A novel unit protection scheme based on superimposed currents

This paper presents a novel power system unit protection scheme which operates on the information contained in the superimposed currents created by a fault. If, at a connecting busbar, more than two transmission lines are monitored, the superimposed currents alone can be used to give directional information for a unit scheme. The resulting unit protection scheme is both simple and reliable. 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 transient voltage information. No special wide bandwidth transducers are required for this scheme.