DK177257B1

DK177257B1 - A Wind Turbine Blade

Info

Publication number: DK177257B1
Application number: DKPA201170133A
Authority: DK
Inventors: Peter Grabau
Original assignee: Envision Energy Denmark Aps
Priority date: 2011-03-22
Filing date: 2011-03-22
Publication date: 2012-08-20

Abstract

A partial pitch wind turbine blade is deseribed wherein the pitch system of the blade is used as a lightning receptor. As the pitch system is of a relatively large dimension, it is able to dissipate the effects of a lightning strike without damage, and removes the needs for additional blade features normally used to conduct lightning around or away from the pitch system.

Description

i DK 177257 B1 A Wind Turbine Blade

Field of the Invention

The present invention relates to a wind turbine blade, in particular a partial pitch 5 wind turbine blade having lightning conduction means.

Background of the Invention

Pitch systems are commonly used in wind turbine blades, to allow for the pitching of sections of a wind turbine blade relative to the airflow at the blade. They normally comprise hollow cylindrical structures having a first pitch section and a second pitch 10 section, with a bearing runway or roll and a plurality of ball bearings provided within the runway located at the interface between the first and second sections. The bearings permit the first pitch section of the pitch system to rotate relative to the second pitch section.

15 With reference to Fig. 1, an enlarged section of a prior art partial pitch wind turbine blade is indicated generally at 10. The blade comprises a first blade section 12 and a second blade section 14, the first and second blade sections 12,14 coupled together using pitch system 16 provided at the pitch junction of the blade 10, between the adjacent ends of the first and second blade sections 12,14. Accordingly, the second 20 blade section 14 is operable to pitch relative to the first blade section 12, via the pitch system 16.

A partial pitch wind turbine blade comprising an inner blade extender section and an outer blade extender section where the outer blade extender section is coupled to the 25 inner blade extender section by a pitch system such that the outer blade section is operable to pitch relative to the inner blade extender section which is know from EP2031245.

As the pitch system is a vital component of the wind turbine architecture, it is stan-30 dard procedure to protect the pitch system 16 from the damaging effects of a lightning strike on the wind turbine blades 10, often by positioning lightning receptors in the first and second blade sections 12,14 to attract lightning strikes away from the 2 DK 177257 B1 pitch system. Chinese Patent Application Publication No. 101793240 A discloses providing a lightning receptor on the exterior of the blade surface, with a lightning down conductor provided as a flexible wire which is routed through the interior of a pitch system provided at the root end of a blade, away from the pitch system bear-5 ings. Great care is taken to ensure that the lightning does not come into contact with the pitch system itself, by positioning the lightning down conductor such that it is spaced from the pitch system. The lightning down conductor can then be connected to the wind turbine tower or directly into the ground to dissipate the lightning strike.

10 Further alterations provided for partial pitch rotor blades include positioning lightning receptors in the blade sections adjacent the pitch system and/or providing Faraday cages about the pitch system to protect the contained components, also while routing any lightning down connectors to avoid the pitch system itself. Such approaches result in additional steps during manufacturing of the wind turbine blades, 15 resulting in increased costs, manufacturing effort, etc.

It is an object of the invention to provide a partial pitch wind turbine blade which does not require such constructional features to provide for the protection of a pitch system from the effects of a lightning strike.

20 Summary of the Invention

Accordingly, there is provided a partial pitch wind turbine blade comprising an inner blade extender section, an outer blade section and a pitch system, said outer blade section coupled to said inner blade extender section by said pitch system such that said outer blade section is operable to pitch relative to said inner blade extender sec-25 tion, wherein said pitch system comprises at least one conductive element, and wherein said partial pitch blade comprises a lightning down conductor coupled to said pitch system.

The pitch system is a substantially circular pitch system of at least 2 metres diameter 30 and wherein said at least one conductive element is provided about the external circumferential surface of said pitch system , and wherein the area of the external circumferential surface of said pitch system is at least 0.5 square metres wherein said at least one conductive element comprises a projecting member provided on the ex- 3 DK 177257 B1 temal surface of said pitch system thus said pitch system acting as a lightning receptor for said partial pitch wind turbine blade

This differs from the partial pitch blade known in EP2031245 and the teaching given 5 in Chinese Patent Application Publication No. 101793240 in that by using the pitch system itself as a lightning conductor, and directly connecting the lightning down connector to the pitch system, the need for individual lightning receptors provided around the pitch junction of a partial pitch blade is removed. This provides for a simpler construction of a partial pitch blade, which does not require relatively compli-10 cated protective elements and wiring in the vicinity of the pitch system. The lightning down conductor can be subsequently arranged to couple to any suitable conductive elements provided in a wind turbine tower structure, for receiving and dissipating a lightning strike.

