1. Xi’an Jiaotong University, Xi’an, China
2. Institute of Advanced Electrical Materials, Qingdao University of Science and Technology, Qingdao, China
3. Electric Power Research Institute, Yunnan Power Gird Company Ltd, Yunnan, Kunming, China
4. State Key Laboratory of Electrical Insulation and Power Equipment, Xi’an Jiaotong University, Xi’an, China