Alternative vacuum interrupter envelopes using glass-ceramic materials

The envelopes for vacuum interrupters may be made of any suitable materials such as glass, glass-ceramic, porcelain or alumina ceramic. Glass-ceramic materials offer superior dielectric properties over alumina ceramic envelopes in addition to their ability to join successfully with many different metals and alloys. In this study many new glass-ceramic compositions have been investigated which offer the required refractory behaviour making glass-ceramic-to-metal seals suitable for a single-shot seal-off cycle. The net-forming of glass-ceramic to metal seal combinations opens up new design avenues with the potential to be cost-effective. Glass-ceramic housings have end-of-life recycling potential and therefore, offer environmental benefits. The study shows that new glass-ceramic-to metal seal envelopes are cost-effective if used in novel shapes and sizes. With novel designs, the total interrupter cost is likely to come down due to the reduction in the number of components, weight of metal components and lower jigging costs. A novel load break switch (LBS) design is presented which uses fewer components thus reducing material cost. A new design to extend LBS to higher voltage ratings is described to make vacuum interrupters suitable for wider applications. It has been shown how different features can be incorporated into the glass-ceramic envelopes to attach vapour shields or provide external sheds or corrugations to enhance their dielectric behaviour.