15 Thereby the objective of the invention is achieved.

Preferably, the pitch system is a substantially circular pitch system of at least 2 metres diameter. Further preferably, the pitch system is approximately 2.4 metres diameter.

20

As the pitch system is of increased dimensions, this allows for the pitch system to more effectively act as a lightning receptor, being a large mass of conductive material provided at a point along the length of the wind turbine blade.

25 Preferably, said at least one conductive element is provided about the external circumferential surface of said pitch system, and wherein the area of the external circumferential surface of said pitch system is at least 0.5 square metres.

The relatively large exposed surface area provides for a good contact point to receive 30 and absorb a lightning strike. The exposed area is calculated using the formula Area = 2 π r h(r being the radius of the pitch system and h being the height of the exposed section of the pitch system). For a pitch system of approximately 2.4 metres diameter, having an exposed section width of approximately 10 centimetres, the exposed area is approximately 0.75 m2.

4 DK 177257 B1

Preferably, said pitch system comprises a plurality of bearings disposed in at least one pitch system runway, and wherein the surface contact area between said bearings and the surface of said runway is selected to conduct a lightning strike through the 5 pitch system without damaging the pitch system components.

Due to the increased dimensions of the pitch system, the contact area between the bearings of the pitch system and the surface of the runways in the pitch system is sufficiently large to effectively pass through the charge received from a lightning 10 strike on the pitch system without damaging the pitch system components.

Preferably, the pitch system comprises a 4-point contact bearing.

Preferably, said at least one conductive element comprises a projecting member pro-15 vided on the external surface of said pitch system.

The provision of a projecting member on the external surface of the pitch system acts as an attractor for a lightning discharge, ensuring that the lightning will strike at the pitch system and not at an adjacent section of the wind turbine blade.

20

Preferably, said blade comprises a plurality of projecting members evenly spaced about the external surface of said pitch system.

By providing an array of projections on the pitch system, this ensures that lightning 25 will always be drawn to the pitch system receptor, regardless of the orientation and/or pitch of the wind turbine blade.

Preferably, said at least one conductive element comprises a lightning rod (or a Franklin rod) provided on said pitch system.

30

Preferably, said partial pitch blade comprises at least one shell member provided at said pitch system, wherein said at least one conductive element is conductively coupled with at least one conductive member provided on the external surface of said at least one shell member.

5 DK 177257 B1

Providing a shell at the pitch system can prevent the pitch system from damage due to the ingress of dirt, moisture, etc. to the pitch system interior. The pitch system can be conductively coupled to the exterior of the shell to act as a suitable lightning re-5 ceptor for the wind turbine blade.

Preferably, said shell member provides an aerodynamic profile at said pitch system.

As the shell provides an aerodynamic profile at the pitch junction, this further reduces 10 any possible aerodynamic losses experienced by the wind turbine blade at the pitch junction, thereby increasing blade efficiency.

Preferably, said shell member comprises at least one lightning receptor provided on the exterior of said shell, said at least one lightning receptor conductively coupled to 15 said pitch system.

Preferably, said shell member acts to bridge a gap formed between the adjacent ends of said inner blade extender section and said outer blade section. Preferably, said shell member projects towards the trailing edge of said partial pitch wind turbine 20 blade. Preferably, said shell member comprises at least one lightning receptor provided at the trailing edge of said wind turbine blade.

Preferably, said blade comprises at least one stall fence provided at said pitch system, wherein at least one lightning receptor is provided at the distal end of said stall fence, 25 said stall fence lightning receptor conductively coupled to said pitch system, and said lightning down conductor.

A stall fence is a projection or barrier provided on the surface of the blade, and can act to prevent different sections of the blade from entering stall at the same time, by 30 preventing span-wise airflow. Using a stall fence at the pitch junction between the inner and outer blade sections can prevent interfering airflow between the different sections, and can accordingly allow for the different blade sections to have different stall characteristics.

