Patent Publication Number: US-11661923-B2

Title: Lift system mountable in a nacelle of a wind turbine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/642,169 filed Feb. 26, 2020, which was a national entry of International Application PCT/CA2018/051449 filed Nov. 15, 2018 claiming priority to Canadian patent application 3,012,945 filed Jul. 31, 2018 and claiming the benefit of U.S. Provisional Patent Application Ser. No. 62/589,778 filed Nov. 22, 2017. 
    
    
     FIELD 
     This application relates to lift systems, especially to a lifting appliance mountable on wind turbines. 
     BACKGROUND 
     Wind turbines require periodic maintenance to remain operable. Due to the extreme height at which many wind turbines operate, maintaining and/or replacing turbine parts (e.g. a rotor, blade, main bearing, main shaft, intermediate shaft, gearbox, etc.) becomes problematic. For reasons of safety and practicality, turbine parts are generally lowered to ground level for maintenance and/or replacement. Typically, a crane is used to lower (and then re-raise) the parts to be maintained or replaced. 
     When replacing a damaged intermediate shaft (“IMS”) from a wind turbine gearbox, current state-of-the-art procedure for removing the gearbox involves using a large conventional crane on the ground, which is a machine having a capacity of 300 tons and a boom length of 100 meters or more. The crane is used to remove the upper housing of the gearbox (weighing approximately 4 tons), after which the IMS is removed and replaced with the crane. This is a tricky procedure and potentially dangerous in high wind speeds. 
     There have been a number of cranes developed in the prior art specifically adapted for maintenance of gearboxes. However, prior art cranes generally suffer from a lack of sufficient lifting capacity, which prevents them from having the ability to remove the upper housing of the gearbox. Accordingly, the upper housing must be lifted using a separate gantry device which lifts the upper housing to allow the IMS to be subsequently lifted with a crane. 
     There remains a need for a turbine-mounted crane that is capable of lifting, moving and lowering an upper housing of a gearbox and/or gearbox components of a wind turbine, particularly the turbine IMS shaft, and which preferably can be rapidly dismounted to permit closing a nacelle atop a tower of the wind turbine. 
     SUMMARY 
     In one aspect, there is provided a lift system mountable in a nacelle of a wind turbine, the lift system comprising: a mounting interface removably securable to a generator in the nacelle of the wind turbine; and, a knuckle boom rotatably and removably mounted on the mounting interface, the knuckle boom comprising an extendable boom arm, the extendable boom arm comprising a translatable boom section slidably mounted on the boom arm. 
     In another aspect, there is provided a lift system mountable in a nacelle of a wind turbine, the lift system comprising: a mounting interface removably securable to a generator in the nacelle of the wind turbine, the mounting interface comprising a first plurality of through apertures; a swivel removably mounted on the mounting interface, the swivel comprising a second plurality of through apertures each concentrically aligned with one through aperture of the first plurality of through apertures when the swivel is mounted on the mounting interface, the swivel secured to the mounting interface by a plurality of non-threaded pins removably inserted through the concentrically aligned through apertures of the first and second plurality of through apertures, the removable non-threaded pin permitting mounting of the swivel on and dismounting of the swivel from the mounting interface; a knuckle boom rotatably mounted on the swivel, the knuckle boom rotatable on the swivel about a vertical axis, the knuckle boom comprising an extendable boom arm, the extendable boom arm comprising a translatable boom section slidably mounted on the boom arm; a power pack mounted on the mounting interface, the power pack comprising an electric motor and a hydraulic pump, the power pack not extending beyond a maximum height to permit closing the nacelle when the mounting interface is mounted on the generator and the knuckle boom is dismounted from the mounting interface; and, a hydraulic motor for operating the swivel, the hydraulic motor connectable to the hydraulic pump by hydraulic lines and quick connect hydraulic fittings. 
     In another aspect, there is provided a method of mounting a lift system in a nacelle on top of a standing wind turbine, the method comprising: lifting a mounting interface of the lift system with a power pack and a swivel mounted thereon up to the nacelle using an existing service crane permanently mounted in the nacelle of the wind turbine, the swivel having a hydraulic motor mounted thereon for operating the swivel, the power pack comprising a hydraulic pump for powering the hydraulic motor and an electric motor for powering the hydraulic pump, the mounting interface comprising a hydraulic fluid reservoir for providing hydraulic fluid to the hydraulic pump; mounting the mounting interface on a generator in the nacelle; lifting a knuckle boom using the service crane, and mounting the knuckle boom on the swivel; lifting a chain bag of the knuckle boom using the service crane, and mounting the chain bag to the knuckle boom; lifting a support bracket of the lift system with a control unit thereon using the service crane, and mounting the support bracket on the mounting interface; and, connecting the control unit to the electric motor in the power pack. 
