electrical protection ppt

7/29/2019 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

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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

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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. 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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- 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

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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 &currents 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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electrical protection ppt

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