6 DK 177257 B1

Preferably, said stall fence substantially covers the gap formed between the adjacent ends of said inner blade extender section and said outer blade section.

Preferably, the partial pitch wind turbine blade is at least 50 metres in length. Pref-5 erably the blade is approximately 60 metres in length, wherein the inner blade extender is approximately 20 metres in length and the outer blade section is approximately 40 metres in length.

There is also provided a partial pitch wind turbine comprising at least two partial 10 pitch blades as described above.

Description of the Invention

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 15 Fig. 1 is a view of the pitch junction of a prior art partial pitch wind turbine blade;

Fig. 2 is a view of the pitch junction of a first embodiment of a partial pitch wind turbine blade according to the invention;

Fig. 3 is a view of the pitch junction of a second embodiment of a partial 20 pitch wind turbine blade according to the invention;

Fig. 4 is a view of the pitch junction of a third embodiment of a partial pitch wind turbine blade according to the invention;

Fig. 5 is a view of the pitch junction of a fourth embodiment of a partial pitch wind turbine blade according to the invention; 25 Fig. 6 is a perspective view of a pitch system for use in the invention; and

Fig. 7 is a cross-sectional view of a portion of the pitch system of Fig. 6.

With reference to Fig. 2, a section of a partial pitch wind turbine blade is indicated at 20. The blade 20 comprises an inner blade extender section 22 and an outer blade 30 section 24, the outer blade section 24 coupled to said inner blade extender section 22 through pitch system 26. The blade 20 is arranged such that the outer blade section 24 is operable to pitch relative to the inner blade extender section 22 using the pitch system 26.

7 DK 177257 B1

The pitch system 26 comprises a substantially circular body having an inner section 26a and an adjacent outer section 26b. The inner and outer pitch sections 26a,26b are coupled via a plurality of ball bearings provided in at least one ball bearing roll or 5 runway (not shown), the ball bearings allowing for the outer pitch section 26b to pitch relative to the inner pitch section 26a. In use, the inner blade extender section 22 is mounted to the inner pitch section 26a of the pitch system 26, and the outer blade section 24 is mounted to the outer pitch section 26b of the pitch system 26.

10 Preferably, the pitch system 26 comprises a 4-point contact bearing, i.e. the ball bearings contact the surface of the runways at four points. It will be understood that the pitch system 26 may comprise a plurality of bearing rolls or runways.

To facilitate the pitching of the outer blade section 24, a gap is defined between the 15 adjacent ends of the blade sections 22,24, the pitch system 26 bridging said gap between the blade sections 22,24. Accordingly, a portion of the external surface 27 of the pitch system 26 is exposed in the gap between the ends of the blade sections 22,24.

20 The pitch system 26 is formed from an electrically conductive material, such that the exposed external surface 27 of the pitch system 26 acts as a lightning receptor for the wind turbine blade 20. As the pitch system 26 of the present invention may be relatively large, the large mass of conductive material provides a strong attraction for a lightning strike.

25

The blade 20 further comprises a first lightning down conductor (indicated by dashed line 28) provided in the inner blade extender section 22 of the blade 20 and a second lightning down conductor (indicated by dashed line 30) provided in the outer blade section 24 of the blade 20. The lightning down conductors 28,30 are operable to con-30 duct a lightning strike through the interior of a wind turbine blade to a connected wind turbine tower and/or to ground.

In the embodiment of Fig. 2, the first lightning down conductor 28 is arranged such that a first end 28a of the conductor 28 is conductively coupled directly to the inner 8 DK 177257 B1 pitch section 26a of the body of the pitch system 26, with a second end (not shown) of the conductor 28 located at the root end of the wind turbine blade 20. The second end of the first down conductor 28 is arranged to connect to conduction means provided in the wind turbine tower structure suitable for absorbing a lightning strike.

5

Similarly, the second lightning down conductor 30 is arranged such that a first end 30a of the conductor 30 is conductively coupled directly to the outer pitch section 26b of the body of the pitch system 26. The second down conductor 30 is further arranged in the outer blade section 24 of the blade 20 such that a second end (not 10 shown) of the down conductor 30 is coupled to a lightning receptor provided at the tip end of the outer blade section 24.

