WO2012105971A1

WO2012105971A1 - Nacelle-mounted maintenance system for wind turbines

Info

Publication number: WO2012105971A1
Application number: PCT/US2011/023480
Authority: WO
Inventors: Matthew K. Smith
Original assignee: Smith Matthew K
Priority date: 2011-02-02
Filing date: 2011-02-02
Publication date: 2012-08-09

Abstract

The nacelle-mounted maintenance system includes a number of temporarily installed devices for handling large, heavy components in a large, tower-mounted wind turbine nacelle (N), particularly a nacelle (N) having a removable top (L). The system includes rollers and tracks (10) that are temporarily installed along opposite upper edges of the nacelle (N) and corresponding edges of the nacelle top (L), enabling the top (L) to be rolled laterally aside rather than lowering it to the ground for access to the nacelle interior. A sequence of increasingly greater capacity portable cranes is lifted to the nacelle (N), with the conventional small capacity on-board crane (C) lifting the first temporary crane (22), the first crane (22) lifting the second crane (26), and the second crane (26) lifting the third crane (30). The third portable crane (30) has sufficient capacity to remove and replace a generator (G) or other large component.

Description

NACELLE-MOUNTED MAINTENANCE SYSTEM FOR WIND TURBINES

TECHNICAL FIELD

The present invention relates generally to heavy maintenance for large capacity wind turbines or wind generators, and particularly to a nacelle-mounted maintenance system for wind turbines that precludes the need for ground-based cranes for the removal and installation of heavy equipment to and from the nacelle.

BACKGROUND ART

The generation of electricity by means of renewable energy has become an increasingly popular concept in recent decades. Large, tower-mounted wind turbines or wind generators have been found to be an efficient means of producing electricity in many areas. As a result, many manufacturers have developed large wind turbines or wind generators for the production of relatively large electrical power output. Of course, these wind turbines or generators from different manufacturers differ from one another in many respects, e.g., the configurations of their power nacelles (bottom, top, or side access, etc.) and various details of the propeller or rotor, gear train, generator, and controls. A universal factor is the size and weight of the components required to generate substantial electrical energy, with the generators alone often weighing ten tons or more in a wind turbine capable of generating one or more megawatts of electrical power.

A major problem that generally occurs with such wind turbines is due to their location in the field. Obviously, such wind turbines are optimally placed where there is a fair amount of wind at most times. As a result they are generally installed at higher elevations in hilly or mountainous terrain, usually with poor road access. Moreover, the nacelles containing the power generating equipment are always installed atop relatively tall towers in order to provide ground clearance for the large diameter rotors used and to raise the rotor height into the higher velocity winds above the ground.

Accordingly, maintenance and repair of such wind turbines is not a trivial task. Large lift capacity helicopters are exceedingly expensive to operate, and the weight of major components that may require removal and replacement may be greater than the lifting capacity of such helicopters in any event. As a result, most major maintenance is accomplished by means of a large, high capacity ground-based crane, with the crane being trucked to the site in sections requiring perhaps fourteen truckloads for a 1.5 megawatt wind turbine. In addition, in many cases the entire top of the nacelle must be removed to access the interior and the large components contained therein, depending upon the manufacturer of the wind turbine. Conventionally, the crane must lift the top from the nacelle and lower it to the ground before the component (generator, etc.) can be disconnected from the remaining apparatus and the crane used to remove the component. The process must then be reversed to install the new or refurbished component and to replace the top of the nacelle. As can be seen, this is an extremely costly operation, with a need clearly being indicated for a more efficient and less costly means of removing and replacing components in a wind turbine nacelle having a removable top. Thus, a nacelle-mounted maintenance system for wind turbines solving the aforementioned problems is desired.

DISCLOSURE OF INVENTION

The nacelle-mounted maintenance system for wind turbines greatly facilitates the removal and replacement of large components to and from the elevated nacelle of such a wind turbine. The system enables workers in the field to open the nacelle as required for access to the interior components of the nacelle, and to remove and replace major components within the nacelle without need of a large ground-based crane or other extremely heavy equipment. All of the components of the system may be carried upon or in a single conventional semi-trailer. The system is adapted particularly for wind turbines wherein the nacelles have removable tops for access to the nacelle interior for major work. The system includes temporarily installed tracks or rollers that are installed along the opposite edges of the top and corresponding opposite edges of the underlying upper edges of the nacelle. The top may then be rolled laterally to one side of the nacelle, without requiring heavy equipment to lower the top to the ground.

