An offshore wind turbine with an annular guiding system

Abstract

An offshore wind turbine generator (1) comprising a hoisting arrangement for hoisting and / or lowering a main component (6) to / from the nacelle (4) is disclosed The hoisting arrangement comprises an up-tower crane (5) and a guiding system. The guiding system comprises an annular element (9) arranged circumferentially with respect to the tower (3), at least two abutment elements (12) mounted on the annular element (9) and arranged in abutment with the tower (3), and at least one hoisting winch connected to the annular element (9) for hoisting and / or lowering the annular element (9) along the tower (3). At least one connecting element (11) interconnects a connecting interface (8) and / or the main component (6) to the guiding system. The at least one hoisting winch is configured to be controlled in a coordinated manner with control of the up-tower crane (5), so as to cause the annular element (9) and the suspended main component (6) to be synchronously hoisted and / or lowered.

Description

[0001] AN OFFSHORE WIND TURBINE WITH AN ANNULAR GUIDING SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to an offshore wind turbine generator with a hoisting arrangement for hoisting and / or lowering a main component to / from an up-tower position, such as to / from a nacelle. The main component being hoisted or lowered is guided by means of a guiding system with an annular element arranged circumferentially with respect to the tower.

[0004] BACKGROUND OF THE INVENTION

[0005] Wind turbine generators are normally provided with a number of heavy main components, such as gearbox, generator, transformer, main bearing, etc. Such main components are often arranged in or near a nacelle located at the top of a tower. Thus, in the case that it is necessary to replace one of the main components, the component to be replaced needs to be lowered from the nacelle, and a replacing component needs to be hoisted to the nacelle and installed there. This requires suitable hoisting gear, e.g. with sufficient hoisting capacity to handle the weight of the main components. Furthermore, the main components need to be guided during the lowering or hoisting, in order to ensure that they are lowered or hoisted in a controlled manner, e.g. minimising the risk of the components colliding with the tower and / or the nacelle structure.

[0006] For onshore wind turbine generators, a ground based crane and a ground based guiding system, e.g. including tag lines, may be applied for lowering and hoisting main components from and to the nacelle. However, for offshore wind turbine generators, this is not an option. Therefore, for offshore wind turbine generators, it is desirable to apply an up-tower crane, e.g. arranged in or on the nacelle, or on the tower at a position near the top of the tower. However, this introduces a risk of collisions between the main component being lowered or hoisted and the tower of the wind turbine generator. Moreover, this risk is increased due to the fact that offshore wind turbine generators are expected to be more exposed to impact from wind and waves than onshore wind turbine generators.

[0007] DESCRIPTION OF THE INVENTION

[0008] It is an object of embodiments of the invention to provide an offshore wind turbine generator with a hoisting arrangement, where the risk of collisions between a main component being lowered from or hoisted to the nacelle is minimised in an easy and reliable manner.

[0009] It is a further object of embodiments of the invention to provide a method for replacing a main component in a nacelle of an offshore wind turbine generator, in which the risk of collisions between the main component being lowered from or hoisted to the nacelle is minimised in an easy and reliable manner.

[0010] According to a first aspect the invention provides an offshore wind turbine generator comprising a foundation, a tower supported by the foundation, a nacelle mounted on the tower, and a hoisting arrangement for hoisting and / or lowering a main component to / from the nacelle, wherein the hoisting arrangement comprises:

[0011] - an up-tower crane arranged in, on or near the nacelle, the up-tower crane comprising a connecting interface for connecting a suspended main component to the up-tower crane,

[0012] - a guiding system, and

[0013] - at least one connecting element interconnecting the connecting interface and / or the main component to the guiding system, so as to enable a suspended main component being hoisted or lowered by means of the up- tower crane to be guided by means of the guiding system, wherein the guiding system comprises: an annular element arranged circumferentially with respect to the tower, at least two abutment elements mounted on the annular element and arranged in abutment with the tower, so as to allow the annular element to slide along the tower,

[0014] - at least one hoisting winch connected to the annular element for hoisting and / or lowering the annular element along the tower, the at least one hoisting winch being configured to be controlled in a coordinated manner with control of the up-tower crane, so as to cause the annular element and the suspended main component to be synchronously hoisted and / or lowered.

