中性点不接地系统单相接地故障零序电流分析

对中性点不接地系统单相接地时零序暂态电流和零序全相电流特性进行分析。指出采用零序暂态电流选线时 ,由于存在无暂态过程的情况 ,因此有局限性 ;而采用零序基波电流选线 ,则必须在同一周波内完成采样 ,尽量增加采样点数 ,并在同一时刻精确测量对应采样点的量值

Discussion on a practicable relay protection scheme for the excitation transformer

It is difficult to size the current transformer at high voltage side of the excitation transformer,since the extreme short circuit current would take place at the large generator outlet of a generator transformer set.So that to decrease the accuracy limit factor an idea to take the protective duty of internal faults cooperating with unclosed differential protections of the generator transformer/main transformer and the relay protection special for the excitation transformer is presented.And some rated transformation ratios of the current transformer are proposed for reference.Meanwhile comparing the differential protection with the over current protection of the excitation transformer,the over current protection is suggested to simplify the relay protection.