Voltage Endurance Test of Vacuum Insulation for Cryocables

Vacuum insulation with cylindrical ceramic spacer insulators has been studied with respect to changes of its ac flashover voltage with time. The distributions of times to failure, which were found to confirm Weibull´s distribution, were used for plotting the regression curves for times up to 350 h. The results show that even at rather low stresses the flashover voltage decreased in time. This phenomenon is connected with the recorded deposition of metal particles from the electrodes on the surface of the spacers during the tests. This possibility of the decrease of the flashover voltage, induced by the deconditioning effects of contaminating conducting particles generated under the working stress by the system itself, must be taken into account when considering the suitableness of using special means of increasing the short-time flashover voltage of vacuum insulation for cryocables.