Investigations on the metal vapour impact on the insulation behaviour of alumina ceramics within vacuum interrupters

Abstract

Basic investigations have been carried out on the dielectric performance of the ceramic (high-purity alumina, Al/sub 2/O/sub 3/) surface after switching. In order to examine the influence of the shielding on the protection of the ceramic surface against metal vapour condensation, different types of vacuum interrupters (VIs) have been tested: VIs with and without shielding. After having performed a high-voltage conditioning of the VIs, DC arcs with arbitrary arcing times were triggered between the contacts simulating the generation of metal vapour during high current interruption. Between the arcing tests, the insulation level of all VIs has been tested by means of an AC high-voltage source. Afterwards the VIs were opened and detailed investigations on the condensation of the metal vapour on the ceramic surface were performed by means of scanning electron microscopy (SEM), energy dispersed X-rays (EDX), and X-ray photon spectrometry (XPS). The conductivity of the surface film resulting from the condensation of the metal vapour was measured in order to compare the material investigations with the electrical behaviour of the surface.