- 1. ASeminar ReportOnPractical TrainingTaken at220 kV G.S.S.
MANSAROVAR, JAIPUR (RRVPNL)AndSubmitted in the partial fulfillment
for award the degree ofBachelor of TechnologyInElectrical
EngineeringFromRajasthan Technical University, KotaSession
2014-2015Submitted To Submitted byMr. D.R. Chitara Ravindra Kumar
GomaAssociate Professor B.Tech. 4th year (7th Sem.)Electrical
Engineering Roll no. 11EKTEE043KITE,Jaipur .Submitted toDepartment
of Electrical EngineeringKAUTILYA INSTITUTE OF TECHNOLOGY AND
ENGINEERING,JAIPUR1
2. ACKNOWLEDGEMENTI feel immense pleasure in conveying my
heartiest thanks and deep sense ofgratitude to Head of the
Electrical Engineering Department of KAUTILYAINSTITUTE OF
TECHNOLOGY AND ENGINEERING, Jaipur for his effortsand for technical
as well as moral support.Engineers and other technical and non
technical staff, for helping in understandingthe various aspects
and constructional detail of work and site in 220kV
Grid-SubStation, Mansarovar, Jaipur.It may not be possible for me
to acknowledge the support of all my friends, but Iam thankful to
all my colleagues and other trainees for their valuable ideas
andsupport during training period.2 3. PREFACEA rapid rise in the
use of electricity is placing a very heavy responsibility
onelectrical undertaking to maintain their electrical network in
perfect condition,young engineers is called upon to do design,
system planning and construction andmaintenance of electric system
before he had much experience and practice soonmay be responsible
for specialize operation in an ever expending industry.Theoretical
knowledge gained in their college courses need to be
supplementedwith practical know-how to face this professional
challenge, so..As a part of our practical training we have to
attempt the rule of RajasthanTechnical University, Kota. I look my
practical training at 220 kV G.S.S.Mansarovar, Jaipur.Since my
training centre was of Grid Sub-station hence I have included all
updatedinformation, to the extent possible, including general
introduction and briefdescription 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 220kV G.S.S. at
Mansarovar, Jaipur.I had taken my first practical training at 220
kV G.S.S. Mansarovar, Jaipur.The period of training was from
02/06/2014 TO 01/07/2014.This report dealt with the practical
knowledge of general theory and technicaldata/detail of equipments,
which I have gained during the training period at 220 kVGSS,
Mansarovar, Jaipur.3 4. CONTENTS1. Introduction..06-08 220kV G.S.S.
Mansarovar, Jaipur..06 Incoming feeders.07 Outgoing feeders.08
Radial feeders..082. Bus bars09-10 Bus bar arrangement...093.
Isolators.....114. Insulators..12-14 Type of insulators12o Pin
type.13o Suspension type13o Strain type.145. Protective
relays...15-17 Distance relays...16 Buchholz relay176. Circuit
Breakers.......18-25 Operating principle.18 Classification of
circuit breakers.18 SF6 Circuit Breaker ..19 Air Blast Circuit
Breaker...21 Oil Circuit Breaker23 Bulk Oil Circuit Breaker24
Minimum Oil Circuit Breaker257. Power Transformers.26-29 Basic
parts of transformer...268. Current transformer...309. Potential
transformer.3110. Capacitive voltage transformer (CVT)31-34
Description..3111. Transformer oil & its testing34-35
Transformer Oil Testing Procedure..3412. Lightening
Arrestor...36-38 220 kV lightening Arrestor Rating...384 5. 13.
Control Panel..3914. Measuring Instruments...4015. Capacitor Bank..
4116. Earthing of the system.42-43 Procedure of Earthing....42
Neutral Earthing.....4217. Ratings.....43-45 Transformers......43
Circuit Breaker...44 Battery Charger...44 Current Transformer..45
Capacitive Voltage Transformer...4518. Power Line Carrier
Communication.......................................................46-4719.
Conclusion.485 6. INTRODUCTIONElectrical power is generated,
transmitted in the form of alternatingcurrent. The electric power
produced at the power stations is delivered to theconsumers through
a large network of transmission & distribution. Thetransmission
network is inevitable long and high power lines are necessary
tomaintain a huge block of power source of generation to the load
centers to interconnected. Power house for increased reliability of
supply greater.The assembly of apparatus used to change some
characteristics (e.g. voltage, ac todc, frequency, power factor
etc.) of electric supply keeping the power constant iscalled a
substation.Depending on the constructional feature, the high
voltage substations may befurther subdivided:(a) Outdoor
substation(b) Indoor substation(c) Base or Underground substation6
7. Incoming feeders7Outgoing feeders220 kV
G.S.S.Mansarovar,Jaipur220 kV G.S.S. Mansarovar, Jaipur1. 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:-1. HEERAPURA2.
