GB2449436A

GB2449436A - Fluid driven generator

Info

Publication number: GB2449436A
Application number: GB0709699A
Authority: GB
Inventors: Jeremy Richard Thake; Christopher Sha Huxley-Reynard; George James Gibberd
Original assignee: Tidal Generation Ltd
Current assignee: Tidal Generation Ltd
Priority date: 2007-05-21
Filing date: 2007-05-21
Publication date: 2008-11-26
Also published as: GB0709699D0

Abstract

A device generates electricity from a moving fluid, the device comprises a generator having a rotating outer ring 7 with magnetic poles on an inner surface thereof, the outer ring 7 being rotatable by a fluid driven bladed rotor 1. The generator also has a stationary inner ring 8 having coils which in use generate electricity. The bladed rotor 1 may be driven by water or wind, and may be directly attached to the outer ring 7 of the generator, or supported separately there from and connected there to by torque transmission means. The blades may have a fixed pitch or may be adjustable. When driven by water, bearings 6 of the device may be water lubricated.

Description

1 2449436 Title: Fluid Powered Generator

Background

Free-stream fluid powered generators such as wind and water-current turbines generally use the kinetic energy in the fluid flow to drive a rotor. For larger machines these rotors are relatively slow moving, and it is common to use a gearbox to increase the rotational speed for input to an electrical generator. Gearboxes have numerous moving and loaded components, and are often a weak point in the system, a problem compounded by the large variability in input power due to turbulence in the fluid flow. A further difficulty is that, as rotor diameter increases to capture more power, the size and weight of the gearbox required increases sharply.

Some existing fluid power generators eliminate the gearbox by using large-diameter, slow-speed electrical generators that are direct-coupled to the rotor. The layouts of these machines fall into two broad categories: the generator is either attached to the centre of the fluid rotor, or to the outside of it.

In the first arrangement the generator is driven by the hub of the fluid rotor. The generator has :... an internal rotor which provides a magnetic field and which is directly coupled to the fluid rotor.

The stator of the generator is a series of coils in a ring around the outside of the generator rotor, * * and electricity is generated in these coils as the field magnetism of the rotor rotates inside it.

The stator is prevented from rotating by being fixed to the structure of the turbine. The * mechanical details of providing bearing support for the fluid rotor and the generator rotor, and of * transmitting torque into the generator rotor, tend to make for very heavy structures, particularly as rotor diameters increase. * **

* In the second arrangement the generator is driven by the outside diameter of the fluid rotor blades, and forms a ring around the rotor rim. While this arrangement works for moderate diameters, at larger sizes the generator becomes a very large, relatively thin hoop. It becomes difficult to maintain sufficient stiffness in the rotor and the stator rings, and to control the gap between the rotor and the stator. The shear size of the generator is likely to make it expensive, and it is problematic to hold the structure in the flow.

The invention described here is a convenient means of eliminating a gearbox in a fluid-powered generator by incorporating a direct-drive generator in a manner that is simple, scaleable, and more robust than existing solutions.

Prior Art

Large electrical direct-drive machines, both motors and generators, are known in a number of industries. By using large numbers of poles, a slow rotational speed can be achieved, allowing the elimination of a gearbox between the electrical machine and the mechanical input or output.

Examples are electrical drives for process industries, generators for direct-drive hydropower, wind and tidal turbines (US Patent No. 6,957,947 illustrates such a turbine for use in water), and rim thrusters for ships. These electrical machines are configured with an internal rotor with magnets (or coils producing the field magnetism) around its roughly-cylindrical outside surface, and an stator made up of coils in a ring surrounding the rotor in which the rotating magnetic field of the rotor generates an alternating current.

It is becoming increasingly common for the field magnetism in such machines to be produced by rare earth permanent magnets. The strength of magnetic field that can be produced by such magnets has increased considerably in recent years, while production costs have become lower, making these a viable and economic option.

In most direct drive electrical machines the gap between the rotor and stator is filled with air, but in some devices, notably certain models of rim thrusters and tidal turbines, this gap may be filled with water.

Statement of the Invention

* The invention uses a large-diameter direct-drive generator to produce power from a fluid-driven rotor. It inverts the normal layout of a direct drive generator by having the stationary element of the generator on the inside containing the coils in which electricity is generated, and the field magnets rotating in a ring on the outside. The main part of the rotor is external to the generator.

Advantages *. : The layout of the fluid-powered generator simplifies the attachment of, and transmission of torque from, the fluid rotor to the electrical rotor for a machine in which the fluid rotor is substantially outside the generator.

Preferably, for a generator working in water, the invention further simplifies the machine by allowing part of the flow to pass through the bearings and in the gap between the generator rotor and stator to provide both lubrication and cooling.

Introduction to Drawings

The invention may more easily be understood by referring to the various figures accompanying this text: * Figure 1 shows two simplified views of the turbine: to the left, a front view of the turbine, and to the right a side view.

* Figure 2 shows an expanded version of the side view in Figure 1, but in cross-section through the fluid generator on its centreline.

* Figure 3 shows a cross-sectional view similar to Figure 2, but is for an alternative embodiment of the invention.

