An electrical protection system detects abnormal conditions and isolates the affected equipment before damage spreads. Instrument transformers or sensors provide current and voltage inputs. Protective relays evaluate those inputs, and circuit breakers or other interrupting devices clear the fault. Fuses combine fault sensing and interruption in one current-responsive device.
A protection scheme must balance sensitivity, selectivity, operating speed, dependability and security. Settings must detect faults inside the assigned zone without tripping for normal load, stable power swings or faults that another device should clear first. Overlapping zones, coordinated backup protection, tested trip circuits and maintained DC supplies reduce the chance of an unprotected fault.