SANGANER3. DURGAPURA(FUTURE). 8. 8Outgoing feeders:132 KV 33 KV1)
Chambal 1) Nirman Nagar I & II2) SMS Stadium 2) Bisalpur Pump
HouseI & II3) Sanganer I & II 3) Kaveri Path4) JMRC I &
II 4) Triveni5) Adinath6) Kiran PathAs this substation following
feeders are established:1. Radial Feeders.2. Tie Feeders 9. BUS
BARSBus Bars are the common electrical component through which a
large no of feedersoperating at same voltage have to be
connected.If the bus bars are of rigid type (Aluminum types) the
structure height are lowand minimum clearance is required. While in
case of strain type of bus barssuitable ACSR conductor are
strung/tensioned by tension insulators discsaccording to system
voltages. In the widely used strain type bus bars stringingtension
is about 500-900 Kg depending upon the size of conductor used.Here
proper clearance would be achieved only if require tension is
achieved. Loosebus bars would effect the clearances when it swings
while over tensioning maydamage insulators. Clamps or even affect
the supporting structures in lowtemperature conditions.The clamping
should be proper, as loose clamp would spark under in full
loadcondition damaging the bus bars itself.3.1) BUS BAR ARRENGEMENT
MAY BE OF FOLLOWING TYPEWHICH IS BEING ADOPTED BY
R.R.V.P.N.L.:-3.1.1) Single bus bar arrangement3.1.2) Double bus
bar arrangementa) Main bus with transformer busb) Main bus-I with
main bus-II3.1.3) Double bus bar arrangement with auxiliary bus.9
10. 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 neededfrom operational consideration. Two supplies from
differentsources 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 loadcurrents. The
arrangement does not permit breaker maintenance withoutcausing
stoppage of supply.3.1.2) DOUBLE BUS BAR ARRANGEMENTS CONTAINS MAIN
BUSWITH AUXILARY BUS :The double bus bar arrangement provides
facility to change over to either busto carry out maintenance on
the other but provide no facility to carry overbreaker maintenance.
The main and transfer bus works the other way round. Itprovides
facility for carrying out breaker maintenance but does not permit
busmaintenance. Whenever maintenance is required on any breaker the
circuit ischanged over to the transfer bus and is controlled
through bus couplerbreaker.Fig.:- Bus Bars10 11. ISOLATORSIsolator"
is one, which can break and make an electric circuit in no
loadcondition. These are normally used in various circuits for the
purposes of Isolationof a certain portion when required for
maintenance etc. Isolation of a certainportion when required for
maintenance etc. "Switching Isolators" are capable of Interrupting
transformer magnetized currents Interrupting line charging current
Load transfer switchingIts main application is in connection with
transformer feeder as this unit makes itpossible to switch out one
transformer, while the other is still on load. The mostcommon type
of isolators is the rotating centre pots type in which each phase
hasthree insulator post, with the outer posts carrying fixed
contacts and connectionswhile the centre post having contact arm
which is arranged to move through 90` onits 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.11 12. INSULATORThe insulator for the overhead lines
provides insulation to the power conductorsfrom the ground so that
currents from conductors do not flow to earth throughsupports. The
insulators are connected to the cross arm of supporting structure
andthe power conductor passes through the clamp of the insulator.
The insulatorsprovide necessary insulation between line conductors
and supports and thusprevent any leakage current from conductors to
earth. In general, the insulatorshould have the following desirable
properties: High mechanical strength in order to withstand
conductor load, wind12load etc. High electrical resistance of
insulator material in order to avoidleakage currents to earth. High
relative permittivity of insulator material in order that
dielectricstrength is high. High ratio of puncture strength to
flash over.These insulators are generally made of glazed porcelain
or toughened glass. Polycome type insulator [solid core] are also
being supplied in place of hast insulatorsif available
indigenously. The design of the insulator is such that the stress
due tocontraction and expansion in any part of the insulator does
not lead to any defect. Itis desirable not to allow porcelain to
come in direct contact with a hard metalscrew thread.4.1) TYPE OF
INSULATORS:4.1.1: Pin type4.1.2: Suspension type4.1.3: Strain
insulator 13. 4.1.1) PIN TYPE: Pin type insulator consist of a
single or multiple shellsadapted to be mounted on a spindle to be
fixed to the cross arm of thesupporting structure. When the upper
most shell is wet due to rain thelower shells are dry and provide
sufficient leakage resistance these areused for transmission and
distribution of electric power at voltage upto voltage 33 KV.
