Surface charge accumulation on insulating plates in SF6 and the effect on DC and AC breakdown voltage of electrode arrangements

Surface charge accumulation on insulating materials, which are located next to electrodes in electrical devices may lead to a change of the electrical field. In some cases the breakdown voltage of electrode arrangements could be exceeded. For the investigations an insulating plate made from PTFE was used. The test set-up allows to charge the specimen, to measure the charge density distribution and to verify the effect of charge on the breakdown voltage of an electrode arrangement. The test set-up was installed into a test vessel to study the effects under SF₆. As a result the formation of a bipolar electrical charge double layer with charge densities of up to -18 nC/cm² on the upper surface of the specimen and up to +15 nC/cm² on the opposite surface was determined. The formation of a bipolar electrical charge double layer could be simulated by numerical field calculation. Placing the charged specimen next to a rod-electrode arrangement causes a reduction of the AC and DC breakdown voltage up to more then 20%.