In the case of a lightning strike at the pitch system 26, the lightning is conducted through the body of the pitch system 26 to the first down conductor 28, and subse-15 quently conducted to the greater wind turbine structure for safe distribution of the lightning strike to ground.

In occasions where a lightning strike may occur at a location on the outer blade section 24 of the blade 20, e.g. at a lightning receptor provided at the tip end of the outer 20 blade section 24, the lightning strike is conducted from the lightning receptor through the second lightning down conductor 30, to the outer pitch section 26b of the pitch system 26. The lightning strike is then conducted through the body of the pitch system 26 to the inner pitch section 26a of the pitch system 26, and down through the first lightning down conductor 28 to the wind turbine tower.

25

Accordingly, the pitch system 26 itself can be used as a lightning receptor and/or a part of the lightning conduction system of the wind turbine blade 20. This is in contrast to prior art systems, which seek to protect the pitch system from the effects of a lightning strike, e.g. by preventing a direct lightning strike on the pitch system and/or 30 routing lightning away from or around the pitch system. The use of the pitch system 26 in this manner provides for a simpler design of wind turbine blade 20, resulting in reduced costs and relatively easier manufacture.

9 DK 177257 B1

The pitch system 26 is preferably selected such that the pitch system 26 can absorb the effects of a lightning strike, without damaging the pitch system components. Accordingly, the pitch system 26 is of a relatively large construction, and the contained bearings and bearing rolls are arranged to withstand a lightning strike passing through 5 the pitch system 26.

Preferably, the pitch system 26 has a diameter of at least 2 metres, most preferably approximately 2.4 metres. Preferably, the gap provided at the pitch junction between the ends of the blade sections 22,24 is selected so that sufficient surface area of the 10 pitch system 26 is exposed to a lightning strike. Preferably the gap is at least 10 centimetres wide.

It will be understood that such a large pitch system 26 provides a sufficient contact area within the pitch system structure between the ball bearings and the surface of the 15 bearing rolls to pass a lightning strike through the body of the pitch system 26 without damage.

The wind turbine blade 20 may also comprise a plurality of secondary lighting receptors 32 provided on the exterior surface of the blade sections 22,24, said lightning 20 receptors 32 conductively connected to said first and second lightning down conductors 28,30.

Further embodiments and enhancements to the blade 20 of Fig. 2 are now described with reference to Figs. 3-5, and indicated respectively at 20a,20b,20c. For the purpose 25 of clarity the same reference numerals have been re-used, where appropriate. Furthermore, first and second lightning down conductors and secondary lightning receptors are not illustrated in Figs. 3-5, but it will be understood that similar conductive elements may be provided in each embodiment of wind turbine blades according to the invention. It will be understood that the features described in each embodiment 30 may be used alone or in combination with the features of the other embodiments.

In Fig. 3, the wind turbine blade 20a comprises a plurality of shaped projections 34 provided on the external surface 27 of the pitch system 26. The projections 34 are formed of a conductive material, and act to attract a lightning strike (indicated at 35) 10 DK 177257 B1 to the pitch system 26. In Fig. 3, a first set of projections 34a are provided on the surface of the inner pitch section 26a and a second set of projections 34b are provided on the surface of the outer pitch section 26b. The projections 34a,34b are arranged in an equally spaced arrangement about the surface of the pitch system 26, to ensure that 5 there is an equal distribution of projections regardless of the pitch angle of the outer pitch section 26b of the pitch system 26.

In the embodiment shown in Fig. 3, the projections 34a,34b are substantially conical in shape, but it will be understood that any suitable shape of projection may be used 10 for the purposes of attracting lightning.

In Fig. 4, the wind turbine blade 20b comprises a pair of lightning rods 36 (also known as Franklin rods) provided at the surface of the pitch system 26. The lightning rods 36 are shaped to attract a lightning strike directly to the pitch system 26,and are 15 conductively coupled to the surface 27 of the pitch system 26. In Fig. 4, a first lightning rod 36a is provided adjacent the inner blade extender section 22 and a second lightning rod 36b is provided adjacent the outer blade section 24. However, it will be understood that any number or arrangement of lightning rods may be used. Furthermore, it will be understood that any suitable shape of lightning rod or Franklin rod 20 may be provided at the pitch system 26.

