Project report of transmission type eletrical substation
Transcript of Project report of transmission type eletrical substation
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Vocational Training
Report
Study of an transmittion type
electric sub-station
During
01- june 2013 to 30 june -
2013
At
csptcl 400/220/33 kv sub-
station, khedamara, bhilai (c.g.)
By shashikant sinha
6th sem, eee, ssitm, bhilai (c.g.)
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acknowledgement
Training work provides an intuitive for
students to utilize theoretical knowledge in
practical work .
I am thankful to Mr. M.K. Parmar, Executive
Engineer, for giving us permission to do training
in this sub-station.
I greatly acknowledge the hearty
cooperation of CSPTCL , KHEDAMARA ,
management, especially ..
Mr. Harish Kumar Dewangan ( Asstt. Engineer)
Mr. O.P. ( Asstt. Engineer)
Mr. Ashish Ratre ( Asstt. Engineer)
for their support and guidance whose work
has assisted in the preparation of our
report.
Above all we would like to acknowledge
our training in charge Mr. SUDHANSHU
TRIPATHI sir who checked our report work ,guided us and came to the rescue by
providing various hints about our report work
.
My friends have helped out along the way ,
by discussing ideas or reading chapters
I heartly offer my profound gratitude toall..
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Introduction
Before describing about the substation, we should have some knowledge that what a
substation do? Or simply what is substation?
Substation serves as a source of energy supply for the local areas of distribution in
which these are located. A substation is convenient place for installing synchronous
condensers at the end of the transmission lines for the purpose of improving power
factor and make measurement to check the operation of the various parts of the
power system.
Here, we discuss the 400/220/33 KV substation situated at Khedamara, Bhilai
(C.G.). This is basically a step down transmission substation which delivers bulk
power from power stations to load centers & large industrial consumers. Here,
regional load dispatch centre have been established for coordinating the activities of
state load dispatch centers. Here, we came to know that the voltage can be of 33,
220, 400 KV depending upon the length of transmission line and the amount of
electrical power to be transmitted.
The above referred substation is under Chhattisgarh State Power Transmission
Company Limited (CSPTCL) which is an undertaking unit of government of
Chhattisgarh.
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Single Line Diagram Of 400/220/33 KV substation
Khedamara, Bhilai (C.G.)
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Total Number Of Lines Incoming & Outgoing At The
Substation
Khedamara substation, Bhilai (C.G.), is a step down transmitting 400/220/33KV
substation type. Supply coming at 400 KV which is step down to 220 KV level and33 KV ( for internal substation supply ). In substation, two main buses are provided
for 400 KV side and two main buses and a single transfer bus is provided for 220
KV side. 400 KV and 220 KV lines are as follows :-
400 KV Lines :-
1) 400 KV PGCIL Raipur I
2) 400 KV Chandrapur
3) 400 KV Koradi
4) 400 KV Seoni
5) 400 KV Korba West ( Bilaspur ) Extension I
6) 400 KV BHATAPARA
7) 400 KV NTPC Korba I
8) 400 KV NTPC Korba II
9) 400 KV Raita
220 KV Lines:-
1) 220 KV BSP I
2) 220 KV BSP - II
3) 220 KV BRSS - I
4) 220 KV BRSS II
5) 220 KV PGCIL
6) 220 KV Urla
7) 220 KV Bemetara I
8) 220 KV Thelkadih - I
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Equipments Installed In Sub-Station
1) Power transformer
2) Current transformer
3) Potential Transformer
4) Capacitive Voltage Transformer
5) Lightening Arrestor
6) Circuit Breaker
7) Relay
8) Reactor
9) Bus-Bar
10) Wave Trap
11) Isolator
12) Insulator
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13) Battery & Battery Charger
14) Control Panel
15) Control Cables & Conductors
16) Power Line Carrier Communication
Power Transformer
A Transformer is a static electrical device that transfers energy by inductive
coupling between its winding circuits. An alternating current in the primary winding
creates a varying magnetic flux in the transformer's core and thus resulting in a
varying magnetic flux through the secondary winding. This varying magnetic
flux induces an alternating electromotive force (emf) orvoltage in the secondary
winding as output.
Power transformers are used for stepping up the voltage for transmission at
generating stations and for stepping down the voltage for further distribution at main
step down transformer substation. Usually naturally cooled, oil immersed cooling
techniques are used for 10MVA capacity transformers. The transformers of rating
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higher than 10MVA usually used blast air cooling method. For very high rating
transformers forced air cooling, watercooling and air blast cooling may be used.
At 400/220/33KV substation, Khedamara, Bhilai, total seven power
transformers were installed of which six 105MVA 1- auto transformers and one
315MVA 3- transformer in which OFAF cooling system had been installed.
