New fault phase selector for double-circuit lines protective relaying based on differential fault current components

Based on differential currents, this paper presents a fault phase selector for the protection of double-circuit lines. After phase-sequence transformation of double-circuit lines, six phases are decoupled into six sequence vectors including the differential and common vectors, which are independent of each other. In particular, as the differential vectors are independent of system impedance, the characteristics of all kinds of differential currents and differential sequence currents for all single-line faults of parallel transmission lines are inferred. This paper takes differential current fault components as phase selectors. The principle of the fault phase is free from the influences of system parameters and fault resistance. As it is easy to obtain the fault components of the differential current and its error is small, the protection theory for double-circuit lines is better than the conventional current balance protection using phase currents or current components. The results of EMTP simulation show that the principle is accurate and effective.