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 theory is developed to illustrate that rotor eccentricity leads to the generation of airgap 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.
This paper puts forward a concept for measuring rotor eccentricity in a wound rotor induction machine. The analysis is fully developed in the theory section then an experimental rig is described and measurements are taken. These are compared to the calculated values. Pole-specific search windings are necessary in a wound rotor machine because standard sideband current measurement techniques are only valid for cage induction machines. The search coils can also be used to suppress unbalanced magnetic pull.
A steady state analysis is developed for a wound rotor induction machine. In this paper the authors derive simple expressions for the mutual and coupling impedance in order to build impedance matrix. The analysis can be used in two ways when dealing with a symmetrical and asymmetrical rotor. The method is verified using an inverted-geometry wound motor; the analysis is then used to investigate an asymmetry fault on a 4 pole wound rotor. Experimental results (torque and current characteristic) are compared with computer predictions for the machine with both open-circuit and short-circuit faults.
Condition monitoring can diagnose the inception of fault mechanisms in induction motors, thus avoiding failure and expensive repairs. Therefore, there is a strong need to develop an efficient condition monitoring. The main target is to achieve a relatively low cost and/or non-invasive system which is still powerful in terms of monitoring for online detection of developing faults. The presented paper addresses rotor eccentricity faults and studies conventional monitoring techniques for induction motors. In order to reduce the unbalanced magnetic pull (UMP) in case of an eccentric rotor, the eccentricitygenerated additional airgap flux waves should be reduced. The radial forces in an induction motor are calculated, and the characteristics of unbalanced magnetic pull are described. Index Terms-condition monitoring, eccentric rotor, induction machines, unbalanced magnetic pull (UMP). Bent rotor Bearing wear Misalignment Detections Methods Stato1• current Axial flux Vibration Torq uc, speed Axial flux Stator current Stator current Vibration Stator current Vibration Axial flux
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