NEW APPROACH TO FLASHOVER IN DIELECTRICS BASED ON A POLARIZATION ENERGY RELAXATION MECHANISM

The polaron concept is used to describe trapping of charge in a dielectric medium. It is shown that trapping is associated with 'defects' identified as being due to a local decrease of the electronic polarizability. The polarization energy around a charge is estimated, using a self-consistent calculation of the local field. In nonpolar dielectrics this energy is 5 eV per charge, in the limit of validity of the Clausius-Mosotti relation. In polar dielectrics it can be much higher. A flashover process is proposed as resulting from the destabilization of the space charge by a variety of perturbations (electrical, mechanical, thermal), followed by the mechanical relaxation of the lattice, initially polarized by the charge.