Surface-potential decay in insulators with field-dependent mobility and injection efficiency

Surface-potential decay characteristics of corona-charged insulators are analyzed theoretically. The effects of field-dependent drift mobility and injection efficiency, as well as time-dependent injection, are included. The theoretical results are compared with existing surface-potential decay data on polyethylene. At the highest initial surface potentials all the surface charge is injected into the insulator on a time scale which is small compared to that of the measurement, and the injected charge drifts under its own self-field to the collecting electrode by means of a field-dependent transport process without significant range limitation. At the lowest initial surface potentials little or no charge is injected, and the surface potential is constant in time. For intermediate initial surface potentials the injection process is time and field dependent, with the time dependence being stronger than an injection process associated with a surface charge density that decreases exponentially in time, but weaker than that for instantaneous complete injection.