Relationship between packet-like space charge behavior and external current in polyethylene under dc high electric field

We have investigated the space charge distribution in low density polyethylene (LDPE). Under high dc electric field, a huge amount of positive packet like charge is observed in LDPE. It moves towards the counter electrode under high dc electric field, and then the breakdown finally occurs. The reason of the generation of the packet like charge is thought that there are two different conductivity in front and rear of the packet-like charge in the sample. However, while such distribution of conductivity in the bulk under dc high electric field is predicted using numerical analysis based on the measurement results, it has not been confirmed experimentally, yet. Therefore, we have tried to find out the existence of the conductivity distribution from the simultaneous measurement results of space charge distribution and external current using the improved pulsed electro-acoustic (PEA) method. In this improved system, space charge distribution and external current measurements are carried out by switching connection of a lower electrode between an electrometer and ground. In this paper, the typical measurement results obtained using the improved system is introduced. Moreover, we examined the relationship between space charge behavior and external current. As the result of simultaneous measurements, it is found that the external current increases during the injection and traveling of positive charge from the anode towards the cathode.