PT1251624E - Cooling of air gap winding of electrical machines - Google Patents

Description

DESCRIPTION

" COOLING OF ELECTRIC MACHINE ENTREFERROWS "

Field of the Invention

This invention relates to the cooling of electric machines and, in particular but not exclusively, to the cooling of stators in induction machines which generate a high magnetic flux density.

Background of the invention

Induction machines have been well known for more than a century. Typically, these machines comprise a generally cylindrical central rotor and an outer annular stator, although linear machines are also known. In addition, it is normal for the coils or conductive windings, which extend longitudinally relative to the stator, to be wound into provided grooves in a rolled iron stator core so as to intensify the flux generated by the stator windings. i.e., the stator windings pass between " teeth " of laminated iron defined by the flanks of the grooves. However, in machines whose windings are able to generate very high flux densities (ie, above 1.5 Tesla in the air gap between the rotor and stator), the use of iron stator teeth becomes undesirable due to the increased reactance and higher iron losses resulting from the magnetic saturation of the stator teeth. Accordingly, in such machines, the iron teeth are conveniently replaced by non-magnetic teeth to support the stator windings. The air gap between the rotor periphery and the start of the stator iron core now extends effectively to the bottom of the stator grooves. Since the stator winding is entirely within this air gap, this type of construction, to which the present invention relates in particular, is known as " winding winding ".

Obviously some kind of cooling of the stators is required for these machines. Generally speaking, the cooling of stators of induction machines is a well known problem which has been solved in various ways, e.g. by means of axially and / or radially extending cooling passages through the stator. WO 01/17094 A1, for example, shows radial cooling air passages provided between adjacent piles of toothed laminates in a stator iron core.

However, such high flux densities as mentioned above allow the design of much smaller machines having higher power densities, which results in a greater generation of heat inside the stator windings, but at the same time, in a very reduced cooling surface area. This requires a cooling system more efficient than the known configurations can provide, in order to prolong the life of the machine. US 4228375 discloses a stator having brackets located between respective pairs of individual winding bars. At least some of the supports include channels (e.g., hoses) for conveying pressurized liquid or gas to ensure tangential propping of the stator.

SUMMARY OF THE INVENTION It is an object of this invention to provide a winding stator winding in an electrical machine of high power density with good cooling combined with good structural winding support.

According to the invention there is provided a stator for an electric machine with an air gap, the stator comprising: an outer, annular stator core coaxial with a longitudinal axis of the machine, a stator winding inside the stator core and comprising a plurality of bobbins having linear conductor portions, and a plurality of bobbin holders, the supports extending along the linear conductor portions of the bobbins, wherein the supports are made of a non-magnetic material and each support is interposed between and in contact with two adjacent linear conductor portions of the coils. CHARACTERIZED BY at least some of the supports defining channels for flow of refrigerant fluid therethrough to thereby draw heat from the coils and by the linear conductive parts of the plurality of coils are arranged in two layers that are engaged in one another in a castellated interface between two layers to provide mechanical strength.

Such a structure is advantageous because it provides an efficient use of space within the stator, since the cross-sectional area of the carrier not required for the winding support can be used for the transport of refrigerant fluid.

Preferably, all the supports define channels for the flow of refrigerant fluid and the non-magnetic material from which they are manufactured is non-metallic, e.g. fiber reinforced plastic.

The linear conductor portions of the coils extend substantially parallel to the longitudinal axis of the machine, the supports providing a support for the coils for substantially all of the linear conductor portions of the coils, whereby the coil cooling is provided for substantially all of its linear conductive parts.

The coolant flow channels can be defined inside or outside the supports. If the channels are within the carriers, the carriers may conveniently comprise hollow enclosures whose walls form the boundaries of the channel, the heat being thereby conducted from the coils through the walls and into the flowing refrigerant fluid through them. However, it is preferred that the channels be defined on the outer portions of the supports between the outer surfaces of the supports and the outer surfaces of the reels so that the heat can be transferred directly from the reels to the refrigerant without passing through an intermediate wall.

In a variant of the invention, the linear conductor portions of the coils are supported by the supports through spacers provided between the supports and the linear conductor portions, the channels of the refrigerant fluid being thereby defined between opposing faces of the linear conductor portions of the coils and the supports.

