Protection & Switchgear For the Protection of Power System and its Components

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

Protection zones:

Protection zones:

Types of protection Human Equipment Earthing Different Protection schemes Unit protection and Non-unit protection

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

Working Principle of pSP:

The protection team: Relays Circuit Breaker (CB) 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

Electrical Relays: Over-Voltage, Over-Current, Over-Frequency 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

unit Protection schemes: Generator protection Motor protection Transformer protection

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

Generator protection Differential protection (Merz-Price 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 Generator protection

A.C. Motor protection Phase to phase Phase to earth Inter-turn 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 A.C. Motor protection

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

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,

Definite time over current (50) & Inverse time over current (51) Basic protection principle

Over voltage (59) & under voltage (27) Voltage balance (Differential) Basic protection principle Basic protection principle

Uses both current and voltage to determine the zone of the fault Based on KVL Three phase system loops, RY,YB,BR, RG, YG, BG Phase comparator principle Phase and ground faults Distance relaying Basic protection principle

S1 = IR ZR – VR S2 = VR Distance relaying

Distance relaying

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

Busbar & transformer differential protection

Line differential protection

Device number identification 21 Z1 – Z4 : phase distance relay for zone 1 to 4 21N z1 – Z4 : ground distance relays for zone 1 to 4 50H : high set instantaneous over current relay 50 : instantaneous over current relay 62 : time delay for tripping 67N : directional relay in neutral SER/DFR : sequence of event recorder/ digital fault recorder Device number identification List box method and fill box method

Others: Bus bar protection Protection against over voltage due to lightning using LA Insulation coordination Earthing Travelling wave ralays

Thank you