WO2016030471A1

WO2016030471A1 - Arrangement for conducting electric current between rotor windings and slip-ring device

Info

Publication number: WO2016030471A1
Application number: PCT/EP2015/069674
Authority: WO
Inventors: Rami Raute; Jori KEITAMO; Hannu Kurkinen; Veikko Haverinen; Laura PYYNY; Klas SANDHOLM
Original assignee: Abb Technology Ag
Priority date: 2014-08-29
Filing date: 2015-08-27
Publication date: 2016-03-03
Also published as: CN105375697A

Abstract

Embodiment of the present disclosure discloses an arrangement for conducting electric current between rotor windings and a slip-ring device (30) in a machine, comprising at least one set of conductive mechanisms each comprising: a conductive element (11) formed with a bar element; a first coupling element (12) adapted to electrically and mechanically couple a first end of the conductive element (11) to the slip -ring device (30); and a second coupling element adapted to electrically and mechanically couple a second end of the conductive element (11) to a rotor winding. This arrangement can conduct larger current, and is easy in manufacturing and mounting.

Description

ARRANGEMENT FOR CONDUCTING ELECTRIC CURRENT

BETWEEN ROTOR WINDINGS AND SLIP-RING DEVICE

FIELD OF THE INVENTION

[0001] Embodiments of the present disclosure relates to the field of an electric machine, especially the arrangement for conducting electric current between rotor windings and a slip-ring device in an eclectic machine, and an electric machine comprising such arrangement.

BACKGROUND OF THE INVENTION

[0002] A slip ring is a known electric transmission device that allows energy flow between a rotating part and a stationary part, for example in a motor or generator. Normally, a slip ring is electrically connected to rotating rotor windings of an electric machine for each phase, so as to provide an electric interface between the rotating rotor windings and a stationary circuit. Carbon brushes are often used to contact the slip rings to realize this electrical connection. For example, for a double-fed induction generator, the slip rings are used to electrically connect the rotating rotor windings to a power source so as to provide field current to the rotor windings. For an asynchronous motor, the slip rings are used to electrically connect the rotating rotor windings to a starting circuit so as to increase the resistance of the rotor windings during a starting period.

[0003] In the prior art, the slip rings are electrically connected to the rotor windings with conductive cables. Since a diameter of the conductive cables is limited, the rated current for the electric machine with the cable connection between the slip rings and the rotor windings would not be too large. Furthermore, a reliable electrical connection between the conductive cable and the slip rings/rotor windings are difficult. In addition, an insulation treatment for the cable connection is also complicated.

SUMMARY OF THE INVENTION

[0004] Hence, in order to overcome one or more of the deficiencies in the prior art mentioned above, one of objectives of embodiments of the present disclosure is to provide an arrangement for conducting electric current between rotor windings and slip-rings in a machine.

[0005] According to one aspect of the invention, there is provided an arrangement for conducting electric current between rotor windings and a slip-ring device. The arrangement comprises at least a set of conductive mechanism each comprising a conductive element formed with a bar element; a first coupling element adapted to electrically and mechanically couple a first end of the conductive element to the slip-ring device; and a second coupling element adapted to eclectically and mechanically couple a second end of the conductive element to a rotor winding.

[0006] Compared to the cable connection in the prior art, the bar element is advantageous. For example, a dimension of the bar element can be easily optimized to be adapted to the rated current of the electric machine. Thus, a larger current can be conducted with this arrangement.

[0007] According to one embodiment, the bar element can be a flat bar element.

[0008] According to one embodiment, the flat bar element can be a copper bar.

[0009] According to one embodiment, the machine can comprise a rotor shaft and an end portion of the rotor shaft has an aperture therein, and at least part of the conductive element can be adapted to be arranged inside the aperture.

[0010] According to one embodiment, the at least part of the conductive element can be adapted to be arranged substantially parallel to the rotor shaft.

[0011] According to one embodiment, the first coupling element and the second coupling element can be configured to at least partially extend in a direction angled to the conductive element. For example, the first coupling element and the second coupling element can be configured to at least partially extend in a direction substantially perpendicular to the conductive element.

[0012] According to one embodiment, the first coupling element can be a L-shaped lug having a first leg configured to be angled to the conductive element and a second leg configured to be substantially parallel to the conductive element. For example, the first leg can be configured to be substantially perpendicular to the conductive element.

