A Novel Configuration of a 20 MW LTS Wind Generator with a Cryogenic Pipe Cooling System

Superconducting generators offer a promising solution for far-offshore wind power that has a capacity of 20 MW and above. This paper proposes a novel configuration for high-power low-temperature superconducting (LTS) wind generators with a thermosiphon helium pipe cooling system on the superconducting excitation rotor. Three groups of cold heads, each with a condenser, are symmetrically arranged circumferentially around the excitation rotor, which has been preliminarily validated to enable natural circulation of helium along the helium cooling pipes without any pump no matter the rotor rotates or keeps standstill at any angle. A conceptual design for a 20 MW LTS wind generator incorporating the novel configuration has been developed, covering electromagnetic, structural, and cryogenic aspects. The design features 72 LTS excitation coils, achieving a radial air-gap flux density of 2.5 T with rated armature voltage and current of 3300 V and 3500 A, respectively. The generator has an air-gap diameter of 7.2 m, an axial length of 1.6 m and an active weight of roughly 130 tons. Preliminary analysis of electromagnetic, structural, and cryogenic performances of the generator has been conducted by 2D finite element simulations and analytical calculations. The maximum magnetic field on the superconducting coils is 6.6 T, and the maximum stresses on the superconducting coils and the torque tubes are 37 MPa and 137 MPa, respectively. The total heat leakages from 300 K to 50 K and from 50 K to 4.2 K within the cryostat are 174.8 W and 4.65 W respectively, sufficiently covered by the combined cooling capacity of nine cold heads in the system, each providing 70 W at 50 K and 1.25 W at 4.2 K. The highest temperature on the superconducting coils is 4.3 K.