GB2623300A

GB2623300A - Electric machines

Info

Publication number: GB2623300A
Application number: GB2214643.5A
Authority: GB
Inventors: Ziani De Ferranti James
Original assignee: J And M Ferranti Tech Ltd
Current assignee: J And M Ferranti Tech Ltd
Priority date: 2022-10-05
Filing date: 2022-10-05
Publication date: 2024-04-17
Also published as: GB202214643D0

Abstract

An electric machine comprising first and second ends spaced apart along a machine axis; a rotor within the machine for rotation about the axis; a stator 26 that surrounds at least part of the rotor, the stator having windings 36 that extend in slots 34 from first and second end faces and including end windings that extend on the face between slots, the faces being spaced apart along the rotor axis, and the stator having a cooling assembly. The cooling assembly includes metal cooling fluid ducts that extend within the slots in thermal contact with the windings whereby fluid flowing in the ducts remove heat, where each fluid duct has an inlet and an outlet being close to the same end of the machine. Inlet and/or outlet manifolds may be provided in thermal contact with the end windings. Each cooling duct may extend from a first end of one of the slots for substantially the entire length of the slot. Each slot may have two cooling ducts extending into the slot from opposite ends. Each cooling duct may extend approximately half the length of the slot. The cooling ducts within a single stator slot may be incorporated into a cooling fin 40. The ducts within a single stator slot may be formed from lengths of pipe. The electric machine may be a motor or a generator.

Description

Electric Machines This invention relates to electric machines. More specifically, it relates to cooling in rotary electric motors and generators.

A significant limiting factor in the power density of electric motors is the ability to disperse excess heat from internal components of the motor. Typically, four cooling arrangements are provided in electric motors: air cooling for example using an open housing or fan forced air; indirect liquid water glycol cooling for example using flow through rotor shaft or stator water jacket; direct liquid cooling such as using oil bath/spray impingement using a we stator and/or rotor; and indirect liquid water glycol cooling in stator slots in the stator using plastics pipes or other structures. In many cases, electric machines utilise combinations of the above strategies where the ultimate objective is to significantly increase the power density of the machine.

Indirect cooling involves passing cooling fluid through ducts that extend through the machine in close contact with electrical conductors. While the thermal performance of the cooling system could be optimised using metal ducts, it is undesirable to locate such components within the magnetic field of the electric machine because this could result in electric currents being induced within the cooling components. Therefore, the conventional approach is to use non-metallic cooling ducts with a consequent limitation of cooling effectiveness.

An aim of this invention is to provide indirect cooling within a stator of an electric machine with improved efficiency through the use of metallic cooling ducts.

To this end, this invention provides an electric machine comprising: a. first and second ends spaced apart along a machine axis; b. a rotor carried within the electric machine for rotation about the machine axis; c. a stator that surrounds at least part of the rotor, the stator having stator windings that extend in slots from first and second end faces and including end windings that extend on the face between slots, the faces being spaced apart along the rotor axis, the stator having a cooling assembly, the cooling assembly including metal cooling fluid ducts that extend within the slots in thermal contact with the stator windings whereby fluid flowing in the fluid ducts can remove heat form the stator; wherein d. each fluid duct has an inlet and an outlet, the inlet and outlet being close to the same end of the machine.

This arrangement ensures that the cooling ducts do not form a conductive path that wraps around a stator tooth so minimising the likelihood that substantial currents will be induced in the cooling ducts.

Embodiments of the invention may include an inlet manifold and an outlet manifold, the inlet of each fluid duct being connected to the inlet manifold and the outlet of each fluid duct being connected to the outlet duct. The inlet manifold and/or the outlet manifold may be in thermal contact with the end windings. This provides cooling for the end windings.

The cooling ducts and manifolds may be parts of a cooling fluid distributor. The cooling fluid distributor may be a single-piece jointless structure, or alternatively may be an assembly of multiple components.

In a first arrangement, each cooling duct extends from a first end of one of the slots for substantially the entire length of the slot. In such embodiments, a cooling arrangement for cooling end windings at a second end of each of the slots is provided.

Alternatively, each cooling duct may have two cooling ducts extending into the slot from opposite ends. For example, each cooling duct may extend approximately half the length of the slot, each slot The fluid ducts may be of various cross-sectional shapes. For example, the cooling ducts within a single stator slot are incorporated into a cooling fin. Alternatively, the cooling ducts within a single stator slot are formed from lengths of pipe.

The fluid ducts may be formed integrally with the manifolds as a complex one-piece component without joints. Alternatively, the fluid ducts may be formed as separate components which are assembled onto the manifolds.

Embodiments of the invention will now be described in detail, by way of example, and with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic longitudinal cross section of a motor being an embodiment of the invention; Figure 2 is a transverse cross-section through a stator body of the embodiment of Figure 1; Figure 3 is an exploded diagrammatic view of a housing and cooling components of a motor embodying the invention; Figure 4 shows in section components of a stator being a sub-assembly of an embodiment of the invention; Figure 5 shows a fin of a drive end cooling fluid distributor of the motor of Figure 1; Figure 6 shows details of a non-drive end cooling fluid distributor of the motor of Figure 1; Figure 7 shows a variation on cooling components of a motor embodying the invention; Figure 8 shows various alternative arrangements of flow channels within stator slots of various embodiments of the invention; Figure 9 shows in diagrammatic form the arrangement of coolant ducts in embodiments of the invention; and Figure 10 shows in diagrammatic form the flow paths of coolant in embodiments of the invention.

