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

摘要

Ground impedance measuring elements (ground elements), which are responsible for removing singlephase-to-ground faults in distance relays, are highly prone to underreach when facing a significant resistancernin 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 elementrnfunctions on the basis of the fault distance and fault resistance it estimates, online during the faults, throughrnthe equation derived from the voltages and currents of the distributed-parameters line model. Hence, it willrnbe particularly applicable to the parallel lines of long length in which the distributed parameters effect isrnsignificant. 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, thernproposed element preserves its security in case of irrelevant-circuit as well as external faults. Simulationrnstudies conducted in MATLAB and PSCAD/EMTDC examine the proposed ground element in a varietyrnof influencing situations, and the results reveal that it accurately trips the faults in thefirst zone with nornincidence of underreach in case of high resistance faults. The accuracy of the proposed element is overrn99.4% and its tripping time within 0.3–1.3 cycles.