A Device for Determining the Rotor Eccentricity of Rotating Electric Machines

Abstract

One common form of damage in rotating electric machines with outriggers the rotor eccentricity, which is accompanied by deterioration in the electromechanical characteristics of an electric machine, while, with a significant displacement of the rotor core, it leads to the strong heating of the stator and rotor cores caused by friction and to damage to the insulation of stator and rotor windings, to short circuits, and to long machine outage. However, the techniques that are known for diagnosing eccentricity have not been widely used due to their difficulty of implementation and insufficient sensitivity, which is limited by the dependence of the diagnostics systems on variations in the mains parameters and the load of the electric machine. The sensitivity of the proposed device does not depend on these factors, since the rotor displacement is controlled by measuring the capacitance relative to the rotor shaft near each end of the electric machine at four points using capacitive sensors evenly spaced along the circumference. The signal from these sensors is fed through the measuring bridges, band-pass filters, and threshold elements to the indicating unit and the block for generating a switching-off signal. The results of diagnostics are evaluated by two reasonable criteria. As a consequence, the diagnostic device is able to determine not only the level of rotor eccentricity, but also the direction of rotor displacement.