This invention is directed to a cooling arrangement that is applicable to a range of electric machines. Therefore, the extent of description of the working and construction of the machine will be limited to that needed to understand the cooling arrangement The example described here is a motor, but it will be understood that the invention has applicability to other types of electric machine, such as generators.

A motor embodying the invention has a machine axis A about which a rotor assembly, a stator assembly and other components are disposed. Spaced along the machine axis A, the motor has a drive end at which a drive output can be taken and a non-driving end at which control gear is located. In Figure 1, the drive end is shown at the left, and the non-drive end at the right Figure 3 is in the opposite orientation, with the drive end on the right With reference to the figures, a motor embodying the invention includes a casing 10 within which an approximately cylindrical chamber is formed, centred about the machine axis A. A shaft 12 is carried on bearings 14, 16 for rotation about the machine axis A. A rotor assembly 20 is carried on the shaft 12, the rotor assembly being fixed for rotation with the shaft. A stator assembly 22 surrounds the rotor assembly 20 and is fixed within the chamber such that rotation with respect to the casing is prevented.

The stator assembly includes a stator body 26. The stator body 26 has a cylindrical shell 30 that has a multiplicity of inwardly projecting teeth 32 that closely approach the rotor assembly 20. Multiple stator slots 34 extend the length of the stator body 26, each stator slot 34 being the space between two adjacent teeth 32. Conductors 36 extend within each stator slot, each conductor extending in a loop, starting at the non-drive end, passing along one stator slot 34 towards the drive end, and returning the along another stator slot 34 to the non-drive end.

The stator assembly further includes a drive end cooling fluid distributor 38 that includes a plurality of cooling fins 40 and a manifold ring SO. The manifold ring SO is generally annular and centred on the machine axis A. The cooling fins 40 project form the manifold ring 50 parallel to the machine axis A. Each cooling fin 40 extends within a stator slot 34 in thermal contact with the conductors 36. The cooling fins 40 extend from the drive end towards the non-drive end without extending the entire length of the stator slot 34. Each cooling fin 40 has a fluid duct 42 that is U-shaped and extends the length of the fin 40. The cooling duct has an inlet port 44 and an outlet port 46. Each fin is connected to a manifold ring 50. The manifold ring SO has two separate fluid channels: an inlet channel 52 and an outlet channel 54. The inlet port 44 of each cooling fin 40 is connected to the inlet channel 52 and the outlet port 46 of each cooling fin 40 is connected to the outlet channel 54. An input pipe 56 is connected to the inlet channel 52 and has an external pipe connector and an output pipe 58 is connected to the outlet channel 52 and has an external pipe connector. Between each pair of adjacent fins 40, there is a concave cooling surface 60. Each of the concave cooling surfaces 60 is in thermal contact with end windings of the stator assembly.

A non-drive end cooling fluid distributor 64 is provided at the non-drive end of the motor. The non-drive end cooling fluid distributor 64 has an annular inlet fluid manifold 66 and an annular outlet fluid manifold 68 centred on the machine axis A. Multiple coolant ducts 70 interconnect the inlet fluid manifold 66 the outlet fluid manifold 68, each coolant duct being in thermal contact with an end winding of the stator assembly. An input pipe 74 is connected to the inlet manifold 66 and has an external pipe connector and an output pipe 76 is connected to the outlet manifold 68 and has an external pipe connector.

The cooling fluid distributors 38, 64 are formed from metal, which is preferred because of its high thermal conductivity and for its integrity, the latter being particularly advantageous for aeronautical applications. The absence of a continuous metal path from one end of the stator to the other avoids causing a magnetic short-circuit, as would happen if conventional plastic direct cooling pipes were replaced with metal. Titanium alloys and stainless steel are preferred metals for construction of the cooling fluid distributors. The cooling fluid distributors may be single-piece jointless structures formed by additive layer manufacturing (otherwise known as 3D printing). Alternatively, they can be assembled from multiple individual components, interconnected, for example, by welding, braising soldering or by way of tube joints such as 0-rings and/or gaskets.

The cooling fluid distributors 38, 64 (at least, those parts that are in contact with electrical conductors) are preferably electrically insulated. This may be achieved, for example, by application of insulating tape or film, heat-shrink film, powder or ceramic coating or by use of spray or dip enamel.

In a complete motor, the cooling fluid distributors 38,64 are connected into a cooling circuit. The cooling circuit delivers cooling fluid to the inputpipe 56)74 of each of the fluid distributors 38, 64.

