Behaviour of an induction motor with equalizing connections in the stator winding

The connections serve to generate a MMF which counteracts the asymmetrically distributed magnetic field in the air gap resulting from asymmetrical construction or assembly of the machine, especially the off-centre position of the rotor in the stator bore. Such an asymmetrical magnetic field induces mechanical vibration of the rotor and stator (with the attendant increased load on the bearings) as well as unbearable noise. Equalizing currents between winding coils make for drastic reduction of radial forces and ensure almost vibration-free operation. An analysis of the magnetic field in an asymmetrically constructed machine without and with equalizing connections, is presented. The theoretical results were confirmed by experiments on a specially built laboratory set-up