Study On Aging Of Polyimide Film Insulation Under High Pulse Voltage Based On Thermally Stimulated Current

The Pulse Width Modulated (PWM) adjustable speed devices are already widely employed in the industry for the significant benefits of control and efficiency. However, the pulse voltage imposed upon the converter-fed motor from converter is entirely different from the normal sinusoidal conditions, fast rising time, high repetition frequency and amplitude. And this special waveform often leads to premature failures of winding insulations and the life expectancy of motor insulation is greatly shortened. As an important insulating material employed in winding insulations, Polyimide (PI) has not been investigated deeply related to the use of such pulse voltage. So understanding the failure mechanism of PI will benefit motor designs, especially the motor insulation system.The aim of this thesis is to investigate the structure change of PI film under pulse voltage. First, a thermally stimulated current (TSC) measurement system used for PI film is developed. Through the test of parasitic galvanic current existing in TSC measurement system, the mechanism of parasitic galvanic current is discussed. Secondly, the TSC of PI films are measured using this measurement system during aging process under different conditions. And the traps property and variations of parameters are investigated. Finally, compared with lifetimes test and scanning electron microscopy (SEM), the degradation of structure in PI film under pulse voltage is investigated. In addition, a new method to estimate the insulation condition of PI film is presented eventually.All the work this thesis introduced benefits the study of failure mechanism in PI film under pulse voltage. And it is also useful to understand the effect of inorganic particles loaded in PI film.