Device For Reducing Harmful Bearing Voltages

Abstract

A device (1) to reduce harmful bearing voltages in an electrical machine (M) fed by a DC link voltage of a DC link. The electrical machine has a rotor (2) and a stator (3) with windings (W), and is insulated to ground. At least two bearings (4), with an outer bearing ring (4a) and an inner bearing ring (4i), are between the rotor (2) and the stator (3). A shielding arrangement (S) is between the windings (W) of the stator (2) and the respective outer bearing rings (4a). A stator electrical connecting arrangement (5) is connected to a potential that is stable with respect to the DC link.

Claims

1. A device for reducing bearing voltages in an electrical machine (M) fed by a DC link voltage of a DC link, comprising: a stator with windings isolated from ground; a rotor; at least two bearings including an outer bearing ring and an inner bearing ring, the bearings are between the rotor and the stator; a shielding arrangement is at least provided between the windings of the stator and the respective outer bearing rings; an electrical connecting arrangement of the stator to a potential that is stable with respect to the DC link; and the connecting arrangement of the stator to the potential that is stable with respect to the DC link is established via an impedance or a capacitance, the shielding arrangement is connected to the stator directly or indirectly via an impedance or a capacitance via an electrical connecting arrangement.

2. The device according to claim 1, wherein the stable potential is the ground reference potential of the commuting electronics or of the inverter.

3. The device according to claim 2, wherein the shielding arrangement is connected to the ground potential.

4. The device according to claim 1, wherein the shielding arrangement is electrically connected via a connecting arrangement to a potential that is stable with respect to the ground potential or to the same stable potential as the stator.

5. The device according to claim 4, wherein the connecting arrangement of the shielding arrangement to a stable potential is established via an impedance or capacitance.

6. The device according to claim 1, wherein the shielding arrangement further comprises a shielding section covering the winding head of the windings.

7. The device according to claim 1, wherein the shielding arrangement further comprises shielding sections between the outer bearing ring and the windings, preferably in bearing pockets.

8. The device according to claim 1, where the shielding arrangement further comprises a number of shielding sections for shielding between grooves, preferably as many as the number of grooves.

Description

DRAWINGS

[0025] Further features and advantages of the disclosure result from the following description of exemplary embodiments with reference to the appended drawings. The following is shown:

[0026] FIG. 1 is a section view through a motor according to a first embodiment.

[0027] FIG. 2 is a perspective view of an embodiment of a shielding arrangement.

[0028] FIG. 3 is a schematic of an equivalent circuit diagram of the capacitance network for a first embodiment.

[0029] FIG. 4 is a schematic of an equivalent circuit diagram of the capacitance network for an alternative embodiment.

DETAILED DESCRIPTION

[0030] The disclosure is described in more detail below based on preferred exemplary embodiments and with reference to FIGS. 1 to 4. The same reference symbols indicate the same functional and/or structural features.

[0031] FIG. 1 illustrates a section view through an electric motor M with a device for reducing bearing voltages at the bearings 4. It has an outer bearing ring 4a and an inner bearing ring 4i according to an exemplary embodiment.

[0032] The motor M has a rotor 2 and a stator 3. The stator is formed of stator panels 3i. A rotor-side and a stator-side outer bearing ring 4a and inner bearing ring 4i are provided, respectively, between the rotor 2 and the stator 3. Further shown are the shaft 10 and the windings W of the motor M. An insulating casting compound 9 is applied around the windings W and an insulating encapsulation 9a is applied along the stator panels 3i.

[0033] If a common mode voltage U.sub.CM is applied to the windings W, a bearing potential with respect to the ground potential PE is generated at each of the bearings 4 due to the capacitive coupling to the winding W. The potential is reduced by the action described below.

[0034] The device shown in FIG. 1, for reducing bearing voltages, includes a shielding arrangement S. A perspective view is shown in FIG. 2. The shielding arrangement S is provided between the windings W of the stator 3 and the respective outer bearing rings 4a.

[0035] As is visible in FIGS. 1 and 2, the shielding arrangement S has a shielding section 20 at its top and bottom. The shielding section 20 covers the winding head 7 of the windings W. The shielding arrangement S has a substantially cylindrical envelope. The envelope includes the shielding sections 20, mentioned above, and the other shielding sections 21. The sections 21 are between the outer bearing ring 4a and the windings W. They are disposed in bearing pockets in the assembled state of the shielding arrangement S. Furthermore, the shielding arrangement S includes multiple shielding sections 23. Sections 23 are attached peripherally at groove distance. They shield in the usable slots between the panel packs 3i of the stator 3.

[0036] FIGS. 3 and 4 show equivalent circuit diagrams of exemplary embodiments. The respective equivalent circuit diagram represents the capacitance network for the respective embodiments with the system-related capacitances C.sub.WS, C.sub.W-LAS, C.sub.W-LA.sub.R, C.sub.WR, C.sub.BS, C.sub.BR, C.sub.RS, C.sub.RE, C.sub.SE, C.sub.Y, C.sub.S-LAS, C.sub.S-iAr, each representing exemplary capacitances between W=winding, LA=outer bearing ring (r=rotor-side, s=stator-side), r=rotor, s=stator, and other capacitances between the respective components of the motor, which will not be explained in detail herein. Furthermore, the potential PE of protective ground is shown in the network. Also, the ground reference potential GND and the common mode voltage U.sub.CM are shown.

[0037] According to the disclosure, a connecting arrangement 5 of the stator 3 to a potential that is stable with respect to the DC link can be established via an impedance or a capacitance C.sub.a. This is shown in both embodiments according to FIGS. 3 and 4.

[0038] The stable potential herein is the ground reference potential GND of the inverter. The shielding arrangement S is directly connected to the stator 3, via an electrical connecting arrangement 8.

[0039] In the embodiment according to FIG. 4, the shielding arrangement S is electrically connected, via a connecting arrangement 6, to a potential that is stable with respect to the ground potential (PE). This is the same potential that the stator 3 is connected, i.e. the ground reference potential GND. The connection of the shielding arrangement S to the ground reference potential GND is made via a capacitance C.sub.SCH. The capacitance C.sub.SCH may optionally be included in FIG. 3.

[0040] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.