GB2505909A

GB2505909A - Salient pole stator coil retainer with coolant passage

Info

Publication number: GB2505909A
Application number: GB1216407.5A
Authority: GB
Inventors: Carl Stanley Winsor; Steven Paul Randall
Original assignee: Nidec SR Drives Ltd
Current assignee: Nidec SR Drives Ltd
Priority date: 2012-09-13
Filing date: 2012-09-13
Publication date: 2014-03-19
Also published as: GB201216407D0

Abstract

A cooling component 30 for an electrical machine is placed in the mouth of a slot between two poles of the stator 12, the component holding the windings 20 securely in the slot. The component carries fluid in tube 34 which absorbs heat from the winding and in some embodiments the fluid is passed to a heat exchanger before being recirculated to the machine. The component can also be shaped so as to streamline the mouth of the slot and reduce the windage loss and acoustic noise which are associated with an irregular stator bore. The tube may be single pass with manifold connections at either end of the component 30 (fig 3 not shown) or may be hairpin shaped 34 and engaged with supply and return manifolds 36,38. Tube 34 may traverse the component a number of times and may be only partially enclosed so as to be disposed in direct contact with the windings. The coolant may be gaseous or liquid (e.g. water or oil) The component may be manufactured in situ by moulding or curing an assembly of subcomponents placed in the slot. Materials may comprise felt or glass mat impregnated with resin.

Description

COOLDJG OF ELECTRICAL MACHINES

This invention relates to the cooling of electrical machines, in particular, although not exclusively, electrical machines which are cooled by a liquid.

Electrical machines typically have windings made from insulated conductors in which current flows and which, unless the material from which the conductor is made is superconducting, have resistive loss. Unless the heat generated by this resistive loss (the s?-called 12R loss) is removed, it heats up the conductors. The continuous rating of the electrical machine is generally restricted by the temperature limit of the insulation material of the winding. Often these limits conform to internationally recognised values, e.g. Class F (145°C), Class H (180°C) etc., and the expertise of the designer is brought to bear on the problem of removing the heat generated by the 12R loss at a rate sufficient to keep the temperature of the winding below the chosen limit.

The problem is made more difficult because of the generally conflicting requirements to provide both good electrical insulation and good thermal conduction. The conductors of the winding are typically coated with an electrically insulating coating, and the completed winding assembly is typically impregnated with resin to give a chosen thickness of resin film. The film contributes to ensuring that the electrical insulation of the winding is of a high quality by filling any pin-holes in the insulation on the wire and consolidating the coil to prevent movement and reducing the resistance of thermal paths.

Nevertheless, most good electrical insulators are also good thermal insulators, so the use of these materials generally makes more difficult the task of providing paths of high thernrnl conductivity for the heat generated by the 12R loss from the winding to a heat sink where the heat may be dissipated.

The problem of heat removal is further compounded on electrical machines which have windings in which a coil spans a single tooth, for example brushless dc machines and switched reluctance machines. While the coils of a conventional distributed winding are generally dispersed across a relatively large number of slots and have intimate contact with the iron of the stator laminations, the short-pitched windings of a salient pole machine generally contact the stator only on two sides of the coil at best, resulting in a heat removal path which has a smaller cross-sectional area.

Various methods are known for improving the efficicncy of the dissipation path for the heat from the winding. For example, the coating of impregnating varnish is sometimes, made very thick, so as to eliminate virtually all the air pockets around the winding and provide a path through the varnish for the heat. This improves the heat transfer, but is often a messy and time-consuming process, involving the use of compounds which constitute health and safety hazards.

Liquid cooling is a known techthque. The flow rate of the liquid can be set to keep the liquid at a relatively low temperature compared with the winding so that the consequential thermal gradient gives high heat transfer from the winding.

It is also known to provide cooling jackets surrounding the stator core. For example, US5859482 (Crowell) discloses a cooling jacket made from conduits which are cast into the frame of the electrical machine. Such a technique is often useful when the machine is relatively long compared with its diameter but, as the lengthldiameter ratio reduces, this method is less and less successful. Using serpentine paths through the stator frame, for example as shown in EP 1719236 --(Bostwick), is a technique sometimes used to improve the efficiency of the jacket. However, while these methods have the advantage of keeping the cooling liquid well separated from the electrical conductors, there is inevitably a significantly long thermal path between the conductors and the coolant.

To attempt to shorten these paths, some have introduced coolant pipes into spaces directly adjacent to the windings. For example, US 3109947 (Thompson) discloses coolant pipes adjacent the end windings and WO 00/01053 (Sjoberg) discloses coolant pipes in the slots of the stator, adjacent the sides of the coils.

