平行线路跨线故障选相元件的动作分析

同走廊架设平行线路广泛应用于输电系统中。与单回线故障相比,跨线故障的故障特征发生变化,因而传统选相元件存在错选故障相的风险。考虑平行线路之间的零序互感作用,提出分别利用戴维南等效和构造存在耦合的复合序网络计算跨线非接地故障和接地故障时故障点处的序电流,进而分析选相元件的动作情况。以两端无电气连接的同杆并架双回线为例,通过对不同跨线故障类型情况下序电流关系式的分析,得出了零序负序电流选相元件的选相情况在跨线非接地故障时仅与故障类型有关,在跨线接地故障时不仅与故障类型有关,而且与回线间互感作用的强弱及零序、正序等值阻抗的比值有关;相电流差突变量选相元件通常情况下能够正确选相的结论。PSCAD仿真结果验证了跨线故障分析方法及选相元件分析结果的正确性。

Analysis on Fault Phase Selector for Cross Country Fault of Parallel Transmission Lines

Parallel transmission lines on the same corridor are commonly used in the transmission system. When a cross country fault occurs, the traditional fault phase selector may not correctly identify the fault phases due to the changes of fault characteristics. An algorithm for the calculation of the sequence currents at the fault point is proposed according to Thevenin''s theorem and the sequence currents at the location of the protection relay are obtained with superposition principle. Finally, the formulas on the relation between sequence currents at the fault point are deduced. Based on the double-circuit transmission lines on the same tower without electrical connection at both ends, it is found that the applicability of the positive and negative sequence current phase selector is related to fault types under cross country non-earth fault conditions, while that under cross country earth fault conditions are related to fault types, mutual inductance as well as the ratio of equivalent zero sequence impedance and positive sequence impedance. In contrast, the phase selector based on the phase current difference change can correctly identify fault phases under different cross country fault conditions of parallel transmission lines on the same corridor. Simulation results based on the PSACD platform show that the analytical method for cross country fault is effective, and the analysis result of fault phase selector is correct. This work is supported by State Grid Corporation of China.