PROTECTION SWITCHGEAR For the Protection of Power System

PROTECTION & SWITCHGEAR For the Protection of Power System and its Components 1

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 2

PROTECTION ZONES: 3

PROTECTION ZONES: 4

TYPES OF PROTECTION � Human � Earthing � Equipment � Different � Unit Protection schemes protection and Non-unit protection 5

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 6

WORKING PRINCIPLE OF PSP: 7

THE PROTECTION TEAM: � Relays � � Electrical � Electromagnetic � Static � Numerical Mechanical � Pressure (Buchholz) � Flow � Thermal Instrument Transformer � DC batteries � � Circuit Breaker (CB) � � � � Air break CB, MCB (3. 6 -12 k. V, 500 MVA) Bulk oil CB (Upto 36 k. V) Minimum Oil CB (3. 6 – 245 k. V) Air blast CB (145 – 1100 k. V, 60 GVA) SF 6 CB (3. 6 – 800 k. V, 50 GVA Vacuum CB (3. 6 – 36 k. V, 2 GVA) Solid state CB 8

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 9

UNIT PROTECTION SCHEMES: � Generator protection � Motor protection � Transformer protection 10

GENERATOR PROTECTION � Generator � Stator winding faults � (phase � Faults 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 11

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 12

FAULTS : � � � � � Phase to phase Phase to earth Inter-turn Prolonged overloading Stalling Unbalanced supply voltage Single phasing Under voltage Reverse phase Loss of synchronism PROTECTION: � � � � � 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 13

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 � 14

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, 15

DEFINITE TIME OVER CURRENT (50) & INVERSE TIME OVER CURRENT (51) Basic protection principle 16

OVER VOLTAGE (59) & UNDER VOLTAGE (27) VOLTAGE BALANCE (DIFFERENTIAL) Basic protection principle 17

q. Uses both current and voltage to determine the zone of the fault q. Based on KVL q. Three phase system loops, RY, YB, BR, RG, YG, BG q. Phase comparator principle q. Phase and ground faults DISTANCE RELAYING Basic protection principle 18

S 1 = I R ZR – V R S 2 = V R DISTANCE RELAYING 19

DISTANCE RELAYING 20

Based on KCL q Used for protection of Generator, Motor, Transformer, Busbar, Transmission line, Reactor q DIFFERENTIAL PROTECTION Basic protection principle 21

BUSBAR & TRANSFORMER DIFFERENTIAL PROTECTION 22

LINE DIFFERENTIAL PROTECTION 23

21 Z 1 – Z 4 : phase distance relay for zone 1 to 4 21 N z 1 – Z 4 : ground distance relays for zone 1 to 4 50 H : high set instantaneous over current relay 50 : instantaneous over current relay 62 : time delay for tripping 67 N : directional relay in neutral SER/DFR : sequence of event recorder/ digital fault recorder DEVICE NUMBER IDENTIFICATION List box method and fill box method 24

OTHERS: Bus bar protection � Protection against over voltage due to lightning using LA � Insulation coordination � Earthing � Travelling wave ralays � � 25

THANK YOU 26