Research on the distance protection performance for untransposed parallel transmission lines based on six-phase parameter information

For untransposed parallel transmission lines, the fault impedance measured by relays will be affected by both the mutual impedance between parallel lines and the coupling effect of different sequence components in the single line. Even the fault phase voltages are compensated by the zero-sequence current in the adjacent line, the errors of measured fault impedances are still quite large. The performance of distance protection may not reach the requirement. A distance protection algorithm based on fault circuit analysis, using the phase components of both lines at the local end and six-phase impedance matrix has been proposed in this paper. This algorithm is simple and immune to the grounding fault with big fault resistance. Simulation results show that this proposed algorithm can calculate the fault impedance more accurately, will almost not cause the cut-down and overreach of protection range, improving the performance of distance protection in untransposed parallel transmission lines apparently.