Wind turbine access panel and method for securing same

Abstract

The invention relates to an access panel configured for fixing to a service aperture in a wind turbine tower wall; wherein the access panel comprises a main panel and an adjacent sub-panel; the sub-panel comprising a bearing surface at an edge thereof; the main panel comprising a reference surface at an edge thereof; the main panel and the sub-panel being abuttable along a common seam; the seam comprising a said sub-panel bearing surface abutting a main panel reference surface; the main panel being dimensioned to close a main region of a tower wall aperture whereas the sub-panel is dimensioned to close a first sub-region of the aperture. The invention includes a method according to which the sub-panel is placed into a tower wall aperture and adjusted to bring its bearing surface into a predetermined position. Thereafter, a main panel is placed in the aperture with its reference surface in abutment with the bearing surface, thereby quickly and easily and reliably locating the main panel for securely fixing in the tower aperture.

Claims

1. A method of handling an access panel at a wind turbine tower service aperture, wherein the aperture extends radially about an aperture main axis and the access panel including a main panel having a reference surface at an edge thereof and a sub-panel having a bearing surface at an edge thereof, the method comprising: placing the sub-panel at a first region of the aperture and adjusting the relative radial position between the sub-panel and the aperture to thereby bring the bearing surface into a predetermined position in relation to the aperture; fixing the sub-panel in position in the aperture; positioning the main panel in the aperture at a main region of the aperture by abutting the reference surface against the bearing surface; and fixing the main panel in position in the aperture.

2. The method according to claim 1, wherein the sub-panel includes one or more radial locators, wherein the method further comprises adjusting the one or more radial locators to thereby controllably vary the position of the bearing surface in the aperture.

3. The method according to claim 1, wherein fixing the sub-panel in position in the aperture further comprises clamping the sub-panel in position in the aperture.

4. The method according to claim 3, further comprising adjusting the clamping force that fixes the sub-panel in position in the aperture.

5. The method according to claim 1, wherein fixing the main panel in position in the aperture further comprises clamping the main panel in position in the aperture.

6. The method according to claim 1, further comprising sealing a common seam formed by abutting the reference surface against the bearing surface.

7. The method according to claim 1, further comprising interlocking the reference surface against the bearing surface.

8. The method according to claim 1, further comprising opening the access panel to move equipment into or out of a wind turbine tower.

9. The method according to claim 8, wherein opening the access panel further comprises: removing the main panel from the aperture; and maintaining the sub-panel in place within the aperture as equipment is moved into or out of the wind turbine tower.

10. The method of claim 9, further comprising accessing the inside of the wind turbine tower to remove the main panel from the aperture.

11. The method of claim 10, further comprising opening an auxiliary door in the main panel to access the inside of the wind turbine tower.

12. The method according to claim 9, further comprising repositioning the main panel in the aperture by abutting the reference surface against the bearing surface.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention and aspects thereof will now be described in more detail, and by way of non-limiting examples, with reference to the not-to-scale, figurative drawings, in which:

(2) FIG. 1 shows a schematic illustration of a wind turbine according to aspects of the invention including a service aperture;

(3) FIG. 2 shows a schematic illustration of a further wind turbine according to aspects of the invention including a service aperture. FIG. 2a shows some details of a variant;

(4) FIG. 3 shows a schematic illustration of a slightly enlarged view of an access panel according to aspects of the invention on a wind turbine tower;

(5) FIG. 3a shows a detail from FIG. 3;

(6) FIG. 4 shows a perspective illustrative view of an interior side of an access panel according to aspects of the invention;

(7) FIG. 4a shows an interior elevation view of an access panel according to aspects of the invention;

(8) FIG. 5 shows a partially cutaway perspective illustrative view of an edge region of a main panel of an access panel according to aspects of the invention:

(9) FIG. 6 shows a partially closed wind turbine tower aperture according to aspects of the invention;

(10) FIG. 7 shows a schematic illustration of wind turbine tower aperture fully closed by an access panel according to aspects of the invention;

