. Off load isolator-It is an isolator which is operated when the isolator is already
disconnected from all sources of supply or when the isolator is already disconnected from
the supply and current may be due to capacitance current of bushings bus bar connections
and very short length of cable.
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2. On load isolator -It is isolator, which is operated in a circuit where there is a parallel
path of low impedance so that no significant change in the voltage across the terminals of
each pole occurs when it is operated .
3.8 Instrument Transformer
Is defined as a transformer intended to feed the measuring instruments, meters,
relays etc. Generally protective system are relays are connected to the secondary
of a current transformer as they cannot withstand high currents. These IT’s help
in reducing these voltages & currents to acceptable level for operation of
voltmeters & ammeters.
3.8.1 Current Transformer
A CT is an instrument transformer in which the secondary current is
substantially reduced proportional to the primary current & differs from it by the
angle which is approx. direction of current . These transformers are different from
general power transformers.
Fig. 3.6
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Shown below are the major differences that are noticeable:
Conventional Transformer Current Transformer
Driving Function: voltage. Driving Function : Current
Secondary load impedance determines the
secondary current.
CT primary current is the determining
and predominated factor.
Corresponding to the secondary current the
primary current flows.
Secondary current follows the primary
current.
3.8.1.2 Function / Application of a CT
1. For Metering function : It transforms the high value Primary Current substantially
low value secondary current which can be fed directly to measuring instruments for
measuring the current & power in the main circuit.
2. For Protection Purpose: The secondary current can also feed Protective Relays which
operate the protective system in the main circuit in case of any abnormality in the system.
Definition of the different terms related with current transformers :
a) Rated Primary Current: The value of primary current on which the primary
performance of the current transformers is specified.
b) Rated Short Time Current: Its defined as r.m.s value of a.c component which the
CT can carry without damage.
c) Rated Secondary Current: The value of secondary current marked on the rating
plate.
d) Rated Exiting Current: The RMS value of current taken by the secondary winding
of a. C.T. When sinusoidal voltage of rated frequency is applied to secondary with
primary winding open.
e) Rated Burden: The burden assigned by the manufacturer at which C.T performs with
specified accuracy.
f) Current Error Ratio Error: The percentage error in the magnitude of secondary
current is defined in the terms of current error.
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3.8.1.3 Burden on C.T.
Rated burden of CTS and VT’s referring to the maximum load in volt-amperes 9
VAO which may be applied across the secondary terminals without the ratio and phase
angle error-exceeding the permissible limits. The burden depends upon the number of
relays and instruments connected and their individuals burden typical values.
3.8.1.4 Various Types of Construction of CTs
A CT has following essential parts
1. Insulation over the core by taps
2. Secondary winding having several turns would on the insulated core.
3. Bar primary passing through the window of the core and terminals.
4. Support porcelain or epoxy insulator.
5. Synthetic resin or oil insulation.
6. 3.8.1.5 CT’s For High Voltage Installations
Separately mounted post type CT’s are suitable for outdoor service. The primary
conductor is at high voltage with respect to the earth. Hence it is insulated by means of
insulation column filed with dielectric oil. In high voltage CT’s the primary and
secondary windings are situated at the upper end of the unit. The primary wdg. Normally
being of bar type. The top – fabricated housing is at line potential and is supported on the
porcelain insulator.
3.8.1.6 Specification Of 400 KV Current Transformers
1. Type – Dead tank, single phase out door, oil immersed & Hermetically sealed .
2. Manufacturer’s Designation – 420 kV CT.
3. Rated voltage ( KV ) – 420
4. Short time thermal rating for One second ( KA rms ). – 40
5. Rated dynamic current of primary 100 ( Kapeak).
6. Flux density at knee point voltage, 14.5 Wb/cm2
7. NO. of primary turns – single
8. No. of secondary turns – 200-1000-500
9. Core area , cum2 – 65.55
10. Core length, (Average magnetic path) cms. – 104.46
11. Type of primary winding – Hair pin type.
12. 1 Temperature rise (degree C) at rated continuous thermal current over max. ambient
temperature at site for –
i) Winding 40
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ii) Oil at top 40
iii) Exposed current carrying parts 55
12.2 Temperate rise at normal rating over max. Ambient temperature site for
i) Winding 40
ii) Oil at top 40
iii) Exposed current carrying parts.
13. Total creep age distance, mm 10500
14. Protection creep age distance 5250
15. One minute power frequency with stand test voltage ( kv rms ) 630