Facilities need to perform installation tests, implement preventive maintenance programs, and perform comprehensive commissioning tests to verify the integrity of both existing protective relay systems and new protection systems. Relion protection and control relays for several application reduce complexity. Long term cost reduction (TCO) for trainings and maintenance by reduce variety of relays A fast and selective arc fault mitigation for air-insulated LV & MV switchgear and Relion protection and control relays and sensor. Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. They are intended to quickly identify a fault and isolate it so the balance of the system continue to run under normal conditions. Also principles of various protective relays and schemes including special protection. In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. Although failure of a protective relay system may have severe local or regional impacts, most protective relay systems are not required to operate to prove they are in working order.