In, a protective relay is a device designed to trip a when a is detected. The first protective relays were electromagnetic devices, relying on coils operating on moving parts to provide detection of abnormal operating conditions such as over-current,, reverse flow, over-frequency, and under-frequency.
Optical Fiber, Copper, and Radio links are the main communication links used. Out of all that, optical fiber is a crucial technology in modern communication. All these technologies have their own pros and cons.