WO1992012343A1

WO1992012343A1 - Wind turbine

Info

Publication number: WO1992012343A1
Application number: PCT/GB1992/000003
Authority: WO
Inventors: Andrew Ferrand Stobart
Original assignee: Resource Conservation Plc
Priority date: 1991-01-04
Filing date: 1992-01-02
Publication date: 1992-07-23
Also published as: AU1157892A; GB9100104D0

Abstract

The present invention relates to an improved wind turbine. A horizontal axis wind turbine (1) includes a fixed shaft (3), a first rotor wheel (5) and a second rotor wheel (7). The first and second rotor wheels (5, 7) are mounted to rotate about fixed shaft (3). Each rotor wheel (5, 7) comprises a substantially planar plate having mounted upon it a plurality of rotor blades (9). The turbine (1) includes an axial air gap generator (11) including two generator components (13, 15). These comprise the field (13) and the armature (15). The field and armature (13, 15) are arranged to contra-rotate about the axis (17) of the shaft (3). One of the generator components (13 ) is mounted upon the first rotor wheel (5) and the second generator component (15) is mounted to rotate with the second rotor wheel (7). The first and second rotor wheels (5, 7) are arranged to contra-rotate and thus cause contra-rotation of field and armature (13, 15) to generate power. The blades (9) are mounted upon each wheel (5, 7) at the periphery of the wheel (5) such that the distance A between the shaft (3) and the mounting position (19) of the blade (9) is greater than the distance B between the generator and the shaft (3).

Description

Wind turbine

Field of the Invention

The present invention relates to an improved wind turbine.

Typically, a wind turbine includes at least one rotating member onto which is mounted a set of blades which are shaped and configured such that wind causes rotation of the rotating member in one direction. The rotating member is coupled to a component of a generator, either the field or armature and the rotation of the rotating member is transmitted to the generator component therefore generating power.

Wind turbines can be classified into two distinct sets. One set comprises vertical axis wind turbines in which the

15 rotating members rotate about a vertical axis, the second set comprising horizontal axis wind turbines in which the rotating members rotate about a substantially horizontal axis. The invention is applicable to horizontal axis wind turbines. The term horizontal axis wind turbine is

20 intended to encompass any wind turbine which includes rotating members which in use rotate about a substantially horizontal axis, even if they may include a mechanism for allowing the unit to be swung out of its in use position in

^5 times of hiσh wind.

Wind turbines may include only one rotating member in which case only one component of the generator rotates. Wind turbines may comprise at least two rotating members which contra-rotate. In this case, one rotating member drives the field component of the generator and the other the armature component of the generator such that rotation of both rotating members causes magnified relative rotation between the field and armature of the generator thus generating more power. One form of windmill using this principle is described in UK Patent No 1 593 969 filed by Trimbles Windmills Limited.

Two types of generators may be used in wind turbines. A number of wind turbines have been developed which include radial air gap generators. Such generators include a field and armature component mounted concentrically about a common joint axis such that the adjacent surfaces of the field and armature components are substantially parallel to trie axis of rotation such that the gap between the two components can be regarded as being radial. Axial air gap generators include a field and armature component which rotate about a common axis but not a joint axis. The field and armature components here are substantially parallel to one another and their adjacent surfaces are substantially perpendicular to the axis of rotation so that the gap between them can be regarded as an axial air gap.

Wind turbines including contra-rotating blades have been proposed which include radial air gap generators. Axial air gap generators have been used in wind turbines which include one rotating member only. Summary of the Invention

According to the invention, there is provided a horizontal axis wind turbine, including a fixed shaft, a first and a second rotor wheel, each rotor wheel being mounted to rotate about the fixed shaft and comprising a substantially planar plate having mounted upon it a plurality of rotor blades, an axial air gap generator including two rotating generator components, a field and an armature, arranged to contra-rotate about the axis cf the shaft, one of the generator components being mounted upon the first rotor wheel and the other being coupled to the second rotor wheel to rotate with the second rotor wheel, the first and second rotor wheels being arranged to contra- rotate to cause contra-rotation of the field and armature to generate power, in which the blades are mounted upon each wheel at the periphery of the wheel such that the distance between the shaft and the mounting position of the blade is greater than the distance between the generator components and the shaft.