[0013] According to one embodiment, the first leg of the first L-shaped lug can be electrically and mechanically coupled to a slip-ring bar in the slip-ring device installed around the end portion of the rotor shaft, and the second leg of the first L-shaped lug can be electrically and mechanically coupled to the first end of the conductive element.

[0014] According to one embodiment, the conductive element can comprise a stepped portion which is in a different plane from the remaining portions of the conductive element. The second leg of the L-shaped lug can be electrically and mechanically coupled to the stepped portion.

[0015] According to one embodiment, the first coupling element can be a flexible coupling element. As such, the thermal extension of the conductive element can be compensated. [0016] According to one embodiment, the second coupling element comprises a conductive sleeve.

[0017] According to one embodiment, the conductive sleeve can be adapted to extend out from the rotor shaft.

[0018] According to one embodiment, the conductive mechanism can further comprise a connection bar adapted to be fixed to the rotor. The connection bar, the conductive sleeve and the second end of the conductive element can be electrically and mechanically connected via a fixing screw throughout the sleeve, and the rotor winding can be electrically connected to the connection bar via a winding connecting bar. Thus, the conductive element can be electrically connected to the rotor winding.

[0019] According to one embodiment, an insulating sleeve can be provided around the conductive sleeve.

[0020] According to one embodiment, an insulation element can be provided around the conductive sleeve and on top of the insulating sleeve.

[0021] According to one embodiment, a fastener is provided to fix the connection bar to the rotor shaft.

[0022] According to one embodiment, the arrangement further can comprise a supporting plate for supporting the first end of the conductive element and the first coupling element of each set of the conductive mechanisms.

[0023] According to one embodiment, the supporting plate can be provided with slots allowing the first coupling element and the first end of the conductive element passing through.

[0024] According to one embodiment, the arrangement can comprise three sets of the conductive mechanisms for three phases of the rotor windings respectively. Each set of the conductive mechanism is isolated from each other and from the shaft.

[0025] According to one embodiment, the arrangement can further comprise at least a supporting element between the first and second ends of the conductive elements configured to support the conductive elements.

[0026] According to one aspect of the invention, a slip-ring electric machine is also provided, comprising rotor windings and a slip-ring device. The machine further comprises the arrangement for conducting electric current between rotor windings and the slip-ring device as mentioned above. It shall be appreciated that the slip-ring electric machine according to embodiments of the present disclosure possesses the advantages of the arrangement as mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] When reading the following detailed description on the exemplary embodiments with reference to the drawings, the aim, features and advantages of the present disclosure become obvious, wherein

[0028] FIG. 1 illustrates the perspective view of a machine having a rotor and slip rings, with an arrangement for conducting electric current between rotor windings and slip-rings according to an embodiment of the present disclosure assembled between the rotor and the slip rings;

[0029] FIG. 2 illustrates the perspective view of an arrangement for conducting electric current between rotor windings and slip-rings according to an embodiment of the present disclosure;

[0030] FIG. 3 illustrates the front view of one set of conductive mechanisms in the arrangement of Fig.2 for one phase; and

[0031] FIG. 4 illustrates the cross-section view of the arrangement of Fig.1 assembled in a machine.

DETAILED DESCRIPTION OF EMBODIMENTS

[0032] Hereinafter, a few exemplary embodiments will be referred to in describing the mechanism and spirit of the present disclosure. It should be understood that these embodiments are merely provided to facilitate those skilled in the art in understanding and in turn implementing the present disclosure, but not for limiting the scope of the present disclosure in any way.

[0033] Various embodiments of the present disclosure are described in detail herein in an exemplary way by referring to the drawings.

[0034] FIG. 1 illustrates a perspective view of a machine having a rotor and a slip ring device, with an arrangement for conducting electric current between rotor windings and a slip-ring device according to one embodiment of the present disclosure assembled between the rotor and the slip rings. The machine can be an electrical machine, such as a motor or a generator. In the exemplary embodiment below, the electric machine can be a three phase machine. However, the present disclosure is not limited therein, and the electric machine can also be a single phase machine.

[0035] As shown in Figure 1, the electric machine can comprise a rotor 10 with three rotor windings (not shown) each corresponding to one phase. A rotor shaft 20 can be extended from the rotor 10 outwardly to a free end. A slip ring device 30 can be mounted on the free end of the rotor shaft 20. An arrangement for conducting electric current between the rotor windings and slip-rings according to an embodiment of the present disclosure is arranged inside the shaft 20.

