Mitigating Noncirculating Bearing Currents by a Correct Stator Magnetic Circuit and Winding Design

Abstract

Mitigating noncirculating bearing currents by a correct stator magnetic circuit and winding design," in IEEE Transactions on Industrial Electronics.

Mitigation of Inverter-Induced Noncirculating Bearing Currents by Introducing Grounded Electrodes into Stator Slot Openings

“…The approach presented here has about the same bearing current reduction potential as the approach of introducing extra wedge insulation presented in [30]. A FEM-based computation, conducted for both approaches with the same machine geometry, gives almost equal BVR reduction indicators.…”

“…Applying the presented approach to frequency-convertersupplied electrical machines could increase the overall reliability of the system by a significant reduction in the noncirculating bearing currents. Even though the introduction of complicated structures (as in [31]) or extra wedges (as in [30]) into the slot opening definitely require special tools and skills, introducing only one thin electrode seems efficient and can be considered a possible practical modification in electrical machines. The installation of grounded electrodes requires minimum space in an electrical machine and in most cases, regardless of the machine size, it can be implemented in the existing winding position while the slot copper space factor remains unchanged.…”

“…During verification with an actual machine, it turned out that the modification proposed in the present paper reduces the shaft voltage amplitude to the same level as the application of thicker wedges. Taking this into account, the choice between the proposed method or countermeasures suggested in [30] should mainly be made on the basis of considerations other than the degree of reduction in the BVR.…”

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

“…The internal capacitance C wr can also be reduced by moving the stator winding away from the rotor. This idea was presented in the article [26], where the authors suggested a change in the slot insulation and an increase in the thickness of the slot wedge. It was demonstrated on the basis of simulations and measurements that increasing the distance between the stator winding and the rotor surface by 76% resulted in a reduction of the BVR coefficient by more than 50%.…”

On the Application of Extended Grounded Slot Electrodes to Reduce Noncirculating Bearing Currents

“…Circulating currents can also be a result of uneven distribution of the current in the stator winding, rotor eccentricity, or imprecise machine geometry [15]. Inductive bearing current forms a closed loop with a "rotor-bearing-stator-bearing-rotor" path, as shown in [10] or [11]. Modern production methods On the application of extended grounded slot electrodes to reduce non-circulating bearing currents make it possible to manufacture machine parts with sufficiently high accuracy, and thus, the given type does not currently pose the most significant danger to bearings.…”