1.1 AN OVERVIEW OF R.S.E.B.
“Rajasthan State Electricity Board” started working form 1 July, 1957. When India
becomes independent its overall installed capacity was hardly 1900 mw. During first year
plan (1951-1956) this capacity was only 2300 MW. The contribution of Rajasthan state
was negligible during 1 & 2 year plans the emphasis was on industrialization for that end it
was considered to make the system of the country reliable. Therefore Rajasthan
state electricity board came into existence in July 1957.
In 1957 RSEB (Rajasthan State Electric Board) is comes in to existence and it satisfactorily
work from 1 July 1957 at that time energy level in Rajasthan is very low . The 1st survey for
energy capacity in Rajasthan is held in 1989 at that time the total electric energy capacity of
Rajasthan is 20116 MW. At that time the main aim of RSEB is to supply electricity to entire
Rajasthan in the most economical way.
The aim of RSEB is to supply electricity to entire Rajasthan state in the most economical
way. Government of Rajasthan on 19th July 2000, issued a gazette notification unbundling
Rajasthan State Electricity Board into Rajasthan Rajya Vidyut Utpadan Nigam Ltd
(RRVUNL), the generation Company; Rajasthan Rajya Vidyut Prasaran Nigam Ltd,
(RRVPNL), the transmission Company and the three regional distribution companies namely
Jaipur Vidyut Vitran Nigam Ltd, (JVVNL) Ajmer Vidyut Vitran Nigam Ltd (AVVNL) and
Jodhpur Vidyut Vitran Nigam Ltd (JVVNL)
The Generation Company owns and operates the thermal power stations at Kota and
Suratgarh, Gas based power station at Ramgarh, Hydel power station at Mahi and mini hydel
stations in the State
The Transmission Company operates all the 400KV, 220 KV, 132 KV and 33KV electricity
lines and system in the State.
The three distribution Companies operate and maintain the electricity system below 66KV in
the State in their respective areas
Rajasthan State Electricity Board has been divided in five main parts are:-
-> Electricity production authority - RRVUNL
-> Electricity transmission authority - RRVPNL
-> Distribution authority for Jaipur - JVVNL
-> Distribution authority for Jodhpur - JVVNL
-> Distribution authority for Ajmer - AVVNL
Power obtain from these stations is transmitted all over Rajasthan with the help of grid
stations. Depending on the purpose, substations may be classified as:-
1. Step up substation
2. Primary grid substation
3. Secondary substation
4. Distribution substation
5. Bulky supply and industrial substation
6. Mining substation
7. Mobile substation
8. Cinematograph substation
Depending on constructional feature substation are classified as:-
1. Outdoor type
2. Indoor type
3. Basement or Underground type
4. Pole mounting open or kilos type
A substation is a part of an electrical generation, transmission, and distribution system. A
substation is an assembly of apparatus, which transform the characteristics of electrical
energy from one form to another say from one voltage level to another level. Hence a
substation is an intermediate link between the generating station and consumer.
Fig. 2.1: 132 KV GSS Sitapura, Jaipur
Fig. 2.2: 132 KV GSS Sitapura, Jaipur
For economic transmission the voltage should be high so it is necessary to step up the
generated voltage for transmission and step down transmitted voltage for distribution. For
this purpose substations are installed. The normal voltages for transmission are 400KV,
220KV, 132KV and for distribution 33KV, 11KV etc.
2.1 CONSTRUCTIONAL FEATURES OF 132KV GSS SITAPURA, JAIPUR
In this substation the power is coming from two lines namely
1. 220 KV INDIRA GANDHI NAGAR
2. 220 KV SANGANER
Outgoing feeders are
1. 33 KV NRI
2. 33 KV SITAPURA
3. 33 KV PRATAP NAGAR
4. 33 KV MICO
5. 33 KV TIJARIA
6. 33 KV STONE MART
7. 33 KV SEZ I
8. 33 KV SEZ II
9. 33 KV RAMCHANDRAPURA
10. 33 KV GONER
11. 33 KV PRATAP APARTMENT
In this substation there are two yards
1. 132 KV Yard
Fig.2.3 132 KV yard
2. 33 KV Yard
Fig.2.4 33 KV yard
There are two bus bars in 132 KV yard and also two bus-bars in 33KV yard. The incoming
feeders are connected to bus-bar through circuit breakers, Isolators, LIGHTNING arrestors,
current-transformers etc. The bus-bars are to have an arrangement of auxiliary bus So that
when some repairing work is to be done an main bus the whole load can be transferred to the
auxiliary bus through bus-coupler.
In this 132 KV GSS the incoming 132 KV supply is stepped down to 33 KV with the help of
transformers which is further supplied to different sub-station according to the load.
132 KV GSS has a large layout consisting of 2 Nos of 40/50 MVA transformers having
voltage ratio respectively 132/33 KV in addition to these transformers. And a 250KVA,
33KV/415V Station Transformer gives the supply to the control room and electrical
equipment of GSS.
Fig. 2.5 Single Line Diagram of GSS, Sitapura
EQUIPMENTS USED IN G.S.S.
Some equipments are used in the GSS for successful operational breaker & a half scheme two
buses, they are:
1. LIGHTNING ARRESTER
3. LINE ISOLATOR
4. WAVE TRAP
5. CIRCUIT BREAKER
6. POTENTIAL TRANSFORMER
7. CURRENT TRANSFORMER
8. BUS BARS
9. POWER TRANSFORMER
10. CONTROL AND RELAY PANEL
11. BATTERY CHARGER
Lightning arrestor is a device, which protects the overhead lines and other electrical apparatus
viz transformer from overhead voltages and Lightning. An electric discharge between cloud
and earth, between cloud and the charge centers of the same cloud is known as lightning. 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
protection against such surges.
Every instrument must be protected from the damage of Lightning stroke. The three
protection sin a substation is essential:-
Protection for transmission line from direct strokes
Protections of power station or substation from direct strokes
Protection of electrical apparatus against traveling waves
Effective protection of equipment against direct strokes requires a shield to prevent Lightning
from striking the electrical conductor together with adequate drainage facilities over insulated
The Thyrite Alugard Lightning arrester consists of a stack of one or more units connected in
series depending on the voltage and the operating condition of the circuit three single pole
arresters are required for 3-phase installation. The arresters are single pole design and they
are suitable for indoor and out-door service.
Each arrester unit consists essentially of permanently sealed Porcelain housing equipped with
pressure relief and containing a number of thyrite value-element discs and exclusive locate
gaps shunted by Thyrite resistors metal fitting cemented of the housing provide means for
bolting arrester units into a stack. Each arrester unit is shipped assembled. No charging or
testing operation is required before placing them in service.
Install arrester electrically as close as possible to the apparatus being protected Line and
ground connections should be short and direct
The arrester ground should be connected to the apparatus grounds and the main station
ground utilizing a reliable common ground network of low resistance. The efficient operation
of the Lightning arrester requires permanent low resistance grounds Station class arresters
should be provided with a ground of a value not exceeding five ohms.
