A new ground impedance measuring element for digital distance relaying of long parallel lines in high fault resistance conditions.

Ground impedance measuring elements (ground elements), which are responsible for removing single-phase-to-ground faults in distance relays, are highly prone to underreach when facing a significant resistance in the fault path. This paper proposes a new ground element with ensured dependability in high fault resistance conditions for the first-zone digital distance relaying of parallel lines. The proposed ground element functions on the basis of the fault distance and fault resistance it estimates, online during the faults, through the equation derived from the voltages and currents of the distributed-parameters line model. Hence, it will be particularly applicable to the parallel lines of long length in which the distributed parameters effect is significant. The proposed element requires only the data acquired at the relaying location. Further, its function is independent of the structural configuration of the system. Unlike conventional ground elements, the proposed element preserves its security in case of irrelevant-circuit as well as external faults. Simulation studies conducted in MATLAB and PSCAD/EMTDC examine the proposed ground element in a variety of influencing situations, and the results reveal that it accurately trips the faults in the first zone with no incidence of underreach in case of high resistance faults. The accuracy of the proposed element is over 99.4% and its tripping time within 0.3-1.3 cycles. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]