| 摘要 |
<p>A dynamo-electric machine, for example a marine propulsion unit or a tidal generator, comprises a stator 14 and a rotor in the form of an impeller 4. The impeller 4 is rim-driven and comprises an annular core 10 of ferromagnetic material, on which are provided layers 16, 18, 20 in the form of an environmental enclosure 20 and electrically conductive sleeves 16, 18. Appropriate selection of the materials and thicknesses of the layers 16, 18, 20 enables the starting performance of the machine to be optimised by using the skin effect which is enhanced by the layer 20 having a high electrical resistance whilst the lower resistance of layers 16,18 and the core 10 allowing the machine to operate efficiently at its rated speed. Layer 16 has a lower resistance that layer 18. Layer 18 may be stainless steel or bronze whilst layer 18 may be aluminium and layer 16 copper. Alternative the layer 20 is non-conductive and layer 18 provides the starting torque. 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.</p> |
