Electrical insulation design and evaluation of 60 kV prototype condenser cone bushing for the superconducting equipment

Abstract

A cryogenic bushing is an essential component to be developed for commercial applications of high voltage (HV) superconducting devices. Due to the steep temperature gradient of the ambient of cryogenic bushing, general gas bushing adopting SF6 gas as an insulating media could not be directly used due to the freezing of SF6 gas. Therefore, condenser type bushing with special material considering cryogenic environment would be better choice for superconducting equipment. Considering these circumstance, we focused on the design of condenser bushing made of fiber reinforced plastic (FRP). In case of the design of the condenser bushing, it is very important to reduce the electric field intensification on the mounted flange part of the cryostat, which is the most vulnerable part of bushings. In this paper, design factors of cryogenic bushing were analyzed, and finally 60kV condenser bushing was fabricated and tested. In order to achieve optimal electric field configuration, the configuration of condenser cone was determined using 2D electric field simulation results. Based on the experimental and the analytical works, 60kV FRP condenser bushing was fabricated. Finally, the fabricated condenser bushing has been tested by applying lightning impulse and AC overvoltage test. From the test results, it was possible to get satisfactory results which confirm the design of cryogenic bushing in cryogenic environment.