In electrical engineering, a protective relay is a relay device designed to trip a circuit breaker when a fault is detected. The rectangular devices are test connection blocks, used for testing and isolation of instrument transformer circuits. 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. A protective relay is an intelligent device that senses abnormal electrical conditions, such as overcurrent, under-voltage, or frequency deviations. Its main purpose is to safeguard electrical equipment like transformers, generators, and transmission lines from damage due to.