Patent Application
20210088025
The present invention relates generally to wind turbines and, more particularly, to wind turbine blades and the manufacture and assembly thereof.
Wind turbines are used to produce electrical energy using the renewable resource of wind flow and without combusting a fossil fuel. Generally, a wind turbine converts kinetic energy into mechanical energy and then subsequently converts the mechanical energy into electrical energy. A horizontal-axis wind turbine includes a tower, a nacelle located at the apex of the tower, and a rotor that is supported in the nacelle. The rotor is coupled either directly or indirectly with a generator, which is housed inside the nacelle. The rotor includes a central hub and a plurality of blades mounted thereto and extending radially therefrom.
Generally, electrical energy production from a wind turbine increases with the size of the wind turbine. Therefore, modern multi-megawatt wind turbines are massive structures and the trend toward larger structures continues. These massive structures are assembled from component parts. As such, many wind turbines have their various component parts delivered in separate pieces to the site of the wind turbine installation. For example, the wind turbine tower, which may be formed by several tower sections, may be delivered to the installation site. The nacelle may be delivered to the installation site and mounted on the tower following its assembly. Lastly, the blades, themselves being quite massive in size, have been conventionally transported individually to the installation site. Each wind turbine blade is raised and secured to a rotor hub normally via a pitch bearing, whereby the load from the wind turbine blade is transferred to the rotor hub.
The massive wind turbine blades are complex structures unto themselves. They are often constructed of a shell, spar caps, and one or more shear webs. The shell is typically a layered composite and forms the exterior surface of the blade that has an aerodynamic foil shape and that encloses the shear webs and spar caps, which provide the structural aspects of the blade. The shear webs and spar caps may take the form of an internal spar that enables the shell to resist flap and edgewise loading during use of the blade.
Conventional wind turbine blades are typically produced by a manually intensive production process performed at a centralized site. In addition, production of large wind turbine blades requires a large amount of capital in the form of large facilities and mould making equipment. In one such process, two large-scale moulds must first be produced. The moulds define the shape of the wind turbine blade. Each mould forms approximately one half of the shell of the wind turbine blade.
Once the moulds are manufactured, a laminate structure that forms the shell of the wind turbine blade is produced from each mould by placing a fiber-resin composite in the mould. A process that may include vacuum infusion may be utilized to infuse a fabric, such as a glass or carbon fiber fabric, with resin in the mould. Robots and other automation may be used to assist in this process and to reduce the otherwise manually intensive process of laying up the moulds. The resin is then cured. The cured fiber-resin composite structure conforms to the mould surface to form one-half of the shell of the wind turbine blade. With the aid of cranes, the two shell halves are extracted from their respective moulds and bonded together. Alternatively, the two shell halves may be bonded together while in their respective moulds. Once bonded, the blades are finished. Alternative methods of making wind turbine blades using various forms of additive manufacturing (3D printing) are also known, but once again, the equipment for making the blade is at a centralized site like the moulds because the scale of wind turbine blades is so large.
These large turbine blades are then transported from the manufacturing facility to the installation site, which may be hundreds to thousands of kilometers away. The transport process is costly and sometimes rendered nearly impossible based on the large size of the finished blades and the terrain that must be traversed to move the blades between the centralized manufacturing site and the final installation location for the wind turbine. Moreover, blades can be subjected to vibrations, shocks, and other damage during transport on trains, boats, vehicles, and the like, and repairing this damage from transport adds significantly to the cost of installing wind turbines. These problems have become more exacerbated as the locations for wind turbine installations become more remote and inaccessible from major routes of transportation. As such, it would be desirable to devise a wind turbine blade manufacture process capable of being carried out on a small scale. This may allow the establishment of small or temporary production sites, preferably nearby a wind turbine installation site. In turn, this may allow to limit the amount of transport that needs to be done with a finalized, assembled wind turbine blade.
