1. State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an 710049, China
2. School of Nuclear Engineering, Purdue University, West Lafayette, Indiana 47907, USA
3. Department of Computational Mathematics, Science and Engineering, Michigan State University, East Lansing, Michigan 48824, USA
4. School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA