| AC traction motors are one of the key equipments of locomotive, and their performance influence the stability and reliability of the locomotive. According to many abroad AC traction motor operating experiences, it has been found that insulation of inverter-fed motors fail prematurely with the adoption of pulse-width modulation (PWM) inverters, particularly the breakdown of interturn insulation. Many research reports confirm that partial discharge (PD), dielectric loss and space charge under PWM are key factors which lead to premature failure of inverter-fed motors. So research on failure mechanism of interturn insulation helps to find characteristic parameters and evaluation method to reflect insulation performance, which is provided with important theoretical basis and practical significance for safe operation of AC traction motor.The reports on aging microcosmic mechanism of interturn insulation of AC traction motor are rare presently. It is necessary to develop systematic test to study using dielectric parameters to estimate running conditions or to evaluate residual life. Similarities and differences of aging status of different insulation materials under square waves need contrast test in depth, which is expected to offer references to solve this question.To those questions above, some research work has been done in this paper. Firstly, polarization and loss of dielectric is introduced simply, and testing systems of dielectric spectrum for different insulation materials are built. A strong emphasis is laid on the study of dielectric spectrum of nanometer and non-nanometer polyimide film in the period of aging process. The relationship between microcosmic molecular structure configuration and macroscopic dielectric property is studied based on dielectric spectrum combining analysis on surface topography of samples under the same aging condition. Secondly, similarities and differences of dielectric property of twisted pairs simulating inter-turn insulation under the effect of AC and square wave pulse are discussed and deeper investigation of dielectric property under different supply voltage waveforms is carried on. Finally, dielectric spectrum of twisted pairs in the period of aging is analyzed comparing to the analysis result of polyimide film, and the aging rule of twisted pairs is achieved. All the work introduced above provides a basis for studying failure mechanism of interturn insulation of AC traction motor and seeking corresponding safety measure. |
