Functional Features: Monitors voltage magnitude, frequency, and phase angle difference across a circuit breaker. It closes its output contact only when all three parameters are within preset limits.

Application Scenarios: Generator paralleling switchgear, bus tie breakers, and automatic transfer schemes.

Working Principle: Compares the sine waves of the two voltage sources. If the phase difference is less than the set “closing angle” and voltages/frequencies match, the relay permits the closing signal to pass.

Precautions: Incorrect CT/PT polarity will cause the relay to malfunction. Ensure the dead band and slip frequency settings are appropriate for the specific generator characteristics.