Causes and Consequences of Dangerous Currents Faults, overloads and switching overcurrents. Introduction to protection, trip circuit of a circuit breaker. Functional characteristics of a relay, zone of protection, primary and backup protection. CTs & Pts Current transformer construction, measurement and protective CTs. Type of potential transformers. Steady state ratio and phase angle errors in CTs and PTs. Transient error in CT and CVT (Capacitive Voltage Transformer). Overcurrent Protection HRC fuse and thermal relay. Overcurrent (OC) relays- instantaneous, definite time, inverse time and inverse definite minimum time overcurrent relays, time and current gradings. Induction disc type relay. Directional overcurrent relay, 30o , 60o and 90o connections, Earth fault relay, Brief description of overcurrent protective schemes for a feeder , parallel feeder and ring mains. Generator Protection Stator protection - differential and percentage differential protection, protection against stator inter-turn faults, stator overheating protection, Rotor protection- protection against excitation and prime mover failure, field earth fault and unbalanced stator currents (negative sequence current protection) Transformer Protection Percentage differential protection, magnetizing inrush current,percentage differential relay with harmonic restraint. Buchholz relay. Differential protection of generator transfer unit. Busbar Protection Differential protection of busbars, high impedance relay scheme, frame leakage protection. Transmission Line Protection Distance protection. Construction, operating principle and characteristics of an electromagnetic impedance relay. Effect of arc resistance. Induction cup type reactance and mho relays. Comparison between impendance, reactance and mho relays. Three stepped distance protection of transmission line. Induction Motor Protection Various faults and abnormal operating conditions, unbalance supply voltage and single phasing. Protection of induction motors- HRC fuse and overcurrent, percentage differential, earth fault and negative sequence voltage relays.