A facility for testing the dielectric strength of liquid nitrogen

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.