A protective relay is an automatic device that detects abnormalities in an electrical circuit and closes its contacts. This action completes the circuit breaker 's trip coil circuit, causing the breaker to trip and disconnect the faulty section from the healthy circuit. Engineering use: Relays are used on feeders, transformers, buses, motors, generators, and transmission lines to protect equipment and improve system. A relay is an electrically operated switch. The switch may have any number of contacts in multiple contact forms, such as make contacts, break contacts, or combinations thereof. Also principles of various protective relays and schemes including special protection. An electrical protection relay is an intermediate device that bridges the function of a current transformer or a similar fault-detecting device to one or more circuit breakers.
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