Mixed-voltage multi-circuit transmission lines can be classified into two types:totally on the same tower and partly on the same tower. Due to its special construction form, cross-voltage fault occurs from time to time. In terms of the latter, an improved method of short circuit calculation of cross-voltage faults on mixed-voltage double-circuit transmission lines is proposed in this paper based on the theory of multiple fault analysis, and the first type can be regarded as a special case. First, consider the cross-voltage fault as the multiple faults of the system. The equivalent two ports network of each sequence can be obtained through the simplification. Second, the fault reference phase is selected and the boundary conditions which are decomposed into symmetrical sequence components of fault reference phase are analyzed for different cross-voltage faults. Furthermore, according to the difference between fault phase and reference phase, the composite sequence network is drawn by using ideal transformer to connect the two ports network of each sequence. And, the fault current can be obtained based on the composite sequence network. Finally, fault model of 500 kV/220 kV mixed-voltage double-circuit lines is constructed in PSCAD. Simulation results verifies the accuracy of this method.%混压同塔输电线路可分为完全同塔和部分同塔两大类.由于其特殊的架设方式,跨电压故障时有发生.该文基于复故障分析法,针对部分同塔情况(完全同塔可视为其中一个特例),提出了一种新的跨电压故障短路电流计算方法.首先,将跨电压故障等效为系统发生复故障,通过网络等效化简,可得各序等效二端口网络;其次,选定故障基准相,针对不同的跨电压故障情况,分析其边界条件,并分解为基准相的对称序分量;进一步,根据复故障中两特殊相与基准相的差异,利用两组移相变压器连接各序二端口网络,得到跨电压故障下的系统复合序网,并据此求解短路电流.最后,在PSCAD中搭建500 kV/220 kV混压部分同塔双回线模型,仿真验证该方法的准确性.
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