Name Plate Details of 105MVA 1- Transformer
COMPANY BHELTYPE OF COOLING ONAN/ONAF/OFAFMVA RATING HV 42.0 / 63.0 /105MVA RATING IV 42.0 / 63.0 / 105MVA RATING LV 12.6 / 18.9 / 31.5
TEMPERATURE RISE OIL 50
TEMPERATURE RISE WINDING 55
NO LOAD VOLTAGE HV 400/
NO LOAD VOLTAGE IV220/ KV
Circuit Diagram of 105 MVA
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NO LOAD VOLTAGE LV 33KVLINE CURRENT HV (AMP) 181.9 / 272.8 / 454.7 ALINE CURRENT IV (AMP) 330.6 / 496.0 / 826.6 ALINE CURRENT LV (AMP) 381.8 / 572.7 / 954.5 A
INSULATION HV 1300KVpINSULATION IV 950KVpINSULATION LV 250KVp
FREQUENCY 50Hz
Name Plate Details of 315MVA 3- Transformer
COMPANY BHELTYPE OF COOLING ONAN/ONAF/OFAFMVA RATING HV 189.0 /252.0 / 315.0
MVA RATING LV 63.0 / 83.0 / 105.0TEMPERATURE RISE OIL 40
TEMPERATURE RISE WINDING 45
NO LOAD VOLTAGE HV 400
NO LOAD VOLTAGE IV 220 KVNO LOAD VOLTAGE LV 33 KV
LINE CURRENT HV (AMP) 454.8 A
LINE CURRENT IV (AMP) 826.6 ALINE CURRENT LV (AMP) 1837 A
INSULATION HV HVIS1050KVpLi1300KVpAC 38KVpINSULATION IV Li 950KVp AC 38KVpINSULATION LV Li 250KVp AC 38KVp
FREQUENCY 50Hz
Testing Of Power Transformer
Insulation Resistance Test
Insulation Resistance test is an essential type test. This test is carried out to
ensure the healthiness of overall insulation system of an electrical power
transformer.
o Procedure of Insulation Resistance test of transformer
First disconnect all the line and neutral terminals of the transformer. Megger leads to be connected to LV and HV bushing studs to measure
Insulation Resistance IR value in between the LV and HV windings.
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Megger leads to be connected to HV bushing studs and transformer tank earth
point to measure Insulation Resistance IR value in between the HV windings
and earth.
Megger leads to be connected to LV bushing studs and transformer tank earth
point to measure Insulation Resistance IR value in between the LV windings
and earth.
NB : It is unnecessary to perform insulation resistance test of transformer perphase wise in three phase transformer. IR values are taken between the windings
collectively as because all the windings on HV side are internally connected
together to form either star or delta and also all the windings on LV side are
internally connected together to form either star or delta.
Measurements are to be taken as follows:
For Auto Transformer: HV-IV to LV, HV-IV to E, LV to E For Two Winding Transformer: HV to LV, HV to E, LV to E
Three Winding Transformer: HV to IV, HV to LV, IV to LV, HV to E, IV to E, LV to E
Oil temperature should be noted at the time of insulation resistance test oftransformer. Since the IR value of transformer insulating oil may vary withtemperature.
IR values to be recorded at intervals of 15 seconds, 1 minute and 10 minutes. With
the duration of application of voltage, IR value increases. The increase in IR is anindication of dryness of insulation.
Polarization Index Test
It is a ratio of the insulation resistance taken of transformer for 60 sec to the
insulation resistance taken of transformer for 15 sec.
Ratio Test
Absor tion Coefficient =
Polarization Index=
Kab Absor tion Coefficient =
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This test can be done using a calibrated voltmeter, but it is preferable to do with a
special apparatus call ratio-meter.
This consists of a small portable transformer with a fixed primary, and a secondary
winding having a large no. of taps connected to two selector switches, one course
and the other fine so that any voltage desired could be obtained for direct reading.
The HV side of the transformer under test is connected to a LV main supply say 400
or 220 volt and the induced voltage on the secondary winding is compared with the
voltage output of the ratio meter, after insuring that the two voltages are in
opposition. Accurate readings are obtained by an ammeter connected between the
two winding so that the circulating current, due to the difference in the potential may
be detected. Ratio test should be conducted on every transformer, as any ratio error
detected in the winding may then be readily rectified. The permissible tolerance is 0.5 % of the declared ratio.
FIG:- Ratio test by using Selector Switch
L.V. WINDING OF Xmer
UNDER TEST
SUPPLY
H.V. WINDING OF
Xmer
UNDER TEST
FINE
GRADUATIONS
RATIO METER
TRANSFORMER
COARSE
GRADUATION A
V
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Short Circuit Test
In this short circuit test, the secondary winding is short circuited and rated secondary
current is circulated, the power input represents total I2R loss in primary plus
secondary winding and also stray losses. In this test the terminals of LV side are
short circuited by means of copper jumpers.
Three phase symmetrical adjustable low voltage is applied to HV winding. The
applied voltage is gradually increased till rated current are circulated via secondary
winding (supplied voltage = 5-10% of rated voltage because higher voltage will burn
the winding).
The measurement of primary voltage, primary current and power input, secondary
current are made during short circuit test. When rated current on secondary side the
input power represents total load loss. This is measured and is adjusted to standard
reference temperature say 75 .The total loss includes copper loss (I2R loss), a small
core loss(5 % of copper loss).
