WO2008132099A1 - Tapping device for tapping electric potential from a shaft of an electric machine, corresponding assembly set and corresponding electric machine - Google Patents

Abstract

A tapping device (8) comprises a brush holder (9), which is made of electrically conductive material and can be connected to a base body of an electric machine. The tapping device (8) further comprises a brush (15), which is made of electrically conductive material. The brush (15) is guided displaceably in a brush guide (14) of the brush holder (9), so that the brush (15) is pressed against a shaft of the electric machine by a spring force (F). The brush (15) is connected to the brush holder (9) in an electrically conductive manner. An electrically insulating intermediate element (20) is provided between the brush (15) and the brush guide (14) so that no direct electric contact occurs between the brush (15) and the brush guide (14).

Description

description

Tapping device for tapping an electrical voltage from a shaft of an electric machine, corresponding mounting kit and corresponding electrical machine

The present invention relates to a gripping device for picking up an electrical voltage from a shaft of an electric machine, wherein the gripping device has a brush holder, which consists of electrically conductive material and is connectable to a main body of the electric machine,

wherein the gripping device comprises a brush, which consists of electrically conductive material, wherein the brush holder has a brush guide, in which the brush is displaceably guided, so that the brush is pressed against the shaft by a spring force,

- Wherein the brush is electrically connected to the brush holder.

The present invention further relates to a mounting kit which consists of a gripper device of the type described above,

wherein the brush holder has a number of through holes for insertion of retaining bolts,

- wherein the mounting kit has a number of retaining bolts,

wherein the retaining bolts can be inserted into the through bores and can be screwed to the main body of the electrical machine, so that the brush holder can be fastened to the main body by means of the retaining bolts,

- Wherein the retaining bolts are made of electrically conductive material and, when the brush holder is fixed by means of the retaining bolts on the base body, are electrically conductively connected to the brush holder and the base body.

The present invention finally relates to an electrical machine, - wherein the electric machine has a base body in which a stator of the electric machine is arranged,

- wherein the electric machine has a shaft which is rotatably mounted in bearings in the main body and on the rotationally fixed a rotor of the electric machine is arranged,

- wherein the electric machine has a tapping device of the type described above,

- Wherein the brush of the tapping device is pressed against the shaft or a shaft rotatably mounted on the slip ring and the brush holder of the tapping device is electrically connected to the base body, so that an electrical voltage occurring in the shaft is derived to the base body.

Such objects are well known.

In electrical machines - especially in generators - occur under certain conditions undesirable electrical shaft voltages see. These shaft voltages cause shaft currents, which can flow as circular currents through the bearings in the machine housing (= the main body) or to an inverter feeding the electric machine. The shaft voltages may in this case have different causes and have different values with regard to their size and their frequency. For example, the shaft voltages may have a relatively low-frequency component, which is usually of the order of a few volts. However, they can also have a relatively high-frequency content, which is on the order of up to 100 volts. If a rotor is fed via the already mentioned converter, the high-frequency shaft voltages can even exceed 1000 volts. If bearing currents flow through the bearings, the shaft voltages can significantly reduce the life of the bearings. For this reason, it is necessary to avoid bearing currents. It is known in the art to use isolated bearings to protect bearings from harmful bearing currents. Furthermore, it is known to perform a campstromgerechte installation and grounding. A third known measure is the wave grounding. In the case of shaft grounding, the shaft voltage is tapped off and guided onto the motor housing by means of a pick-off device of the type described above.

The brush can run directly on the shaft. Alternatively, it can run on a non-rotatably mounted on the shaft slip ring. In both cases, the tapping causes a short circuit between the shaft and the main body of the electric machine. The brushes are pressed against the intended running surface in the brush guides by a spring force.