[0015] Thus, according to the first aspect the invention provides an offshore wind turbine generator. In the present context the term 'offshore wind turbine generator' should be interpreted to mean a wind turbine generator that is positioned at an offshore location, such as at sea or on a lake.

[0016] The offshore wind turbine generator comprises a foundation, a tower supported by the foundation and a nacelle mounted on the tower. A number of main components, e.g. a gearbox, a generator, a transformer, a main bearing, etc., are housed in the nacelle.

[0017] The offshore wind turbine generator further comprises a hoisting arrangement for hoisting and / or lowering a main component to / from the nacelle, e.g. as part of a process for replacing one of the main components being housed in the nacelle.

[0018] The hoisting arrangement comprises an up-tower crane arranged in, on or near the nacelle, e.g. on an upper part of the tower, such as immediately below the nacelle, and a guiding system. The up-tower crane comprises a connecting interface for connecting a main component to the up-tower crane, thus allowing the main component to be suspended from the up-tower crane while being lowered or hoisted. The connecting interface could, e.g., be in the form of a hook arranged at an end of a hoisting wire, or it could be any other suitable kind of connecting interface which allows a main component to be detachably connected to the up-tower crane, so as to enable that the main component is lowered or hoisted by means of the up-tower crane.

[0019] When a main component is being lowered from or hoisted to the nacelle by means of the up-tower crane, the connecting interface of the up-tower crane and / or the main component is / are connected to the guiding system by means of at least one connecting element. The main component is thus guided by means of the guiding system from a down-tower position to an up-tower position, or from an up-tower position to a down-tower position. This will be described in further detail below.

[0020] The guiding system comprises an annular element, at least two abutment elements and at least one hoisting winch. The annular element is arranged circumferentially with respect to the tower, i.e. it fully or partly encircles the tower. For instance, a centre point of the annular element may substantially coincide with a longitudinal centre axis defined by the tower.

[0021] The at least two abutment elements are mounted on the annular element, and they are arranged in abutment with the tower. Thus, each of the at least two abutment elements establishes a connection between the tower and the annular element being arranged circumferentially with respect thereto. Accordingly, the annular element supports against the tower, via the abutment elements, and thereby the annular element is allowed to slide along the tower, the tower thereby forming a guide for movement of the annular element.

[0022] The annular element is further connected to the at least one hoisting winch. Accordingly, the annular element can be hoisted and / or lowered by appropriately operating the at least one hoisting winch. Since the annular element is arranged circumferentially with respect to the tower, and in abutment with the tower via the at least two abutment elements, the hoisting or lowering movement of the annular element is guided by the tower. Accordingly, the path followed by the annular element is well defined. In particular, movements of the annular element along a direction being substantially transverse the longitudinal centre axis defined by the tower are essentially prevented. The at least one hoisting winch is configured to be controlled in a coordinated manner with control of the up-tower crane. Thus, the lowering or hoisting movement of a main component being suspended from the up-tower crane is coordinated with the lowering or hoisting movement of the annular element. Accordingly, the suspended main component and the annular element are moved in a synchronous manner.

[0023] Since the connecting interface of the up-tower crane and / or the main component is / are connected to the guiding system, e.g. to the annular element, by means of the at least one connecting element, the hoisting and / or lowering movement of the suspended main component is further guided by the tower in the same manner as the guiding of the annular element described above. Accordingly, movements of the main component along a direction being substantially transverse the longitudinal centre axis defined by the tower are essentially prevented, and thereby the risk of collisions between the suspended main component and the tower is minimised. The coordinated control of the at least one hoisting winch and the up-tower crane ensures that accurate guidance of the main component is maintained throughout the entire hoisting or lowering movement.

[0024] Thus, the risk of collisions between a main component being hoisted or lowered and the tower is minimised in an easy, accurate, reliable and cost effective manner.

