Electrostatic shielding for bearings discharge currents attenuation: analysis of its effectiveness, losses and impact on the motor performance – a study for design guidelines

Abstract

The authors deal with the use of electrostatic shielding to mitigate the electric discharge machining (EDM) currents on the induction machine bearings. Employing 2D and 3D models, several finite element analysis (FEA) simulations were thoroughly made addressing the shielding effectiveness to attenuate the shaft-to-frame voltage and the associated eddy current losses for different shield widths, thicknesses and materials. The obtained results provide very good guidelines for the practical design of the shielding device. In addition, comparisons between frequency-and time-domain models highlight the importance of considering factors such as the saturation of the iron core, the rotor movement and non-sinusoidal sources to compute the eddy current losses in the shield. Besides, the authors present a comprehensive theoretical review of the EDM currents, where the main influencing factors and action mechanisms are compiled in a clear and didactic approach, for the purpose of broad comprehension.

Analysis of Impact of Design Solutions of an Electric Machine with Permanent Magnets for Bearing Voltages with Inverter Power Supply

“…The reduction of C wr can also be executed by using an electrostatic shield placed in the space between the stator winding and the rotor. The solutions described in the literature include the cases of shielding winding along the entire length of the stator iron core [22,23] as well as shielding of end-windings [24,25].…”

A Review of Modeling and Mitigation Techniques for Bearing Currents in Electrical Machines With Variable-Frequency Drives

“…Hence, it cannot capture the unequal sharing of voltage between various turns in one winding coil, resulting in errors in the predictions of common mode current, shaft voltage and bearing current. Furthermore, the end-winding effect is usually neglected in such simplified analytical methods, which can underestimate the winding-rotor capacitance 𝐶 𝑤𝑟 by ~90% as reported in [60].…”

“…9) was constructed in [67], for the purposes of comparing the 2D and 3D models without end windings. In [60], 3D FEM models were built with end-windings to investigate the electrostatic shielding effects and compare the winding-rotor capacitances of models with and without end-windings. The results showed that the end-windings have significant effects on the winding-to-rotor capacitance, and neglecting their contribution can underestimate the winding-rotor capacitance by 40%-90%.…”

Inverter-Fed Motor Drive System: A Systematic Analysis of Condition Monitoring and Practical Diagnostic Techniques

“…• Calculation difficulty in the material and geometry. [208][209][210] 4.5.2. Diagnostic of Bearing Currents Faults Inverter-fed IM drives have more potential impact on generating more shaft voltages and subsequently cause bearing current, so their diagnostic is a pre-condition for a prognostic of the overall power system [211].…”