[0036] As shown in Figure 1, the slip ring device 30 can comprise a support 31, and three slip rings 32 are arranged on the support 31 isolated from each other. Each slip ring 32 is electrically connected to one rotor winding via the above arrangement as the electrical interface for one phase. When the slip rings 32 are rotating along with the rotor 10, a brush element connected to a stationary circuit (not shown) can contact the slip rings 32 to create current channels from the rotor windings to the stationary circuit.

[0037] In the exemplary embodiment as shown in Fig.l, the arrangement for conducting electric current between rotor windings and slip-rings comprises three sets of conductive mechanisms for three phases of the rotor windings respectively. FIG. 2 illustrates the perspective view of the arrangement assembled in the rotor shaft in Fig. l. The three sets of conductive mechanisms are identical from each other. The only difference is that the three sets of the conductive mechanisms are respectively connected to the three windings of the rotor 10, and respectively connected to the three slip rings 32, so as to respectively create electrical connections in the three phases of the electrical machine.

[0038] As shown in Figure 2, the three sets of conductive mechanisms can be arranged in a symmetric manner with respect to the axis of the shaft 20 within the shaft 20. Each of the sets is isolated from the other sets, and also from the shaft 20 and other parts of the rotor 10 except for the corresponding winding.

[0039] FIG.3 illustrates the front view of one set of the conductive mechanisms in the arrangement of Fig.2 for one phase. According to one embodiment of the present disclosure, as shown in Figure 3, each set of conductive mechanisms comprises a conductive element 11 formed by a bar element, a first coupling element 12 adapted to electrically and mechanically couple a first end of the conductive element 11 to a slip-ring device 30, and a second coupling element adapted to eclectically and mechanically couple a second end of the conductive element 11 to a rotor winding.

[0040] Referring to Fig.4, the rotor shaft 20 has an aperture on the free end of the rotor shaft 20. According to the exemplary embodiment as shown in Figure 4, the conductive element 11 is substantially arranged inside this aperture, preferably substantially parallel to the shaft 20. The conductive element 11 can connect the slip ring 32 and the rotor winding at its opposite ends respectively.

[0041] Preferably, the conductive element 11 is a flat bar element, which is preferably made of copper. The dimension of the flat bar element can be designed according to the rated current of the electric machine. It is appreciated that the conductive element 11 is not necessary to be exactly flat or straight but may also have some curvature or other shapes. Further, the cross section of the conductive element 11 may also be any shape, as long as the conductive element 11 is adapted to be arranged inside the shaft 20.

[0042] In exemplary embodiments, as shown Figures 3 and 4, the first coupling element 12 is a L-shaped lug having a first leg and a second leg angled to each other. The second leg of the first coupling element 12 can be fixed to the first end of the conductive element 11 via a first fixing screw 41 throughout the screw holes on the second leg and the first end of the conductive element 11. The first leg of the first coupling element 12 can be fixed to a slip ring connection bar (not shown) in the support 31 of the slip ring device 30 via a second fixing screw 42. Thus, the conductive element 11 is mechanically fixed to the slip ring device 30 at the first end. According to exemplary embodiments, upon assembled on the conductive element 11, the first leg of the first coupling element 12 would be angled to the conductive element 11, and the second leg of the first coupling element 12 would be substantially parallel to the conductive element 11. Preferably, the first leg of the first coupling element 12 is substantially perpendicular to the conductive element 11.

[0043] If the portion of the conductive element 11 connected to the first coupling element 12 is substantially parallel to the axis of the rotor shaft 20, the angle between the first leg and the second leg of the first coupling element 12 can be about 90 degrees, so as to facilitate the first leg of the first coupling element 12 to be fitted to the end face of the slip ring support 31 in an orientation perpendicular to the conductive element 11.

[0044] The first coupling element 12 is conductive and also acts as an electrical connector. The second fixing screw 42 passing through the first leg of the first coupling element 12 extends into the slip ring support 31, and is electrically connected to the slip ring connection bar. The slip ring connection bar (not shown) is electrically connected to a corresponding slip ring 32 inside the slip ring support 31. Depending on the position of the connected slip ring 32 on the support 31, the second fixing screw 42 may also pass through other one or two slip rings 32. In a known manner, the second fixing screw 42 keeps insulated from the other one or two slip rings 32. As such, the conductive element 11 is electrically connected to the corresponding slip ring 32 via the first coupling element 12, the second fixing screw 42 and the slip ring connection bar, while keep insulated from the other slip rings.