In practice, it has been found that during operation of the picking device, material migrations occur in the area of the brush guides, which prevent the brushes from being moved (clamps). When it comes to such a brought terminals of the brush, formed by the further wear of the brush an air gap between the shaft and brushes, so that the electrical energy of the shaft voltage can only be reduced via the bearings or by means of electrical flashovers to the housing. Such no longer functioning tapping devices can result in severe bearing damage. Especially with rotor-fed machines, where high voltage peaks can occur, there is even a risk of personal injury.

In the prior art it is known to prevent the terminals of the brushes in the brush guides in that the retaining bolts, by means of which the brush holder is connected to the base body, provided with an electrically insulating sheath and the brushes via strands directly to the

Retaining bolts are connected. In this case, the current flows directly over the brush strands. Transverse currents in the brush guides practically do not occur. This approach However, increases the impedance of the tapping device as a whole, so that in the sequence remains a higher residual wave voltage.

The object of the present invention is to further develop a tapping device of the type described above and the objects corresponding thereto in such a way that the problems of the prior art are avoided.

The object is achieved for a tapping device of the type described above in that an electrically insulating intermediate element is arranged between the brush and the brush guide, so that there is no direct electrical contact between the brush and the brush guide. This ensures that the current can no longer flow directly from the brush into the brush guide.

The object is further achieved by a mounting kit of the type described above, wherein the tapping device is designed as described above, ie, the electrically insulating intermediate element is arranged between the brush and the brush guide.

The object is finally achieved by an electric machine of the aforementioned type, wherein in the tapping device between the brush and the brush guide, an electrically insulating intermediate element of the type described above is arranged.

The intermediate element preferably sets a distance of the brush from the brush guide such that the brush is capacitively coupled to the brush guide at frequencies well above the mains frequency. Because this reduces the negative effects on the impedance to a minimum. In particular, capacitive currents (non-interfering) can continue to oscillate between the brush and the brush guide. The intermediate element is preferably formed as a molded part. This makes it easy to install and fix.

The intermediate element can be mechanically firmly connected to the brush. Preferably, however, it is mechanically firmly connected to the brush guide.

As already mentioned, the brush holder usually has a number of through holes for insertion of the already mentioned retaining bolts.

A preferred embodiment of the electrical machine is that it has a converter unit, by means of which a voltage can be fed into the electrical machine. The voltage can in this case be fed in particular in the rotor.

The electrical machine can be designed as an electric motor. Preferably, however, it is designed as a generator.

Further advantages and details will become apparent from the following description of exemplary embodiments in conjunction with the drawings. In a schematic representation:

1 shows schematically an electrical machine,

2 shows a detail of FIG. 1,

3 schematically a tapping device,

4 and 5 a section through the tapping device of

3 along a line IV-IV and along a

Line V-V and

6 shows an intermediate element.

According to FIG. 1, an electrical machine has a main body 1. In the main body 1, a stator 2 of the electrical machine is arranged. The stator 2 cooperates with a rotor 3 of the electric machine, which is arranged rotationally fixed on a shaft 4. The shaft 4 is mounted in bearings 5, so that the shaft 4 is rotatable about a rotation axis 6. In the shaft 4 of the electric machine shaft voltages can occur during operation. One possible cause for the occurrence of shaft voltages is that a voltage Ul is fed into the electric machine by means of a converter unit 7 of the electric machine. Particularly high shaft voltage can occur here when the voltage Ul is fed into the rotor 3.

The electric machine of FIG. 1 is generally designed as a generator. In individual cases, however, it may also be designed as an electric motor. Particularly high shaft voltages can occur when the electric machine is designed as a generator fed to the rotor, that is to say when the voltage U1 is fed into the rotor 3 and a useful voltage U2 is tapped off via the stator 2.

When the shaft voltages cause currents to flow over the bearings 5, the currents can significantly reduce the life of the bearings 5. For this reason, the electric machine has at least one gripper device 8. According to FIG. 1, even each bearing 5 is assigned its own gripping device 8.

Each picking device 8 locally picks up the shaft voltage occurring at the respective point and carries the shaft voltage onto the base body 1. The main body 1 is in turn usually connected to ground. The configuration of the tapping device 8 is the essential subject of the present invention.

