Progress of 275 kV-3 kA YBCO HTS cable

A 275 kV-3 kA high temperature superconducting (HTS) cable has been developed in the Materials & Power Applications of Coated Conductors (M-PACC) project. AC loss reduction of a two-layer HTS conductor was undertaken by removing the edges of YBCO tapes with low critical current density. The HTS conductor using these tapes was fabricated, and low loss of 0.235 W/m at 3 kA_rms was achieved. The 275 kV-3 kA cable was designed, and the 2 m model cables were fabricated. This cable had 325 mm² copper stranded former inside the HTS conductor and a 310 mm² copper shield layer on the HTS shield layer for over-current protection. These cables withstood an over-current of 63.0 kA for 0.6 s, which is the worst situation for 275 kV systems. The partial discharge (PD) and V-t characteristics of a liquid nitrogen (LN₂)/polypropylene (PP) laminated paper composite insulation system have been integrated into the design of the insulation for the 275 kV cable. The results revealed that the PD inception stress (PDIE) did not depend on the insulation thickness, and that lifetime indices of V-t characteristics at PD inception were as high as about 80-100.