Comparative study on thermo-mechanical insulation aging of evaporative cooled and air cooled stator bar

During the lifetime of generator-motor, insulation system of stator bar is gradually deteriorated by different reasons such as voltage, operating temperature, thermal cycle, mechanical vibration and environmental aspects. Compared with hydro-generator, thermal cycle has greater impact on the insulation aging process of generator-motor because of its much more frequent start/stop operations. Compared with traditional air cooled stator bar, evaporative cooled stator bar has lower working copper strands temperature, smaller temperature difference between copper strand and groundwall insulation, and less thermal variation during start/stop operation[1] To evaluate different effects of the above two cooling methods on the deterioration of the insulation, 100 times thermal cycle testing is finished and magnitude of partial discharge is measured every ten thermal cycle. Variation trend of partial discharge during thermal cycle testing has been summarized in this paper, which indicates different influence of the above two cooling method on thermo-mechanical insulation aging.