Electric field enhancement within moulded samples of low density polyethene-a means of failure characterised by voltage ramp tests and space charge measurement

The work reported here presents evidence that the stress enhancing factor operating is that of a space charge hetero-field which enhances the applied field at the electrode up to a value of ~1 MV/mm, which is sufficient to cause `intrinsic´ breakdown in polyethene. Here, breakdown would be caused by the effective elimination of the barrier to charge injection, causing a destructive injection current. This mechanism would also be consistent with the `wormhole´ breakdown structures typically observed for majority of ramp failures in the region of characteristic field