Investigation of electrical breakdown strength of interfaces. Study of interfaces between electrical insulation materials used in high voltage products exposed to electrical AC and DC fields

Abstract

Usage of cable systems has increased during the last decades both for AC and DC solutions. To make the cable system functional cable accessories is needed used for example when connecting or terminating a cable. When an accessory is installed to a cable an interface is created between the insulation of the cable and the insulation of the accessory. This interface is exposed to an electric field stressing the interface both radial and tangential. This master thesis has focused on finding the electrical breakdown strength of above mentioned interface when exposed to an electric field directed tangential to the interface. Experiments have been performed on small samples, imitating interfaces in high voltage accessories. The samples has been tested with interfaces of different material combinations, with varying surface structures and when stressed to either a DC or AC field. All samples had an interfacial pressure of 0.5 Bar. The results of the experiments show no difference in breakdown strength when comparing the two tested types of surface structure, simulating a cut and grinded surface. The material combination of XLPE/EPDM has proven to have a stronger interface in comparison with the material combination of XLPE/SiR. Finally the samples stressed to alternating electric field broke down at lower field intensities in comparison to the samples stressed with DC-electric field.