部分站用变配电线路中常出现越级跳闸的问题，造成停电范围扩大，严重威胁供电可靠性，本文首先分析了造成继电保护越级跳闸原因，包括支路保护整定设置不当、上下级保护配合不合理、断路器等元器件故障等，进而对继电保护整定原则和级间配合进行了改进分析，并设计了零序电流保护与脱扣器结合的继电保护方案，现场实验结果表明，该方案可有效解决越级跳闸问题，避免了停电范围扩大及其带来的繁重检修任务，提高供电可靠性。
Over-level tripping often occurs in some substations of electric distribution grid, which may cause and expand power outages and seriously threaten the reliability of power supply. This paper ana-lyzes the causes of the relay protection tripping, including improper setting of branch protection; unreasonable protection coordination between upper and lower levels; failure of components such as circuit breakers etc. Then, a novel relay protection scheme combining zero-sequence current protection and trip unit is designed to improve the setting arrangement and inter-stage cooperation of the relay protection. Field test results show that the scheme proposed by this paper can effectively solve the problem of over-level tripping, and avoid the expansion of power outage and the heavy maintenance tasks brought by it. It can effectively improve the reliability of power supply.