Study On The Thermal Effect On Insulation Performance Of Inverter-Fed Traction Motor

The insulation system of inverter traction motor does not only have to bear stronger electrical stress, but also have to subject to the influence of mechanical forces, temperature factor and humidity factor in the square-wave pulse condition. It would lead to the premature failure of insulation system, which threaten the safe operation of the locomotive. Therefore, the research on the mechanism of insulation failure is desperately needed. Domestic and foreign experts have done some work about the insulation failure of inverter-fed motor now, and their research results have been used in some projects. Based on the existing results, this paper will study the temperature factor that influences the insulation characteristics of inverter-fed motor magnet wire, which will further improve the failure mechanisms thesis of insulation system.Partial discharge (PD) measurement is known as a necessary method to evaluate state insulating, because PD is an important factor leading to insulation failure. The paper built a PD test system on the basis of square-wave pulse power and the PD characteristics of magnet wire under different temperatures were measured. Then it compared with the PD properties of nano material and common material. The test results showed that numbers of discharge increase but the maximum discharge reduces as the temperature increasing at the same cycles.The paper explores the temperature spectrum of dielectric loss tangent (tan8) value at different aging time and different aging frequency by using delta2000device. The test results show that tanδ increases gradually as the temperature increasing In the low temperature region, and comes to max value at about130℃and then decreases with a small amplitude.In addition, a set of aging device for magnet wire of inverter-fed motor based on the IEC60851-5was designed, which is used to study the breakdown voltage and aging life of magnet wire under different temperature condition. The results show that the breakdown voltage of the sample has a declining trend with the increasing of the temperature and the breakdown voltage of nona material is lower than the common material under the same temperature, which is due to the internal structure of material is changed by the nano particles. The aging life of sample reduced gradually along with the rising of temperature, then compared the influence on aging life of different test voltage and test frequency. According to the inverse power function, the mathematical model of aging life was established. At last, the morphology of magnet wire at the breakdown point was analyzed by the technology of scanning electron microscopy (SEM) and researched the chemical composition of insulation material at the breakdown point. The test result showed that the breakdown point was black powder because insulation layer was carbonized and the C element content is too high.