These are given on the drawings. These are the maximum recommended. The term
‘clearance’ means the actual distance between any part of the arrester or disconnecting device
at line potential, and any object at ground potential or other phase potential.
The thyrite station-class arrester is designed to limit the surge voltages to a safe value by
discharging the surge current to ground; and to interrupt the small power frequency follow
current before the first current zero. The arrester rating is a define limit of its ability to
interrupt power follow current. It is important, therefore, to assure that the system power
frequency voltage from line to ground under any condition switching, fault, overvoltage
never exceeds the arrester’s rating.
It consist of a isolator in series and connected in such a way that long isolator is in upward
and short isolator is in downward so that initially large potential up to earth is decreased to
zero. An ideal arrestor must therefore have the following properties:
1. It should be able to drain the surge energy from the line in a minimum time.
2. Should offer high resistance to the flow of power current.
3. Performance of the arresters should be such that no system disturbances are
introduced by its operation.
4. Should be always in perfect from to perform the function assigned to it
5. After allowing the surge to pass, it should close up so as not to permit power current
to flow to ground.
Fig 4.1: L.A. IN SITAPURA G.S.S.
Lightning, is a form of visible discharge of electricity between rain clouds or between a rain
cloud and the earth The electric discharge is seen in the form of a brilliant arc, sometimes
several kilometers long, stretching between the discharge points How thunderclouds become
charged is not fully understood, but most thunderclouds are negatively charged at the base
and positively charged at the top However formed, the negative charge at the base of the
cloud induces a positive charge on the earth beneath it, which acts as the second plate of a
When the electrical potential between two clouds or between a cloud and the earth reaches a
sufficiently high value (about 10,000 V per cm or about 25,000 V per in), the air becomes
ionized along a narrow path and a Lightning flash results.
Many meteorologists believe that this is how a negative charge is carried to the ground and
the total negative charge of the surface of the Earth is maintained.
The possibility of discharge is high on tall trees and buildings rather than to ground
Buildings are protected from Lightning by metallic Lightning rods extending to the ground
from a point above the highest part of the roof The conductor has a pointed edge on one side
and the other side is connected to a long thick copper strip which runs down the building The
lower end of the strip is properly earthed When Lightning strikes it hits the rod and current
flows down through the copper strip These rods form a low-resistance path for the Lightning
discharge and prevent it from travelling through the structure itself.
CAPACITIVE VOLTAGE TRANSFORMER (C.V.T.)
CVTs are special king of PTs using capacitors to step down the voltage. A capacitor voltage
transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used
in power systems to step down extra high voltage signals and provide a low voltage signal,
for measurement or to operate a protective relay In its most basic form the device consists of
three parts: two capacitors across which the transmission line signal is split, an inductive
element to tune the device to the line frequency, and a transformer to isolate and further step
down the voltage for the instrumentation or protective relay The device has at least four
terminals: a terminal for connection to the high voltage signal, a ground terminal, and two
secondary terminals which connect to the instrumentation or protective relay CVTs are
typically single-phase devices used for measuring voltages in excess of one hundred kilovolts
where the use of voltage transformers would be uneconomical In practice, capacitor C1 is
often constructed as a stack of smaller capacitors connected in series This provides a large
voltage drop across C1 and a relatively small voltage drop across C2.
The CVT is also useful in communication systems CVTs in combination with wave traps are
used for filtering high frequency communication signals from power frequency This forms a
carrier communication network throughout the transmission network .
Fig.5.1: capacitor voltage transformer
1) Capacitive voltage transformer can be effectively as potential sources for measuring,
metering protection, carrier communication and other vital functions of an electrical network.
2) Capacitive voltage transformers are constructed in single or multi-unit porcelain
housing with their associated magnetic units. For EHV system.
3) In the case of EHV CVTs the multi-unit construction offers a number of advantages easy
of transport and storing, Convenience in handling and erection etc.
1) The capacitive voltage transformer comprises of a capacitor divider with its associated
Electro-magnetic unit. The divider provides an accurate proportioned voltage, while the
magnetic unit transformers this voltage, both in magnitude and to convenient levels suitable
for measuring phase metering, protection etc. all W.S.I.capacitor units has metallic bellows to
compensate the volumetric expansion of oil inside the porcelain. In the multiunit stack, all the
potential point are electrically tied and suitably shielded to overcome the effects of corona,
2) Capacitive voltage transformers are available for system voltage of 33KV to 420KV.
3) Packing and transportation:
3.1) all the capacitor units of capacitive voltage X-mer are securely packed in woolen crates.
The electro-magnetic unit form an integral part with the capacitor unit is hermetically
associated with the electromagnetic unit; the wooden crate for this is exclusive and is sized
heavier taller than for the capacitor unit alone.
3.2) each woolen crate is identified with the corresponding serial number of the unit.
3.3) each capacitor unit has one nameplate designing the rating of the unit Position of the unit
in the complete assembly is also indicated in the nameplate by a suffix T or M
RATINGS OF CVT:-
Insulation Level : 460KV
Rated Voltage factor : 1.2/cont.
Time : 1.5/30 sec
Highest system Voltage : 145KV
Primary Voltage : 132/1.732KV
Secondary Voltage : 33/1.732KV
Weight : 850Kg.
Potential Transformer is designed for monitoring single-phase and three-phase power line
voltages in power metering applications.
The primary terminals can be connected either in line-to-line or in line-to-neutral
configuration. Fused transformer models are designated by a suffix of "F" for one fuse or
"FF" for two fuses. A Potential Transformer is a special type of transformer that allows
meters to take readings from electrical service connections with higher voltage (potential)
than the meter is normally capable of handling without at potential transformer.
6.1 Potential Transformer
Potential transformers are instrument transformers. They have a large number of primary
turns and a few number of secondary turns. It is used to control the large value of voltage.
Potential Transformer is designed for monitoring single-phase and three-phase power line
voltages in power metering applications.
The primary terminals can be connected either in line-to-line or in line-to-neutral
configuration Fused transformer models are designated by a suffix of "F" for one fuse or "FF" for two
An isolator switch is part of an electrical circuit and is most often found in industrial
applications. They are commonly fitted to domestic extractor fans when used in bathrooms in
the UK. The switch electrically isolates the circuit or circuits that are connected to it. Such a
switch is not used normally as an instrument to turn on/off the circuit in the way that a light
switch does. Either the switch isolates circuits that are continually powered or is a key
element which enables an electrical engineer to safely work on the protected circuit.
Isolator switches may be fitted with the ability for the switch to padlock such that inadvertent
operation is not possible (see: Lock).In some designs the isolator switch has the additional
ability to earth the isolated circuit thereby providing additional safety. Such an arrangement
would apply to circuits which inter-connect power distribution systems where both end of the
circuit need to be isolated. The major difference between an isolator and a circuit breaker is
that an isolator is an off-load device, whereas a circuit breaker is an on-load device.
