1. Engineering Research Center of Advanced Lighting Technology, Ministry of Education, Department of Light Souces and Illuminating Engineering, Fudan University, No.220 Handan Road, Shanghai 200433, China
2. Department of Electrical Engineering, Shanghai Jiao Tong University, 800 Dongchuan Road, Minhang, Shanghai 200240, China
3. Key Laboratory for Sulfur Hexafluoride Gas Analysis and Purification of SGCC, Anhui Electric Power Research Institute of SGCC, Hefei 230022, China