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POWERGRID CORPORATION OF
INDIA LIMITED
765/400/220 kV WARDHA SUB STATION
TRAINING REPORT
SUB STATION OVERVIEWMay - June 2012
Submitted by:
Javvaji Krishna TejaElectrical and Electronics engineering
Visvesvaraya National Institute of
Technology, Nagpur.
Bachu RameshElectrical and Electronics engineering
Visvesvaraya National Institute of
Technology, Nagpur.
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POWERGRID CORPORATION OF
INDIA LIMITED
765/400/220 kV WARDHA SUB STATION
TRAINING REPORT
SUB STATION OVERVIEWMay - June 2012
Submitted by:
Rajan DubeyElectrical Engineering
Anjuman College of Engineering and
Technology
Akash Barse
Electrical EngineeringAnjuman College of Engineering and
Technology
Mohammad AsifElectrical Engineering
Anjuman College of Engineering and
Technology
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Index
Sr. No. Contents Page No.
1. Mission and Objectives of PowerGrid 5
2. Introduction of Wardha Substation 6
3 Single Line Diagram 7
4. Bus Switching Schemes 105. Lightning Arrester 12
6. Wave Trap 12
7. Current Transformer 13
8. Capacitive Voltage Transformer 14
9. Circuit Breaker 14
10. Isolator 16
11. Reactor 16
12. InterConnecting Transformer 18
13. Protection 19
14. Relay 21
15. Line/ Transformer/ Bus Bar Protection 23
16. Testing 24
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Acknowledgement:
We express with reverence our indebtedness to our guide Shri. PatanjaliSharma Sir, Chief Manager, Wardha Sub Station, for standing by us right from the
beginning of our training.
We are greatly thankful to the Shri. Nitin Bhoyar, Managerfor providing usan opportunity to do training work.
We express our sincere thanks to Shri. Kaushal Sir, Shinde Sir, Chimankarsir, Vinit Sir, Patnaik Sir, Patel Sir and each and every staff member for their
valuable advises and guidance to the training work.
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Mission Of PowerGrid
ESTABLISHMENT & OPERATION OF REGIONAL & NATIONAL POWER GRIDS TO
FACILITATE TRANSFER OF POWER WITHIN & ACROSS THE REGIONS WITH
RELIABILITY, SECURITY & ECONOMY ON SOUND COMMERCIAL PRINCIPLES
Objectives of Powergrid
To ensure requisite capital investment in power transmission sector by mobilizingresources on its own / through private participation.
To provide transmission system matching with generation capacity addition in the centralsector.
To augment and strengthen Regional Grids to and develop a strong National Grid tofacilitate exchange of power between Regions.
To extend the National Grid to a SAARC Grid by interconnecting neighboring countriesviz. Bhutan, Nepal, Bangladesh etc.
To Undertake diversification in synergic area of Telecommunication as a InfrastructureService Provider.
To assist state power utilities in Distribution Sector under Accelerated PowerDevelopment and Reforms Programme of the GOI.
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Introduction of Wardha SubStation:
This report is a brief description of 765kV/400kV/220kV substation at Wardha maintained
by Power Grid Corporation of India limited. It is located 16km away from Wardha at Deoli,
MIDC area. It is a transmission substation where power is taken from Seoni and transmitted toParli, Badnera, Maudha, MSEB etc. The future prospective of this substation is to have a
1200kV line.
Fig.1: Power map of Western Region
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Single Line Diagram
765KV
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220KV
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Bus Switching Schemes
Single Main Scheme Double Main Scheme Single Main & Transfer Scheme Double Main with by-pass isolator scheme Double Main & Transfer Scheme One & Half Breaker Scheme Double breaker Scheme Ring Bus Scheme
At wardha substation, we use one and half breaker schemefor 765/400 KV
lines and double main transfer schemefor 220KVlines.
One and half breaker scheme:
In this scheme, two circuit have three breakers, the middle breaker ties the two circuitsand hence is called the tie breaker.
Breaker or bus maintenance is possible without any shut down of the feeder Even if both the buses are out of service, power can be transferred from one feeder to
another feeder through tie breaker
Fig.2: One and half breaker scheme
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Double Main and Transfer Bus Scheme:
In this bus scheme, in addition to the two main buses there will be a separate transfer busalso.