When to carry out inspection or repair in the substation installation a disconnection switch is
used called isolator. Its work is to disconnect the unit or section from all other line parts on
installation in order to insure the complete safety of staff working. The isolator works at no
load condition. They do not have any making or breaking capacity.
On fundamental basis the isolating switches can broadly divided into following categories: -
1. Bus isolator
2. Line isolator cum earthling switch
3. Transformer isolating switch.
The operation of an isolator may be hand operated without using any supply or may be power
operated which uses externally supplied energy switch which is in the form of electrical
energy or energy stored in spring or counter weight.
In a horizontal break, center rotating double break isolator, 3 strokes are found. Poles are
provided on each phase. The two strokes on side are fixed and center one is rotating. The
center position can rotate about its vertical axis at an angle of 90. In closed position, the
isolating stroke mounts on galvanized steel rolled frame. The three poles corresponding to 3
phases are connected by means of steel shaft.
Isolators are of two types -
1. Single pole isolator
2. Three pole isolator
Construction of Isolator:
Isolator for three-phase we provided in such a manner that for each phase one frame of
isolator. These three isolator must be operated all together. In each frame, line is connected to
terminal stud. Terminal stud is coupled with contact. Contact arm are supported by isolators.
Contacts are made or broken by motor operated mechanism. When contact is to be open then
both arms are rotated in opposite direction, so that contact is broken. Same time earthing pole
moves upward to make contact with a female contact situated adjoined to terminal stud.
Hence, that terminal gets earthen. On these criteria isolator can be carried out manually but
for quick operation motor is used.
To communicate between two G.S.S. we use power line itself. Power line carrying 50Hz
power supply also carries communication signals at high frequency. Wave Trap is a device
used for this purpose. It traps the frequency of desired level for communication and sends it
to P.L.C.C. department. It is used to trap the communication signals & send PLCC room
Rejection filters are known as the line traps consisting of a parallel resonant circuit ( L and C
in parallel) tuned to the carrier frequency are connected in series at each and of the protected
line such a circuit offer high impedance to the flow of carrier frequency current thus
preventing the dissipation. The carrier current used for PLC Communication have to be
prevented from entering the power equipments such as attenuation or even complete loss of
communication signals. For this purpose wave trap or line trap are used between transmission
line and power station equipment to avoid carrier power dissipation in the power plant reduce
cross talks with other PLC Circuits connected to the same power station.
Ensure proper operating conditions and signal levels at the PLC transmit receive equipment
irrespective of switching conditions of the power circuit and equipments in the stations.
Line Matching Filter & Protective Equipments
For matching the transmitter and receiver unit to coupling capacitor and power line matching
filters are provided. These flitters normally have air corral transformers with capacitor
The matching transformer is insulated for 7-10 KV between the two windings and perform
two functions. Firstly, it isolates the communication equipment from the power line.
Secondly, it serves to match.
The transmitter consists of an oscillator and an amplifier. The oscillator generates a frequency
signal within 50 to 500 HZ frequency bands the transmitter is provided so that it modulates
the carrier with protective signal. The modulation process usually involves taking one half
cycle of 50 HZ signal and using this to create block to carrier.
The receivers usually consist of and alternate matching transformer band pass filter and
The amplifier detector converts a small incoming signal in to a signal capable of operating a
relatively intensive carrier receiver relay. The transmitter and receiver at the two ends of
protected each corresponds to local as far as transmitting.
A circuit breaker is an automatically operated electrical switch designed to protect an
electrical circuit from damage caused by overload or short circuit Its basic function is to
detect a fault condition and, by interrupting continuity, to immediately discontinue electrical
flow Unlike a fuse, which operates once and then has to be replaced, a circuit breaker can be
reset (either manually or automatically) to resume normal operation Circuit breakers are
made in varying sizes, from small devices that protect an individual household appliance up
to large switchgear designed to protect high voltage circuits feeding an entire city.
In any circuit, carrying a large amount of current, if a contact is opened then normally a spark
is produced due to fact that current traverses its path through air gap Arcing is harmful as it
can damage precious equipment media are provided between contacts. This is one of the
important equipment in power system It protects the system by isolating the faulty section
while the healthy one is keep on working Every system is susceptible to fault or damages
while can be caused due to overloading, short-circuiting, earth fault etc. thus to protect the
system and isolate the faulty section C B are required Apart from breaking and making
contacts, a C B should be capable of doing
1. Continuously carry the maximum current at point of installation
2. Make and break the circuit under abnormal and normal condition
3. Close or open the faulty section only where fault exists
There are different arc quenching media:-
1) Air blast
3) SF6 gas
In 132 KV GSS, SF6 gas circuit breaker are used, as for greater capacity GSS SF6 type
breakers are very efficient.
9.1 AIR BLAST CIRCUIT BREAKER
Air blast circuit breakers are normally only used at low voltage levels but are available with
high current ratings up to 6000 A and short circuit ratings up to 100 kA at 500V.The air blast
circuit breakers according to type of flow of blast of compressed air around the contacts are
three namely (i) Axial (ii) Radial (iii) cross flow of blast air type.
Construction & working:
The physical size of such units, which contain large arc chutes, quickly makes them
uneconomic as voltages increase above 3.6KV. Their simplicity stems from the fact that they
use ambient air as the arc quenching medium. As the circuit breaker contacts open the arc is
formed and encouraged by strong thermal convection effects and electromagnetic forces to
stretch across splitter plates. The elongation assists cooling and deionization of the air/contact
metallic vapor mixture. The long arc resistance also improves the arc power factor and
therefore aids arc extinction at current zero as current and circuit breaker voltage are more in
phase. Transient recovery voltage oscillations are also damped thus reducing over voltages.
Arc products must be carefully vented away from the main contact area and out of the
switchgear enclosure. As we know many MCB and MCCB low-voltage current limiting
devices are only designed to have a limited ability to repeatedly interrupt short circuit
currents. Care must therefore be taken when specifying such devices. Air circuit breaker with
fully repeatable high short circuit capability as typically found in a primary substation
auxiliary supply switchboard.
9.2 OIL CIRCUIT BREAKER
Mineral oil has good dielectric strength and thermal conductive properties. Its insulation level
is, however, dependent upon the level of impurities. Therefore regular checks on oil quality
are necessary in order to ensure satisfactory circuit breaker or oil-immersed switch
performance. Carbon deposits form in the oil (especially after heavy short circuit interrupting
duties) as a result of decomposition under the arcing process. Oil oxygen instability,
characterized by the formation of acids and sludge, must be minimized if cooling properties
are to be maintained. Insulation strength is particularly dependent upon oil moisture content.
