Prospects for magnetization of large PM rotors: conclusions from a development case study

A development feasibility study has been conducted for magnetizing the rotor of a 1.7 MVA, 20-r/min, permanent magnets (PMs) excited synchronous wind turbine generator. Various technical problem areas and their likely influence on the overall design concept, are reviewed. Thus, some particularly important problems are identified: KERI's conventional facilities ensure sufficient energy for magnetizing, pair by pair, of all the PMs of the rotor. A rotor and inductor optimal arrangement for a magnetizing system's configuration is required in order to avoid a wrong, strong magnetization of the neighboring poles. It is also necessary to take into account the mechanical strength of the magnetizing inductor winding to withstand electromagnetic forces. This paper presents the result of the analytical calculation of such a specialized inductor and a PC Spice-based software simulation of the magnetizer circuit; finally, a transient finite element method (FEM) simulation of the inductors connected by the external electric circuit has been done. All three methods confirm the possibility for a successful magnetization, pair by pair, of all rotor poles. Design proposals are detailed and conclusions are relevant for magnetizing large rotors with surface-mounted PMs in general.