A facility for testing the dielectric strength of liquid nitrogen

Abstract

For superconducting high voltage devices liquid nitrogen can not only be used as cooling liquid but also for electrical insulation purposes. Under the programme of a 110 kV fault current limiter project the breakdown and withstand voltages of liquid nitrogen are examined in a new cryogenic high voltage test facility named "Fatelini". Target withstand voltages for this new facility itself are 200 kV AC rms and 300 kV for standard lightning impulses. The liquid nitrogen can be pressurized till 0.3 MPa. Firstly a sphere to plane arrangement is used where the gap length can be adjusted in steps of 1 mm from outside of the cryostat in order to avoid long warm up and cool down times. The test facility is described in detail and the maximum voltage values which are reached so far are presented.

Cryogenic testing of a 25 kV RIS bushing

“…For this application the bushings are intended to be subjected partially to cryogenic conditions within a liquid nitrogen bath cryostat exceeding the standards for conventional outdoor applications, which are limited to temperatures down to -40 °C [1] or -70 °C [2]. The market for such cryogenic bushings is relatively small and therefore commercial bushings explicitly declared for cryogenic use [3] are difficult to obtain.…”

Experimental Design and Test of 100 kV Extra High Voltage Prototype Bushing With ${\rm CF}_{4}$ as Insulation Gas for Superconducting Equipment

“…Among the several technical and economic issues yet to be solved for the commercialization of superconducting devices for extra high voltage (EHV) power systems, one of the critical barriers for EHV applications is the optimum design and development of high voltage cryogenic bushings which could withstand both severe insulation requirements and a steep temperature gradient due to the cryogenic environment [4], [5].…”