     In an embodiment, the lift system may further comprise a swivel removably mounted on the mounting interface. The knuckle boom may be rigidly mounted on the swivel. The swivel may be rotatable to rotate the knuckle boom mounted thereon about a vertical axis. The swivel may comprise a rotatable portion on which the knuckle boom is mounted. The swivel may comprise a fixed portion comprising a first through aperture. The mounting interface may comprise a second through aperture concentrically aligned with the first through aperture when the swivel is mounted on the mounting interface. The swivel may be secured to the mounting interface by a non-threaded pin removably inserted through the first and second through apertures. The removable non-threaded pin permits mounting of the swivel on and dismounting of the swivel from the mounting interface. The first through aperture, the second through aperture and the removable non-threaded pin may comprise a plurality of (for example four) first through apertures, second through apertures and removable non-threaded pins. 
     The mounting interface may further comprise a third through aperture through which a support pin may be inserted. The swivel may comprise a support surface having an indent in which the support pin is engaged so that the swivel rests on the support pin when the swivel is mounted on the mounting interface. The third through aperture and the support pin may comprise a plurality of (for example four) third through apertures and support pins. 
     The mounting interface may comprise clamps that engage protruding elements of the generator to securely and removably mount the mounting interface on a top of the generator. The clamps may comprise hooking portions that engage the protruding elements. The clamps may comprise bolts for tightening the clamps on the generator. 
     In an embodiment, the lift system may further comprise a hydraulic motor for operating the swivel. The hydraulic motor may be mounted on the swivel or on the mounting interface, preferably on the swivel. 
     In an embodiment, the lift system may further comprise a power pack mounted on the mounting interface. The power pack may comprise a hydraulic pump and an electric motor to power the hydraulic pump. The hydraulic pump may be fluidly connected to the hydraulic motor to power the hydraulic motor. The hydraulic pump may be connectable to the hydraulic motor through hydraulic lines and hydraulic fittings. The hydraulic fittings are preferably quick connect hydraulic fittings. The hydraulic pump may be fluidly connected to a hydraulic manifold, the hydraulic manifold fluidly connected to the hydraulic motor and to hydraulically operated components (e.g. hydraulic cylinders) of the knuckle boom. The hydraulic pump may be fluidly connected to one or more hydraulic fluid reservoirs to receive hydraulic fluid for powering the hydraulic motor and the hydraulically operated components of the knuckle boom. The mounting interface may comprise the one or more hydraulic fluid reservoirs. The one or more hydraulic fluid reservoirs may be one or more hollow side rails of the mounting interface in fluid communication with the hydraulic pump mounted on the mounting interface. The power pack mounted on the mounting interface preferably does not extend beyond a maximum height so that the nacelle may be closed when the mounting interface remains mounted on the generator and the knuckle boom is dismounted from the mounting interface. Doors of the nacelle may be completely closed when the knuckle boom is dismounted and the mounting interface remains mounted on the generator. 
     In an embodiment, the lift system may further comprise a support bracket removably mounted on the mounting interface, the support bracket adapted to securely support a control unit thereon. The support bracket and the mounting interface may comprise mated through apertures that receive removable mounting pins to mount the support bracket on the mounting interface. 
     The lift system is modular. The modularity of the lift system permits lifting components of the lift system up to the nacelle using the existing service crane of the wind turbine, and rapidly dismounting the knuckle boom to permit closing doors of the nacelle in the event of inclement weather without dismounting all of the lift system components from the nacelle. The lift system is capable of lifting heavier loads than the existing service cranes in the nacelles of commercial wind turbines. For example, the lift system is capable of lifting an upper housing of a gearbox of a commercial wind turbine. 
