Gss herapura report

INDEX

LAYOUT pg. no
1. INTRODUCTION [SUB STATION] -1
2. BUS BARS -4
3. ISOLATORS -7
4. PROTECTIVE RELAYS -11
5. CIRCUIT BREAKERS -16
6. POWER TRANSFORMER -25
7. CURRENT TRANSFORMER -31
8. CAPACITIVE VOLTAGE TRANSFORMERS -33
9. TRASNFORMER OIL AND ITS TESTING -36
10. LIGHTENING ARRESTORS -38
11. CONTROL ROOM -41
12. EARTHING OF THE SYSTEM -44
13. POWER LINE CARRIER COMMUNICATION -46
14. CORONA -47
CONCLUSION
REFERENCES

INTRODUCTION

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-stations may be
further subdivided:
a) Out door substation.
b) Indoor substation.
c) Basement or Underground substation.

2 Dept. of Electrical Engg.

fig 1

220 KV G.S.S. SANGANER

1) It is an outdoor type substation.
2) It is primary as well as distribution substation.
3) One and half breaker scheme is applied.


The power mainly comes from HIRAPURA-1 and HIRAPURA-2 & KOTA
THERMAL .

Out going feeders
1) One feeder of 220kv to KTPS
2) One feeder of 220kv to Sakatpura.
3) One feeder of 220kv to KTPS2
4) One feeder of 220kv to Phulera
5) One feeder of 400kv to Merta
6) One feeder of 220kv to Sanganer

At this substation following feeders are established.

1. TIE FEEDERS.
2. RADIAL FEEDERS.

TIE FEEDERS:
There are 220KV tie feeders as follows.
1.220 KV KOTA-JAIPUR 1st & 2nd
2. Inter state 220KV KOTA –DELHI
3. Tie from 220 KV Heerapura.
4. 220KV KTPS first & second.

RADIAL FEEDERS


1. 220 KV JAIPUR –KOTA 1st & 2nd feeders
2. 132KV KOTA –BUNDI 1st
3. 132KV KOTA –SAWAI MADHOPUR 1st & 2nd
4.132 KV KOTA –SANGOD
5. 132 KV KOTA –MORAR

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 heights are low
and minimum clearance is required. While in case of strain type of bus bars
suitable ACSR conductors are strung / tensioned by tension insulator 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 effect 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.


BUS BAR ARRANGEMENT MAY BE OF FOLLOWING TYPES WHICH
ARE BEING ADOPTED BY R.R.V.P.N.L
1.) Single bus arrangement.
2.) Double bus bar arrangement.
a) Main bus with transformer bus.
b.) Main bus-I with Main bus-II.
3.) Double bus bar arrangement with auxiliary bus.

DOUBLE BUS BAR CONTAINING MAIN BUS I WITH MAIN BUS II:

1. Each load may be fed from either bus.
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 necessary. 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
supply.

DOUBLE BUS BAR ARRANGEMENTS CONTAINS MAIN BUS WITH
AUXILIARY 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 breaker.

fig 2


ISOLATORS

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
insulator are being used in R.S.E.B-
a) Isolator without earth blades.
b) Isolator with earth blade.


c) Tendon isolator.

INSULATORS

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 permitivity will be lowered.
5. High ratio of puncture strength to flash over.

These insulators are generally made of glazed porcelain or toughened glass. Poly
come type 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.

TYPES OF INSULATORS:

There are three types of insulators used for overhead lines:

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 voltage 33KV. Beyond
operating voltage of 33KV the pin type insulators thus become too bulky
and hence uneconomical.

Fig 3.1
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.

Fig 3.2
3. Strain 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
insulators are used as strain insulator.


Fig 3.3

PROTECTIVE RELAYS

A Protective relay is a device that detects the fault and initiates the operation of the
circuit breaker to isolate 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.

Relay circuit connections can be divided in three parts:
1.) Primary winding of a 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.)Third part is the tripping circuit, which may be either a.c. or d.c. . It consists of a
source of a supply, the trip coil of a circuit breaker and the relays stationary
contacts.

When a short circuit occurs at 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, the relay ensures the safety of the circuit
equipment
from damage and normal working of the healthy portion of the system.


Fig 4
Basic qualities that a protective relay must possess are:

1.) Selectivity
2.) Speed
3.) Sensitivity
4.) Reliability
5.) Simplicity
6.) Economy

DIFFERENTIAL RELAYS


A differential relay 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 pick up value, the relay will operate and open the C.B. to isolate
the faulty section.