The system further includes three portable, temporarily installed cranes of increasingly greater capacity, each of which is lifted into the open top of the nacelle in turn. The nacelle or upper tower includes a conventional relatively light capacity on-board crane that is used to lift the first of the three temporary cranes, with the first temporary crane then lifting the second temporary crane, and the second crane in turn lifting the base and upper sections of the third or largest capacity temporary crane into place. The base of the largest capacity crane is secured to hard points within the nacelle, and the upper mast of this largest crane is lifted from the surface and erected on the base of this largest crane. The assembled high capacity crane is then used to remove and replace major components within the nacelle, e.g., the generator, which may weigh up to ten tons or perhaps more. When the major component or components have been removed and replaced as required, the temporary cranes are removed and lowered to the ground in reverse order of their installation, the top is rolled back into place, and the temporary tracks and rollers are removed from the top and nacelle and lowered to the ground using the conventional crane of the wind turbine.

These and other features of the present invention will become readily apparent upon further review of the following specification and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is an environmental perspective view of a wind turbine nacelle with the nacelle walls and top shown in broken lines, showing the upper hatch open and the conventional light duty on-board crane lifting the lid roller tracks of a nacelle-mounted maintenance system for wind turbines according to the present invention up to the nacelle as a first step in the installation of the system.

Fig. 2 is an exploded perspective view of the wind turbine nacelle with the lid removed to show the installation of the lid roller tracks of a nacelle-mounted maintenance system for wind turbines according to the present invention between the lid and nacelle.

Fig. 3 is an elevation view in section through the upper portion of the nacelle after installation of the lid roller tracks of Fig. 2 between the nacelle and lid, with the lid being closed over the nacelle.

Fig. 4 is an elevation view in section similar to Fig. 3, but showing the nacelle lid opened on its previously installed tracks.

Fig. 5 is a perspective view of the nacelle with the lid rolled open and the on-board crane being used to lift the first of three temporary cranes of the nacelle-mounted maintenance system for wind turbines according to the present invention from the surface to the nacelle.

Fig. 6 is a perspective view showing the first temporary crane of Fig. 5 installed on the nacelle and being used to lift the second temporary crane of the system from the surface to the nacelle.

Fig. 7 is a perspective view showing the second temporary crane of Fig. 6 installed and being used to lift the base of the heaviest capacity temporary crane of the system from the surface to the nacelle. Fig. 8 is a perspective view showing the base of the largest capacity temporary crane of Fig. 7 installed on the nacelle and the second temporary crane being used to lift the upper portion of the largest capacity crane.

Fig. 9 is a perspective view similar to Figs. 5 through 8, but showing the upper portion of the largest capacity temporary crane in its folded state and secured to its base.

Fig. 10 is a perspective view similar to Figs. 5 through 9, but showing the erected largest capacity temporary crane being used to lift or lower a generator or other heavy component to or from the nacelle.

Similar reference characters denote corresponding features consistently throughout the attached drawings.

BEST MODES FOR CARRYING OUT THE INVENTION

The nacelle-mounted maintenance system for wind turbines is a system providing for the heavy maintenance of wind turbines and the like. The system obviates the need for multiple truckloads of equipment in order to access, remove, and replace large and heavy components in the tower-mounted nacelle. The system includes two sets of roller track assemblies that are installed between the upper edge of the nacelle and its overlying lid, thus permitting the lid to be rolled back to expose the interior of the nacelle without requiring complete removal of the lid and lowering the lid to the surface. The system also includes a plurality of different capacity portable cranes, each successively larger capacity crane being lifted to the nacelle by the previous smaller capacity crane. The largest capacity crane then removes and replaces the heavy component (e.g., generator) from within the nacelle, and the process is reversed to complete the job. While the system and equipment used may be expanded to be applied to a large number of different wind turbine configurations, it is particularly well adapted for use with large capacity General Electric wind turbines having a generating capacity on the order of 1.5 megawatts. Such wind turbines are provided with removable lids or roofs on their nacelles, and are also equipped with a conventional light duty on-board crane.

