Designing the Vacuum Interrupter for Applications ≥ 72.5 kV

In view of the increasing global market for high voltage (HV) vacuum circuit breakers in the voltage rating ≥ 72.5 kV, it is necessary to focus our attention on developing the vacuum interrupters (VIs) for these ratings. VCBs have already penetrated the 72.5 kV market and trials are progressing with introducing up to 145 kV VIs into the power networks. Prototype of the 252 kV VI has already been demonstrated. It is therefore, logical for SUPERGRID to introduce not only the capability to design, develop and prototype manufacture these ratings but also explore new designs and processes which could be introduced for voltage ratings ≥ 252 kV.

This paper explores the development areas and novel concepts for designing the HV VIs for the market needs. It highlights different available tools such as modelling the mechanical layout, electromagnetic and thermal modelling and the vacuum demountable unit which help considerably in designing and understanding the fundamentals of different novel concepts and the arc control structures for different voltage ratings. Results of the study of different design aspects, different components processing routes, high vacuum seal-off and post seal-off processing techniques have been presented which help in understanding to improve the quality, performance and the environmental signature of the HV VIs. Based on the study of existing literature and ideas derived from other technologies, novel approaches to design and manufacture VIs have been outlined for possible study and development.

For improved VI layout designs, selection of new materials and components such as bellows, ceramic housing, contact electrode, OFHC copper conductor, getter and other structural materials have been examined. Similarly, processes such as electropolishing, components cleaning, increasing the process seal-off temperature and pressure measurement techniques have been looked at. For improving the voltage performance of multi-break and long-gap VIs, effect of loose particles due to processes and arcing electrodes and processes such as in-process cleaning, HV conditioning have been discussed.