Let's have a discussion on basic concept of protection system in power systemand coordination of protection relays. In the picture the basic connection of protection relay has been shown. It is quite simple. The secondary of current transfor. Let's have a discussion on basic concept of protection system in power systemand coordination of protection relays. In the picture the basic connection of protection relay has been shown. It is quite simple. The secondary of current transformer is connected to the current coil of relay and secondary of voltage transformer is connected to the voltag. The objective of power system protection is to quickly isolate a faulty section of the electrical power system, ensuring the rest of the system operates smoothly without significant damage from fault currents. Circuit breakers automatically isolate the faulty section from the healthy system by opening during a fault, triggered by a signal from a pr. ReliabilityThe most important requisite of protective relay is reliability. They remain inoperative for a long time before a fault occurs; but if a fault occurs, the relays must respond instantly and correctly.SelectivityThe relay must be operated in only those conditions for which relays are commissioned in the electrical powersystem. There may be some typical condition during fault for which some relays should not be operated or operated after some definite time delay hence protection relay must be sufficiently capable to select appropriate condition for which it would be operated.SwitchgearConsists of mainly bulk oil circuit breaker, minimum oil circuit breaker, SF6 circuit breaker, air blast circuit breaker and vacuum circuit breaker etc. Different operating mechanisms such as solenoid, spring, pneumatic, hydraulic etc. are employed in the circuit breaker. Circuit breakeris the main part of protection system in power system and it automatically isolate the faulty portion of the system by opening its contacts.Protective GearConsists of mainly power system protection relays like current relays, voltage relays, impedance relays, power relays, frequency relays, etc. based on operating paramete.