Fault identification system for use in protective relays for power transmission lines

Abstract

The angle between the negative sequence and zero sequence currents for a power signal on a transmission line is measured and compared against a plurality of successive angle ranges from 0.degree. to 360.degree.. If the angle is 0.degree..+-.30.degree., an AG fault is indicated and a first section output is produced blocking ground elements BG and CG and phase-to-phase elements AB and CA. An angle of 120.degree..+-.30.degree. indicates a BG fault, resulting in a second output blocking ground elements AG and CG and phase-to-phase elements AB and BC, while a phase angle of 240.degree..+-.30.degree. indicates a CG fault, resulting in a third output blocking ground elements AG and BG and phase-to-phase elements BC and CA. If the phase angle is not covered by the above three primary ranges, then a second stage of comparisons are made, including determining the magnitudes of the phase-to-phase distance elements, and then comparing the phase-to-phase resistance of the lowest of those with the apparent resistance of the one ground element, i.e. AG, BG or CG, associated with the non-primary (secondary) range of angles which includes the measured phase angle. If selected criteria are met, then an output is asserted to block the ground and phase-to-phase elements noted above associated with that ground element.

Dependencies are inferred from the claim text.