Power system protection

Power system protection detects abnormal electrical conditions and selectively disconnects affected equipment. It limits damage while keeping healthy parts of the electrical network in service.

Protective relay: A device that detects electrical abnormalities and issues commands to disconnect equipment. It turns measurements of a fault into a trip command.
Electrical fault: An abnormal condition in an electrical system that disrupts intended current flow or voltage. Protection schemes are designed around the faults that can occur on power networks.
Distance protection: A transmission-line protection method that estimates fault distance from measured voltage and current. It protects lines by tripping for faults within configured electrical reach zones.
Primary protection: The first protection scheme assigned to detect and clear faults in a defined system zone. It is intended to clear faults faster and more selectively than backup schemes.
Wide-area protection: Protection that uses measurements and communications across multiple parts of a power system. It extends decision-making beyond the local signals used by conventional schemes.
Circuit breaker: A switching device designed to interrupt current, including current flowing during a fault. It opens the circuit when a relay identifies equipment that must be isolated.
Short circuit: An unintended low-impedance connection between conductors at different electrical potentials. Short circuits produce large currents that commonly trigger protective devices.
Differential protection: A protection method that compares currents entering and leaving a defined equipment zone. A mismatch identifies internal faults in transformers, generators, buses, or lines.
Backup protection: A secondary protection scheme that clears a fault if primary protection or its breaker fails. It trades speed or selectivity for continued fault clearing when the primary path fails.
Phasor measurement unit: A device that measures synchronized voltage and current phasors using a common time reference. Synchronized measurements can support faster, system-wide protection logic.

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