Low-current self-adaptive protection method with selectivity

The invention discloses a low-current self-adaptive protection method with selectivity, and the method comprises the following steps: when a single-phase earth fault occurs in a line, accurately judging upstream and downstream sections of the fault by using a transient zero-sequence voltage break variable as a starting condition and using a reactive power direction method as an action criterion, and adopting a switching action equation with inverse time limit characteristic, wherein time delay does not need to be configured, and the method has selectivity automatically and is not influenced byan operation mode. The problem that a time constant value needs to be set in advance according to a switch position and needs to be reset according to line operation mode changes in graded constant time limit protection can be effectively solved. 本发明公开了一种具有选择性的小电流自适应保护方法，当线路发生单相接地故障时，利用暂态零序电压突变量作为启动条件，采用无功功率方向法作为动作判据，准确判断故障上、下游区段，采用反时限特性的开关动作方程，不用配置时间延时，自动具有选择性，且不受运行方式影响。能够有效解决分级定时限保护中需根据开关位置事先设定时间定值和线路运行方式变化需重新设置时间定值问题。