1. State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, China
2. State Key Laboratory of HVDC Transmission Technology, China Southern Power Grid, Electric Power Research Institute, Guangzhou, China
3. College of Water Resources and Architectural Engineering, Northwest A&F University, Yangling, China
4. Department of Energy Technology, Aalborg University, Aalborg, Denmark