What type of relay scheme is a pilot wire relay scheme classified as?

A pilot wire relay scheme is classified as a differential relaying scheme. This classification is based on how the pilot wire scheme operates in relation to the currents and voltages in the system.

In a differential relay setup, the primary principle is to compare the electrical quantities (typically current) at two different points in a power system. The relay is designed to detect any difference in the current entering and leaving a particular section of the network, such as a transformer or a transmission line. If a fault occurs within the monitored section, it will cause a significant imbalance in the currents, triggering the relay to operate and isolate the faulty part of the system.

This specific functionality of measuring the difference (or differential) between two currents is what distinguishes it from other types of relaying schemes. Overcurrent relaying, for example, operates on threshold levels of current exceeding set limits rather than directly comparing two different currents. Distance relaying focuses on the impedance between the relay location and the fault, while voltage relaying detects abnormal voltage conditions. Hence, the pilot wire scheme’s method of operation closely aligns with the principles of differential relaying.