[0045] The first coupling element 12 can be a flexible conductive element. According to exemplary embodiments, once the conductive element 11 thermally expands in the direction of the shaft under large current, the first leg of the first coupling element 12 angled to the conductive element 11 can be forced by the conductive element 11 to bend towards the direction away from the end face of the slip ring support 31, while maintaining the mechanical and electrical connection between the conductive element 11 and the slip ring 32 via the first coupling element 12. As such, the thermal expansion of the conductive element 11 is compensated.

[0046] It can be seen from Figs. l and 4, the first coupling element 12 locates outside the rotor shaft 20, and the first end of the conductive element 11 is also outside the rotor shaft 20. This provides convenience for the user to mount the first fixing screw and second fixing screw.

[0047] In order to further provide convenience in assembling and decent air insulation distance, the conductive element 11 may have a stepped portion 17 on the first end (most clearly shown in Fig.2), and the second leg of the first coupling element 12 can be fixed to the stepped portion. The stepped portion 17 is in a different plane from the remaining portions of the conductive element 11. When assembling the conductive element 11, the stepped portion 17 is arranged away from the axis of the shaft 20. Thus, there is more space between the first ends of the adjacent conductive elements 11 for mounting the first fixing screw. As such, the first fixing screws 41 for the respective conductive elements 11 would not interfere in each other and electrical communication among the three phases is avoided.

[0048] Preferably, a supporting plate 50 is provided on the first end of the conductive element 11, to support the first end of the conductive element 11 and the first coupling element 12. Referring to Fig. l, the supporting plate 50 preferably has a disc shape. The supporting plate 50 has slots allowing the second leg of the first coupling element 12 and the first end of the conductive element 11 passing through. The number of the slots corresponds to the number of the conductive elements 11 in this arrangement.

[0049] Before the second leg of the first coupling element 12 fixed to the conductive element 11 with the first fixing screw 41, the supporting plate 50 is pushed towards the end face of the slip ring support 31, and the second leg of the first coupling element 12 and the first end of the conductive element 11 for each set of the conductive mechanisms pass through the corresponding slot on the supporting plate 50. Thereafter, the first fixing screw 41 can be mounted to fix the second leg of the first coupling element 12 and the first end of the conductive element 11. The dimension of the slots is arranged to allow the second leg of the first coupling element 12 and the first end of the conductive element 11 passing through. As shown in Figure 1, after the second leg of the first coupling element 12 fixed to the conductive element 11 with the first fixing screw 41, the first fixing screw 42 can used to prevent the supporting plate 50 from moving outwardly. Thus, the supporting plate 50 can be retained in position in the axis direction of the rotor shaft 20.

[0050] Due to the supporting plate 50, the first end of the conductive elements 11 for the three sets of conductive mechanisms are fixed with respect to each in the radial direction. Thus, when the conductive elements 11 are rotating along the rotor shaft 20 with a high speed in operation, the centrifugal force on the first end of the conductive elements 11 can be counteracted. Accordingly, the deformation or movement of the first end of the conductive elements 11 are avoided, which results in more firm connection between the conductive elements 11 and the slip ring device 30.

[0051] It is appreciated that the supporting plate 50 is non-conductive so as to keep the conductive elements 11 being insulated from each other.

[0052] According to one embodiment, as shown in Figures 4, the second coupling element can comprise a sleeve 13 which is fixed to the other end of the conductive element 11 with a third fixing screw 43. The sleeve 13 can be also angled (preferably substantially perpendicular) to the shaft 20. As shown in Figure 4, upon assembled to the conductive element 11, the sleeve 13 extends out of the shaft 20 from a hole on the circumferential wall of the shaft 20.

[0053] As shown in Figures 2-4, a connection bar 14 can be also provided for each phase. The connection bar 14 is fixed to a winding connecting bar 60 in the rotor 10 (see Fig. 1) via a conductive fastener, for example a screw. The winding connecting bar 60 can be further electrically connected to the corresponding rotor winding (not shown). Preferably, the connection bar 14 is L- shaped so as to provide a portion parallel to the axis of the shaft 20 for facilitating the connection between the connection bar 14 and the sleeve 13.

