中文摘要：

提出了适用于不同电压等级四回线故障分析方法。不同电压等级四回线的线路参数不对称,无法用传统的12序分量进行故障分析。不同电压等级的四回线基本上由两个内部参数对称的同杆双回线组成。分别采用传统6序分量法进行解耦,可以实现双回线的同向、反向的正负序的完全解耦,同向正负序系统阻抗修正为原来的两倍,反向正负序系统阻抗为零。剩下的没有完全解耦的同向、反向零序分量,利用环流法解耦,解耦后系统侧的零序阻抗需要修正。以某一电压等级为基准,将两个双回线的零序系统阻抗折算到该电压等级中,然后将同一端的两个零序系统阻抗并联在四回线上。最后,根据四回线故障（包括金属性短路和有过渡电阻的短路,线路断线）边界条件列出方程组,利用解方程组法算出各序电流,再利用反解耦方法得到短路故障的故障电流和断线故障的断口电压、电流。仿真验证表明该方法适用于不同电压等级四回线的故障分析,且故障分析计算具有精确性、实用性和有效性。

英文摘要：

Fault analysis method for four-parallel lines under different voltage levels was presented. Traditional twelve sequence component method can not be used in four-parallel lines under different voltage levels because of asymmetric parameters. Four-parallel lines under different voltage levels are generally made up of two-parallel lines, which is under symmetry parameter. Four-parallel lines are decoupled into completely same and differential positive and negative sequence components. System impedance must be modified to be twice than the original system impedance on same sequence components. System impedance is zero on differential sequence components. The left coupling zero sequence components can be decoupled by circumfluence theory and system impedance of zero sequence need to be modified. The modified zero sequence system impedance of two parallel lines need to be converted to the same voltage level. At last, according to the boundary conditions of faults of four-parallel lines, the related sequence networks are introduced for calculation of fault current in short-circuit fault, disconnection voltage and current in disconnection fault. Simulation results demonstrate that the new sequence component method is appropriate for fault analysis of four-parallel lines under different voltage levels and the short circuit analysis and calculation is proved to be correct, practical and valid.