(11) FIG. 8 shows a schematic illustration of a fixing element according to aspects of the invention;

(12) FIGS. 9a and 9b show a schematic illustration of further aspects of a fixing element according to aspects of the invention;

(13) FIG. 10 shows a schematic illustration of a locator according to aspects of the invention;

(14) FIGS. 11a and 11b show a schematic illustration of further aspects of a locator according to aspects of the invention;

EXAMPLES OF ASPECTS OF THE INVENTION

(15) The towers 2 illustrated in FIGS. 1 and 2 are shown with a schematically indicated access panel 10 according to aspects of the invention and fitted over a service aperture 7 in the tower wall 8. In both FIGS. 1 and 2, the service aperture is provided in a base region of the tower 2. In FIG. 1, the service aperture 10 is shown provided in a base region of the tower 2, close to a foundation near ground level, while in FIG. 2a, it is shown (dashed lines) in a transition piece 120 also known as an intermediate segment, which may connect the tower to a jacket or to a monopile type foundation 150 suggested in the illustration in dotted lines. For the purposes of this disclosure, a base region of a tower may be deemed to include a transition piece or intermediate segment 150. In some aspects, an external platform may be provided in a base region of a tower 2, as suggested in FIG. 2. In the illustrations of FIGS. 1 and 2, the access panel 10 is shown in two parts, a main panel and a sub-panel, details of which are discussed below. Also visible in the access panel 10 is an optional auxiliary door 90 which allows access for service personnel without requiring opening of the entire access panel.

(16) FIG. 3 shows some more detail of a tower 2 base region including a service aperture 7 covered by an access panel 10 in which is optionally located an auxiliary door 90 for access by service personnel. The access panel 10 can be clearly seen in two parts, namely a main panel 60 and a sub-panel 80. These two elements abut along a common seam 76 defining an abutting contact boundary between the two panels of the access panel. The sub-panel 80 is shown here with a ventilation aperture 38 by way of optional additional feature. In some embodiments no such ventilation aperture 38 may be provided, or it may be provided elsewhere in the tower 2, in some cases for example, at a location higher up the tower 2 (not shown). A hoisting point 19 is illustrated on the main panel 60 of the access panel 10 and is shown schematically in greater detail (FIG. 3a) in a cutaway side view of an access panel top portion. The illustrated exemplary hoisting point 19 comprises a back plate 18 with an eye 17 rigidly fixed thereto. The backplate 18 is securely fixed to the main panel 60 at an upper region thereof and allows the main panel 60 to be suspended in a more or less vertical orientation when hoisted by a lifting device such as a crane (not shown). Also indicated in FIG. 3 is the rim 9 of the service aperture 7 shown by way of a dotted line. Optionally, the access panel may, at an exterior topmost portion thereof, be provided in the shape of a pointed gable to deter bird-nesting tendencies which might otherwise conflict with a need to open the access panel. In this context the term topmost denotes the highest part of the access panel when it is in position at a tower wall aperture.

(17) The access panel 10 is generally shaped and configured to be seatingly fitted and secured at the tower service aperture 7. To that end, the access panel 10 and the service aperture have a generally similar shape, wherein the access panel 10 is dimensioned such that it is large enough to completely fill the service aperture 7 and to exhibit a slight radial overlap, extending over and onto the tower wall outside surface 31. The example shown in FIG. 4 is of a generally oval-shaped aperture 7 and access panel 10, wherein the opposite longitudinal sides of the oval shape are generally straight and parallel. The ends of the aperture 7 are generally curved and the access panel 10 may advantageously be correspondingly curved at its ends. As mentioned, in embodiments, there may be a small departure from a strict curved end of an access panel or portion thereof provided always that the overall extent of the access panel 10, including all its parts, is sufficient to cover the radial extent of the service aperture 7.