Fig. 1 of the drawings illustrates an initial step in the process. Most of the apparatus shown in Fig. 1 is conventional, i.e., a wind turbine W having a nacelle N (shown in broken lines in Fig. 1) atop a tower T, with the nacelle N containing a generator G driven by a rotor or propeller R (shown partially in Fig. 2) through a rotor shaft S and gearbox B. The nacelle N has a removable lid L or roof, with the lid L having a hatch H therein. A relatively light duty on-board crane C is conventionally stored within the upper tower or nacelle N or the top of the tower T, and may be deployed in different ways depending upon the specific model and manufacture of the wind turbine. In some wind turbines, the on-board crane is extended through a rear door, or a lower door is opened for the operation of a winch. In others, the on- board crane remains in the upper tower, with equipment being transferred by hand from the crane to the nacelle. In Fig. 1, the conventional on-board crane C is shown erected from within the nacelle N, with its mast extended upwardly through the open hatch H and its davit or boom extended laterally so that its distal end will clear the side of the nacelle N. Its cable or line is shown lifting a roller track assembly 10 upwardly to the nacelle N, where the roller track assembly 10 will be taken into the nacelle N through the open hatch H for installation. The specific deployment of the conventional on-board crane C as shown in Fig. 1 may not be in accordance with the deployment used by various wind turbine manufacturers, but serves as a generic illustration of the deployment and operation of the on-board crane C.

Fig. 2 provides an exploded perspective view, showing the relative positions of the two roller track assemblies 10 for their installation. First and second roller track assemblies 10 are removably installed at opposite ends of the nacelle N between the lower portion of the nacelle N and its lid or roof L. Conventionally, the nacelle lid L is bolted to the lower portion of the nacelle N by a large number of bolts that secure the inner flanges F of the nacelle N and its lid L to one another. The installation of the roller track assemblies 10 is accomplished by removing the bolts from one end and along most of each side of the nacelle and lid attachment, thereby allowing the free end of the lid L to be flexed upwardly by a suitable jack or other lifting tool, which may be lifted to the nacelle N by the low capacity onboard crane C along with the roller track assemblies 10. The nacelle N and its lid L are generally formed of glass fiber composite materials that provide sufficient flexibility to allow one end of the lid L to be raised by several inches even though the opposite end of the lid L is still secured to the underlying nacelle N.

Each roller track assembly 10 comprises a lower or nacelle attachment track 12 having opposite nacelle attachment end flanges 14 and an upper or lid attachment track 16 having opposite lid attachment end flanges 18. The two tracks 12 and 16 are joined by roller assemblies and brackets 20. The first roller track assembly 10 is installed between the nacelle N and its lid L by bolting the two nacelle attachment end flanges 14 of the lower track 12 to the nacelle flanges F and by bolting the two lid attachment end flanges 18 of the upper track 16 to the nacelle flanges F of the lid L, with the result being essentially as shown in Fig. 3 of the drawings. The remaining bolts securing the opposite end of the nacelle lid L to the o

nacelle N are then removed, and the second roller track assembly 10 is installed between the nacelle N and its lid L, substantially as shown for the first roller track installation illustrated in Fig. 3. The upper portion of the on-board crane C is lowered or removed to allow the lid L to be rolled laterally from its position above the nacelle N to open the nacelle N, generally as shown in Fig. 4 of the drawings.

Fig. 5 illustrates the next step in the procedure. It is necessary to install and use a sequence of increasingly larger capacity cranes in order to eventually install a temporary or portable crane having sufficient lifting capacity to handle a large component (e.g., generator, etc.) in a large-capacity wind turbine. This is because the lighter capacity cranes do not have the lifting capability to lift the weight of a crane having sufficient lifting capacity to handle a multi-ton load, such as a wind turbine generator, which may weigh as much as ten tons or more. For example, the on-board crane C may have a capacity of only about five hundred pounds in order to provide relatively lightweight, thereby enabling technicians to assemble and handle this crane manually. While this is sufficient for lifting relatively lightweight components (including the first portable crane 22) to and from the nacelle N, the on-board crane C has insufficient capacity to handle loads much heavier than the first portable crane 22. Accordingly, the light-duty on-board crane C is extended from its base within the nacelle N and its cable is lowered to the surface to lift the first crane 22 of three temporarily installed portable cranes to the nacelle N. The first portable crane 22 is shown being lifted to the nacelle N by the on-board crane C in Fig. 5. This light-duty portable crane 22 may have a lifting capacity of around one thousand pounds or so, and weighs perhaps a few hundred pounds, including its powered winch 24 (e.g., electrically or hydraulically powered, etc.), cable, and other equipment. As noted in the discussion of the on-board crane C in Fig. 1, the illustration of the deployment and operation of the on-board crane C in Fig. 5 is generic, and any conventional on-board crane C is serviceable that can be deployed to hoist the first portable crane 22 to the nacelle N.

