MODELLING & SIMULATION OF DIFFERENTIAL RELAY FOR PROTECTION OF POWER TRANSFORMER

Abstract

Internal fault is the main problem in today’s power system instruments. A differential relay is used for power transformer, bus-bars and generators etc. Although this relay is not use-full for external faults but is most important use-full during internal faults in an instruments. These configuration uses in three phase. For current project, differential relay is designed for 250 MVA, 735/315KV power transformer. CTs are used on both side of transformer and on each phase on both sides. Although CTs are not available in simulation tool box, therefore a general single phase transformer with modifying its specifications according to current transformer is used. With help of CTs current on both side of transformer entering in relay is equal. In differential relay two types of coils is used one is operating coil and other are restraining coils. During no fault or external fault, current in operating coil is zero and during internal fault operating coils current above a certain limit so relay gives trip signal to circuit breaker. The simulation is carried out for various fault as L-G, LL-G, LLL-G. The circuit breaker separates faulty part of circuit from healthy circuit. This relay has developed in Matlab- Simulink environment