According to FIGS. 2 and 3, the tapping device 8 has a brush holder 9. the brush holder 9 has a number of through holes 10. In the through holes 10 retaining bolts 11 can be used. The retaining bolts 11 can be screwed into corresponding threaded holes 12 of the main body 1. As a result, the brush holder 9 can be fastened to the base body 1. The main body 1 is usually made of an electrically conductive material, such as a metal, in particular cast iron. The brush holder 9 is usually made of an electrically conductive material, for example made of metal, in particular cast iron. The retaining bolts 11 are usually also made of an electrically conductive material, such as steel. Thus, there is an electrically conductive connection of the brush holder 9 to the main body 1 via the retaining bolts 11. Optionally, a direct electrical contact of the brush holder 9 with the main body 1 may additionally exist. This is not necessary. Rather, it could even be an insulating layer 13 between the brush holder 9 and the base body 1 may be arranged.

The brush holder 9 has at least one brush guide 14. According to FIG. 3, at least two brush guides 14 are present. In each brush guide 14, a brush 15 is arranged in each case, which is displaceably guided in a displacement direction 16. Each brush 15 is acted upon by a pressure spring 17 with a spring force F. By means of the spring forces F, the brushes 15 are pressed against the shaft 4. The brushes 15 are made of an electrically conductive material. For example, they can consist of a coal-metal mixture. They are electrically connected to the brush holder 9. If the pressure springs 17 are made of metal, it is possible, for example, for the electrically conductive connection of the brushes 15 to the brush holder 9 to be effected via the pressure springs 17. Preferably, however, assume from the remote from the shaft 4 ends 18 of the brushes 15 stranded conductor 19, which are connected to the brush holder 9 at a suitable location.

Due to the configuration of the brushes 15, the brush holder 9 and the retaining pin 11 as electrically conductive elements and by their electrically conductive connection with each other thus there is a continuous electrically conductive connection of the shaft 4 via the brush 16, the brush holder 9 and the holding elements 11 to the main body 1. As a result, the wave voltages occurring in the shaft 4 are derived to the base body 1.

Between the brushes 1 and the brush guides 14, an electrically insulating intermediate element 20 is arranged in each case. As a result, there is no direct electrical contact between the respective brush 15 and the respective brush guide 14. For the sake of good order, it should be pointed out in this connection that the brush guides 14 are only those parts of the brush holder 9 which (relative to the respective displacement direction 16 of the respective brush 15) extend tangentially around the respective displacement direction 16 around.

The intermediate elements 20 may be mechanically fixedly connected to the brush guides 14. This is shown in the left half of FIG. 3 and in FIG. In this embodiment, the brush 15 is displaceable relative to the intermediate element 20. This embodiment is preferred. Alternatively, however, the intermediate elements 20 may be mechanically fixed to the brushes 15. This is shown in the right half of FIG 3 and FIG 5. In this case, the intermediate elements 20 move together with the respective brush 15th

The intermediate element 20 is - see FIG 6 - preferably formed as a molded part. It may, for example, have the rectangular (special case: square) cross-section shown in FIG. It can for example consist of paper or plastic.

In a preferred embodiment, the intermediate element 20 has a thickness d which is less than 1 mm. The thickness d is preferably between 20 μm and 500 μm. In particular, the thickness d is more preferably between 50 μm and 200 μm, for example 100 μm. Furthermore, the intermediate element 20 preferably has a dielectric constant ε which is between 1.5 and 10. For example, the dielectric constant ε between 2 and 5, in particular between 3 and 3.5. By such a configuration, the intermediate element 20 sets a distance (which corresponds generally to the thickness d of the intermediate element 20) of the respective brush 15 of the respective brush guide 14 such that the brush 15 at frequencies well above the mains frequency (50 Hz or 60 Hz) is capacitively coupled to the brush guide 14. Because capacitive currents that oscillate in the two-digit kHz range, in particular between 20 kHz and 50 kHz, between the brush 15 on the one hand and the brush guides 14 on the other hand, are harmless for the reliability of the tapping device 8 according to the invention.