Beyond operating voltage of 33 KV the pin typeinsulators thus
become too bulky and hence uneconomical.Fig.:- Pin Type
Insulator4.1.2) SUSPENSION TYPE: Suspension type insulators consist
of anumber of porcelain disc connected in series by metal links in
theform of a string. Its working voltage is 66KV. Each disc is
designedfor low voltage for 11KV.Fig.:- Suspension type
insulators13 14. 4.1.3) STRAIN TYPE INSULATOR: The strain
insulators are exactlyidentical in shape with the suspension
insulators. These strings areplaced in the horizontal plane rather
than the vertical plane. Theseinsulators are used where line is
subjected to greater tension. For lowvoltage lines (< 11KV)
shackle insulator are used as strain insulator.Fig.:- Strain
Insulators14 15. PROTECTIVE RELAYSRelays must be able to evaluate a
wide variety of parameters to establish thatcorrective action is
required. Obviously, a relay cannot prevent the fault. Itsprimary
purpose is to detect the fault and take the necessary action to
minimize thedamage to the equipment or to the system. The most
common parameters whichreflect the presence of a fault are the
voltages and currents at the terminals of theprotected apparatus or
at the appropriate zone boundaries. The fundamentalproblem in power
system protection is to define the quantities that can
differentiatebetween normal and abnormal conditions. This problem
is compounded by the factthat normal in the present sense means
outside the zone of protection. Thisaspect, which is of the
greatest significance in designing a secure relaying
system,dominates the design of all protection systems.Fig.:
-Relays15 16. 167.1) Distance Relays:Distance relays respond to the
voltage and current, i.e., the impedance, at therelay location. The
impedance per mile is fairly constant so these relays respond tothe
distance between the relay location and the fault location. As the
powersystems become more complex and the fault current varies with
changes ingeneration and system configuration, directional over
current relays becomedifficult to apply and to set for all
contingencies, whereas the distance relay settingis 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 nondirectional and is used
primarily as a fault detector.7.2.2) Admittance Relay:The
admittance relay is the most commonly used distance relay. It is
thetripping relay in pilot schemes and as the backup relay in step
distanceschemes. In the electromechanical design it is circular,
and in the solid statedesign, 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
thereactance of the protected line. It is non directional and is
used tosupplement the admittance relay as a tripping relay to make
the overallprotection independent of resistance. It is particularly
useful on short lineswhere the fault arc resistance is the same
order of magnitude as the linelength. 17. 17Buchholz Relay:This has
two Floats, one of them with surge catching baffle and
gascollecting space at top. This is mounted in the connecting pipe
line betweenconservator and main tank. This is the most dependable
protection for agiven transformer.Gas evolution at a slow rate that
is associated with minor faults inside thetransformers gives rise
to the operation or top float whose contacts are wiredfor alarm.
There is a glass window with marking to read the volume of
gascollected in the relay. Any major fault in transformer creates a
surge and thesurge element in the relay trips the transformer. Size
of the relay varies withoil volume in the transformer and the
mounting angle also is specified forproper operation of the
relay.Fig.:-Buchholz Relay 18. CIRCUIT BREAKERThe function of
relays and circuit breakers in the operation of a power system is
toprevent or limit damage during faults or overloads, and to
minimize their effect onthe remainder of the system. This is
accomplished by dividing the system intoprotective zones separated
by circuit breakers. During a fault, the zone whichincludes the
faulted apparatus is de-energized and disconnected from the
system.In addition to its protective function, a circuit breaker is
also used for circuitswitching under normal conditions.Each having
its protective relays for determining the existence of a fault in
thatzone and having circuit breakers for disconnecting that zone
from the system. It isdesirable to restrict the amount of system
disconnected by a given fault; as forexample to a single
transformer, line section, machine, or bus section.
However,economic considerations frequently limit the number of
circuit breakers to thoserequired for normal operation and some
compromises result in the relay protection.Some of the
manufacturers are ABB, AREVA, Cutler-Hammer (Eaton),
MitsubishiElectric, Pennsylvania Breaker, Schneider Electric,
Siemens, Toshiba, KonarHVS and others.Circuit breaker can be
classified as "live tank", where the enclosure that containsthe
breaking mechanism is at line potential, or dead tank with the
enclosure atearth potential. High-voltage AC circuit breakers are
routinely available withratings up to 765,000 volts.6.1) Various
types of circuit breakers:-186.1.1) SF6 Circuit Breaker6.1.2) Air
Blast Circuit Breaker6.1.3) Oil Circuit Breaker 19. 6.1.4) Bulk Oil
Circuit Breaker (MOCB)6.1.5) Minimum Oil Circuit Breaker196.1.1)
SF6 CIRCUIT BREAKER:-Sulphur hexafluoride has proved its-self as an
excellent insulating and arcquenching medium. It has been
extensively used during the last 30 years incircuit breakers,
gas-insulated switchgear (GIS), high voltage capacitors,bushings,
and gas insulated transmission lines. In SF6 breakers the
contactsare surrounded by low pressure SF6 gas. At the moment the
contacts areopened, a small amount of gas is compressed and forced
through the arc toextinguish it.Fig. 8-SF6 Circuit Breaker 20. 220
kV SF6 C.B. RATINGS:-Manufacture: BHEL Hyderabad.Type: DCVF
(220-245 kV)Rated voltage: 245 kVRated Frequency: 50 HzRated power
Frequency voltage: 460 kVRated Impulse withstands
voltage:Lightning: 1450 kV20Normal current Rating:At 50 c ambient:
1120 AmpAt 40 c Ambient: 1250 AmpShort time current rating: 20 kV
for 1 sec.Rated operating duty: 0 to o.3 sec. c-0-3min-mbRated
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 kVc. Asymmetry current: 25 kVMaking capacity:
100kV 21. 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 ACRated closing voltage: 220 V DCADVANTAGES OF SF6
CIRCUIT BREAKER:1. Due to the superior arc quenching property of
SF6, such circuit breakers21have very short arching time.2. Since
the dielectric strength of SF6 gas is 2 to 3 times that of air,
suchbreakers can interrupt much larger currents.3. The SF6 circuit
breaker gives noiseless operation due to its closed gascircuit and
no exhaust to the atmosphere unlike the air blast
circuitbreaker.Switching: 1050 kV6.1.2) AIR BLAST CIRCUIT
BREAKER:The principle of arc interruption in air blast circuit
breakers is to direct ablast of air, at high pressure and velocity,
to the arc. Fresh and dry air of the 22. air blast will replace the
ionized hot gases within the arc zone and the arclength is
considerably increased. Consequently the arc may be interrupted
atthe first natural current zero. In this type of breaker, the
contacts aresurrounded by compressed air. When the contacts are
opened thecompressed air is released in forced blast through the
arc to the atmosphereextinguishing the arc in the process.Fig.
