Protection System Protection system and its elements, functions of protective relaying, protective zones, primary and backup protection, desirable qualities of protective relaying, basic terminology. Relays : Electromagnetic, attracted and induction type relays, thermal relay, gas actuated relay, design considerations of electromagnetic relay. Relay Application and Characteristics Amplitude and phase comparators, over current relays, directional relays, distance relays, differential relay. Static Relays Comparison with electromagnetic relay, classification and their description, over current relays, directional relay, distance relays, differential relay. Protection of Transmission Line Over current protection, distance protection, pilot wire protection, carrier current protection, protection of bus, auto reclosing. Circuit Breaking Properties of arc, arc extinction theories, restriking voltage transient, current chopping, resistance switching, capacitive current interruption, short line interruption, circuit breaker ratings. Testing of Circuit Breaker Classification, testing station and equipments, testing procedure, direct and indirect testing. Apparatus Protection Protection of transformer, generator and motor. Circuit Breaker Operating modes, selection of circuit breakers constructional features and operation of Bulk Oil, Minimum Oil, Air Blast, SF6, Vacuum and d.c. circuit breakers.