Abstract:
In order to achieve lower cost of energy the typical
power rating of large wind turbine generators has steadily
increased over recent years. However, with the mast-top weight
of multi-megawatt generators exceeding 100 tonnes, installation
becomes increasingly costly and difficult. Direct drive turbine
designs can give significant weight and cost reductions. We have
developed a design for a lightweight direct drive transverse flux
generator with a rating of 2 MW. The design features a multi-pole
permanent magnet rotor with a single global HTS stator coil of
between 4 and 6 m diameter for each phase. As one consequence
of this design approach, the HTS conductor is exposed to leakage
field from the magnets and the self-field of the generated current.
The magnitude of the loss associated with these time-varying fields
is crucial to the viability of the HTS generator concept. The stator
design seeks to minimize exposure of the HTS tape to alternating
magnetic fields perpendicular to the face of the tape in order to
reduce the AC loss in the stator coils to an acceptable level. For a
coil operating at 50 Hz, the total AC loss is calculated as 15.1 W/m.
Thus, AC losses within each of the three 6 m diameter HTS global
coils of a 2 MW generator would be 285 W. The thermal load
for the cryogenic system of the 2 MW generator is estimated to
total 936 W, with the majority (90%) due to AC loss. Assuming
a cryogenic specific power of 20, the energy required to cool the
2 MW generator represents less than 1% of total output.
