Validation of a novel unit protection scheme for long transmission lines based on superimposed fault currents

This paper presents results for single phase to ground faults which validate the principles of a novel unit protection scheme. The novel unit scheme operates on the information contained in the superimposed currents created by a fault. If, at a substation busbar more than two transmission line circuits are monitored, the superimposed currents alone can be used 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 a comparable unit scheme which require transient voltage information. Results, using recorded transients from single phase to ground faults on the 400 W ScottishPower transmission system, are given to demonstrate the potential of this scheme, which shows the scheme is both simple and reliable.