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Transcript of electrical Protection Ppt
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Def: A COMPLETE ARRANGEMENT OF PROTECTIONEQUIPMENT AND OTHER DEVICES REQUIRED TO ACHIEVE A
SPECIFIED FUNCTION BASED ON A PROTECTION PRINCIPLE.
Need: WHEN EQUIPMENT FAILS, THE ENERGY IS RELEASEDAND EVERY COMPONENT IN THE SYSTEM IS AT RISK. THE
PROTECTIVE RELAYING SYSTEM MONITORS THE SYSTEM
AND INITIATE ACTION ACCORDINGLY.
What is Protection System ?
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Purpose of Protection System:
The protective relaying system senses the abnormal condition of powersystem and gives an alarm or isolates the defective system from the
healthy system.
A fault in an electrical system is defined as a defect in its electrical
circuit due to which the current is diverted from the intended path.
Faults are generally caused by breaking of conductors or failure ofinsulation. Some other causes of fault conditions include:
Mechanical failure
Environment disturbances
Excessive internal & external stresses
Operating error
Equipment malfunctions
The fault impedance being low, the fault current are relatively very
high and flows towards the fault.
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Requirements of Protection system:
Selectivity - ability to select the faulty part of in system &disconnect the faulty part without disturbing rest of the
healthy system.
Speed of Operation The faulty section should be isolated
as fast as possible to minimize the damage to equipmentsand increase the stability of operation of healthy system.
Sensitivity - ability to operate with low value of actuatingquantities.
Reliability - ability to operate under the faulty conditionsonly.
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Types of Protective equipment
FUSES
MINIATURE CIRCUIT BREAKERS (MCB)
PROTECTIVE RELAYS
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FUSES
A Fuse is a short piece of metal,
inserted in the circuit, which melts
when excessive current flows
through the circuit and thus breaks
the faulty circuit.
The fuse element is generally made of material having low
of low melting point, high conductivity and leastdeterioration due to oxidation, e.g. silver, copper etc. it is
inserted in series in the circuit to be protected.
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Classification of Fuses:
i. Low-voltage fuses
Semi-enclosed rewirable fuse
High rupturing capacity (HRC) cartridge fuse
HRC fuse with tripping device
ii. High-voltage fuses
Cartridge type Liquid type
Metal clad fuses
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Miniature Circuit Breakers (MCBs)
MCBs is a type of switch with thermal contacts. It can
open or close a circuit under all conditions viz. no load, full
load or fault conditions. It can be operated manually
under normal conditions and automatically under faultconditions.
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Protection Relay
A protection relay is a device that detects the fault and
initiates the operation of the circuit breaker to isolate the
defective system from the rest of the healthy system.
The relay detects the abnormal condition by constantlymeasuring the electrical quantities e.g. voltage, current,
frequency, phase angle, status of circuit breakers , etc.
In changes of one or more quantities, the relay senses the
faults, its type and location of the fault.
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Essential Requirements of ProtectiveSystem:-
1. Current Transformers or CT :-
CT,s are required to scale down theprimery current to suitable level so that
relay can use it. CT,s can be single coreor multi core. Each core can be singleratio or multi-ratio. Separate cores are
needed for metering or protectionpurposes. Normally secondary current is1A or 5A as per requirement.
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2. Potential Transformers or VoltageTransformers or PT/ VT,s :-
PT,s are needed to scale down thePrimery voltage to suitable level so that
it is useful for the relay. Normallysecondary voltage is 110 V or 110/3Volts as per requirement. PTs or VT,s
are of single or three phase system.
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3-Auxiliary AC or DC Supply:-
Reliable and steady auxiliary supply is needed sothat in all adverse operating conditions, it isavailable to the protective system to detect thefaulty condition, and the relay could isolate the
faulty system from the healthy system with theaid of circuit breakers.
Normally DC with battery chargers are used asreliable and steady auxiliary supply system.
Normally 12 V, 24 V, 48 V, 110 V or 220 V DCauxiliary supply system are used.
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4. Circuit Breakers:
Circuit breakers or CB,s are very much needed tooperate the electrical circuits in all the operatingconditions i.e. on no-Load, on Full-load.
CB are also required to isolate the faulty systemfrom healthy system on receipt of command fromthe protective system in the shortest possibletime.
