5-M Single-Phase HTS Transmission Cable Tests

Abstract

Two 5-m, single-phase, High-Temperature Superconducting (HTS) transmission cables have been built and tested at Oak Ridge National Laboratory (ORNL) in a joint program between Southwire Company and ORNL. The active conductor of the cable consists of layers of Bi-2223/Ag tapes helically wound on a flexible former, followed by layers of cryogenic dielectric tapes, and then HTS shield layers. Subcooled liquid nitrogen at temperatures of 70–80 K and pressures of 3–7 bar flows down the inner pipe, turns around at a termination, and returns through the annulus between the cable and the vacuum-jacketed outer pipe to cool the cable. The DC V-I curves of the cables have been mapped as a function of temperature and the critical currents measured. The cables have exceeded the performance goal of 1250-A AC at 7.2 kV line-ground voltage. The AC loss measurements showed a loss of about 1 W/m for one and 0.7 W/m for the second cable at 76 K. High voltage measurements showed partial discharge at only background level for voltage up to 18 kV AC (2.5 times design value). Stable cable temperature was maintained at 1250-A rms at temperatures up to 80.5 K, where the operating current is almost twice the cable’s critical current. These test results provide confidence in the design approach and the extrapolation to the next phase: development of a 30-m, three-phase cable.