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 protective relays and their associated schemes shall achieve reliability, security, speed and properly coordinated. Protective Relays - Technical Seminar Nov 2016 - Copyright: IEEE 1 Power System Protective Relays: Principles & Practices Presenter: Rasheek Rifaat, P. For example, unselective protection operation during a medium voltage network fault will cause an outage for an unnecessarily large number of consumers. Based on simple examples of the generator-transformer unit protection from symmetrical short circuits, it was shown that the sensitivity factor is not a sufficiently objective measure of sensitivity of the. A protective relay is an intelligent electrical device designed to detect faults in power systems and initiate corrective actions such as tripping a circuit breaker. Its main purpose is to safeguard electrical equipment like transformers, generators, and transmission lines from damage due to. Engineering use: Relays are used on feeders, transformers, buses, motors, generators, and transmission lines to protect equipment and improve system reliability. What controls it: Relay performance depends on the protected zone, CT/PT inputs, pickup settings, time delay, breaker clearing time, trip.