9-Air Blast Circuit BreakerAdvantages:An air blast circuit breaker
has the following advantages over an oil circuitbreaker:22 The risk
of fire is eliminated 23. The arcing products are completely
removed by the blast whereas the oildeteriorates with successive
operations; the expense of regular oil isreplacement is avoided The
growth of dielectric strength is so rapid that final contact gap
needed forarc extinction is very small. this reduces the size of
device The arcing time is very small due to the rapid build up of
dielectric strengthbetween contacts. Therefore, the arc energy is
only a fraction that in oilcircuit breakers, thus resulting in less
burning of contacts Due to lesser arc energy, air blast circuit
breakers are very suitable forconditions where frequent operation
is required The energy supplied for arc extinction is obtained from
high pressure air andis 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 of23restricting voltage.
Considerable maintenance is required for the compressor plant
whichsupplies the air blast Air blast circuit breakers are finding
wide applications in high voltageinstallations. Majority of circuit
breakers for voltages beyond 110 kV are ofthis type.6.1.3) OIL
CIRCUIT BREAKER:Circuit breaking in oil has been adopted since the
early stages of circuitbreakers manufacture. The oil in oil-filled
breakers serves the purpose ofinsulating the live parts from the
earthed ones and provides an excellent medium 24. for arc
interruption. Oil circuit breakers of the various types are used in
almost allvoltage ranges and ratings. However, they are commonly
used at voltages below115KV leaving the higher voltages for air
blast and SF6 breakers. The contacts ofan oil breaker are submerged
in insulating oil, which helps to cool and extinguishthe arc that
forms when the contacts are opened. Oil circuit breakers are
classifiedinto two main types namely: bulk oil circuit breakers and
minimum oil circuitbreakers.The advantages of using oil as an arc
quenching medium are:1. It absorbs the arc energy to decompose the
oil into gases, which haveexcellent cooling properties.2. It acts
as an insulator and permits smaller clearance between
liveconductors and earthed components.The disadvantages of oil as
an arc quenching medium are:1. Its inflammable and there is risk of
fire2. It may form an explosive mixture with air.3. The arcing
products remain in the oil and it reduces the quality of oil
afterseveral 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 lowestvoltages
up to 115KV. However, they are still used in the systems having
voltagesup 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
ametallic tank. Arc interruption depends on the head of oil above
the contacts andthe speed of contact separation. The head of oil
above the arc should be sufficient24 25. to cool the gases, mainly
hydrogen, produced by oil decomposition. A small aircushion at the
top of the oil together with the produced gases will increase
thepressure 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. Withfrequent breaking
and making heavy currents the oil will deteriorate and may leadto
circuit breaker failure. This has led to the design of minimum oil
circuit breakersworking on the same principles of arc control as
those used in bulk oil breakers. Inthis type of breakers the
interrupter chamber is separated from the other parts andarcing is
confined to a small volume of oil. The lower chamber contains
theoperating mechanism and the upper one contains the moving and
fixed contactstogether with the control device. Both chambers are
made of an insulating materialsuch as porcelain. The oil in both
chambers is completely separated from eachother. By this
arrangement the amount of oil needed for arc interruption and
theclearances to earth are roused. However, conditioning or
changing the oil in theinterrupter chamber is more frequent than in
the bulk oil breakers. This is due tocarbonization and slugging
from arcs interrupted chamber is equipped with adischarge vent and
silica gel breather to permit a small gas cushion on top of theoil.
