1. School of Applied Science, Harbin University of Science and Technology, 52 Xuefu Road, Harbin 150080, P. R. China
2. Key Laboratory of Engineering Dielectrics and Its Application, Ministry
of Education, Harbin University of Science and Technology, 52 Xuefu
Road, Harbin 150080, P. R. China
3. State Key Laboratory of Electrical Insulation
and Power Equipment, Xi’an Jiaotong University, 28 Xianning
West Road, Xi’an 710049, P.R. China