AC losses in superconducting cables designed for generator field windings

In order to evaluate a conductor design suitable for a superconducting generator field winding, the loss behavior of different types of superconductors has been investigated. The cabled conductors tested have identical dimensions and nominal currents of 6000 A at 7 T but different matrix configurations, comprising pure Cu or Cu/CuNi matrices. Two different field variation modes were applied to the specimens: triangular and sinusoidal sweeps up to 6 Hz. From the experimental results the different loss components were separated according to theory. The maximum interstrand coupling loss amounts to a factor of less than two compared with filament coupling in the case of Cu matrix conductors. Since in a generator rotor the winding is additionally compressed by centrifugal forces, investigation of the loss behavior of sample coils under mechanical pressure was started in a modified apparatus.