Single break minimum oil breakers are available in the voltage
range 13.8 to34.5 KV.25 26. POWER TRANSFORMERDistribution
transformers reduce the voltage of the primary circuit to the
voltagerequired by customers. This voltage varies and is usually:
120/240 volts single phase for residential customers, 480Y/277 or
208Y/120 for commercial or light industry customers.Three-phase pad
mounted transformers are used with an underground primarycircuit
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 thensent via
underground cables to the separate customers.26Parts of
Transformer:-8.1) Windings:Winding shall be of electrolytic grade
copper free from scales & burrs. Windingsshall be made in dust
proof and conditioned atmosphere. Coils shall be insulatedthat
impulse and power frequency voltage stresses are minimum. Coils
assemblyshall be suitably supported between adjacent sections by
insulating spacers andbarriers. Bracing and other insulation used
in assembly of the winding shall bearranged to ensure a free
circulation of the oil and to reduce the hot spot of thewinding.
All windings of the transformers having voltage less than 66 kV
shall befully insulated. Tapping shall be so arranged as to
preserve the magnetic balance ofthe transformer at all voltage
ratio. All leads from the windings to the terminal 27. board and
bushing shall be rigidly supported to prevent injury from vibration
shortcircuit stresses.Fig. 11-Power Transformer8.2) Tanks and
fittings:Tank shall be of welded construction & fabricated from
tested quality low carbonsteel of adequate thickness. After
completion of welding, all joints shall besubjected to dye
penetration testing.At least two adequately sized inspection
openings one at each end of the tank shallbe provided for easy
access to bushing & earth connections. Turrets & other
partssurrounding the conductor of individual phase shall be
non-magnetic. The maintank body including tap changing compartment,
radiators shall be capable ofwithstanding 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 topand bottom (80mm size) lifting
lugs, top and bottom oil filling valves, air release27 28. plug at
the top, a drain and sampling valve and thermometer pocket fitted
withcaptive screw cap on the inlet and outlet.(b.) Cooling fans
shall not be directly mounted on radiator bank which may causeundue
vibration. These shall be located so as to prevent ingress of rain
water. Eachfan shall be suitably protected by galvanized wire
guard.Fig. 12-Radiator with fan8.4.2) Temperature Indicators:Most
of the transformer (small transformers have only OTI) are provided
withindicators that displace oil temperature and winding
temperature. There arethermometers pockets provided in the tank top
cover which hold the sensingbulls in them. Oil temperature measured
is that of the top oil, where as thewinding temperature measurement
is indirect.Fig. 14-Winding and oil temperature indicator28 29.
298.4.3) Silica Gel Breather:Both transformer oil and cellulosic
paper are highly hygroscopic. Paperbeing more hygroscopic than the
mineral oil The moisture, if not excludedfrom the oil surface in
conservator, thus will find its way finally into thepaper
insulation and causes reduction insulation strength of transformer.
Tominimize this conservator is allowed to breathe only through the
silica gelcolumn, which absorbs the moisture in air before it
enters the conservator airsurface.Fig.:-Silica gel Breather8.4.4)
Conservator:With the variation of temperature there is
corresponding variation in the oilvolume. To account for this, an
expansion vessel called conservator is addedto the transformer with
a connecting pipe to the main tank. In smallertransformers this
vessel is open to atmosphere through dehydrating breathers(to keep
the air dry). In larger transformers, an air bag is mounted inside
theconservator with the inside of bag open to atmosphere through
the breathersand the outside surface of the bag in contact with the
oil surface. 30. CURRENT TRANSFORMERAs you all know this is the
device which provides the pre-decoded fraction of theprimary
current passing through the line/bus main circuit. Such as primary
current60A, 75A, 150A, 240A, 300A, 400A, to the secondary output of
1A to 5A.When connecting the jumpers, mostly secondary connections
is taken to threeunction boxes where star delta formation is
connected for three phase and finalleads taken to protection
/metering scheme.Fig.:-Current TransformersIt can be used to supply
information for measuring power flows and the electricalinputs for
the operation of protective relays associated with the transmission
anddistribution circuit or for power transformer. These current
transformers have theprimary winding connected in series with the
conductor carrying the current to bemeasured or controlled. The
secondary winding is thus insulated from the highvoltage and can
then be connected to low voltage metering circuits.30 31. POTENTIAL
TRANSFORMERA potential transformer (PT) is used to transform the
high voltage of a power lineto a lower value, which is in the range
of an ac voltmeter or the potential coil of anac 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
voltagemeasurement in highvoltage transmission network,
particularly for systems voltage of 132KV andabove where it becomes
