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PROTECTION & SWITCHGEARFor the Protection of Power System and its Components

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FAULTS IN POWER SYSTEM:

Definition : ? Over voltage/Under voltage Over current

Over load, short circuit, Over frequency/Under frequency Phase imbalance/ Single phasing/

Sometimes opens in the circuit Mechanical faults

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PROTECTION ZONES:

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PROTECTION ZONES:

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TYPES OF PROTECTION

Human Earthing

Equipment Different Protection schemes

Unit protection and Non-unit protection

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CLASSIFICATION OF PROTECTION SCHEMES:

In unit type Differential Protection Carrier aided protection,

Non-unit type Over current, over/under voltage,

over/under frequency, distance protection

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WORKING PRINCIPLE OF PSP:

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THE PROTECTION TEAM:

Relays Electrical

Electromagnetic Static Numerical

Mechanical Pressure (Buchholz) Flow Thermal

Circuit Breaker (CB) Air break CB, MCB

(3.6 -12kV, 500 MVA) Bulk oil CB

(Upto 36 kV) Minimum Oil CB

(3.6 – 245 kV) Air blast CB

(145 – 1100 kV, 60 GVA) SF6 CB

(3.6 – 800 kV, 50 GVA Vacuum CB

(3.6 – 36 kV, 2 GVA) Solid state CB

Instrument Transformer

DC batteries

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ELECTRICAL RELAYS:

According to characteristic quantities and application can be classified as:

Over-Voltage, Over-Current, Over-Frequency Under-Voltage, Under-Frequency Directional Power Relay Differential Relay, Distance Relay

Reactance Relay, Impedance Relay, Mho Relay, offset Mho relay, Quadrilateral Relay

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UNIT PROTECTION SCHEMES:

Generator protection Motor protection Transformer protection

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GENERATOR PROTECTION

Generator Faults Stator winding faults

(phase to earth, phase to phase, inter-turn) Rotor circuit faults

Conductor to earth, inter-turn fault, rotor open circuit, loss of excitation, unbalance stator current

Abnormal operating condition Failure of prime mover, field failure, unbalance

loading, over voltage at generator terminal, over loading, over speed, ventilation failure

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GENERATOR PROTECTION

STATOR PROTECTION ROTOR FAULT PROTECTION

Differential protection(Merz-Price protection)(Biased differential protection)

Stator Inter-turn prot. Balanced earth fault

prot Stator over heating

prot. Negative sequence prot. Protection against

motoring

Rotor earth fault prot. Loss of Excitation prot. Auto. Field suppression Rotor overheating Rotor temp. alarm Vibration Protection Bearing overheating Over speed protection

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A.C. MOTOR PROTECTION

FAULTS : PROTECTION:

Phase to phase Phase to earth Inter-turn Prolonged overloading Stalling Unbalanced supply

voltage Single phasing Under voltage Reverse phase Loss of synchronism

Stator Over current Stator over heating Rotor over heating Under voltage Unbalanced and single

phasing Reverse phase Ammortisseur over

heating Loss of excitation Loss of synchronism Field winding over heating

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TRANSFORMER PROTECTION:

Buchholz protection Core balance leakage protection Combined leakage and overload protection Differential protection (Biased) Harmonic restraint relay Magnetic balance protection Restricted earth fault Frame leakage protection Generator transformer unit protection

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LINE & FEEDER PROTECTION

Over current and earth fault protection Time graded protection for

Radial, parallel and ring main feeder using directional power relay

Current graded protection Differential pilot wire protection Carrier current protection Distance protection

Impedance relay, reactance relay, Mho relay, offset Mho relay, quadrilateral relay,

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DEFINITE TIME OVER CURRENT (50) & INVERSE TIME OVER CURRENT (51)Basic protection principle

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OVER VOLTAGE (59) & UNDER VOLTAGE (27)

Basic protection principle

VOLTAGE BALANCE (DIFFERENTIAL)Basic protection principle

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DISTANCE RELAYINGBasic protection principle

Uses both current and voltage to determine the zone of the faultBased on KVLThree phase system loops, RY,YB,BR, RG, YG, BGPhase comparator principlePhase and ground faults

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DISTANCE RELAYING

S1 = IR ZR – VR

S2 = VR

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DISTANCE RELAYING

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DIFFERENTIAL PROTECTIONBasic protection principle

Based on KCL Used for protection of Generator, Motor, Transformer, Busbar, Transmission line, Reactor

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BUSBAR & TRANSFORMER DIFFERENTIAL PROTECTION

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LINE DIFFERENTIAL PROTECTION

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DEVICE NUMBER IDENTIFICATION

21 Z1 – Z4 : phase distance relay for zone 1 to 421N z1 – Z4 : ground distance relays for zone 1 to 450H : high set instantaneous over current relay50 : instantaneous over current relay62 : time delay for tripping67N : directional relay in neutralSER/DFR : sequence of event recorder/ digital fault recorder

List box method and fill box method

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OTHERS:

Bus bar protection Protection against over voltage due to

lightning using LA Insulation coordination Earthing Travelling wave ralays

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THANK YOU