中文摘要：

HUANG Zhen was a graduate from elec trical power system and its automation of Xi＇an Jiaotong University witha B. So. degree in 1991 and from electrical power system and its automation from Electrical Power Science Research Institute of China with a M. Sc. degree in 1996. He is work- ing in Sichuan Province Electrical Power Corporation. He is responsible for dispatching, operation and maintenance of electrical power network. WU Guang-ning was a graduate from electrical engineering of Xi＇an Jiaotong University with the B. Sc. , M. Sc and Ph. D. degree in 1997. He is a professor in the School of Electrical Engineering, Southwest Jiaotong University. His research interests include condition monitoring, fault diagnosis and insulation life span evaluation for electric power equipment. JIANG Wei was born in Chongqing, China, on Aug 27, 1979. He received the B. Sc. degree in hydroelectricity engineering in 2002, and the M. Sc. degree in 2005, from Xihua University, Chengdu. He is currently pursuing the Ph.D. de- gree in the School of Electrical Engineering at Southwest Jiaotong University. Currently, he is doing research about transformer DC bias caused by HVDC; transmission system. XIAO Hua was a graduate from electrical power system and its automation of ChongQing University with the B. Sc. degree in 2007. She is currently pursuing the M. Sc. degree in the school of Electrical Engineering at Southwest Jiaotong University. She is doing research work about influence of transformer caused by HVDC. ZHOU Li-ren was born in Shanghai, China, on 31 January 1985. He received B. So. degree in electrical engineering from Southwest Jiaotong University, China, in 2007. He is now pursuing M. Se. degree in the Sehool of Electrical Engineering in Southwest Jiaotong University, Chengdu. GUAN Lan was a graduate from biology science of Sichuan Agriculture University with the B. Sc. degree in 2006. He is currently pursuing the M. Se. degree in the school of Electrical Engineering at South- west Jiaotong University. He is doing re