[0025] The tower may be conical, and the at least two abutment elements may be mounted with a variable distance to the annular element. When the tower is conical, the distance between an inner surface of the annular element and an outer surface of the tower will depend on the vertical position of the annular element along the tower, in the sense that the distance will be largest at the top of the tower, near the nacelle, and smallest at the bottom of the tower, near the base and the connection to the foundation. Therefore, according to this embodiment, the at least two abutment elements are configured in such a manner that their distance to the annular element is variable. Thereby the position of the abutment elements can be adjusted during the lowering or hoisting of the annular element, depending on the vertical position of the annular element, so as to adapt to the conical shape of the tower and to ensure that the abutment elements remain in abutting contact with the tower during the entire lowering or hoisting process. Accordingly, accurate and reliable guiding of the annular element is ensured throughout the lowering or hoisting.

[0026] The distance between the at least two abutment elements and the annular element may be actively controllable. This could, e.g., be obtained by means of actuators connected to each of the abutment elements. According to this embodiment, the abutment elements are actively, and preferably continuously, positioned at a distance from the annular element which arranges the abutment elements in abutting contact with the tower, as the annular element is lowered or hoisted. Thereby the required abutment is efficiently ensured, without risking that the abutting contact inhibits the lowering or hoisting movement of the annular element.

[0027] As an alternative, the distance between the at least two abutment elements and the annular element may be passively controlled, e.g. by means of biasing elements, such as springs, biasing the abutment elements in a direction away from the annular element and towards the tower. This will at least ensure appropriate abutment as the annular element is hoisted, and the distance between the annular element and the tower therefore increases. However, during lowering of the annular element it must be ensured that the lowering is performed in such a manner that a sufficient force is applied to the abutment elements for pushing them towards the annular element, against the biasing force.

[0028] The annular element may be a rigid element. For instance, the annular element may be formed from a number of beams or arms joined together to form an annular structure. This ensures that the guiding provided by the annular element and the tower in cooperation is very accurate and reliable.

[0029] The guiding system may comprise at least two hoisting winches. The at least two hoisting winches may be connected to the annular element via at least two different connecting points. The at least two hoisting winches may advantageously be synchronously controlled, so as to ensure uniform lowering or hoisting of the annular element.

[0030] The connecting element may be a rigid element, e.g. in the form of one or more arms. According to this embodiment, the connection between the connecting interface of the up-tower crane and / or the main component and the guiding system is a rigid connection. This ensures that a substantially constant and well defined distance is maintained between the suspended main component and the guiding system, e.g. between the main component and the annular element, and thereby also with a safe distance to the tower. Thus, it is ensured that the suspended main component is guided in a safe, reliable and well defined manner.

[0031] The foundation may be a floating foundation. According to this embodiment, the foundation of the wind turbine generator is not fixedly connected to the seabed. Instead, the foundation is connected to one or more anchoring points on or in the seabed via wires, chains or similar connectors. Thus, the exact position of the wind turbine generator is allowed to shift within a certain area defined by the position of the one or more anchoring points and the length of the connectors, subject to impact from wind and waves. Furthermore, offshore wind turbine generators with floating foundations follow vertical movements of passing waves, and they may tilt due to the impact of waves. Thus, offshore wind turbine generators with floating foundations are more exposed to impact from wind and waves than offshore wind turbines with fixed foundations. Accordingly, the risk of horizontal movements of suspended main components, and thereby collisions with the tower, may be considered particularly high in such wind turbine generators, and therefore the present invention is particularly relevant in this case.

[0032] As an alternative, the foundation may be a fixed foundation, such as a jacket, a monopile or other suitable kinds of bottom fixed structures.

[0033] The suspended main component may be a gearbox, part of a gearbox, a generator, a sub-component for a generator, a main bearing, a blade bearing or a transformer. All of these components are relatively heavy, and they are often arranged in or near the nacelle. Thus, it is relevant to lower or hoist such components by means of a hosting arrangement as described above.

[0034] Each of the at least two abutment elements may comprise one or more wheels. According to this embodiment, the abutment elements may roll along the tower during hoisting or lowering of the annular element, thus minimising friction between the abutment elements and the tower. As an alternative, the abutment elements may be provided with sliding surfaces.

[0035] The at least one connecting element may interconnect the connecting interface and / or the main component with the annular element. According to this embodiment, the main component is kept at a distance from the annular element which is defined by the dimensions of the at least one connecting element. The annual element, in turn, ensures that a certain distance to the tower is maintained.