(18) In aspects, of the invention a wind turbine tower 2 may comprise a tower top region and a tower base region and a longitudinally extending generally cylindrical wall 8. A tower wall 8 may in particular have a wall diameter which progressively decreases in a direction from the base region towards the top region. The tower wall 8 may have having a wall thickness which progressively decreases in a direction from the base region towards the top region. The tower 2 may in particular define an interior region within the wall 8 an exterior outwith the wall 8. The tower wall 8 is provided with a service aperture 7 in its base region, which aperture extends radially about an aperture main axis and which aperture 7 is dimensioned to allow passage therethrough of personnel and equipment between the exterior and the interior region. The tower 2 according to the invention further comprises an access panel 10 removably fixed at the tower aperture 7 and as herein described or defined.

(19) In further optional aspects, the tower wall 8, at a region adjacent the service aperture 7, for example within 1 m of the aperture edge face 32, comprises neither through-holes nor structural welds. In this context, a structural weld may be a weld which directly or indirectly supports the weight of the access panel 10 or at least a substantial or major part of it.

(20) Preferably, the tower wall 8 has a weather- and waterproof painted surface extending over substantially all the exterior region of the wall 8 adjacent the aperture 7. Preferably, the painted surface extends all around an inner rim 9 of the aperture 7 and preferably the painted surface extends about substantially all of an interior wall region 33 and exterior wall region 31 adjacent the aperture 7.

(21) A view of the access panel 10 can be seen in FIG. 4 which illustrates the panel from a generally interior perspective view. A main panel 60 is shown with an optional raised side wall 16. Also sub-panel 80 has a raised side wall 15. In embodiments, the side wall 16, 15 of the access panel 10 may have a variable depth in order better to accommodate a possible curvature of the tower aperture wall 8. In embodiments, a cover panel 63 of the main panel 60 may be planar, in particular, it may preferably be substantially flat. In embodiments, it may be provided with a slight curvature equal to or less than the tower wall 8 curvature at its service aperture 7 region. Also the sub-panel 80 has a generally planar cover panel portion 83. As with the main panel cover portion 63, the sub-panel cover portion may also be planar, being either substantially flat or slightly curved. In general, it is preferred for the planar cover portion 63, 83 of the main and sub-panel to be conformed to each other. In some aspects, it may be preferred to provide the cover panel 83 of the sub-panel 80 separate from a sub-panel frame although this is not illustrated. Also shown in FIG. 4 is an optional facing rim 55 around the side wall 16 of the access panel 10 which may provide a broader connection surface between the access panel 10 and a tower wall 8. The facing rim 55 or simply the rim of the side wall 16 may preferably be provided with a sealing bead 57 (not shown in FIG. 4) to improve a weatherproof connection between the access panel 10 and a tower wall 8 and to prevent damage to the tower wall outer surface 31 treatment (if any) such as weatherproof paint.

(22) The access panel extends radially about a main axis 23 which may also be called a closure axis. It denotes an axis normal to the plane of the access panel 10, in particular, normal to a cover panel 63 thereof. It may be coincident with the main axis of a tower wall aperture 7 when fitted in position thereat. The generally planar access panel 10 extends generally radially about the main axis 23. The access panel 10 may comprise fixing elements 40 although these are only partially illustrated for simplicity. In particular the fixing elements 40 may comprise axial clamps 41 of whichfor simplicityonly the anchor portions 42 are shown in FIG. 4. These are fixed to the main panel 60 and also to the sub-panel 80. The number and distribution of the axial clamps 41 may be varied according to circumstances such as according to the overall size of the access panel 10. In addition, the sub-panel 80, is shown having radial locators 70 which are adjustable in a generally radial direction 24 of the access panel 10 and thereby also in a radial direction of the sub-panel 80. Adjustment of the locators 70 moves a foot 74 of the locator 70 in a radial direction 24, that is to say in a direction generally outward or outboard from the sub-panel 80 and generally parallel to the dominant plane of the sub-panel 80. In this context, the dominant plane of the access panel 10 or sub-panel 80 or main panel 60 may be considered to coincide with the plane of its respective cover panel 63, 83. It may lie parallel to the dominant plane of a tower wall service aperture 7, when the access panel 10 is fitted therein.

