WO2019012178A1

WO2019012178A1 - A rotor of an induction machine and a method for assembling a cage winding of the rotor

Info

Publication number: WO2019012178A1
Application number: PCT/FI2018/050393
Authority: WO
Inventors: Matti Nikkinen; Michiel BOSCH
Original assignee: The Switch Drive Systems Oy
Priority date: 2017-07-11
Filing date: 2018-05-24
Publication date: 2019-01-17
Also published as: FI128259B; FI20175678A1

Abstract

A rotor of an induction machine comprises a rotor core structure (102) and a cage winding. The cage winding comprises conductor bars (103, 104) and end-ring structures at ends of the cage winding. Each end-ring structure comprises axially successive first and second end-rings (105, 106, 107, 108). The ends of the conductor bars are arranged to protrude axially out from the rotor core structure so that longer ones of the ends protrude a longer distance than shorter ones of the ends. The longer ends protrude through openings of the first end-rings and through openings of the second end-rings and are attached to the second end-rings, whereas the shorter ends protrude through openings of the first end-rings only and are attached to the first end-rings. Thus, reliable mechanical attachments can be made between the conductor bars and both of the first and second end-rings.

Description

A rotor of an induction machine and a method for assembling a cage winding of the rotor

Field of the technology The disclosure relates generally to rotating electric machines. More particularly, the disclosure relates to a rotor of an induction machine. Furthermore, the disclosure relates to an induction machine and to a method for assembling a cage winding of a rotor of an induction machine.

Background Rotating electric machines, such as motors and generators, generally comprise a stator and a rotor which are arranged so that a magnetic flux is developed between these two. A rotor of an induction machine comprises typically a rotor core structure, a shaft, and a cage winding. The cage winding comprises conductor bars and end- rings. The conductor bars are located in slots of the rotor core structure. The end- rings are connected to the ends of the conductor bars at the end-regions of the rotor core structure. The rotor core structure is typically a laminated structure composed of ferromagnetic steel sheets which are electrically insulated from each other and which are stacked in the axial direction of the rotor. However, especially in many high-speed induction machines, a rotor core structure is made of solid steel. The rotor core structure made of solid steel may constitute, together with the shaft of the rotor, a single piece of solid steel.

In many induction machines, the conductor bars and the end-rings are manufactured as separate pieces of electrically conductive material and the end- rings are attached to the ends of the conductor bars with electrically conductive joints. The material of the conductor bars and of the end-rings can be for example copper or aluminum. The conductor bars can be attached to the end-rings for example by soldering, welding, brazing, or clenching the ends of the conductor bars axially to form tight fits with walls of openings of the end-rings through which the conductor bars are protruding. In order to obtain desired electrical properties, the axial thickness of end-rings needs to be in many cases from 40 mm to 60 mm. The required axial thickness may cause challenges in availability of material pieces suitable for making the end-rings, in costs of the material pieces, and/or in the manufacturing process of the end-rings.

The publication US201 1080067 describes an end-ring structure which comprises two axially successive end-rings at both ends of a cage winding. This approach facilitates the manufacture of the end-rings because each end-ring is thinner in the axial direction. Furthermore, suitable material pieces are available more easily and with lower costs. This approach is however not free from challenges. One of the challenges is that end-rings which are axially closer to a rotor core structure may be difficult to attach to conductor bars and thus these end-rings may get mechanically loose due to for example temperature variations and differences in thermal expansion coefficients of materials of a rotor.

