High-Frequency No-Load Losses of Cage Induction Motors

An analysis is presented of the high-frequency losses occurring on no-load in cage induction motors having open stator slots. The theory covers both the important rotor constructions in which the rotor slots are either skewed or unskewed. The component losses calculated are surface and tooth-pulsation iron losses in both rotor and stator, and rotor I2R losses including those due to circumferential conduction between the bars and the coreplates of skewed machines. Computed losses are compared with tests on 35 large motors and, in the cases with skewed rotors, the correlation is used to find an effective mean value of bar-to-bar resistance. Examples are included in which the losses were predicted with satisfactory accuracy, without prior knowledge of test figures. The analysis and the computer program are useful in assessing designs and in comparing alternative constructions such as skewed or unskewed rotors and open or semiclosed stator slots.