Developments relating to litz wire in the insulation systems of generators for renewable energies

As new designs for generators applied in the renewable energy market appear and rated power continues to increase, litz-wire winding technology has brought its advantages to machine and process efficiency. The division into many strands increases flexibility, facilitating the processing of larger and special windings, and reduces high-frequency winding resistance, reducing losses. The use of litz wire, however, impacts the insulation system. The litz-wire profile locally enhances electric field strength, with implications for the mainwall and turn insulations. Conductor mica tape can provide appropriate turn insulation, but influences wire flexibility, coil consolidation, and finally resin penetration during impregnation. During vacuum-pressure impregnation, resin should penetrate both the region between turns and the litz wire itself, without draining during curing. This can impose new requirements on the impregnation process and on the choice of resin, which must deal with low pressure and lack of catalyst inside the litz wire. The paper reports on considerations and investigations of such aspects in real generator designs.