What measurement is crucial for a distance relay to function effectively?

For a distance relay to function effectively, the crucial measurement is the proportionality between voltage and current. This relationship is fundamental in determining the impedance of the line being monitored.

Distance relays operate based on the concept of impedance, which is the ratio of voltage to current. By measuring both voltage and current, the relay calculates the impedance of the line. If the calculated impedance falls within a predetermined setting, it indicates a fault condition, such as a short circuit, and the relay will take action, such as tripping the associated circuit breaker to isolate the fault.

This reliance on voltage and current measurements ensures that the relay can evaluate conditions in real-time and make decisions based on those evaluations to maintain system reliability and safety.