Since separate transfer bus is available there will be no need of transferring the load fromone bus to the other bus unlike in a main cum transfer bus arrangement.
Fig.3: Double main transfer scheme overview
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Substation Equipments
Line equipment Lightning arrester Wave trap Transformer Reactor Capacitive voltage transformer Potential Transformer
Bay equipment Isolator Circuit Breaker Current transformer
Lightning ArrestersLightning Arresters need low resistance during flow of lightning current to limit surge
voltage and high resistance to limit discharge current.In wardha substation, the capacity of LA used for 765KV line is 624KV and that for
400KV is 390KV recently being replaced by 336KV.
.
Wave trapThe function of wave trap is to avoid high frequency signal to enter in the substation. It
allows only 50Hz signals to enter.
The capacities of wave traps used at wardha substation are 0.5mH, 1mH or 2mH.
Fig.4: 400kV lightening arrestor Fig.5: 400kv wave trap
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Current Transformer
The function of Current Transformer is same as that of step down transformer which step
down the high current to a measurable current.
At wardha substation, the CTs used are :
765KV: 3000/1 400KV: 2000/1 220KV: 1600/1
Types of CTs
Dead Tank Designo Hair Pin Designo Eye Bolt Design
Live tank Design
Fig.6: live tank current transformer Fig.7: Dead tank current transformer
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Capacitive Voltage Transformer
The function of CVT is: It steps down the high voltage level into low voltage/measurable level. In hot line communication like Power Line Carrier Communication through phase to
phase coupling device.At wardha substation the CVTs used are of 765/400/220 KV capacity.
Fig.8: 400kv capacitive voltage transformer
Circuit Breaker
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 afault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike
a fuse, which operates once and then must be replaced, a circuit breaker can be reset (eithermanually 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.
TYPES OF CIRCUIT BREAKER
Fig.9:Usage of circuit breakers depending on voltage level
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Circuit-breakers lie at the heart of any switchgear installation.
Fig.10: Modes of operation of circuit breaker
Mode of operation
The current path is formed by the terminal plates [(1) and (8)], the contact support (2), the
base (7) and the moving contact cylinder (6). In closed state the operating current flows through
the main contact (4). An arcing contact (5) acts parallel to this.
Breaking operating currents
During the opening process, the main contact (4) opens first and the current commutates
on the still closed arcing contact. If this contact is subsequently opened, an arc is drawn betweenthe contacts (5). At the same time, the contact cylinder (6) moves into the base (7) and
compresses the quenching gas there. The gas then flows in the reverse direction through the
contact cylinder (6) towards the arcing contact (5) and quenches the arc there.
Breaking fault currents
In the event of high short-circuit currents, the quenching gas on the arcing contact is heated
substantially by the energy of the arc. This leads to a rise in pressure in the contact cylinder. In
this case the energy for creation of. the required quenching pressure does not have to be
produced by the operating mechanism. Subsequently, the fixed arcing contact releases the
outflow through the nozzle (3). The gas flows out of the contact cylinder back into the nozzleand quenches the arc.
The specific properties of the twin nozzle system are beneficial for restrike-free switching of low
inductive and capacitive currents. Thanks to its high arc resistance the system is especially
suitable for the breaking of certain types of fault such as those close to generators.
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Isolator
An isolator (UK terminology) or disconnector (US terminology) is a switch used to
isolate a section of a circuit from any energised conductors, by presenting a visible break in the
circuit. Isolators are not designed to break load currents (unless fitted with optional arc-breaking
feature) or to break fault currents.
Types of isolater
Type of Isolator Horizontal Centre Break Isolator (HCB) Horizontal Double Break Isolator (HDB) Pantograph Isolator (Panto) Vertical Break Isolator (VB) Knee type Isolator for 765kV Staggered
Knee type Isolator in close position
Fig.11: 765kv knee type isolator in close view
Reactor:
It is a simple shunt inductor or series capacitor installed to bring down the voltage at thereceiving end of a long transmission line, where the voltage is being boosted due the
Ferranti effect. It is line equipment, installed immediately at the incoming / outgoing ends after the
lighting arrestor and potential transformer in the line.