CB status is also available to the protective systemto properly take the decision of the fault.
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5.Precautions while developing/ studyingschematics:
- All the schematics are made withoutany ac/dc supplies,
- All the pressure switches are in zeropressure state,
- All relays are in non-operating state andtheir contacts are in normal state,
- No current/ voltage from CT/ PT isavailable.
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Various types of Relays according to principleof operation are as follows:
1) Electromagnetic Attraction Relayi. Attracted armature type
ii. Solenoid type
iii. Balanced beam type
The relay operates by virtue of a plunger being attracted into a
solenoid or an armature being attracted towards the pole of
an electromagnet which in turn operates the associated
contacts bank. These types of relays may be operated by dc
or ac quantities like as voltage, current etc. Normally this
type of relays are used for supply status, CB status, Contact
multiplication etc. 16
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2) Electromagnetic Induction RelayThese relays operate on the principle of Induction motor and
are widely used for protective relaying purposesinvolving a.c. quantities. An Induction relay essentially
consists of a pivoted aluminium disc placed in two
alternating magnetic fields of same frequency but
displaced in time and space. The torque is produced in
the disc by the interaction of one of the magnetic fields
with the currents induced in the disc by the other.
In order to obtain the phase difference in the flux and hence
the operating torque, following three types of structures
are used:
a) Shaded-pole structure
b) Watt-hour meter structure
c) Induction cup structure.17
El t ti I d ti R l
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Electromagnetic Induction Relay
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STATIC RELAY
In Static Relays, the measurement is performed by
electronic/magnetic/optical or other components
without mechanical motion. Static relays have
versatile characteristics, offer low burden andincorporate several protective/control/monitoring
functions in one compact unit.
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MICROPROCESSOR based Numerical Relays:In 1980s, programmable static relays incorporating
Microprocessorhave been introduced.
A programmable protection & control system has a
Microprocessor or Microcomputer in its circuit. With
the help of the logic and the Microprocessor, the
integrated system can perform several functions of
Data acquisition, Data processing, Data transmission,
protection & control.
Earlier for each of these functions, separateElectromagnetic or Static units were used along with
complex inter module wiring.
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A/DConverter
MICROPROCESSORInput Unit
Data Logger
Data Request& Display
VT
CTCB
Trip coil
Block Diagram of a simple Microprocessor based Digital Static Relay
Setting
Input Unit
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Relay Based on actuating parameters
-Over-current Relays,
-Under/ Over voltage relays,
-Over/ under frequency relays,
-Power directional relays,
-Over-fluxing relays etc.
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Relays based on OperatingCharacteristics:-
-Instantaneous Relays,
-Definite time delay relays,
-Inverse definite minimum time delayrelays (IDMT),
-Voltage restraint over current relay,
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Relays based on their uses:
1-Differential Protection Relay
2.Restricted E/F Relay,
3.Distance Protection Relay,
4. Negative Phase Sequence Relay,
5. Neutral Over-current Relay,
6. Neutral Voltage Displacement Relay,
7. Over Fluxing Relay,
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8. Over/ under voltage Relay,
9. Over-current Relay,10. Bus-bar Protection Relay,
11. Breaker Failure Relay,
12.Direction O/C & Directional E/FRelays
13.Over/ Under Frequency Relay,
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The Protection scheme of Vishnuprayag
Hydro Power Project(4x100MW)isclassified as :
Generator Protection
Generator Transformer Protection
Bus-bar Protection
Bus Coupler protection
Transmission Line Protection
Shunt Reactor protection
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Generator/ Unit ProtectionsRelay : Model-REG216, Make-ABB
Main-I (GRP-1) Protection comprising :
i. Generator Differential
ii. Under Impedance
iii. Negative Phase Sequenceiv. Gen. Over Current (Inst. & IDMT type)
v. 100% Stator Earth Fault
vi. Reverse Power
vii. Over Voltageviii. Loss of Excitation
ix. Balance Voltage
x. Gen. Thermal Protection29
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Main-II (GRP-2) Protection comprising :
i. Gen.-transformer Over all Differential
ii. 95% Stator Earth Fault
iii. Under Frequency
iv. Over Frequency
v. Under Voltage
vi. Over Flux
vii. UAT Restricted Earth Fault
viii. UAT Over Current
ix. UAT Earth fault
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SingleLineDiagramo
fProtectionsc
hemeof
GeneratorU
nit
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SingleLineDiagramo
fProtectionsc
hemeof
GeneratorU
nit
Trip Logic of Protection scheme of GRP-1 (Main-I)
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Trip Logic of Protection scheme of GRP 1 (Main I)
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LED Indications provided on GRP 1 (Main I)
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LED Indications provided on GRP-1 (Main-I)
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Details of LED Indications provided on GRP-1 (Main-I)
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Details of LED Indications provided on GRP 1 (Main I)
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LED Indications provided on GRP 2 (Main II)
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LED Indications provided on GRP-2 (Main-II)
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Details of LED Indications provided on GRP-2 (Main-II)
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Details of LED Indications provided on GRP 2 (Main II)
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Unit Protection Settings
Main-1 Settings ( GRP-1 Panel )
