Some aspects of solid salient pole synchronous motors

Abstract

The electromagnetic behaviour of solid salient pole synchronous motors is considered in relation to certain problems of practical importance. Part I is concerned with the development of a small synchronous motor using a rare earth permanent magnet material and Part II with the asynchronous performance of solid salient pole synchronous motors. In Part I, a description is given of a direct search technique developed to obtain the equivalent circuit parameters of a small voltage-controlled two-phase induction servomotor from test results. These equivalent circuit parameters are then used as the basis for comparing constructional changes in the servomotor rotors. These results demonstrate that the two-phase voltage-controlled induction servomotor is inherently inefficient. A two-phase synchronous servomotor was constructed employing samarium cobalt permanent magnets in the rotor. Maximum efficiencies over a wide range of frequencies are obtained of approximately three times those of an equally sized induction servomotor. In Part II, a direct search computer program is developed to predict the asynchronous current and torque of large solid salient pole synchronous motors. A full investigation of the of the Gorges effect is carried out and the effect of varying field resistance and armature resistance upon the asynchronous characteristics is measured on two small solid salient pole synchronous motors. Tests on these two motors show that an open-circuited field winding, whenever practically possible, is advantageous. Tests on six large solid salient pole synchronous narrators show close agreement with the predicted figures for asynchronous values of torque and current obtained from the computational direct search method.

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