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. Definite time delay means that the protection operate time dose not change or depend on the. The latest generation of medium voltage (MV) protection relays provides a robust solution for upgrading electrical system safety. By detecting faults promptly and. Relay cabinets include microprocessors, control devices, and communication systems for monitoring network parameters, signaling abnormal conditions, and facilitating remote control and monitoring of circuit breakers and other components. Relay panels are enclosed or segregated metal structures that.