However, it has been found that the best way of defining the coolant flow channels is by forming each contact surface of the carrier coils with at least one depression therein, the depression extending longitudinally relative to thereby being the limits of the refrigerant flow channels defined by the depressed portions of the outer surfaces of the supports and the outer surfaces of the coils. Preferably, at least two such channels are defined between each linear conductive part and each adjacent carrier. To avoid undue stress on the supports, it is preferred that the depressions in the coil contact surfaces of the supports have a slightly curved concave shape when viewed in cross-section to their longitudinal extensions.

Preferably, coolant inlet and outlet manifolds communicate with respective axially opposite ends of the channels to facilitate the flow of refrigerant fluid through the channels. 5

The coils include end windings for connecting linear conductor portions of the coils to each other, the end windings being located in the inlet and outlet manifolds so that the same cooling fluid is used to cool the end windings and the linear conductive parts . The stator winding comprises two layers or levels, these being respectively a radially inner layer and a radially outer layer of the linear conductor portions of the coils. In this type of winding, the end windings comprise connections between the two layers. To provide mechanical resistance to machine-generated reaction torque forces, the two layers are engaged in one another in a castellated interface between the two layers. The cast formations may comprise supports having different radial extensions so that at least some of the supports in at least one of the layers extend between the linear conductor portions of the coils in the adjacent layer. In addition or alternatively, the stator winding may be engaged in the stator core at a staggered interface therebetween by utilizing the device to cause the radially outer ends of some or all of the supports adjacent the core to extend radially beyond linear coaxial conductor portions penetrating axially provided grooves provided in the stator core.

The linear conductor portions of the coils may be provided by bundles of rectangular conductors, the larger dimensions of the rectangular bundles extending in the radial direction. Within the bundles, the conductors may also be rectangular and are preferably formed by wires of small diameter, the wires being insulated from one another within the conductors. The invention further provides an electric motor or generator having a stator as described above.

Brief description of the drawings

The following is now by way of example only a description of embodiments of the invention with reference to the accompanying drawings, in which: Figure 1 shows a partial longitudinal section through an induction machine with air gap according to a first embodiment of the present invention; Figure 2A shows a cross-sectional view of line A-A of Figure 1; Figure 2B is a perspective view of a detail of the cut shown in Figure 2A; Figure 3 relates to a second and preferred embodiment of the invention and is a view similar to Figure 2A but showing a smaller cross-section in an enlarged manner. 7

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The electric motor 2 shown in Figure 1 comprises an internal rotor 4, indicated diagrammatically by dashed lines, and an external stator 5. The rotor 4 is firmly mounted on a shaft 6 rotatably secured in an axial central line C by bearings 7 which are supported by end walls 8 of a machine housing 9. The stator 5 is secured within an outer cylindrical stator frame 10 which, in turn, forms part of a generally cylindrical side wall 11 of the housing 9.

Within the machine housing 9, a fluid impervious annular reservoir 12 surrounds the stator 5 and separates the rotor 4 from the stator. The stator itself comprises a winding 13 comprising a number of coils and a laminated iron core 14, the laminates being shown diagrammatically by vertical shaded lines. The coils in the winding 13 are connected to an electrical power source (not shown) to generate an electromagnetic field which interacts with the rotor 4 to rotate it and produce a useful output torque on the shaft 6.

Although the winding 13 is mounted within the iron core 14, there is no magnetic material extending between circumferentially adjacent turns of the winding, i. i.e., for the reasons advanced above in the Background of the invention, the winding 13 is a winding winding. As best seen in Figures 2A and 2B, the windings of the winding comprise bulky beams 16 of conductors 18, each beam 16 having an insulation layer 22 around its periphery and a substantially rectangular cross-section which is elongate in the radial direction. In this particular example, each conductor bundle 16 consists of fourteen conductors 18, arranged in two columns of seven, although more or less conductors may be used, as required by any particular nominal power of the machine. The conductors 18 also have a substantially rectangular or square cross-section (although alternative shapes are possible), each conductor being isolated from the other conductors 18 within the bundle 16 to minimize the formation of eddy currents, which would reduce the yield of the machine 2. The insulation of the conductor bundles 16, and of the conductors 18 within the bundles, may be achieved by normal means known in the industry, for example by wrapping in glass fiber tape or the like.

Since the configuration of the winding winding causes practically all of the magnetic flux to pass through the stator winding conductors 18, it is also necessary to minimize the induction of eddy currents within the conductors themselves, which otherwise would circulate around the conductor cross-section. These eddy currents are minimized by forming each conductor 18 from a large number of small diameter wires (for example, 1 mm), each wire being coated with a varnish to insulate it from neighboring wires as known in the industry.