The oil should be carefully dried and filtered before use. Oil has a coefficient of expansion of
about 0.0008per°C and care must be taken to ensure correct equipment oil levels.
The oil can be moved into arc zone after the current reaches zero by the following actions.
(i)By the pressure caused by the natural head of the oil,
(ii) By the pressure generated by the action of the arc itself (iii) by the pressure caused by
Thus the oil circuit breakers may be classified as:
(i)Plain break oil circuit breakers.
(ii) Self blast or self-generated or arc control oil circuit oil circuit breakers.
(iii) Externally generated pressure oil circuit breakers of forced blast oil circuit breakers or
impulse oil circuit breakers.
Oil, as an arc quenching medium, has the following advantages and dis-advantages.
(i)arc energy is absorbed in decomposing of oil (ii)The gas formed, which is mainly hydrogen
have a high diffusion rate and high head absorption in changing from the diatomic to
monotonic state and thus provides good cooling properties. (iii)Surrounding oil presents the
cooling surface in close proximity to the arc.(iv)The oil used such as transformer oil is a very
good insulator and allows smaller cleaner between live conductors and earth
components.(v)The oil has ability to flow into the arc space after current is zero.
(i)There is a risk of formation of explosive mixture with air(ii)Oil is easily in flammable and
may causes fire hazards(iii)Owing to formation of carbon particles in the oil due to heat, the
oil is to be kept clean and thus requires periodical replacement.
9.3 SF6 BREAKER
The outstanding physical and chemical properties of SF6 gas makes it an ideal dielectric
media for use in power switchgear. These properties of SF6 gas makes it an ideal dielectric
media for use in power switchgear, these properties are included:
1) High dielectric strength
2) Unique arc quenching ability
3) Excellent thermal stability
4) Good thermal conductivity
In addition, at normal temperature SF6 is chemically inert, inflammable, noncorrosive and
non-condensable at low temperatures.
Working of circuit breaker:
Interrupter unit fixed contacts that are connected through a moving contact. Fixed contacts
are of rod shape. There contacts are known as male contacts.
In closed position, fixed contacts are joined by a moving contact known as female contact.
This female contact is of hollow cylindrical shape. Main parts of female contacts are blast
cylinder, contact tube and guide tube. In closed position female contact overlaps male
Contact tube shorts two made contacts and current completes its path from one male contact
to another through contact. Counteracting piston moves towards contact compressing the SF6
present in blast cylinder. When it is required to open the contacts then piston is forced to
move vertically download by hydraulic or pneumatic pressure.
This piston pulls operating rod pulls blast cylinder using bell and crank mechanism. Contact
tube moves away from contact. Counteracting piston moves towards contact compressing the
SF6 present in blast cylinder. When contact between male and female contacts is just going to
break. Then counteracting piston reaches its extreme position performing maximum
compression of SF6 gas .when arc is produced, SF6 at very high pressure quenches the arc.
Fig.9.1 SF6 Circuit Breaker
Rating of SF6 breaker:
Type: pneumatic operated
Rated Voltage 145KV
Rated normal current 2000A
Rated Lightning withstand impulse voltage: 650KV
Rated short circuit breaking current: 31.5KA
Rated short time withstand current and duration: 31.5KA, 3 sec.
Rated line charging, breaking current: 50A
Rated SF6 gas pressure at 200c (abs.): 7.0bar
Closing and opening device supply voltage: 110Vdc
Auxiliary circuit supply voltage: 240Vac
Rated air pressure: 22bar
Rated frequency: 50Hz
Maximum weight: 1750Kg.
9.4 Vacuum Circuit Breaker
Vacuum interrupter tubes or ‘bottles’ with ceramic and metal casings are evacuated to
pressures of some 10-6 to 10-9 bar to achieve high dielectric strength. The contact separation
required at such low pressures is only some 0 to 20mm and low energy mechanisms may be
used to operate the contacts through expandable bellows. Below figure shows a cut away
view of such a device. The engineering technology required to make a reliable vacuum
interrupter revolves around the contact design. Interruption of a short circuit current.
Figure 9.2 vacuum circuit breaker
When current in a circuit is too high to directly apply to measuring instruments, a current
transformer produces a reduced current accurately proportional to the current in the circuit,
which can be conveniently connected to measuring and recording instruments. A current
transformer also isolates the measuring instruments from what may be very high. Current
transformer is an instrument transformer which is mainly used for measuring currents where
very high currents are flowing.
According to the construction of the current transformer the primary winding of transformer
is in series with high current carrying line & measuring instrument is connected to the
Figure 10.1 CURRENT TRANSFORMER
The current transformer is mounted one of the power transformer leads; it can be associated
with an Lv or Hv lead; depending on voltage and current consideration. A section of the lead
is demountable locally to enable the current transformer to removed, should the necessity
arise, without disturbing the main connection. The secondary of CT is connected to the
heating coil directly located under the main cover in the oil. On the larger transformers the
various connections may be brought up to terminals in the main the cover for external
RATINGS OF CT:-
Frequency : 50 Hz
Highest System Voltage : 145 KV
Short Time Current : 40KA
Rated Current : 600A
Current ratio : 600-300-150/1
Min. Knee Potential Voltage : 850 V at 150/1
Max. Exciting Current : 100MA at 150/1
Max. Sec. Winding Resistance: 2.5 ohm at 150/1
BUS BAR SYSTEM
The conductors used
(i) For 400KV line : Taran Tulla and Marculla conductor.
(ii) For 132KV line : Zebra conductor is used composite of Aluminium strands and Steel
(iii) For 132KV line : Panther conductor is used composite of Aluminium strands and
The material used in these conductors is generally Aluminium Conductor Steel Reinforced
(ACSR). The conductors run over the towers cross arms of sufficient height with the
consideration to keep safe clearance of sagged conductors from ground level and from the
objects (trees, buildings etc.) either side also.
Figure 11.1 Bus bar
This bus bar arrangement is very useful for working purpose as every GSS. It is a conductor
to which a number of cut .Are connected in 132 KV GSS there are two bus running parallel
to the each other, one is main and another is auxiliary bus is only for standby, in case of
failure of one we can keep the supply continues.
If more loads are coming at the GSS then we can disconnect any feeder through circuit
breaker which is connected to the bus bar. This remaining all the feeders will be in running
position .if we want to work with any human damage. In this case all the feeders will be on
conditions. According to bus voltage the material is used .Al is used because of the property
& features and it is cheap.
