Anomalous discharging current in polymethylpentene

Discharging current which is measured after voltage application on a dielectric solid usually flows in the opposite direction to the applied field. Anomalous discharging current which flows in the same direction as the applied field is observed in polymethylpentene at temperatures higher than 100 °C. The effects of electrical stress and voltage application period on the appearance of anomalous current were examined. On the condition when the discharging current becomes anomalous, layers of hetero charges accumulated during voltage application are observed with the pulsed electroacoustic method. The accumulated charges decrease significantly after the anomalous discharging current was observed for 5 minutes. On the assumption that charge movement is ruled by the electric field formed by space charges, simulation of discharging current was carried out. The simulated discharging current agrees well with the experimental data, when it is calculated by assuming the mobility of positive charge to be μ_p = 2.5 × 10^-10 cm²/Vs and that of the negative charge to be μ_n = 7 × 10^-11 cm²/Vs.