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Description
Most conventional wind power generators need a high amount of rare-earth permanent magnet material (RE-PM).
Gearless low-speed solutions (≈10 rpm) require ≈0.5 ton/MW of RE-PMs. Most work on High-Temperature Superconductors (HTS) in wind power generators has been focused on this type so far and requires high amounts of HTS tapes.
Geared mid-speed solutions (400…600 rpm) need only ≈50 kg/MW RE-PMs.
Using HTS in a mid-speed generator (with typically 2 or 3 planetary gear stages and without a spur gear stage) indicates a potentially improved business case by restricting the HTS tape need to less than 3 km for a 13 MW generator.
In this work, we report on the design and first experimental results on the development of an HTS rotor. The goal of the project “SPEEDY_HTS” is to replace the conventional rotor of an existing 6 MW, 24-pole generator at 602 rpm and a 3-phase voltage of 750 Vac by a rotor with coils based on HTS. According to the simulations, this extends the power of the generator up to 13 MW in the same machine housing. Thus, the power density is far beyond the limits of conventional generator technology.
However, introducing the HTS rotor into the existing generator faces several major challenges:
1) balancing the different heat loads and the cooling capacity (at the target operating temperature of 30 K),
2) providing the very high excitation ampere-turns required for the larger air gap and the respective magnetic field,
3) meeting the dynamic excitation requirements for grid stability,
4) inclusion of a central, warm pitch-control shaft/ tube with a rotational speed differing from that of the rotor,
5) using a rotating feedthrough for the cooling system.
We report on these five challenges and describe the developed solutions.
The 24 poles of the HTS rotor are designed as double-window-frame coils using 12-mm wide HTS tape and being connected in series. The HTS rotor coil design is weakly-non-insulated characterized by a considerable, but low, turn-to-turn resistance.
First results on coil properties are given, too.
This work is funded by the German Ministry of Economy and Climate, FKZ03EE3094E, and by the Program Oriented Funding by the German Ministry of Research, Program MTET, High-Temperature Superconductivity, 38.05.03.
