GB2496366A

GB2496366A - Wind turbine having an inflatable brake

Info

Publication number: GB2496366A
Application number: GB1116202.1A
Authority: GB
Inventors: Michael Andrew Wastling; David Irving
Original assignee: EVANCE WIND TURBINES Ltd
Current assignee: EVANCE WIND TURBINES Ltd
Priority date: 2011-09-20
Filing date: 2011-09-20
Publication date: 2013-05-15
Also published as: GB201116202D0

Abstract

A wind turbine, preferably a 5kW direct drive wind turbine, having an inflatable tube brake 8 for emergency overspeed protection. The inflatable tube brake 8 preferably acting between a fixed part 4 and a rotating part 6 at the maximum hub diameter of the turbine. The inflatable tube brake preferably acts directly between the parts, and is fibre-reinforced with the friction surface being a flexible surface of the tube 8. The tube 8 may be inflated with a gas, either by a chemical reaction or compressed air, or a fluid, preferably water to a pressure of 1 to 2 bar. The brake may comprise a valve or a centrifugal trigger restrained by a spring 16 provided with an over-centre cam 17. The tension in the spring 16 may be adjustable. Two inflatable tubes 8 may be used, which may be independently inflatable.

Description

High Torque Overspeed Brake Rotating machines such as wind turbines need overspeed protection.

Ideally the last resort' overspeed protection should be able to function independently of all the other mechanical and electrical systems on the machine, and also after a lightning strike. It is also beneficial if the overspeed brake can bring the machine to a complete standstill and hold it stationary until a service team arrive.

On wind turbines overspeed protection can be provided in many different ways: * Tip brakes * Electrical brakes operating through the generator.

* Disk brakes operating on the high speed shaft of a machine with a gearbox * Disk brakes operating on the low speed shaft, or on the main shaft of a direct drive machine.

* Full span blade pitching * Yawing the machine out of the wind Disk brakes can be designed to be fail safe. Typically the braking force is provided by a spring and the brake is held off by hydraulic, pneumatic, or electro-mechanical systems. However the braking torque required on a low speed shaft brake is very high, and this demands large springs and large callipers. In addition such systems require hydraulic, pneumatic or electrical systems that generally have wearing parts that require maintenance. Such systems represent a significant overhead in the capital and maintenance cost of small and medium sized turbines.

Tip brakes are complicated and interfere with the structure of the blade itself.

Full span blade pitching is also complicated and expensive to achieve on a small or medium sized turbine. Both these systems do not bring the machine to a complete standstill. If the machine is to be serviced at height then another braking system is required to hold the machine stationary.

On small and medium sized wind turbines it is advantageous to have the blades fixed in pitch and to use a direct drive generator to control the speed of the machine and provide braking. In this case it is essential to have a last resort braking system which is independent of the rest of the machine.

Inflatable tube brakes are known and have been in use for many years In their normal embodiment an inflatable tube acts against a series of brake pads which contract (or expand) onto a drum in a purpose built unit. (US Pat 2010/0236883) The invention here proposed is that an over speed brake consists of a fibre reinforced inflatable tube which acts directly between a rotating and a stationary part of the machine. The brake ideally acts at the maximum diameter of the hub of the machine which, on a direct drive wind turbine, is large.

Since the brake is to provide last resort emergency overspeed protection it will only be used on very few occasions in the life of the machine, possibly never.

The surface of the tube will act as the friction surface and the tube will easily be able to tolerate the amount of wear produced by a few emergency stops.

Since the diameter of the tube ring is large the contact area is also large. This means that a modest inflation pressure (one to two bar) will produce a large braking torque. The tube is formed as a large diameter ring, similar to bicycle tyres known as tubulars' where the inner tube and tyre are combined into one. The side walls are reinforced with strong fibres running at + / -45 degrees and there is a wear resistance surface on the outside circumference.

The tube is inflated from a small dedicated compressed air cylinder. An on / off valve is placed in the connecting pipe between the air cylinder and the tube. The tube and the air cylinder are mounted on the stationary part of the machine. A striking plate is attached to the valve, and a centrifugal trigger (mounted on the rotating part of the machine) acts on this striking plate at a certain RPM which opens the valve and inflates the tube. Since the pressure in the cylinder is fairly low (less than 5 Bar) the force on the valve is small and it is easily rotated by the centrifugal trigger.