The total measured in this test is useful in determining the efficiency of power
transformer. This short circuit test reveals the various defects in the conducting
circuit ex- wrong transposition of conductors in the windings, breaks and fractures in
the parallel conductors, the use of conductors of wrong section, bad contacts etc.
z
Transform
erUnderTest
A2
A W
V
A1
Short
Circuit
HV LV
Variable
Voltage
Supply
Fig:- Short
circuit test of
1 Xmer
Fig:- Short circuit test
of 3- Xmer
3-
Transform
erUnder
Test
A
W
HV LV
Variable 3-
Reduced
Supply
Voltage W
V
V
HV
LV
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Current Transformer
A current transformer (CT) is used for measurement of alternating electric
currents in power supply line.
Current transformers, together with voltage transformers (VT) are knownas instrument transformers.
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 voltage in the monitored circuit.
Current transformers are commonly used in metering andprotective relays in
the electrical power industry.
Like any othertransformer, a current transformer has a primary winding, a magnetic
core, and a secondary winding. The alternating current flowing in the primary
produces an alternating magnetic field in the core, which then induces an alternating
current in the secondary winding circuit.
An essential objective of current transformer design is to ensure that the
primary and secondary circuits are efficiently coupled, so that the secondary current
bears an accurate relationship to the primary current. .A current transformer is
intended to operate normally with the rated current of the network flowing via the
primary winding which is inserted in series with network.
Name Plate Details of Current Transformer
COMPANY TELK HIGHEST SYSTEM VOLTAGE 420 KVRATED PRIMARY CURRENT 2000 A
RATIO 500-1000-2000/1 ASHORT TIME CURRENT 40 KA = Sec 1.0
FREQUENCY 50 HzINSULATION LEVEL KV 630/1425
SWITCHING IMPULSE VOLTAGE 1050 KVCORE NO. 1,2,4,5 PROTECTION
CORE NO. 3 METERING
Circuit Diagram of 420KV Current Transformer
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Burden on CT
The standard burden for voltage transformer is usually expressed in volt-amperes at
a specified power factor. The secondary load of a current transformer is usually
called the "burden" which is used to distinguish it from the load of the circuit whose
current is being measured. The burden, in a CT metering circuit is the
(largely resistive) impedance presented to its secondary winding. Burden refers to
the maximum load expressed in volt-amperes which may be applied across the
secondary terminal of CT in order to smoothly drive the load applied at secondary
terminal on current transformer.
Zb =
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Testing of Current Transformer (CT)
Polarity test
Each current transformer should be individually tested to verify that the polarity
marking on the primary and secondary windings are correct .The following figure
shows the test unit for this.
The ammeter A is a robust, moving coil,
permanent magnet centre zero type instrument. A
low voltage battery is used to energies the
primary windings through a single pole pushbutton. On closing the push button, with above
CT ammeter marking, the ammeter should give a
positive flick, indicating correct polarity of the
CT.
Primary Injection Test
This tets is carried out to ensure the CT ratio of current transformers. If this tets iscarried out after CT secondary wiring is completed it ensures not only the correct
ratio of CTs but also the correctness of the entire CT secondary wiring comprising
protection and metering portions.
The testing equipment consists of a loading (injection) transformer ,
controlled by a variable transformer to get the required current on the primary side of
the CT under test.
For carrying out the ratio test on CTs the following circuit is made use of.
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Secondary / Loop Resistance Test
Secondary resistance test is to verify the CT secondary winding resistance with
specified one and no discontinuity in the winding. This value can be used in other
calculations.
Burden test
Burden test is to ensure the connected burden to CT is within the rated burden,
identified on the nameplate.
Injected the rated secondary current of the CT, from CT terminals towards
load side by isolating the CT secondary with all connected load and observe the
voltage drop across the injection points. The burden VA can be calculated as
Magnetizing Curve Test
Magnetization Curve test is to confirm the magnetization characteristics of CT with
nameplate specification.
This test shall be conducted before ratio test and after secondary resistance and
polarity test, since residual magnetism left in the core due to DC test (polarity,
resistance), which leads additional error in ratio test.
The meters used for this test shall be having true RMS measurement.
The circuit connection shall be made as shown Figure. The primary should be openduring test.
Ohmmeter
Note-2
Ohmmeter
Note-1
Burden
P2
P1
S2
S1
Loop resistance to ensure load is connected properly
and circuits not left open. The circuit connection shall be
made for secondary resistance. Measure the dc resistance value
and record. The same shall be done for all taps and cores. These
values are influenced by temperature, so ambient temperature
must be recorded during this test. The circuit connection shall
be made as shown Figurefor loop resistance. Measure the dc
resistance including CT and load, phase by phase and values
can be compared between them.
Burden VA = Voltage drop * rated CT sec. Current.
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Demagnetization test
Before start the test demagnetize the core by Inject voltage on secondary terminals
and increase up to where considerable increment in current with small voltage
increment. Now start decreasing the voltage to zero, the rate at which increased.
Magnetization test
Now increase the voltage and monitor the excitation current up to the CT reaching
near to saturation point. Record the reading of voltage and current at several points.Plot the curve and evaluate the Vk and Img from the graph.
Turns Ratio Test
This test is to ensure the turns ratio of CT at all taps. The circuit connection shall be
made. The primary current of minimum of on primary side of CT with secondaries
shorted an measured and recorded for all cores.