It has been described above that the brushes 15 are pressed directly onto the shaft 4. However, it is of course also possible to rotate on the shaft 4 to arrange a slip ring 21 and to press the brushes 15 to the slip ring 21.

The above description is only for explanation of the present invention. The scope of the present invention, however, is intended to be determined solely by the appended claims.

Claims

claims 1. tapping device for tapping an electrical voltage from a shaft (4) of an electrical machine, - wherein the tapping device has a brush holder (9), which consists of electrically conductive material and is connectable to a base body (1) of the electric machine, - wherein the tapping device has a brush (15), which consists of electrically conductive material, - Wherein the brush holder (9) has a brush guide (14), in which the brush (15) is displaceably guided, so that the brush (15) via a spring force (F) to the shaft (4) is pressable, - wherein the brush (15) is electrically conductively connected to the brush holder (9), - Between the brush (15) and the brush guide (14) an electrically insulating intermediate element (20) is arranged so that no direct electrical contact between see the brush (15) and the brush guide (14). 2. tapping device according to claim 1, characterized in that the intermediate element (20) a distance (d) of the brush (15) of the brush guide (14) such that the brush (15) at frequencies well above the mains frequency with the brush guide ( 14) is capacitively coupled. 3. Gripper device according to claim 1 or 2, characterized in that the intermediate element (20) is designed as a molded part. 4. tapping device according to claim 1, 2 or 3, characterized in that the intermediate element (20) with the brush (15) is mechanically fixed. 5. gripper device according to claim 1, 2 or 3, d a d u r c h e c e n e c e s in that the intermediate element (20) with the brush guide (14) is mechanically fixed. 6. tapping device according to one of the above claims, d a c h e c e n e c e s in that the brush holder (9) has a number of through holes (10) for insertion of retaining bolts (11). 7. mounting kit, consisting of a tapping device (8) according to claim 6 and a number of retaining bolts (11), - wherein the retaining bolts (11) can be inserted into the through bores (10) and screwed to the main body (1) of the electric machine, so that the brush holder (9) can be fastened to the main body (1) by means of the retaining bolts (11), - Wherein the retaining bolts (11) consist of electrically conductive material and, when the brush holder (9) by means of the retaining bolts (11) is fixed to the base body (1), electrically connected to the brush holder (9) and the base body (1) are. 8. Electrical machine, - wherein the electric machine has a main body (1), in which a stator (2) of the electric machine is arranged, - wherein the electric machine has a shaft (4) which is rotatably mounted in bearings (5) in the base body (1) and on which a rotor (3) of the electrical machine is rotatably mounted, - wherein the electric machine has a tapping device (8) according to one of claims 1 to 6, - Wherein the brush (15) of the tapping device (8) to the shaft (4) or one on the shaft (4) rotatably mounted slip ring (21) is pressed and the brush holder (9) of the tapping device (8) with the main body (1 ) is electrically connected, so that one in the shaft (4) occurring electrical voltage to the base body (1) is derived. 9. Electrical machine according to claim 8, characterized in that the brush holder (9) has a number of through holes (10) that in the through holes (10) retaining bolts (11) are inserted, which consist of electrically conductive material that the retaining bolts ( 11) are screwed to the base body (1) and thus the brush holder (9) on the base body (1) is fixed and that the retaining bolts (11) with the brush holder (9) and the base body (1) are electrically connected. 10. An electric machine according to claim 8 or 9, characterized in that the electric machine has a converter unit (7) by means of which a voltage (U1) can be fed into the electric machine. 11. Electric machine according to claim 10, characterized in that the voltage (U1) can be fed into the rotor (3). 12. Electrical machine according to one of claims 8 to 11, d a d u c h e c e n e c e s in that the electric machine is designed as a generator.