Self-excited synchronous motors

The theory and applications of self-excited synchronous motors have been repeatedly discussed in the literature, but the subject has been usually presented as a study of some special variety of this type. It now seems timely to give an outline of the general theory of the subject as a basis of comparison of the proposed types and a starting point for further development work. The study of a self-exicted motor is mainly a study of its exciting system. The writer shows that any combination of the exciting circuits is equivalent to one comparatively simple type, and studies two problems in connection with this standard type; (1) determination of performance of a given motor; (2) determination of design constants giving a desired performance. In this study stress is laid on the elements peculiar to this type of motor; but no attempt is made to treat fully the elements which the self-excited motor has in common with other, better known, motor types. The current locus of the motor is found to be a circle, and it is shown that any circle in the plane can be obtained by a suitable choice of the exciting system. The subject of synchronising is treated by a method showing an intimate connection between the synchronising process and the synchronous operation. The discussion of synchronising can thus be limited to the standard type, because the equivalence of the synchronous operation means also the equivalence of the synchronising features. It is shown that very high torque can be obtained during synchronising. The theory is applied to a brief study of a few types of the self-excited motor.