The secondary circuits of synchronous induction motors

Abstract

The use of synchronous induction motors has steadily increased in the last 15 years, and much information about them is now contained piecemeal in various papers. No critical account of the various types of secondary circuit and of the ways of exciting them is yet available, however, and in the first part of this paper the author considers these systematically. The characteristics desirable are first elucidated, and each winding is then considered in the light of these characteristics. Their properties are finally summarized in tabular form.The second part of the paper describes experiments by the author on the load reactance of synchronous induction motors. The relation between load and synchronous reactance for a machine with a barrel rotor is established practically, as is also the dependence of both these quantities on the secondary wave form. A correction for “magnetic backlash” is introduced.The third part of the paper deals shortly with parasitic currents in secondary circuits, with oscillograms of these currents.The appendices give mathematical results for secondary wave forms, ratings, starting torques and exciting currents. These results serve as standards with which actual results can be compared.