[0036] According to a second aspect the invention provides a method for replacing a main component in a nacelle of an offshore wind turbine generator, the offshore wind turbine generator comprising a foundation, a tower supported by the foundation, a nacelle mounted on the tower, and a hoisting arrangement, the hoisting arrangement comprising a guiding system, the method comprising the steps of:

[0037] - arranging an annular element of the guiding system circumferentially with respect to the tower, and arranging at least two abutment elements mounted on the annular element in abutment with the tower,

[0038] - connecting the annular element to at least one hoisting winch of the guiding system,

[0039] - dismantling the main component from an installed position in the nacelle, connecting the main component to a connecting interface of an up-tower crane of the hoisting arrangement, connecting the connecting interface and / or the main component to the annular element by means of at least one connecting element, and

[0040] - lowering the main component from the nacelle towards a down-tower position of the offshore wind turbine generator, by means of the up-tower crane, while guiding the main component by means of the guiding system by lowering the annular element by operating the at least one hoisting winch synchronously with operation of the up-tower crane, and while keeping the at least two abutment elements in abutment with the tower.

[0041] The method according to the second aspect of the invention may advantageously be performed at an offshore wind turbine generator according to the first aspect of the invention. The remarks set forth above with reference to the first aspect of the invention are therefore equally applicable here.

[0042] In the method according to the second aspect of the invention, an annular element of the guiding system is initially arranged circumferentially with respect to the tower, the annular element having at least two abutment elements mounted thereon. Furthermore, the at least two abutment elements are arranged in abutment with the tower, so as to enable the annular element to be guided by the tower. The annular element is further connected to at least one hoisting winch.

[0043] Next, a main component to be replaced is dismantled from an installed position in the nacelle, and possibly moved within the nacelle to a position where it is possible for the dismantled main component to exit the nacelle. Next, the dismantled main component is connected to a connecting interface of an up- tower crane of the hoisting arrangement of the offshore wind turbine generator.

[0044] Furthermore, the connecting interface and / or the main component connected thereto, is / are connected to the annular element by means of at least one connecting element, e.g. at least one rigid connecting element.

[0045] The main component is then lowered from the nacelle towards a down-tower position of the offshore wind turbine generator. This is done by appropriately operating the up-tower crane, while the at least one hoisting winch is operated synchronously with the operation of the up-tower crane. Thereby the annular element is lowered synchronously with the lowering of the main component, which is connected thereto by means of the at least one connecting element. Thus, the main component is guided by means of the synchronously moving annular element.

[0046] Furthermore, the at least two abutment elements are kept in abutment with the tower during the lowering process described above. Thereby the annular element is guided by the tower. Accordingly, during the lowering process, the main component is guided by the synchronously moving annular element, and the annular element is, in turn, guided by the tower. Thus, accurate and reliable guiding of the main component is obtained, and the risk of collisions between the main component and the tower is efficiently minimised.

[0047] The tower may be conical, and the method may further comprise the step of actively controlling a distance between the annular element and each of the at least two abutment elements during the step of lowering the main component and the annular element, so as to keep the at least two abutment elements in abutment with the tower. This has already been described in detail above with reference to the first aspect of the invention.

[0048] When the lowering of the main component has been completed, a replacement main component may be connected to the connecting interface of the up-tower crane, and the replacement main component may be hoisted towards the nacelle by means of the up-tower crane, while being guided by means of the guiding system, essentially in the manner described above. Once the replacement main component has reached the nacelle, it may be installed therein, thus replacing the previously lowered main component.

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The invention will now be described in further detail with reference to the accompanying drawings in which Fig. 1 shows an offshore wind turbine generator according to an embodiment of the invention, and

[0051] Figs. 2-5 illustrate details of the offshore wind turbine generator of Fig. 1 during replacement of a main component in accordance with a method according to an embodiment of the invention.

