1. State Key Lab of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi’an Jiaotong University, Xi’an 710049, P. R. China
2. School of Automobile, Chang’an University, Xi’an 710064, P. R. China
3. Jiaxing Power Supply Company of State Grid, Zhejiang Electric Power Co., Ltd., Jiaxing 314000, P. R. China