Based on Characteristic the protection relay can be categorized as: Instantaneous relays. Voltage restraint over current relay. Protective relays can be categorized based on their operating mechanisms into electromagnetic. Protective relays are power system protection devices that monitor current, voltage, frequency, impedance, or differential quantities and command circuit breakers when faults or abnormal conditions occur. Type of medias and network topologies in communications provide different opportunities to advance the speed, security, dependability, and sensitivity of protection relays.