(23) The sub-panel 80 comprises a bearing surface 86 along one edge thereof. In the illustration, the bearing surface presents a planar, flanged face although this is not essential. The bearing surface 86 is configured to co-operate with and to abuttinlgy connect with a correspondingly shaped reference surface 66 provided along one edge of the main panel 60. The abbutting, co-operating bearing and reference surface thereby constitute a seam 76. For improved weatherproofing, a sealing bead may optionally be provided along the seam 76. The seam 76 comprises two mutually separable or releasable parts. In particular, the seam 76 may comprise reference surface 66 and a bearing surface 86. It is not intended to be a permanent fixed connection. The configuration of the respective bearing and reference surfaces 86, 66 may be varied to be overlapping or engaging if desired. Preferably, the sub-panel 80 bearing surface 86 presents a support and locating surface for the main panel 60.

(24) FIG. 4a shows an elevation view of an access panel 10 similar to the panel of FIG. 4, with some slight constructional variations. A pointed gable is shown atop the access panel 10 and the exemplary fixing elements 40 are illustrated in position at the periphery of the access panel 10. The cover panel 63 of the main panel 60 is shown as a composite panel made from connected pieces of panelling. In particular, the gabling is created using additional panel portions although these are not separate panels from the main panel 60 as they are not independent or separately positionable in the aperture 7. In the illustrated embodiment, the sub-panel comprises four locators 70. The sub-panel 80 is configured to extend across a first sub-region of an aperture 7 which extends in a vertical, height direction of the aperture of less than one fifth of the overall aperture height, measured from the inside edge face of the aperture 7.

(25) In FIG. 5, there is shown a more detailed perspective cutaway view from below an exemplary main panel 60 in which a reference surface 66 is provided in the form of a groove, thereby configured to abuttingly co-operate with a projecting bearing surface 86 of a sub-panel 80 which may seatingly engage inside the groove 66. Also visible in FIG. 5 is a sealing bead 57 along the facing edge of the raised side wall 16. Fixing elements 40 illustrated in the form of axial clamps 41 are shown by way of example, further details of which are discussed below. The axial clamps 41 act to provide a fixing or clamping force generally along a clamping axis 43, parallel to a main- or closure axis 23 of the access panel 10.

(26) In FIG. 6, there is shown a sub-panel 80 of an access panel 10 from a viewpoint within the tower 2 showing a tower wall 8 interior surface 33 in a region surrounding the service aperture 7. The sub-panel 80 comprises locators 70 which are radial locators. The example which is illustrated shows two locators at the sub-panel 80 although in some cases a single one may suffice. Alternatively, three or four locators 70 may be preferred at a sub-panel 80. The sub-panel 80 is shown covering a first sub-region 54 of the service aperture 7, while a main region 52 thereof is open. For simplicity, fixing elements 40 are shown only in part, namely in the form of anchoring portions 40 connected to the sub-panel 80. As discussed in the context of FIG. 4, the locators 70 allow radial adjustment of the sub-panel 80 such that the sub-panel bearing surface 86 may be accurately positioned in a bearing position in the aperture 7. Hence, in FIG. 6, the sub-panel may be said to be positioned in the aperture 7 although not securely fixed thereto. The precise seating of the sub-panel 80 may be carried out by adjusting the locators 70 such that the bearing surface 86 is positioned accurately in a predetermined bearing position within the aperture 7. In the example illustrated, the bearing surface 86 may extend, in its predetermined position, substantially across a curved end region of the aperture 7. In preferred aspects, the bearing surface 86 may be substantially planar although a surface with a slight curvature such as a concavity may assist rapid seating of a corresponding reference surface 66.