     Further features will be described or will become apparent in the course of the following detailed description. It should be understood that each feature described herein may be utilized in any combination with any one or more of the other described features, and that each feature does not necessarily rely on the presence of another feature except where evident to one of skill in the art. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For clearer understanding, preferred embodiments will now be described in detail by way of example, with reference to the accompanying drawings, in which: 
         FIG.  1    depicts a rear perspective view of a lift system mounted on a generator of a wind turbine; 
         FIG.  2    depicts a front perspective view of the lift system of  FIG.  1    mounted on the generator showing a knuckle boom of the lift system swiveled into a different position; 
         FIG.  3    depicts a rear perspective view of the lift system of  FIG.  1    without showing the generator; 
         FIG.  4    depicts another perspective view of the lift system of  FIG.  3    showing a knuckle boom of the lift system swiveled into a different position; 
         FIG.  5    depicts a rear perspective view of a mounting interface of the lift system of  FIG.  1   ; 
         FIG.  6    depicts a front perspective view of the mounting interface of  FIG.  5   ; 
         FIG.  7    depicts a top view of the mounting interface of  FIG.  5   ; 
         FIG.  8    depicts a side view of the mounting interface of  FIG.  5   ; 
         FIG.  9    depicts an exploded front perspective view of the mounting interface of  FIG.  5   ; 
         FIG.  10    depicts a rear perspective view of the exploded view of  FIG.  9   ; 
         FIG.  11    depicts a magnified top front perspective view showing a swivel mounted on the mounting interface of  FIG.  5   ; 
         FIG.  12    depicts a bottom front perspective view  FIG.  10   ; 
         FIG.  13    depicts a magnified outside view of a pin arrangement for mounting the swivel on the interface; 
         FIG.  14    depicts a magnified inside view of a pin arrangement for mounting the swivel on the interface; 
         FIG.  15    depicts a front perspective view of the mounting interface of the lift system of  FIG.  1    mounted on the generator, the generator mounted inside an open nacelle of the wind turbine; 
         FIG.  16    depicts a front perspective view of the inside of the nacelle shown in  FIG.  15    with the nacelle closed; 
         FIG.  17    depicts a rear perspective view of the lift system mounted on the generator in the open nacelle of the wind turbine; 
         FIG.  18    depicts a front perspective view of the lift system of  FIG.  17    showing the knuckle boom swiveled into a different position; 
         FIG.  19    depicts a magnified view of the mounting interface with the knuckle boom mounted thereon; 
         FIG.  20    depicts the lift system of  FIG.  17    with the knuckle boom deployed in a fully retracted configuration; 
         FIG.  21    depicts the lift system of  FIG.  20    with the knuckle boom partially extended; 
         FIG.  22    depicts the lift system of  FIG.  20    with the knuckle boom fully extended; 
         FIG.  23    depicts the lift system of  FIG.  17    lifting an intermediate speed (IMS) shaft inside the nacelle of the wind turbine; 
         FIG.  24    depicts the lift system of  FIG.  23    deploying the IMS shaft outside the nacelle for lowering the shaft to the ground; and, 
         FIG.  25    depicts the IMS shaft being lowered to the ground by the lift system. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to the Figures, a lift system  1  is particularly useful for lifting and lowering a gearbox  110  or components of the gearbox  110  (e.g. an intermediate speed (IMS) shaft  112 ) in a nacelle  100  of a standing wind turbine. Although the lift system  1  is particularly useful for lifting and lowering components of a gearbox, the lift system  1  may also be used to lift and lower other components of the wind turbine. The lift system  1  is configured to be mounted on top of a generator  114  in the nacelle  100 . 
