1. State Key Laboratory of Electrical Insulation and Power EquipmentSchool of Electrical Engineering, Xi'an Jiaotong UniversityXi'anPeople's Republic of China
2. Department of Electronic and Electrical EngineeringUniversity of BathBathUK
3. State Key Laboratory of HVDCElectric Power Research Institute of China Southern Power GridGuangzhouPeople's Republic of China