Influence of rotor-bar stiffness on the critical speed of an induction motor with an aluminium squirrel cage

Most authors, dealing with electromagnetically induced vibrational phenomena in rotating machines, consider the mechanical parameters (spring constant, damping coefficient) to be known. In the paper we will show that the generally made approximations for the calculation of these mechanical parameters are no longer acceptable when considering aluminium rotors. Therefore a more accurate method has been worked out taking into account the rotor-cage stiffness. The results are then compared with experimentally obtained values. These experiments have been made using the modal analysis method.