Power System Fault Calculation under Special Circumstances and Corresponding Effect on Protective Relaying

This paper presents the power system fault calculation model for multi-circuit lines with mutual zero-sequence impedance and describes the procedure of the common and integrated node zero-sequence admittance matrix. It makes the complex fault calculation be able to extend faulted location into the inside of coupling lines. The transformation for 4-circuit coupling lines from sequence-component model to phase-component model is depicted so as to improve utilizing the multiple-coupling-line model in EMTP. The precision of fault calculation is verified by the results derived from EMTP package. Aiming at the typical operating conditions on the actual 4-circuit lines with 6-pair mutual impedance, the characteristics related to the measured impedance of earth-fault protective relaying are analyzed through the use of the fault calculation results. Adjusting the distance relay´s zero-sequence current compensation factor and adopting automatic inter-tripping technique can help to reduce mutual coupling effects