SLOW SPEED ELECTRICAL GENERATORON A POWER WINDMILLThis invention relates to windmills for generating electricity.
Hitherto it has been thought necessary that a windmill for generating electrical power should have a gearbox at the top of its tower in order to increase the speed from that of the rotor - usually about 30-35 rpm - up to an economical generator speed which might be 1,500 rpm for a system generating electricity at 50Hz. Such an arrangement utilising a gearbox to effect a radical change of speed has been accepted as an inevitable necessity.
By contrast, I propose avoiding a radical change in speed effected with a gearbox. According to this invention, there is provided an electrical power-generating windmill having a generator with a multiplicity of poles, the generator having a rotor directly coupled to the windmill rotor so as to rotate at the windmill rotor's speed.
For a 50 Hz system such a generator could have 176 poles, requiring a rotor speed of 34.09 rpm.
The generator could be constructed as a cylinder with a diameter very much greater than its axial length.
Such a generator typically, based say on an output of 650KW, could be just over 6 metres diameter at the air gap between the rotor and the stator, while the axial length of the effective part of the rotor is 225mm. In effect such a generator is a large thin ring assembly.
In my preferred form of construction I propose that the rotor is directly attached to the rotor of the windmill, thereby enabling the generator to use the bearings of the windmill rotor rather than requiring its own, separate bearings. The stator could then be mounted on a supporting structure, e.g. brackets or some form of framework, extending forwardly from the windmill's turntable or slewing ring.
The invention has the benefit of avoiding the need for an expensive three-spindled gearbox to bring about a change in speed from less than 50 rpm to something in excess of 1,000 rpm. Not only does it avoid the cost of this gearbox it also avoids the need to maintain it and the noise of gear rumble. The number of moving parts at the top of the windmill tower can be kept to a single assembly which by reason of its simplicity can be expected to have a very long life.
An embodiment of the invention is illustrated in the accompanying drawings in which:Fig. 1 is a front elevation of the windmill rotor and the top of the windmill tower;Fig. 2 is a side elevation of the windmill rotor and the top of the tower; andFig. 3 is a plan view.
The windmill shown in the drawings has a supporting tower 2 at the top of which is a turntable 4.
Mounted on this turntable 4 are bearings 6 in which a shaft 7 carrying the windmill rotor 8 is journalled. Also mounted on the turntable 4 is the tail 10 of the windmill.
The construction of the rotor 8 and tail 10 may be as described and claimed in my pending European applications 90303640.8, 90303642.4 and 90303643.2.
Thus, as shown by Fig. 1 the windmill rotor which is to be turned by the wind consists of two annuli 12, 14 between which are mounted a plurality of blades 16. The annuli 12, 14 are carried on an arrangement of spokes 17 and cross-struts 18. The invention is not however limited to such a construction of windmill rotor. The invention could be put into practice with other forms of windmill rotor.
The windmill's generator is in the form of a thin ring 22 concentric with the rotor shaft. More specifically, this generator consists of two concentric rings. The outer ring is the stator and is carried by a supporting structure consisting primarily of three arms 24 secured to the turntable 4 and projecting forwardly from it. The supporting structure of the stator would also include reinforcements extending between the three arms 24 but omitted from the drawings for the sake of clarity.
Rotating inside the stator is the rotor of the generator.
This is bolted to brackets attached to spokes 16 of the windmill rotor so that the generator rotor and the windmill rotor turn in unison and are both supported by the bearings 6.
Construction of the generator can follow conventional principles in that the stator incorporates the windings in which electric current is generated and the rotor incorporates the windings which create the (rotating) magnetic field. However, the number of magnetic poles is much higher than conventional. Consequently the frequency with which magnetic poles pass any winding of the stator is similar to that in a conventional generator with fewer poles but a greater rotational speed.
To produce power with a fairly high power factor, it is preferable that the generator is of the salient pole synchronous type.
The invention is not limited to a generator of this preferred type, however, neither is it essential that the rotor should carry the field windings. The inverse arrangement with the field windings on the rotor could be used if preferred.