线路遭雷击引起发电机组差动保护动作分析

Analysis of a Differential Protection Action of Hydro-turbine Generator Unit due to Lightning Strike on Transmission Lines

针对水轮发电机组因外送线路遭遇雷击跳闸事故,对事故发生过程的现象和数据进行分析、对比,发现是由于发电机差动保护两侧采样电流互感器型号及性能参数不一致,当外部短路时,电流互感器饱和点不一样,即一侧CT饱和,一侧CT不饱和,使两侧CT采样数据误差增大,进而产生不平衡电流增加较大,微机保护采样运算值至保护整定动作值或大于整定动作值时,保护动作跳闸。通过对差动保护电流互感器重新选型更换,5G机组运行至今,期间110 kV线路经历了数次雷击,没有再发生雷击跳闸事故。

A tripping accident of a hydro-turbine generator unit due to lightning strike on the outgoing transmission line is analyzed. It is found that the model and performance parameters of the sampling current transformers on two sides of the generator differential protection are inconsistent. In case of external short circuit, the saturation points of the current transformers are different, that is, the CT on one side is saturated while the one on the other side is unsaturated, which will increase the CT sampling data error of two sides, resulting in a large increase of the unbalanced current. When the microcomputer protection sampling operation value reaches or is greater than the setting action value, the protection action leads to tripping accident. Thus, the differential protection current transformer is re-selected and replaced. Since the treatment, the 110 kV line has experienced several lightning strikes, and no lightning induced tripping accident occurred.