Detailed Description

Referring to Figure 1, the machine has a rotor I which has one or more blades 2 attached externally to a hub 3. The rotor 3 is turned about an axis 5 by the fluid flow, which is approximately parallel to axis 5. The rotor 1 has a bearing arrangement which locates it on the body or nacelle of the machine 4, allowing it to rotate relative to the nacelle 4. The nacelle is held in the flow so that the current flows past it. This may be achieved in a variety of ways, for example, by attaching it to a rigid foundation that is located on the ground below the machine, attaching it to some other structure, or providing sufficient buoyancy or dynamic lift that it holds itself up in the fluid and tethenng it to the ground with suitable ropes, chains, rods, beams or similar elements. The nacelle may swivel, yaw or pivot in such a way that it aligns with the direction of flow, or it may be fixed.

Referring to Figure 2, the rotor I is located on the nacelle by bearings 6 whose axes coincide with the axis of rotation 5. The main working elements of the electrical generator are 7 and 8.

: .. * The rotating part of the generator is its rotor 7 which produces the field magnetism and which is *.

attached to the hub 3 of the fluid rotor I and rotates with it. The stator 8 is fixed to the nacelle 4 and does not rotate, and contains the coils in which electrical power is produced.

s The generator may operate on principles similar to those of a number of different types of known generator, for example with permanent magnet or electromagnetic field excitation, * electricity generation being synchronous or asynchronous with the rotational speed. The * : . innovation is to invert the normal arrangement of the generator for this application such that the stationary coils 8 are on the inside of the generator, and the rotating magnetic field 7 is on the outside.

In a preferred embodiment no active electrical connections are required from the nacelle 4 to the generator rotor 7, by using permanent magnets in the rotor 7 to produce the field excitation.

Alternatively the rotor 7 could be made with current coils excited by the field of the stator in a manner similar to that of a standard induction generator. Other embodiments could have active electrical excitation of the field coils by having slip-rings or a rotating transformer to supply power from the nacelle 4 to the rotor 7.

A particular preferred embodiment for when the fluid generator is designed to operate in water has plain bearings that use water to lubricate them. In this embodiment, the bearings and the gap 9 between the generator rotor 7 and stator 8 can be filled with water, and seals are not required to keep water out. Alternatively, non-contact labyrinth seals can be used to keep debris out of the bearings 6 and gap 9 while allowing some flow of water into the gap 9. The advantage of having water present is that it can provide lubncation and cooling to the bearings 6, and cooling for the generator. Water is excluded from the rotor 7 and stator 8 by suitable encapsulation of the rotor 7 or stator 8 or treatment of the surfaces in contact with the water.

This embodiment has considerable simplicity over other arrangements. Other embodiments require various leak-proof seals to keep the bearings 6 or the gap 9 dry or filled with a separate lubricating fluid.

The embodiment in Figure 2 shows the bearings 6 supporting both the fluid rotor and the generator rotor. Another embodiment is illustrated in Figure 3, which again shows a cross-section through the fluid-driven generator. Here the rotor 1 rotates on its own set of bearings 10, while the generator has an independent set of beanngs 11. A coupling 14 transmits torque from the hub 3 to the structure 12 supporting the generator rotor 7.

The embodiment in Figure 2 has blades that are fixed to the rotor hub 3. The blades can also have bearings at their roots and a mechanism to pitch them so as to change the angle of attack of the blade foil sections to the incoming flow. In the embodiment in Figure 3 the blades 2 are shown connected to the hub 3 with bearings 15 that allow them to rotate around their axes. The . pitch mechanism is not shown, but many different mechanisms are known to those skilled in the *... art. * * * S..

The embodiment in Figure 3 illustrates seals 13 that are used to exclude water from the * S. * S * generator. I. S * S S * *S ** . * *S * *S

Claims

Claims: 1. A device to generate electricity from the kinetic energy of

moving fluid in which the generator has: a. a rotating outer ring with magnetic poles on its inside surface directly driven by a hub which is turned by the dynamic forces of the fluid on the blade or blades which are attached to the outside of the hub, and b. a stationary inner ring fixed to the body of machine with coils around its circumference in which is generated the output power.
2. A device according to claim I for generating electricity from water currents.
3. A device according to claim 2 in which the water-driven rotor is directly attached to the outer rotor of the generator, and the inner stator is fixed to the body of the machine.
4. A device according to claim 2 in which the water-driven rotor is supported separately from the generator, and torque is transmitted from the water-driven rotor to the generator rotor.
5. A device according to claims 3 or 4 in which the blades are attached to the rotor at a *.::: permanently fixed pitch setting about their radial axis relative to the rotor.
6. A device according to claims 3 or 4 in which the blades can be pitched about their radial * *.

:.: * axes to change their angle of attack to the flow.

:
7. A device according to claims, 3 or 4 in which part of the water flow is allowed to pass *: * through the bearings and the gap between the generator rotor and stator.

*:*.
8. A device according to claim 7 in which water-lubricated plain bearings are used.
9. A device according to claim I for generating electncity from wind.
10. A device according to claim 9 in which the wind-driven rotor is directly attached to the outer rotor of the generator, and the inner stator is fixed to the body of the machine.
II. A device according to claim 9 in which the wind-driven rotor is supported separately from the generator, and torque is transmitted from the wind-driven rotor to the generator rotor.
12. A device according to claims 10 or 11 in which the blades are attached to the rotor at permanently fixed pitch setting about their radial axes relative to the rotor.
13. A device according to claims 10 or 11 in which the blades can be pitched about their radial axes to change their angle of attack to the flow.