As is generally described above, conventional manufacturing techniques require a large capital investment, large factories, and long lead times. Furthermore, some of the conventional blade assembly processes require extensive manual labor, which adds to the cost of the blades and the wind turbine. Overall, with a centralized mould manufacturing process, the cost of producing blades and the transportation costs can limit adoption of wind turbine technology.
Several systems and methods have started to be developed for addressing the transport cost and logistics problems, but further improvement remains possible. In this regard, one example of a blade manufacturing method is described in International Patent Application Publication No. WO 2017/092766 to Vestas Wind Systems, the original Applicant of the present application In that published application, a method for assembling a wind turbine from a series of 3D printed sections is described. As shown in
Additional conventional examples of wind turbine blade manufacturing systems and methods are shown in Chinese Patent Application Publication No. CN102200100 (splicing together partial portions of a wind turbine blade) by DEC Dongfang Turbine Co.; European Patent No. 2 246 558 (separate leading edge segments joined to remainder of blade) by General Electric Company; U.S. Pat. No. 7,393,184 (modular wind turbine blades constructed by running tension cables through sections of airfoil body) by General Electric Company; U.S. Pat. No. 7,854,594 (segmented wind turbine blade with segments connected by internal spar) by General Electric Company; and International Patent Application Publication No. WO 2005/064156 (segmented wind turbine blade with hinged sections) by Airbus. These applications and patents describe various methods of constructing and using segmented wind turbine blades, but the manufacturing costs remain high and the assembly process can be very complicated in some of these designs. Therefore, alternative methods of wind turbine blade construction are desirable.
Accordingly, there is a need for improved wind turbine blades and methods for manufacturing wind turbine blades that reduce the capital investment required and eliminate the high costs of human labor and any transportation issues associated with many conventional designs.
A system and method are described herein for manufacturing a wind turbine blade. The system and method automate many of the construction and assembly steps so that human labor costs are minimized as well in blade production. The invention therefore addresses many of the drawbacks discussed above with conventional wind turbine blade manufacturing and transport practices. Furthermore, the wind turbine blade manufacturing system and method described herein may be implemented a proximate to the final installation site of a wind turbine that is to use the blade. The blade thereby may not need to be transported in a final assembled form to the final installation site over long distances, which reduces costs significantly, especially when the installation site is remote as is becoming more typical in the expanding footprint of wind energy.
In one embodiment, the wind turbine blade made by the system and method of this invention includes a plurality of shell core sections, a plurality of strengthening elements, and an outer surface material layer. The shell core sections are coupled together end-to-end to collectively define a span length of the blade between a root end and a tip. Each of the shell core sections defines a sidewall forming a tubular structure and defining an external surface. The sidewall includes a plurality of external grooves recessed into the external surface. The strengthening elements are positioned to extend within the external grooves and along the span length, such that the strengthening elements are configured to reinforce the blade under bearing loads during use of the wind turbine. The outer surface material layer covers the external surface and the strengthening elements, and the outer surface material layer thereby defines an external profile of the blade. The plurality of strengthening elements, and the outer surface material layer are consolidated together by curing of the outer surface material layer. Preferably, the shell core sections, the strengthening elements, and the outer surface material layer are collectively assembled and cured into a final consolidated part by a manufacturing system located proximate to the site of installation for the wind turbine that is to use the wind turbine blade.
In one aspect, each of the shell core sections in the wind turbine blade is formed by additive manufacturing, e.g., 3D printing. Alternatively, each of the shell core sections is formed by moulding. Regardless of the method chosen for forming the shell core sections, these sections can be manufactured from raw materials at a site away from or proximate to the site of installation for the wind turbine. They may be transported in the shell core section form because these individually-formed shell core sections are small relative to the final blade. In some embodiments, each of the shell core sections includes opposing ends having interlocking structures, which engage one another on adjacent shell core sections to maintain adjacent shell core sections in abutting end-to-end contact.
