GENERATOR

Abstract: An electric generator comprises: a housing; a stator disposed fixedly relative to this housing and having a number of pole-forming ferromagnetic cores ordered in a circle, around which are arranged respective windings of insulated, electrically conductive wires; a rotor mounted rotatably relative to the housing and comprising a number of magnets arranged in a circle, and has the characteristic that the magnets are supported by a metal first ring which is supported by a second ring consisting of cured plastic reinforced with fibres, which rings are arranged in a housing; the field in the magnets has a direction corresponding to the axial direction of the rotor; the cores extend in axial direction of the rotor; and the cores and the associated windings are embedded in cured plastic reinforced with fibres, and form with this fibre-reinforced plastic a closed round structure with a central zone substantially consisting of only reinforced plastic.

Description: GENERATOR The invention relates to an electric generator, for instance for a wind turbine. A usual generator has a structure such that it is heavy, for instance as a result of the necessity of applying a transmission, using which the rotation speed of the turbine rotor is modified, in particular increased, to that of the generator rotor. A further drawback of known generators is that their electrical efficiency leaves something to be desired. An important cause of this lies in the fact that due to the structure of known generators there is the necessity of leaving quite a large air gap between the magnet means normally forming part of a rotor on the one hand and the stator poles on the other. The stator poles form part of ferromagnetic cores around which windings of an insulated electrically conducting wire are arranged. It is an object of the invention to provide an electric generator which is not subject to the drawbacks of the known generators and which moreover lends itself to manufacture with very small tolerances by means of simple production processes. It a further object of the invention to construct an electric generator such that it has smaller dimensions and a lower weight. For instance for use of a generator in combination with a wind turbine, a low weight is important to reduce the mechanical load on a support construction, for instance a post, a column or the like. The support construction can hereby be lighter and take a less expensive form. The above stated objectives are generally realized with an electric generator comprising: a housing; a stator disposed fixedly relative to this housing and having a number of pole-forming cores of laminated ferromagnetic material ordered in a circle, around which cores are arranged respective windings of insulated, electrically conductive wires, which windings are connected electrically to electrical connections, via which electrical energy can be taken off during operation of the generator; a rotor mounted rotatably relative to the housing and comprising a number of magnets arranged in a circle, wherein during rotation of the rotor the magnets pass over said poles and thus cause respective voltages over said windings; characterized in that the magnets arranged in a circle are supported by a metal, for instance ferromagnetic first ring, for instance via glue connections, which metal ring is supported by a second ring consisting of cured plastic reinforced with fibres, which rings are arranged in a housing; the field in the magnets has a direction corresponding to the axial direction of the rotor; the cores extend in axial direction of the rotor; and the cores and the associated windings are embedded in cured plastic reinforced with fibres, and form with this fibre-reinforced plastic a closed round structure, for instance a disc, with a central zone substantially consisting of only reinforced plastic. In a specific embodiment the generator has the special feature that the reinforced plastic is epoxy reinforced with glass fibres. Depending on the space available and the permissible weight of the generator, the generator can comprise according to an aspect of the invention a rotor provided on two sides with respective circles of magnets, which circles of magnets co-act with two respective stators. With such an embodiment, wherein the rotors have to have a precise, mutually corresponding structure, particularly in respect of the mutual positioning of the magnets, it is possible to achieve that the rotor is loaded substantially symmetrically to both sides, thus avoiding that the magnets and cores exert a force on each other such that the disc-shaped rotor has a tendency to bulge. This same advantage can be achieved with an embodiment in which the cores form on both their ends respective poles which co-act with the magnets, grouped in respective circles, of two rotors rigidly coupled to each other and disposed on either side of the stator. The generator preferably has the special feature that the magnet material contains neodymium. This latter embodiment can particularly be developed such that the magnet material is NeFeB. Magnets of the described type have the great advantage of being able to generate a very great field strength, which can greatly enhance the transmission efficiency of the generator. A preferred embodiment has the special feature that the rotor is arranged in a plastic casing. In the same manner a preferred embodiment of the generator according to the invention has the feature that the stator is arranged in a plastic casing. Due to these described structures a very good protection of the rotor and/or the stator is obtained, including the magnets and the electric stator windings, against weather influences, chemical corrosion and the like. Production of the rotor and/or the stator can take place by making use of casting techniques in combination with vacuum-forming. As already described above, it is of the greatest importance that the air gap between rotor and stator is as small and constant as possible. In order to ensure that this air gap is very controllable and that no danger exists or can occur of small axial aberrations between the rotor and the stator, the generator can have the special feature according to an aspect of the invention that the rotor is mounted on its outer edge relative to the stator, for