Thus the blades are mounted "outboard" of the generator components relative to the shaft. This is advantageous since there is a lower bending moment applied to the blades and the stress forces are transferred to the wheel and then to the generator components in a short path moving generally inwards towards the shaft.

An advantage of using an axial air gap generator is that the weight and cost of the generator can be reduced by a factor of, for example, up to 30%. This reduction in weight means that the wind turbine can be much more responsive to wind and therefore generate more power.

Although it is not essential it is preferred that each rotor wheel comprises a circular planar plate. Preferably, the generator component mounted upon the first rotor wheel is bolted to one face of the wheel, preferably the opposite face to that on which the blades are mounted. Preferably, the second component is coupled to the second rotor wheel via a torque tube. The distance between the two wheels is dependent upon the length of the blade and upon the blade chord (i.e width) and shape.

The construction of the blades is standard and will be apparent to the skilled addressee of the specification.

The invention allows a construction of equipment for the collection of wind energy with fewer components and thus less cost.

Preferably, the rotor wheels are mounted upon bearings on the fixed shaft lying in the horizontal plane so that the shaft supports the whole assembly. The shaft may be supported from below but is preferably supported from above being suspended from an arm projecting from a larger support structure. Typically, such a structure will include a number of arms, each supporting one or more turbines. Guide vanes, nose cones and other aerodynamic devices are preferably fixed to the central shaft.

Although the number of blades mounted upon each rotor wheel can readily be varied, it is important that the number of blades mounted upon the first rotor wheel is not 0 equal to the number of blades mounted upon the second rotor wheel. It has been found that in a contra-rotating wind turbine if the number of blades on the contra-rotating rotors is equal there is a danger of destructive standing waves being created. It is important that the rotor wheel which in use will face the wind direction, hereinafter referred to as the "front" rotor wheel is the one which has fewer blades mounted upon it. This has the effect that the front rotor wheel is more responsive to the wind because it is lighter and therefore rotates more quickly than the "rear" rotor wheel. It has been found that an effective turbine is created with three blades mounted upon the front rotor wheel and five blades being mounted upon the rear rotor wheel. Preferably, the front rotor wheel is that which comprises the second rotor wheel which is coupled to a generator component via a torque tube. Preferably, the torque tube is attached to the wheel by bolts surrounded by buffers of rubber which minimise the transmission of shocks. This is important because the front wheel which is the lighter of the wheels has a faster reaction to the wind speed.

Preferably, the field component of the axial air gap generator comprises a pair of annular members having windings mounted upon them. In this case, one annular is bolted unon the first rotor wheel and the second annular member is mounted parallel to the first annular component and bolted to a cage member projecting from and bolted to the first rotor wheel. The armature member comprises an annular member mounted to rotate between the two annular components.

Preferably, the field is mounted upon the first rotor wheel and the armature is coupled to rotate with the second rotor wheel.

Preferably, the power is taken off the generator by a set of slip rings. Preferably, the generator is a three phase induction type generator.

Brief Description of the Drawings A wind turbine and a structure having a plurality of such turbines mounted upon it will now be described, by way of example only, with reference to the accompanying drawings, in which:-

Figure 1 is a section through half a wind turbine; Figure 2 is a schematic view showing part of the electrical circuit;

Figure 3 is a further circuit diagram; Figure 4 is a front view of the support structure; Figure 5 is a side elevation of the support structure; and Figure 6 is an enlarged view showing the suspension of one wind turbine unit.

Description of the Preferred Embodinmβnt A horizontal axis wind turbine 1 includes a fixed shaft 3, a first rotor wheel 5 and a second rotor wheel 7. The first and second rotor wheels 5, 7 are mounted to rotate about fixed shaft 3. Each rotor wheel 5, 7 comprises a substantially planar plate having mounted upon it a plurality of rotor blades 9. The turbine 1 includes an axial air gap generator 11 including two generator components 13, 15. These comprise the field 13 and the armature 15. The field and armature 13, 15 are arranged to contra-rotate about the axis 17 of the shaft 3. One of the generator components 13 is mounted upon the first rotor wheel 5 and the second generator component 15 is mounted to rotate with the second rotor wheel 7. The first and second rotor wheels 5, 7 are arranged to contra-rotate and thus cause contra-rotation of field and armature 13, 15 to generate power. The blades 9 are mounted upon each wheel 5, 7 at the periphery of the wheel 5 such that the distance A between the shaft 3 and the mounting position 19 of the blade 9 is greater than the distance B between the generator component and the shaft 3.