Summary

The following presents a simplified summary in order to provide a basic understanding of some embodiments of the invention. The summary is not an extensive overview of the invention. It is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. The following summary merely presents some concepts of the invention in a simplified form as a prelude to a more detailed description of exemplifying embodiments of the invention. In this document, the word "geometric" when used as a prefix means a geometric concept that is not necessarily a part of any physical object. The geometric concept can be for example a geometric point, a straight or curved geometric line, a geometric plane, a non-planar geometric surface, a geometric space, or any other geometric entity that is zero, one, two, or three dimensional. In accordance with the invention, there is provided a new rotor for an induction machine. A rotor according to the invention comprises:

- a rotor core structure,

- a plurality of conductor bars in slots of the rotor core structure, and - two end-ring structures electrically connecting ends of the conductor bars to each other at both ends of a cage winding constituted by the conductor bars and the end-ring structures, each of the end-ring structures comprising a first end-ring and a second end-ring axially successive to each other. The conductor bars are located in the slots of the rotor core structure so that, at each end of the cage winding, ends of the conductor bars protrude axially out from the rotor core structure so that longer ones of the ends protrude axially a longer distance than shorter ones of the ends. The longer ends of the conductor bars protrude through first openings of the first end-rings and through openings of the second end-rings and are attached to the second end-rings, whereas the shorter ends of the conductor bars protrude through second openings of the first end-rings without protruding through the second end-rings. The shorter ends of the conductor bars are attached to the first end-rings.

As the shorter ends of the conductor bars are attached to the first end-rings, the risk that the first end-rings get mechanically loose, e.g. due to temperature variations, is reduced.

In accordance with the invention, there is provided also a new induction machine. An induction machine according to the invention comprises:

- a stator comprising stator windings, and - a rotor according to the invention, the rotor being rotatably supported with respect to the stator.

In accordance with the invention, there is provided also a new method for assembling a cage winding of a rotor of an induction machine. A method according to the invention comprises: - placing conductor bars into slots of a rotor core structure so that, at each end of the rotor core structure, ends of the conductor bars protrude axially out from the rotor core structure so that longer ones of the ends protrude axially a longer distance than shorter ones of the ends, - placing first end-rings so that the shorter and longer ends of the conductor bars protrude through openings of the first end-rings,

- attaching the shorter ends of the conductor bars to the first end-rings,

- placing second end-rings so that only the longer ends of the conductor bars protrude through openings of the second end-rings, and

- attaching the longer ends of the conductor bars to the second end-rings.

Exemplifying and non-limiting embodiments of the invention are described in accompanied dependent claims.

Various exemplifying and non-limiting embodiments of the invention both as to constructions and to methods of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific exemplifying embodiments when read in conjunction with the accompanying drawings.

The verbs "to comprise" and "to include" are used in this document as open limitations that neither exclude nor require the existence of also un-recited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated. Furthermore, it is to be understood that the use of "a" or "an", i.e. a singular form, throughout this document does not exclude a plurality.

Brief description of the figures Exemplifying and non-limiting embodiments of the invention and their advantages are explained in greater detail below in the sense of examples and with reference to the accompanying drawings, in which: figures 1 a, 1 b, 1 c, and 1 d illustrate a rotor according to an exemplifying and non- limiting embodiment of the invention, figures 2a and 2b illustrate a detail of a rotor according to an exemplifying and non- limiting embodiment of the invention, figure 3 illustrates an electric machine according to an exemplifying and non-limiting embodiment of the invention, and figure 4 shows a flowchart of a method according to an exemplifying and non-limiting embodiment of the invention for assembling a cage winding of a rotor of an induction machine.

Description of exemplifying and non-limiting embodiments

The specific examples provided in the description given below should not be construed as limiting the scope and/or the applicability of the appended claims. Furthermore, it is to be understood that lists and groups of examples provided in the description given below are not exhaustive unless otherwise explicitly stated.

