P级TA饱和对数字式比率制动特性差动保护的影响

长期以来，比率制动曲线的比率制动部分历来都和电流互感器（TA）的抗饱和能力联系在一起，认为只要有了比率制动特性，差动保护就不会误动，但事实并非如此，长期统计表明有些原因不明的误动或多或少地和TA的暂态饱和有关，通过对非TPY级TA饱和的变压器区外故障动模数据分析，得出比率制动特性差动保护在P级TA暂态饱和情况下可能会误动的结论。同时，还详细阐述了选择合理的出口判据次数，数字滤波算法，数据窗的长度能提高差动保护抗TA暂态饱和能力的影响。

Impaction of P-type CT saturation on digital ratio-restrained differential protection

For a long time ,the ratio-restrained characteristic is assumed to avoid CT saturation and the differential protection with ratio-restrained characteristic is considered able to function properly.The statistical data indicate that some unknown malfunctions of differentia l protection may be caused by CT saturation.Through the dynamic simulation analysis of non-TPY-type CT saturation at out-area fault,it is concluded that the differental protection with ratio-restrained characteristic may function improperly under P-type CT transient saturation.The influence of trip judgment times,digital filter algorithm and data-window width on the ability against CT saturation is discussed.