Calculation of Radial Forces in Cage Induction Motors at Start - The Effect of Rotor Differential

Abstract

In this paper, the radial forces in an induction motor are calculated using finite element analysis. These radial forces (or unbalanced magnetic pull-UMP) are generated when the rotor is eccentric. The work illustrates the importance of higher winding harmonics and rotor differential leakage in the starting UMP. Examples of a 6 pole machine with 26 and 40 bar rotors show that increasing the bar number and air-gap length will reduce the UMP. Further studies are carried out using parameter variation and a 10-pole machine is also addressed, where experimental results exist, in order to validate the calculation.