[0052] DETAILED DESCRIPTION OF THE DRAWINGS

[0053] Fig. 1 shows an offshore wind turbine generator 1 according to an embodiment of the invention. The offshore wind turbine generator 1 comprises a foundation (not shown) with a landing platform 2. The foundation could, e.g., be a floating foundation. A tower 3 is supported by the foundation, and a nacelle 4 is mounted on top of the tower 3. The nacelle 4 houses various main components, e.g. in the form of a gearbox, a generator, a transformer and / or a main bearing.

[0054] An up-tower crane 5 is mounted in or on the nacelle 4 and protrudes from the top of the nacelle 4. A main component 6 to be lowered from the nacelle 4 is connected to the up-tower crane 5 via a wire 7 and a connecting interface 8, e.g. in the form of a hook or similar device allowing the main component 6 to be connected or attached to the wire 7, and thus to the hoisting mechanism of the up-tower crane 5. Thus, the main component 6 is suspended from the up-tower crane 5.

[0055] The offshore wind turbine generator 1 further comprises an annular element 9 arranged circumferentially with respect to the tower 3. The annular element 9 is connected to at least one hoisting winch (not shown) arranged in the nacelle, via a number of wires 10, two of which are shown. Accordingly, the annular element 9 can be hoisted or lowered along the tower 3 by appropriately operating the at least one hoisting winch.

[0056] The annular element 9 further has at least two abutment elements (not shown) mounted thereon, the abutment elements being arranged in abutment with the tower 2. When the annular element 9 is hoisted or lowered along the tower 3 as described above, the abutment elements remain in abutment with the tower 3, even though the tower 3 is conical, and thereby the movement of the annular element 9 is guided by the tower 3.

[0057] The main component 6 and / or the connecting interface 8 is / are connected to the annular element 9 by means of a connecting element 11. Accordingly, when the main component 6 is hoisted or lowered by appropriately operating the up-tower crane 5, it is guided by the annular element 9 which is in turn guided by the tower 3, as described above. Furthermore, the at least one hoisting winch and the up-tower crane 5 are controlled in a coordinated or synchronous manner. Thus, the hoisting or lowering movements of the annular element 9 and the main component 6, respectively, are coordinated or synchronized. This ensures that the guiding of the main component 6 described above is provided in a very easy, accurate and reliable manner, thus minimising the risk of collisions between the main component 6 and the tower 3 or other parts of the offshore wind turbine generator 1.

[0058] Figs. 2 and 3 show an upper part of the wind turbine generator 1 of Fig. 1, showing the upper part of the tower 3, the nacelle 4 and the up-tower crane 5. Fig. 2 is a perspective view and Fig. 3 is a front view. The connecting element 11 interconnecting the annular element 9 and the main component 6 and / or the connecting interface 8 can be clearly seen.

[0059] In Fig. 2 three abutment elements 12 are shown, each being mounted on the annular element 9 and arranged in abutment with the tower 3. Fig. 3 shows two of the abutment elements 12. The position of each abutment element 12 relative to the annular element 9 can be adjusted by means of an actuator 13. Thus, regardless of a distance between an inner circumference of the annular element 9 and the tower 3, the abutment elements 12 can be arranged in abutment with the tower 3 by means of the actuators 13.

[0060] In Figs. 2 and 3, the annular element 9 as well as the main component 6 is arranged at an up-tower position, immediately below the nacelle 4. Due to the conical shape of the tower 3, the cross sectional diameter of the tower 3 is the smallest possible, and therefore the distance between the inner circumference of the annular element 9 and the tower 3 is the largest possible. Accordingly, in this position the abutment elements 12 must be arranged with a large distance to the annular element 9, in order to ensure that they are arranged in abutment with the tower 3. In Fig. 4, the main component 6 and the annular element 9 have been lowered along the tower 3 to a position defining a distance to the nacelle as well as to the landing platform. This could, e.g., be the position shown in Fig. 1. Since the cross sectional diameter of the tower 3 is larger at this position than in the position illustrated in Figs. 2 and 3, the abutment elements 12 have been moved closer to the annular element 9, by means of the actuators 13, in order to ensure that the abutment elements 12 remain in abutment with the tower 3, while avoiding that this abutting contact inhibits the downward movement of the annular element 9.

[0061] In Fig. 5, the main component 6 and the annular element 9 have been moved to a down-tower position close to the landing platform 2. It can be seen that the abutment elements 12 have been moved even closer to the annular element 9, in accordance with the even larger cross sectional diameter of the tower 3.