The shaft 3 comprises a steel or aluminium shaft of length 800 millimetres and a diameter of 75 millimetres. Mounted about shaft 3 are three bearing sleeves 21, 23 and 25 for mounting the rotors for rotation about the shaft 3. The bearing sleeves 21, 23 and 25 are used for mounting the bearings which ensures accurate alignment. 0 The second rotor wheel 7 is arranged such that it is the "front" rotor wheel in that it faces the direction of the wind. The front rotor wheel 7 is a circular plate which has mounted upon it three blades 9 which are mounted upon one face of the rotor wheel 7 by blade mounting blocks 27 which are mounted to the wheel 7 by bolt 29. The rotor wheel 7 is mounted via screws 31 to hub 33. Hub 33 which rotates over bearings designated generally at 35 lying between hub 33 and bearing sleeve 25) . An oil seal 37 is bolted to hub 33 via screws 39. Hub 33 is bolted to torque tube 41 via bolts 43 surrounded by rubber sleeve 45 which acts as a buffer to minimise the transmission of shocks.

The torque tube 41 is bolted via a similar set of bolts 47 and rubber buffers 49 to a hub 51 mounted to rotate via bearing 53 and oil seal 55 about bearing sleeve 23. The hub 51 is bolted via bolts 57 to the armature member 15 of the axial air gap generator 11. The diameter of the armature 15 is 600 millimetres. Armature 15 comprises a permanent magnet. First rotor wheel 5 is also a circular plate which has mounted upon it five blades 9 of similar construction to those bolted to the second rotor wheel only mounted in opposite sense to as to cause rotation in the opposition direction. Blade 9 is mounted similarly via mounting blocks 27 and hnlts 29. τh<? first rotor wheel 5 is mounted by bolts 59 to hub 61 which rotate via bearing 63 and oil seal about bearing sleeve 21. Bolted to the face of the first rotor wheel opposite the face on which the blades 9 are mounted is bracket 67 on which the field windings 13 are mounted. The field windings 13 comprise two annular components 69, 70 arranged parallel to one another and between which the armature 15 rotates. Bolted to the first rotor wheel 5 is cage member 73 of L-shaped cross section onto which is mounted bracket 75 and second winding 71. The contra-rotation of wheels 5, 7 causes contra-rotation of the field and armature components 13, 15 to generate power.

The bearings 35, 53 and 63 are all sealed bearings incorporating oil seals. They are heavy thrust bearings. The diameter of each rotor wheel 5, 7 is approximately 800mm with the outer diameter of the field components 13 being approximately 600mm in comparison.

Typically the diameter of the circle described by the outer tip of the blades 9 is 6m. Each blade 9 is aerofoil shaped. The shape and structure of a suitable blade will be apparent to the skilled addressee of the specification.

The distance between the rotor wheels 5 and 7 is 400mm. The optimum for this dimension is dependent upon the blade length and blade chord.

The field and amature components 13, 15 are set by- adjusting the bearings position. In this way the axial air gap can be readily reduced to a minimum.

The circuit of the air gap generator 11 is shown in more detail in Figures 2 and 3. The field component comprises a three phase winding coupled to slip ring brushes 77 which are rotatable about shaft 3 and mounted in slip ring housing 79. As the armature 15 rotates with respect to the windings 13 current is induced in the windings 13 which is transmitted via current conductors 81 to the slip ring brushes 77 which passes to a power sensor circuit 83 then to an inverter 85.

To obtain maximum efficiency from a wind turbine, the ratio between the tip speed of the blades 9 and the wind speed must be maintained at a value which gives maximum power collection.