     The lift system  1  comprises a knuckle boom  5  rigidly mounted on a swivel  4 . The knuckle boom  5  comprises an articulated boom arm  9 , having three sections  9   a ,  9   b ,  9   c , pivotally attached to a pedestal  6 , the pedestal  6  having a base plate  7  rigidly mounted to the swivel  4 . The swivel  4  is mounted on a mounting interface  2 , the mounting interface  2  mounted on a top of the generator  114 . A chain hoist  15  is disposed proximate a distal end of the knuckle boom  5 , the hoist  15  operable to raise and lower an object (e.g. the intermediate speed (IMS) shaft  112 ) connected to a hook  16  of the hoist  15  with a fixed sling. The chain hoist  15  hanging from the distal end of the knuckle boom  5  contains a cable or chain, which winds and unwinds when the objected is lifted and lowered. A chain bag  18  hanging beside the hoist  15  contains a sufficient length of chain to permit the hoist  15  to lower objects to the ground from the top of the wind turbine. The lift system  1  further comprises a hydraulic motor  13  mounted on the swivel  4  and a power pack mounted on the mounting interface  2 . The power pack comprises an electric motor  14  and a hydraulic pump  12 , the electric motor  14  operating the hydraulic pump  12  (see  FIG.  20   ). The hydraulic pump  12  pumps hydraulic fluid to power the hydraulic motor  13 , and to power hydraulic components (e.g. hydraulic cylinders) of the knuckle boom  5  as well as to power the hoist  15 . The hoist  15  may be powered directly by the electric motor  14 , if desired. The electric motor  14  may receive power from the generator  114  through electrical connections to the power pack. If desired, the lifting system  1  may further comprise a support bracket  10  mounted on the mounting interface  2  and configured to rigidly but removably support a control unit  11  thereon. The control unit  11  may include a transformer, and can be used to adapt mains power of the generator  114  to an operating voltage of the electric motor  14 . The electric motor  14  may be situated under the support bracket  10 , and the power pack including the electric motor  14  and the hydraulic pump  12  do not extend significantly above the height of the mounting interface  2 . 
     The mounting interface  2  serves as an interface between the generator  114  and the other components of the lift system  1  in order to support the lift system  1  on the generator  114 . The mounting interface  2  comprises a pair of spaced-apart substantially parallel side rails  21 , individually identified as a first side rail  21   a  and a second side rail  21   b , connected by a pair of spaced apart end brackets  22 , individually identified as a front-end bracket  22   a  and a rear-end bracket  22   b , located at or proximate front and rear ends of the side rails  21 . The side rails  21  may be connected to the end brackets  22  by virtue of being integrally formed from the same piece of material (e.g. steel), by welding the side rails  20  to the end brackets  22 , or by using connectors, for example bolts. The side rails  21  together with the end brackets  22  form a quadrilateral, for example a rectangle. The front ends of the side rails  21  are closer to a rotor of the wind turbine than the rear ends of the side rails  21  when the mounting interface  2  is mounted on the generator  114 . 
     The side rails  21  are hollow, having interior cavities  23  (see  FIG.  9    and  FIG.  10   ) in which hydraulic fluid may be stored to provide a hydraulic fluid reservoir for operating the hydraulic components of the lift system  1 . The ends of the side rails  21  may be permanently closed, or may have openings, which are covered and sealed by cover plates  25  (see  FIG.  9    and  FIG.  10   , only one labeled) secured to the ends by bolts  24  (see  FIG.  9    and  FIG.  10   , only one labeled). The open ends of the side rails  21  permit filling, emptying and cleaning of the interior cavities  23 . Access holes  26  through the side rails  21  permit hydraulic hoses to pass from under the knuckle boom  5  to a hydraulic manifold. Hydraulic fluid ports (not shown) on inner sides of the side rails  21  permit the installation of hose fittings to fluidly connect the hydraulic fluid reservoirs to the hydraulic pump  12  (see  FIG.  20   ). 
     With specific reference to  FIG.  5    and  FIG.  10   , the end brackets  22  of the mounting interface  2  comprise middle sections transversely extending between and connected to the side rails  20 , and pairs of feet  27  generally vertically oriented and perpendicular to both the middle section and the side rails  20 . One or more of the feet  27  comprise hooking portions  28  that protrude from the feet  27  proximate bottoms of the feet  27 , and bolting assemblies  29 . The hooking portions  28  engage appropriate structures on the generator  114 , while the bolting assemblies  29  engage protruding portions of the generator  114  to secure the mounting interface  2  on the generator  114  with the hooking portions  28  tightly engaging the appropriate structures on the generator  114  when bolts of the bolting assemblies  29  are tightened. Together, the hooking portions  28  and the bolting assemblies  29  act as clamps to clamp the mounting interface  2  on the generator  114 . 
     The mounting interface  2  further comprises two sets of swivel mounting flanges  41  extending inwardly between the side rails  20 , the swivel mounting flanges  41  providing structure to which the swivel  4  is mounted, as described further below. The mounting interface  2  further comprises two sets of support bracket mounting flanges  51  protruding outwardly from sides of the side rails  20 , the support bracket mounting flanges  51  providing structure to which the support bracket  10  is mounted, as described further below. 
