The influence of space charge formation on polymer degradation investigated by means of PD

The partial-discharge (PD) measurement technique is used to study the effect of space charge formation, caused by injection and conduction mechanisms, on the degradation of low-density polyethylene. Besides the amplitude of the field strength, the duration of electrical stress plays an important role in the degradation process. Several electrochemical processes occurring under the influence of injected charges (oxidation, molecule cracking, and crosslinking) change the morphology of the polymer. Another time-dependent process (in the time scale of minutes) is the storage of stable space charges in deep traps. These mechanisms condition the polymer according to the history of stress, so that the inception of partial discharges is not purely field determined. These long-time effects are superimposed by conduction phenomena related to space charge movement. The results of the experiments indicate that PD measurements can give information about conduction and charge storage mechanisms in polymer insulating materials