[0054] Referring to Figs. l and 4, when assembling the second coupling element, the sleeve 13 is firstly put into the hole on the circumferential wall of the shaft 20. Then, the sleeve 13 is aligned with the mounting hole on the second end of the conductive element 11 inside the shaft 20. Then, the connection bar 14 is put on top of the sleeve 13 with one mounting hole aligning with the through hole in the sleeve. Thereafter, a conductive third fixing screw 43 is mounted through a mounting hole on the connection bar 14, the through hole in the sleeve 13 and the mounting hole on the second end of the conductive element 11 in sequence. Thereby, the connection bar 14, the sleeve 13 and the conductive element 11 are fixed together. Further, the connection bar 14 can be electrically coupled to the winding connecting bar 60 in any known manner, for example, by fixing screws. As such, the second end of the conductive element 11 is mechanically fixed to the rotor via the sleeve 13 and the connection bar 14.

[0055] In order to reinforce the mechanical connection, a fourth fixing screw 44 can be provided to further fix the connection bar 14 to the rotor 20.

[0056] Because the first and second ends of the conductive bar element 11 are respectively fixed to the slip ring device 30 and the rotor 10 with fixing screws, the conductive element 11 would not shake inside the shaft 20 during rotation along with the rotor 10. The screw connection is also more reliable compared to other connections for the cables.

[0057] The sleeve 13, the third fixing screw 43 going through the sleeve 13 and the connection bar 14 are conductive and also act as electrical connectors. As such, the conductive element 11 is also electrically connected to one rotor winding via the sleeve 13, the third fixing screw 43, the connection bar 14 and the winding connecting bar 60.

[0058] The distances from the conductive sleeve 13, the conductive third fixing screw 43 and the conductive connection bar 14 to other conductive surfaces in the machine are configured so as to meet the requirement of air insulation and creepage insulation to the other conductive surfaces.

[0059] Preferably, an insulating sleeve 16 can provided around the conductive sleeve 13 to improve the air insulation and creepage insulation to the other conductive surfaces.

[0060] Preferably, an insulation element 15 can be preferably provided around the sleeve 13 and on top of the insulating sleeve 16 to further improve the insulation. The insulation element 15 may also surround the fourth fixing screw 44 fixed to the rotor shaft 20, and may have sheds for increase the creepage distance. The insulation element 15 may be also advantageous in mechanical connecting the connection bar 14 to the rotor 20 and the sleeve 30, as it provides larger area for contacting.

[0061] By the above first coupling element 12 and the second coupling element 13, the conductive element 11 is firmly fixed inside the shaft 10, and also electrically connected between the rotor winding and the slip ring. Because each set of the conductive mechanisms comprises the same structure as described above, this arrangement provides the respective electrical connection between the rotor winding and the slip ring for each of the three phases of the machine.

[0062] Preferably, as shown in Figure 2, at least a supporting element 18 can be also provided between the first and second ends of the conductive element 11 to support and isolate the three conductive elements 11 of the three sets of conductive mechanisms from each other and from the rotor shaft 20. As such, it is assured that the conductive elements 11 in the three sets would not deform under centrifugal force, and would not contact each other and the rotor shaft 20 to cause undesired electrical communication.

[0063] Compared to the cable connection in the prior art, the flat bar conductive element is advantageous. The dimension of the flat bar element can be easily optimized to be adapted to the rated current of the electric machine. Thus, a larger current can be conducted with this arrangement. Furthermore, the mechanical and electrical connection between the rotor windings and the slip rings is more reliable since the wire connection is avoided. In addition, this arrangement is easy in manufacturing because all the elements can be produced as series production and the arrangement can be casted with resin in connection with the rotor resining. Due to the easy manufacturing, the cost for this arrangement is low.

[0064] It is appreciated that the arrangement according to the present disclosure is adapted for various kinds of electrical machines, including but not limited to synchronous/ asynchronous /double-fed motor or generator. It is also appreciated that the number of the sets of the conductive mechanisms in the arrangement can also be more or less than three, which depends on the number of the phases in the electrical machine.

[0065] By studying the drawings, the disclosure of the present text, and the attached Claims, those skilled in the art may understand and implement other modifications of the disclosed embodiments during the implementation of the present disclosure. In the claims, "comprising" does not exclude other elements or steps, and "a" or "one" does not exclude the plural concept. The simple fact of illustrating specific methods in the dependent claims, which are mutually different from each other, does not indicate that the combination of these methods cannot be used advantageously. The labels in drawings of the claims should not be interpreted as limiting the scopes thereof.