A transformer is a device that transfers electrical energy from one circuit to another through
inductively coupled conductor -the transformer's coils. A varying current in the first or
primary winding creates a varying magnetic flux in the transformer's core and thus a varying
magnetic field through the secondary winding. This varying magnetic field induces a varying
electro-motive force, or voltage in the secondary winding this effect is called mutual
If a load is connected to the secondary, an electric current will flow in the secondary winding
and electrical energy will be transferred from the primary circuit through the transformer to
the load. By appropriate selection of the ratio of turns, a transformer thus allows an
alternating current voltage to be "stepped up" by making Ns greater than Np, or "stepped
down" by making Ns less than Np
Fig.12.1: POWER TRANSFORMER
Very high cost of transformers is due to three parts:-
Now we describe the three major parts of transformer
Core is the main part of the transformer It is subjected to magnetic flux For efficient
operation, it is essential that the core of transformer must be constructed from laminated
magnetic material of low hysteresis loss and high permeability Transformers for use at
power or audio frequencies typically have cores made of high permeability silicon The steel
has permeability many times that of space and the core thus serves to greatly reduce the
magnetizing current, and confine the flux to a path which closely couples the windings Early
transformer developers soon realized that cores constructed from solid iron resulted in
prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting
of bundles of insulated iron wires Later designs constructed the core by stacking layers of
thin steel laminations, a principle that has remained in use Each lamination is insulated from
its neighbors by a thin non-conducting layer of insulation The universal transformer equation
indicates a minimum cross-sectional area for the core to avoid saturation
The effect of laminations is to confine eddy currents to highly elliptical paths that enclose
little flux, and so reduce their magnitude Thinner laminations reduce losses, but are more
laborious and expensive to construct Thin laminations are generally used on high frequency
transformers, with some types of very thin steel laminations able to operate up to 10 kHz.
A steel core's remanence means that it retains a static magnetic field when power is
removed When power is then reapplied, the residual field will cause a high inrush current
until the effect of the remaining magnetism is reduced, usually after a few cycles of the
applied alternating current Overcurrent protection devices such as fuses must be selected to
allow this harmless inrush to passion transformers connected to long, overhead power
transmission lines, induced currents due to geomagnetic disturbances during solar storms can
cause saturation of the core and operation of transformer protection devices.
Core type transformers use concentric type of winding Each limb is wound with a group of
coil consisting of both primary and secondary winding, which are concentric to each other
Low voltage winding is placed near to the core (which is at earth potential) and high voltage
winding is placed outside, however L T and H T windings are inter-leaved to reduce the
It is found that the magnetic properties of transformer sheet steel vary in accordance with the
direction of the grain oriented by rolling, sheet are cut as far as possible along the grain which
is the direction in which the material has a higher permeability It must be made In building
the core, considerable pressure is used to minimize air gaps between the plates, which would
constitute avoiding loosed of area and might contribute to noisy operation The reduction of
core sectional area due to presence of insulating material is of the order of 10%.
The winding is layered type and used either rectangular or round conductors. In a cylindrical
winding. Using rectangular conductor, the conductors are wound on the flat side with three-
layer side parallel to the core axis. The winding using rectangular conductors may be
simultaneously wound from or more parallel conductors.
The layered winding may have conductors wound in one, two or more layers and is therefore
accordingly called one, two or multi- layer winding. The windings using rectangular
conductors are usually two layered because this case it is easier to secure the lead out ends.
The windings designed for heavy currents are wound with a number of conductors connected
in parallel located side by side in one layer. The parallel conductors have the same length and
are located in the magnetic field or almost the same flux density and hence it is not necessary
to make any transposition of conductors. A wedged shaped packing is used at each of two
entrance ends of winding in order to level it, the packing is made of press bar strips.
Cylindrical winding using circular conductors are multi layered. They are wound on a solid
paper Bakelite cylinder.
Oil in transformers construction, serves the double purpose of cooling and insulating. For use
in transformer tank, oil has to fulfil certain specifications and must be carefully selected. All
type of oils are good insulators. Animal oil are good insulator but they are too viscous that
they tend to form fatty acids, which attack fibrous materials (e.g. Cotton) and therefore are
undesirable for transformers. Vegetable oils are opt to be inconsistent in quality and like
animal oils, tend to form to form destructive fatty acids. Mineral oils are suitable for electric
purpose; some have a bituminous and other have a paraffin base. The crude oil as tapped, is
distilling producing a range of volatile spirits and oils ranging from the very light to the
heavy paraffin wax or bitumen.
WINDING TEMPERATURE INDICATOR
Winding temperature indicator consists essentially of a current transformer and a thermal unit
comprising a heating coil and a thermometric device. The thermal unit, which is designed to
have a thermal performance similar to that of the win windings of the power X-mer, is
influenced by two factors:
(1) The temperature of the surrounding oil, and
(2) The current flowing through the heater coil, which will raise the temperature of the unit
above that of the surrounding oil.
The CT secondary current is chosen to the max ‘hot spot’ winding gradient occurring in
either Hv or Lv windings of the power transformer. Thus the thermal unit’s capable of
simulating the hottest-spot temperature of the transformer windings under al conditions.
The bulb of a capillary type dial thermometer is screwed into a blind pocket, which is fitted
inside the heating coil. This type of pocket enables the dial thermometer to be removed from
the transformer without having to lower the oil level.
The heating coil with its blind type pocket fitted inside is supported independently under the
cover of the transformer; hence it is always in the hottest oil. The dial thermometer is
provided with one or more sets of contacts for alarm/ or trip circuit and at time for controlling
cooking equipment when forced cooling is called for.
OIL TEMPERATURE INDICATOR
An oil temperature indicator has been provided for measuring the transformer top oil
temperature. The heat sensitive device of the thermometer is placed in an oil pocket mounted
at the transformer cover, the thermometer has two adjustable mercury contacts and a
maximum reading pointer. The contact may be used to close circuit for alarm and tripping
device. The mercury switches are accessible by removing the top cover of the instrument and
are adjustable for different temperature ratings by location of the mount a repeater dial is for
remote indication of the oil temperature in the control room. The thermometer is housed in
the marshalling box.
OIL SURGE REALY FOR OLTC GEAR
An oil- operated relay having one set of contracts is designed to trip the transformer between
the oil conservator. The relay is designed to trip the transformer on the occurrence of violent
oil surges arising out of any malfunction in the OLTC operation. The conservator for the
OLTC gear is separate from the main transformer conservator forms the conservator forms
the conservator for the OLTC the terminals from the relay are wired to the terminal block
located in the marshalling box.
The marshalling box is of sheet steel, weatherproof construction, mounted on the side of the
transformer. It is provided with a hinged door and pad lock, and housed the following
instrument and terminal block:-
(a) Winding temperature indicator
(b) Oil temperature indicator
(c) Terminal block for alarm and contacts of buchholz relay
(d) Terminal block for oil level alarm and contacts of Magnetic oil level Gauge.
(f) Heater with switch
(g) Magnetic oil gauge
The oil level gauge is mounted on the flat end of the con servitor. The indicator reads the oil
level inside the conservator and initiates an alarm by closing the mercury contacts switch
when the oil level is below the predetermined minimum. The contacts from the oil level
gauge are wired to the terminal block located in the marshaling box.