Sl.No. ProtectionLED
No.Function Curve/Setting Time Delay
1 Over Voltage Stage-1 (59) 06 Alarm 1.15 Un 2.00 sec
2 Over Voltage Stage-2 (59) 23 ESD 1.25 Un Inst.
3 Under Voltage (27) 07 Alarm 0.70 Un 2.00 sec
4 Balance Voltage-1 (60) 05 Alarm 0.20 Un 0.04 sec
5 Balance Voltage-2 (60) 28 PSD 0.20 Un 1.00 sec
6 Inst. Over current (50) 21 ESD 1.60 Un 0.50 sec
7 Time Delayed Over Current (51) 22 ESD 1.30 In 2.00 sec8 UAT E/f Protn. (51) 31 PSD 5.00 In 0.02 sec
9 UAT O/C Protn (Inverse time) (51) 30 PSD IB =0.50 In, k=0.05 IDMT
10 Definite Time NPS-1 (46) 04 PSD I2 =0.05 In 5.00 sec
11 Inverse Time NPS-2 (46) 26 PSD IB =0.78 In IDMT
12 Reverse Power (32) 25 PSD -0.05 PN 3 sec
13 Loss of Excitation (40) 32 ESD XA = -1.11 Un/In
XB = -0.18 Un/In
0.2 sec
14 GT Restricted E/F Protn. (51 N) 29 ESD IB =0.10 In As per curve
15 100% Stator E/F(64 S) 24 ESDT/f ratio-50
REs-0.91k1 sec
16 Under Impedance (21) 18 ESD 0.176 Un/ In 3 sec
17 Gen Differential (87 G) 17 ESD g setting = 0.10 Inv setting = 0.25
Inst. 39
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Unit Protection Settings
Main-2 Settings : ( GRP-2 Panel )
Sl.No
.Protection
LED
No.Function Curve/Setting Time Delay
1 Over Voltage Stage-1 (59) 03 Alarm 1.15 Un 2.00 sec
2 Over Voltage Stage-2 (59) 17 ESD 1.25 Un 0.00 sec
3 Under Voltage Stage-1 (27) 04 Alarm 0.85 Un 10.0 sec
4 Under Voltage Stage-2 (27) 20 ESD 0.80 Un 3.20 sec
5 Over Frequency Stage-1 (81) 07 Alarm 52.0 Hz 1.00 sec
6 Over Frequency Stage-2 (81) 23 PSD 52.5 Hz 1.00 sec
7 Under Frequency Stage-1 (81) 06 Alarm 48.5 Hz 1.00 sec
8 Under Frequency Stage-2 (81) 22 PSD 47.0 Hz 2.00 sec
9 Over Fluxing Stage-1 (24) 05 Alarm 1.15 Un/fn 2.00 sec
10 Over Fluxing Stage-2 (24) 21 PSD 1.1 UB/fn 0.05 min
11 UAT Restricted E/F Protn. (51 N) 26 PSD IB =0.4 In, k=0.01As per curve
12 GT/F Time Delayed O/C (51) 27 ESD 1.3 In 3.00 sec
13 Gen. Trans. Neu. O/C (51 N) 18 PSD IB =0.30 InAs per curve
14 95% Stator E/F(59/27) 24 ESD 0.05 Un 0.05 sec
15 Overall Differential (87 T) 25 ESD
g setting = 0.20 In
v setting = 0.5 Inst. 40
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Generator TransformerProtection :
i. Differential Protection
ii. Back-up Over Current
iii. Neutral Over Current
iv. Restricted Earth Fault
v. Winding Temperature High
vi. Oil Temperature High
vii. Buchholz Gas Relayviii. Pressure Relief Valve
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Bus-Bar Protection & Breakerfailure Protection :Relay : Model-REB500, Make-ABB
-Bus bar protection is provided so that in case
of fault on any of the bus-bar, the faulty
bus will be isolated and other bus willcontinue to function without any
interruption.