An inverter system 85 under external processor control from control processor 87 ensures that the above conditions are maintained. A signal indicative of wind speed is fed from generator 11 to control processor 87.

DC links from each of the optimising converters 89 which are interconnected and fed to a larger DC AC inverter 91 - which in turn feeds the mains network indicated generally as 92 under control of line detector 94. A pressure detector 93 which is mounted on the first rotor wheel 5 feeds to a tachometer 95 which measures the rotational speed and feeds this information to the control processor 10 87.

Any further circuits required will be apparent to the skilled addressee of the specification.

A structure 97 is in the form of a frame having mounted upon it nine turbines 99 of the form shown in Figure 1, 2 and 3. As can be seen in Figure 4 and 5, each wind turbine unit is mounted to rotate about a horizontal axis and comprises a generally circular unit of diameter 6 metres and a nose cone 101. The unit is suspended from the shaft 3 which is mounted on a U-shaped mounting member 103 which 0 is coupled to mounting arm 105 via a flexible mounting 107 which allows the unit to rotate backwards in the direction 109 to up to 45 degrees from the vertical position. A stop (not shown) prevents movement forward so that the unbalanced weight of the unit partially counteracts the 5 wind force reducing loading on the tower supports. The blow back movement is to limit wind forces and generation in high winds.

Claims

1 A horizontal axis wind turbine (1) including a fixed shaft (3), a first and second rotor wheel (5,7), each roto. wheel (5,7) being mounted to rotate about the fixed shaft (3) and comprising a substantially planar plate having mounted upon it a plurality of rotor blades (9), an axial air gap generator (11) including two rotating generator components, a field (13) and an armature (15), arranged to contra-rotate about the axis of the shaft (3), one of the generator components (13) being mounted upon the first rotor wheel (5) and the other (15) being coupled to the second rotor wheel (7) to rotate with the second rotor wheel (7), the first and second rotor wheels (5, 7) being arranged to contra-rotate to cause contra-rotation of the field (13) and armature (15) to generate power, in which the blades (9) are mounted upon each wheel (5, 7) at the periphery of the wheel such that the distance (A) between the shaft (3) and the mounting position (19) of the blade (9) is greater than the distance (B) between the generator components and the shaft (3).

2 A horizontal axis wind turbine according to claim 1, in which the generator component (13) mounted upon first rotor wheel (5) is bolted to a face of the wheel (5) opposite to the face on which blades (9) are mounted.

3 A horizontal axis wind turbine according to claims 1 or 2, in which the other component (15) is coupled to the second rotor wheel 7 via a torque tube (41) .

4 A horizontal axis wind turbine according to claims 1, 2 or 3 in which the rotor wheels (5,7) are mounted upon bearings (35,63) on the fixed shaft (3) lying in the horizontal plane so that the shaft (3) supports the whole assembly. 5 A horizontal axis wind turbine according to claim 4, in which the shaf (3) is supported from above suspended from an arm 105 projecting from a larger support structure 97.

6 A horizontal axis wind turbine according to any one of the preceding claims in which three blades (9) are mounted upon the front rotor wheel (7) and five blades (9) are mounted upon the rear rotor wheel (5).

7 A horizontal axis wind turbine according to any one of the preceding claims in which the front rotor wheel (7) is that which comprises the second rotor wheel coupled to the other generator component (15).

8 A horizontal axis wind turbine according to claim 8, in which the front rotor wheel (7) is coupled to the generator component (15) by a torque tube (41) attached to the wheel (7) by bolts 43 surrounded by buffers (45) to minimise shock transmission.

9 A horizontal axis wind turbine according to any one of the preceding claims in which the field component (13) comprises a pair of annular members (69,71) having windings mounted upon them, one annular member (6 ) being bolted to the first wheel (5) and the second annular member (71) being mounted parallel to the first annular member (69) and bolted to a cage member (73) projecting from and bolted to the first rotor wheel (5), and the armature (15) comprises an annular member mounted to rotate between the two annular field components (69,71).

10 A horizontal axis wind turbine according to any one of the preceding claims, in which the field (13) is mounted upon the first rotor wheel (5) and the armature (15) is coupled to rotate with the second rotor wheel (7).