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 kV ScottishPower transmission system, are given to demonstrate the potential of this scheme, which shows the scheme is both simple and reliable.