(27) In FIG. 7, there is additionally illustrated a main panel 60 with fixing elements 40 which may be axial clamps 41. Also the sub-panel 80 is shown, in this example, with fixing elements 40 which secure the access panel 10 in position at the service aperture 7. In this illustration, the access panel 10 is shown fixed in position by the fixing elements 40. In other words, both the main- and sub-panels 60, 80 are independently fixed in position and contacting each other, thereby making up the access panel 10 which covers the full radial extent of the service aperture 7.

(28) Also visible in FIG. 7 is a reference surface 66 of the main panel 60 in abutting relationship with the bearing surface 86 and thereby forming a connection in the form of a common seam 76. The seam 76 may additionally comprise a sealing strip (not shown) to improve its properties against the influence of weather outside the tower. The main panel is shown without radial locators 70 although these may optionally be provided if desired although it is not essential to do so and faster installation of the main panel 60 may be achieved without locators. Preferably, the main panel 60 is located in position in the aperture 7 by placing it against the bearing surface 86 of the previously installed sub-panel 80 such that its reference surface 66 co-operates therewith. Moreover, the view illustrated in FIG. 7 is from within the tower 2: it can be seen that with the fixing elements 40 and locators 70 positioned on the interior surfaces of the elements of the access panel 10 are accessible from within the tower 2. Securing the access panel 10 in position or releasing it from its secured position may thereby advantageously be carried out from within the tower 2.

(29) An optional auxiliary door 90 may also be provided in the access panel 90. As can be appreciated from the relatively smaller dimensions of the auxiliary door 90 in relation to the service aperture 7, the door is intended for use by personnel while the dimensions of the aperture 7 allow for the passage through it of large pieces of equipment, larger than the auxiliary door dimensions. Since it is not envisaged to need to move large pieces of equipment through the service aperture 7, its fixing elements 40 may be of a significantly different type than the opening mechanism of the auxiliary door 90 which may be expected to be in relatively frequent use. Where an auxiliary door 90 is encompassed within the main panel 60, the positioning of the main panel 60 across a main region 52 of the aperture 7 thereby also puts the auxiliary door 90 into position.

(30) Locators 70 which allow to adjust and to hold the position of a part of an access panel 10, such as a sub-panel 80, in a tower wall aperture 7 may take a variety of forms in accordance with the invention. One embodiment of a radial locator will be described with reference to FIGS. 10, 11a and 11b. A similar locator 70 can also be seen in FIG. 4. A locator may comprise a radially displaceable foot 74, capable of being moved and adjusted in a radial direction 24 of the access panel 10 generally parallel to the plane of the panel. The foot 74 may preferably comprise a pad made from an elastic material such as rubber or synthetic rubber and which offers a high level of friction when contacting a counter surface or when urged thereagainst. The foot 74 is fixed to an adjustment shaft 77 which is held in a support flange 72 illustrated in the form of a bracket fixed or welded at its base to a part of the access panel 10 such as a sub-panel 80 in particular a cover panel 83 thereof. The support flange 72 may comprise a projecting portion 79 which may be a main plate, the projecting portion being fixed to the access panel 10 or a portion 60, 80 thereof and being provided with an aperture or recess. A prop 78 may extend from the support flange 72 projecting portion 79 to the access panel 10 to provide an abutment for a pushing action of the locator foot 74 and shaft 77. An adjuster 75 in the form of a nut may be actuated to controllably impart a translation of the shaft 77 in a radial direction 24. In particular, actuating the adjuster 75 has a surface which pushes against a surface of the support flange 72 to thereby urge the shaft 77 and the foot 74 at a radially outermost end thereof in a radially outward direction. Conversely, actuation of the adjuster 75 in an opposite direction allows the locator shaft 77 and its foot 74 to retract inwards towards the support flange 72. A tightening nut 73 on the shaft 77 may be used to tighten the foot 74 and shaft 77 in a retracted or extended position. In embodiments, the tightening nut 73 may be on a side of the support opposite the actuator 75. In embodiments, an adjuster 75 may take the form of a radially flared nut with a waisted portion projecting through an aperture in the support flange 72. A driving surface of the flared nut may be provided at the flared portion or at the waisted portion. In each case, the actuator 75 driving surface can be provided such that the driving surface is positioned at a face of the support flange 72 bracket opposite a prop 78, thereby assuring improved access by an adjustment tool when adjusting the shaft 77 and foot 74 radially inward or outward. When placed in a tower wall aperture, the foot 74 may be brought to bear against an aperture edge face. The relative position of the associated sub-panel 80 in the aperture 7 can be controllably adjusted and varied by actuating the adjuster 75 and tightening as necessary to set it in position at a relative distance from the aperture edge 32 which may in particular correspond to a predetermined position of the bearing surface 86 of the sub-panel 80.

