Preliminary ageing tests on a superconducting cable dielectric

A lifetime of at least 25 years must be established for the commercial acceptance of the superconducting power cable that is under development. Establishment of lifetime requires accelerated testing. Limits to the degree of frequency acceleration are examined and frequency-accelerated ageing tests on a sample of the cable dielectric system are described. The sample was stressed at 10 MV/m with the dielectric impregnated with supercritical helium gas at 8 K and a density of 110 kg/m3 for an equivalent 60 Hz time period of 531 days. During this period the partial discharge inception stress declined from 12.3 MV/m to 7.1 MV/m. Examination of the sample after the test revealed erosion of the vapor-deposited aluminum layer on the screen tapes.