Once the first portable crane 22 has been lifted to the nacelle N it is installed in the nacelle N generally as shown in Fig. 6, i.e., by mounting it upon a hard point within the nacelle N, such as a conventional gearbox pillow support (not shown) within the nacelle N. This first portable crane 22 is then used to lift the medium capacity second portable crane 26 up to the nacelle N for temporary installation therein. The second portable crane 26 is also powered, e.g., having an electric or hydraulic winch 28, with the second crane 26 having a lifting capacity on the order of three thousand pounds capacity. The weight of this second portable crane 26 is too great for the light duty on-board crane C, but can be handled by the somewhat greater capacity of the first portable crane 22. The second portable crane 26 may be installed opposite the first portable crane 22 to the opposite gearbox pillow support within the nacelle N from that used to mount the first portable crane 22, with the longer boom or arm of the second portable crane 26 extended across the width of the nacelle N, generally as shown in Figs. 7 and 8 of the drawings.

Once the second or medium capacity portable crane 26 has been installed, the first or lighter capacity portable crane 22 is removed from its installation within the nacelle N and lowered to the surface by the second portable crane 26. The second crane 26 is then used to lift the components of the third or last portable crane 30 to the nacelle N; this third portable crane 30 is shown in its entirety in Figs. 9 and 10. Fig. 7 illustrates the lifting of the base portion 32 of the third, highest capacity portable crane 30 to the nacelle N, with Fig. 8 showing the base portion 32 installed in the nacelle N and the upper portion 34 being lifted to the nacelle N. The third portable crane 30 has a capacity preferably of at least ten tons (twenty thousand pounds) in order to handle the weight of a major wind turbine component such as the generator G. As a result, the assembled third crane 30 is too heavy for the second portable crane 26 to lift as a single unit and it must be broken down into at least two separate components, i.e., a base portion 32 and upper portion 34, as well as additional bracing required to provide a solid installation.

The base 32 of this third portable crane is installed upon a hard point within the nacelle N opposite the mounting of the second portable crane 26, e.g., the conventional gearbox pillow support opposite that to which the second portable crane 26 is installed. The lifting capacity and corresponding loads that may be imposed upon the third portable crane 30 are sufficiently high as to produce potentially damaging bending loads upon the base 32 of the third crane and the structure to which it is attached within the nacelle N. Accordingly, an additional longitudinally disposed brace 36 is lifted from the surface by the intermediate capacity portable crane 26 and installed between a suitable hard point within the nacelle N and the upper end of the base 32 of the third crane 30, with a laterally disposed brace 38 being installed from the upper end of the base 32 and a laterally opposite hard point such as the opposite gearbox pillow block support to which the second portable crane 26 is installed. When this has been accomplished, the upper portion 34 and powered winch 40 (shown installed in Fig. 10) of the third, heavy duty portable crane 30 may be lifted from the surface, by the second or intermediate capacity portable crane 26 as shown in Fig. 8.

The upper portion 34 of the third portable crane 30 is pivotally or foldably attached to the base portion 32 of the third crane, generally as shown in Fig. 9 of the drawings. The i>

adjacent mating ends of the lower and upper portions 32 and 34 of the third portable crane 30 have mating lugs or ears for the installation of a hinge pintle therethrough, with the completed hinge 42 structure being shown in Figs. 9 and 10. The lower portion 32 of the third crane 30 also has a powered extender 44 extending therefrom, e.g., hydraulic strut, etc. The upper end of this strut or extender 44 is attached to the upper portion 34 of the third crane 30 after the lower and upper portions 32 and 34 are assembled, with the extender 44 serving to erect the massive upper portion 34 from its folded state as shown in Fig. 9 to its extended state as shown in Fig. 10.