In Fig, 5, the wind turbine blade 20c comprises a pair of shell elements 38a,38b provided at the pitch junction between the ends of the blade sections 22,24. The shell elements 38a,38b shown in Fig. 5 are arranged to cover the pitch system 26 (shown 25 in outline) and further extend into the gap provided between the trailing edges of the blade sections 22,24, but it will be understood that any suitable shape of shell elements 38a,38b may be provided, e.g. the shell elements 38a,38b may be provided only about the pitch system 26, or may be provided only at the gap between the trailing edges of the blade sections 22,24.

30

The shell elements 38a,38b can act to bridge the gap provided at the pitch junction between the blade sections 22,24, and accordingly reduce aerodynamic losses formed at the pitch junction, e.g. due to tip losses, and/or the leakage of air from the pressure side of the wind turbine blade 20c to the suction side. The shell elements 38a,38b are 11 DK 177257 B1 coupled to the pitch system 26, such that the first shell element 38a is coupled to the inner pitch section 26a and the second shell element 38b is coupled to the outer pitch section 26b.

5 A plurality of lightning receptors 40,41 are provided on the exterior of the shell elements 38a,38b, the lightning receptors 40,41 conductively coupled to the body of the pitch system 26. In the event of a lightning strike on a lightning receptor 40,41, the lightning is conducted from the receptor 40,41 to the body of the pitch system 26, and from there via a lightning down conductor (not shown) to the greater wind tur-10 bine structure and ground.

In the embodiment shown in Fig. 5, a plurality of lightning receptors 40 are provided adjacent the location of the pitch system 26, with additional receptors 41 provided on the shell elements 38a,38b located at the trailing edge of the wind turbine blade 20c.

15 However, it will be understood that any arrangement of lightning receptors 40,41 on the shell elements 38a,38b may be used, e.g. the receptors 40 may be evenly spaced about the entire shell member body.

In the embodiment of Fig. 5, the shell elements 38a,38b are shaped to have an aero-20 dynamic airfoil profile substantially corresponding to the profile of the adjacent blade sections 22,24. It will be understood that the shell elements 38a,38b may comprise any suitable airfoil profile for use at the pitch junction. Additionally or alternatively, it will be understood that the shell elements 38a,38b may be shaped to provide a seal about the pitch system 26, to prevent the ingress of moisture and/or dirt to the pitch 25 system interior.

It will be understood that the above described projections 34a,34b; lightning rods 36a,36b; and shell element lightning receptors 40,41 are arranged to be conductively coupled through the body of the pitch system 26 to contained lightning down conduc-30 tors 28,30, to allow for the conduction of a lightning strike from the pitch system 26 to the greater wind turbine structure and ground.

A further embodiment may utilise at least one stall fence (not shown) provided at the pitch system 26, projecting from the surface of the blade 20,20a,20b,20c at least par- 12 DK 177257 B1 tially above said pitch system 26. The stall fence acts to prevent span-wise airflow along the surface of the blade, and can additionally act to cover the gap provided between the adjacent ends of the inner and outer blade sections 22,24. At least one lightning receptor is provided in the upper end of the stall fence, the stall fence light-5 ning receptor conductively coupled through the body of the pitch system 26 to the lightning down conductors 28,30. The elevated height of such a stall fence lightning receptor, relative to the adjacent blade surfaces, would provide increased attraction for a lightning strike, which can then be conducted directly through the contained pitch system and to the coupled lightning down conductor.

10

An example of a pitch system which may be used in the blades of the invention is indicated at 126 in Figs. 6 and 7. The pitch system 126 comprises an inner pitch ring 128 and an outer pitch ring 130. The inner pitch ring 128 is of a smaller diameter than, but concentric with, the outer pitch ring 130, such that the pitch system 126 has 15 a combined circular ring structure. In use, an inner blade extender section of a partial pitch blade (being relatively wider) is coupled to the outer pitch ring 130 of the pitch system 26, and the corresponding outer blade section (being relatively narrower) is coupled to the inner pitch ring 128.

