Switchgear and Protection

PART - A Switches and Fuses : Isolating switch, Load breaking switch, Fuse law, Cut-off characteristics : Time current characteristics, Fuse material, HRC fuse, Liquid fuse, Application of fuse. Principles of Circuit Breakers : Principles of a.c. circuit breaking, Principles of d.c. circuit breaking, Problems encountered in d.c. breaking, Initiation of arc, Maintenance of arc, Arc interruption - high resistance and low resistance interruption, Arc interruption theories - Slepian's theory and energy balance theory, Restriking voltage, Recovery voltage, Rate of rise of restriking voltage, Current chopping, Capacitance switching, Resistance switching, Rating of circuit breakers. Circuits Breakers : Air circuit breakers - Air break and air blast circuit breakers, Oil circuit breakers - Single break, Double break, Minimum OCB SF6 breaker - Preparation of gas, Puffer and nonpuffer type of SF6 breakers. Vacuum Circuit Breakers : Construction, Principle of operation. Advantages and disadvantages of different types of circuit breakers, Testing of circuit breakers, Unit testing, Synthetic testing short circuit test layout. PART - B Protective Relaying : Requirement of protective relaying, Zones of protection, Primary and backup protection, Essential qualities of protective relaying, Classification of protective relays. Induction Type Relay : Nondirectional and directional overcurrent relays, IDMT and directional characteristics. Differential relay - Principles of operation, Percentage differential relay, Bias characteristics, Distance relay - Three stepped distance protection, Impedance relay, Reactance relay, Mho relay, Buchholz relay, Negative sequence relay, Microprocessor based overcurrent relay - Block diagram approach. Protection Schemes : Generator protection Merz price protection, Prime mover faults, Stator and rotor faults, Protection against abnormal conditions - Unbalanced loading, Loss of excitation, Over speeding. Transformer Protection - Differential protection, Differential relay with harmonic restraint, Inter turn faults induction motor protection - Protection against electrical faults such as phase fault, Ground fault and abnormal operating conditions such as single phasing, Phase reversal, Overload.