Thermal aging effect on charging and discharging currents in polymers under DC stress

An experimental investigation of the charging and discharging currents in polypropylene and polystyrene under 1000 V DC stress were presented. The results showed a distinct difference between the charging and discharging currents. As known, the charging current after the DC voltage application decreases rapidly during the first hundred seconds then approached a stabilisation. The discharging current flowing in the opposite direction of the charging current was observed. It was concluded that space charge have formed in the sample. The charging and discharging currents for both the polypropylene and the polystyrene increased with increasing thermal aging time at 80degC. It was established that the rise in the current depends on the thermal aging time which induces anomalous discharging current flowing in the same direction as the applied field.