According to Kao's model of electrical discharge and breakdown in cond
ensed insulating materials, charge carrier injection from electrical c
ontacts and subsequent dissociative trapping, and recombination play a
decisive role in the breaking of polymer chains and the creation of f
ree radicals or low-weight molecules, and hence traps. We believe that
electrical aging is due to this gradual degradation process. The incr
ease in structural degradation and trap concentration reflects the deg
ree of electrical aging and hence the lifetime of the electrically str
essed polymers. On the basis of this concept, we have derived a theore
tical formula for the prediction of the lifetime of insulating polymer
s. We have also carried out experiments on polypropylene films at high
electric fields. It is found that destructive breakdown occurs when t
he accumulation of field induced traps reaches a certain critical valu
e. Experimental results are in good agreement with our theoretical mod
el. (C) 1998 American Institute of Physics.