Design and Test of a Double Pancake Coil for SMES Application Wound by HTS Roebel Cable

A double pancake coil wound by HTS Roebel cable was designed, fabricated, and tested at 77 K. This coil winding had eight turns with the inner diameter of 340 mm and a total conductor length of 10 m. With ten ReBCO strands, the transposition length of the cable was 300 mm. To avoid delamination of ReBCO strands, this coil was impregnated with paraffin wax by a vacuum impregnation method. For protecting ReBCO strands, protective copper plates (PCP) were inserted and soldered between cable surface and external current terminal. The voltage probes were not directly soldered on strands, but on the PCP instead. The critical current and central flux density of the coil were measured at 77 K. With the criterion of 1 μV/cm, the critical current was 1025 A at 77 K. Finally, the additional resistance and the heat loss at 77 and 20 K caused by adding the PCP were estimated.