Direct rotor bar cooling for induction motors

Abstract

A rotor assembly for use in an induction machine includes: a rotor core having a plurality of conductor bar slots spaced circumferentially around the rotor core; a rotor shaft including a fluid supply channel configured to receive fluid from a fluid source; and a conductor bar received within the conductor bar slot, the conductor bar receiving fluid from the fluid supply channel through a hole formed in or on an outer surface of the conductor bar.

Description

Technical Field

[0001] This application relates to induction motors, and more particularly, to a rotor assembly for cooling an induction motor. Background Art

[0002] Rotating electrical machines can exist in different forms. For example, a rotating electrical machine can be a synchronous machine, such as a permanent magnet synchronous machine. Or a rotating electrical machine can be an asynchronous machine, such as an induction motor. Generally, synchronous machines have a greater continuous performance rating compared to induction motors. That is, induction motors may have a lower continuous speed and torque rating compared to synchronous motors. One factor that may contribute to this disadvantage may be the thermal capacity of the induction motor. To increase the continuous speed and torque rating, it would be helpful to more effectively cool the induction motor. Summary of the Invention

[0003] In one implementation, a rotor assembly used in an induction motor includes: a rotor core having a plurality of conductor bar slots circumferentially spaced around the rotor core; a rotor shaft including a fluid supply channel configured to receive fluid from a fluid source; and conductor bars received in the conductor bar slots, the conductor bars receiving fluid from the fluid supply channel through holes formed in the conductor bars or on the outer surface of the conductor bars.

[0004] In another implementation, a rotor assembly used in an induction motor includes: a rotor core having a plurality of conductor bar slots circumferentially spaced around the rotor core; a rotor shaft including a fluid supply channel configured to receive fluid from a fluid source; and conductor bars received in the conductor bar slots, the conductor bars having a shaped outer surface having at least one concave region and at least one contact surface that engages a bar-facing surface of the conductor bar slot.

[0005] In yet another implementation, a rotor assembly used in an induction motor includes: a rotor core having a plurality of conductor bar slots circumferentially spaced around the rotor core; a rotor shaft including a fluid supply channel configured to receive fluid from a fluid source; and conductor bars received in the conductor bar slots, the conductor bars having a shaped outer surface having at least one concave region, and the conductor bars having a shorter radial length compared to the conductor bar slots. Brief Description of the Drawings

[0006] Figure 1 is a cross-sectional view depicting an implementation of the rotor assembly;

[0007] Figure 2 is another cross-sectional view depicting an implementation of the rotor assembly;

[0008] Figure 3 is a cross-sectional view depicting another implementation of the rotor assembly;

[0009] Figure 4a is a cross-sectional view depicting a portion of an implementation of a rotor assembly installed in a stator;

[0010] Figure 4b is another cross-sectional view depicting a portion of an implementation of a rotor assembly installed in a stator;

[0011] Figure 5 is a cross-sectional view depicting yet another implementation of the rotor assembly;

[0012] Figure 6 is a cross-sectional view depicting a portion of an implementation of a rotor assembly installed in a stator;

[0013] Figure 7 is a graph depicting an estimate of the torque-speed curve using the rotor assembly;

[0014] Figure 8 is another graph depicting an estimate of the torque-speed curve using the rotor assembly; and

[0015] Figure 9 is another graph depicting an estimate of the torque-speed curve using the rotor assembly. DETAILED DESCRIPTION

[0016] An induction motor may include a rotor assembly having metal conductor bars circumferentially spaced about a rotor axis and fixed within slots of the assembly. Fluid channels formed in the rotor assembly may receive fluid from a source and communicate the fluid directly over the outer surfaces of the conductor bars and / or within the bars to reduce the temperature of the induction motor. The shape, location, and orientation of the fluid channels may exist in a plurality of different forms.