(31) The particular design of the fixing elements 40 which are illustrated by way of example as axial clamps 41 will be discussed with reference to FIGS. 8, 9a and 9b. An axial clamp 41 comprises an anchor 42, which in this case is shown in the form of a boss which is fixed or welded to the access panel 10 or cover panel 83, 63 thereof. In some embodiments, the anchor 42 may be provided at the side wall 16 or 15 of a main- or sub-panel 60, 80. A clamp head 45 is shown optionally having a narrow waist 35 and a flared claw 36. A shank 49 has a main axis 43 which may be parallel to a closure axis in relation to the access panel 10 or aperture 7. The shank 49 connects the clamp head 45 and the anchor 42 via an adjustment actuator 44 and a shim 46. In embodiments, the shank 49 may be in the form of a threaded bolt. In the embodiment illustrated, the axial clamp 41 thereby optionally comprises a clamp force adjuster 44, a threaded part of which is also the main shank 49 of the axial clamp 41. In the case illustrated, the clamp force adjuster 44 comprises a threaded shaft and a nut. In the case illustrated, actuation of the clamp force adjuster 44 has the dual effect of applying a clamping force via the claw portion 36 and adjusting the effective length of the main shank 49. The clamp head 45 is preferably made of a resilient, elastically deformable material which is deformable under clamping forces applied by manually tightening of the axial clamp 41. The clamp head 45 preferably has a smooth surface and has sufficiently low hardness and sufficient elasticity such that it is not susceptible to scratch or damage a coating on the surface of the tower wall 8. The waist 35 presents an axially extending alignment surface 47 which serves to radially position the access panel 10 against an edge face 32 of the service aperture 7.

(32) Advantageously, the clamp head 45 further comprises an axially tapered surface 48 adjacent and extending radially inward of the alignment surface 47. Thus when the clamp head 45 is drawn axially along the shank 49 towards the anchor 42 in which the shank 49 is held, the tapered surface 48 engages with the inner rim 9 of the tower wall aperture 7 and is caused to slide over it while at the same time pushing the access panel 10 into its intended position. The clamp head preferably exhibits rotational symmetry about its main axis 43 which coincides with a main longitudinal axis of a clamp shank 49.

(33) In operation, a clamping face of the claw 36 abuts against the interior surface 33 of the tower wall 8. The force adjuster 44 may be actuated by tightening it to put the shank 49 under tension and transmit a claiming force F to an interior surface 33 of the tower wall aperture region. The claw 36 thereby serves to pull the access panel 10 securely to abut and rest against the outside surface 31 of the tower wall 8. A sealing bead 57 at the access panel 10 side wall 16 may provide an improved weather proof connection of the access panel 10 when it is fixed and secured in position.

(34) According to aspects of the invention, fixing elements 40 enable the access panel 10 to be secured in place at the aperture 7 preferably without requiring holes to be drilled in the tower wall 8 or welds to be applied thereto. Advantageously therefore, in a tower 2 according to aspects of the invention, there may be no structural welds on the tower wall 8 or no large welds or no welds of any kind.