As the power is transmitted over long lines at high voltages the high capacitance of thetransmission line compared to its resistance and inductance will result in generation of
reactive power which ultimately results in boosting up of voltage at the receiving end ofthe transmission line.
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Thus, a shunt inductor or a series capacitor is installed at the line ends to consume thisreactive power generated along the transmission line and pull down the voltage to
appropriate level of transmission.
Reactors are generally installed on either side substations of the transmission lines , atappropriate ratings calculated as for the (each leg shunt capacitance) Pi-model of the
line.
The reactors used in wardha substation:
There are 10 single phase reactors and 5three phase reactors in wardhasubstation.
Among the ten single phase reactors 3 of them are used in incoming line of seoni-1 dia 3 of them are used in incoming line of seoni-2 dia 3 of them are used as bus reactors (maintains bus bar voltages) The other one is a spare reactor.
All 5three phase reactors are used in 400kv yard in different lines for the samepurposes as described.
Fig.12:a single phase reactor installed Fig.13:a three phase reactor installed
in 765kv yard at wardha substation in 400kv yard at wardha substation
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InterConnecting Transformer:
It is a static piece of device which is used for stepping down / stepping up of voltagelevels keeping power constant at a given frequency of operation.
It works on the principle of mutual induction It is line equipment installed at the incoming/outgoing ends of the line where ever a change
in voltage level is desired.
The use of transformer in the power system as lead to the reduction of generating costs andtransmission and distribution losses by providing a provision to have Generation at low voltage level ( economical) Transmission at high voltage (low losses) Distribution at low voltage ( to suit consumer requirements)Interconnecting Transformers used in wardha substation:
There are 10single phase and 3three phase interconnecting transformers in wardhasubstation
All the ten single phase transformers are auto transformers rated 765/400 kv, which areused to connect 765kv yard to the 400kv yard
3 of them are used in outgoing line of seoni-1 dia 3 of them are used in outgoing line of seoni-2 dia 3 of them are used in bus reactors dia The other one is a spare transformer.
All 3three phase transformers are star-delta-star transformers rated 400/33/220 kv,which are used to connect 400kv yard to the 220kv yard
The tertiary winding of the 3-phase transformer is to trap the third harmonic current. Inwardha substation, the tertiary winding of ICT1 in the 400kv yard is planned to be used
as a backup power source for substation equipment in future.
Fig.3:A single phase ICT installed Fig.4:A three phase ICT installedin 765kv yard at wardha substation in 400kv yard at wardha substation
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WHAT IS A PROTECTION?
Humans need protection from external disease, sun and whether. All the internal
parts of the human beings are protected naturally. Heart and lungs are protected by ribs bones
from external impact. Brain is protected by skull. Eyes are protected by eyelids and by closing
eyes. We need cloths to protect us from external environment conditions.
Similarly electrical equipment needs protection from any external or internal faults
which may produce a detrimental effect on it.
Electrical faults in the power system:
Transients Faults Permanent faults
Requirements of Protection System:
SENSITIVITY: The relay shall be sensitive to operate for minimum quantity ofoperating parameter.
SELECTIVITY: The relay/scheme should be able to select the faulty section andisolate.
SPEED: The relay should operate faster so that fault is isolated as fast as possible. RELIABILITY: The relay/scheme should operate for all types of faults with
repeatability and reliability. COST: The relay/scheme should be economical.
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ELEMENTS OF PROTECTION
CB
Feeder
Bus
CV
Relay
DC SOURCE
CT
Tri Ckt
Current
Voltage
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General Line Protection
Relay
A protective relayis an electromechanical apparatus, often with more than one coil,
designed to calculate operating conditions on an electrical circuit and trip circuit breakers when a
fault is detected. Unlike switching type relays with fixed and usually ill-defined operating
voltage thresholds and operating times, protective relays have well-established, selectable,
time/current (or other operating parameter) operating characteristics. Protection relays respond to
such conditions as over-current, over-voltage, reverse power flow, over- and under- frequency.
Distance relays trip for faults up to a certain distance away from a substation but not beyond that
point.
