Influence of surface discharge on the deterioration characteristics of ethylene-propylene rubber cable insulation under alternating current high voltage

To investigate partial discharge-induced deterioration characteristics of ethylene-propylene rubber (EPR) cable insulation under repeated alternating current (AC) voltage on high-speed trains, an experimental platform with a column-plate EPR insulation model is established. The surface condition and breakdown voltage of insulation samples after discharge treatment are observed and measured. In addition, a fitting formula to evaluate the deterioration extent of EPR samples is proposed. The results show that under repeated discharge pretreatments, the volume resistivity increases first and decreases afterwards when discharge magnitude is low. When partial discharge (PD) intensity increases to 100 pC, the volume and surface resistivity decrease monotonously, and the decreasing rate is positively correlated with PD intensity. During PD pre-treatment, a white circle appears near the electrode and turns to pale yellow with PD intensity. For PD pretreatments of 50 and 100 pC, withstand voltage of EPR insulation increase first and decrease afterwards, and the downward trend is slow. For PD pre-treatments of 200 and 400 pC, the withstand voltage decreases significantly with the degradation time. The fitting formula model shows that under the action of a strong electric field, the relationship between the reliability of EPR insulation samples, the probability and rate of molecular chain breakage, and the intensity of discharge activity is not linear.