Figures 1 a, 1 b, and 1 c show section views of a rotor 101 according to an exemplifying and non-limiting embodiment of the invention. The section shown in figure 1 a is taken along a geometric fraction line A-A shown in figures 1 b and 1 c, and the geometric section surface is perpendicular to the xy-plane of a coordinate system 199. The section shown in figure 1 b is taken along a geometric line B1 -B1 shown in figure 1 a, and the geometric section plane is parallel with the xy-plane of the coordinate system 199. The section shown in figure 1 c is taken along a geometric line B2-B2 shown in figure 1 a, and the geometric section plane is parallel with the xy-plane of the coordinate system 199. The rotor 101 comprises a rotor core structure 102. In this exemplifying case, the rotor core structure 102 is made of solid ferromagnetic steel and the rotor core structure and a shaft 1 14 of the rotor constitute a single piece of solid steel. It is, however, also possible that a rotor according to an exemplifying and non-limiting embodiment comprises a rotor core structure that comprises a stack of ferromagnetic steel sheets so that the ferromagnetic steel sheets are electrically insulated from each other and stacked on each other in the axial direction of the rotor.

The rotor 101 comprises a cage winding that comprises a plurality of conductor bars located in slots of the ferromagnetic core structure 102. In figures 1 a and 1 b, two of the conductor bars are denoted with references 103 and 104. In this exemplifying case, the slots of the rotor core structure are open slots having slot openings on the airgap surface of the rotor core structure 102. It is, however, also possible that a rotor according to an exemplifying and non-limiting embodiment comprises a rotor core structure that comprises closed slots. The cage winding comprises two end- ring structures 1 15 and 1 16. The end-ring structure 1 15 connects ends of the conductor bars electrically to each other at a first end of the rotor core structure 102. Correspondingly, the end-ring structure 1 16 connects ends of the conductor bars electrically to each other at the second end of rotor core structure 102. The end-ring structure 1 15 comprises a first end-ring 105 and a second end-ring 106 which are axially successive to each other and in contact with each other. Correspondingly, the end-ring structure 1 16 comprises an end-ring 107 and an end-ring 108 which are axially successive to each other and in contact with each other.

The conductor bars are located in the slots of the rotor core structure 102 so that, at each end of the rotor core structure, ends of the conductor bars protrude axially out from the rotor core structure so that longer ones of the ends protrude axially a longer distance than shorter ones of the ends. As illustrated in figure 1 a, the conductor bar 103 has its longer end at the first end of the rotor core structure and its shorter end at the second end of the rotor core structure, whereas the conductor bar 104 has its shorter end at the first end of the rotor core structure and its longer end at the second end of the rotor core structure. The longer ends of the conductor bars protrude through first openings of the end-rings 105 and 107 and through openings of the end-rings 106 and 108. The longer ends are attached to the end- rings 106 and 108. The shorter ends of the conductor bars protrude through second openings of the end-rings 105 and 107 without protruding through the end-rings 106 and 108. The shorter ends are attached to the end-rings 105 and 107. As illustrated in figures 1 a and 1 c, the end-ring 106 has openings for the longer ends only. Correspondingly, the end-ring 108 has openings for the longer ends only. As the shorter ends of the conductor bars are attached to the end-rings 105 and 107, the risk that the end-rings 105 and 107 get mechanically loose, e.g. due to temperature variations, is reduced. In this exemplifying case, the openings of the end-rings 105- 108 are apertures so that the end-rings are capable of radially supporting the ends of the conductor bars. It is, however, also possible that the openings are slots on the outer circumferences of the end-rings or on the inner circumferences of the end- rings.

The shorter ends of the conductor bars can be attached to the end-rings 105 and 107 for example so that the shorter ends are axially clenched to form tight fits with walls of the openings of the end-rings 105 and 106. Correspondingly, the longer ends of the conductor bars can be attached to the end-rings 106 and 108 for example so that the longer ends are axially clenched to form tight fits with walls of the openings of the end-rings 106 and 108. It is, however, also possible that the ends of the conductor bars are attached to the end-ring structures by soldering, brazing, or welding.

