Zero-sequence voltages of UHV untransposed double-circuit lines and their influence on pilot protection

For untransposed double-circuit transmission lines on the same tower, there are zero-sequence voltages exerting on both ends of double-circuit transmission lines under normal operation and external phase-to-phase fault conditions. The amplitude and phase of the zero-sequence voltages are affected by wire parameters, wire orientations, the types of external phase to phase fault and system parameters. The zero sequence voltage may reach threshold value of zero-sequence power direction component, causing zero sequence power direction component maloperation with high zero sequence current. This paper analyzes the cause of zero-sequence voltages and their influence on pilot protection. Theoretical analysis and simulation results prove that system zero sequence impedance has influence on zero sequence voltage and zero sequence current. This paper will has great meaning to fault analysis of double-circuit transmission lines and protection configuration.