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Potential Transformer
Potential Transformer orVoltage Transformer are used in electrical
power system for stepping down the system voltage to a safe value which can be fed
to low ratings meters and relays. Commercially available relays and meters used for
protection and metering, are designed for low voltage.There are three primary types
of voltage transformers (VT): electromagnetic, capacitor, and optical. Theelectromagnetic voltage transformer is a wire-wound transformer. The capacitor
voltage transformer uses a capacitance potential divider and is used at higher
voltages due to a lower cost than an electromagnetic VT. An optical voltage
transformer exploits the electrical properties of optical materials.
Primary winding of potential transformer are connected in parallel with the
main bus bar of the switchgear installation and to the secondary winding, various
indicating and metering instruments and relays are connected. When the rated high
voltage is applied to the primary of a PT the voltage of 110v appears across the
secondary winding. The ratio of the rated primary voltage to the rated secondary
voltage is known as turn or transformation ratio.
Fig-Circuit Diagram
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Name Plate Details of Potential Transformer
Normal system voltage 33 KVHighest system voltage 36 KV
Frequency 50 HzImpulse withstand voltage 170 KVp
Transformation ratio 150/5 A, 100/5 A, 50/5 A, 25/5 A
Rated output (VA burden) 15 VA
Burden of Potential Transformer
The standard burden for voltage transformer in secondary terminal is usually
expressed in volt-amperes at a specified power factor. The secondary load of a
potential transformer is usually called the "burden" which is used to distinguish it
from the load of the circuit whose voltage is being measured. The burden, in a PT
metering circuit is the (largely resistive) impedance presented to its secondary
winding. Burden refers to the maximum load expressed in volt-amperes which may
be applied across the secondary terminal of PT in order to smoothly drive the load
applied at secondary terminal on PT.
Testing of Voltage Transformer (PT)
IR values
For taking to earth value primary earth of terminal N is to be open while
in service it should be earth. The primary to earth IR value should be
taken by 5 KV range while secondary to earth value should be taken with
500V range.
Polarity Test
Zb =
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Polarity of potential transformer can be checked with the help of dry cell.
I n case of 220KV class PT deflection will be less hence we can check it
by giving voltage in secondary and connecting multi meter in secondary.
Ratio Test
Ratio of PT can be checked by application of single phase ac supply to
primary and measuring voltages in secondary.
Capacitor Voltage Transformer
A capacitor voltage transformer (CVT), orcapacitance coupled voltage
transformer (CCVT) is a transformerused inpower systems to step down extra
high voltage signals and provide a low voltage signal, for measurement or to operate
aprotective 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,
A transformerto isolate and further step down the voltage for the
instrumentation or protective relay. The tuning of the divider to the line
frequency makes the overall division ratio less sensitive to changes in the
burden of the connected metering or protection devices.
The CVT provides following two purposes :
1. It is used for metering and protection purpose i.e. it steps down the service high
voltage into low voltage which feeds the potential coil of metering instruments
with proper calibration and also informs the protective relays.
2. It also provides a path for high frequency power line carrier communication
current or signals so that speech and data can be transmitted and received.
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Name Plate Details of Capacitor Voltage Transformer
PRIMARY SYSTEM VOLTAGE400000/ V
SECONDARY OUTPUT VOLTAGE110/ V 110/ V 110/ V
SECONDARY TERMINAL 1a-1n 2a-2n 3a-3n1a-1n 2a-2n 3a-3n
RATED BURDEN (VA) 100 100 100
CLASS 3P 3P 0.2*Protection Metering
FREQUENCY 48-51 Hz 49.5-50.5Hz
TOTAL SIMULTANEOUS BURDEN 100VA
INSULATION LEVEL 630/1425 KVp
HIGHEST SYSTEM VOLTAGE 420KV
CIRCUIT CAPACITANCE VALUE Cn=8800pf ; C1=9313pf ; C2=160000pf
Note:- link-3 to be removed only when carrier protection is used.
Danger:- Earth Link-1 of primary terminal box & earth link-3 of secondaryterminal box must not be removed while 400KV terminal is alive.
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Lightening Arrestor
A lightning arrester is a device used on electrical powersystemsand telecommunications systems to protect the insulation and conductors of the
system from the damaging effects oflightning. The typical
lightning arrester has a high-voltage terminal and a ground
terminal. When a lightning surge travels along the power line to
the arrester, the current from the surge is diverted through the
arrestor and gets to the earth. It is connected between the line
and the earth but before the connected equipments in the
substation. At 440/220/33 KV substation , Zinc-oxide (ZnO)type lightning arrester has been installed.
Properties of Zinc-oxide :
1. ZnO has relatively large direct band gap of 3.3eV at room
temperature.
2. Due to large band gap it induces higher breakdown voltage.
3. It has the ability to sustain large electric fields.
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4. It has low electronic noise and high temperature and high power operation.
5. It exhibits piezo-electric characteristics in thin film form.
6. They are light sensitive and luminescent.
ZnO lightning arrester is mainly constitutes of zinc-oxide variastor. Each variastor
has its own switching voltage. When lightning strikes the LA, the variastor get
punctured and thus allow thundering and lightning to circulate current via variastor
inflow the earth.
ZnO VARIASTOR Variastor is a voltage dependent resistor. Below their
breakdown voltage they offer infinite resistance. Once their breakdown voltage
exceeds they allow the circulating current to pass through it by offering negligible
resistance path.
