Henan Electric Power Company，Zhengzhou450052，China

When two-phase fault or three-phase fault occurs，owing to line asymmetry parameters and current transformer transfer characteristics，unbalanced zero-sequence current occur in protective equipment samples which will affect the correct operation of the pilot zero-sequence protection.By referring to two incidents of the power grid，an analysis is made of the causes of the protection equipment incorrect action，and the feasibility of various improvements of pilot zero-sequence protection is studied.Finally，countermeasures for two-phase fault and three-phase fault are proposed.And the effectiveness of the measures is verified by dynamic simulation test.