Investigation on Insulation Electrical Aging Mechanism of Inverter- Fed AC Traction MotorsInverter - fed traction motors used in motor train unit are regarded as the research object for insulation electric aging mechanism, based on re-search productions of insulation technique of inverter-fed motors . High frequency equivalent circuit model s of cable and stator winding are established to simulate over-voltage of motor terminal sand uneven voltage distribution of windings. A novel high frequency high voltage test system has been developed to carry out life time tests of traction motor windings. Change tendency of dielectric loss , partial discharge and thermally stimulated current (TSC) are used to deduce insulation electric breakage mechanism.High frequency equivalent circuit models of cable and stator winding are established to simulate over voltage of motor terminals and uneven voltage distribution of windings. The simulation results show that the over-voltage is the function of rise time , cable length and reflection ratio on motor terminals. Critical length and critical rise time is corresponding one to one. The over-voltage is up to the maximum value as long as the cable length is reater than the critical lengthA novel high frequency high voltage test system has been developed in place of inverters to carry out insulation aging test. Pulse square waves are generated by IGBT and are enlarged by high frequency and high voltage transformers in the device. The maximum value of high frequency and high voltage square waves is up to 10 kV. The results of life tests of motor windings indicate that he relationship of insulation lifetime and the amplitude of pulses is the inverse power law model , the relationship of insulation lifetime and the frequency of pulses is exponential model under continuous pulses condition. When the test ambient temperature is below 200，the temperature has little influence on insulation lifetime of magnet wire with corona resistant film insulation.A novel partial discharge detection device was developed by impulse current sensor , hand computer. According to the character is tics of the tested signals , a new algorithm based on wave let- envelope detection technique is proposed to filter EMI from the test system and space electromagnetic waves. Because of the influence of very large dV/dt and high frequency plus - minus voltage discharges under continuous square waves condition are different from those under sine voltage condition. On the one hand , larger dV/dt leads to higher breakdown voltage.On the other hand, high frequency plus-minus voltage conversion causes a lot of space charge cumulated on the insulation surface. Large break down space charge result in discharge pulses with short rise time and large magnitude . The number, magnitude and power of partial discharges increase with the temperature , frequency and voltage change of square waves. The number of partial discharge become large with the frequency of square wave increase in the unit time , but it becomes small in one period of square wave. Contrast tests are carried out under AC and 10kHz square wave pulse conditions. The differences between AC aging and square wave pulse aging are studied based on change curves of dielectric loss, partial discharge pattern and TSC. These curves prove that square wave pulses bring more defects than AC voltage to the insulation materials. Under qua re wave pulse condition , the two key factors which to insulation aging are discharge ad space charge. Damage actions of partial discharges and space charges are intensified with voltage , frequency and temperature increasing. Due to the destruction of discharges under the square wave condition , the weaknesses of insulation structure will break down rapidly if partial discharges occur. Discharge channel comes into being as a result of the cooperation of partial discharges and space charges. Insulation surfaces are destroyed by partial discharges. Injection and draw - off of electric charges generating by charges result in molecular chain fracture inside insulation structure. Subsequently, discharge channels are expanded along the breaking point in the insulation. Finally, the process leads to insulation is the use of power semiconductor devices will be the role of on-off frequency to another frequency power conversion power control devices. We are now mainly used in cross-frequency converter - direct - way to pay (VVVF inverter or variable frequency vector control), before the adoption of power-frequency AC power into DC power rectifier and then converted to DC power supply frequency and voltage can be controlled AC power to supply the motor. Inverter circuit in general by the rectifier, intermediate DC link, inverter and control of four parts. Part of three-phase bridge rectifier is not controlled rectifier, inverter part of three-phase bridge inverter IGBT and PWM output waveform, the middle of DC link for the filteri