**7. Conclusion**

It has been shown that a system combining a magnetic speed multiplier and a high-speed generator is an interesting alternative to the use of a direct drive generator. The high per‐ formance level of the magnetic gear discoid structure allows the design of a more compact system with better efficiency.

In this context, despite its limited capacity in the transmission of torque, the magnetic speed multiplier has many advantages over its mechanical counterpart, but the cost will inevitably be higher because of the use of expensive materials.

The absence of maintenance of the magnetic device could nevertheless tip the economic bal‐ ance towards the latter.

The magnetic gear discoid structure is particularly suitable for power levels of tens of kilo‐ watts. The design made in paragraph 5, for a 10 kW wind turbine, confirms this. The same calculations show that a speed multiplier for a wind turbine of 40 kW (approx. 4000 Nm at 100 RPM), would have an external diameter of 800 mm, which is reasonable considering the mechanical structure.

For significantly higher powers, above 100 kilowatts, the design of a large diameter discoid structure becomes difficult, particularly because of the axial forces acting on the discs, ac‐ cording to what was discussed in Section 5. The solution is no longer economically viable.

At the opposite side of the power scale, for a wind turbine of a few hundred watts to several kilowatts, the use of a multiplier, mechanical or magnetic, is unwise. A structure of directdrive generator, like that of Figure 10, for example, allows a more economical and more reli‐ able design.

Magnetic gear technology is not yet fully developed and many of the mechanical problems in cylindrical or discoid design are yet to be resolved.