Objectives of Relay Protection
Protect persons and equipment in the surrounding of the power system. Protect apparatus in the power system. Separate faulty parts from the rest of the power system to facilitate the operation of the
healthy part of the system.
Types of Protective Relays
Overcurrent relay
An "overcurrent relay" is a type of protective relay which operates when the load current exceedsa preset value. The ANSI device number is 50 for an instantaneous overcurrent (IOC), 51 for atime over current (TOC). In a typical application the overcurrent relay is connected to a current
transformer and calibrated to operate at or above a specific current level. When the relay
operates, one or more contacts will operate and energize to trip (open) a circuit breaker.
Distance relay
The most common form of protection on high voltage transmission systems is distance relay
protection. Power lines have set impedance per kilometre and using this value and comparing
voltage and current the distance to a fault can be determined. The ANSI standard device number
for a distance relay is 21.
Current differential protection
Another common form of protection for apparatus such as transformers, generators, busses and
power lines is current differential. This type of protection works on the basic theory ofKirchhoff's current law which states that the sum of the currents entering and exiting a node will
equal zero. It is important to note the direction of the currents as well as the magnitude, as they
are vectors. It requires a set of current transformers (smaller transformers that transform currents
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down to a level which can be measured) at each end of the power line, or each side of the
transformer. The current protection relay then compares the currents and calculates the
difference between the two. As an example, a power line from one substationto another willhave a current differential relay at both substations which communicate with each other.
Static relays
Static relays with no or few moving parts became practical with the introduction of
the transistor. Static relays offer the advantage of higher sensitivity than purely
electromechanical relays, because power to operate output contacts is derived froma separate supply, not from the signal circuits. Static relays eliminated or reducedcontact bounce, and could provide fast operation, long life and low maintenance.
Numerical Protective Relays
The functions of electromechanical protection systems are now being replaced bymicroprocessor-based digital protective relays, sometimes called "numeric relays".
A microprocessor-based digital protection relay can replace the functions of many discrete
electromechanical instruments.
These convert voltage and currents to digital form and process the resulting measurements using
a microprocessor. The digital relay can emulate functions of many discrete electromechanical
relays in one device, simplifying protection design and maintenance. Each digital relay can run
self-test routines to confirm its readyness and alarm if a fault is detected. Numeric relays can also
provide functions such as communications (SCADA) interface, monitoring of contact inputs,metering, waveform analysis, and other useful features. Digital relays can, for example, store two
sets of protection parameters, which allows the behavior of the relay to be changed during
maintenance of attached equipment.
Basis of Classifications of Relays Quantity of response: Voltage, current, frequency, power etc. Function: Detection, time-delay, tripping, alarm, signaling, flag, contact multiplication Construction: Electromagnetic, Static or Numerical
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Transmission Line Protections
Distance Protection. SOTF. Over voltage Protection. VT Fuse fails. Power Swing Blocking. DEF Protection.
Transformer Protections
Differential Protection REF Protection Over flux protection Over current and Earth fault protection Mechanical Protections- PRV, Buchholz, WTI, OTI .
Bus Bar Protection
The Differential Current protection principle is used to protect the Bus Bars. Here thecurrent entering the bus and leaving the bus are summed up. The sum should be zero.
Bus Bar Scheme at Wardha S/sNumerical Distributed Bus Bar Scheme ( CU and PU)
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Testing in powergrid
FIELD TESTS
DEW POINT MEASUREMENT FOR LARGE TRANSFORMER FILLED WITH DRYAIR OR NITROGEN FILLED
WINDING RESISTANCE MEASUREMENT VECTOR GROUP AND POLARITY VOLTAGE RATIO TEST
MEASUREMENT OF MAGNETIZING CURRENT
MAGNETIC BALANCE TEST ON THREE PHASE TRANSFORMER INSULATION RESISTANCE MEASUREMENT MEASUREMENT OF CAPACITANCE AND DISSIPATION FACTOR
DISSOLVED GAS ANALYSIS ( DGA )
Pre Commissioning Tests
Polarity Test Magnetization Curve Test Ratio Test Primary Current Injection Test Secondary Current Injection Test
Trasformer oil testing
BDV( breakdown voltage) PPM(parts per million) Dissolved gas analysis Resistivity
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