Superconducting permanent magnet generators (SCPMGs) are a potential candidate for 10 MW direct-drive wind turbine applications. This paper presents two 10 MW SCPMG designs using MgB<sub>2</sub> cables for the armature winding and investigates the short-circuit characteristics of the designed SCPMGs. The first part of the results shows that the SCPMGs can double the shear stress of a conventional low-speed permanent magnet (PM) generator (from 65 kPa to 130 kPa) whilst avoiding demagnetization of the PMs in rated-load operation. However, the power factor has to drop to a range of 0.7-0.8. The second part of the results shows that during a sudden three-phase short circuit, the superconducting armature winding is prone to quench and the PMs are likely to be demagnetized in both proposed designs.

In recent years, permanent magnet superconducting (PMSC) generators have become a candidate for applying superconducting (SC) generators in large direct-drive wind turbines. This configuration keeps the SC armature winding and its cooling system stationary and eliminates rotational cooling couplings. However, the low excitation by permanent magnets may lead to poor power factors if the armature current is high. Furthermore, the permanent magnets are prone to demagnetization when the armature reaction is strong. This paper investigates the design challenges regarding the power factor, demagnetization and short circuit characteristics by analyzing two PMSC generator designs. The results show that the power factor cannot be as high as 0.9 and a low power factor such as 0.6 can take advantage of the high current carrying capability of the SC armature winding. However, this low power factor will cause demagnetization. The armature current may cause quenching of the SC wires during a three-phase short circuit. Demagnetization of the permanent magnets during the short circuit is strong and could be an intrinsic weakness of a PMSC generator.