防范交流失压引起距离Ⅲ段保护误动的措施探讨

Discussion on measures to prevent malfunction of distance protection Ⅲ due to AC voltage losing

距离III段保护作为本线和相邻线路的后备保护,动作区往往采用阻抗偏移特性。由于保护在启动后退出PT断线判别功能,非故障线路距离III段保护在区外故障伴随交流失压时容易误动,严重时会引发变电站母线全停。为防止距离Ⅲ段保护误动,从电压回路和动作特性两个方面提出防范对策:1)公共电压的直流电源、重动回路及切换回路均按双重化设计,从源头上避免交流失压;2)根据电流值有条件开放阻抗偏移特性,提高距离III段保护的容错能力。

Distance protection III is backup protection of own line and adjacent line. Its action zone often has impedance offset characteristics. Because the PT breakage discriminating element will exit once the protection starts, the distance protection III of non-fault line will trip incorrectly when external fault occurs accompanied by AC voltage losing, even leading to all blackout of substation bus in serious case. To prevent malfunction of distance protection III, two measures are put forward based on voltage circuit and action characteristics： 1） DC power supply, reinitiated circuit and switch circuit of public voltage are all dual-designed which can avoid AC voltage losing from the source; 2） the impedance offset characteristics is opened conditionally according to the current value which improve the tolerance ability of distance protection III.