Main Insulation Aging State Evaluation of Generator Stator Bar Based on the Branch Way Model of the PDC Method

Large generator stator bars will be subject to thermal stress during operation, resulting in insulation deterioration. At present, there is a lack of a good means to evaluate the deterioration of the main insulation of generator stator bars. To clarify the feasibility and effectiveness of the polarization and depolarizing current method to evaluate the performance of the main insulation of stator bar of large generators in actual operation, relevant research was carried out in this article. In this article, some short samples of stator bars were intercepted. At 120°C and 170°C, thermal aging was performed for 0,10,30 days and 15, 20 days respectively. The polarization and depolarizing current test was carried out on the aged samples. According to the polarization and depolarizing current test results, the number of branch ways was identified. It was found that under the condition of thermal aging at all temperatures and time, the number of main insulation branch ways of stator bars did not change. So, the model of the main insulation in the process of polarization/depolarization and the corresponding parameters of the model were defined. According to the PDC test results, it was found that the generator insulation solidified in the early stage of thermal aging at 120°C, and the insulation performance became better. At the late stage of 120°C thermal aging and 170°C thermal aging, the insulation performance deteriorated. This was proved by the variation of characteristic parameters of the polarization and depolarizing current branch way model.