Primary side is the line current and secondary side is connected to the relay. Multiple relays can use the same CT. 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. The selection and applications of. Combines protection, sensors, control power, and circuit breaker in a single package Typically added to a breaker close circuit to prevent accidental reclosure after a trip. Three fundamental components required for each circuit breaker. So, if a fault happens on any line, it will be cleared by its relay and circuit. To introduce all kinds of circuit breakers and relays for protection of Generators, Transformers and feeder bus bars from Over voltages and other hazards. To understand the phenomenon of Over Voltages and its classification. Apply technology to. A zone of protection in electrical system protection refers to the area or segment of an electrical power system that is protected by a particular protective relay.