In the present embodiment, the entire stator winding 13 consists of a large number of individual conductive coils. The coils are comprised of conductor bundles 16, each coil 14 turns being disposed at two levels or layers 26, 28, each layer comprising the aforementioned two seven-conductor columns. The conductors are linear through their field generating portion L 9 (Fig. 1) where they cross the air gap between the stator core 14 and the rotor 4, but to construct each coil (and in doing so, make connections between the layers), it is necessary to join the ends of the rectilinear portions of the conductors to one another by means of loops known as end windings 34, which project substantially axially beyond the ends of the stator core 14. As shown in FIG.

After forming and assembling the conductive coils, including their end coils, with their " diamond " final and well-known design required for the stator winding 13, they are subjected to a vacuum pressure impregnation and cure process, as well known in the industry, to impregnate them everywhere (including between the wires inside the conductors 18) with a suitable thermosetting resin resistant to heat. This increases the insulation and mechanical strength of the winding and prevents the penetration of corrosive atmospheric constituents, such as oxygen and water vapor, into the winding. The vacuum impregnation process may be carried out at the most convenient time during the manufacture of the machine, as exemplified below.

An insulation separating layer 30 is inserted between radially adjacent conductor bundles 16 during assembly of the stator winding to provide a gap between the layers 26, 28 and thereby allow a greater insulation thickness at the transition between the rectilinear portions of the stator windings coils and the end windings 34.

As will yet be seen in Figures 2A and 2B, the conductor bundles 16, in their layers 26 and 28, are held in position and supported by several " or non-magnetic support struts 20A, 20B, respectively, which replace the " teeth " of rolled iron between which the stator windings would normally be trapped in a machine having a lower magnetic flux density. As will be understood from the Figures, the conductor bundles 16 and their supports 20A, 20B extend axially, lying substantially parallel to the longitudinal axis C. As shown in FIG.

Since the winding 13 is a winding winding, the conductor bundles 16 must be able to react to the torque created by the interaction of the electromagnetic fields of the rotor and stator. The supports 20A, 20B therefore complement the mechanical strength of the resin impregnated winding.

As will be seen from Figure 2A, the conductor bundles 16 in the layer 26 are radially and axially aligned with the conductor bundles in the layer 28 and the supports 20A in the layers 26 and 20B in the layer 28 are also aligned , radially and axially, to each other. However, the conductor bundles 16 in each layer 26, 28 have rectangular sections and also have the same dimensions and therefore to make an intimate contact between the supports 20A, 20B and the conductor bundles 26 through the radial extension of the the stator winding is required to taper in the radial direction from a maximum width on the radially outer circumference of the stator winding to a minimum width on the radially inner circumference of the stator winding. This accommodates the increased circumferential spacing between bundles of adjacent conductors on the radially outer circumference of the stator winding relative to their spacing on their inner circumference. 11

It should be noted that the holders 20A in the inner layer 26 are, for a given value, radially longer than the conductor bundles 16, while the holders 20B in the outermost layer 28 are radially shorter than the conductor bundles 16 by the same value. The supports 20A in the layer 26 therefore extend radially outwardly between the field generating parts of the coils in the adjacent layer 28. Therefore, as seen in radial cut, the interface region between layers 26 and 28 resembles the crenels of a castle. In this way, the two layers 26, 28 are engaged with one another or interconnected to react more effectively to the induced rotor torque. The person skilled in the art will, of course, realize that variations in this design of interconnection are possible. For example, the layer 26 could be provided with the radially shorter supports and the layer 28 could have the radially longer or radially longer and shorter supports could be alternated in both layers in a complementary manner to produce a casting formation of two steps. Alternatively, only supports selected from the carriers in each of the rows could be radially longer or shorter than the conductor beams, the other carriers having the same radial length as the beams. In another alternative, it may be possible to produce a non-magnetic two-layer stator core structure with adequate strength without a castellated interface between the two layers. In this case, all the supports in the two layers could have the same radial extension as their adjacent conductor bundles and the core structure would simply be based on the resistance of, e.g. a thermosetting resin or other high temperature adhesive bond at the interface between the two layers. 12

Yet another winding reinforcing feature of the illustrated embodiment is shown in Figure 2A. As shown by dashed lines, it would be possible for the radially outer end 36 of some or all of the supports 20B to extend radially outwardly into correspondingly extending axially provided grooves on the inner surface of the stator core 14, thereby providing In this way, a castellated interface interconnected between the stator winding 13 and stator core 14 for reaction of the induced rotor torque.