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 the main tank. It is a universal practice to use
BUCHHOLZ relay on all such oil immersed transformers having ratings in excess
of 750kVA.

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.

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 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.

ADVANTAGES


(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 protection.

DISADVANTAGES

(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.

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.

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 energised and the
moving contacts are pulled apart, thereby opening the circuit.
When the contacts of the C.B. are seperated under fault conditions, an arc is
struck between them. The current is thus able to continue until the discharge
ceaeses. 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.


ARC PHENOMENON

When a short circuit occurs, a heavy current flows 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
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.

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 elimination
(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.

SULPHUR HEXAFLOURIDE (SF6) CIRCUIT BREAKER

In such breakers, sulphur hexaflouride (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 service.

CONSTRUCTION


The cylindrical large size steel tanks are mounted horizontally parallel to
each other. Each tank consists of SF6 under pressure. The interruption is of multi
break 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 bushing are also insulated with SF6 the conductor is in the from 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 beginnings.


Fig 5
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 synchronised 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 causes the extinction of the arc. After
the breaker operation the valve is closed by the action of a set of springs.

400 KV SF6 C.B. [RATINGS]: -

Manufacture: BHEL Hyderabad.
Type: HLR245/2503 B.S.
Rated voltage: Normally 420 KV, maximum 440 KV.
Rated frequency: 50 HZ.
Rated power frequency: voltage: 520 KV
Rated Impulse withstand voltage:
Lightning: 1425KV
Switching: 1050KV


Normal current rating
At 50 c ambient: 2240Amps
At 40 c ambient: 2500Amps

Short time current rating: 40 KA for 3 sec.
Rated operating duty: 0 to 0.3 sec. c-0-3min-mb.
Rated short circuit duration: 1 sec.

BREAKING CAPACITY [BASED ON SPECIFIED DUTY CYCLE]:
(a) Capacity at rated voltage: 29000MVA [440KV].
(b) Symmetry current: 40 KA.
(c) Asymmetry current: 49 KA.

Making capacity: 100KA [peak]
Rated pressure of hydraulic operating (gauge): 250-350bar.
Rated pressure of SF6 gas at degree: 7.5bars.

Weight of complete breaker: 11700 Kg.
Weight of SF6 gas: 76.5Kg.
Rated trip coil voltage: 220 V. AC.
Rated closing voltage: 220 V. DC.


First poll to clear factor: 1.3

ADVANTAGES OF SF6 CIRCUIT BREAKER:

1. Due to the superior arc quenching property of SF6, such circuit breakers

have very short arching time.
2. Since the dielectric strength of SF6 gas is 2 to 3 times that of air, such

breakers can interrupt much larger currents.
3. The SF6 circuit 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 auxiliary equipment.
7. Since SF6 breakers are totally enclosed and sealed from atmosphere they are
particularly suitable where explosion hazard exists e.g., coal mines.


DEMERITS OF SF6 CIRCUIT BREKER:

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 environment.
6. Dust of Teflon & sulfide should be removed.
7. Special facilities are needed for transporting the gas.

APPLICATIONS

SF6 C.B. have been developed for voltages 115 KV to 230 KV, power ratings 10
MVA to 20 MVA and interrupting time less than 3 cycles.

S.N I.E. MAK TYPE VOLTAGE CURREN STC SF6/HY
O E T D
1 552A 3AT3 3AT3 420/520 2000A 40KA/S 7.5/350
2 552T DO DO DO DO DO DO
3 552B MG FAR2 DO 3150A DO 7/300
4 452T NGEF S2M420 420/610/1425 2000A DO 8/35
5 252A BHEL 3AT3 420/520/1050 DO DO 7.5/350
6 252B ABB EL(V) 420/1050 3150 40KA/3S 7/31.5


POWER 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 400
KV, 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.

BASIC PARTS OF TRANSFORMER

The following are the inherent parts of a modern day transformer:


1. Primary and secondary coils (circuit) or windings.
2. Core
3. Main Tank
4. Conservator
5. Breather
6. Radiator
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

Fig 6.1

DESCRIPTION OF PLANT:


The three transformer are oil immersed with rating of 250 MVA
& one with 315 MVA. However a synchronous loading of 100MVA at 0.8 power
factor (lag) and 18 MVA 0.8 pf (lag) on the tertiary can also be loaded to 20MVA
loading with 100MVA 0.8 pf on LV without exceeding the generated temperature
rise.
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.