Name Plate Details of Zinc-Oxide Lightning Arrestor
SYSTEM VOLTAGE 420 KV
RATED VOLTAGE 390 KV
CURRENT 10 KApMCOV 303 KV
PR. RELIEF CURRENT 40 KA
Circuit Breaker
A circuit breaker is made to operate mainly on
two occasions:-
One is during the maintenance operation and the
other is during any abnormal condition in the
power system.
A circuit breaker is a mechanical device
designed to close or open contact members, thus
closing or opening an electrical circuit under
normal or abnormal conditions.
In the 400/220/33 KV substation,
KHEDAMARA, the circuit breaker used are:-
400 KV side SF6(sulphur hexafluoride) circuit breaker
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220 KV side SF6 (sulphur hexafluoride) & Minimum oil circuit breaker
(MOCB).
33 KV side SF6(sulphur hexafluoride) circuit breaker & vacuum circuit
Breaker (VCB).
Minimum oil Circuit Breakers (MOCB):
Minimum Oil Circuit Breakers Mainly Consists of:
Breaker Pole
Base frame
Operating mechanism
Support structures
These designs place the interrupting units in insulating chambers at live Potential.
Unit Ratings: Up to 245 KV : two interrupters per pole
Operating Mechanism:
The operating mechanism mainly consists of a set of closing springs to close the
breaker with the required speed, a spring charging motor for charging of the closing
springs, limit switch mainly to break and make the power supply to the motor
depending upon the position of the closing springs trip/close, coils to trip/close the
breaker, control panel, auxiliary switch, levers, set of catches blocking devices etc.
for the effective and accurate functioning.
Working Principle or arc quenching in minimum oil circuitbreaker:
Working Principle of minimum oil circuit breaker orarc quenching in minimum
oil circuit breaker is described below. In a minimum oil circuit breaker, the arc
drawn across the current carrying contacts is contained inside the arcing chamber.
Hence the hydrogen bubble formed by the vaporized oil is trapped inside the
chamber. As the contacts continue to move, after its certain travel an exit vent
becomes available for exhausting the trapped hydrogen gas. There are two different
types of arcing chamber is available in terms of venting are provided in the arcing
chambers. One is axial venting and other is radial venting. In axial venting, gases
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(mostly Hydrogen), produced due to vaporization of oil and decomposition of oil
during arc, will sweep the arc in axial or longitudinal direction
SF6 Gas Circuit
Breakers :-
A circuit breaker in which
the contacts open and close in
SF6 media. Sulphur
hexafluoride (SF6) gas is an
alternative to air as an
interrupting medium. SF6 is a
colour less nontoxic gas, with
good thermal conductivity and
density approximately five
times that of air. SF6 is
chemically inert up to
temperature of 1500C and will
not react with metals, plastics,
and other materials commonly
used in the construction of
high voltage circuit breakers.
Available up to 800KV and
above. Most suitable for metal
clad and hybrid HV
substations.
Single Interrupter: 245 KV
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SF6 Circuit Breaker Name-Plate Details
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Company AREVAType GL316 with CR
Rated Voltage 420 KVFrequency 50 HZ
Power frequency withstand voltage
Open contacts 610 KVrmsTo earth 520 KVrms
Lighting impulse withstand voltage 1425KVpSwitching surge withstand voltage 1050KVp
Rated Short circuit Breaking CurrentSymmetrical 50 KA
Asymmetrical 61.2KARated Making Capacity 100 KA
Rated duration of short Circuit current time 3 S
Total Break Time 50 mSTotal Make time 160 Ms
Rated out of phase current 10 KALine charging breaking current 600A
First pole to clear factor 1.3Rated supply voltage
DC 220 VOperation Sequence O 0.3s CO
3min CO
AC 415 VRated SF6 Gas pressure at 20o C 6 Kgf/cm2
Rated air pressure 15 Kgf/cm2
Normal current 3150 AImpulse Level 1425 KVp
Year of Manufacture 2008
Relay
The relay is a protective device interposed between the main circuit and the
circuit breaker in such a manner that any abnormality in the circuit acts on the
relay, which in turn, if abnormality is of a dangerous character, causes breaker toopen and so to isolate the faulty element . The protective relay insures the safety
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of the circuit equipment from any damage which might otherwise caused by the
fault. Relays have three essential elements as illustrated below.
Sensing element
It is also called measuring element, it responds to the change in the actuatingquantity, The current in a protected system in case of over current relay.
Comparing element
It serves to compare the action of the actuating quantity on the relay with a
preselected relay setting.
Control Element
On a pickup of the relay, it accomplishes a sudden change in the control quantity
such as closing of the operative current circuit
Reactor
Trip Coil
Fault
A
Circuit to
be
protected
Trip
Circuit
Relay
contact
Relay Coil
Battery
Busbar
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A Reactor is a coil having large inductive reactance in comparison to its ohmic
resistance. Reactors for
power systems in general
use and for industrial use
in particular exist as two
distinct functional types
series reactors for
fault-current limitation
and shunt reactors, either
for reactive
compensation and as two
construction types: air-
core air-insulated types
and liquid-insulated iron-
core types.