Due to its high power density, the physical size of the illustrated machine is smaller than machines with lower power density with the same rated power. Accordingly, the surface area for cooling is reduced. The invention takes advantage of the absence of magnetic iron teeth to provide an efficient stator cooling system. Since stator support teeth or struts 20A, 20B are only required to separate and support the coils, the supports may be in the form of hollow shells, as shown in Figures 2A and 2B, the supports being open at axially opposite ends of the stator, thereby creating axially extending channels 24 with open ends along and through which a cooling medium can pass. It is preferred that the supports 20A and 20B are made of a suitable glass fiber reinforced (or perhaps graphite fiber) reinforced composite material. A wall thickness suitable for the supports is in the order of 2 mm. The supports may be fabricated from a glass fiber reinforced composite material. Alternatively, the supports may be fabricated from a non-magnetic material which is also a good thermal conductor. However, this is not essential because the surface area of the supports through which heat transfer may occur may be large enough to provide sufficient cooling.

As seen in Figure 1, the reservoir 12 surrounding the stator 5 is divided by the stator into a coolant manifold 38 and a coolant manifold 40. The end windings 34 extend into the manifolds. A coolant inlet 42 is provided in a radially outer top or region of the coolant manifold 38 and a coolant outlet 44 is provided in a radially inner bottom or region of the outlet manifold 40. To ensure an identical cooling effect on all parts of the end windings 34 in the inlet manifold 38, the refrigerant fluid from the inlet 42 enters the inlet manifold by means of a toroidal ring 45 which extends around the inner circumference of the inlet manifold 38 collector. The wall of the toroid 45 has a large number of through holes, the holes being spaced around the inner circumference of the manifold so that the refrigerant fluid is evenly distributed through the end windings. Baffles 46 are provided to prevent flow stagnation at the corners of the inlet and outlet manifolds and to standardize the flow of refrigerant fluid into and out of the stator refrigerant fluid channels 24A, 24B provided by the brackets 20A, 20B. A further deflector or evacuator 50 is provided to ensure that the end windings 34 are fully immersed in the refrigerant fluid as it flows through them to cool them by direct contact with their external insulation. 14

In use, a refrigerant fluid, in which case an inert insulation liquid refrigerant is pumped into the inlet manifold 38 via the liquid inlet 42. A preferred refrigerant is Midel 7131 ™, which is manufactured by M & I Materials Ltd. This fluid is typically used for the cooling of transformers and has a specific heat of 2100 J kg -1 K1, about half of that of the water. Inert coolant fluid is preferred over water because of the intrinsic corrosion and electrical risks associated with water. The pressure created by the pumping causes the liquid to flow through the supports 20A, 20B to the outlet manifold 40. As the liquid passes through the supports 20, heat transfer takes place and heat is removed from the conductors 18 within the conductor bundles 16, thus cooling the conductors. After the liquid has reached the outlet manifold, it passes over the evacuator 50 and is pumped out of the liquid outlet 44. It is then cooled in a suitable heat exchanger before being transferred to the liquid inlet 42 to restart the cycle.

When cooling in accordance with the invention, to maintain a low temperature in the stator winding, the electric efficiency is increased, since losses in the winding will be reduced due to a lower copper resistivity at lower temperatures.

Alternative refrigerant fluids may be used, if desired, if the cooling function to be effected by them is equivalent to their cooling capacities, e.g. pressurized air, or other gases or water. 15

Alternative designs may be utilized for a cooling channel, e.g. the supports 20A, 20B may be closed at their ends rather than open, and narrow channels (again open at both ends of the stator to communicate with the coolant inlet and outlet manifolds) may be created at the interfaces of the bundles of conductors and of the supports by axially inserting spacing strips axially therebetween. Accordingly, the refrigerant would directly contact the outer insulation of the conductor bundles 16, facilitating more efficient cooling of the stator winding. Figure 3 shows the most preferred embodiment of the invention which utilizes the aforementioned principle of direct contact of the refrigerant fluid with the outer insulation 322 of the bundles 316 of rectangular conductors. Again, the turns of the stator electrical coils are arranged at two levels 326, 328 and the conductors 318 within the bundles 316 are rectangular. The coils / conducting beams are generally constructed in the same manner as in the first embodiment, but this time each beam consists of eighteen conductors, arranged in two columns of nine, to facilitate the production of a higher power of the conductor. than in the first embodiment.

