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PROTECTION SYSTEM & TESTING

August

Def: A COMPLETE ARRANGEMENT OF PROTECTION EQUIPMENT AND OTHER DEVICES REQUIRED TO ACHIEVE A SPECIFIED FUNCTION BASED ON A PROTECTION PRINCIPLE.

Need: WHEN EQUIPMENT FAILS, THE ENERGY IS RELEASED AND 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 power system 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 of insulation. Some other causes of fault conditions include: Mechanical failure Environment disturbances Excessive internal & external stresses Operating error Equipment malfunctionsThe 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 equipments and increase the stability of operation of healthy system.Sensitivity - ability to operate with low value of actuating quantities.Reliability - ability to operate under the faulty conditions only.

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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 least deterioration 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 fault conditions.

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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 constantly measuring 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 Protective System:-

1. Current Transformers or CT :- CT,s are required to scale down the

primery current to suitable level so that relay can use it. CT,s can be single core or multi core. Each core can be single ratio or multi-ratio. Separate cores are needed for metering or protection purposes. Normally secondary current is 1A or 5A as per requirement.

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2. Potential Transformers or Voltage Transformers or PT/ VT,s :-

PT,s are needed to scale down the Primery voltage to suitable level so that it is useful for the relay. Normally secondary voltage is 110 V or 110/√3 Volts 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 so that in all adverse operating conditions, it is available to the protective system to detect the faulty condition, and the relay could isolate the faulty system from the healthy system with the aid of circuit breakers.

Normally DC with battery chargers are used as reliable and steady auxiliary supply system.

Normally 12 V, 24 V, 48 V, 110 V or 220 V DC auxiliary supply system are used.

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4. Circuit Breakers:

Circuit breakers or CB,s are very much needed to operate the electrical circuits in all the operating conditions i.e. on no-Load, on Full-load.

CB are also required to isolate the faulty system from healthy system on receipt of command from the protective system in the shortest possible time.

CB status is also available to the protective system to properly take the decision of the fault.

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5.Precautions while developing/ studying schematics:

- All the schematics are made without any ac/dc supplies,

- All the pressure switches are in zero pressure state,

- All relays are in non-operating state and their contacts are in normal state,

- No current/ voltage from CT/ PT is available.

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Various types of Relays according to principle of operation are as follows:

1) Electromagnetic Attraction Relayi. Attracted armature type ii. Solenoid typeiii. 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

2) Electromagnetic Induction RelayThese relays operate on the principle of Induction motor and

are widely used for protective relaying purposes involving 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 structureb) Watt-hour meter structurec) Induction cup structure.

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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 and incorporate several protective/control/monitoring functions in one compact unit.

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MICROPROCESSOR based Numerical Relays: In 1980s, programmable static relays incorporating

Microprocessor have 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, separate Electromagnetic or Static units were used along with complex inter module wiring.

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A/D Convert

er

MICROPROCESSOR

Input Unit

Data Logger

Data Request &

Display

VT

CT CB

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 Operating Characteristics:-

-Instantaneous Relays,-Definite time delay relays,-Inverse definite minimum time

delay relays (IDMT),-Voltage restraint over current relay,

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Relays based on their uses:

1-Differential Protection Relay2.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, 24

8. Over/ under voltage Relay,9. Over-current Relay,10. Bus-bar Protection Relay,11. Breaker Failure Relay,12.Direction O/C & Directional E/F

Relays13.Over/ Under Frequency Relay,

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Other type devices used as Relays:

- Oil Temperature Relays,- Winding Temperature Relays,- Oil surge Relays (OSR),- Buchholtz Gas Relay,- Pressure Relief valves (PRV),- Pressure Switches,- Level Gauges,- Flow meters, etc

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The Protection scheme of Vishnuprayag Hydro Power Project(4x100MW) is classified as : Generator Protection Generator Transformer Protection Bus-bar Protection Bus Coupler protection Transmission Line Protection Shunt Reactor protection

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Generator/ Unit Protections Relay : 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 Faultvi. Reverse Power vii. Over Voltageviii. Loss of Excitationix. Balance Voltagex. Gen. Thermal Protection

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Main-II (GRP-2) Protection comprising :

i. Gen.-transformer Over all Differential ii. 95% Stator Earth Faultiii. Under Frequencyiv. Over Frequencyv. Under Voltagevi. Over Fluxvii. UAT Restricted Earth Fault viii. UAT Over Currentix. UAT Earth fault

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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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Details of LED Indications provided on GRP-1 (Main-I)

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Trip Logic of Protection scheme of 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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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 IDMT12 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/In0.2 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-0.91kΩ 1 sec

16 Under Impedance (21) 18 ESD 0.176 Un/ In 3 sec

17 Gen Differential (87 G) 17 ESDg setting = 0.10 In

v setting = 0.25Inst. 39

Unit Protection Settings

Main-2 Settings : ( GRP-2 Panel )

Sl.No.