When the upper portion 34 of the third, heavy duty crane 30 has been attached to the lower portion 32 and the powered extension strut 44 connected between the two components 32 and 34, generally as shown in Fig. 9, the upper portion 34 of the highest capacity third portable crane 30 may be erected by actuating the extender or strut 44, resulting in a configuration generally as shown in Fig. 10 of the drawings. The radially extending arms or davit 46 of the third crane 30 may be swung or pivoted atop the upper portion 34 to position the distal end over the component (e.g., generator G) to be removed from the nacelle N. The component is disassembled from the remaining structure of the nacelle N, and lifted over the wall of the nacelle N by means of the third crane 30. The generator G (or other massive component) may then be lowered to the surface, generally as illustrated in Fig. 10 of the drawings.

The process is reversed for the installation of a replacement unit in the nacelle N. A new or repaired generator G or other component may be lifted back into the nacelle N by the high capacity third portable crane 30, with the appearance of this portion of the replacement operation being very much as shown in Fig. 10. Once the new or repaired component has been installed, the third crane 30 is used to lift the second or intermediate capacity crane 26 back up to the nacelle N, where it is temporarily installed laterally opposite the third crane 30. Once this has been accomplished, the upper portion 34 of the third crane 30 is removed and lowered to the surface by the intermediate capacity crane 26, somewhat as appears in Fig. 8 of the drawings. The longitudinal and lateral braces 36 and 38 of the lower portion 32 are then removed and lowered to the surface, with the lower portion 32 following, generally as shown in Fig. 7. The intermediate capacity second portable crane 26 is then used to lift the light capacity first portable crane 22 up to the nacelle N. Once the first portable crane 22 has been installed, it is used to lower the second portable crane 26 to the surface, somewhat as shown in Fig. 6 of the drawings. When the second portable crane 26 has been lowered to the surface, the first or lightest capacity portable crane 22 is removed from its installation in the nacelle N and the on-board crane C is erected. The on-board crane C is then used to lower the light capacity first portable crane 22 to the surface, generally as pictured in Fig. 5 of the drawings. The on- board crane C is then lowered (if necessary, depending upon the specific configuration and installation of the on-board crane) to permit the lid L of the nacelle N to be rolled back into position directly above the nacelle N, generally as shown in the elevation view in section of Fig. 3. One set of the two roller track assemblies 10 is then unbolted from its attachment to the lid and nacelle flanges F, and at least a few bolts are reinstalled to secure the lid and nacelle flanges F to one another at the end where the roller track assembly 10 was removed. The on-board crane C may then be extended through the hatch H in the nacelle lid L, or through a rear door or floor hatch, etc., depending upon the specific configuration of the wind turbine, and used to lower the removed roller track assembly 10 to the surface. The remaining roller track assembly 10 is then removed and the remaining lid attachment bolts installed to secure the nacelle lid L to the nacelle N, and the last removed roller track assembly 10 is lowered to the surface by the on-board crane C. The on-board crane C is then lowered and removed from its installation in the nacelle C, if so installed, and stowed in its conventional storage location at the top of the tower T or other location, as needed. The hatch cover is then reinstalled in the hatch H of the nacelle lid L to complete the operation.

The above-described maintenance system for wind turbines is particularly adaptable for use with large capacity wind turbines of General Electric manufacture, which have top opening nacelles generally as shown and described herein. However, it will be seen that the maintenance system disclosed herein may be adapted to various models of wind turbines, depending upon their specific configurations. In any adaptation, the system is particularly advantageous in that it eliminates the need for a large and tall, high capacity ground-based or "downtower" crane to accomplish the removal and installation of heavy components in a tower-mounted wind generator nacelle. The equipment required for the present maintenance system may be carried upon or in a single semi-trailer, as opposed to the numerous large and bulky components required for the assembly of a ground-based crane, which may require up to fourteen semi-trailer loads to carry all of the components of such a large ground-based crane. Accordingly, the present nacelle-mounted maintenance system for wind turbines will greatly reduce the cost of maintenance equipment transport, with associated reductions in delivery and setup time for such equipment and a corresponding reduction in downtime for the operators of such turbines. _{j q}

It is to be understood that the present invention is not limited to the embodiment described above, but encompasses any and all embodiments within the scope of the following claims.

Claims

1. A nacelle-mounted maintenance system for a wind turbine, the wind turbine having a light capacity on-board crane and a tower-mounted nacelle, the nacelle having a lid removably attached thereto, the maintenance system comprising:

first and second roller track assemblies, the roller track assemblies being adapted for lifting to the nacelle by the on-board crane and for temporary installation between the nacelle and the lid of the nacelle; and

a plurality of portable cranes, each of the portable cranes being adapted for temporary installation within the nacelle, each of the portable cranes having a different lifting capacity from one another.

