Breakdown processes in low density polyethylene and cross-linked polyethylene under DC high stress

The relationship between an electrical breakdown and a space charge accumulation in low-density polyethylene (LDPE) and cross-linked polyethylene (XLPE) was investigated under high dc stress using the pulsed electro-acoustic (PEA) measurement system with a circuit for an external current measurement. It has been found that the space charge accumulation strongly affects the breakdown characteristics in both materials. However, there is a difference how the accumulation affects the breakdown in them, but it was hard to know why the difference generated. Therefore, we tried to measure conduction current simultaneously with the PEA measurement. Judging from the obtained results, it was found that the breakdown mechanism under dc high stress in XLPE was different from that in LDPE. In LDPE, the breakdown occurred under a much higher electric field, which was induced by a huge amount of the space charge accumulation, than the applied average one. In XLPE, on the other hand, it was found that the breakdown suddenly occurred after a continuous large conduction current flowed under a little enhanced electric field. The former phenomenon may be caused by an “electronic” breakdown process and the latter is concluded with a “thermal” process.