A one way Schrader type' valve can be incorporated into the tube so that once inflated it remains inflated until the pressure is released manually.

Ideally the tube will expand radially, but it could also expand axially, or a combination of the two. If the expansion is radial then this can be outwards (in the case of a machine with the stationary part on the inside) or inwards (in the case of a machine with the stationary part on the outside) When the brake has been tripped it will remain on until it is reset manually. If there has been an overspeed then the machine will need to be inspected by a service team.

When the brake is reset the valve between the tube and the cylinder is closed first. Then a separate valve connected to the tube is opened to release the air.

If the tube has been stretched onto its mounting ring (on a radial outwardly expanding version) then the elasticity in the tube will force the air out and the tube will naturally lie flat. Otherwise a small vacuum pump can be attached to suck all the air out and make the tube lie flat. Then the air release valve is closed and the air cylinder is re-charged using a hand pump or portable compressor. Finally the centrifugal trigger is re-set and the machine is ready to go again.

As part of the normal maintenance of the machine the pressure in the air cylinder is checked using a gauge permanently mounted on the cylinder, or a tyre pressure gauge. Also the spring pressure on the trigger is checked and adjusted.

Since the friction surface is the flexible surface of the tube, the steel ring on which it bears does not have to be machined to a high standard of accuracy.

Also the gap between the stationary ring and the rotating ring does not have to be maintained to a high standard of accuracy. On the preferred version of a radially expanding tube, the normal forces generated by the expansion of the tube are reacted through hoop stresses in the rotating and stationary rings.

In the version described there are 2 tubes lying side by side, each with its own air cylinder and trigger. This provides the security of having two independent systems and also 4 tube walls to take the shear force rather than two. There is also a greater area to dissipate heat A more sophisticated version could incorporate a pressure regulating valve on the air cylinder. Then the pressure in the cylinder could be kept higher (say 10 Bar), and there would be a reserve of air under pressure in the cylinder. If there was a small leak in the tube or piping then as soon as the pressure dropped below the pressure setting on the valve (say 2 Bar) more air would be released into the tube.

On a larger machine heat dissipation could be a problem. In this case the tube could be inflated with water instead of air. The cylinder would be half filled with water and mounted with the feed pipe at the bottom. The volume in the cylinder above the water would contain air at pressure. The water is forced into the tube when the valve is opened by the trigger in the same way as before. A pressure relief valve could be incorporated in case the water boils.

Alternatively the rotating ring could be made of aluminium to dissipate heat more quickly.

An alternative method of inflating the tube would be to use gas generated in a chemical reaction as in a car air bag. The centrifugal trigger would replace the inertia trigger on an air bag.

The advantages of the inflatable tube brake as an emergency overspeed brake are: * Last resort overspeed braking is provided independent of the other systems on the machine.

* There are no electrical components so the system is not vulnerable to a lightning strike.

* High braking torque can be produced with modest inflation pressure.

* Mechanical forces are kept low, and are evenly distributed.

* Parts are simple and cheap to make * The machine is brought to a complete standstill.

* The brake can be incorporated into the mechanical parts of the machine at the maximum diameter of the hub.

A specific embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings in which Fig I is a vertical section through a 5 kW, horizontal axis, direct drive wind turbine. The centrifugal triggers, striking plates and valves are omitted for clarity.

Fig 2 is a view of the trigger mechanism at approximately full size, (area A in Fig 1) with the trigger in its normal running position and the tubes deflated Fig 3 is a view of the trigger in the tripped position with the tubes inflated Fig 4 is an elevation and section of the inflatable tube itself.

Referring to fig 1 a direct drive wind turbine consists of a stationary part (1) and a rotating part (2), which rotates about the axis (20). The blades (3) are attached to the rotating part. All the rotating parts are shown cross hatched for clarity.

On the outside diameter of the stationary part a steel ring (4) supports the electrical coils (5) and is attached to the main supporting structure of the stationary part (1).

Outside this ring a further steel ring (6) is attached to the rotating part. The attachment can either be a steel plate (7) or a lattice of steel spokes similar to a bicycle wheel.

