1. Hubei Electric Power Planning, Design and Research Institute Co., Ltd.,Wuhan,China,430040
2. School of Electrical Engineering, Chongqing University,State Key Laboratory of Power Transmission Equipment Technology,Chongqing,China,400044
3. State Grid Chengdu Electric Power Supply Company,Chengdu,China,610000
4. School of Electrical Engineering, Sichuan University,Chengdu,China,610065