Noninsulating properties of insulating materials

In this paper we discuss three phenomena which represent field induced deviations from thermodynamic equilibrium of an insulating material. Water treeing is shown to have at its origin a strong field induced change in the electrochemical potential of ionic impurities. This is the driving force for electrochemical processes which lead to the observed damage. Field induced high mobility carriers generated by detrapping or impact ionization lead to prebreakdown currents and electroluminescence. In most cases we are dealing with far from equilibrium but quasistationary solutions of the corresponding equations. All three phenomena involve field induced transport processes in an insulator. The transport processes form the physical basis for field induced ageing processes.