On a 5 kW turbine the gap between the two rings is typically 15mm, the diameter of the outer ring is 660 mm, and the diameter of the inner ring is 630 mm.

Two inflatable tubes (8) are bonded to the stationary inner ring (4). They pass around the full circumference of the ring (1980 mm) They are shown inflated in Fig 1 but in the normal operating condition of the turbine they are deflated and occupy a depth of 5mm (fig 2). This leaves 10 mm clearance in the normal running of the machine.

An air cylinder (9) (Fig 1) is connected by a pipe (10) to each tube.

Between the pipe (10) and the tube (8) there is a valve (11) (Fig 2). Attached to this valve is a striking plate (12). Rotation of this striking plate about the axis (22) will open the valve and allow air from the cylinder to inflate the tube.

The striking plate is shown in the radial position when the valve is closed.

Attached to the outer rotating ring (6) is a centrifugal trigger (14) (fig 2) The trigger is restrained from moving outwards by a spring (16) on an over centre' cam (17). At a certain RPM centrifugal force on the trigger will overcome the spring and the trigger will rotate in the direction of the arrow about the axis (21). This will cause the heel of the trigger (15) to impinge on * ) the striking plate (12) which opens the valves (11) allowing air in the cylinders to inflate the tubes which, in turn, applies a braking force to the outer ring (6) Once the trigger starts to rotate outwards under the influence of centrifugal force the geometry of the cam means that the effect of the spring gets less.

After 45 degrees of rotation the spring passes over centre' and after that, spring tension acts together with centrifugal force to pull the trigger to its maximum rotation of 90 degrees. Once the trigger has been tripped it must be reset manually Each tube has its own air cylinder, valve and striking plate.

There are two triggers for security and balance, but the system would work equally well with one trigger.

The spring has an adjuster (18) so that spring tension can be accurately adjusted when the machine is serviced. A spring balance is attached to the trigger weight (23) and the spring tension is adjusted until the weight just starts to move at the correct tension in the spring balance. As the wind turbine rotates about its axis (20) the trigger at the bottom will trip first because gravity is assisting it. The spring tension must be adjusted when the trigger is at the bottom.

If the inflatable tube brake is fitted to a direct drive wind turbine in which the generator is used to provide braking in normal operation, then the inflatable tube brake can be used to bring the machine to a complete standstill, which the electrical brake cannot do. Electrical or other means can be used to open one of the valves (11) independent of the centrifugal trigger. Since the turbine will be almost brought to a standstill under the action of the electrical brake wear on the tube will be negligible when used for this purpose.

Fig 4 shows one tube on its own, inflated. Section B-B is shown at approximately fulJ size In order to facilitate the replacement of the tube the tube ring could be made with stopped ends (i.e. not a continuous ring).

Calculations for a typical 5 kW direct drive wind turbine, horizontal axis Inflation Pressure Diameter of braking surface 660 mm Braking torque required 900 Nm Braking force required @ 330 mm rad = 900/0.33 = 2727N F=muR Take mu = 0.3 R = 272710.3 = 9090 N Assume each tube is 2 cm wide, then contact area of each tube is: 3. 142 * 66 *2 = 415 cmA2 Total contact area = 830 cmA2 I Bar=lONpercmA2 Therefore pressure required in the tubes to give 9090 N force over 830 cmA2 = 1.1 Bar If it was considered necessary for one tube to be able to stop the machine on its own then the inflation pressure would need to be 2.2 bar.

Heat dissipation Assume the energy to be dissipated in stopping the machine is 31,000 J Specific heat of synthetic rubber = 1.8 K joules / Kg / degree C = 1.8 J/grmldegreeC Specific Density = 1.0 Assume half of the heat is absorbed by the steel and half by the rubber.