In the exemplifying rotor 101 illustrated in figures 1 a-1 c, the conductor bars are arranged so that, at each end of the cage winding, every second end of the conductor bars is a longer end and every second end is correspondingly a shorter end. In other words, at each end of the cage winding, there is between adjacent ones of the shorter ends of the conductor bars one of the longer ends of the conductor bars, and between adjacent ones of the longer ends of the conductor bars one of the shorter ends of the conductor bars.

In the exemplifying rotor 101 illustrated in figures 1 a-1 c, each of the conductor bars comprises a first end-portion, a middle-portion, and a second end-portion so that the middle-portion is wider in a radial direction than the first and second end-portions and the first end-portion is axially longer than the second end-portion. Figure 1d shows the conductor bars 103 and 104 separately from the other parts of the rotor 101 . In figure 1 d, the first end-portion of the conductor bar 103 is denoted with a reference 109, the middle-portion of the conductor bar 103 is denoted with a reference 1 10, and the second end-portion of the conductor bar 103 is denoted with a reference 1 1 1 . The conductor bars are located in the slots of the rotor core structure so that the first end-portions constitute the longer ends of the conductor bars and the second end-portions constitute the shorter ends of the conductor bars. As can be understood based on figures 1 a and 1 d, the conductor bars can be similar to each other but adjacent conductor bars are oppositely directed in the slots of the rotor core structure. The end-ring structure 1 15 may further comprise an electrically conductive layer that is between the end-rings 105 and 106 and in contact with the end-rings 105 and 106. Correspondingly, the end-ring structure 1 16 may comprise an electrically conductive layer that is between the end-rings 107 and 108 and in contact with the end-rings 107 and 108. The material of the electrically conductive layers is advantageously different from the material of the end-rings. The material of each electrically conductive layer can be for example tin or other material having a high electrical conductivity so as to ensure a good galvanic contact between the end- rings of each end-ring structure. The electrically conductive layer can be for example a coating of tin on an axially facing surface of an end-ring. It is also possible that the electrically conductive layer is constituted by two coatings on axially facing surfaces of the end-rings.

Figures 2a and 2b illustrate a detail of a rotor according to an exemplifying and non- limiting embodiment of the invention. Figure 2a shows a section taken along a geometric line A-A shown in figure 2b. The geometric section plane relating to figure 2a is parallel with the yz-plane of a coordinate system 299. Figure 2b shows a section taken along a geometric line B-B shown in figure 2a. The geometric section plane relating to figure 2b is parallel with the xy-plane of the coordinate system 299. The axial direction of the rotor is parallel with the z-axis of the coordinate system 299. In this exemplifying case, the rotor comprises wedges at the openings of the slots of the rotor core structure 202 so that the conductor bars are radially between the wedges and the bottoms of the slots of the rotor core structure. The wedges are arranged to radially support the conductor bars. In figures 2a and 2b, one of the wedges is denoted with a reference 212 and one of the conductor bars is denoted with a reference 203. Axially successive end-rings of one of the end-ring structures are denoted with references 205 and 206. The wedges can be made of for example electrically conductive and/or non-magnetic material such as e.g. copper or brass.

In a rotor according to an exemplifying and non-limiting embodiment of the invention, each of the end-ring structures comprises a first end-ring, a second end-ring, and a third end-ring axially successive to each other. At each end of the cage winding, first ones of the ends of the conductor bars protrude through first openings of the first end-ring, through first openings of the second end-ring, and through openings of the third end-ring and are attached to the third end-ring, and second ones of the ends of the conductor bars protrude through second openings of the first end-ring and through second openings of the second end-ring without protruding through the third end-ring and are attached to the second end-ring, and third ones of the ends of the conductor bars protrude through third openings of the first end-ring without protruding through the second and third end-rings and are attached to the first end- ring. The above-mentioned principle can be generalized to cases where each of the end-ring structures comprises more than three end-rings.