(h) Cooling equipment
The transformer having mixed cooling ONAF and ONAF is provided with detachable
radiators foxed to the tank wall through valves. The ONAF cooling equipment comprises of
four 457 mm dia fans, each blowing 3600 cu.ft. Of air per minute on the radiator element
directed in such a way that the no longer effective they turn pink. At the bottom of the
breather a cup containing the transformer oil is screwed this oil acts as a seal, preventing the
crystals from absorbing moisture except when breathing is taking place.
Oil cooling is normally achieved by heat exchange to the surrounding air. Sometimes a water
jacket acts as the secondary cooling medium. Fans may be mounted directly onto the
radiators and it is customary to use a number of separate fans rather than one or two large
fans. Oil pumps for OFAF cooling are mounted in the return pipe at the bottom of the
radiators. The motors driving the pumps often use the transformer oil as their cooling
With ODAF cooling, the oil-to-air coolers tend to be compact and use relatively large fan
blowers. With this arrangement the cooling effectiveness is very dependent on proper
operation of the fans and oil pumps since the small amount of
Cooling surface area gives relatively poor cooling by natural convection alone. Water cooling
(ODWF) has similar characteristics to the ODAF cooling described above and is sometimes
found in power station situations where ample and well-maintained supplies of cooling water
are available. Cooling effectiveness is dependent upon the flow of cooling water and
therefore on proper operation of the water pumps. Natural cooling with the out-of-service
water pumps is very limited. Operational experience has not always been good, with
corrosion and leakage problems, and the complexity of water pumps, pipes, valves and flow
monitoring equipment. The ODAF arrangement is probably favorable as a replacement for
the ODWF designs. Double wall cooler pipes give added protection against water leakage.
The inner tube carries the water and any leakage into the outer tube is detected and causes an
alarm. This more secure arrangement is at the expense of slightly reduced heat transfer for a
given pipe size. Normal practice with cooling plant is to duplicate systems so that a failure of
one need not directly affect operation of the transformer. Two separate radiators or radiator
banks and duplicate oil pumps may be specified. In the larger ODAF cooling designs there
may be four independent unit coolers giving a degree of redundancy. The transformer may be
rated for full output with three out of the four coolers in service. Dry type transformers will
normally be naturally air-cooled (classification AN) or incorporate fans (classification AF).
TAPPINGS AND TAP CHANGER
The transformer has an on load tap changer to cater for a variation of +5% to -15% in the HV
voltage in 14 equal steps of 1.43% each for a constant power output. The tappings from the
HV tapping winding are connected to a 15 position ‘66’KV Crompton greaves make high-speed
resistor transition on load tap-changer. The tap-changer may be either manually
operated or motor driven.
The motor driving mechanism is also described in the leaflet and is arranged for the
following types of control.
Local electrical independent
Remote electrical independent
Remote electrical group parallel control
Tap changer is used to change the HV voltage. We use tap changer in HV side only because
in HV side current is less hence it is easy to handle lower amount of current. Tap changers
are of two types.
1) No Load Tap changer
2) On Load tap changer
No Load Tap changer in this type tap changer, we have to cut off load before changing the
taps. These kinds of tap changer are used in small transformers only.
On Load tap changer
In this type tap changer load remains connected to transformer while changing the taps. This
kind of tap changer requires special construction. Tapping winding is placed over HV
winding. Generally, tapping winding is divided in 6 parts by the combination of these 6
winding and HV winding 17 different tap positions are used.
A relay is an electrically operated switch Current flowing through the coil of the relay
creates a magnetic field which attracts a lever and changes the switch contacts The coil
current can be on or off so relays have two switch positions and they are double throw
Relays allow one circuit to switch a second circuit which can be completely separate
from the first For example a low voltage battery circuit can use a relay to switch a 230V AC
mains circuit There is no electrical connection inside the relay between the two circuits, the
link is magnetic and mechanical.
The coil of a relay passes a relatively large current, typically 30mA for a 12V relay,
but it can be as much as 100mA for relays designed to operate from lower voltages. Most
ICs (chips) cannot provide this current and a transistor is usually used to amplify the small IC
current to the larger value required for the relay coil The maximum output current for the
popular 555 timer IC is 200mA so these devices can supply relay coils directly without
Relays are usually SPDT or DPDT but they can have many more sets of switch
contacts, for example relays with 4 sets of changeover contacts are readily available.
Types of Relays
These are called normally opened, normally closed in GSS control room there is panel in
which the relays are set and there are many types of relays
1. Over voltage relays
2. Over current relays
3. I D M T fault relay
4. Earth fault relay
5. Buchholz’s relay
6. Differential relay
OVER VOLTAGE RELAY: - This protection is required to avoid damage of system
in case line becomes open circuited at one end These fault would trip the local circuit
breaker thus block the local and remote ends This relay is operated i e , energized by
CVT connected to lines.
OVER CURRENT RELAY: -This relay has the upper electromagnet of non-directional
relay connected in series with lower non-directional electromagnet When
the fault current flow through relay current coil which produces flux in lower magnet
of directional element. Thus the directional relay has the winding over the
electromagnets of non-directional element and produces a flux in lower magnet and
thus over current operates.
EARTH FAULT RELAY: -when a conductor breaks due to some reason and it is
earthen then earth fault occurs. The fault current is very high thus, there is need to of
over current relay this relay has minimum operating time.
DIRECTIONAL RELAY: - It allows flowing the current only in one direction then
only this relay operates. It has a winding connected through the voltage coil of relay
to lower magnet winding called current coil Which is energized by C T if fault
occurs This relay operates when v/I is less than theoretical value The v/I is normally
DIFFERENTIAL RELAY: - This relay operates when phase difference of two
electrical quantities exceeds the predetermined value. It has always two electrical
quantities; hence in 400KV GSS for transformer differential relay is used.
INVERSE TIME CHARACTERISTICS RELAY: - The relay using here having
the inverse time characteristics having the time delays dependent upon current value
This characteristic is being available in relay of special design There are:-
i. Electromagnetic Induction type
ii. Permanent magnetic moving coil type
iii. Static type
BUCHHOLZ’S RELAY: -
It is the protective device of the transformer When any fault occurs in the transformer
then it indicates about fault and we disconnect the transformer from the circuit It is
used in the power transformer It is connected between the tank and conservator It
has two floats on which two mercury switch are attached One float is used for the
bell indication and other float is used for the tripping In the normal position the relay
is filled with the oil and contacts of the mercury switch are opened When the earth
fault occurs in the transformer then it increases the temperature of oil and oil flows
into the conservator through relay On the way it makes the contacts of the tripping
circuit short So we can say that this relay works as circuit breaker .
In order to avoid current leakage to the Earth, through the supporting structure provide to the
conductor of overhead transmission lines, insulators are used. The conductors are secured to
the supporting structures by means of insulating feature, which do not allow current to flow
through these support and hence finally to the earth . Bus support insulators are porcelain or
fiberglass insulators that serve to the bus bar switches and other support structures and to
prevent leakage current from flowing through the structure or to ground. These insulators are
similar in function to other insulator used in substations and transmission poles and towers.