[0017] REFERENCE Figure 1 AND Figure 2, an implementation of a rotor assembly 10a housed by an induction motor 12 is shown. The induction motor includes the rotor assembly 10a and a stator 14 having a stator winding 16 that houses the rotor assembly 10a. The stator winding 16 is housed within stator slots (not shown) and may be slightly exposed outside the slots at the radial side 18 of the stator 14 at the end turns 20. When conducting current, the stator winding 16 causes the rotor assembly 10a to undergo an angular displacement relative to the stator 14. The term "induction motor" or "induction motor" should be understood to mean an asynchronous rotating electric machine or motor, which is different from a synchronous machine. The rotor assembly described herein is used by an induction motor or an asynchronous rotating electric machine and can conduct current through its conductor bars. The rotor core 22 can be formed by a stack of thin steel layers aligned along the rotor axis (x) and extending axially. The layers making up the stack can have a specific shape that, when combined, forms conductor bar slots 24. For example, each layer can be shaped to closely follow the outer surface of the conductive bar 26a, so that when the bar 26a is housed by the rotor assembly 10b within the conductor bar slot 24, during the operation of the induction motor, the bar 26a is firmly held by the assembly 10a. The rotor core 22 and the conductor bar 26a can be designed in different ways. For example, each conductor bar slot 24 in the rotor core 22 can contain more than one conductor bar 26a, and these bars 26a can be placed adjacent to each other in the slot 24 with a gap 28 therebetween. The gap 28 can form at least a part of a fluid channel that can communicate fluid from a source over or through the conductor bars 26a. These layers can be bonded or otherwise mechanically connected together to form an integral structure.

[0018] In this implementation of the rotor assembly 10a, the conductor bar 26a includes at least one hole 30 formed within the surface of the bar 26a such that the hole 30 is not parallel to the rotor axis (x). The hole 30 can extend from one end 32 of the conductor bar 26a to the opposite end 34 of the conductor bar 26a. However, other implementations are possible where the hole 30 extends from one point on the outer surface of the bar 26a to another point. The diameter of the hole 30 can vary depending on the desired flow rate. When the conductor bar 26a is positioned within the rotor core 22, the hole 30 is positioned to receive fluid near the midpoint (P) position of the rotor core 22 between adjacent conductor bars 26a. Given the non-parallel orientation of the hole 30, one opening of the hole 30 will be closer to the fluid source than the other opening. During the formation of the conductor bar, the hole 30 can be formed as part of a casting process. Alternatively, in other implementations, the hole 30 can be milled after the conductor bar 26a has been formed. In the implementation discussed herein, the conductor bar 26a can be made of copper, but other metals are possible, such as aluminum.

[0019] The rotor shaft 31 may be fixed to the rotor core 22 about the rotor shaft axis (x). In this implementation, the rotor shaft 31 may include a fluid supply channel 33 within the shaft such that the channel opens at one end of the shaft 31 to receive fluid from a fluid source (not shown). The fluid may move axially along the axis (x) such that the fluid may move radially outward into the rotor core 22 and to the midpoint (P) in the hole 30.

[0020] Figure 3 Figures 4, 4a and 4b depict another implementation of the rotor assembly 10b housed by the induction motor 12. The rotor assembly 10b may be formed by a stack of thin steel layers aligned along and axially extending along the rotor shaft axis (x). The layers making up the stack may have a specific shape that, when combined, includes conductor bar slots 24 and forms the rotor core 22. For example, each layer may be formed to closely follow the outer surface of the conductive bars 26b such that when the bars 26b are housed by the rotor assembly 10b, they are held securely during the operation of the induction motor. However, the relationship between the outer surface of the conductor bars and the bar-facing surfaces of the conductor bar slots may vary within the rotor assembly 10b. In this implementation, at least some portion of the conductor bar 26b may have a shaped outer surface 40 that at least partially forms a fluid channel between the outer surface 40 of the conductor bar 26b and the bar-facing surface 42 of the conductor bar slot 24, which channels fluid onto the outer surface 40 of the bar 26b. The shaped outer surface 40 of the conductor bar 26b may also include a slot engagement surface 44 that directly abuts the bar-facing surface 42 of the conductor bar 26b. Other portions of the conductor bar 26c may have a reduced thickness that leaves a space between the outer surface 40 of the bar 26c and the bar-facing surface 42 of the conductor bar slot 24 when the bar 26c is positioned in the conductor bar slot 24. This space may permit fluid to flow within the conductor bar slot 24 over the outer surface 40 of the conductor bars 26b / 26c.