20 With reference to the cross-sectional view of Fig. 7, the pitch system 126 comprises two adjacent rolls of bearings 132a, 132b provided in runways 134 located at the surface interface between the inner pitch ring 128 and the outer pitch ring 130. The pitch system 126 is arranged to provide sufficient contact areas between the bearings 132a,132b and the surfaces of the pitch rings 128,130 to safely conduct a lightning 25 strike through the body of the pitch system 126 without damage to the pitch system 126.

In use of said wind turbine blades 20,20a,20b,20c, the root end (not shown) of the inner blade extender 22 is mounted to a rotor hub of a wind turbine, the rotor hub 30 provided at a nacelle on top of a wind turbine tower. The rotor hub is arranged to rotate on said nacelle, wherein the outer blade sections 24 may be pitched relative to the inner blade extenders 22 in order to control the wind turbine operation (in effect adjusting the angle of attack of the airflow at the outer blade sections).

13 DK 177257 B1

It will be understood that the invention may apply to a wind turbine comprising any number of partial pitch blades. The invention is particularly advantageous for two-bladed partial pitch wind turbines, as the rotation of a two-bladed wind turbine will result in positions wherein the blades are substantially horizontal in orientation, at 5 which time the relatively large pitch systems of the blades are likely to be the most attractive exposed conductive elements of the wind turbine, and thereby most likely to receive a lightning strike. In such systems, the use of the blade pitch system as a lightning conductor, and accordingly coupled to lightning down conductors, provides a relatively simple and efficient blade construction.

10

It will be understood that the invention may be used in combination with any other suitable lightning receptor means not shown in the accompanying figures, e.g. lightning receptors provided at the outer distal ends of the wind turbine blades, lightning receptors provided at the upper end of the wind turbine tower and nacelle, etc.

15

The invention is not limited to the embodiment described herein, and may be modified or adapted without departing from the scope of the present invention.

Claims

A partial-pitch wind turbine blade (10, 20) comprising an inner wing extender section (12, 22), an outer wing section (14, 24) and a pitch system (16, 26), wherein the outer wing section (14,24) is coupled to said inner wing extender section (12, 22) by said pitch system (16,26) such that the outer wing section (14, 24) is adapted to rotate in proportion to said inner wing extender section (12, 22), wherein said pitch system (16, 26) comprises at least one conductive element and said partial pitch wing (10, 20) comprises a lightning conductor (28, 30) coupled to the pitch system 10 (16, 26), wherein said pitch system (16, 26) is essentially a circular pitch system (16, 26) of at least 2 meters in diameter and said at least one conductor element is provided around the outer peripheral surface of the pitch system (16, 26) and wherein the area of the outer peripheral surface of the pitch system (16, 26) is at least 0.5 square meter, characterized in that said m one conductive element comprising a protruding portion (34) provided on the outer surface of said pitch system (16, 26), said pitch system (16,26) acting as a lightning receptor for said partial-pitch wind turbine blade (10,20).

A partial-pitch wind turbine blade (10, 20) according to claim 1, characterized in that said 20 wings comprise a plurality of protruding elements (34) at regular intervals around the outer surface of said pitch system (16, 26).

A partial-pitch wind turbine blade (10, 20) according to any one of claims 1 or 2, characterized in that said at least one conductive element comprises a lightning conductor provided on the pitch system (16, 26).

A partial pitch wind turbine blade (10, 20) according to any one of the preceding claims, characterized in that said split pitch wing comprises at least one shell element (38) provided by said pitch system (16, 26), wherein said at least one conductive member is conductively coupled to at least one conductive member (40, 41) provided on the outer surface of said at least one shell member (38).

A partial-pitch wind turbine blade (10, 20) according to claim 4, characterized in that said DK 177257 B1 2 shell element (38) provides an aerodynamic profile at said pitch system (16, 26).

A partial-pitch wind turbine blade (10, 20) according to any one of the preceding claims, characterized in that the blade (10, 20) comprises at least one stall fence provided by said pitch system (16, 26), wherein at least one lightning receptor (40, 41) is provided at the far end of said stall fence, said stall fence lightning receptor (40, 41) being conductively coupled to said pitch system (16, 26) and said lightning conductor (28, 30). 10

A partial-pitch wind turbine comprising at least two partial-pitch blades (10, 20) according to any one of claims 1-6.