1. State Grid East Inner Mongolia Electric Power Supply Co., Ltd., Hohhot010010, P. R. China
2. State Grid East Inner Mongolia Electric Power Research Institute, Hohhot010020, P. R. China
3. Center of Nanomaterials for Renewable Energy, State Key Laboratory of Electrical Insulation and Power Equipment, School of Electrical Engineering, Xi’an Jiaotong University, Xi’an710049, Shaanxi, P. R. China