High-temperature superconducting tri-axial power cable

Abstract

Encouraged by the positive test results of a 1.5-m long prototype tri-axial cable, the Southwire/ORNL team has conceived, designed and built a 5-m tri-axial cable with three-phase terminations. The three concentric superconducting phases are made of BSCCO-2223 HTS tapes, separated by layers of cold-dielectric tape. A copper braid is added as the grounding shield. The completed tri-axial cable is enclosed in a flexible cryostat. Cooling of the cable and terminations is achieved by liquid nitrogen flowing through the annulus between the cable and the cryostat. The terminations used in the cable tests are cooled by a separate liquid nitrogen stream. The resulting three-phase, cold dielectric, cable and termination design is nearly as compact as the single-phase, co-axial design developed previously by Southwire/ORNL and represents the highest known cable current density achievable in an electric AC power cable. DC testing of the 5-m cable includes V– I curves for each of the concentric HTS phases, cable heat loads at varying DC currents, liquid nitrogen flow-pressure measurements, and over-current tests. AC testing of the cable includes ac loss measurements, induced-current in the Cu-shield measurements and operation at the line voltage test. The ac losses are measured calorimetrically by measuring the temperature differential of the coolant across the cable length due to the ac loss in the superconductors. Both balanced and un-balanced currents among the three phases are used in ac loss and induced current measurements.