Detection of Rotor Eccentricity in Wound Rotor Induction Machines Using Pole-Specific Search Coils

This paper addresses the need to detect the rotor radial position in an electrical machine. When it is not centered, it is referred to as rotor eccentricity. Cage induction machines can use the detection of sideband currents, and this is studied extensively elsewhere. Wound rotor induction machines do not generate the same sidebands, so an alternative detection method is needed. These machines are now popular generators in wind turbines. A simple method using pole-specific search coils is introduced, and a theory is developed to illustrate that rotor eccentricity leads to the generation of air-gap flux waves with pole-pairs that are pm +/- 1. This is tested using search coils in a 4-pole wound rotor machine. The method is found to successfully indicate the presence of rotor eccentricity.