2. The nacelle-mounted maintenance system for a wind turbine according to claim 1 , wherein the plurality of portable cranes comprises a first portable crane having a light lifting capacity, a second portable crane having a medium lifting capacity, and a third portable crane having a heavy lifting capacity.

3. The nacelle-mounted maintenance system for a wind turbine according to claim 1, further including a wind turbine in combination therewith.

4. The nacelle-mounted maintenance system for a wind turbine according to claim 1, wherein each of the portable cranes is selected from the group consisting of electrically powered cranes and hydraulically powered cranes.

5. The nacelle-mounted maintenance system for a wind turbine according to claim 1, wherein the plurality of portable cranes includes a third portable crane having a heavy lifting capacity, the third portable crane having a base and an upper portion temporarily and foldably attached to the base.

6. The nacelle-mounted maintenance system for a wind turbine according to claim 5, further including a powered extender disposed between the base and the upper portion of the third portable crane.

7. The nacelle-mounted maintenance system for a wind turbine according to claim 5, wherein the third portable crane further includes a longitudinally disposed brace and a laterally disposed brace.

8. A nacelle-mounted maintenance system for a wind turbine, the wind turbine having a light capacity on-board crane and a tower-mounted nacelle, the nacelle having a lid removably attached thereto, the maintenance system comprising:

a nacelle lid support apparatus adapted for lifting to the nacelle by the on-board crane for temporary installation between the nacelle and the lid;

a first, light capacity portable crane adapted for lifting to the nacelle by the on-board crane and for temporary installation in the nacelle;

a second, medium capacity portable crane adapted for lifting to the nacelle by the first portable crane and for temporary installation in the nacelle; and

a third, heavy capacity portable crane adapted for lifting to the nacelle by the second portable crane and for temporary installation in the nacelle.

9. The nacelle-mounted maintenance system for a wind turbine according to claim 8, wherein the nacelle lid support apparatus comprises first and second roller track assemblies.

10. The nacelle-mounted maintenance system for a wind turbine according to claim 8, further including a wind turbine in combination therewith.

11. The nacelle-mounted maintenance system for a wind turbine according to claim 8, wherein each of the portable cranes is selected from the group consisting of electrically powered cranes and hydraulically powered cranes.

12. The nacelle-mounted maintenance system for a wind turbine according to claim 8, wherein the third portable crane has a base and an upper portion temporarily and foldably attached to the base.

13. The nacelle-mounted maintenance system for a wind turbine according to claim 12, further including a powered extender disposed between the base and the upper portion of the third portable crane.

14. The nacelle-mounted maintenance system for a wind turbine according to claim 8, wherein the third portable crane further includes a longitudinally disposed brace and a laterally disposed brace.

15. A wind turbine and a nacelle-mounted maintenance system therefor, comprising in combination:

a wind turbine tower;

a light capacity on-board crane disposed with the tower;

a nacelle permanently mounted atop the tower;

a nacelle lid removably attached atop the nacelle;

a nacelle lid support apparatus adapted for lifting to the nacelle by the on-board crane for temporary installation between the nacelle and the lid; and

16. The wind turbine and nacelle-mounted maintenance system combination according to claim 15, wherein the nacelle lid support apparatus comprises first and second roller track assemblies.

17. The wind turbine and nacelle-mounted maintenance system combination according to claim 15, wherein the plurality of portable cranes comprise a first portable crane having a light lifting capacity, a second portable crane having a medium lifting capacity, and a third portable crane having a heavy lifting capacity.

18. The wind turbine and nacelle-mounted maintenance system combination according to claim 15, wherein each of the portable cranes is selected from the group consisting of electrically powered cranes and hydraulically powered cranes.

19. The wind turbine and nacelle-mounted maintenance system combination according to claim 15, wherein the plurality of portable cranes includes a third portable crane having a heavy lifting capacity, the third portable crane having a base and an upper portion temporarily and foldably attached to the base.

20. The wind turbine and nacelle-mounted maintenance system combination according to claim 1 , further including:

a powered extender disposed between the base and the upper portion of the third portable crane;

a longitudinally disposed brace; and

a laterally disposed brace.