High-field induced electrical aging in polypropylene films

According to Kao's model of electrical discharge and breakdown in condensed insulating materials, charge carrier injection from electrical contacts and subsequent dissociative trapping, and recombination play a decisive role in the breaking of polymer chains and the creation of free radicals or low-weight molecules, and hence traps. We believe that electrical aging is due to this gradual degradation process. The increase in structural degradation and trap concentration reflects the degree of electrical aging and hence the lifetime of the electrically stressed polymers. On the basis of this concept, we have derived a theoretical formula for the prediction of the lifetime of insulating polymers. We have also carried out experiments on polypropylene films at high electric fields. It is found that destructive breakdown occurs when the accumulation of field induced traps reaches a certain critical value. Experimental results are in good agreement with our theoretical model. (C) 1998 American Institute of Physics.