increasingly more economical. It enables measurement ofthe line to
earth voltage to be made with simultaneous provision for
carrierfrequency coupling, which has reached wide application in
modern high voltagenetwork for tele-metering remote control and
telephonecommunication purpose.CAPACITIVE VOLTAGE TRANSFORMERS
(CVT)A capacitor voltage transformer (CVT) is a transformer used in
power systems tostep-down extra high voltage signals and provide
low voltage signals either formeasurement or to operate a
protective relay. In its most basic form the deviceconsists of
three parts: two capacitors across which the voltage signal is
split, aninductive element used to tune the device to the supply
frequency and atransformer used to isolate and further step-down
the voltage for theinstrumentation or protective relay. The device
has at least four terminals, a high-31 32. voltage terminal for
connection to the high voltage signal, a ground terminal and
atleast one set of secondary terminals for connection to the
instrumentation orprotective relay. CVTs are typically single-phase
devices used for measuringvoltages in excess of one hundred
kilovolts where the use of voltage transformerswould be
uneconomical. In practice the first capacitor, C1, is often
replaced by astack of capacitors connected in series. This results
in a large voltage drop acrossthe stack of capacitors that replaced
the first capacitor and a comparatively smallvoltage drop across
the second capacitor, C2, and hence the secondary terminals.Fig.:-
CVT connectionThe porcelain in multi unit stack, all the potentials
points are electrically tied andsuitably shielded to overcome the
effect of corona RIV etc. Capacitive voltagetransformers are
available for system voltage.CVT is affected by the supply
frequency switching transient and magnitude ofconnected Burdon. The
CVT is more economical than an electromagnetic voltagetransformer
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 connectedin series act like potential dividers, provided,
the current taken by burden isnegligible compared with current
passing through the series connected capacitor.32 33. Capacitive
voltage transformer is being used more and more for
voltagemeasurement in high voltage transmission network,
particularly for systemsvoltage of 132KV and above where it becomes
increasingly more economical. Itenables measurement of the line to
earth voltage to be made with simultaneousprovision for carrier
frequency coupling, which has reached wide application inmodern
high voltage network for tele-metering remote control and
telephonecommunication purpose.The capacitance type voltage
transformers are of two type:33 Coupling Capacitor type Pushing
Type 34. TRANSFORMER OIL & ITS TESTINGThe insulation oil of
voltage- and current-transformers fulfills the purpose ofinsulating
as well as cooling. Thus, the dielectric quality of transformer is
a matterof secure operation of a transformer.Since transformer oil
deteriorates in its isolation and cooling behavior due toageing 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 sequencesand procedures are defined by various
international standards.Periodic execution of transformer oil
testing is as well in the very interest ofenergy supplying
companies, as potential damage to the transformer insulation canbe
avoided by well timed substitution of the transformer oil. Lifetime
of plant canbe substantially increased and the requirement for new
investment may be delayed.34Transformer Oil Testing ProcedureTo
assess the insulating property of dielectric transformer oil, a
sample of thetransformer oil is taken and its breakdown voltage is
measured. The transformer oil is filled in the vessel of the
testing device. Two standard-complianttest electrodes with a
typical clearance of 2.5 mm are surrounded bythe dielectric oil.
35. A test voltage is applied to the electrodes and is continuously
increased up tothe breakdown voltage with a constant,
standard-compliant slew rate of e.g. 2kV/s. At a certain voltage
level breakdown occurs in an electric arc, leading to a35collapse
of the test voltage. An instant after ignition of the arc, the test
voltage is switched off automaticallyby the testing device. Ultra
fast switch off is highly desirable, as thecarbonization due to the
electric arc must be limited to keep the additionalpollution as low
as possible. The transformer oil testing device measures and
reports the root meansquare value of the breakdown voltage. After
the transformer oil test is completed, the insultaion oil is
stirredautomatically and the test sequence is performed repeatedly.
(Typically 5Repetitions, depending on the standard) As a result the
breakdown voltage is calculated as mean value of the
individualmeasurements. 36. LIGHTNING ARRESTORA lightning arrester
(in Europe: surge arrester) is a device used on powersystems and
telecommunications systems to protect the insulation and
conductorsof the system from the damaging effects of lightning. The
typical lightning arresterhas a high-voltage terminal and a ground
terminal. When a lightning surge (orswitching 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 astructure, preventing damage to electronic
instruments within and ensuring thesafety of individuals near them.
