New approach to micromachine construction

Although digital computers may be used to study power systems, there is still scope for the employment of model systems; and in these, the most difficult items to model are the alternators, because the mechanical and electrical parameters must both be scaled correctly. Much has been written on modelling, and it is clear that the apparently attractive technique of exact geometric scaling is unacceptable unless some of the basic parameters such as mass density, resistivity and permeability may be given significantly changed values in the model. Unfortunately, the required changes are all in directions which are difficult to achieve; i.e. a large reduction in the resistivities of the various materials is desirable. In the past, model machines have been built with negative resistances in series with some of the windings to give the desired effects, but these built with negative resistances in series with some of th ewindings to give the desired effects, but these components have had to be set accuratley and controlled very precisely. Eveb when this has been done, ideal conditions have not been achieved because such components cannot be included in all the circuits. This paper details the design and construction of a geometrically scaled model of a 100MVA alternator in which high conductivity was obtained by immersing the machine in liquid nitrogen. The other parameters were adjusted to satisfy the necessary similarity criteria; e.g. magnetic material with a very high permeability was used, and thelamination thickness was chosen to give the correct effective iron-path conductivity. The results of tests performed on the completed model to determine the various impedances and time constants are given, and it is shown that these quantities approach the ideal values, indicating that the model is acceptable.