Eddy current loss estimation for direct drive wind turbine generators with superconducting excitation winding by numerical and analytical models

Direct drive wind turbine generators with superconducting excitation winding are studied with focus on the electromagnetic damper design. A semi‐analytical eddy current model is built for parametric design studies based on a vector potential approach. The considered generators employ open stator slots and exhibit strong saturation effects, so that an analytical expression for the source terms is not adequate. Whilst the field equations are solved analytically, an equivalent current loading, accounting for slotting effects and saturation, is obtained by magnetostatic models applying the 2D finite element method (FEM). The proposed framework for the extraction of the current loading is universal and may also be applied to other machine types (e.g., permanent magnet synchronous machines, [PMSM]). In relation to transient FEM models, a considerable time‐saving can be achieved, which is particularly beneficial in case of large models, for example, in case of fractional slot windings or intermittent feeding schemes. The eddy current loss in warm and cold rotor parts in a direct drive generator in the 7 MW power class are computed with the semi‐analytical and transient 2D FEM models under variation of the damper geometry and the stator winding configuration. Minimum damper dimensions as well as constraints regarding applicable stator windings are derived.