Validation of a novel unit protection scheme based on superimposed fault currents

This paper presents a novel unit protection scheme which is based on the directional information contained in the superimposed currents created by a fault alone. If, at a connecting busbar more than two transmission lines are monitored, it is shown that the superimposed currents alone are sufficient to give directional information for a unit scheme. Current transformers have a much greater bandwidth than voltage transformers, so this scheme has a much faster response time than comparable unit schemes which require both voltage and current information. Results, using recorded transients from events on a real 400 kV transmission system, are given to demonstrate the potential of this scheme. The scheme is simple, reliable and ultra fast. It is suitable for long transmission lines and its speed is limited only by the communications channel