同塔混压四回线下的单回线故障零序方向元件动作特性分析

同塔混压四回线发生故障时，由于近距离物理条件，不仅要考虑相间互感，也要考虑不同电压等级系统之间的互感对故障分析及保护产生的较大影响。针对弱电强磁与强电联系两种场景下同塔混压四回线中单回线发生接地故障的情况，首先阐述零序去耦等值电路的建立依据，然后对零序方向元件的动作特性及主要影响因素进行理论分析。结果表明对于弱电强磁场景，不同电压等级之间的零序互感对零序方向元件动作行为的影响可以忽略不计。对于强电联系场景，零序互感、电气强度及故障位置综合影响零序方向元件的动作行为。基于ATP-EMTP建立1 000 kV/500 kV同塔混压四回线模型，对单回线故障条件下的零序方向元件动作行为进行了建模仿真，验证了理论分析的正确性。

Performance analysis of a zero-sequence directional relay for a single-circuit fault in mixed-voltage four-circuit transmission lines on the same tower

When a fault occurs in mixed-voltage four-circuit transmission lines on the same tower, because of their close physical proximity, there is mutual inductance between phases, but also there is the fact that the existence of mutual inductance between different voltage systems will have a great influence on fault analysis and protection. The basis for establishing a zero-sequence decoupling circuit is explained for the circumstance that a single-circuit fault occurs in a mixed-voltage four-circuit transmission line on the same tower under weak-electric and strong-magnetic conditions and with a strong-electric connection. Then, the performance of the zero-sequence direction relay and the main influencing factors are analyzed. The results show that the zero-sequence mutual inductance between different voltage level systems has a negligible effect on the performance of the zero-sequence directional relay under weak-electric and strong-magnetic conditions. The zero-sequence mutual inductance, electrical strength and fault location comprehensively affect the performance of zero-sequence directional relay under strong-electric connection conditions. An ATP-EMTP 1 000 kV/500 kV model of the mixed-voltage four-circuit transmission line on the same tower is established and the performance of the zero-sequence direction relay under single-circuit fault conditions is simulated to verify the accuracy of the theoretical analysis. The work is supported by the Scientific Research Project of China Electric Power Research Institute (No. SGDK0000JBJS1907459).