Polarization and Depolarization Current Characteristics of Degradation Stator Insulation of A Rotating Machine

This paper presents the dielectric analysis of the simulated degradation stator bars compared with unmodified stator bars. The stator bars used in the experiments were acquired from the 30 year in-service synchronous machine of a hydro power plant. The simulated degradation stator bars were prepared and comprised of outer corona protection degradation stator bars, partial discharge (PD) stator bars and thermal degradation stator bars. In case of the outer corona protection degradation, the outer corona protection surface was abraded for small damages. For PD degradation bar, the PD existing bars were used for the experiment. In case of thermal degradation stator bars, they were divided into three groups, the first group of stator bars was heated in the oven at 100°C for 12 hours. The second and third group stator bar was heated at 120 and 140 °C respectively for 12 hours as well. After preparing the test objects, the polarization and depolarization current (PDC) were performed with the mentioned stator bars. The PDC test results were recorded. The test results showed that the polarization currents and depolarization currents, the conduction currents and the capacitances of the simulated degradation stator bars were clearly different from these of the unmodified stator bars. Other analysis parts are reported also in the paper. This paper suggests that PDC test technique is one of the effective methods for evaluation of the stator bar insulation characteristics.