Study On Partial Discharge Activity And Effect Mechanism For Insulation Of Inverter-Fed Motor

With the development of high power semiconductor devices, frequency control drive systems are widely used in the field of locomotive traction. Pulse Width Modulated (PWM) technique which provides motor supply voltages is characterized by square waveforms, width modulated, with steep rise front slew rate up and high pulse repetition frequency. For this reason, electrical insulation of traction motor can be premature failures under such pulse waveforms. Because design and manufacture technology of AC motor is not completely suitable for traction motor supplied by such adjustable speed drives anymore, it is essential that comprehensive research for electrical insulation of electric motor supplied by PWM voltage. The thesis is based on the latest research results at home and abroad, and partial discharge (PD) which is one of the major factors leading to aging of insulations is used as main objects. Activity and mechanism of PD of insulation system of traction motor supplied by adjustable speed drives is investigated. These reasearch results will greatly promote advancement of theory of aging and breakdown under such pulse condition. As a result, frequency control technique can be widely used.As the PD signal belongs to random signal, occurring probability and discharge amplitude are largely influenced by the delay-time of initial electron. However, the appearance of initial electron is generally random, so statistics and analysis of that signal is always the hot issue home and abroad, which needs to be further researched. Moreover, a unified viewpoint on PD activities and mechanism of insulation under different square pulses have not been reached presently, which also needs to be further studied.This thesis develops research work aiming at the above problems. Firstly, set up the insulation aging and PD measurement method. Ultraviolet lighting was added during the process of PD measurement, which was used to excite photoionization, add the appearance probability of initial electron, and decrease the influence of time delay. Secondly, SEM analysis of samples aged under different conditions was conducted. The insulation damage degree caused by PD was more directly understood from microcosmic level and meanwhile compare the corona-resistant capability of different insulating materials. Finally, the influence of pulse voltage with different parameters on PD activities and mechanism of nano-polyimide film, common polyimide film, and twisted pair of stator winding was mainly researched. This thesis lays a solid foundation for the research on damage mechanism of inter-turn insulation of inverter-fed motor under high voltage square wave pulse and corresponding protection countermeasures.