The present invention relates to a wind turbine of the horizon ^¬ tal axis, direct-drive type, wherein the wind turbine comprises - a hub provided with one or more blades,

- a generator with a centreline that is technically horizontal, the generator comprising an inner rotor which is driven by the hub and an outer stator, the stator comprising a front plate, a back plate and stacked, arcuate laminates. Such a wind turbine is known in the art. In particular CN101222159 discloses a wind turbine according to the preamble wherein the stator is in thermal contact with an outer shell, the shell being provided with ribs to allow dissipation of heat from the generator to the atmosphere. There is a trend toward larger and larger wind turbines. A major problem designing larger wind turbines is the way power and weight scale. A hypothetical doubling of the length of the rotor diameter of a wind turbine will square its output, but increase its weight with a power of three. An increase in weight has a detrimental effect, in that it increases cost tremendously. This has an adverse effect on the cost of the electricity produced with the wind turbine. Thus, there is a major challenge to design a wind turbine that is both strong and light (for its size) .

The object of the present invention is to provide a wind tur- bine with a reduced weight.

To this end, the wind turbine according to the preamble is characterized in that the front plate and the back plate are connected by tension rods so as to form a stator unit with the stacked, arcuate laminates being sandwiched between the back plate and the front-plate under compression, wherein of a first arcuate laminate in contact with a second arcuate laminate stacked against it the outer edge of the first arcuate laminate is at a larger distance from the centreline of the generator than the outer edge of the second arcuate laminate so as to increase the outer surface area of the stator for dissipating heat to the atmosphere.

A major saving in weight is achieved by eliminating the shell, allowing the heat from the generator to dissipate into the atmosphere via the protruding first arcuate laminate, and preferably first arc- tuate laminates. The arcuate laminates provide for the structural integrity of the generator, more specifically of the stator. In general, one of the front plate and the back plate, usually the back plate, will be provided directly or indirectly (usually via a carrier cone) with one or more bearings, the inner bearing of which is connected to the rotor of the generator. Direct-drive generators tend to have a very large diameter. For this reason, the laminates are generally arcuate segments placed end-to-end. Generally, the laminate segments will independently be of a size of 360° / n where n is an inte- ger :> 2. They are generally placed staggered (i.e. overlapping) with respect to each other to provide the greatest mechanical strength. The stack will usually be impregnated with a resin, for example using vacuum pressure impregnation. US6467725 in the name of Lucas Industries Ltd discloses an electrical generator for use with a gas tur- bine, the rotor of which comprises a stack of laminations held under compressive load. It is mentioned that it is advantageous if the stator is made of laminates as well. Laminates, or laminations as they are also called, are quite thin, such as in the order of 0.2 mm. The term "technically horizontal" means that the centreline of the gen- erator makes an angle with the horizontal of up to +15°, in practice usually +4-8°. The expression "the outer edge of the first arcuate laminate is at a larger distance from the centreline of the generator than the outer edge of the second arcuate laminate" means that, as seen in the direction of the centreline, a rotational angle exists where the distance the outer edge of an arcuate laminate is at a larger distance from the centreline of the generator than the outer edge of a second arcuate laminate immediately adjacent to it in the direction of the centreline (i.e. stacked against it) .

According to a preferred embodiment, there is a first series of arcuate laminates having an outer edge at a first distance from the centreline of the generator sandwiched between a second series and another second series of arcuate laminates having an outer edge at a second distance from the centreline of the generator, the first distance being larger than the second distance, the first series forming a cooling rib.

In practice, there will be more than one cooling rib (formed by multiple first series) . Such a wind turbine can be cheap because of savings on the generator, thanks to the laminates being of a simple design .

According to a preferred embodiment, the outer surface of the stator is covered with a water-impermeable protective coating. This helps to ensure the longevity of the generator, which is especially important for placement of wind turbines at sea, where the cost of maintenance is very high.

According to a preferred embodiment, the arcuate segments have at least one through-hole, and the tension rods pass through the through-holes.

This allows for a very rigid stator structure.

According to a preferred embodiment, the back plate has a sandwich structure.

This brings the weight of the generator even further down. According to a preferred embodiment, the centreline of the generator is at an angle of >2° to the horizontal.

This helps to ensure that water runs of the outside of the stator, improving the longevity of the generator and reducing the cost of maintenance . The present invention also relates to a direct-drive generator comprising an inner rotor and an outer stator, the stator comprising a front plate, a back plate and stacked, arcuate laminates, characterized in that the front plate and the back plate are connected by tension rods so as to form a stator unit with the stacked arcuate laminates being sandwiched between the back plate and the front-plate under compression, wherein of a first arcuate laminate in contact with a second arcuate laminate stacked against it the outer edge of the first arcuate laminate is at a larger distance from the centreline of the generator than the outer edge of the second arcuate lami- nate so as to increase the outer surface area of the stator for dissipating heat to the atmosphere.

This generator is very suitable for wind turbines or other open-air applications. The favourable embodiments of the generator as discussed in the subclaims are incorporated by reference, their ad- vantages being already discussed for the wind turbine above, and incorporated by reference.

The present invention will now be illustrated with reference to the drawing, wherein fig. 1 shows the top part of a wind turbine according to the invention; fig. 2 shows a frontal cross-sectional view of the top half of a direct drive generator; and fig. 3 shows a cross-sectional view of a detail of a generator according to the invention.