     With specific reference to  FIG.  1    and  FIG.  8   , when the side rails  20  of the mounting interface  2  are substantially parallel to the ground, top surfaces of the swivel  4  and the support bracket  10  are angled with respect to the ground. However, when mounted on the top of the generator  114 , the mounting interface  2  is angled rearwardly downward, which results in the top surfaces of the swivel  4  and the support bracket  10  being substantially parallel to the ground. 
     With specific reference to  FIG.  9    to  FIG.  14   , the swivel  4  comprises a rotating portion  33  having an upper surface on which the base plate  7  of the pedestal  6  is bolted. The rotating portion  33  is operatively connected to the hydraulic motor  13 , which provides power for rotating the rotating portion  33 , and therefore the knuckle boom  5 , through 360° about a vertical axis in a plane parallel to the ground. The swivel further comprises a fixed swivel body  31  in which the rotating portion  33  rotates. The swivel body  31  comprises a pair of spaced-apart arcuate mounting arms  32 . Ends of the mounting arms  32  have through apertures  35  for receiving removable non-threaded mounting pins  36  therethrough. When the swivel  4  is in a mounted position on the mounting interface  2 , each mounting arm  32  is engaged between the swivel mounting flanges  41  of one of the sets of the swivel mounting flanges  41 . Each set of the swivel mounting flanges  41  comprises two spaced apart swivel mounting flanges  41 , each swivel mounting flange  41  in a set comprising first through apertures  45  at both ends of the swivel mounting flange  41 , which align with similar first through apertures  45  at the ends of the other swivel mounting flange  41  in the set. The two sets of swivel mounting flanges  41  are spaced apart at a distance such that one mounting arm  32  of the swivel  4  may slide between the swivel mounting flanges  41  of one set, while the other mounting arm  32  of the swivel  4  may slide between the swivel mounting flanges  41  of the other set. When the swivel  4  is in the mounted position, the through apertures  35  in the mounting arms  32  align with the first through apertures  45  in the swivel mounting flanges  41 , and the mounting pins  36  may be inserted through the aligned apertures to secure the swivel  4  on the mounting interface  2 . 
     Further support and security for the swivel  4  on the mounting interface  2  are provided by support pins  37  on which the mounting arms  32  rest when the swivel  4  is in the mounted position (see  FIG.  12   ,  FIG.  13    and  FIG.  14   ). Proximate the ends and on bottom edges of the mounting arms  32 , the mounting arms  32  comprise indents  38  shaped and positioned so that the mounting arms  32  rest on the support pins  37 . The support pins  37  are inserted through second through apertures  42  at the ends of the swivel mounting flanges  41  and secured in place with cotter pins  43 . Aperture-containing brace plates  44  at the ends of each swivel mounting flange  41  may help provide structural support around the first and second through apertures in the swivel mounting flanges  41 . The support pins  37  firmly lock the swivel  4  to the interface  2  when the swivel  4  is operated to rotate the knuckle boom  5 . 
     The removable pin arrangement for mounting the swivel  4  on the mounting interface  2  permits rapid mounting and dismounting of the knuckle boom  5  from the mounting interface  2 . To rapidly dismount the knuckle boom  5 , hydraulic lines  17  (see  FIG.  19   ) between the hydraulic pump  12  and the hydraulic motor  13  may be disconnected from quick connect hydraulic fittings on the hydraulic motor  13 , and the four removable mounting pins  36  may be removed. The knuckle boom  5  together with the swivel  4  may then be lifted off the mounting interface  2  and lowered to the ground by an existing service crane mounted in the nacelle  100 . The existing service crane is generally a crane rated as being able to lift a maximum of 1000 kg when equipped with a heavier chain hoist. The existing service cranes that are typically provided with wind turbines fold down into a compact space within the nacelle  100  so that the nacelle  100  can be normally closed. However, the existing service cranes are insufficient for lifting heavier components of the wind turbine (e.g. gearbox components which weigh about 4 tons), hence the need for the lift system  1 . The existing service crane is normally mounted in the nacelle  100  at a different location than the mounting interface  2 , so that both the existing service crane and the lift system  1  can co-exist in the nacelle  100 . Clamshell doors  101  of the nacelle  100  may be closed while the mounting interface  2  (with the power pack) remains mounted on the generator  114  (see  FIG.  15    and  FIG.  16   ). The dismounting operation may take as little as about 30-60 minutes. Remounting the knuckle boom  5  together with the swivel  4  may be quickly accomplished by reversing the steps. 