Interposed between adjacent coils, and in a leaktight and supported contact with both coil levels, there are radially extending support teeth or struts 320 that differ significantly from the support struts of Figures 1 and 2.

First, in order to achieve rigidity and strength, the support struts 320 have a solid, unitary construction 16 (although they may have an internal cavity if such a construction were sufficiently rigid and strong) and extend without joints or division since the inner circumference of the stator core 314 to nearly the inner inner circumference of the fluid impermeable annular reservoir 312 surrounding the stator. In the present case, they are considered to be molded from a suitable composite material, reinforced with glass or graphite fibers for reasons of strength and hardness.

Second, the radially outer ends of all support struts 320 are in the shape of " swift tails " 335 when viewed in cross-section and are housed in grooves or complementary channels 336 which extend axially along the inner diameter of the stator core. This results in a circumferentially staggered or castellated interface between the winding assembly and the core 314 that reacts to the winding torque and enhances the stiffness of the winding assembly.

Thirdly, each flank of each support strut 320 is provided with depressions or grooves 323 molded thereon on the outer surfaces of the supports. In conjunction with the outer surfaces of the rectilinear conductor portions of the coils, the holders thereby define channels 324 for the flow of refrigerant fluid therethrough in direct contact with the insulation 322 of the conductor bundles. The depressions 323 are shown having a concavely transverse cross-section curved in the radial direction, instead of being provided with internal corners, to avoid over-tensioning any part of the supports 320. In Figure 3, two channels 324 are defined between each part and each adjacent support, although more or fewer channels may be provided as necessary to adequately eliminate heat from the conductor bundles.

To allow the thermal expansion of the stator coil levels 326, 326 during operation of the machine at high power, a small gap X of the order of two millimeters is provided between the outer circumference of the reservoir 312 and the radially inner circumference of the stator winding assembly. Insulation spacers 330 are provided between the two winding levels 326, 328 and other insulation spacers 331 are provided between the radially outer level 328 and the stator core 314.

Referring again to Figures 1 and 2, the stator assembly 5 of this embodiment will be described from its component parts and, in respect thereof, another feature should be noted in Figure 2B. To assist the conductor bundles 16 to be attached to their supports 20A during assembly of the stator winding, and to increase the strength of the assembled winding, the supports 20A are provided with indentations or recesses 32 at various locations equally spaced along the their axial lengths. At these locations, the recesses reduce the radial dimension of the supports 20A to that of the circumferentially adjacent conductive beam 16 to facilitate wrapping of a glass fiber web 33 or the like around both articles to secure them together. The inner layer of the supports 20A may be tape-attached to its conductor bundles before the conductor bundles are assembled with their end windings to form the bobbins. Once this has been done, the outer layer of the holders 20B may be slid into place. It will of course be understood that the holders 20A, 20B and the coils of the stator winding 13 in their two layers are mounted to one another so as to form a stator winding assembly before the winding is attached to the core 14 of stator to produce the complete stator 5.

On the other hand, the preferred stator winding assembly of Figure 3 may be produced by simply mounting the coils and then sliding the brackets 320 into place between the conductors 316. The remaining assembly process is the same as for the embodiments of both Figures 2 and 3, but will only be described with the identification of the reference numerals of the

Figure 1. After the stator winding 13 is fully assembled, the stator core 14 is constructed around it. The laminates comprise thin magnetic sheet (e.g., with a thickness of less than 1 mm) with low losses pre-coated with insulation on both sides. The laminates are manufactured as ring segments and formed in a series of packages of laminates, these being mounted on the stator winding 13 to form complete rings. The core is held together by welding anchor bars (not shown) by the backs under the laminates. These anchor bars are then welded to a circular steel compression plate crown 52 provided at each axially opposite end of the stator core. Anchor bars are contracted when cooled and act as springs to maintain perfect contact between the laminates over the life of the machine. 19

After the stator core is mounted on the finished stator winding, the entire stator 5 is then passed through a resin pressure impregnation and curing process which terminates the stator winding insulation process and holds the stator assembly together. Subsequently, the stator housing 12 may be constructed around the stator 5.

While the illustrated embodiments of the invention have a winding in which the coils occupy two layers, one skilled in the art will appreciate that it is possible to provide a winding having only one layer. A single layer winding of this type could potentially generate a higher specific output power. However, if one wants to use a high number of phases and poles, as is desired to increase the flexibility and control of the machine, the interconnections of the end windings for a single layer winding would take up a lot of space, which would give rise to an increase in the overall diameter of the machine.