Reactors are used in combination with shunt capacitors to form harmonic filters or to
detune reactive compensation capacitor banks.
A shunt reactor is a reactor that is connected between the phase conductor and
neutral (or ground). A series reactor is connected in series with the phase conductor.
In this 400/220/33 KV sub-station, KHEDAMARA, only shunt reactors are installed.
Shunt Reactor
For Extra high voltage (EHV)
transmission lines, due to long
distance, the space between the
overhead line and the groundnaturally forms a capacitor parallel
to the transmission line , which
causes an increase of voltage along
the distance.
A shunt reactor is a reactor that is
connected between the phase
conductor and neutral (or ground).
Shunt reactors are installed to
offset the capacitive effect of transmission lines and thereby stabilizing the system
voltage within acceptable limits.
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Name Plate Details Of Shunt Reactor
50000 KVAR 50 Hz TYPE Air Core SSLR
3 Phase
S-S653/IEC-
289
Type of
cooling ONAN
Rated Voltage 420000 V
Rated Current 68.7 A Continuous Rating
Basic Insulation Oil Capacity
Line Neutral Power Frequency 630 KV
Lightning Impulse 1425KV 550 KV Radiator unit 4000 L
Switching Impulse 1080
KV
----
DATE MARCH 1982Power Frequency 630KV
230 KV
Impedance Weights
Positive Sequence 3460
Shield & Winding 58200 Kg
Tank & Fittings 23300 Kg
Zero Sequence 3460
Radiator Unit 10900 Kg
Oil 26100 Kg
Total 118500 Kg
Maximum Temperature Rise Up Tanking WeightOIL 4.5
at 441 KV
UPPER TANK 8500 Kg
WINDING 5.0 MIDDLE
TANK
5000 Kg
Up Tank Height
Upper tank 7900 mmMiddle tank 6600 mm
Bus-Bars
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Bus bar term is used for a main bar or conductor carrying an electric current to
which many connections can be made.
Bus bars are merely convenient means of connecting switches and other
equipment into various arrangements. The usual arrangement of connections in most
of the substation permits working on almost any piece of equipment withoutinterruption to incoming or outgoing feeders.
In some arrangements two buses are provided to which the incoming or
outgoing feeders and the principal equipment may be connected.
One bus is usually called the main bus and the other auxiliary or transfer bus .
Bus bar arrangement in CSPTCL 400/220/33 KV substation, KHEDAMARA:
220 KV BUS BAR ARRANGEMENT:-
Here the 220 kv bus arrangement Scheme is DOUBLE MAIN AND TRANSFER
BUS.
This is combination of MAIN AND TRNASFER BUS BAR SCHEME
and DUPLICATE BUS BAR SCHEME.
In this scheme loads are distributed on the two buses each with its own
transformer feed for normal operation, so that one bus fault will not cause a
complete outage of the station.
400 KV side-
2 Main buses :-
Main Bus 1
Main Bus 2
220 KVside-
2 Main bus & 1 Transfer bus
Main Bus 1
Main Bus 2
TRANSF
ER BUS
BUS-1
BUS-2
CBISOLATO
R
BUS COUPLER
CB
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Wave Trap
A wave trap is a parallel resonant circuit (inductor-capacitor tank circuit )
installed on the power line at local
substation. It is tuned to resonate at a
specific frequency or frequencies. These
frequencies are equivalent to the
transmission frequencies of the local
power line carrier transreciever.
This is relevant in power line carrier
communication.
Properly tuned, the wave trap shows its
highest magnitude of impedance (Z) at these carrier frequencies (105 KHZ and
above) , while permitting the 50 Hz power frequency to pass.
Wave trap is also known as line trap. A wave
trap traps the high frequency communication
signals sent on the line from the remote
substation and diverting them to thetelecom/teleportation panel in the substation
control room (through coupling capacitor &
LMU).
If wave traps are absent, the signal loss is more
& communication will be ineffective.
TUNING CIRCUITTYPE BBT Main Coil Inductance 1.0 mHNr. T 1676 Frequency Band 70/220 KHzWeight 9 Kg Protective Level(BIL) 140 KV
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Isolator
Circuit breaker always trip the circuit but open contacts of breaker cannot
be visible physically from outside of the breaker and that is why it is recommended
not to touch any electrical circuit just by switching off the circuit breaker. So for
better safety there must be some arrangement so that one can see open condition of
the section of the circuit before touching it. Such an apparatus is the isolating switch
(or isolator).
Isolator is a mechanical switch which isolates a part of circuit from system
as when required. Electrical isolators separate a part of the system from rest for safe
maintenance works.
So definition of isolator can be rewritten as, Isolator is a manually operated
mechanical switch which separates a part of the electrical power system normally at
off load condition.
Types of Electrical Isolators:
There are different types of isolators available depending upon system requirement
viz
As no arc quenching technique is provided in isolator it must be operated when there
is no chance of current flowing through the circuit. No live circuit should be closed
or open by isolator operation.
For voltages up to 145KV system, hand operated isolators are used whereas for
higher voltage systems like 245 KV or 420 KV and above motorized isolators are
used.
Constructional features of Double Break Isolators:-
These have three stacks of post insulators .The central post insulator carries a tubular
or flat male contact which can be rotated horizontally with rotation of central post
insulator. This rod type contact is also called moving contact.
