PD mechanism and pattern investigation for stator winding insulation of HV motors

The high voltage (HV) motor suffers from insulation failure due to long term partial discharge (PD) which is a great threat to its normal operation. This is why online monitoring and fault diagnosis of PD activities of HV motors is becoming more and more important to date. To perform the online monitoring of the PD activity, pattern distributions of the harmful PD should be understood to guarantee detecting accuracy in the fault identification process. In this paper, three types of partial discharge, including slot discharge, bar-to-bar discharge, and corona discharge at the junction section of the semi-conductive tapes and the corona release tapes, are induced using stator coils embedded into a stator core slot model. The phase resolved partial discharge (PRPD) representation is adopted to get distribution characteristics of the PD. The PD mechanisms are illustrated using dielectric barrier discharge model. The experimental results show that a sharp increase at the onset of the positive discharge could be helpful to distinguish slot discharge from corona discharge. The relatively high amplitude and the narrow section of the phase distribution of partial discharge at the positive half voltage cycle are chosen to characterize the bar-to-bar discharge. Because of the block of insulating medium, the discharge current cannot develop into spark or electric arc but could be turned to several visible stable discharge filaments.