Primary Protection: It is the first protection line that detects the fault and quickly disables it. The secondary protection system provides a backup to the primary. The main purpose of a protection and control relay is to recognize any abnormal power system condition (s), or abnormally operating system component (s). This. Protective relays and devices have been developed over 100 years ago to provide “lastline”of defense for the electrical systems. Types of Protective Relays: Protective relays are categorized by their mechanism (electromagnetic, static, mechanical) and function. Generator protection covers: phase-to-phase short circuits in stator windings, stator ground faults, inter-turn short circuits in stator windings, external short circuits, symmetrical overload, stator overvoltage, single- and double-point grounding in the excitation circuit, and loss of excitation.
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