Effect of multi-physical field long-term aging on DC partial discharge of BOPP films

As the key insulation medium of dry DC capacitors, biaxially oriented polypropylene (BOPP) films are prone to partial discharge (PD) during long-term operation. To investigate the influence of long-term multi-physical aging on DC PD in BOPP films, this study conducted aging experiments on 5.8 μm BOPP films. Three typical PD defect models (corona discharge, internal discharge, and surface discharge) were designed. Using the pulse current method, the PD characteristics under positive DC voltage were systematically studied. Results indicate that surface discharge defects exhibited PD cluster distributions in discharge magnitude vs time patterns, with corona discharge repetition rates demonstrating an initial increase followed by a decreasing trend under prolonged voltage application. Internal discharge defects manifested hill-like features. With progressive aging, the PD inception voltage (PDIV) decreased for all three defect types. Among these, internal discharge defects exhibited the lowest PDIV of 0.6 kV in aged specimens under DC voltage. The repetition rate of surface discharge and internal discharge increased significantly, while that of corona discharge decreased. There is a correlation between the two adjacent discharges of corona discharge and internal discharge, showing a “memory effect.” During PD development in the three aged film defect models, internal discharge defects generated the highest discharge counts. In contrast, both surface and internal discharge defects produced the largest discharge magnitudes, with surface discharge defects exhibiting maximum skewness and kurtosis in their distribution patterns. It is expected that these results can provide theoretical foundations and experimental references for online monitoring and fault diagnosis of DC partial discharge in power capacitors.