Development of Tri-axial superconducting cable system for type test

Abstract

We developed a tri-axial superconducting cable system with the rated voltage of 22kV and operating current of 3 kA at liquid nitrogen temperature. We designed the superconducting cable and the termination that was cooled subcooled liquid nitrogen. We used in-house YBCO tapes and a winding machine to prepare the conductor that the Ic -value of 4,200 A or more per phase at liquid nitrogen temperature. The outer diameters of the conductor and the cryostat were approximately 50 mm and 130 mm, respectively. The length, the diameter and weight of each termination were approximately 4,000 mm, 450 mm and 600 kg. The thickness of the insulation layer, which was made from made from PPL paper, was determined by estimation of minimum break down electrical field from Weibull distribution analysis of results, which were obtained by break down tests of the model cables. Regarding the cooling condition of the cooling system, the liquid nitrogen temperatures of the inlet and the outlet of cable system was designed to be 65 K and 70 K, respectively. We manufactured a 25 m tri-axial superconducting cable, and cut out it to get 2 m samples for the Ic test and voltage test at liquid nitrogen temperature. The critical current of each phase was higher than 4,500 A. There was no break-down of each insulation phase at 52 kV for 30 minutes the voltage test. We also manufactured a pair of termination connection for system test and no break-down occurred each insulation phase at 52 kV for 30 minutes. We performed type test of cable system including the superconducting cable and the termination, based on “Recommendations for Testing of Superconducting cables (CIGRE Technical Brochures 538)” [1].