Phase-resolved study on partial discharge for degradation diagnosis in polymeric insulating materials using model electrode system

Using MGI (metal-gap-insulator) and IGI (insulator-gap-insulator) electrode systems with 0.1 mm- or 4.0 mm-thick LDPE samples, we studied the temporal change of PD characteristics. The PD pattern and statistical parameter (PD inception phase) changed with aging time. The IGI electrode system showed a similar change in PD pattern with degradation to that of the MGI electrode system. The PDs in MGI electrodes with the 4.0 mm-thick sample showed new PD characteristics which were absent in the 0.1 mm-thick sample. This was attributed to pit formation just before breakdown. There results suggest the possibility of insulation diagnosis from the beginning to the last stage of PD degradation.