However, if the coolant pipes are made from an electrically conducting material, there are the added problems of insulating them from the electrical conductors and of avoiding conducting ioops into which circulating currents can be induced to flow.

Another proposed method is to use liquid coolant passing through the winding conductors themselves. This technique is more applicable to large machines in the multi-megawatt range, where the great expense of the complex alTangements needed to provide both fluid seals and electrical insulation on the individual conductors is offset by the large saving in the running cost of the machine.

Though this technique has been proposed for much smaller machines in very specialised applications, for example, as described in US 5489810 (Ferreira), the saving has failed to justi& the complexity.

There is therefore a need for a cooling arrangement for electrical machines which avoids a long thermal path between the conductors and the coolant but does not compromise the integrity of the insulation of the machine.

In one aspect of the invention,there is provided a stator for an electrical machine as set out in claim 1. In another aspect of the invention, there is provided an electrical machine as set out in claim 11. In yet a flirther aspect of the invention, a method of making a stator is provided as set out in claim 13. Another aspect of the invention provides a method of making a stator as set out in claim 14.

Optional features of embodiments of the invention are set out in the dependent claims referring to the claims above.

In some embodiments, there is provided a stator for an electrical machine. The stator includes a back portion and a plurality of salient poles projecting from the back portion and defming a slot between a pair of poles. A cooling component is disposed in the lot to hold a winding wound on the stator between the cooling component and the back portion. A coolant conduit in the cooling component enables coolant to be passed through the tube to cool the winding.

Advantageously, by enabling coolant flow though a conduit embedded in a cooling component which also holds the winding in place, an efficient cooling arrangement is provided which provides cooling in a hot-spot between the heat sinks provided by the stator poles in a space efficient manner.

In some embodiments, a tube is embedded in the cooling component for carrying the coolant. By providing a tube for the coolant flow, integrity of the coolant path is facilitated and connection of the coolant conduit to supply and return manifolds is facilitated, increasing design freedom.

The tube enters and exits the cooling component on one and the same end of the cooling component in some embodiments. In some embodiments, the tube is configured to have at least one bend within the cooling component. The tube -may be made from any suitable material and, in particular, may be flexible andlor an electric isolator.

In ome embodiments, the cooling component may have been moulded in place in the slot.

In some embodiments, the cooling component has a face substantially aligned with the pole faces of the poles adjacent to it. In particular, the stator may be for a rotating machine and the face of the cooling component and adjacent pole faces together may define a portion of a substantially smooth bore of the stator. By repeating this arrangement around the stator, a smooth bore can be provided.

This facilitates the reduction of acoustic noise and windage losses, as described in more detail below.

In some embodiments, an electrical machine is provided which has a stator as described above, the coolant conduit being connected between a coolant supply manifold and a coolant return manifold. As explained above, in some embodiments, the use of a tube for conveying the coolant allows convenient and efficient connection to the manifolds. In one particular embodiment, with or without the tube, the coolant supply and return manifolds are disposed at one and the same end of the stator. Advantageously, the end may be chosen so as to be the end opposed to the end of the stator at which electrical connections are provided, to utilise the available space.

In some embodiments, a method is provided for making a stator for an electrical machine, wherein the stator has a stator body defming a plurality of salient poles projecting from a back portion and defming a slot between a pair of poles. The method includes disposing a winding in the slot and disposing a first one or more layers of material impregnated with uncured insulating resin in the slot on the winding. As a final step in the method, the resin is cured, providing a profiled member in the mouth of the slot, which retains the winding in place.

In some embodiments, a tube is disposed on the first one or more layers and one or more second layers of material impregnated with uncured insulating resin are disposed on the first one or more layers and the tube. The tube has ends extending from the first and second one or more layers. Thus, a cooling component as described above is provided after curing.

In some embodiments, a method of making a stator for an electrical machine is provided, wherein the stator has a stator body defming a plurality of salient poles projecting from a back portion and defming a slot between a pair of poles. The method includes disposing a winding in the slot. Then a tube and one or more layers of material impregnated with uncured insulating resin are disposed in the slot. The tube has ends extending from the one or more layers, so that, after curing the resin, a cooling component as described above is provided. In some embodiments, the method may include disposing the tube in direct contact with the winding.

In any of the methods described above, the method may further comprise placing a former across the slot to control the face of the material between adjacent poles before curing the insulating resin.

