Double-disc alternator with AC-side excitation

The paper describes an unusual form of alternator, which has a disc-type geometry, which uses AC-side excitation to provide brushless operation. Some of the merits and drawbacks of this form of machine are discussed. The alternator is free of the usual penalties associated with this type of machine, and in particular there are no auxilliary airgaps, and the main flux is heteropolar in action. Methods of predicting the main parameters of the machine are shown to provide results that agree closely with measurements. Load tests with a 7.5 kW prototype show that all losses remain at acceptable levels and overall efficiencies range from just over 90% at half load to around 85% at full load. Some preliminary results on the magnitude of enviromental losses owing to eddy currents produced by the stray fields are given. It is thought that the encouraging results produced by the first prototype machine justify further work, and several particular areas of research are discussed.