Patent ID: 6498709
Filing Date: 2002-12-24
Classification: H02H

Abstract:
A digital distance relay for deciding whether a fault point is within a stipulated operation region by obtaining an impedance up to the fault point through a line equation of a transmission line including terms of resistances and reactances using data of voltage and current of AC power supply system periodically sampled, the relay comprising:a first means for calculating positive-phase resistance Rcal and positive-phase reactance Xcal; a second means for storing load current a stipulated time period prior to the fault was detected; a third means for detecting current in same phase as fault current flowing through the fault point; a fourth means for detecting relative phase of the current detected by the third means relative to current for directly calculating the positive-phase resistance Rcal and the positive-phase reactance Xcal; a fifth means for deciding whether the impedance is within a specified region by applying a value proportional to the relative phase detected by the fourth means; and a sixth means for deciding the fault point is within the stipulated operation region if: (a) when the load current stored by the second means indicates a sending current direction, the positive-phase resistance Rcal and positive-phase reactance Xcal are within a stipulated region based on a stipulated positive-phase resistance and a stipulated positive-phase reactance, and the impedance is decided within the specified region by the fifth means; or (b) when the load current stored by the second means indicates a receiving current direction, the positive-phase resistance Rcal and positive-phase reactance Xcal are within a stipulated region based on a stipulated positive-phase resistance and a stipulated positive-phase reactance, or the impedance is decided within the specified region by the fifth means.