The female type contacts are fixed on the top of the other post insulators which
fitted at both sides of the central post insulator. The female contacts are generally inthe form of spring loaded figure contacts. The rotational movement of male contact
causes to come itself into female contacts and isolators becomes closed. The rotation
Double Break Isolator, Centre Break Isolator, Pantograph type Isolator
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of male contact in opposite direction make to it out from female contacts and
isolators becomes open.
Rotation of the central post insulator is done by a driving lever mechanism at the
base of the post insulator and it connected to operating handle (in case of hand
operation) or motor (in case of motorized operation) of the isolator through amechanical tie rod.
Constructional features of Single Break Isolators:-
The contact arm is divided
into two parts one carries male
contact and other female contact.The contact arm moves due to
rotation of the post insulator upon
which the contact arms are fitted.
Rotation of both post insulators
stacks in opposite to each other
causes to close the isolator by
closing the contact arm. Counter
rotation of both post insulators
stacks open the contact arm and
isolator becomes in off condition. This motorized form of this type of isolators is
generally used but emergency hand driven mechanism is also provided.
Insulator
Over head electrical conductors used for transmitting electric power is mostly bare
and not covered with any insulation medium. The bare
line conductors are connected to the transmission
towers through the insulators. Insulators act as
insulating medium for flow of leakage current from
conductor to ground through tower structures. Some of
the insulating materials are Porcelain, Glass and
Steatite materials.
The porcelain insulators employed in substations are of
the post and bushing type. They serve as supports and insulation of the bus bars.
Female Contact ofIsolatorFemale Contact ofIsolator
Male Contact ofIsolatorMale Contact ofIsolator
MaleContact ofIsolator
MaleContact ofIsolator
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A post insulator consists of porcelain body, cast iron cap and flanged iron base. The
hole in the cap is threaded so that the bus-bars are either directly bolted to the cap or
fixed by means of bus-bars clamp. Post insulators are available with round oval and
square flanged bases for fixing with aid of one, two or four bolts. Each base in
addition also has an earthing bolt.
A bushing insulator consists of porcelain shell body, upper and lower locating
washers used for fixing the position of bus bar or rod in shell , and mounting flange
with holes drilled for fixing bolts and supplied with an earthing bolt.
For the current rating above 2000 A, the bushings are designed to allow the main
bus-bars to be passed directly through them.
Batteries
All power plants and substations
require DC supply for protection
and control purposes and DC
supply is obtained from
secondary or storage batteries.
Storage batteries are of two types
namely lead acid and alkaline
batteries. Lead acid batteries aremost commonly used in power
stations and substations because
of their higher cell voltage and
lower cost.
Battery Chargers
As the name says battery chargers are used tocharge the storage batteries in the substation.The
interruption of DC supply to load cannot be
afforded in any circumstances so battery chargers
are employed for keeping the storage batteries
charged. Mainly there are two types of battery
chargers according to their usage :-
(i) Float Charger (ii) Boost
Charger
Float Charger
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Float charger is static type comprising of Silicon Controlled Rectifiers (SCR)
connected in three phase banks along with other necessary circuit to supply a
stabilized DC out-put. Provision is made to have step less and smooth voltage setting
in the auto mode and also for adjustment in manual mode in case the automatic
constant voltage controller fails.
Float charger have built in current limiting feature to droop the output voltage on
currents more than 100% of the rated current and it is ensured that the output voltage
of the charger across battery terminals remains below 2 Volt/cell if output current is
125% or more of the rated current.
Boost Charger
Boost charger have
adequate rating to quick
charge the battery fully
within 14 hrs. after an
emergency during
which complete DC
load is met by thebattery. Current rating
of Boost charger is
20Amps for 200AH and
30 amps for 300AH
battery sets .
Boost charger
incorporate static
components, comprising
of SCRs with
semiconductor fuses
and trip indication as in
float charger. Boost
charger, apart from its
normal constant current
operation, is also
capable of constant
voltage operation which
enables it to operate as a
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float charger delivering stabilized DC output voltage within +/- 1% from no-load to
full load. In case of float charger failure, suitable electrical circuitry is provided for
this purpose.
In the constant current mode, it has a current stability of +/- 2% of the set value.
Constant current setting have step-less range from 20% to 100% of full rate current.
Further, the boost charger has a provision of manual mode of operation.
Control Room
The
control
room is
the
nervecentre of
a
substation. The various controls performed form here are the voltage adjustment,load control, emergency tripping, etc. And the equipments and the instruments
housed in a control room are synchronizing equipment, voltage regulators, relays,Fig:- A view of control room of 400 KV substation, Khedamara Bhilai (C .G.)
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ammeter, voltmeters, wattmeter, kWh meters, kVARh meters, temperature gauges,
water level indicators and other appliances, as well as a mimic diagram and suitable
indicating equipment to show the opened or closed position of circuit breaker,
isolators, etc.
The location of control room in relation to other sections is also important. It shouldbe located away from the sources of noise and it should be near to the switch house
so as to save control cables used for interconnection. The control room should be
neat and clean and well ventilated, well lighted, and free from draughts. The
instruments should have scales clearly marked and properly calibrated and all the
apparatus and circuits should be labelled so that they are clearly visible.