     While the removable pin arrangement is desirable for rapid dismounting/remounting of the knuckle boom  5 , the knuckle boom  5  could be dismounted from the swivel  4  by removing all of the bolts attaching the base plate  7  to the swivel  4 . The knuckle boom  5  is then be lowered to the ground, but the swivel  4  may be dismounted from the mounting interface  2  and moved to a different location inside the nacelle  100  in order to close the clamshell doors  101 . However, removing and replacing all of the bolts attaching the base plate  7  to the swivel  4  requires much more time, and is therefore less desirable in an emergency situation. Further, while not desirable, the swivel  4  could be mounted to the mounting interface  2  by threaded bolts or other connectors that require considerably more time to remove and replace than the removable pin arrangement described above. 
     With specific reference to  FIG.  5    to  FIG.  10   , the support bracket  10  comprises a top plate  53  attached to a pair of spaced-apart arcuate mounting legs  52 . Ends of the mounting legs  52  have through apertures  55  for receiving removable non-threaded mounting pins  56  therethrough. When the support bracket  10  is in a mounted position on the mounting interface  2 , each mounting leg  52  is engaged between the support bracket mounting flanges  51  of one of the sets of the support bracket mounting flanges  51 . Each set of the support bracket mounting flanges  51  comprises two spaced apart support bracket mounting flanges  51 , each support bracket mounting flange  51  in a set comprising through apertures  57 , which align with similar through apertures  57  of the other support bracket mounting flange  51  in the set. The two sets of support bracket mounting flanges  51  are spaced apart at a distance such that one mounting leg  52  of the support bracket  10  may slide between the support bracket mounting flanges  51  of one set, while the other mounting leg  52  of the support bracket  10  may slide between the support bracket mounting flanges  51  of the other set. When the support bracket  10  is in the mounted position, the through apertures  55  in the mounting legs  52  align with the through apertures  57  in the support bracket mounting flanges  51 , and the mounting pins  56  may be inserted through the aligned apertures to secure the support bracket  10  on the mounting interface  2 . The top plate  53  of the support bracket  10  provides a horizontal surface on which the control unit  11  may be securely mounted (see  FIG.  17    and  FIG.  18   ). 
     The removable pin arrangement for mounting the support bracket  10  on the mounting interface  2  permits rapid mounting and dismounting of the support bracket  10  with the control unit  11  thereon. To rapidly dismount the support bracket  10 , quick connect electrical fittings for electrical lines (not shown) between the power pack and the control unit  11  may be disconnected, and the four removable mounting pins  56  may be removed. The support bracket  10  together with the control unit  11  may then be lifted off the mounting interface  2  and lowered to the ground by an existing service crane mounted in the nacelle  100 . The clamshell doors  101  of the nacelle  100  may be closed while the mounting interface  2  (with the power pack) remains mounted on the generator  114  (see  FIG.  15    and  FIG.  16   ). The dismounting operation may take as little as about 30-60 minutes. Remounting the support bracket  10  with the control unit  11  thereon may be quickly accomplished by reversing the steps. 
     With specific reference to  FIG.  18    to  FIG.  20   , the power pack (including the hydraulic pump  12  and the electric motor  14 ) is mounted on the mounting interface  2  proximate the swivel  4  and the support bracket  10  in order to locate the power pack close to the hydraulic components on the swivel  4  and the knuckle boom  5 , and close to the control unit  11  to reduce the length of the hydraulic lines  17  and electrical lines (not shown) required to connect the power pack to the various hydraulic and electrical components of the lift system  1 . The hydraulic motor  13  is mounted on the swivel  4 , and accompanies the swivel  4  when the swivel  4  is dismounted from the mounting interface  2 . The power pack is positioned so that the power pack, including the hydraulic pump  12  and the electric motor  14 , does not extend significantly above the height of the mounting interface  2 , thereby ensuring sufficient clearance above the mounting interface  2  to be able to close the clamshell doors  101  of the nacelle  100  without needing to dismount the mounting interface  2  from the generator  114  (see  FIG.  16   ). 
     Quick connect power fittings (hydraulic and electrical) and the pin arrangements for mounting the swivel  4  and the support bracket  10  on the mounting interface  2  provide modularity to the lift system  1 , which advantageously permits rapidly dismounting various components of the lift system  1  and closing the nacelle  100  in emergency situations, for example in inclement weather, while the mounting interface  2 , with the power pack, remains mounted on the generator  114 . When the emergency is over, the nacelle  100  can be re-opened and the various components can be rapidly remounted. 
