Owing to the small equivalent resistance and special internal structure

the inrush current of high-voltage built-in high-impedance transformer is large and decays slowly. A malfunction of the protection occurred as the zero-sequence of magnetizing inrush current is too large during a closing experiment on high-voltage built-in high-impedance transformer by a transformer substation of Guangdong. According to the recorded wave of actual spot data

the malfunction of the zero-sequence overcurrent protection and the zero-sequence protection Ⅳ line may occur since the zero sequence of magnetizing inrush current is large and decays slowly. To solve this problem

the characteristics of magnetizing inrush current are analyzed deeply along with the structure as reasons why the inrush current of high-voltage built-in high-impedance transformer is large and decays slowly. Then the influencing factors on inrush current zero-sequence component of transformer closing are simulated by using PSCAD/EMTDC. It is proposed that when putting a new transformer into operation

the extreme condition of the longest magnetizing inrush decay time be taken into account so that the time limit of zero-sequence protection Ⅳ can be re-set to ensure the transformer normal operation. This work is supported by National Natural Science Foundation of China (No. 51377059) and Guangdong Provincial Natural Science Foundation (No. S2013010012885).