A stiffening technique to improve the dynamical response of cage rotors

In this paper a stiffening technique for cage rotors of induction machines is proposed and analyzed, aimed at reducing the mechanical oscillations excited by the traction torque harmonics. The solution is simple, consisting of stiffening blocks inserted between couples of adjacent copper bars, overhanging from the rotor stack. The insertion of the stiffening blocks yields an increase of the lowest natural frequencies of the rotor, shifting them beyond the frequency range of the main torque harmonics. As a consequence, the fatigue stress arising at the junction between bars and end-rings during service are reduced, and the operative life of the rotor is increased.