Self-excitation of induction motors with series capacitors

INDUCTION motors with series capacitors connected in the supply circuit can under certain conditions become unstable. Upon application of the voltage the rotor will come up to partial speed and continue to rotate at this reduced speed. This phenomenon should not be confused with ferro-resonance which is accompanied by violent wave distortion, abnormally large magnetizing currents, and fluctuations in voltage. Both of these phenomena were analyzed as applied to induction motors by Butler and Concordia.¹ It is the purpose of this paper to present further thoughts regarding the stability problem. A new approach is utilized which is much simpler and at the same time provides a clearer conception of the physical processes involved. Somewhat different conclusions result with the use of this analysis than with the analysis of others. In this analysis conventional induction motor nomenclature and symbols will be used as it is believed that induction motor engineers will better understand the problem by this procedure.