A Rim Driven Electrical Machine with an actuate stator assemblies for interaction with fluid flow

A marine propulsion/tidal generator dynamo-electric machine comprises a housing 12 with at least one stator 16,324,418 (fig 4), each stator extending only partially around the circumference of the rotor 14,304 so as to have arcuately separated ends. In use the single stator 418 option may have the stator located at the lower part of the rotor. The rim driven impeller 304 comprises blades surrounded by an annular laminated ferromagnetic ring core 310 provided with conductive sleeves 316,318 and an environmental enclosure sleeve 320, which may be electrically conductive. Appropriate selection of the materials and thicknesses of the layers 316, 318, 320 enables the starting performance to be optimised using skin effects enhanced by the layer 320 having a high electrical resistance whilst the lower resistance of layers 316,318 and the core 310 allowing the machine to operate efficiently at its rated speed. Layer 316 has a lower resistance that layer 318. Layer 320 may be stainless steel or bronze whilst layers 316 318 may be copper and aluminium respectively. The core may include conductive bars forming a squirrel cage or may include permanent magnets. At least the inner sleeve may be provides with apertures to form a cage structure.