Figure 3 illustrates an induction machine according to an exemplifying and non- limiting embodiment of the invention. The induction machine comprises a rotor 301 according to an embodiment of the invention and a stator 302. The rotor 301 is rotatably supported with respect to the stator 302. Arrangements for rotatably supporting the rotor 301 with respect to the stator 302 are not shown in figure 3. The stator 302 comprises stator windings 313 for generating a rotating magnetic field in response to being supplied with alternating currents. The stator windings 313 can be for example a three-phase winding. The rotor 301 can be for example such as illustrated in figures 1 a-1d or such as illustrated in figures 2a and 2b.

Figure 4 shows a flowchart of a method according to an exemplifying and non- limiting embodiment of the invention for assembling a cage winding of a rotor of an induction machine. The method comprises the following actions:

- action 401 : placing conductor bars into slots of a rotor core structure so that, at each end of the rotor core structure, ends of the conductor bars protrude axially out from the rotor core structure so that longer ones of the ends protrude axially a longer distance than shorter ones of the ends, - action 402: placing first end-rings so that the shorter and longer ends of the conductor bars protrude through openings of the first end-rings,

- action 403: attaching the shorter ends of the conductor bars to the first end- rings,

- action 404: placing second end-rings so that only the longer ends of the conductor bars protrude through openings of the second end-rings, and - action 405: attaching the longer ends of the conductor bars to the second end-rings.

In a method according to an exemplifying and non-limiting embodiment of the invention, the conductor bars are placed into the slots of the rotor core structure so that, at each end of the rotor core structure, there is between adjacent ones of the shorter ends of the conductor bars one of the longer ends of the conductor bars, and between adjacent ones of the longer ends of the conductor bars one of the shorter ends of the conductor bars.

In a method according to an exemplifying and non-limiting embodiment of the invention, each of the conductor bars comprises a first end-portion, a middle-portion, and a second end-portion so that the middle-portion is wider in a radial direction than the first and second end-portions and the first end-portion is axially longer than the second end-portion. The conductor bars are placed in the slots of the rotor core structure so that the first end-portions constitute the longer ends of the conductor bars and the second end-portions constitute the shorter ends of the conductor bars.

In a method according to an exemplifying and non-limiting embodiment of the invention, the shorter ends of the conductor bars are attached to the first end-rings by clenching the shorter ends axially to form tight fits with walls of the openings of the first end-rings, and the longer ends of the conductor bars are attached to the second end-rings by clenching the longer ends axially to form tight fits with walls of the openings of the second end-rings. It is also possible that the ends of the conductor bars are attached to the end-ring structures by soldering, brazing, or welding.

The specific examples provided in the description given above should not be construed as limiting the scope and/or the applicability of the appended claims. Lists and groups of examples provided in the description given above are not exhaustive unless otherwise explicitly stated.

Claims

What is claimed is:

1 . A rotor (101 , 301 ) for an induction machine, the rotor comprising:

- a rotor core structure (102),

- a plurality of conductor bars (103, 104, 203) in slots of the rotor core structure, and

- two end-ring structures (1 15, 1 16) electrically connecting ends of the conductor bars to each other at both ends of a cage winding constituted by the conductor bars and the end-ring structures, each of the end-ring structures comprising a first end-ring (105, 107) and a second end-ring (106, 108) axially successive to each other, characterized in that:

- the conductor bars are located in the slots of the rotor core structure so that, at each end of the cage winding, ends of the conductor bars protrude axially out from the rotor core structure so that longer ones of the ends protrude axially a longer distance than shorter ones of the ends,

- the longer ones of the ends of the conductor bars protrude through first openings of the first end-rings (105, 107) and through openings of the second end-rings (106, 108) and are attached to the second end-rings, and

- the shorter ones of the ends of the conductor bars protrude through second openings of the first end-rings (105, 107) without protruding through the second end-rings and are attached to the first end-rings.

2. A rotor according to claim 1 , wherein, at each end of the cage winding, there is between adjacent ones of the shorter ends of the conductor bars one of the longer ends of the conductor bars, and between adjacent ones of the longer ends of the conductor bars one of the shorter ends of the conductor bars.