- Breaker failure protection is provided toisolate the faulty breaker from the system,
in case CB fail to isolate the fault.
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The Central unit & Bay relay comprising of :
i. Bus bar Differential protection,
ii. Breaker Failure Protection (LBB)
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Bus-Coupler ProtectionRelay : Model-SPAJ140C, Make-ABB
Provided to trip the buscoupler CB in case
of over-loading of bus-coupler or fault
on any of the bus-bar
i . Over Current Protection,
ii. Earth Fault Protection
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Single Line Diagram of Protection scheme of Bus Coupler
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Trip Logic of Protection scheme of Bus Coupler
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Transmission Line Protections
Main-I (Relay-REL521), Main-II (Relay-REL316) &Back-up (Relay-REX521) protection comprises of
following functions :
i. Under Impedance
ii. Over Voltage
iii. Back-up Over Current
iv. Back-up Earth fault
v. Breaker Failure protectionvi. Auto-Reclosure Scheme
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Single Line Diagram of Protection scheme of Transmission Lines
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Single Line Diagram of Protection scheme of Transmission Lines
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Trip Logic of Protection scheme of Transmission Lines
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Setting Criterion of Line Protection:
1. Zone-1: 80% of Principal Line Section;
2. Zone-2: 100% of Principal Line Section+ 50% of the Adjoining Shortest Line
(check that Zone-2 > 120% of Principal
Line Section
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3. Zone-3: 1.2 x (100% of Principal LineSection + 100% of the Adjoining
longest Line )
4. Zone-4 : 1.2 x (100% of Principal Line
Section + Single T/F of remote end )
5. Reverse Zone: 25% of Zone-1
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Shunt Reactor ProtectionRelay : Model-REG316, Make-ABB
i. Differential Protection
ii. Restricted Earth Fault
iii. Back-up Impedance Protection,
iv. Winding Temperature High
v. Oil Temperature High
vi. Buchholz Gas Relay protection
vii.Pressure Relief Valve
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Some Additional Features/ SchemesUsed in Protective Circuits:
1.Trip Circuit Supervision Scheme: It isused to continuously monitor the
tripping circuit & trip coil of circuitbreakers,
2.Trip Coil supervision Scheme: It is used
to continuously monitor the trip coil ofthe tripping relays,
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3 Pole discrepancy scheme : In single
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3.Pole discrepancy scheme : In singlepole circuit breakers, If due to any
reason, one or two poles of the CBtrips, the remaining pole trips after ashort time delay. Normally it is of theorder of 0.8 to 1.0 sec. It may be with
CB schematic or outside.
4. Auto-reclosing Scheme: On tripping ofLine CB on Temporary line fault, the
scheme provides auto Reclosure of LineCB after a pre-set short time delay.
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The scheme may be single phase auto-
reclosing or three phase auto-reclosingor both.
Normally single phase auto-reclosing
scheme are employed. Three phaseauto-reclosing scheme are best suitedfor radial lines.
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5 C i I t t i i S h
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5. Carrier Inter-tripping Schemes :-
Normally 80% of Principal Line Section is
covered by Zone-1 of the Lineprotection, the rest of the 20% iscovered by Zone-2 protection with a
minimum delay of 0.4 sec.
To cover end 20% line fault in Zone-1
time also, Various carrier based carrierinter-tripping schemes are used:-
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A. Permissive Under-reach carrier intertripping Scheme,
B. Permissive Over-reach carrier intertripping Scheme,
C. Carrier Blocking Scheme,D. Carrier Acceleration Scheme
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Testing of ProtectiveRelays schemes&
Associated Equipments.
