Study on Necessity of Overvoltage Protection for Secondary Winding Neutral-point of Voltage Transformer: Numerical Analysis on Potential Distribution of Ground Grid during Ground Fault or Lightning Stroke

In view of the multiple protection misoperation accidents caused by incorrect breakdown of discharge gap at the secondary winding neutral-point of voltage transformer in Guangdong power grid in recent years,test and theoretical study are made on the necessity of installing overvoltage protection at the secondary winding neutral-point of voltage transformer.Through numerical analysis and experimental verification of the potential difference between two points of substation ground grid under the situation of power-frequency earth fault,direct or extremely near lightning stroke,the transient and stable potential difference levels between two points of ground grid are determined,and the necessity of installing lightning overvoltage protection at the secondary winding neutral-point of voltage transformer is confirmed.