1. State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, No. 28 Xianning West Road, Xi'an, Shaanxi Province 710049, China
2. CSIRO Manufacturing, P.O. Box 218, Lindfield, New South Wales 2070, Australia
3. School of Automation, Northwestern Polytechnical University, Xi'an, Shaanxi 710072, China