Breakdown strength of solid ∣ solid interfaces

The longitudinal breakdown strength of Interfaces is low because combination of two solid dielectrics enhances the risk of cavities and moisture at the interfaces. This paper presents the measured results of AC 50Hz breakdown voltage test of XLPE - XLPE interfaces assembled either under water or in standard laboratory conditions in air. A theoretical model for the voltage drops across contact spots and voids is proposed for both dry and wet interfaces. The model utilizes the estimated void dimension and number of voids formed at the interface in order to estimate the difference between the breakdown voltage of dry and wet interfaces. The estimated difference between the breakdown voltages was compared with the measured value. There is moderate agreement between the estimated results and the measured ones. The measured breakdown strength of wet interfaces was around 4.5 kV/mm whereas that of dry ones was measured to be around 8.0 kV/mm. In the case of wet interfaces, the nominal voltage of connectors may be designed based on the electric field of approximately 0.5 kV/mm along the interface.