Degradation characteristics of oil-immersed pressboard samples induced by partial discharges under DC voltage

Abstract

To investigate partial discharge-induced degradation characteristics of oil-immersed pressboard under DC voltage, an experimental platform with needle-plane oil-pressboard insulation model is established. The surface condition and DC breakdown voltage of pressboard samples after PD pretreatment are observed and measured. In addition, a fitting formula to evaluate the degradation extent of pressboard samples is proposed. The results show that under constant PD pretreatments, surface roughness of pressboard samples decreases first and increases afterwards. The changing rate is positively correlated with PD intensity. During PD pretreatment, a “whitish-colored circular region” appears at samples' surface and grows with PD intensity. For PD pretreatments of 500 pC and 1000 pC, DC breakdown voltage of pressboard samples remains unchanged. The breakdown spot has no clear carbonization nor creepage trace. For PD pretreatments of 2000 pC and 3000 pC, DC breakdown voltage decreases. The breakdown spot is obviously carbonized and creepage paths emerge around spots. Further analysis indicates that degradation of oil-immersed pressboard samples due to DC PDs is the result of motion activation process induced by electrical and thermal effects under DC electric field.