Fig 6.2

RATING DATAS.

Type of cooling: ONAN / ONAF/ ODAF


MVA
HV: 189 / 252 / 315
IV: 189 / 252 / 315
LV: 63 / 84 / 105

VOLTS
HV: 400 KV
IV: 220 KV
LV: 33 KV

LINE AMPERES
HV: 273 / 364 / 455
IV: 497 / 662 / 828
LV: 1104 / 1471 /1839

IMPEDANCE VOLTAGE
HV to IV 12.65% on 315 MVA Base
HV to LV 39.16 % on 315MVA Base
IV to LV 26.66 % on 315 MVA Base

NUMBER OF PHASES
Three HV, LV, IV
FREQUENCY IN Hz
50 Hz


YEAR OF MANUFACTURE: 1985

Mass of Core & Windings: 1,32,000 kg
Mass of Oil: 65,150 kg
Total weight: 261,200 kg
Oil in tank: 73,200 kg
Oil in radiator: 8400 kg

Oil in tap changer: 83,850 kg
Transportation mass: 168,000 kg
Unmaking height: 7760 mm
Unmaking mass 18000 Kg

Guaranteed maximum temperature rise of:
Oil 45ºC
Winding 50ºC

COOLING FANS:

Rating: 2000 m3 of air per minute.
Type: 915 mm dial GEC (India) make.
Numbers per transformer: two


Fan motor: direct on line starts weather proof.
Squirrel cage IM 1400 W 400/440
Volt 3-φ , 50 Hz 720 rpm

PUMPS:
Rating: 1818 liters per minute.
Type: a landless A to 8c sentiment.
Number of pump per transformer: one working, one standby.
Pump motor: direct on line starts weather proof.
Squirrel cage IM


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 7

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.


CAPACITIVE VOLTAGE TRANSFORMERS (CVT)

Capacitive voltage transformers are special kind of power
transformers using capacitors to step down the voltage.

DESCRIPTION:


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 unit stack, all the
potential points are electrically tied and suitably shielded to overcome the effect
of corona RIV etc. Capacitive voltage transformers are available for system
voltages of 33 KV to 420KV.

Fig 8

APPLICATION:

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 are constructed in single or multi unit porcelain housing with there
associated magnetic units. For EHV systemcuts 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.

RATING OF CVT

Voltage: 22/sqrt 3 KV
Total o/p: 500MVA
Operating voltage: 400/sqrt 3 max.
Voltage factor: 1.5/30 sec.
Test voltage: 630 KV for 1 min
Impulse withstands voltage: 1.2/ 50 µs. 1425KV max.
Frequency : 50Hz
High frequency capacitance: 4400pF
Primary capacitance: 4657pF
Secondary capacitance: 80000 pF

S no Ie Make Ratio Burden Class Sec cap
1 Bassi Wsi/cve/420 400 200,200, 3p,3p,0.5 80000pf
/1425 100
2 Bassi 2 Wsi/cve/420 400 200,200, 3p,3p,0.5 80000pf
/1425 100
3 Bus 1 Wsi/cve/420 400 200,200, 3p,3p,0.5 80000pf


/1425 100
4 Bus 2 Wsi/cve/420 400 200,200, 3p,3p,0.5 80000pf
/1425 100

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:

BREAKDOWN VOLTAGE:
The voltage at which the oil breaks down when subjected to an electric field.

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.


For checking above values, various tests are done. These are
categorized as:
1. Physical test.
2. Chemical test.
3. Electrical test.

The results must be close to standard results that are follows-

S.N TYPE OF TEST STD. RESULTS
1. Density (gm/cubic cm.)at 27°C .85 to .89
2. Flash point >125°C
3. B.D.V Test K.V (rms.) >50 KV
4. Tan delta at 90°C < 20%
5. Water content (PPM.) 25(max.)above 145KV
6. Gas contents (PPM.)
(a) Hydrogen 100 to150
(b) Methane 50 to 70
(c) Ethane 30 to 50
(d) Ethylene 100 to 150
(e) Acetylene 20 to 30
(f) Carbon dioxide 3000 to 3500
(h) Carbon mono-oxide 200 to300


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.

THYRITE TYPE:
Ground wire run over the tower provides an adequate protection
against lighting and reduce 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 a 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 againretain its original property

A standard cell is rated for 1KV and is formed into a disc, which is sprayed on
both the sides of to give good contact with each disc. The dimensions of the discs
are stacked i.e. 16 cm in diameter and 17.5 cm thick these discs are stacked one
upon each other and they are further placed in to a porcelien container with a
suitable arrangement of gap between them.