The invention can be put into practice in various ways, some of which will now be described by way of example with reference to the accompanying drawings in which:-Figure 1 shows views of a prior art electrical machine; S Figure 2 shows an enlarged view of part of an electrical machine; Figure 3 shows a schematic view of coolant paths; and Figurc 4 shows a schematic view of alternative coolant paths.

Figure 1 shows side and end views of a rotating electrical machine which has salient poles on the stator 10. Such stators are typical of, eg, switched reluctance, brush!ess DC, and permanent magnet machines. The stator 10 comprises a stator body 12 which is made of a stack of laminations of a suitable magnetisable steel.

The stator body includes a set of radially inwardly projecting stator poles 14.

Energising coils 20 are arranged around some or each individual pole 14. These coils have portions 16 which overhang the ends of the stator and portions 18, generally referred to as coil sides, which extend axially along the stator poles 14.

By connecting the coils together in groups, a stator having a number of phases according to the number of groups is created. The connection of the windings into groups will depend on the type of motor that is being constructed and is well-known in the art.

The rotor body 22 is arranged on bearings (not shown) to rotate around the central axis of the stator. The rotor is constructed similarly to the stator in that it is fonned from laminations of electrical sheet steel. It has a number of rotor poles 24. The number of poles and the types of rotor that can be used in conjunction with the various numbers phase windings will be well known to the person of ordinary skill in the art and will not be described in further detail here.

It will be seen from Figure 1 that the coils sides are close to the stator only in the region of the poles, and are sunounded by air on at least two sides. This can lead to difficulty in extracting the heat generated by 12R loss from the coils. Further, S it can be seen that the inner surface of the stator assembly is not a true cylinder, but has a larger diameter in the vicinity of the slots in which the coils are placed.

When the rotor rotates in this non-unifonn space, the resulting turbulence generally leads to the generation of acoustic noise. In addition, there is a loss associated with the turbulence, usually refened to as the "windage" loss. While the windage loss is typically small in low-speed machines, say up to several hundred revs/mm, it becomes increasingly significant as the speed rises and is a major factor in the design of high-speed machines. In addition, the windage loss can heat the air to such a temperature that the hot air is a danger to the insulation of the coils.

Figure 2 shows an enlarged view of part of the cross-section of a stator where the mouth of the slot has been fitted with a cooling component. In this embodiment, the cooling component 30 comprises a profiled part 32 and a tube 34, passing axially through the profiled part. The profiled part 32 is made from an insulating material which is sufficiently rigid to be formed to the correct shape to fit the mouth of the slot and to retain the coils 20 in place. The part 32 may be machined from a larger piece or extruded or moulded to its finished shape.

Preferably its shape is such that it fits tightly against the sides of the stator poles and the faces of the coil sides 18 so that when it is inserted axIally into the stator it holds the coils securely. Preferably an inward-facing face of the cooling component 30 is profiled to a radius equal to (or closely approximating to) that of the stator pole faces, so that the bore of the completed stator assembly approaches a true cylinder. This has the benefit of reducing the windage loss (thus improving the efficiency) and the acoustic noise emitted from the machine.

In Figure 2, the tube 34 is shown positioned close to the corners of the coil sides 20 which are remote from the stator poles. This is advantageous, since these corners of the coils are generally those with the longest thermal path to a heat sink, so tend to run significantly hotter than the othei parts of the coil. This provides an effective method of removing heat from this hot-spot and therefore improves the performance of the electrical machine.

The material from which the profiled component is made can be any of the well-known electrically insulating materials which are frequently employed for components of electrical equipment, eg synthetic resin bonded glass fabric available as TUFNOL® Grade 1OG/24 or 6G/92 or an epoxy glass material such as Vetronite Gil.

The tube 34 can be made from any suitable material. Preferably it is made from a flexible, electrically insulating material, so as to allow easy connection and to avoid any possibility of compromising the insulation system of the windings. A suitable material is polytetrafluoroethylene (ptfe), e.g. in the fonn of extruded tube from Polyflon Technology Limited. In other embodiments, the tube 34 is riot continuous through the cooling component 30. The fluid can pass through a passageway directly in the cooling component 30 itself, with two separate tubes attached to each end of the component to convey fluid to and from the component. Thus, a coolant carrying conduit can be formed in any suitable way in the profiled part 32, using a tube, moulded or machined directly into the part, or otherwise.

The following description of embodiments of coolant paths refer to the tube 34 (or 34') for simplicity, but li will be understood that reference to the tube 34 or 34' can be replaced in the following with any suitably interconnected conduit formed directly in the profiled part 32.

