1. State Key Laboratory of Electrical Insulation and Power EquipmentSchool of Electrical EngineeringXi'an Jiaotong UniversityXi'anPeople's Republic of China
2. Department of Electrical EngineeringTsinghua UniversityBeijingPeople's Republic of China
3. School of Materials Science and EngineeringTianjin University of TechnologyTianjinPeople's Republic of China