(35) During use, when installing an access panel 10 according to the invention at the service aperture 7 of a wind turbine tower 2, a bearing surface 86 is pre-established in the aperture 7 by positioning a sub-panel 80 of the access panel 10 such that its bearing surface 86 adopts a predetermined and fixed bearing position in the aperture 7. This operation can be carried out using relatively modest equipment or tools because the dimensions of the sub-panel 80 may be relatively manageable. In most instances, a sub-panel may be expected not to exceed a maximum dimension of about 1 or 2 metres across. If made of a lightweight material such as aluminum, it may be light enough to be handled into position at a tower wall aperture 7 by one or two service personnel. Adjustments to its potion can also be carried out manually using hand held tools and by one or two members of service personnel. Also a fixing operation of the sub-panel 80, once its bearing surface has adopted the predetermined desired relative position in the aperture 7, preferably using fixing elements such as axial clamps 41 described herein, may be carried out by one or two service personnel and hand held tools. A reasonably precise positioning of the sub-panel may be of importance in ensuring a durable and weatherproof fit of the access panel 10 over a service aperture 7. Moreover, in embodiments in which an auxiliary door 90 is provided encompassed in the access panel 10, there is a need for the access panel 10 to be robustly held in position in order to sustain physical usage of the door 90 repeatedly over time. For fixing the sub-panel in position, any appropriate fixing means 40 may be contemplated, including quick-fasteners such as hinged lever type sprung fasteners, latching dogs or other suitable types of clasp or clamp.

(36) Once the sub-panel 80 is securely in position, the much larger main panel 60 may be more swiftly brought into position. Given its considerably larger size and greater weight, the main panel 60 is expected to be suspended from a crane (not shown) by a hoisting point 19 during installation. The size of the main panel 60 makes it not only heavy but susceptible to be caught by gusts of wind making bringing it into position in the aperture 7 particularly difficult, especially under windy conditions. While suspended from the crane, its reference surface 66 may be easily abutted against the bearing surface 86 of the sub-panel 80. The predetermined adjusted position of the bearing surface 86 is measured to take account of the respective, know dimensions of the aperture 7 and of the main panel 60. When the reference surface 66 abuts the bearing surface, a previously determined acceptable fit of the main panel 60 and thereby of the access panel 10 as a whole at the aperture 7 is easily guaranteed without further operations or adjustments. In aspects of the invention, the reference surface 66 and the bearing surface 86 may be configured to mutually interlock such as in a tongue-and groove type arrangement which adds to the effectiveness of the operation of fittingly connecting the two elements. After positioning the main panel 60, it can be fixed using any suitable fixing elements 40 as discussed in relation to the sub-panel and examples of which are described or defined herein. The axial clamps 41 specifically described herein may provide an additional measure to enhance the fit of the main panel 60 and access panel 10 as a whole, such as an axially tapered portion of a surface which abuts a service aperture wall edge surface 32.

(37) When moving large components such as a transformer or other pieces of equipment though the tower wall service aperture 7, the aperture 7 can be opened by removing the main panel 60 of the access panel using a crane as described previously, while leaving the sub-panel 80 in place. After completing moving of large components, the aperture 7 may be swiftly closed again without requiring alignment in relation to the aperture 7 because the bearing surface 86 of the sub-panel 80 provides the requisite guidance into position. The access panel 10 according to the invention is thereby easier to install and easier to operate when needed.

(38) As described herein, additional aspects of the invention include a set of fixing elements at an access panel which fixing elements 40 allow the access panel to be fixed in place, secured, and operated when the access panel 10 is required to be removed, all without weakening the tower wall 8 and without damaging weather-proof coatings thereon. Thereby, the tower access aperture 7 may be configured without a structural aperture framein other words, the tower aperture 7 may have a non-structural aperture frame. Similarly, the access panel 10 according to aspects of the invention may preferably be non-structural in relation to the tower 2.

(39) As will be appreciated, in some aspects presented herein, the access panel 10 of the present invention may be suitable for implementation in outdoor structures other than wind turbines and into which access is occasionally required for personnel or equipment and in which fitting of the access panel or provision of a wall aperture may present similar challenges to those described herein in the context of wind turbine towers.