Although the illustrated embodiment relates in particular to an electric motor, the described stator construction could also be applied to generators.

Lisbon, January 27, 2009 20

Claims (21)

A stator (5) for an electric machine (2) with an air gap, the stator comprising: an outer, annular stator stator core (14) coaxial with a longitudinal axis (C) of the machine, a winding (13) of stator within the stator core and comprising a plurality of coils having linear conductor portions (16), and a plurality of supports (20A, 20B) for the coils, the supports extending along the linear conductor portions of the coils, wherein the supports are made of a non-magnetic material and each support is interposed between and in contact with two adjacent linear conductor portions (16) of the coils characterized in that at least some of the supports define channels (24A, 24B) for the flow of cooling fluid therethrough to thereby draw heat from the coils and that the linear conductive portions (16) of the plurality of coils are arranged in two layers (26, 28) that are nested the other in a castellated interface between two corresponding layers (20A, 20B) of supports to provide mechanical strength. Stator according to claim 1, wherein the supports define channels for the flow of refrigerant fluid therein. 1 Stator according to claim 1 or claim 2, wherein the non-magnetic material, from which the supports are manufactured, is non-metallic. A stator according to any preceding claim, wherein the supports provide support and cooling for the coils through the linear conductor portions of the coils. Stator according to any preceding claim, wherein the coolant flow channels (24A, 24B) are defined within the supports. Stator according to any one of claims 1 to 4, wherein the coolant flow channels (324) are defined outside the supports. Stator according to claim 5, wherein the supports (20A, 20B) comprise hollow housings whose walls form the boundaries of the channel, the heat being, during the operation of the machine, being conducted from the coils (16), through the walls and into the refrigerant flowing through the supports. A stator according to claim 6, wherein the channels (324) are defined between the outer surfaces of the supports and the outer surfaces (322) of the coils so that during the operation of the machine the heat can be directly transferred of the coils to the coolant flowing in the channels without crossing an intermediate wall. 2 Stator according to claim 8, wherein the linear conductor portions of the coils are supported by the supports through spacers provided between the supports and the linear conductive parts, the limits of the channels of the refrigerant fluid being defined between the separators and opposing faces of the linear conductor parts of the coils and the supports. A stator according to claim 8, wherein the channels (324) comprise at least one depression in each coil contact surface of the carrier (320), the at least one depression extending longitudinally in relation to the carrier, whereby the limits of the coolant flow channels defined by depressed portions of the outer surfaces of the supports and the outer surfaces (322) of the coils are defined. A stator according to claim 10, wherein the depressions in the coil contact surfaces of the supports have a curved concave shape when viewed in cross-section to their longitudinal extensions. A stator according to any one of claims 9 to 11, wherein at least two channels (324) are defined between each linear conductive portion (16) and each adjacent support (320). A stator according to any preceding claim, wherein coolant inlet and outlet manifolds (38, 40) communicate with respective opposite ends of the channels to facilitate passage of refrigerant fluid through the channels. 3 A stator according to claim 13, wherein the coils include end windings (34) for connecting the linear conductor portions (16) of the coils to each other, the end windings being located in the manifolds (38, 40) inlet and outlet ports so that the same cooling fluid cools the end windings and the linear conductor portions of the coils. A stator according to any preceding claim, wherein the end windings (34) comprise connections between the two stator winding layers (26, 28). A stator according to any preceding claim, wherein the cast formations comprise supports (20A, 20B) having different radial extensions so that at least some of the supports in at least one of the layers (26) extend between the linear conductive parts (16) in the adjacent layer (28). A stator according to any preceding claim, wherein the stator winding (13) is engaged in the stator core (14) at a staggered interface therebetween, in that the radially outer ends (36) of at least one of the stator windings some of the supports 20B adjacent the stator core extend radially beyond the linear conductor portions of the coils into axially extending slots provided in the stator core. Stator according to any preceding claim, wherein the linear conductor portions (16) of the coils are provided by bundles of rectangular conductors (18), the largest dimensions of the rectangular beams extending in the radial direction. A stator according to claim 18, wherein the conductors (18) within the bundles are rectangular in shape and are formed of wires, the wires being insulated from one another within the conductors. Stator according to any preceding claim, wherein the supports comprise a fiber reinforced composite material. An electric motor or generator having a stator according to any preceding claim. Lisbon, January 27, 2009 5