These gaps serves as the purpose of preventing any current flow during
normal operating voltage in case of any transients the gap are punctured. The
Thyrite type arrestor will discharge several thousands ampere without the slightest
tendency of flashover on the edges of most important of the advance is that there is
absolutely no time lag in its performance.

400KV LIGHTNENIG ARRESTOR

manufacture: English electric company
no of phases: one
rated voltage: 360 KV
nominal discharge current (8×20µs) 10KA
high current impulse(4×110 µs ) 100KA
long duration rating(200 µs) 500KA

Sno Ie Make Type Current Voltage
1 Bassi1 Wsi Cpl 10KA 360KV
2 bassi2 Elpro Alugard2 10KA 360KV
3 ILT1 Elpro Alugard2 10KA 360KV
4 ILT2 Elpro Alugard2 10KA 360KVh
5 ILT3 WSI CDV303 10KA 398KV
6 ILT4 WSI CDV03 10KA 398KV


CONTROL PANEL

The diagram made on the control panel is known as mimic diagram.

COLOUR CODING

* 33KV GREEN
* 132 KV BLACK
* 220KV BROWN
* 440 VOLTS VOILET/INDIGO
* 110 VOLTS ORANGE

 REACTOR

It is used to lower the over excited capacitor. Capacitor bank is connected in shunt
over the reactor. Capacitors main purpose is to boost up the voltage. so when we
want to lower the voltage we use reactors. it is also use to stop the sudden change.
the commonly used reactor is NGR(Neutral ground reactor).


 CIRCUIT BREAKER
There is a one and half breaker scheme i.e. 3 breakers for 2 buses used in 400 KV
G.S.S.

 BUS COUPLERS
It is used to equalize the load on both Bus bars.

 DISTURBANCE RECORDER
It records the distance & fault on graph with voltage w.r.t time.

 EVENT LOGGER
it monitors as well as provides the details as a printed material.
These details may contain the sequence of operation, switching time, closing time
etc.

 ON LOAD TAP CHANGER (OLTC)
In this method a number of tappings are provided on the secondary of the
transformer. The voltage drop in the line is supplied by changing the secondary
emf of the transformer through the adjustment of its number of turns by using
transition resistor
which are placed in between each tapping.


In supply system, tap changing has to be performed on load so that here is no
interruption to supply. By using transition resister therefore shut down is not
required.

Fig 11
 NO LOAD TAP CHANGER (NLTC)
in this we change the tap manually for which we have to shut down the
transformer.
When the load increases the voltage across the primary drops but the secondary
voltage can be kept at the previous value by placing the movable arm on to a
higher stud. Whenever a tapping is to be changed in this type of transformer, the
load is kept off and hence the name off load tap-changing transformer.

 SYNCHRONOSCOPE

A synchronoscope is used to determine the correct instance of closing the switch
with connect the new supply to bus bar the correct instance of synchronizing is
indicated when bus bar and incoming voltage


* are equal in magnitude
* are equal in phase
* have the same frequency
the phase sequence is same

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 depending on
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.
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 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 plate.
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 feature 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.


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 power network.
PLCC system in Rajasthan: -

1 HEERAPURA: JAIPUR, AJMER, BYAWAR, BHILWARA, PALI, JODHPUR
2 HISSAR: KHETRI, HEERAPURA, KOTA, RAPP
3 HEERAPURA: KOTS, JSP, RPS, GSD
4 BHILWARA: RPS
5 PALI: FALANA
6 HEERAPURA: ALWAR, BHARATPUR
7 NEEMUCH: DEBARI
8 DEBARI: SIROHI


9 DEBARI: ZAWAR MINES
10 HEERAPURA: SIKAR, RATANGARH, BIKANER
11 HANUM, ANGARH: HISSAR, SHRIGANGANAGAR
12 HEERAPURA: BADHERPUB

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, power loss and radio interference. The higher the voltage is raised, the
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.

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.


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.

Advantages
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.

Disadvantages

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 action.
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 communication lines.


CONCLUSION

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 220KV GSS has
broadened my knowledge and has widened my thinking as a professional.


REFERENCES:
Principles of Power System-by V.K.MEHTA

Electrical Power System-by C.L.WADHWA

REPORT BY-

Kapil Kumar

SKIT,JAIPUR


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