instance with at least one roller bearing, a slide bearing, an air bearing or a magnetic bearing. A possible tendency towards bulging, as already mentioned above, is hereby also effectively prevented. An important aspect of the invention lies in specific parts being manufactured from plastic, which may optionally be reinforced with fibres. As described, use can for instance be made of epoxy reinforced with glass fibres. Since such a cured plastic or composite mass has a poor heat conduction, there would be the danger of for instance the windings extending round the cores being heated to a temperature above a permitted maximum value. According to an aspect of the invention use can therefore advantageously be made of a variant in which the windings are cooled by a forced medium flow, for instance an air flow. Alternatively or in combination with said forced cooling, the generator can have the special feature that at least one cooling conduit through which heat transport medium can flow extends through each core. The heat transport medium can be for instance a gas such as air or a liquid such as water or thermal oil. Such a cooling conduit can be embodied as a conduit or tube of copper or plastic or be embodied in other appropriate manner. A specific embodiment has the special feature that the cores are supported by a ring consisting substantially of laminated erromagnetic material. This embodiment is particularly important in a configuration in which to each core carrying an electrical winding is added a core not provided with a winding. The two said cores together form a magnetic circuit. The magnetic reluctance of this circuit is reduced by said ferromagnetic ring. Said embodiment with a ring of laminated ferromagnetic material can advantageously be embodied such that the ring consists substantially of wound band material. In this embodiment the blades are mutually separated in per se known manner by layers of paper, plastic, lacquer or the like. This measure is per se common in the construction of generators, motors, transformers and the like. The invention will now be elucidated with reference to the annexed drawings. Herein: figure 1 shows a perspective view of a wind turbine according to the invention; figure 2 shows a cut-away perspective view of a part of the wind turbine of figure 1; figure 3 shows on a larger scale the generator depicted in figure 2; figure 4 shows the detail IV according to figure 3; figure 5 is an exploded view of the structure according to figures 2 and 3; figure 6 is a view corresponding with figure 3 of a variant; figure 7 is a schematic representation of a part of the arrangement of the magnets relative to the poles; figure 8 is a complete view of the structure shown in figure 7, omitting the hatching; and figure 9 is a schematic cross-sectional view of a core 16 with cooling conduit received therein. Figure 1 shows a wind turbine with an electric generator 2 according to the invention to be described in detail hereinbelow. Wind turbine 1 comprises a post 3 which is anchored in the ground. The post supports generator 2; this latter supports a turbine rotor 4 with three aerodynamic turbine blades 5, 6, 7. An arrow 8 indicates that generator 2 is rotatable with rotor 4 such that the axial direction of turbine rotor 4 can always be placed in a desired direction relative to the wind direction. Not shown is that for aerodynamic reasons the blades 5 can be pivotable round their longitudinal axis. Turbine rotor 4 has a dome-shaped cap 9 in which a bearing 10 is arranged in the manner shown particularly clearly in figures 2 and 3. Coupled to a support column 11 placed rotatably relative to post 3 is a horizontal shaft 12, which is also shown particularly clearly in figures 2 and 3. A disc 13 consisting of epoxy reinforced with glass-fibre and having ventilation openings 14 is coupled to this shaft. This disc serves as stator disc and bears an iron ring 15 as drawn in figure 4 and figure 5 which carries respective pairs of cores 16,17 of laminated ferromagnetic material, in particular steel. Steel is a material combining a good structural strength with favourable ferromagnetic properties. Respective windings consisting of insulated copper wire are arranged around cores 16. These windings are designated with reference numeral 18. The pairs of cores 16,17 are disposed in the manner shown in figure 5. Cores 16,17 are connected to iron ring 15 by respective glue connections. Stator disc 13,15,16,17,18 is wholly embedded in said epoxy material such that poles 29,30, i.e. the free ends of cores 16,17, can also withstand weather influences and chemical corrosion. Shaft 12 supports turbine rotor 4 via bearing 10. This rotor further comprises a rotatable rotor housing 19 which is rotatably coupled via an edge bearing 20 to the widened outer edge 21 of stator disc 13 while maintaining a precise mutual positioning. This positioning is important in respect of the fact that rotor housing 19 bears an annular casing 22 in which an annular fibreglass-epoxy structure 23 is received. Via steel ring 24 this latter carries NeFeB magnets 25 which are adhered with glue to ring 24. Magnets 25 are ordered in the form of a circle. With reference to figures 7 and 8 will be shown how these are placed relative to poles 29,30. As shown particularly in figure 4, an air gap 31 is situated between poles 29,30 and the surfaces of magnets 25 directed toward these poles. It is noted herein that these magnets and the associated ring 24 are also encased with epoxy, whereby the corrosion resistance of the rotor is very good, as already described in the case of the stator. The small dimensions of air gap 31 are of essential importance for a favourable transmission efficiency of generator 2. In this respect the edge bearing 20 fulfils an important function. The air gap can hereby have a fixed value which is very small compared to the prior art. The ventilation holes 24 serve for forced cooling of generator 2. In the present case of a wind turbine generator the forced cooling can take place by air. A simple forced cooling can be realized by for instance providing holes 14 on their outer side with simple blades. In another case, in which the generator is for instance used in a hydroelectric power station, the forced cooling can take place by making use of the