1. School of Physics, Beijing Institute of Technology (BIT), Beijing 100081, China
2. Global Energy Interconnection Development and Cooperation Organization (GEIDCO), Beijing 100031, China
3. State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University (XJTU), Xi'an 710049, China
4. Department of Electrical Engineering, Tsinghua University (THU), Beijing 100084, China