The invention relates to a sampling point
differential protection misoperation prevention method, belonging to the technical field of
relay protection of power systems. The method comprises the following steps of: firstly, performing difference calculation to differential current and
brake current sampling points, and judging whether the differenced differential current and
brake current sampling values meet a rate
brake condition, wherein influence of unsaturated CT attenuation
direct current component on the synthesized differential current may be weakened through a difference
algorithm; and judging whether a criterion for opening sampling point
differential protection is satisfied according to ratio of the sampling values of the differenced differential current and brake current. The method solves a problem of misoperation of sampling point
differential protection caused by too fast attenuation of the
direct component when external fault single CT is saturated and unsaturated CT current contains large
direct current component and flows through a low current converter of a protection device. Meanwhile, by the method, sampling point differential protection causes no misoperation when waveform is abnormal, and causes reliable operation when normal failure happens, thus, reliability of sampling point differential protection is improved.