CQ-05 1 Measurement and Calculation of Unbalanced Magnetic Pull in Wound Rotor Induction Machine David G. Dorrell, Senior Member, and Obaid Kayani School of Electrical, Mechanical and Mechatronic Systems University of Technology Sydney, Broadway, Sydney, NSW 2007, Australia This paper addresses the measurement and calculation of unbalanced magnetic pull (UMP) in a wound rotor induction machine. A new rig for measuring UMP is presented. To the authors’ knowledge this type of rig has not been tested before. The paper details the force calculation method and a method for splitting the UMP and torque. Wound rotor induction machines are now popular as generators in wind turbines. It is important to maintain good operation and low bearing wear, and the UMP in these machines is higher than the cage-rotor equivalent because the cage damps the UMP. There is little literature on the UMP in a wound rotor machine. Index Terms—Induction motors, unbalanced magnetic pull, force. I. INTRODUCTION HIS PAPER addresses the measurement and calculation of unbalanced magnetic pull (UMP) in a wound rotor induction machine when the rotor is not centered (termed rotor eccentricity). These machines have seen a resurgence in use as generators in wind turbines and control of the UMP will help reduce bearing wear. There are two forms of rotor eccentricity. When the rotor is turning on its own axis but not on the stator bore axis it is called static eccentricity. This tends to produce a steady pull in the direction of minimum airgap and is due to worn or misaligned bearings. If the shaft is bent the rotor may not be turning on its own axis but is still rotating on the stator bore axis and this produces a rotating force vector on the rotor at rotational speed; this is termed dynamic eccentricity. Obviously both can and will exist together. The most simple to put into a machine in an experimental rig is static eccentricity and this is what is done here. A new rig for measuring UMP is presented in this paper. To the authors’ knowledge this type of rig has not been tested before. Wound rotor induction machines are now popular as generators in wind turbines. It is important to maintain good operation and low bearing wear, and the UMP in these machines is higher than the cage-rotor equivalent because the cage damps the UMP [1]. There is little literature on UMP in wound rotor machines. There have been many papers that have addressed UMP in electrical machines [2]-[4] but few have measured it. While in bearingless machines can be related to the control currents [5] and more complex strain gauge methods are discussed in [6], a good method is to use piezoelectric transducers. They can be used in a mounting plate with the stator mounted on the plate and the rotor separately mounted on pedestals. This was done in [7]. In [8] load cells were used to try to measure the UMP however these types of device do move when a force is exerted so that the amount of eccentricity is not constant. A more versatile method is to incorporate transducers into the rotor support pedestals and this has now been done in this study as illustrated in Fig. 1. In this paper the UMP is measured in a wound rotor T Fig. 1. Test rig configuration.