SWITCHGEAR AND PROTECTION

Circuit Breakers - 1 Elementary principles of arc interruption, Recovery, Restriking voltage and recovery voltages, Restriking phenomenon, Average and max. RRRV, Numerical problems, Current chopping and resistance switching, CB ratings and specifications : Types and Numerical problems, Auto reclosures. Circuit Breakers - 2 Description and operation of following types of circuit breakers : Minimum oil circuit breakers, Air blast circuit breakers, Vaccum and SF6 circuit breakers. Electromagnetic and Static Relays Principle of operation and construction of attracted armature, Balanced beam, Induction disc and induction cup relays. Relays classification : Instantaneous, DMT and IDMT types. Application of relays : Over current/Under voltage relays, Direction relays, Differential relays and percentage differential relays. Universal torque equation, Distance relays : Impedance, Reactance and mho and offset mho relays, Characteristics of distance relays and comparison. Static relays : Static relays versus electromagnetic relays. Generator Protection Protection of generators against stator faults, Rotor faults and abnormal conditions. Restricted earth fault and inter-turn fault protection, Numerical problems on % winding unprotected. Transformer Protection Protection of transformers : Percentage differential protection, Numerical problem on design of CTs ratio, Buchholtz relay protection. Feeder and Busbar Protection Protection of lines : Over current, Carrier current and three-zone distance relay protection using impedance relays, Translay relay. Protection of busbars - Differential protection. Neutral Grounding Grounded and ungrounded neutral systems - Effects of ungrounded neutral on system performance, Methods of neutral grounding : Solid, Resistance, Reactance-Arcing grounds and grounding practices. Protection against Overvoltages Generation of overvoltages in power systems, Protection against lightning overvoltages - Valve type and Zinc-Oxide lightning arresters, Insulation co-ordination-BIL, Impulse ratio, Standard impulse test wave, Volt-time characteristics.