Effect of coating electrodes with an aluminium oxide layer on the electric strength of unconditioned vacuum insulation systems

The paper presents the results of investigations of the electric strength of vacuum insulation systems that were not subjected to conditioning. Plane electrodes with rounded-off edges of Rogowski´s profile were used in the investigations. The electrodes with 50 mm diameter, were made of aluminium. The aluminium oxide layer on aluminium electrodes was obtained by electrolytic oxidation of polished and degreased aluminium electrodes. The aluminium oxide layer obtained in such a way was about 15 μm thick. The paper shows the influence of fundamental factors defining the conditions of vacuum insulation system on its electric strength, such as: the value of pressure (within the scope of approximately 1 Pa-1 mPa) and at constant value pressure approximately 1 mPa, the length of vacuum gap, and the presence of aluminium oxide layer coating the surfaces of aluminium electrodes. The experiments have shown that the aluminium oxide layer coating the surfaces of aluminium electrodes causes, at the pressure of 2 mPa, 100% increase of electric strength of unconditioned vacuum insulation systems