Development of a Large-Capacity Superconducting Cable for 1000 KV A-Class Power Transformers

We have designed and fabricated a large-capacity superconducting cable for l000kVA-class power transformers. The cable is a triply-stacked multi-strand (6x6x6) type. The elementary strand has 19,050 NbTi filaments of 0.63mm thick in CuNi matrix. The test cable is installed as the secondary winding in a superconducting transformer with iron core in a room-temperature space. The primary winding is the second-level subcable of the secondary one and the turn ratio is nearly 14. The designed capacity of the test cable is 4.545 kA at the secondary voltage of 220V. The peak value of the current, 6.43kA(peak), is 78% of the critical current on the load line. The maximum current of the cable at 60Hz operation was 3.78kA(peak). The attained level of the secondary winding is 47% of the critical current. In the 60Hz operation of a small coil wound by the test cable, premature quench was initiated from the terminals of the cable connected with copper plates. It is suggested from the experimental results that the degradation in maximum current of the test cable is related to current transfer between the cable and the copper terminal plate.