Research On Fault Analysis And Protection Of Mult-circuit Transmission Lines On The Same Tower

Due to the shared transmission corridor and tower,mult-circuit transmission lines can effectively increase the transmission capacity,improve the reliability of power supply,and greatly reduce the construction cost of transmission project.Therefore,it is widely used in EHV/UHV transmission systems at home and abroad.With the application of transmission lines in form of partially on same tower,multi-voltage level,and phase conductor untransposition,the EHV/UHV transmission lines exhibit complex electromagnetic coupling characteristics.This paper focuses on the electromagnetic coupling between phases and circuits of multi-circuit transmission lines and its significant impact on normal operation and protective relaying.Due to the close distance between transmission lines erected on the same tower,the electromagnetic coupling and electrostatic coupling between circuits are more significant.Firstly,the typical tower structure,wire arrangement and transmission corridor of double-circuit lines and multi-circuit lines are elaborated.In addition,the symmetrical component transformation method and equidirectional opposite component transformation method commonly used in fault analysis of multi-circuit lines are elaborated.The overvoltage under cross-line faults of multi-voltage transmission lines is also analyzed.The mutual inductance coupling and parameter difference have a significant impact on distance relaying under cross-line faults of multi-voltage multi-circuit transmission lines.In response to this problem,this paper proposes a cross-line impedance calculation method suitable for multi-voltage double-circuit lines and quadruple-circuit lines based on the fault loop under cross-line faults.Furthermore,a novel distance relaying for cross-line faults of multi-voltage lines based on cross-line impedance is proposed.The cross-line impedance theoretically reflects the fault distance under cross-line faults and is not affected by ground transition resistance.Focus on the parameter asymmetry and electrical unbalance caused by the electromagnetic coupling between circuits of multi-circuit transmission lines,this paper takes the triple-circuit line as an example to analyze the causes of unbalanced current,and summarizes the effects of phase arrangement and line load on unbalanced current.The mal-operation cause of zero-sequence overcurrent relaying of lateral adjacent circuits caused by ground faults of one circuit is analyzed.A lateral coordination scheme of zero-sequence overcurrent relaying for multi-circuit lines considering the impact of electromagnetic coupling is proposed.Simulation results show that the proposed scheme can achieve effective operating coordination of zero-sequence overcurrent relaying on the cross-sections of multi-circuit lines,and avoid the maloperation of zero-sequence overcurrent relaying under the impact of unbalanced current.