Aluminium windings for hydroelectric generators: a critical analysis

There has been considerable progress in substituting aluminium for copper in electrical apparatus such as busbars and transformers, but little or none in rotating electrical machines. Making certain simplifying assumptions, the paper evolves a mathematical analysis for salient-pole generators by which the losses, dimensions and cost of a generator with aluminium windings, with the same rating and short-circuit ratio (s.c.r.) as one with copper windings, can be evaluated. An extension of the analysis permits a price comparison to be made both without and with the capitalisation of losses. These results are displayed as families of curves with either gap diameter, or cost of copper, as the independent variables. An appendix considers the substitution of aluminium for copper in the stator winding only. Worked examples are given of a medium-speed and a low-speed hydroelectric generator, and the results show that, for the medium-speed type to become an economic proposition with aluminium windings, the price of copper must increase by about 20%, whilst for the low-speed type an increase in the price of copper of only about 5% is sufficient. These conclusions may be modified in countries developing their industrial capacity with ample indigenous aluminium, but importing copper. Here the reduction of the drain on foreign credits by restricting the import of copper may be the paramount consideration.