Electric field reduction due to charge accumulation in a dielectric-covered electrode system

Outlines for increased insulation performance of an air gap through the use of dielectric coatings are given. Theoretically, it is shown that the homo geneous electric field in a plane-parallel electrode system can be reduced if the electrodes are covered with a thick dielectric coating. Free charges will be affected by the electric field between the electrodes and are depo sited at the dielectric surfaces. As a consequence, a counteracting electri c field component results, which accordingly causes a reduction of the tota l electric field in the air gap and an enhancement of the field in the diel ectric layers, i.e. the electric field is forced into the dielectric coatin gs by the charges. This effect gives important implications in HV engineeri ng. Introductory experiments supporting the idea have been carried out with promising results. It was confirmed that the withstand voltage of a plane- parallel electrode geometry with an open air gap, for de as well as unipola r impulse voltage, could be increased considerably if the electrodes were c overed with thick polymeric layers. Charge formation at the electrode surfa ces as well as in the air gap is believed to be responsible for this effect . In today's insulation systems, this is known to work only for time-indepe ndent electric fields, i.e. generally de voltages. Further experimental wor k is required and will be performed in order to scrutinize thoroughly and c larify the phenomenon, its capabilities and limitations.