The tube 34 or 34' carries fluid which absorbs heat from the coils. In some embodiments, one end of the tube is connected to a supply manifold at one end of the stator and the other end is connected to a return manifold at the other end 1 0 of the stator. Figure 3 shows a simplified representation of one cooling component connected in this fashion to manifolds. In practice, more than one slot would likely have a cooling component, preferably every slot with coils. In use, thc fluid flows into the supply manifold 36 as shown by the arrow 40; through the tube 34 in the cooling component 30 where it absorbs heat from the coils; and through the return manifold 38, as shown by arrow 42. The fluid can then be discarded or passed through a heat exchanger to reduce its temperature before returning to the supply manifold, as known in the art.

In some embodiments, the tube is flexible. In these embodiments, in particular, the supply and return manifolds can be placed in any suitable space arid the tube can be easily led to them, rather than the manifolds being in places where they interfere with space required for winding connections.

A yet further embodiment is shown in Figure 4. The tube 34' runs in two axial directions within the cooling component 30, increasing the surface area of the tube near the windings and therefore improving the heat transfer. The supply and return manifolds can now conveniently be at the same end of the stator, preferably the end opposite that at which the inter-coil connections are made to form the phases of the winding, where there is more space.

It will be clear that the tube 34' may traverse the cooling component 30 more than twice. As the number of traverses is increascd, a choice would be made to balance the increase in surface area with the flow resistance caused b the longer path and the reduction in strength of the cooling component as more space is taken up by the tube. In further embodiments, the tube is laid in a zig-zag path within the cooling component. In some embodiments, the tube 34 is not fully enclosed within the profiled member 32, butrather is only partially enclosed and disposed to be in direct contact with the winding 20 (whether the winding includes a layer of insulator or not, the term "direct contact" is understood to include both contact with the conductor of the winding or any corresponding insulator, as the case may be).

The cooling fluid may be gaseous (e.g. one of the commonly known refrigerant gasses) but is preferably liquid. Suitable liquids are water (with a suitable antifreeze if required), an oil of a relatively low viscosity (and which may used for other lubrication purposes in the drive-train of which the electrical machine is part), or another industrial coolant.

The descriptions above have described a cooling component 30 which is made as a separate component and then inserted into the stator slot to hold the windings in place. However, it is not necessary for this approach to be followed. In other embodiments, the component is manufactured in situ by placing an assembly of sub-components into the mouth of the slot and subsequently forming them into a rigid assembly by moulding and curing at least one of the components. For example, a material comprising a felt or glass mat impregnated with an insulating resin in its uncured stage can be used. Such materials are routinely used in the electrical machines industry for wrapping coils which are then pressed to shape and cured by heating, thus forming a consolidated coil which is then placed into the stator. They are generally known as "pre-preg" materials, since they contain all the ingredients necessary to achieve impregnation when subjected to the required heat and pressure. For example, a suitable material might be the L-556 Glass Fibre Epoxy Pre-Preg mat from Umeco plc, Leamington Spa, UK.

This mat material can be laid into the mouth of the slot; the tube 34 laid in place; further layer(s) of mat laid to build to the required thickness; a former placed across the slot to control the front face of the assembly; and suitable heat and/or pressure applied to cure the component and produce a rigid component which will retain the coils in their correct position and help to streamline the face of the stator. This method of construction could also be used without including a tube or other conduits, so that some slots could carry tubes or conduits and some not.

Equally, this method of construction could be used without embedding tubes or other conduits at all.

This method has the advantage that a relatively thin cooling component can be produced, so that the amount of winding space is maximised for given stator dimensions. In line with the above discussions, many variations of the method are possible, using no tube at all, a tube placed between layers of material or a tube placed between the winding and the material so as to be indirect contact with the winding.

The present disclosure is also equally applicable to linear machines3 and to inverted machines, in which the rotor is arranged on the outside of the stator. It applies equally to machines operated as motors or generators.

It will be apparent to the person of ordinary skill in the art that variations and S modifications can be made without departing from the invention. Accordingly, the above description of embodiments is made by way of example and not for the purposes of limitation. The present invention is intended to be limited only by the scope of the following claims.