Smaller versions of lightning arresters, alsocalled surge
protectors, are devices that are connected between each
electricalconductor in power and communications systems and the
Earth. These prevent theflow of the normal power or signal currents
to ground, but provide a path overwhich high-voltage lightning
current flows, bypassing the connected equipment.Their purpose is
to limit the rise in voltage when a communications or power lineis
struck by lightning or is near to a lightning strike.If protection
fails or is absent, lightning that strikes the electrical system
introducesthousands of kilovolts that may damage the transmission
lines, and can also causesevere damage to transformers and other
electrical or electronic devices.Lightning-produced extreme voltage
spikes in incoming power lines can damageelectrical home
appliances.Potential target for a lightning strike, such as a
television antenna, is attached tothe terminal labeled A in the
photograph. Terminal E is attached to a long rodburied in the
ground. Ordinarily no current will flow between the antenna and
the36 37. ground because there is extremely high resistance between
B and C, and alsobetween C and D. The voltage of a lightning
strike, however, is many times higherthan that needed to move
electrons through the two air gaps. The result is thatelectrons go
through the lightning arrester rather than traveling on to the
televisionset and destroying it.A lightning arrester may be a spark
gap or may have a block of a semiconducting material such as
silicon carbide or zinc oxide. Some spark gaps areopen 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 gasto ionize when the voltage across the gap reaches
a specified level. Other designsof lightning arresters use a
glow-discharge tube (essentially like a neon glow lamp)connected
between the protected conductor and ground, or voltage-activated
solid-state37switches 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 devicevents the occasional internal explosion
without shattering the porcelain cylinder.Lightning arresters are
rated by the peak current they can withstand, the amount ofenergy
they can absorb, and the break over voltage that they require to
beginconduction. They are applied as part of a lightning protection
system, incombination with air terminals and bonding. 38. 220 kV
LIGHTNENING ARRESTOR:Manufacture: English electric companyNo. of
phase: OneRated voltage: 360 kVNominal discharge current: (820s) 10
kAHigh current impulse: (4 100s) 100 kALong distribution rating:
(200s) 500 kA38 39. CONTROL PANELControl panel contain meters,
control switches and recorders located in the controlbuilding, also
called the dog house. These are used to control the
substationequipment to send power from one circuit to another or to
open or to shut downcircuits when needed.Fig.:-Control Room in GSS
Mansarovar, Jaipur39 40. 12.1) MEASURING INSTRUMENT USED:12.1.1)
ENERGY METER: To measure the energy transmitted energy metersare
fitted to the panel to different feeders the energy transmitted
isrecorded after one hour regularly for it MWHr, meter is
provided.12.1.2) WATTMETERS: It is attached to each feeder to
record the power40exported from GSS.12.1.3) FREQUENCY METER: To
measure the frequency at each feederthere 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) AMMETER: It is
provided to measure the line current. It is alsoavailable in both
the forms analogue as well as digital.12.1.6) MAXIMUM DEMAND
INDICATOR: There are also mounted thecontrol panel to record the
average power over successive predeterminedperiod.12.1.7) MVAR
METER: It is to measure the reactive power of the circuit. 41.
CAPACITOR BANKThe capacitor bank provides reactive power at grid
substation. The voltageregulation problem frequently reduces so of
circulation of reactive power.Unlike the active power, reactive
power can be produced, transmitted and absorbedof course with in
the certain limit, which have always to be workout. At any pointin
the system shunt capacitor are commonly used in all voltage and in
all size.Fig. 20-Capacitor BankBenefits of using the capacitor bank
are many and the reason is that capacitorreduces the reactive
current flowing in the whole system from generator to thepoint of
installation.1 .Increased voltage level at the load2. Reduced
system losses3. Increase power factor of loading current41 42.
EARTHING OF THE SYSTEMThe provision of an earthing system for an
electric system is necessary by thefollowing reason. In the event
of over voltage on the system due to lightening discharge orother
system fault. These parts of equipment, which are normally dead,
asfor as voltage, are concerned do not attain dangerously high
potential. In a three phase, circuit the neutral of the system is
earthed in order tostabilize 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 todeal with more
faults current. The resistance of earth and current path should
below enough to prevent voltage rise between earth and neutral. The
earth electrodemust be driven in to the ground to a sufficient
depth to as to obtain lower value ofearth resistance. To sufficient
lowered earth resistance a number of electrodes areinserted in the
earth to a depth, they are connected together to form a mesh.