Within the drive end cooling fluid distributor 38, cooling fluid enters the inlet channel 52 where it cools the end windings through the concave cooling surfaces 60 and from which it flows into the inlet port 44 of each cooling fin 40. The fluid then passes along the length of the fluid duct 42, in a U-shaped path, removing heat from within the stator slots, before passing through the outlet port 46 to be received in the outlet channel 54. Cooling fluid then leaves the drive end cooling fluid distributor 38 through the output pipe 58 to continue is passage through the cooling circuit Within the non-drive end cooling fluid distributor 64, cooling fluid enters the inlet manifold 66 from which it flows through the coolant ducts 70 to the outlet fluid manifold 68, removing heat form the non-drive end windings as it does. Fluid then leaves the non-drive end cooling fluid distributor 64 through the output pipe 76 to continue is passage through the cooling circuit In this embodiment, the cooling circuit also provides a flow of cooling fluid to bearing housings 80, 82 and to a helical cooling channel 84 formed in the casing 10 through multiple valves and interconnection pipes, as shown in Figure 3. Alternatively, the stator may be provided with a cooling circuit separate for that cooling other components, such as the bearings. This allows for different cooling regimes to be applied to different components within the machine. An example of when this may be advantageous is in embodiments that include superconducting components, which will typically be cooled to a much lower temperature than other components of the machine.

Figure 8 shows an alternative arrangement of cooling elements within a stator of a motor embodying the invention. This embodiment includes two similar or identical fluid distributors 138, 138' of a form corresponding to that of the drive end cooling fluid distributor 38 described above. Each of the cooling fins 140, 140' extends just less than half the length of each stator slots. The cooling fins 140, 140 extend into the slot from opposite ends to approach, but not to meet, one another. This allows substantially the entire length of the slotto be cooled without creating a magnetic short-circuit path.

Flow ducts within the stator slots may vary in shape and position. Various alternative arrangements being shown in Figure 9. The flow ducts are shown with narrowly-spaced hatching, the direction of the hatching indicating the direction of flow within the duct The arrangement of cooling ducts in embodiments of the invention is shown in simplified form in Figure 9. At each end of the stator, there is a respective cooling fluid distributor 138, 138'.

Each of these distributors supplies a flow of cooling fluid to multiple cooling fins 140, 140'. Each cooling fin 140, 140' extends into the stator between adjacent pairs of stator teeth 132. The fins 140 of the first cooling fluid distributor 138 approach but do not meet the cooling fins 140' of the second cooling fluid distributor 138'. This prevents an electric current flowing through the fins in a loop around the stator. The length of the fins 140 that extend from the first cooling fluid distributor 138 is denoted a and the length of the fins 140' that extend from the second cooling fluid distributor 138' is denoted b. The ratio of the lengths a, b of the fins can vary within the range 0 < a:b <1.

Figure 10 indicates diagrammatically the path that cooling fluid follows within the stator. Fluid enters each cooling fluid distributor 138, 138' from which it is distributed in parallel to each fin 140, 140'. The cooling fluid follows a U-shaped path within the fins 140, 140' to exit from the same end of the stator that it entered. This avoids formation any electrical or magnetic conductive path that extends in a loop around the stator.

Claims

Claims 1. An electric machine comprising: a. first and second ends spaced apart along a machine axis; b. a rotor carried within the electric machine for rotation about the machine axis; c. a stator that surrounds at least part of the rotor, the stator having stator windings that extend in slots from first and second end faces and including end windings that extend on the face between slots, the faces being spaced apart along the rotor axis, the stator having a cooling assembly, the cooling assembly including metal cooling fluid ducts that extend within the slots in thermal contact with the stator windings whereby fluid flowing in the fluid ducts can remove heat form the stator; wherein d. each fluid duct has an inlet and an outlet, the inlet and outlet being close to the same end of the machine.
2. An electric machine according to claim 1 that includes an inlet manifold and an outlet manifold, the inlet of each fluid duct being connected to the inlet manifold and the outlet of each fluid duct being connected to the outlet duct
3. An electric machine according to claim 2 in which the inlet manifold and/or the outlet manifold is in thermal contact with the end windings.
4. An electric machine according to claim 2 or claim 3 in which the cooling ducts and manifolds are parts of a cooling fluid distributor.
5. An electric machine according to claim 4 in which the cooling fluid distributor is a single-piece jointless structure.
6. An electric machine according to claim 4 in which the cooling fluid distributor is an assembly of multiple components.
7. An electric machine according to any preceding claim in which each cooling duct extends from a first end of one of the slots for substantially the entire length of the slot
8. An electric machine according to claim 7 which further includes a cooling arrangement for cooling end windings at a second end of each of the slots.
9. An electric machine according to any one of claims 1 to 7 in which each slot having two cooling ducts extending into the slot from opposite ends.
10. An electric machine according to claim 9 in which each cooling duct extends approximately half the length of the slot
11. An electric machine according to any preceding claim in which the cooling ducts within a single stator slot are incorporated into a cooling fin.
12. An electric machine according to any one of claims 1 to 10 in which the cooling ducts within a single stator slot are formed from lengths of pipe.
13. An electric machine according to any preceding claim in which the cooling ducts and the manifold are parts of a one-piece component
14. An electric machine according to any one of claims 1 to 13 in which the fluid and the manifold are parts of an assembly.
15. An electric machine according to any preceding claim that is a motor.
16. An electric machine according to any preceding claim that is a generator.