Equivalent Circuits and Performance Calculations of Canned Motors

In this paper, new equivalent circuits and procedures are given for calculating the speed-, torque-, current-curves, and stray losses of induction motors having solid steel rotors as well as slot-embedded squirrel-cage bars. The new procedures include effects of eddy currents in the solid steel rotor in parallel with the squirrel-cage bar currents, using two alternative forms of the equivalent circuit. It was found that the presence of the solid iron reduced the zigzag leakage reactance of the rotor bars, allowing more tooth frequency currents to flow in these bars; thereby markedly increasing the stray load loss when the air gap is small. By increasing the air gap, this type of loss is markedly reduced. The losses due to phase-belt harmonics can be reduced by interspersing. The test results are in excellent agreement with the calculated values.