Study on the development of PD parameters during the process of multi-stress aging of stator winding

The PD detection technology has been an efficient method to evaluate the condition of solid insulation since its occurrence and is now used widely in the field of electric engineering. In this paper, the development of PD parameters during the process of multi-stress aging of stator winding is studied in order to evaluate the condition of solid insulation of a large generator in service by PD detection technology. The thermal, electrical and mechanical stresses were applied to the specimens of stator bar by the aging system simultaneously. Moreover, a practical anti-corona scheme is adopted to improve the electrical field distribution at the end of specimen and a new measuring electrode system is used to assure the accuracy of PD measurement and the feasibility of long-term multistress aging. The partial discharge is measured before multi-stress aging and after 600 h aging by using HAEFELY TE571 partial discharge analyzer. The PD phase-resolved quantities distribution, time-resolved quantities distribution and three-dimensional distribution were analyzed in this paper. The maximum magnitude, number, energy, current of discharge increase and the center discharge moves to the negative half of the voltage cycle from the positive half according to the discharge three-dimensional distribution. In addition, the phase range of discharge widens apparently.