A new fault resistance compensation scheme for distance relays of parallel lines with untransposed conductors

Abstract

Line to ground (L-G) faults with a highly-resistive fault current path can be considered as the main reason for the distance relays underreach. This paper presents a new scheme to compensate commercial distance relays for the high fault resistance, without making any changes in its conventional structure, and is applicable to the under-operation relays. It operates on relay feeding signals measured by instrument transformers and corrects them in a way that the relay is enabled to calculate the desired fault impedance in case of high-resistance faults (HRFs). For this objective, a straightforward time-domain formula is creatively obtained first for a fast and accurate evaluation of the fault distance in case of L-G faults. The evaluated fault distance is then utilized to generate the signals correcting the relay feeding signals. The proposed approach is developed for the parallel lines with untransposed conductors on both circuits, hence it is intended for the lines at the HV and MV levels. Being readily implementable, preserving the relay security, insignificantly affecting the relay tripping time, being insensitive to the noise and fully eliminating the HRF-caused underreach are the features the proposed approach includes, which are verified by comprehensive simulation studies in PACAD/EMTDC for a variety of fault and system loading conditions.