中文摘要：

距离III段在事故过负荷情况下动作是连锁跳闸的重要原因,对电网安全构成严重威胁。该问题的解决包含3部分：事故过负荷的识别;在不危及设备安全前提下,保护可靠闭锁;在危及设备安全的情况下,保护可靠动作。对事故过负荷的有效识别是解决该问题的第1步,然而目前国内外研究尚未完全解决识别问题,其根本原因是对事故过负荷下保护动作的分析不够深入彻底。针对该缺陷,分别从时间动态过程、空间网络及前提条件等3个方面剖析事故过负荷及距离III段的动作行为,为彻底解决事故过负荷的识别和闭锁问题铺平道路。

英文摘要：

The undesirable action of zone-III distance relay under post-fault overload is an important cause of cascading tripping, which poses a serious threat to the stability and security of power grids. Solution of this problem includes three parts： identification of post-fault overload; relay blocking if the electrical equipments are safe; tripping if the equipments are endangered. To effectively identify post-fault overload is the first step to solve this problem. However, the problem has not been solved thoroughly due to imperfect analysis of action of protection under post-fault overload. In order to solve the problem, this paper analyzed the post-fault overload and the overreach action of zone-III distance relay from their dynamic process, spatial network and preconditions separately, which points out the way to solve the identification of post-fault overload.