[0021] In this implementation, the rotor core 22 may accommodate the conductor bars 26b / 26c within the conductor bar slots 24. Each bar within a conductor bar slot 24 may have a different shape along the axial length of the bar 26; one portion of the bar 26b has one shape while another portion of the bar 26c has another different shape. The conductor bars 26b / 26c with differently shaped portions may fill the conductor bar slots 24 that extend circumferentially around the rotor core 22. The conductor bar 26b having a shaped outer surface 40 positioned adjacent to the radial face of the rotor core 22 may be referred to as an end stack, whereas the conductor bar 26c having a different shaped outer surface positioned between the end stacks and extending circumferentially around the core 22 may be referred to as an intermediate stack. The intermediate stack may include conductor bars 26c having a shape in the form of a reduced thickness such that there is a space between the conductor bar 26c and the bar-facing surface 42 of the conductor bar slot 24. The rotor shaft 31 may be coupled to the rotor assembly 10b along the rotor shaft axis (x) and includes a fluid supply passage 31 that extends axially along the rotor shaft axis (x) and radially outward from the axis (x) towards the intermediate stack. Fluid may travel axially along the rotor shaft axis (x) to a midpoint (P), at which point the fluid may then radially outward from the axis (x) into the rotor core 22 and into the conductor bar slots 24 of the intermediate stack. As the fluid flows radially outward, the fluid contacts the conductor bar 26c having a reduced thickness. Rotation of the rotor assembly 10b may direct the fluid axially towards the end stack.

[0022] The conductor bar 26b in the end stack may have a shaped surface 40 that both permits fluid to flow axially on the shaped outer surface 40 of the bar 26b parallel to the rotor shaft axis (x) within the conductor bar slot 24 and also directly contacts the bar-facing surface 42 of the slot 24 to securely position the bar 26b within the rotor core 22. For example, the shaped surface 40 may be created at least in part by a concave region 48 on the outer surface 40 of the conductor bar 26b that extends from one end of the bar 26b adjacent to the intermediate stack and the other end of the bar 26b adjacent to the radial face 46 of the rotor core 22. The concave region 48 may form part of a fluid passage and permits fluid to flow from the intermediate stack along the outer surface 40 of the conductor bar 26b within the end stack towards the radial face 46 of the rotor core 22, thereby exiting the core 22 and then flowing radially outwardly over the end turns 20 of the stator 14. Additionally, the conductor bar 26b may have a contact surface 50 that secures the bar 26b within the slot 24 and prevents movement of the bar 26b within the slot 24.

[0023] Another implementation of the rotor assembly 10c is in Figure 5 and Figure 6is shown. The rotor assembly 10c uniformly includes conductor bars 26d within the conductor bar slots 24, which have a shaped surface that both permits fluid to flow axially on the shaped outer surface 40 of the bar 26d parallel to the rotor axis (x) within the conductor bar slot 24 and also permits direct contact with the bar-facing surface 42 of the slot 24 to securely position the bar 26d within the rotor core 22. For example, the shaped surface 40 can be created at least in part by a concave region 48 on the outer surface 40 of the conductor bar 26d that extends from one end of the bar 26d to the other end of the bar 26d adjacent to the radial face 46 of the rotor core 22. The concave region 48 can form part of a fluid channel and permits fluid to flow on the outer surface 40 of the conductor bar 26d to the radial face 46 of the rotor core 22, thereby exiting the core 22 and then flowing radially outwardly on the end turns 20 of the stator 14. The rotor core 22 can be extruded and shaped to hold the bar 26 in place during operation. The tight fit between the bar 26 and the rotor core 22 can also contribute to cooling the assembly. Additionally, the conductor bar 26d can have a contact surface 50 that secures the bar 26d within the slot 24 and prevents movement of the bar 26d relative to the slot 24. The conductor bars 26d can also be sized such that they have a radial length (R) that is less than the radial length of the conductor bar slot 24. When the conductor bars 26d are received within the conductor bar slots 24, the distal ends 52 of the bars 26d can directly abut a portion of the slot 24 while a fluid channel can be formed between the bar 26d and the bar-facing surface 42 of the slot 26d in the region 54 closest to the rotor axis (x). In this sense, the fluid channel can include the concave region 48 as well as the region 54 between the bar and the slot.

[0024] The rotor shaft 31 can be coupled to the rotor assembly 10d along the rotor axis (x) and includes a fluid supply channel 33 that extends axially along the rotor axis (x) and radially outwardly towards the rotor core 22. Fluid can travel through the fluid supply channel 33 to an end point (E), at which point the fluid can then move radially outwardly from the axis (x) along the radial face 46 of the rotor core 22, where the fluid can be directed into the conductor bar slots 24 and axially communicated parallel to the rotor axis (x). Rotation of the rotor assembly 10d can axially direct the fluid towards the opposite radial face 56 of the rotor core 22.