Volume of rubber being heated (2mm thick, 830 cmA2 contact area) = 166 cmA3 = 166 grms Temperature rise in rubber = 15500/166*1.8 = 51 degrees C

Claims

<claim-text>CLAIMS1. A wind turbine comprising or including on inflatable tube brake.</claim-text> <claim-text>
2. An emergency overspeed protection braking system for a wind turbine.comprising on inflatable tube brake.</claim-text> <claim-text>
3. A wind turbine or system claimed in ckiim I or claim 2. in which the wind turbine isa direct drive wind turbine.</claim-text> <claim-text>
4. A wind turbine or system as claimed in any of claims 1 to 3. in which the wind turbine comprises a rotating part and a thed part, and the broke acts between * the pads.* * 15
5. A wind turbine or system as claimed in claim 4, in which the brake acts directly</claim-text> <claim-text>S 5.SS*</claim-text> <claim-text>* * between the parts. * ** * * * S...</claim-text> <claim-text>*:" 6. A wind turbine or system as claimed in claim 4 or ciaim 5, in which the tube is mounted on the stationary part.</claim-text> <claim-text>T A wind turbine or syslern as claimed in any of claims 4 to 6, in which the inflations means is mounted on the stationary part ft A wind turbine or system as claimed in any preceding claim, in which the brake acts at generally the maximum diameter of a hub ot the machine.</claim-text> <claim-text>9. A wind turbine or system as claimed in any preceding claim, in which the broke brings the turbine to a complete standstill.</claim-text> <claim-text>10. A wind turbine or system as clacmed in any preceding claim, in which when the broke has been tripped it remains on until it is reset manuay.</claim-text> <claim-text>1. A wind turbine or system as claimed in any preceding claim, in wNch the tube expands radially and/or axiafly.</claim-text> <claim-text>12. A wind turbine or system as claimed in claim 11, in which the radial expansion is outwards.</claim-text> <claim-text>13. A wind turbine or system as claimed in in claim 11, in which the radial expansion is inwards. S.</claim-text> <claim-text>* . 14. A wind turbine or system as claimed in any preceding c)aim, in which the tube * comprises a fibre-reinforced inflatable tube. r': 5</claim-text> <claim-text>15. A wind turbine or system as claimed in any preceding claim, in which the fñction : *". surface is the flexible surface of the tube. a...</claim-text> <claim-text>*5se** * .
6. A wind turbine or system as ckiimed in any preceding claim, in which the tube is intSated with a gas.</claim-text> <claim-text>17. A wind turbine or system as claimed in claim 16, in which the gas is generated in a chemical reaction.</claim-text> <claim-text>18. A wind turbine o' system as claimed in any preceding claim, in which the tube is inflated with air.</claim-text> <claim-text>19. A wind turbine or system as claimed in claim 18, in which the tube is inflated from a compressed air cylinder.</claim-text> <claim-text>20. A wind turbine or system as claimed in any of claims I to 15, in which the tube is intlated with water.</claim-text> <claim-text>21. A wind turbine or system as claimed in any preceding claim, in which the inflation pressure in the tube in use is in the range 1 to 2 bar.</claim-text> <claim-text>22. A wind turbine or system as claimed iii any preceding claim, in which the broke comprises a valve. l0</claim-text> <claim-text>23. A wind turbine or system as claimed in any preceding claim, in which the broke comprises a trigger.-* . . * ** * a.</claim-text> <claim-text>* 24. A wind turbine or system as claimed in claim 23. in which the trigger is a :": 15 centrifugal trigger.</claim-text> <claim-text>: *" 25. A wind turbine or system as claimed in claim 23 or claim 24, in which the trigger r is restrained by a spring.</claim-text> <claim-text>26. A wind turbine or system as claimed in claim 25, in which the spring is provided on an over-centre cam.</claim-text> <claim-text>27. A wind turbine or system as claimed in claim 25 or claim 26, in which the tension of the spring is adjustable.</claim-text> <claim-text>28. A wind turbine as claimed in any of claims 23 to 27, in which there are provided means for activating brake independently of the trigger.</claim-text> <claim-text>29. A wind turbine or system as doirned in any preceding claim, in which the brake comprises a striking plate.