Self-Excitation of Induction Motors

It has been known for some time that an induction machine whose rotor is driven mechanically may become selfexcited if capacitors are connected across its terminals. The present paper is concerned with the predetermination of the machine characteristics when operating under such conditions. The frequency of excitation is very close to the synchronous frequeney corresponding to the speed of the rotor. The voltage to which the machine will excite is dependent upon its no- load excitation characteristics at that frequency, the criterion to be satisfied being that the lagging volt-amperes of excitation equal the leading volt-amperes of the capacitors. Under load, similar criteria must be satisfied. Voltage conditions are determined by a cut-and-try solution such that the summation of reactive volt-amperes equals zero. The slip is then obtained from the relation that the summation of the real power equals zero. These relations have been applied to various types of loads, such as pure resistance and inductive resistance, single-phase and three-phase and also to induction-motor load. Excellent checks between test and calculated results have been obtained.