[0025] Figures 7 - 9 Performance estimates of rotor assemblies are depicted without fluid channels, with fluid channels inside the conductor bars, and with fluid flowing on the outer surface of the conductor bars, respectively. Figure 7 An estimate of the torque-speed curve for an induction motor without conductor bar cooling is depicted, having a torque of ~147 Nm and a power of ~93 kW. Figure 8Depicts an estimate of the torque-speed curve for an induction motor having holes in the conductor bars for assisting cooling, having a torque of ~151 Nm and a power of ~102 kW. And Figure 9 Depicts an estimate of the torque-speed curve for an induction motor assisted by fluid flowing on the outer surface of the conductor bars, having a torque of ~152 Nm and a power of ~110 kW.

[0026] It should be understood that the foregoing is a description of one or more embodiments of the present invention. The present invention is not limited to the specific embodiment(s) disclosed herein, but rather is defined solely by the claims that follow. Furthermore, the statements contained in the foregoing description relate to specific embodiments and should not be construed as limiting the scope of the invention or the definition of terms used in the claims, unless a term or phrase is expressly defined above. Various other embodiments and various changes and modifications of the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes and modifications are intended to be within the scope of the appended claims.

[0027] As used in this specification and the claims, the terms "e.g.", "for example", "for instance", "such as", and "like" and the verbs "comprising", "having", "including", and their other verb forms (when used in conjunction with a listing of one or more parts or other items) should each be construed as open-ended, such that the listing should not be regarded as excluding other additional parts or items. Other terms should be construed in their broadest reasonable sense unless they are used in a context that requires a different interpretation.

Claims

1. A rotor assembly for use in an induction motor, comprising: a rotor core having a plurality of conductor bar slots spaced circumferentially around the rotor core; a rotor shaft comprising a fluid supply channel configured to receive fluid from a fluid source; as well as A conductor bar is received in the conductor bar slot, the conductor bar receiving fluid from the fluid supply channel through a hole formed in the conductor bar or on an outer surface of the conductor bar.

2. The rotor assembly of claim 1 further comprising a hole that is non-parallel to the rotor shaft axis.

3. The rotor assembly of claim 1 further comprising a plurality of conductor bars axially disposed within a single conductor bar slot and gaps between the conductor bars that receive fluid radially outward from the rotor shaft axis.

4. The rotor assembly of claim 1 further comprising a conductor bar having a contoured outer surface.

5. The rotor assembly according to claim 4, wherein: The contoured outer surface includes a concave region.

6. The rotor assembly according to claim 4, wherein: The contoured outer surface comprises a contact surface abutting a bar-facing surface of the conductor bar slot.

7. The rotor assembly according to claim 1, wherein: The fluid exits the rotor core and moves radially outward to contact the end turns of the stator.

8. The rotor assembly according to claim 1, wherein: The fluid from the fluid supply passage is initially supplied to a radial face of the rotor core.

9. A rotor assembly for use in an induction motor, comprising: a rotor core having a plurality of conductor bar slots spaced circumferentially around the rotor core; a rotor shaft comprising a fluid supply channel configured to receive fluid from a fluid source; as well as A conductor bar is received within the conductor bar slot, the conductor bar having a contoured outer surface having at least one concave region and at least one contact surface engaging a bar-facing surface of the conductor bar slot.

10. The rotor assembly of claim 9, further comprising: an end stack comprising a conductor strip having said contoured outer surface; and an intermediate stack comprising conductor strips having a reduced thickness.

11. The rotor assembly of claim 9 further comprising a plurality of conductor bars axially disposed within a single conductor bar slot and gaps between the rotor bars that receive fluid radially outward from the rotor shaft axis.

12. The rotor assembly according to claim 9, wherein: The fluid exits the rotor core and moves radially outward to contact the end turns of the stator.

13. A rotor assembly for use in an induction motor, comprising: a rotor core having a plurality of conductor bar slots spaced circumferentially around the rotor core; a rotor shaft comprising a fluid supply channel configured to receive fluid from a fluid source; as well as A conductor bar is received in the conductor bar slot, the conductor bar having a contoured outer surface having at least one concave region, and the conductor bar having a shorter radial length than the conductor bar slot.

14. The rotor assembly according to claim 13, wherein: The conductor bars received in the conductor bar slots are uniformly shaped.

15. The rotor assembly according to claim 13, wherein: The fluid exits the rotor core and moves radially outward to contact the end turns of the stator.

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