Lifetime and factors affecting electrical degradation of solid dielectrics

The intrinsic electric strength of many insulating solids appears to be in excess of 10 MV /cm. Values in this region have been measured on thin carefully prepared samples with pulsed voltages. In practical applications, however, design stresses well below this value are used mainly, because of reliability requirements, since volume breakdown may be caused by anyone of a number of factors, at stress values which are only a fraction of the intrinsic electric strength of the material. These factors include thermal instability, electrochemical and electromechanical processes, chemical or thermal deterioration and partial discharge erosion or channel propagation, which latter has probably most influence on the lifetime of dielectrics.