Theresistance of earth should be for the mesh in generally inserted
in the earth at 0.5mdepth the several point of mesh then connected
to earth electrode or groundconduction. The earth electrode is
metal plate copper is used for earth plate.15.2) NEUTRAL
EARTHING:Neutral earthing of power transformer all power system
operates with groundedneutral. Grounding of neutral offers several
advantages the neutral point of42 43. generator transformer is
connected to earth directly or through a reactance in somecases the
neutral point is earthed through an adjustable reactor of
reactancematched with the line. The earth fault protection is based
on the method of neutral43earthing.RATINGS17.1) TRANSFORMER:Total
No. of transformers = 6 No. of transformers220/132
KV------------------------------------ 100MVA 2132/33
KV--------------------------------------20/25MVA
2132/33KV---------------------------------------40/50MVA 1132/11
KV---------------------------------------10/12.5 MVA 1MAKE
Company220/133 KV, 100MVA X-Mer
1----------------------------------- TELK220/133KV, 100 MVA X-Mer
2---------------------------------- ALSTOM132/33 KV, 20/25 MVA
X-Mer 1---------------------------------- TELK132/33 KV, 20/25 MVA
X-Mer 2-----------------------------------BBL132/33 KV, 40/50 MVA
X-Mer 3-----------------------------------T&R132/33 KV, 10/12.5
MVA X-Mer 1---------------------------------EMCO 44. 4417.2)
CIRCUIT BREAKER:No. of 220KV breaker - 6No. of 132KV breaker -
13No. of 33KV breaker - 12No. of Capacitor Bank (33kv) - 4No. of
11KV breaker - 7SF6 CBBREAKER SERIAL NO. 030228RATED VOLTAGE
145KVNORMAL CURRENT 1250AFREQUENCY 5OHzLIGHTNING IMPULSE WITHSTAND
650KV (Peak)FIRST POLE TO CLEAR TO CLEAR FACTOR 1-2SHORT TIME
WITHSTAND CURRENT 31.5KADURATION OF SHORT CIRCUIT 3 Sec.(SHORT
CIRCUIT SYM. 31.5KABREAKING CURRENT) ASYM. 37.5KASHORT TIME MAKING
CURRENT 8.0KAOUT OF PHASE BREAKING CURRENT 7.9KAOPERATING SEQUENCE
0-0.3-CO-3min-COSF6 GAS PRESSURE AT 20C 6.3 BarTOTAL MASS OF CB
1300KgMASS OF SF6 GAS 8.7Kg17.3) BATTERY CHARGER:Battery Charger
220AH VDC HBL NIFE LTD. 45. 440AH VDC HBL NIFE LTD.Capacitor
BankNo.-1 BHEL 38KV 6.6MVARCapacitor BankNo.-2 BHEL 38KV
7.2MVARCapacitor BankNo.-1 ABB 38KV 7.2MVARCapacitor BankNo.-1 WS
38KV 7.2MVAR4517.4) CURRENT TRANSFORMER:FREQUENCY 50HzHIGHEST
SYSTEM VOLTAGE 245KVSHORT TIME CURRENT 40KA/15RATED CURRENT
600ACURRENT RATIO 600-300-150/1MIN. KNEE POTENTIAL VOLTAGE 850V at
150/1MAX. EXCITING CURRENT 100MA at 150/1MAX. SEC. WINDING
RESISTANCE 2.5OHM at 150/117.5) CAPACITIVE VOLTAGE
TRANSFORMER:SERIAL NO. 0173537INSULATION LEVEL 460KVRATED VOLTAGE
FACTOR 1.2/contTIME 1.5/30sec.HIGHEST SYSTEM VOLTAGE 245KVPRIMARY
VOLTAGE 22OKV/1.732TYPE OUTDOOR Wgt. 850KgPHASE SINGLE TBONP.CAT
50CSECONDARY VOLTAGE 110/1.732 110/1.732RATED BURDON 220Va
110VaFREQUENCY 49.5-50.5Hz 46. Power Line Carrier
Communication46IntroductionPower Line Carrier Communication (PLCC)
provides forsignal transmission down transmission line conductors
orinsulated ground wires. Protection signaling, speech and
datatransmission for system operation and control,
managementinformation systems etc. are the main needs which are met
byPLCC.PLCC is the most economical and reliable method
ofcommunication because of the higher mechanical strength
andinsulation level of high voltage power line which contribute to
theincreased reliability of communication and lower attenuation
overthe larger distances involves.High frequency signals in the
range of 50 KHZ to 400 KHZcommonly known as the carrier signal and
to result it with theprotected section of line suitable coupling
apparatus and linetraps are employed at both ends of the protected
section. Here inSanganer and also in other sub-station this system
is used. Themain application of power line carrier has been from
the purposeof supervisory control telephone communication,
telemeteringand relaying.PLCC EquipmentThe essential units of power
line carrier equipment consists of :-a. Wave trapb. Coupling
Capacitorc. LMU and protective equipments. 47. MeritsThe severity
that a power line can withstand is much more thanthat odd
communication line due to higher mechanical strength oftransmission
line power lines generally provide the shortest routebetween the
Power Station and the Receiving Stations.The carrier signals suffer
less attenuation, owing to large crosssectional area of power
lineLarger spacing between conductors reduces the capacitanceswhich
results in lesser attenuation of higher frequencies.Large spacing
also reduces the cross talk to a certain extent.The construction of
a separate communication line is avoided.47DemeritsUtmost care is
required to safeguard the carrier equipment andpersons using them
against high voltage and currents on the line.Noise introduced by
power line is far more than in the case ofcommunication line. This
is due to the discharge acrossinsulators and corona etc.Induced
voltage surges in the power line may affect the connected
carrierequipment. 48. CONCLUSIONA technician needs to have not just
theoretical but practical as well and soevery student is supposed
to undergo practical training session after 2nd year whereI have
imbibed the knowledge about transmission, distribution, generation
andmaintenance with economical issues related to it.During our 30
days training session we were acquainted with the repairing ofthe
transformers and also the testing of oil which is a major component
oftransformer.At last I would like to say that practical training
taken at 220 kV GSS hasbroadened my knowledge and widened my
thinking as a professional.48
