Testing of an MgB₂ coil for a wind turbine generator pole

We report on the testing of a 1 m long and 0.5 m wide racetrack coil wound from 4.5 km of MgB₂ tape-shaped superconductors with a copper strip soldered to the nickel matrix. The cross-section of the coil corresponds to what is needed for the field windings of a 10 MW direct drive wind turbine generator pole, but where the straight section has been shortened. Ten double pancake sub-coils were wet-wound, with epoxy as the only electrical insulation, and assembled. The entire coil was cooled down to 14 K, and the direct current was ramped up. Voltage measurements were made over the double pancake coils. For eight of the ten double pancake coils, excessive voltages appeared at currents much lower than the design current. These voltages may either be attributed to the wire quality or to the winding process. A quench was observed at 149 A, which is in reasonable agreement with the predicted load line of the coil obtained by scaling wire transport measurements at 1 T and 20 K with hysteretic magnetization measurements in the range 1-5 T and 5-20 K.