ProtectionLED 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=0.01 As 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 In As per curve

14 95% Stator E/F(59/27) 24 ESD 0.05 Un 0.05 sec

15 Overall Differential (87 T) 25 ESDg setting = 0.20 In

v setting = 0.5Inst. 40

Generator Transformer Protection :

i. Differential Protectionii. Back-up Over Currentiii. Neutral Over Currentiv. Restricted Earth Faultv. Winding Temperature Highvi. Oil Temperature Highvii. Buchholz Gas Relayviii. Pressure Relief Valve

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Bus-Bar Protection & Breaker failure 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 will continue to function without any interruption.

- Breaker failure protection is provided to isolate 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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Single Line Diagram of Protection scheme of Bus Bar

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Bus-Coupler Protection Relay : 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 Impedanceii. Over Voltageiii. Back-up Over Currentiv. Back-up Earth faultv. Breaker Failure protectionvi. Auto-Reclosure Scheme

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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 Line Section + 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 Protection Relay : Model-REG316, Make-ABB

i. Differential Protectionii. Restricted Earth Faultiii. Back-up Impedance Protection, iv. Winding Temperature Highv. Oil Temperature Highvi. Buchholz Gas Relay protectionvii. Pressure Relief Valve

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Some Additional Features/ Schemes Used in Protective Circuits:

1.Trip Circuit Supervision Scheme: It is used to continuously monitor the tripping circuit & trip coil of circuit breakers,

2.Trip Coil supervision Scheme: It is used to continuously monitor the trip coil of the tripping relays,

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3.Pole discrepancy scheme : In single pole circuit breakers, If due to any reason, one or two poles of the CB trips, the remaining pole trips after a short time delay. Normally it is of the order of 0.8 to 1.0 sec. It may be with CB schematic or outside.

4. Auto-reclosing Scheme: On tripping of Line CB on Temporary line fault, the scheme provides auto Reclosure of Line CB after a pre-set short time delay.

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The scheme may be single phase auto-reclosing or three phase auto-reclosing or both.

Normally single phase auto-reclosing scheme are employed. Three phase auto-reclosing scheme are best suited for radial lines.

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5. Carrier Inter-tripping Schemes :-

Normally 80% of Principal Line Section is covered by Zone-1 of the Line protection, the rest of the 20% is covered 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 carrier inter-tripping schemes are used:-

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A. Permissive Under-reach carrier inter tripping Scheme,

B. Permissive Over-reach carrier inter tripping Scheme,

C. Carrier Blocking Scheme,D. Carrier Acceleration Scheme

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Testing of Protective Relays schemes

& Associated

Equipments.

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Testing of Current Transformers :

- Insulation Test 1. Primary winding to Earth by

5kV megger 2. Secondary winding to Earth (For

each core) by 250V or 500 V megger,

3. Primary winding to all the secondary winding by 5kV megger,

4. Core to core of secondary windings by 250V or 500 V megger,

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- Ratio Test of each core by Primary injection,

- 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

5kV megger after isolating from earth

2. Secondary winding to Earth (For each core) by 250V or 500 V megger,

3. Primary winding to all the secondary winding by 5kV megger,

4. Core to core of secondary windings by 250V or 500 V megger,

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- Ratio Test of each core by injecting voltage on Primary terminal and measuring voltages on secondary cores,

- Polarity Test of cores with reference to Primary Terminal,

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Primary Injection of CT,s:

- Primary injection of current transformers is carried out with the help of Primary Injection Test Kits. The current is measured in all the current circuits of all the phases one by one to ensure that during actual operation current will flow only in the correct phase and not otherwise,

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- During Primary injection we have to ensure that the current in metering circuit is flowing from the metering core only and current in protection circuit is flowing from the protection core only otherwise the protection is likely fail during fault conditions.

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Secondary Injection Of PT,s:

- Injection of Potential circuit is carried out with the help of Secondary Injection Test Kits or with the help of Single phase variac, Rheostat etc. The voltage is measured in all voltage circuits of all the phases one by one to ensure that during actual operation voltage will flow in the correct phase only and not otherwise,

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Checking of DC Schemes:

-The wiring of complete scheme is checked 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 on various settings with the help of Secondary Relay Testing Kit Like as Doble, Omricon, TURH, ZFB etc.

-The operating time of the relays is also measured to ensure the operation of relays 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 Breakers:

-Closing/ Opening operation of Circuit Breaker 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 are actuated one by one and their operation 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:After the system is energized, the

following checks are required to be carried 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

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- Operation of MW meter, PF meter, Energy meter etc and their running in proper direction,

- Trip circuit supervision in healthy state,

- Relays are measuring correct voltage & currents as per load condition.

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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

side6. Checking proper operation of

OLTC.

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Testing Of Reactors:

Following Tests are performed to Check the 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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