Protection relays mainly work on the two basic principles such as; electromagnetic attraction and induction. 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. Product Specialist (West Region) for Digital Substation Products at ABB Inc. Currently residing in Denver, Colorado. An electrically operated switch like a relay plays a key role in controlling an electrical circuit through an independent low-power signal, otherwise used where a number of circuits should be controlled through the single signal. First, relays were used as signal repeaters within long-distance. This handbook covers the code of practice in protection circuitry including standard lead and device numbers, mode of connections at terminal strips, colour codes in multicore cables, dos and donts in execution.
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