This paper deals with the novel idea of controlling the electric stress in a
hybrid air–solid dielectric insulation. In a parallel-plate electrode system,
the electric stress can be reduced if the electrodes are covered with thick
non-conducting dielectric coatings. Free charges are generated by
microdischarges developing between the electrodes and are deposited at the
dielectric surfaces. As a consequence, a counteracting electric field
component results, which causes a reduction of the electric field in the air
gap and an enhancement of the field in the dielectric coatings; i.e. the
electric stress is forced into the dielectric coatings by the charges.
A computation of the threshold voltage of the microdischarges is presented.
The charge simulation technique is used for field calculation, irrespective of
the thickness of the dielectric layer and the values of the charges deposited
on the dielectric surfaces. The calculated threshold voltages are compared
with those estimated before and those measured for different gap lengths.