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Testing of Current Transformers :
- Insulation Test
1. Primary winding to Earth by 5kVmegger
2. Secondary winding to Earth (Foreach core) by 250V or 500 V megger,
3. Primary winding to all the secondarywinding by 5kV megger,
4. Core to core of secondary windingsby 250V or 500 V megger,
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R ti T t f h b P i
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- Ratio Test of each core by Primaryinjection,
- Polarity Test of cores,- Magnetizing Characteristics or knee
point voltage test for identifying
metering/ Protection cores
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Testing of Potential Transformers:
- Insulation Test
1. Primary winding to Earth by 5kVmegger after isolating from earth
2. Secondary winding to Earth (Foreach core) by 250V or 500 V megger,
3. Primary winding to all the secondarywinding by 5kV megger,
4. Core to core of secondary windingsby 250V or 500 V megger,
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- Ratio Test of each core by injectingvoltage on Primary terminal andmeasuring voltages on secondary cores,
- Polarity Test of cores with reference toPrimary Terminal,
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Primary Injection of CT,s:
- Primary injection of currenttransformers is carried out with the
help of Primary Injection Test Kits. Thecurrent is measured in all the currentcircuits of all the phases one by one toensure that during actual operationcurrent will flow only in the correctphase and not otherwise,
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- During Primary injection we have toensure that the current in metering circuitis flowing from the metering core only andcurrent in protection circuit is flowing fromthe protection core only otherwise theprotection is likely fail during faultconditions.
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Secondary Injection Of PT,s:
- Injection of Potential circuit is carriedout with the help of Secondary Injection
Test Kits or with the help of Singlephase variac, Rheostat etc. The voltageis measured in all voltage circuits of allthe phases one by one to ensure thatduring actual operation voltage will flowin the correct phase only and nototherwise,
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Checking of DC Schemes:
-The wiring of complete scheme ischecked and corrected according to
scheme.- Auxiliary DC supply is given to the panel
and DC supply is checked at various
points in the scheme/ Relays- The operation of DC relays checked as
per schematics.
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Testing Of Relays:
-All the relays are tested for operation onvarious settings with the help of
Secondary Relay Testing Kit Like asDoble, Omricon, TURH, ZFB etc.
-The operating time of the relays is also
measured to ensure the operation ofrelays within permissible limits.
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Power System Simulator (DOBLE Test Kit)
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Power System Simulator (DOBLE Test Kit)
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Closing/ Opening operation of Circuit
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Closing/ Opening operation of CircuitBreakers:
-Closing/ Opening operation of CircuitBreaker is checked from Control/Relay
Panels- Tripping of Circuit Breaker is checked by
operation of Protective Scheme with the
aid of secondary injection test Kit.
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Checking of Alarm & Indications:
- All the alarms & Indications areactuated one by one and theiroperation is checked/ ensured on the
panels.Checking of Stability of Relays :
- Check for the stability of Differential
Relays, Restricted Earth Fault Relays,Bus-bar protection Relays etc.
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On load checking the system:
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On load checking the system:
After the system is energized, the
following checks are required to becarried out :-
- Checking of DC auxiliary supply at
various points in the panels,- Checking of CT/ PT supplies to relays,
meters etc.,
- Checking of healthiness of relays- Checking of proper operation of
voltmeter/ Ampere meter in all the
phases 75
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- Operation of MW meter, PF meter,
Energy meter etc and their running inproper direction,
- Trip circuit supervision in healthy state,
- Relays are measuring correct voltage ¤ts as per load condition.
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Testing Of Transformers
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Testing Of TransformersFollowing Tests are performed to Check
the healthiness of Transformers:-1.Insulation Resistance- HV-E, LV-E, HV-
LV by 5KV/ 10KV Megger.
2. Turn ratio Test3. Open circuit Test from HV & LV side,
4. Short Circuit Test from HV to LV,
5. Magnetic Balance Test from Star side
6. Checking proper operation of OLTC.
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Testing Of Reactors:
Following Tests are performed to Checkthe healthiness of Reactors:-
1. Insulation Resistance- HV-E by 5KV/10KV Megger.
2. Open circuit Test from HV,
3. Magnetic Balance Test from HV
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