Fig. 1 shows a wind turbine 100 with a tower 101, a nacelle 102, a hub 103 and blades 104. The nacelle 102 comprises a direct drive generator 105 with concentric cooling ribs 106 and strengthen- ing ribs 107. The hub 103 and generator 105 are at an angle of 6° to the horizontal, allowing any rainwater falling on the generator 105 to be drained easily. The cooling ribs 106 are formed by first series of stacked laminates (this is shown symbolically in fig. 3), between second and another second series of stacked laminates, the former having an outer edge that is at a larger distance from the centreline than the outer edges of the laminates of the second and another second series of stacked laminates.

Fig. 2 shows a cross-sectional view of the top half of the generator 105 with the rotor 109 and stator 111 of the generator 105. Permanent magnets (not shown here but indicated in fig. 3) of the rotor 109 face arcuate laminates 110 of the stator 111. The arcuate laminates 110 are made of a ferro-metal and have a thickness of 0.6 mm (shown with exaggerated thickness and reduced number in fig. 3) . The arcuate laminates 110 have through-holes 112 for tension rods, as will be explained later. Indicated in figure 2 (but more clearly visible in fig. 3) is that the arcuate laminates are provided as a stack of arcuate laminates 110, the outer edge of a lower lying stack of laminates being indicated with a broken line. In the stack, the end-to-end region of two arcuate laminates are covered by another ar- cuate laminate. An arcuate laminate 110 overlaps with 2 arcuate laminates behind it; with one of the two for 2/3rd of its length, and for the remainder with the other arcuate laminate. The end-to-end regions of the visible arcuate laminates 110 are indicated with 120' ; the end-to-end regions of arcuate laminates behind these visible arcuate laminates are indicated with reference number 120' ' , and the end-to- end regions of the arcuate laminates behind these are indicated with reference number 120''' . The through-holes 112 of adjacent laminates of the stack are in register so as to allow the tension rods to pass through the full stack of arcuate laminates 110.

Fig. 2 shows the teeth 130 of the arcuate laminates 110 in which the copper windings (not shown) are inserted. More importantly, it shows the outer edge 151 of first arcuate laminates protruding beyond the outer edges 152 of second arcuate laminates at the outer circumference of the stator 111 for dissipating heat to the atmosphere. The outer edges 151 of stacked first arcuate laminates 110 form the cooling ribs 106 of the generator 105. There are also strengthening ribs 107 provided over the circumference of the generator 105, which cover the end-to-end regions (120) of the arcuate laminates 110 to help ensure that no moisture enters the generator 105. They are welded over their full length to the stator 111 (before being impregnated with resin) . In the embodi- ment of fig. 3, these strengthening ribs 107 are strips of stainless steal that are partially sunk into the concentric cooling ribs 106.

The outside of the generator 105, more specifically the stator 111 is coated with a weather-resistant and in particular moisture- impermeable coating. This can be done in accordance to well- established ISO standards, in particular those for Class 5 protection in marine environments, which offer protection for 20 years and more. Here, the stator is provided with Thermally Sprayed Aluminium, a coating well-known for components used in the off-shore industry. If desired, a sealant may be applied on top of the TSA layer for even better protection against corrosion.

Fig. 3 shows part of the stator 111, and in particular a section of the stack of arcuate laminates 110 under compression between a front plate 161 and a back plate 162. A threaded tension rod 171 is with its threaded end inserted in a threaded hole of the back plate 162, and at the other end of the tension rod 171 a nut 172 has been provided. Hydraulic pressure is applied to the tension rod 171 while the nut 172 is being tightened.

The back plate 162 has a sandwich structure and more specifically has a nose 163 to create room (circular space 164) for the end turns of the copper windings 207 around the teeth 130 shown in fig. 2 (this figure doesn't show the windings 207 but this is well known to the person skilled in the art) . Also at the front end there is a circular space 165 for this purpose. The back plate 162 is rigidly connected to a carrier cone 165, which in turn is rigidly connected with the inner bearing ring 197 of a bearing 166 (schematically shown) . The outer bearing ring 196 of the bearing 166 is rigidly connected to a first rotor flange 167. To ensure rigidity of the rotor 109, there is a second flange 170 parallel to the first rotor flange 167 that is connected to the second rotor flange 170 by a stiffening plate 293. At its outer circumference, the rotor 109 is provided with magnets 168. The inner circumference of the second flange 197 is used as an annular brake disk 169 (brak- ing callipers not shown) . There is an air gap at 181 between the inner circumference of the annular break disk 169 and the carrier cone 165. The rotor 109 and the stator 111 are separated by a small air gap 281

The gap 211 between housing member 201 and the bearing section 166 is preferably provided with a seal 202, as is known in the art.

Fig. 3 shows a the preferred embodiment of the invention, wherein the first arcuate laminates are the first and last of a first ^■ series of laminates, and in contact with second arcuate laminates similarly the first and last of a second series of laminates. While several components of the generator 105 have been discussed, and steps in the manufacture thereof have been indicated (such as creating the stack of arcuate laminates), it is remarked that both these components and these steps are known. The invention differs in the presence of protruding ribs formed by first arcuate laminations for direct cooling of the stator to the atmosphere.