No-Load Conditions of Single-Phase Induction Motors and Phase Converters

This paper shows methods and derives formulas for the determination of the fields, the stator and rotor magnetizing currents, and the tertiary voltages for phase converters and single-phase induction motors at no-load. Previous publications on this subject, including text books, are usually rather vague and incomplete, especially with regard to the secondary magnetizing currents and the field forms. Furthermore, numerous conflicting statements are found in previous literature, thus leaving the subject, as a whole, in a rather confusing condition. This paper treats a large number of different cases along similar lines, thereby coordinating and explaining many phenomena previously observed, and it should, therefore, form a desirable basis for further investigations and discussion of this subject matter. The treatment of all cases is rather uniformly based on the following fundamental considerations. The sum of all e.m.fs. must be zero in both the primary and secondary circuits. With the impressed primary e.m.f. known, this leads to definite conditions governing the primary counter e.m.fs. The same law applied to the secondary circuits gives the condition that the induced voltages must be equal and opposite to the ohmic drops. Having thus certain laws governing the voltages to be induced in the windings, we have at once certain laws governing the fluxes for inducing these voltages.