Claims

CLAIMS1. An offshore wind turbine generator (1) comprising a foundation, a tower (3) supported by the foundation, a nacelle (4) mounted on the tower (3), and a hoisting arrangement for hoisting and / or lowering a main component (6) to / from the nacelle (4), wherein the hoisting arrangement comprises:- an up-tower crane (5) arranged in, on or near the nacelle (4), the up- tower crane (5) comprising a connecting interface (8) for connecting a suspended main component (6) to the up-tower crane (5),- a guiding system, and- at least one connecting element (11) interconnecting the connecting interface (8) and / or the main component (6) to the guiding system, so as to enable a suspended main component (6) being hoisted or lowered by means of the up-tower crane (5) to be guided by means of the guiding system, wherein the guiding system comprises:- an annular element (9) arranged circumferentially with respect to the tower (3),- at least two abutment elements (12) mounted on the annular element (9) and arranged in abutment with the tower (3), so as to allow the annular element (9) to slide along the tower (3),- at least one hoisting winch connected to the annular element (9) for hoisting and / or lowering the annular element (9) along the tower (3), the at least one hoisting winch being configured to be controlled in a coordinated manner with control of the up-tower crane (5), so as to cause the annular element (9) and the suspended main component (6) to be synchronously hoisted and / or lowered.

2. The wind turbine generator (1) according to claim 1, wherein the tower (3) is conical, and wherein the at least two abutment elements (12) are mounted with a variable distance to the annular element (9).

3. The wind turbine generator (1) according to claim 2, wherein the distance between the at least two abutment elements (12) and the annular element (9) is actively controllable.

4. The wind turbine generator (1) according to any of the preceding claims, wherein the annular element (9) is a rigid element.

5. The wind turbine generator (1) according to any of the preceding claims, wherein the guiding system comprises at least two hoisting winches.

6. The wind turbine generator (1) according to any of the preceding claims, wherein the connecting element (11) is a rigid element.

7. The wind turbine generator (1) according to any of the preceding claims, wherein the foundation is a floating foundation.

8. The wind turbine generator (1) according to any of the preceding claims, wherein the suspended main component (6) is a gearbox, part of a gearbox, a generator, a main bearing, a blade bearing or a transformer.

9. The wind turbine generator (1) according to any of the preceding claims, wherein each of the at least two abutment elements (12) comprises one or more wheels.

10. The wind turbine generator (1) according to any of the preceding claims, wherein the at least one connecting element (11) interconnects the connecting interface (8) and / or the main component (6) with the annular element (9).

11. A method for replacing a main component (6) in a nacelle (4) of an offshore wind turbine generator (1), the offshore wind turbine generator (1) comprising a foundation, a tower (3) supported by the foundation, a nacelle (4) mounted onthe tower (3), and a hoisting arrangement, the hoisting arrangement comprising a guiding system, the method comprising the steps of:- arranging an annular element (9) of the guiding system circumferentially with respect to the tower (3), and arranging at least two abutment elements (12) mounted on the annular element (9) in abutment with the tower (3),- connecting the annular element (9) to at least one hoisting winch of the guiding system,- dismantling the main component (6) from an installed position in the nacelle (4),- connecting the main component (6) to a connecting interface (8) of an up-tower crane (5) of the hoisting arrangement,- connecting the connecting interface (8) and / or the main component (6) to the annular element (9) by means of at least one connecting element (11), and- lowering the main component (6) from the nacelle (4) towards a downtower position of the offshore wind turbine generator (1), by means of the up-tower crane (5), while guiding the main component (6) by means of the guiding system by lowering the annular element (9) by operating the at least one hoisting winch synchronously with operation of the up-tower crane (5), and while keeping the at least two abutment elements (12) in abutment with the tower (3).

12. The method according to claim 11, wherein the tower (3) is conical, and wherein the method further comprises the step of actively controlling a distance between the annular element (9) and each of the at least two abutment elements (12) during the step of lowering the main component (6) and the annular element (9), so as to keep the at least two abutment elements (12) in abutment with the tower (3).

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