Cryogenic high voltage testing of a 25 kV RIS bushing

High voltage bushings used for superconducting power engineering applications are exposed to cryogenic temperature stress. Dry bushings based on low hygroscopic materials are preferable for such an application. Resin impregnated synthetic (RIS) bushings are less hygroscopic than the well-established resin impregnated paper (RIP) bushings and have demonstrated their usability for room temperature high voltage application since few years. A conventional 25 kV, 2 kA room temperature RIS bushing was assembled to an open bath cryostat and subjected to five thermal cycles with liquid nitrogen as coolant. High voltage tests with AC, DC and impulse waveforms were successfully performed under cryogenic and room temperature conditions during these thermal cycles. No degradation of the bushing was found after the thermo-mechanical stress. Only the dissipation factor for the C2 test tap measurement showed a relevant difference to the manufacturer values. This paper focuses on the high voltage testing of the RIS bushing.