Insulation for Rotating Machines Type II Under Different Electrical Stress Conditions

with the increasing application of power electronic components in driving rotating machines, the electrical stress factors were significantly changed. This paper deals with the investigation of lifetime characteristics for insulation of type II rotating machines performed by breakdown measurement of pulse voltage at the different waveforms and rise time. The results were compared with those gathered at power frequency, using different time scaling parameters (number of pulses, effective time). It is found that the effective time of stress voltage provides a clearer perception to study the lifetime behaviour than the number of pulses, especially for comparing the effect of the different applied voltage waveforms on acceleration aging. The results indicate that the rise time of the pulse voltage is considered the main influence on the life of insulations, it leads to insulation failure in a lower time. Additionally, the effect of combined stress (electrical, thermal, mechanical) was studied by using a specially developed sample, which included the curved parts of windings. It was found that the most critical part of such "coil-windings" are those curved parts because they are stressed not only by higher mechanical but also by larger electrical field strength.