1. School of Electrical Engineering Hebei University of Science and Technology Shijiazhuang 050018 China
2. Hebei Provincial Key Laboratory of Electromagnetic and Structural Performance of Power Transmission and Transformation Equipment Baoding Tianwei Baobian Electric Co., Ltd Bao Ding 071056 China
3. Hebei Weixun Electric Power Automation Equipment Co., Ltd Heng Shui 053000 China