     With specific reference to  FIG.  20    to  FIG.  25   , the knuckle boom  5  comprises the base plate  7 , the pedestal  6  and the articulated boom arm  9 . The knuckle boom  5  is attached to the swivel  4  by base plate  7 , and the pedestal  6  is vertically oriented and rigidly attached to the base plate  7 . The articulated boom arm  9  comprises a first boom section  9   a  pivotally mounted to the pedestal  6  at or proximate a proximal end of the first boom section  9   a . The articulated boom arm  9  further comprises a second boom section  9   b  pivotally mounted to the first boom section  9   a  at or proximate a distal end of the first boom section  9   a  and at or proximate a proximal end of the second boom section  9   b . The articulated boom arm  9  further comprises a third boom section  9   c  translatably mounted alongside the second boom section  9   b.    
     The swivel  4  permits rotation of the knuckle boom  5  around a full 360° circle in a horizontal plane so that the knuckle boom  5  can operate within and outside the nacelle  100 , and can operate on all sides of the nacelle  100 . Actuators  8 , individually labeled as  8   a ,  8   b  and  8   c , control pivoting and translation of the articulated boom  9 . The actuators  8   a ,  8   b ,  8   c  may be any suitable actuators or combination of actuators, for example hydraulic cylinders, linear actuators, pneumatic cylinders, screw actuators, etc. The actuator  8   a  controls pivoting of the first boom section  9   a  in a vertical plane. The actuator  8   b  controls pivoting of the second boom section  9   b  in a vertical plane. The actuator  8   c  controls translation of the third boom section  9   c  in a direction in which the second boom section  9   b  is pointing. Thus, operation of the actuator  8   c  effectively increases and decreases the reach of the knuckle boom  5  by extending and retracting the third boom section  9   c , which slides alongside the second boom section  9   b  relative to the second boom section  9   b . While the second boom section  9   b  is pivotable on the first boom section  9   a , which affects the reach of the second boom section  9   b , the second boom section  9   b  does not slide. Using the translatable third boom section  9   c  to further increase and decrease the reach of the knuckle boom  5  is convenient for operators working on the gearbox  110 , which is located some distance from the generator  114 . The knuckle boom  5  described above provides the required reach, while staying within an acceptable weight limitation for the knuckle boom  5 . 
     Each of the modular components of the lift system  1  are sized to be lifted by the existing service crane on the wind turbine. Disassembly points and overall weight of each modular component are carefully selected in view of a lifting procedure for raising the entire lift system  1  up to the nacelle  100  where the lift system  1  is assembled. The procedure for raising the lift system  1  up to the nacelle  100  comprises:
         1. opening the clamshell doors  101  and erecting the existing service crane;   2. using the existing service crane to lift an intermediate lifting hoist, which extends the capacity of the service crane cable from 250 kg to 1000 kg;   3. lifting the mounting interface  2  with the power pack and swivel  4  thereon using the service crane and intermediate hoist, and mounting the mounting interface  2  on the generator  114  in the nacelle  100 ;   4. lifting the knuckle boom  5  using the service crane and intermediate hoist, and mounting the base plate  7  to the swivel  4 ;   5. lifting the chain hoist  15  using the service crane and intermediate hoist, and mounting the chain hoist  15  to the knuckle boom  5 ;   6. lifting the support bracket  10  with the control unit  11  thereon using the service crane and intermediate hoist, and mounting the support bracket  10  on the mounting interface  2 ;   7. connecting the control unit  11  to the electric motor  14  in the power pack; and,   8. optionally lowering the existing service crane to its normal location within the nacelle  100 , if it is not anticipated that it will be required for inclement weather.       

     The lift system  1  allows a single crane to be used to raise and lower an upper housing of the gearbox  110 , to lift and lower a canopy of the nacelle  100  and to lift and lower gearbox components, due, at least in part, to the longer reach provided by the knuckle boom  5  with the translating third boom section  9   c , the greater lift capacity and the sufficiently low weight that the lift system  1  can be raised up to the nacelle  100  using the limited existing service crane. 
     The novel features will become apparent to those of skill in the art upon examination of the description. It should be understood, however, that the scope of the claims should not be limited by the embodiments, but should be given the broadest interpretation consistent with the wording of the claims and the specification as a whole.