Claims

CLAIMS: 1. A stator for an electrical machine, the stator including: a hack portion; a plurality of salient poles projecting from the back portion and defining a slot between a pair of poles; a cooling component disposed in the slot to hold a winding wound on the stator between the cooling component and the back portion; and a coolant conduit in the cooling component to enable coolant to be passed through the cooling component to cool the winding.
2. A stator as claimed in claim 1, wherein the cooling conduit comprises a tube embedded in the cooling component.
3. A stator as claimed in claim 2, wherein the tube enters and exits the cooling component on one end of the cooling component.
4. A stator as claimed in claim 2 or 3, wherein the tube extends from the cooling component for connection to a source of coolant.
5. A stator as claimed in any one of claims 2 to 4, wherein the tube is flexible.
6. A stator as claimed in any preceding claim, in which the coolant conduit is configured to have at least one bend within the cooling component.
7. A stator as claimed in any preceding claim, in which the tube is in direct contact with the winding.
8. A stator as claimed in any preceding claim, wherein the cooling component has been moulded in place in the slot.
9. A stator as claimed in any preceding claim, wherein the salient poles each have a pole face facing away from the back portion and the cooling component has a face substantially aligned with the pole faces adjacent to it.
10. A stator as claimed in any preceding claim, wherein the stator is for a rotating machine and a face of the cooling component and adjacent pole faces define a portion of a substantially smooth bore of the stator.
11. An electrical machine comprising a stator as claimed in any preceding claim, the coolant conduit being connected between a coolant supply manifold and a coolant return manifold.
12. An electrical machine as claimed in claim 11, the coolant supply and return manifolds being disposed at one end of the stator.
13. A method of making a stator for an electrical machine, wherein the stator has a stator body defining a plurality of salient poles projecting from a back portion and defining a slot between a pair of poles, the method including: disposing a winding in the slot; disposing a first one or more layers of material impregnated with uncured insulating resn in the slot on the winding; and 16 I curing the insulating resin.
14. A method as claimed in claim 13, the method including: disposing a tube on the first one or more layers; disposing one or more second layers of material impregnated with uncured $ insulating resin on the first one or more layers and tube, wherein the tube has ends extending from the first and second one or more layers.
15. A method of making a stator for an electrical machine, wherein the stator has a stator body defining a plurality of salient poles projecting from a back portion and defining a slot between a pair of poles, the method including: disposing a winding in the slot; disposing a tube and one or more layers of material impregnated with uncured insulating resin in the slot after the winding, wherein the tube has ends extending from the one or more layers; and curing the insulating resin.
16. A method as claimed in claim 15, the method including disposing the tube in direct contact with the winding.
17. A method as claimed in any one of claims 13 to 16, the method comprising placing a former across the slot to control a face of the material between adjacent poles before curing the insulating resin.Amendments to the claims have been made as follows:CLAIMS1. A method of making a stator for an electrical machine, wherein the stator has a stator body defining a plurality of salient poles projecting from a back portion and defining a slot between a pair of poles, the method including: disposing a winding in the slot; disposing a first one or more layers of material impregnated with uncured insulating resin in the slot on the winding; and curing the insulating resin.2. A method as claimed in claim 1, the method including: disposing a tube on the first one or more layers; CD disposing one or more second layers of material impregnated with uncured insulating resin on the first one or more layers and tube, wherein the tube has 0) 15 ends extending from thc first and sccond one or more layers.3. A method of making a stator for an electrical machine, wherein the stator has a stator body defining a plurality of salient poles projecting from a back portion and defining a slot between a pair of poles, the method including: disposing a winding in the slot; disposing a tube and one or more layers of material impregnated with uncured insulating resin in the slot after the winding, wherein the tube has ends extending from the one or more layers; and curing the insulating resin.4. A method as claimed in claim 3, the method including disposing the tube in direct contact with the winding.5. A method as claimed iii any one of claims 2 to 4, wherein the ends extend on one side of the layers.6. A method as claimed in any one of claims 2 to 5, wherein tile tube is flexible.7. A method as claimed in any one of claims 2 to 6, wherein the tube is configured to have at least one bend in the region of the slot.8. A method as claimed in any one of claims 2 to 7, wherein the stator has salient poles, each having a pole face facing away from the back portion, and an outer layer of the one or more layers has a face substantially aligned with the C') pole faces adjacent to it.0) 15 9. A mcthod as claimed in any onc of claims 2 to 8, whcrcin the stator is for 0 a rotating machine and a face layer of the one or more layers and adjacent pole faces define a portion of a substantially smooth bore of the stator.10. A method of making an electrical machine comprising making a stator in accordance with a method as claimed in any one of claims 2 to 9, the method comprising connecting the tube between a coolant supply manifold and a coolant return manifold to enable cooling of the winding.11. A method as claimed in claim 10, wherein the coolant supply and return manifolds are disposed at one end of the stator.12. A method as claimed iii any one of claims I to II, the method comprising placing a former across the slot to control a face of the material between adjacent poles before curing the insulating resin. C') a,LU