Detection of stator slot magnetic wedge failures for induction motors without disassembly

Abstract

The recent trend in large ac machines is to employ magnetic stator slot wedges for improving the motor efficiency, power factor, and power density. The mechanical strength of magnetic wedges is weak compared to the epoxy glass wedges, and many cases of loose and missing wedges have recently been increasingly reported. Magnetic wedge failure deteriorates the performance and reliability of the motor, but there is no method available for testing the wedge quality other than visual inspection after rotor removal. Monitoring of overall wedge condition without motor disassembly can help reduce the cost of maintenance and risk of degradation in performance. In this paper, a new off-line standstill test method for detecting magnetic wedge problems for ac machines without motor disassembly is proposed. An experimental study on 380 V, 5.5 kW and 6.6 kV, 3.4 MW motors with magnetic wedges is performed to verify the effectiveness of the new test method. It is shown that the new method can provide reliable monitoring of magnetic wedge problems over time, independent of other faults or motor design.

Analysis and Design of Innovative Magnetic Wedges for High Efficiency Permanent Magnet Synchronous Machines

“…Finally, the radial forces acting on the internal stator surface were evaluated. The idea of this evaluation comes from the evidence that magnetic wedges are more brittle and hence more susceptible to failure compared to non-magnetic ones, as highlighted in [32]. An interesting analysis referring to a large synchronous wound field machine of 5 MW was reported in [33], where the results showed that the shape of the magnetic wedge also has significant effect on the stator interior surface force distribution.…”

Efficiency Assessment of Induction Motors Operating Under Different Faulty Conditions

“…They are much more frequent in fabricated copper motors, in which the bars are brazed to the end rings. Moreover, they are especially likely in large motors that drive high inertias and with frequent heavy startups [3], [16]. Under those conditions, the abrupt thermal gradients in the bars lead to electro-dynamical stresses between the bars and end rings that facilitate the appearance of small cracks in the connection between the bar and end ring [3,16].…”

Neural Network-Based Diagnostic Tool for Detecting Stator Inter-Turn Faults in Line Start Permanent Magnet Synchronous Motors

“…The associate editor coordinating the review of this manuscript and approving it for publication was Jiansong Liu. costs) and, more importantly, prevent unscheduled downtime that results in the loss of production time and income [4]- [6].…”