Research On Electrical Ageing Mechanism Of Inverter-Fed Traction Motor Insulation

In the process of large power semiconductor devices, frequency control drive systems are widely used in the field of locomotive traction. Railway traffic develops rapidly in China, which attracts more and more attention on the security and reliability of locomotive. AC traction motors are one of the key equipments of locomotive, and their performance is important on locomotive. Insulation of AC traction motor faces the continuous square wave pulses from traction inverter, but not the conventional AC voltage. Design and manufacture technology of large power traction motor is rapidly progressed in china. However, there is no sufficient standard nor common recognition as to the properties of continuous square wave pulse voltage stress and warranty requirements of winding insulations.In order to investigate the influence of square wave pulse with short rise time on winding insulation, AC traction system of express locomotive is used as subject. Combining with actual manufacture situation and referring to the latest research in abroad, terminal voltage and voltage distribution in winding of AC traction motor are calculated. Then, high frequency high voltage test system is developed to test dielectric property of winding insulation. Subsequently, partial discharges in the condition of continuous square wave pulse are measured and analyzed to understand damage to insulation caused by partial discharges. At last, aging tests are carried out and it is proved that partial discharge and space charge lead to insulation aging.Square wave pulses from traction inverter not only bring more harmonic loss, but also lead to over-voltage on terminal of traction motor and uneven voltage distribution of winding. In order to investigate influences of rise time and cable length on over-voltage and voltage distribution, high frequency equivalent circuit models of cable and stator winding are established. Finite difference solution is adopted to get the results. The results show that over-voltage is the function of rise time and cable length and voltage distribution in winding has relation to rise time, cable length and motor structure.Insulation property under square wave pulse is important for winding insulation design. A novel high frequency high voltage test system is developed to test dielectric property of insulation materials. This test system is made up of square...