flow- pass water as cooling medium. Water can also be a very suitable cooling medium in the case the generator according to the invention is used on board ships. Not drawn is that provisions have to be present to take off the electrical energy generated in windings 18 during rotation of the rotor and make it suitable for use. Referring to figure 3, it will be apparent that turbine rotor 4 is supported by bearings 10 and 20 for rotation relative to the fixedly disposed stator. Figure 4 shows detail IV of figure 2 on enlarged scale. Figure 5 shows an exploded view of the structure according to figures 2 and 3. Figure 6 shows a structure which differs from the structure according to figures 2,3,4 and 5 insofar that the rotor takes a double-sided form. Ring 24 bears two circles of magnets respectively 25,25' which co-act with respectively stator 15,16,17,18,29,30 and a second stator 15', 16', 17', 18', 29' ,30' . The rotor 24,25,25' in double form is disposed strictly symmetrically with equal mutual distances or air gaps relative to poles 29,30; 29 ',30'. Rotor 26 is hereby loaded substantially symmetrically by stators 27 and 28. When there is a precise symmetrical load, the edge bearing 20, which is shown particularly clearly in figure 5 in the single- sided embodiment, can be omitted without problem. Not shown is that the embodiment of figure 6 could be modified in the sense that the place of stators 27,28 be taken by two rotors of the type shown in figure 5, between which is situated the double-sided stator taking the place of rotor 26. Figure 7 shows the pairs of poles 29,30 with the associated windings and, with hatching, the magnets 25. Attention is drawn to the fact that the magnets take an oblique position relative to the purely radial direction. Thus is ensured that the output voltage of each winding 18 has a substantially sine-shaped progression without the abrupt phenomena occurring during switch-on and switch-off. Figure 8 shows the structure in question. Here is shown that each stator is sub-divided into six identical segments, wherein diagonally opposed segments co-act electrically with each other such that the three pairs of segments have a three-phase structure. As will be apparent from the figure, poles 29,30 extend in this view in substantially radial direction. For the sake of clarity only a few windings 18 are drawn in stylized form. Attention is drawn to the fact that the drawn pairs of segments I-IV, II-V, III-VI have respective phase shifts of 120°. This can be seen from the relevant relative positions of magnets 25 relative to poles 29,30 in the drawn position. These phase shifts of 120° correspond with the necessary phase shift in a three- phase configuration. Figure 9 shows a core 16, wherein for the sake of clarity the winding 18 is not drawn. Core 16 comprises an internal cooling conduit 34 with an inlet tube stub 32 and an outlet tube stub 33 (see also figure 4) . It is particularly important that end zones 35,36 of core 16 are effectively cooled by cooling medium flowing through cooling conduit 34. The heat accumulation is greatest in these zones and the most effective cooling is therefore required.

Claims: CLAIMS 1. Electric generator comprising: a housing; a stator disposed fixedly relative to this housing and having a number of pole-forming cores of laminated ferromagnetic material ordered in a circle, around which cores are arranged respective windings of insulated, electrically conductive wires, which windings are connected electrically to electrical connections, via which electrical energy can be taken off during operation of the generator; a rotor mounted rotatably relative to the housing and comprising a number of magnets arranged in a circle, wherein during rotation of the rotor the magnets pass over said poles and thus cause respective voltages over said windings; characterized in that the magnets arranged in a circle are supported by a metal, for instance ferromagnetic first ring, for instance via glue connections, which metal ring is supported by a second ring consisting of cured plastic reinforced with fibres, which rings are arranged in a housing; the field in the magnets has a direction corresponding to the axial direction of the rotor; the cores extend in axial direction of the rotor; and the cores and the associated windings are embedded in cured plastic reinforced with fibres, and form with this fibre-reinforced plastic a closed round structure, for instance a disc, with a central zone substantially consisting of only reinforced plastic. 2. Generator as claimed in claim 1, wherein the reinforced plastic is epoxy reinforced with glass fibres . 3. Generator as claimed in claim 1, comprising a rotor provided on two sides with respective circles of magnets, which circles of magnets co-act with two respective stators. 4. Generator as claimed in claim 1, wherein the cores form on both their ends respective poles which co- act with the magnets, grouped in respective circles, of two rotors rigidly coupled to each other and disposed on either side of the stator. 5. Generator as claimed in claim 1, wherein the magnet material contains neodymium. 6. Generator as claimed in claim 5, wherein the magnet material is NeFeB. 7. Generator as claimed in claim 1, wherein the rotor is arranged in a plastic casing. 8. Generator as claimed in claim 1, wherein the stator is arranged in a plastic casing. 9. Generator as claimed in claim 1, wherein the rotor is mounted on its outer edge relative to the stator, for instance with at least one roller bearing, a slide bearing, an air bearing or a magnetic bearing. 10. Generator as claimed in claim 1, wherein the windings are cooled by a forced medium flow, for instance an air flow. 11. Generator as claimed in claim 1, wherein at least one cooling conduit through which heat transport medium can flow extends through each core. 12. Generator as claimed in claim 1, wherein the cores are supported by a ring consisting substantially of laminated ferromagnetic material. 13. Generator as claimed in claim 1, wherein the ring consists substantially of wound band material.

Inventors: ROELOFS ROBERT, ROELOFS, ROBERT
Applicants: AERPAC HOLDING B V, ROELOFS ROBERT, AERPAC HOLDING B.V., ROELOFS, ROBERT
Application year: 2000
Main classification: H02K21
IPC codes: F03D9, H02K3, H02K5, H02K21