This type of relay is applicable to all parts of the power system and is often the primary choice for protection. 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. The selection and applications of. One of the main requirements to relay protection is the sensitivity requirement, which implies consistent tripping during the short circuit (s c) events in the protected zone. The sensitivity should be sufficient to ensure reliable protec-tion during s c at the end of its specified zone under. speed, sensitivity, dependability, security, and selectivity. The paper considers the use of various communications channels, including direct relay-to-relay fib r-optic channels and multiplexed digital fiber-optic networks. Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function. Both protective relays and monitoring relays may be sensitive to voltages, power or phase, current, or frequency. Most are not simple, electromechanical devices like a circuit breaker.