An Insulator should have following characteristic:-
High Insulation resistance.
1. High mechanical strength
2. No internal impurity or crack Disc
Generally Porcelain or glass is used as material for insulators. Porcelain because of its low
cost.is more common. Insulators can be classified in following ways:-
1. Pin Type: - These are designed to be mounted on a pin, which in turn is installed on
the cross arm of a pole. As the name suggests, the pin type insulator is mounted on a
pin on the cross-arm on the pole. There is a groove on the upper end of the insulator.
The conductor passes through this groove and is tied to the insulator with annealed
wire of the same material as the conductor. Pin type insulators are used for
transmission and distribution of electric power at voltages up to 33 kV. Beyond
operating voltage of 33 kV, the pin type insulators become too bulky and hence
Figure-14.1 Pin Type Insulator
2. Suspension Type:-These insulators hang from the cross arm, there by forming a
string. For voltages greater than 33 kV, it is a usual practice to use suspension type
insulators shown in Figure. Consist of a number of porcelain discs connected in series
by metal links in the form of a string. The conductor is suspended at the bottom end of
this string while the other end of the string is secured to the cross-arm of the tower.
The number of disc units used depends on the voltage.
Figure-14.2 Suspension Type Insulator
3. Strain insulator - A dead end or anchor pole or tower is used where a straight section
of line ends, or angles off in another direction. These poles must withstand the lateral
(horizontal) tension of the long straight section of wire. In order to support this lateral
load, strain insulators are used. For low voltage lines (less than 11 kV), shackle
insulators are used as strain insulators. However, for high voltage transmission lines,
strings of cap-and-pin (disc) insulators are used, attached to the cross arm in a
horizontal direction. When the tension load in lines is exceedingly high, such as at
long river spans, two or more strings are used in parallel.
Figure-14.3 Strain Type Insulator
4. Shackle insulator - In early days, the shackle insulators were used as strain
insulators. But now a day, they are frequently used for low voltage distribution lines.
Such insulators can be used either in a horizontal position or in a vertical position.
They can be directly fixed to the pole with a bolt or to the cross arm.
POWER LINE CARRIER COMMUNICATION
Power line communication or power line carrier (PLC), also known as Power line Digital
Subscriber Line (PDSL), mains communication, power line telecom (PLT), or power line
networking (PLN), is a system for carrying data on a conductor also used for electric power
transmission. Broadband over Power Lines (BPL) uses PLC by sending and receiving
information bearing signals over power lines.
Electrical power is transmitted over high voltage transmission lines, distributed over medium
voltage, and used inside buildings at lower voltages. Power line communications can be
applied at each stage. Most PLC technologies limit themselves to one set of wires (for
example, premises wiring), but some can cross between two levels (for example, both the
distribution network and premises wiring). Typically the transformer prevents propagating
the signal so multiple PLC technologies are bridged to form very large networks.
All power line communications systems operate by impressing a modulated carrier signal on
the wiring system. Different types of power line communications use different frequency
bands, depending on the signal transmission characteristics of the power wiring used. Since
the power wiring system was originally intended for transmission of AC power, in
conventional use, the power wire circuits have only a limited ability to carry higher
frequencies. The propagation problem is a limiting factor for each type of power line
communications. A new discovery called E-Line that allows a single power conductor on an
overhead power line to operate as a waveguide to provide low attenuation propagation of RF
through microwave energy lines while providing information rate of multiple Gbps is an
exception to this limitation.
15.2 MAJOR SYSTEM COMPONENTS EQUIPMENT
The major components of a PLC channel are shown in Figure. The problem associated with
the PLC channel is the requirement to put the carrier signal onto the high voltage line without
damaging the carrier equipment. Once the signal is on the power line it must be directed in
the proper direction in order for it to be received at the remote line terminal.
15.3 BASIC PRINCIPLE OF PLCC
In PLCC the higher mechanical strength and insulation level of high voltage power lines
result in increased reliability of communication and lower attenuation over long distances.
Since telephone communication system cannot be directly connected to the high voltage
lines, suitably designed coupling devices have therefore to be employed. These usually
consist of high voltage capacitors or capacitor with potential devices used in conjunction with
suitable line matching units (LMU’s) for matching the impedance of line to that of the
coaxial cable connecting the unit to the PLC transmit-receive equipment.
Also the carrier currents used for communication have to be prevented from entering the
power equipment used in G.S.S as this would result in high attenuation or even complete loss
of communication signals when earthed at isolator. Wave traps usually have one or more
suitably designed capacitors connected in parallel with the choke coils so as to resonate at
carrier frequencies and thus offers even high impedance to the flow of RF currents.
15.4 LINE TRAPS OR WAVE TRAPS:-
The carrier energy on the transmission line must be directed toward the remote line terminal
and not toward the station bus, and it must be isolated from bus impedance variations. This
task is performed by the line trap. The line trap is usually a form of a parallel resonant circuit
which is tuned to the carrier energy frequency. A parallel resonant circuit has high impedance
at its tuned frequency, and it then causes most of the carrier energy to flow toward the remote
line terminal. The coil of the line trap provides a low impedance path for the flow of the
power frequency energy. Since the power flow is rather large at times, the coil used in a line
trap must be large in terms of physical size.
Once the carrier energy is on the power line, any control of the signal has been given over to
nature until it reaches the other end. During the process of traveling to the other end the
signal is attenuated, and also noise from the environment is added to the signal. At the
receiving terminal the signal is decoupled from the power line in much the same way that it
was coupled at the transmitting terminal. The signal is then sent to the receivers in the control
house via the coaxial cable.
15.5 COUPLING CAPACITORS:-
The coupling capacitor is used as part of the tuning circuit. The coupling capacitor is the
device which provides a low.
Impedance path for the carrier energy to the high voltage line and at the same time, it blocks
the power frequency current by being a high impedance path at those frequencies. It can
perform its function of dropping line voltage across its capacitance if the low voltage end is at
ground potential. Since it is desirable to connect the line tuner output to this low voltage point
a device must be used to provide a high impedance path to ground for the carrier signal and a
low impedance path for the power frequency current. This device is an inductor and is called
a drain coil.
It is desirable to have the coupling capacitor value as large as possible in order to lower the
loss of carrier energy and keep the bandwidth of the coupling system as wide as possible.
However, due to the high voltage that must be handled and financial budget limitations, the
coupling capacitor values are not as high as one might desire. Technology has enabled
suppliers to continually increase the capacitance of the coupling capacitor for the same price
thus improving performance.
