1. Electric Power Research Institute, CSG EHV Power Transmission Company, Guangzhou 510663, China
2. Joint Laboratory of DC Power Transmission Equipment and Submarine Cable Safe Operation, CSG EHV Power Transmission Company, Guangzhou 510663, China
3. Key Laboratory of Optoelectronic Technology and Systems, Ministry of Education, College of Optoelectronic Engineering, Chongqing University, Chongqing 400044, China
4. Key Laboratory of Engineering Dielectrics and Its Application, Ministry of Education, Harbin University of Science and Technology, Harbin 150080, China