3. A rotor according to claim 1 or 2, wherein each of the conductor bars comprises a first end-portion (109), a middle-portion (1 10), and a second end-portion (1 1 1 ) so that the middle-portion is wider in a radial direction than the first and second end- portions and the first end-portion is axially longer than the second end-portion, and the conductor bars are located in the slots of the rotor core structure so that the first end-portions constitute the longer ones of the ends of the conductor bars and the second end-portions constitute the shorter ones of the ends of the conductor bars.

4. A rotor according to any of claims 1 -3, wherein the shorter ends of the conductor bars are axially clenched to form tight fits with walls of the openings of the first end-rings, and the longer ends of the conductor bars are axially clenched to form tight fits with walls of the openings of the second end-rings.

5. A rotor according to any of claims 1 -3, wherein the shorter ends of the conductor bars are attached to the first end-rings and the longer ends of the conductor bars are attached to the second end-rings with an attachment technique selected from the following list: soldering, brazing, welding.

6. A rotor according to any of claims 1 -4, wherein the slots of the rotor core structure are open slots having slot openings on an airgap surface of the rotor core structure.

7. A rotor according to claim 5, wherein the rotor further comprises wedges (212) at the openings of the slots of the rotor core structure so that the conductor bars (203) are radially between the wedges and bottoms of the slots of the rotor core structure.

8. A rotor according to any of claims 1 -7, wherein the openings of the first and second end-rings (105-108) are apertures of the first and second end-rings so as to radially support the ends of the conductor bars.

9. A rotor according to any of claims 1 -8, wherein each of the end-ring structures (1 15, 1 16) comprises an electrically conductive layer between the first and second end-rings and in contact with the first and second end-rings, material of the electrically conductive layer being different from material of the first and second end- rings.

10. An induction machine comprising: - a stator (302) comprising stator windings (313), and

- a rotor (301 ) according to any of claims 1 -9 and rotatably supported with respect to the stator.

1 1 . A method for assembling a cage winding of a rotor of an induction machine, characterized in that the method comprises:

- placing (401 ) conductor bars into slots of a rotor core structure so that, at each end of the rotor core structure, ends of the conductor bars protrude axially out from the rotor core structure so that longer ones of the ends protrude axially a longer distance than shorter ones of the ends, - placing (402) first end-rings so that the shorter and longer ones of the ends of the conductor bars protrude through openings of the first end-rings,

- attaching (403) the shorter ones of the ends of the conductor bars to the first end-rings,

- placing (404) second end-rings so that only the longer ones of the ends of the conductor bars protrude through openings of the second end-rings, and

- attaching (405) the longer ones of the ends of the conductor bars to the second end-rings.

12. A method according to claim 1 1 , wherein the conductor bars are placed into the slots of the rotor core structure so that, at each end of the rotor core structure, there is between adjacent ones of the shorter ends of the conductor bars one of the longer ends of the conductor bars, and between adjacent ones of the longer ends of the conductor bars one of the shorter ends of the conductor bars.

13. A method according to claim 1 1 or 12, wherein each of the conductor bars comprises a first end-portion, a middle-portion, and a second end-portion so that the middle-portion is wider in a radial direction than the first and second end-portions and the first end-portion is axially longer than the second end-portion, and the conductor bars are placed in the slots of the rotor core structure so that the first end- portions constitute the longer ones of the ends of the conductor bars and the second end-portions constitute the shorter ones of the ends of the conductor bars.

14. A method according to any of claims 1 1 -13, wherein the shorter ones of the ends of the conductor bars are attached to the first end-rings by clenching the shorter ones of the ends axially to form tight fits with walls of the openings of the first end-rings, and the longer ones of the ends of the conductor bars are attached to the second end-rings by clenching the longer ones of the ends axially to form tight fits with walls of the openings of the second end-rings.