Study on aging characteristics for inverter-fed traction Motor inter-turn insulation based on analysis of dielectric characteristic parameters

It has been shown that the supply waveforms generated by the power converters play a major role in inverter-fed traction motor insulation degradation. The electrical characterization of these insulating materials is often carried out through aging tests which may provide estimation of life under different stress levels and conditions. However, deeper investigation of aging phenomena due to supply voltage waveforms is needed, especially regarding the relation between aging factors and stress conditions. Accelerated aging tests under different supply voltage waveforms and temperature were conducted on twisted pairs simulating inter-turn insulation of inverter-fed traction motor. Tandelta and sample capacity were measured under different testing voltages. Based on analysis of dielectric loss and mechanics of square wave pulses, the experimental results show that PDIV is increasing with the increase of voltage amplitude in the early aging stage. PDIV is affected significantly by space charge accumulation under bipolar waveforms, which is almost independent of frequency among three factors. Little change of temperature has a strong impact on insulation. Impulse amplitude, frequency and temperature have a cooperative effect, which show that strengthening or weakening of each factor will alter trend of other factors effect on insulation.