Operation of Synchronous Generators in the Asynchronous Mode

The paper discusses some of the limiting factors associated with the asynchronous operation of synchronous generators. Expressions of the various quantities required for the theoretical analysis are derived on the basis of an idealized model of a generator which is connected to an infinite bus. The generator is assumed to be operating at a constant slip. The results obtained from the experimental investigations which have been conducted on a 5 kVA salient-pole synchronous generator under asynchronous operation, are presented. These experimental results are used to verify the validity of the model used for the theoretical analysis. The theoretical analysis is then applied to study the behaviour of a 45 MVA hydro-generator and of an 82.5 MVA turbo-generator when operating asynchronously with different modes of the field winding connections. Comments are made on the nature of the variations of asynchronous power, armature current, pulsating power, reactive power demand, field current and field voltage as functions of slip.