15.6 DRAINAGE COILS:-
The drainage coil has a pondered iron core that serves to ground the power frequency
charging to appear in the output of the unit. The coarse voltage arrester consists of an air gap,
which sparks over at about 2 KV and protects the matching unit against line surges. The
grounding switch is kept open during normal operation and is closed if anything is to be done
on the communication equipment without interruption to power flow on the line. The
matching transformer is isolated for 7 to 10 KV between the two winding and former two
functions. Firstly it isolates the communication equipment for the power line. Secondly it
serves to match the characteristic impedance of the power line 400-600 ohms to that of the
co-axial vacuum arrester (which sparks) is over at about 250 V is provided for giving
additional protection to the communication equipment.
15.7 ADVANTAGES & DISADVANTAGES OF PLCC
1. No separate wires are needed for communication purposes as the power lines
themselves carry power as well as the communication signals. Hence the cost of
constructing separate telephone lines is saved.
2. When compared with ordinary lines the power lines have appreciably higher
mechanical strength. They would normally remain unaffected under the condition
which might seriously damage telephone lines.
3. Power lines usually provide the shortest route between the power stations.
4. Power lines have large cross-sectional area resulting in very low resisntanc3 per unit
length. Consequently the carrier signal suffers lesser attenuation than when travel on
usual telephone lines of equal lengths.
5. Power lines are well insulated to provide negligible leakage between conductors and
ground even in adverse weather conditions.
6. Largest spacing between conductors reduces capacitance which results in smaller
attenuation at high frequencies. The large spacing also reduces the cross talk to a
1. Proper care has to be taken to guard carrier equipment and persons using them against
high voltage and currents on the line.
2. Reflections are produced on spur lines connected to high voltage lines. This increases
attenuation and create other problems.
3. High voltage lines have transformer connections, which attenuate carrier currents.
Sub-station equipments adversely affect the carrier currents.
4. Noise introduced by power lines is much more than in case of telephone lines. This
due to the noise generated by discharge across insulators, corona and switching
To remote control of power switch gear requires the provision of suitable control plates
located at a suitable point remote from immediate vicinity of CB’s and other equipments.
In GSS the separate control room provided for remote protection of 132KV switch yards
transformer incoming feeder, outing feeders. Bus bar has their own control plant in their
control rooms. The control panel carrier the appropriate relays. Necessary meters indicating
lamp control switches and fuses. There are meters for reading purpose. A circuit concerning
the panel is shown on the panel with standard colour.
On each panel a control switch is provided for remote operation of circuit breaker. There are
two indicators which show that weather circuit breaker is closed or open. A control switch for
each insulator is also provided. The position indicator of isolator is also done with the help of
single lamp and indicator. The colour of signal lamps are as follows:-
Red:- for circuit breaker or isolator is close option
Green - for circuit breaker is in open position.
Amber - indicates abnormal condition requiring action.
In addition to used indication an alarm is also providing for indicating abnormal condition
when any protective relay or tripping relay has operated. Its constants energies on auxiliary
alarm. Relay which on operation completes the alarm belt circuit.
There is a hinged Synchronizing panel mounted at the end of control panel. Before coupling
any incoming feeders to the bus bar. It just be synchronized with switches. When the
synchronous copy shows zero we close the circuit breaker.
Synchronoscope is used to determine the correct instant of closing the switch which connect
the new supply to bus bar. The correct instant of synchronizing when bus bar incoming
1. Are in phase
2. Are equal in magnitude
3. Are in some phase sequence
4. Having same frequency
5. The voltage can be checked by voltmeter the function of synchronoscope is to
indicate the difference in phase and frequency.
Fig.16.1: panel of control room
ENERGY METER: - These are fitted on different panel to record transmitted energy
and recorded in energy hours. For this purpose MWH meter have been provided.
WATT METER: - This is mounted on each feeder panel to record import or export
FREQUENCY METER: - Provided to each feeder to measure frequency which
analog or digital.
VOLT METER: - Provided on each panel or the purpose of indication of voltage.
AMMETER: - These are used to indication the line current.
MVAR METER: - Provided for indicating power factor of import and export.
MAXIMUM INDICATOR DEMAND: - Chief requirement of these indicators to
record the minimum power factor taken by feeder during a particular period. This
record the average power successive predetermined period.
In a GSS, Separate dc supply is maintained for signaling remote position control, alarm
circuit etc. There is a battery room which has 55 batteries of 2 volt. Therefore D.C. power
available is for functioning of the control panels. A battery charger to charge the
battery. Various parts of lead acid batteries:-
Fig.17.1: a view of battery room
5. Terminal port
6. Vent plugs
CHARGING OF BATTERIES:-
It is the first charging given to batteries by which the positive plates are converted to
“lead peroxide”, whereas the –ve plates will converted to spongy lead. Also in a fully
charged battery the electrolyte specific gravity will be at its highest venue of 1.2.
When a fully charged battery delivers its energy out by meeting a load the lead
peroxide of the +ve plates slowly gets converted to lead sulphate and the spongy lead
of the –ve plates also gets converted into lead sulphate during this time the specific
gravity of the electrolyte also decreases the value around 1.00 and the terminal
voltage also decreases from its initial to a lower value which may be around 1.85 or
Capacitor banks are used to improve the quality of the electrical supply and the efficient
operation of the power system. Studies show that a flat voltage profile on the system can
significantly reduce line losses. Capacitor banks are relatively inexpensive and can be easily
installed anywhere on the network.
Fig.18.1:- CAPACITOR BANK
The capacitor unit is made up of individual capacitor elements, arranged in parallel/ series
connected groups, within a steel enclosure. The internal discharge device is a resistor that
reduces the unit residual voltage to 50V or less in 5 min. Capacitor units are available in a
variety of voltage ratings (240 V to 24940V) and sizes (2.5 KVAR to about 1000
KVAR).capacitor bank used for 33 KV at GSS has 2 units of 7.2 MVAR.
It was a very good experience of taking vocational training at 132KV GSS Sitapura, Jaipur.
All the Employees working there were very helpful and were always ready to guide us. They
gave their best to make us understand.
The Assistant Engineer, Junior Engineer & Technicians gave us the detailed theory. Training
at 132KV GSS Sitapura, Jaipur gives the insight of the real instruments used. There are many
instruments like transformer, CT, PT, CVT, LA, Relay, PLCC, Bus Bars, Capacitor bank,
Insulator, Isolator, Control Room, and Battery Room etc.
The training at grid substation was very helpful. It has improved my theoretical concepts of
electrical power transmission and distribution. Protection of various apparatus was a great
thing. Maintenance of transformer, circuit breaker, isolator, insulator, bus bar etc. was
I had a chance to see the remote control of the equipments from control room itself, which
was very interesting. All in all the training at 132KV GSS Sitapura, Jaipur was a memorable
1. Electrical Technology By B.L.Theraja & A.K.Theraja
2. Power System Protection And Switchgear By Badri Ram & D N Vishwakarma
3. Power System By J.B.Gupta
8. Electrical Machine By P.S.bhimbra
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