Insulation design of cryogenic bushing for superconducting electric power applications

Recently, the superconductivity projects to develop commercial superconducting devices for extra high voltage transmission lines have been undergoing in many countries. One of the critical components to be developed for high voltage superconducting devices, including superconducting transformers, cables, and fault current limiters, is a high voltage bushing, to supply high current to devices without insulating difficulties, that is designed for cryogenic environments. Unfortunately, suitable bushings for HTS equipment were not fully developed for some cryogenic insulation issues. Such high voltage bushings would need to provide electrical insulation capabilities from room temperature to cryogenic temperatures.In this paper, design factors of cryogenic bushings were discussed and test results of specimen were introduced in detail. First, the dielectric strength of three kinds of metals has been measured with uniform and non-uniform electrodes by withstand voltage of impulse and AC breakdown test in LN2. Second, puncture breakdown voltage of glass fiber reinforced plastics (GFRPs) plates has been analyzed with non-uniform electrodes. Finally, creepage discharge voltages were measured according to the configuration of non-uniform and uniform electrode on the FRP plate. From the test results, we obtained the basic design factors of extra high voltage condenser bushing, which could be used in cryogenic environment.

► In this paper, design factors of cryogenic bushings were discussed and test results of specimen were introduced in detail.
► We focused on the comparative study of breakdown characteristics of different electrode materials.
► Puncture and creepage breakdown characteristics were analyzed based on the withstand voltage.
► We obtained the basic design factors of extra high voltage condenser bushing.
► We obtained the basic design factors of extra high voltage condenser bushing, which could be used in cryogenic environment.