The on-board traction transformers are the power source of the high speed and heavy load trains; however

there are some problems

such as the complexity of the structure

the bad operation environment

the shortage of maintenance or excessive maintenance of traditional scheduled repair. In addition

the insulation system of on-board traction transformers is affected by the voltage fluctuations

inrush current

poor heat

harmonics

and mechanical vibration. Therefore

the structure of oil tank and winding and the operating characteristics are studied. The effects of the above-mentioned operating environments and conditions on the insulation system of on-board traction transformers are analyzed. Moreover

the critical problems existing in the research of on-board traction transformer are summarized

the frameworks and flowcharts of prediction and health management（PHM） are given

and the logical relationship of PHM is illustrated. Then

the research status and development of condition monitoring and assessment

fault diagnosis and prediction

and maintenance decision for on-board traction transformer at home and abroad are systematically analyzed

and the future development trend of on-board transformer PHM combining with the special operating characteristics is discussed and prospected in detail.