Cryogenic testing of a 25 kV RIS bushing

Abstract

High voltage bushings for cryogenic current or voltage leads must master safely the special thermal stress in addition to the high voltage requirements. Resin impregnated synthetic (RIS) bushings have proven their usability for room temperature high voltage application since few years. Such paper free bushings are less hygroscopic than paper based bushings, which can be an advantage for components exposed to cryogenic temperatures on one side and to air conditions on the other. A conventional 25 kV, 2 kA room temperature RIS bushing was assembled to an open bath cryostat and subjected to five thermal cycles. High voltage tests were successfully performed under cryogenic conditions. No degradation of the bushing was found after the thermo-mechanical stress of the fast cool downs and one fast warm up. This paper focuses on the thermal tests.