Claims

WHAT IS CLAIMED IS:

1. An arrangement for conducting electric current between rotor windings and a slip-ring device (30) in a machine, comprising at least one set of conductive mechanisms each includes:

a conductive element (11) formed with a bar element;

a first coupling element (12) adapted to electrically and mechanically couple a first end of the conductive element (11) to the slip-ring device (30); and

a second coupling element adapted to electrically and mechanically couple a second end of the conductive element (11) to the rotor windings.

2. The arrangement according to Claim 1, wherein the bar element (11) is a flat bar element.

3. The arrangement according to Claim 1 or 2, wherein the bar element (11) is a copper bar.

4. The arrangement according to any one of Claims 1-3, wherein the machine comprises a rotor shaft (20) and an end portion of the rotor shaft (20) has an aperture therein, and wherein at least part of the conductive element (11) is adapted to be arranged inside the aperture.

5. The arrangement according to Claim 4, wherein the at least part of the conductive element (11) is adapted to be arranged substantially parallel to the rotor shaft (20).

6. The arrangement according to any one of Claims 1-5, wherein the first coupling element (12) and the second coupling element are configured to at least partially extend in a direction angled to the conductive element (11).

7. The arrangement according to Claim 6, wherein the first coupling element (12) and the second coupling element are configured to at least partially extend in a direction substantially perpendicular to the conductive element (11).

8. The arrangement according to any one of Claims 1-7, wherein the first coupling element (12) is a L- shaped lug having a first leg configured to be angled to the conductive element (11) and a second leg configured to be substantially parallel to the conductive element (11).

9. The arrangement according to Claim 8, wherein the first leg of the first L-shaped lug is electrically and mechanically coupled to a slip-ring bar in the slip-ring device (30) installed around the end portion of the rotor shaft (20), and the second leg of the first L-shaped lug is electrically and mechanically coupled to the first end of the conductive element (11).

10. The arrangement according to Claim 8, wherein the conductive element (11) comprises a stepped portion (17) which is in a different plane from the remaining portions of the conductive element (11);

wherein the second leg of the L-shaped lug is electrically and mechanically coupled to the stepped portion (17).

11. The arrangement according to any one of Claims 1-10, wherein the first coupling element (12) is a flexible coupling element.

12. The arrangement according to any of Claims 1-11, wherein the second coupling element comprises a conductive sleeve (13) adapted to extend out from the rotor shaft (20).

13. The arrangement according to Claim 12, wherein the second coupling element further comprises a connection bar (14) adapted to be electrically coupled to the conductive sleeve (13) and a rotor winding.

14. The arrangement according to Claim 13, wherein the connection bar (14), the conductive sleeve (13) and the second end of the conductive element (11) are electrically and mechanically coupled via a conductive fixer (43) throughout the conductive sleeve (13).

15. The arrangement according to Claim 13 or 14, wherein the connection bar (14) is electrically connected to a winding connecting bar (60) in a rotor (10).

16. The arrangement according to any of Claims 11-15, wherein an insulating sleeve (16) is provided around the conductive sleeve (13).

17. The arrangement according to any of Claims 11-16, wherein an insulation element (15) is provided around the conductive sleeve (13) and on top of the insulating sleeve (16).

18. The arrangement according to any of Claims 13-17, wherein a fixer (44) is provided to fix the connection bar (14) to the rotor shaft (20).

19. The arrangement according to any one of Claims 1-18, wherein the arrangement further comprises a supporting plate (50) for supporting the first end of the conductive element (11) and the first coupling element (12) of each set of the conductive mechanisms.

20. The arrangement according to Claim 19, wherein the supporting plate (50) is provided with slots allowing the first coupling element (12) and the first end of the conductive element (11) passing through.

21. The arrangement according to any one of the preceding claims, comprising three sets of the conductive mechanisms for three phases of the rotor windings respectively;

wherein each set of the conductive mechanism is isolated from each other and from the shaft (20).

22. The arrangement according to any one of the preceding claims, wherein the arrangement further comprising at least a supporting element (18) between the first and second ends of the conductive elements (11) configured to support the conductive elements (11).

23. A slip-ring electric machine, comprising rotor windings, a slip-ring device (30), and the arrangement for conducting electric current between the rotor windings and the slip-ring device according to any one of Claims 1-22.