Instantaneous Overcurrent Protection (IOCP) is the fastest short-circuit protection scheme in power systems, but its limited reach necessitates coordination with other protections (e., TOC, OC) for complete system security. The selected protection principle affects the operating speed of the protection, which has a significant im-pact on the harm caused by short circuits. Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. Protection against high fault current. Definite time over. In Radial Distribution Systems, time-graded protection works well.