1. State Key Laboratory of Power Transmission Equipment Technology, School of Electrical Engineering, Chongqing University, Chongqing, 400044, P. R. China
2. Department of Applied Physics, Chongqing University, Chongqing, 400044, P. R. China
3. School of Geosciences and Info-Physics, Central South University, Changsha, 410083, P. R. China