Transient Signals and Their Processing in an Ultra High-Speed Directional Relay for EHV/UHV Transmission Line Protection

This article describes an ultra high- speed directional comparison relay (UHS relay) based on the evaluation of transient signals generated by the occurrence of a fault. The use of a replica impedance in the current circuit results in a pick-up sensitivity which is largely independent of source impedances. The discrimination between phases even in the case of long transmission lines is assured through the provision of a second measuring criterion.