</claim-text> <claim-text>30. A wind turbine as claimed in claim 29, in which the striking plate is attached to the valve and the trigger acts on the striking plate 31. A wind turbine or system as claimed in any preceding claim, in which the tube comprises a pressure release valve.32. A wind turbine or system as claimed in any preceding claim, in which the tube comprises a one-way pressure release valve.33. A wind turbine or system as claimed in claim 32, in which the one-way valve is a *...n Schrader type valve. a a... * a34. A wind turbine or system as claimed in any preceding claim, in which two : ," intlalable tubes are provided. *S *05St S *35. A wind turbine or system as claimed in claim 34, ri which the tubes are independently intlatabe.36. A wind turbine or system as claimed in any preceding claim, in which the wind turbine is a 5kW turbine.37. A wind turbine substantially as hereinbef are described with reIerence to, and as shown in, the accompanying drawings.38. A system substantially as hereirbefore described with reference to, and as shown in, the accompanying drawings.Amendments to the claims have been filed as follows.CLAIMSL A direct drive wind turbine comprising or including an inflatable tube brake.2. A direct drive wind turbine emergency oversped protection braking system the system comprising an inflatable tube brake.3. A wind turbine or system as claimed in claim I or claim 2,in which the brake acts at generally the maximum diameter of a hub at the machine.4. A wind turbine or system as claimed in any of claims 1 to 3, in which the wind turbine comprises a rotating part and a fixed part, and the brake acts between the parts. e5. A wind turbine or system as claimed in claim 4, in which the brake acts directly * between the parts. -*w.6. A wind turbine or system as claimed in claim 4 or claim 5, in which the tube is 20 mounted on the stationary part.S S..
7. A wind turbine or system as claimed in any of claims 4 to 6, in which the inflotions means is mounted on the stationary part.
8. A wind turbine or system as claimed in any preceding claim, in which the brake brings the fyrbine to a complete standstill.
9. A wind turbine or system as claimed in any preceding claim, in which when the brake has been tripped it remains on until it is reset manually.
10. A wind turbine or system as claimed in any preceding claim, in which the tube expands radially and/or axially.
11. A wind turbine or system as claimed in claim 10, in which the radial expansion is outwards.
12. A wind turbine or system as claimed in in claim 10, in which the radial expansion is inwards.
13. A wind turbine or system as claimed in any preceding claim, in which the tube comprises a fibre-reinforced inflatable tube.
14, A wind turbine or system as claimed in any preceding claim, in which the friction surface is the flexible surface of the tube. * * * .* * IS
15. A wind turbine or system as claimed in any preceding claim, in which the tube is * *** inflated with a gas.
16. A wind turbine or system as claimed in claim 15, in which the gas is generated in a chemical reaction.
17. A wind turbine or system as claimed in any preceding claim, in which Ihe tube is inflated with air.* 25
18. A wind turbine or system as claimed in claim 17, in which the tube is inflated from a compressed air cylinder.
19. A wind turbine or system as claimed in any of claims ito 14, in which the.tube is inflated with water.
20. A wind turbine or system as claimed in any preceding claim. in which the inflation pressure in the tube in use is in the range I to 2 bar.
21. A wind turbine or system as claimed in any preceding claim, in which the brake comprises a valve.
22. A wind turbine or system as claimed in any preceding claim, in which the brake comprises a trigger.
23. A wind turbine or system as claimed in claim 22, in which the tngger is a centrifugal trigger.
24. A wind turbine or system as claimed in claim 22 or claim 23, in which the trigger is restrained by a spring. *-... * ** **25. A wind turbine or system as claimed in claim 24, in which the spring is provided on an over-centre cam. "a.26. A wind turbine or system as claimed in claim 24cr claim
25. in which the tension of the spring is adjustable.27. A wind turbine as claimed in any of claims 22 to 26, in which there are provided means for activating brake independently of the trigger.28. A wind turbine or system as claimed in any preceding claim, in which the brake comprises a striking plate.29. A wind turbine or system as claimed in any preceding claim, in which the tube comprises a pressure release valve.3D, A wind turbine or system as claimed in any preceding claim, in which the tube comprises a one-way pressure release valve.-3?, A wind turbine or system as claimed in claim 30, in which the one-way valve is a Schroder type valve.ID 32. A wind turbine or system as claimed in any preceding claim, in which two inflatable tubes are provided.33. A wind turbine or system as claimed in claim 32, in which the tubes ore independently inflatable. * * * * * *34. A wind turbine or system as claimed in any preceding claim, in which the wind turbine is a 5kW turbine.35. A direct drive wind turbine substantia)ly as hereinbefore descñbed with reference to, and as shown in, the accompanying drawings.36. A direct drive wind turbine emergency overspeed brake system substantially as hereinbetore described with reference to. and as shown in, the accarnpanying di'awings.</claim-text>