混压同塔线路跨电压接地故障对距离保护的影响分析

不同电压等级同塔(混压同塔)输电线易发生跨电压故障,这种故障类型对输电线路继电保护提出了更高的要求。接地距离保护是高压输电线路的主保护之一。混压同塔跨电压接地故障对故障线路接地距离阻抗继电器测量阻抗的影响因素包含两方面,一是相邻线路与本线路之间的零序互感,二是另一条故障线路的故障电流。文中综合考虑以上因素,以单相跨单相接地的跨电压接地故障类型为例,首先提出了适用于混压同塔跨电压故障的故障电流计算方法,然后以此为基础提出两种因素作用下故障线路接地距离继电器的测量阻抗计算方法,最后分析了另一电压等级线路与本线路电源电动势相角差与测量阻抗的关系,并分别给出了接地距离保护正确动作与不正确动作时的此相角差范围,并且给出了相应的解决措施。在PSCAD软件中建立了500kV/220kV同塔四回线路模型,验证了理论分析的正确性。

Influence on Distance Protection Caused by Earthed Cross-voltage Fault in Multi-circuit Transmission Lines System

The mixed-voltage multi-circuit transmission lines system cross-voltage fault prone, which makes higher requirements on relay protection. Earth-fault distance protection is one of the main protections of high voltage transmission lines. The earthed cross-voltage fault in mixed-voltage transmission lines is influenced by two factors, one is zero-sequence mutual inductance of adjacent lines, the other is the fault current of another fault circuit. By taking both factors into consideration, a method of calculating the cross-voltage fault in mixed-voltage transmission lines is proposed. Then the impedance measuring expression considering two factors is calculated. Finally, the relationship between impedance measuring and electromotive force phase difference of the two systems are analyzed. The ranges of the phase in which the earth-fault distance protection can operate and mal-operate are given, respectively. Corresponding measures are recommended. A 500 kV/220 kV four-circuit model is built in PSCAD to verify the correctness of the analysis. This work is supported by National Basic Research Program of China (973 Program) (No. 2012CB215206) and the Fundamental Research Funds for the Central Universities (No. 2015XS12).