Control Cables and conductors
The control cables and conduit
system is required for affecting
automatic controls. The controlsystem generally operates at 110 or
220 volts and the cables
employed for this purpose are
multi core cables having 2
core, 4 core, 10 core, 12 core,14
core,19 core.
The conductors are of various types but for transmission purposes ACSR
(Aluminum Conductor Steel Reinforced ) & AAAC ( All Aluminum Alloy
Conductors ) are used as they are ideal for long distance transmission of power
without major losses.
The conductors inside the control cables are categorized by the name of animals on
the scale of the maximum amount of current they can withheld. So different
conductors with their current rating are:-
Serial No. Conductor Current ( in Amperes )1. Moose Conductor 850
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2. Zebra Conductor 740
3. Panther Conductor 510
4. Dog Conductor 254
5. Racoon Conductor 197
6. Rabbit Conductor 148
7. Squirrel Conductor 100
Mainly moose conductor are used in 400 KV side, zebra conductor are used in
220 KV side, panther conductor are used in 132 KV side and dog conductor
are used in 33KV side.
In 400 KV substation, Khedamara, ACSR moose conductors are used
Power Line Carrier Communication
Coupling devices are used for isolation of carrier equipment from higher
tension voltage system and to provide a low impedance path for carrier
frequency. Generally CVTs are used with LMU.
Wave traps are used to confine the carrier signals between two carrier
equipments located at the respective substation and to provide high impedance
to carrier frequency. Rated for full current.
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Testing Of Transformer Oil
Breakdown Voltage Test
(BDV Test)
To assess the insulating property of
dielectric transformer oil, a sample of
the transformer oil is taken and
its breakdown voltage is measured.
The transformer oil is filled in the
vessel of the testing device. Two
standard-compliant test electrodes
with a typical clearance of 2.5 mm
are surrounded by the dielectric oil.
A test voltage is applied to the electrodes and is continuously increased up
to the breakdown voltage with a constant, standard-compliant slew rate of e.g. 2
kV/s.
At a certain voltage level breakdown occures in an electric arc, leading to a
collapse of the test voltage.
An instant after ignition of the arc, the test voltage is switched off
automatically by the testing device. Ultra fast switch off is highly desirable, as the
carbonisation due to the electric arc must be limited to keep the additional pollution
as low as possible.
The transformer oil testing device measures and reports the root mean
square value of the breakdown voltage.
After the transformer oil test is completed, the insultaion oil is stirred
automatically and the test sequence is performed repeatedly. (Typically 5
Repetitions, depending on the standard)
As a result the breakdown voltage is calculated as mean value of the
individual measurements.
Conclusion: The lower the resulting breakdown voltage, the poorer the quality of
the transformer oil.
PPM test (Karl Fisher Test)
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The instrument used for this purpose in 400 KV substation, Khedamara is MKC-520.
The MKC-520 is a Karl Fisher Coulometric Titrator, by which we can measure
micro amount of water content which exists in liquid or in solid sample material. The
measurement is easy to perform, fast in operation with its results of higher precision
and accuracy.
Principle Of Measurement
In the Karl Fisher content measurement, water
reacts with iodine and sulphur dioxide in
presence of base and alcohal.
H2O + I2 + SO2 + CH3OH + 3RN
[RNH]SO4CH3 + 2[RNH]I ------------------(1)
In the volumetric titration, iodine is added as a
titrant. In the coulometric technique, iodine is
electrolytically generated in the anolyte, which
contains iodide.
2I- I2 + 2e- ---------------------------(2)
As long as water is present in the titration cell the generated iodine reacts according
to (1). As soon as all the water reacts, excess of iodine appears in the anolyte. This
iodine is detected by the
platinum elcetrode and the iodine
production is stopped. Accordingto the Faradays law, the quantity
of iodine produced is
proportional to the current
generated. In equation (1), I2 and
H2O react with each other in 1:1
proportion.
Therefore a mole of water (18g)
is equivalent to 2 x 96500
coulombs/ 1 mg of H2O. The
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total amount of moisture can thus be determined by measuring the total consumption
of eletricity.
of Transform
Maintenance of Isolator
Procedure for Replacing selection of 220 KV Selection isolator of
315 MVA ICT-2 due to red-hot state
Code taken from State load despatch centre (SLDC).
LT load of station transformer-2shifted to station transformer no.1
LT breaker of station transformer-2 switched off.
33KV side breaker switched off.
220KV side breaker of 315 MVA ICT-2switched off.
400KV main breaker and tie breaker switched off.
220KV side line isolator made open.
400KV side selection isolators are also made open.
33KV side isolator of 105 MVAunit 5,6 and 7 open.
33KV side isolator of 33/0.4KV station transformer no-2 made open.
Isolator of 33KV PT also opens.
Permit taken.
Discharge is connected to 400 KV and 220KV side.
After job has been finished the discharge is disconnected from 400KV and
220KV side.
Permit is returned.
All isolators of 400KV, 220KV, 33KV are again connected.
Again code taken from load dispatch centre to charge the transformer.
Charging is done to the transformer from 400KV side then 220KV side
then 33KV side.
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