In another aspect, the strengthening elements in the blade are defined by carbon fiber rovings that are configured to transfer loads across multiple ones of the plurality of shell core sections. The strengthening elements in the external grooves therefore define load pathways or “highways” for carrying the varying loads applied to a wind turbine blade in use as a result of wind and wind gusts. The size of the external grooves and the corresponding size of the strengthening elements may be generally uniform across the external surface in some embodiments, but alternatively, the size of the external grooves and the density per area of the strengthening elements can vary over different portions of the external surface of the shell core sections. For example, the blade typically includes a web extending within the tubular structure of the shell core sections to reinforce the blade, and the web connects to the sidewall at sparcap regions. The external grooves and the density per area of the strengthening elements are larger adjacent the sparcap regions in this embodiment, as compared to other regions of the blade. In one aspect, the system may be configured for additive manufacturing of the outer surface material layer. The system may be configured for depositing uncured material on the shell core sections and on the strengthening elements. Deposited, uncured material may thereby envelop the strengthening elements. The system may further be configured to consolidate together the plurality of strengthening elements and the outer surface material layer by curing of the outer surface material layer. Other configurations of the strengthening element density are possible in other embodiments consistent with the invention.
In a further aspect, the wind turbine blade includes a web extending within the tubular structure of the shell core sections and along the span length to reinforce the blade, and at least one web flange extending within the tubular structure and positioned between the web and the shell core sections. The web flange(s) strengthen the blade at junctions of the web and the shell core sections. At least one of, if not both of, the web and the web flange are formed from a different material than the shell core sections. These different materials can be provided by the additive manufacturing and moulding processes, when those are used to form the shell core sections, or these elements can be added to the plurality of shell core sections after these sections are connected. In such embodiments, the shell core sections may define an elongated recess or groove configured to receive the web. The wind turbine blade manufactured by the system and method described herein may be used with wind turbines of various sizes and configurations, with similar or better functionality than the conventional designs.
In another embodiment of the invention, a manufacturing system is provided for assembling a wind turbine blade. The system may be located proximate to a site of installation for a wind turbine. The system includes a creel of feeders configured to apply strengthening elements onto a plurality of shell core sections coupled together end-to-end and fed through the creel. The shell core sections include a sidewall defining an external surface with a plurality of external grooves recessed into the external surface such that the strengthening elements are laid into the external grooves. The manufacturing system may be a local manufacturing system. The manufacturing system also includes a deposition station positioned to receive the shell core sections and strengthening elements from the creel. The deposition station is configured to apply an outer surface material layer in fluid form to cover the external surface and the plurality of strengthening elements. A curing station is positioned to receive the shell core sections, the strengthening elements, and the outer surface material layer from the deposition station. The curing station heats and consolidates these elements together into a final consolidated part, with the outer surface material layer defining an external profile of the blade following curing. Preferably, the creel of feeders, the deposition station, and the curing station may each be located proximate to the site of installation for the wind turbine. The blade can then be installed at the wind turbine, which is advantageously proximate to the location of assembly/manufacture.
The manufacturing system in one aspect includes a tensioner configured to apply tension force to the strengthening elements applied to the plurality of shell core sections. The system may also include a shell section supply station configured to supply the shell core sections to the blade manufacturing system. The shell core section supply station may deliver the shell core sections to the creel for further assembly steps. The blade manufacturing system may optionally include a shell core manufacturing station, to produce the shell core sections from raw material. Optionally shell core sections may be pre-manufactured at a separate site at a shell core section manufacturing site, and transported to the wind turbine blade manufacturing location. The shell section manufacturing station or site may include at least one mould, or a 3D printer configured to form the shell core sections by additive manufacturing. In some embodiments, the shell section manufacturing station also forms a reinforcement web and/or web flange(s) inside the shell core sections.
In a further embodiment of the invention, a method for manufacturing a wind turbine blade is provided. The method may preferably be conducted proximate to a site of installation for a wind turbine using the blade. The method includes connecting a plurality of shell core sections together in abutting end-to-end contact. Each of the shell core sections is configured to define a portion of a span length of the wind turbine blade, and each of the shell core sections defines a sidewall with an external surface and a plurality of external grooves recessed into the external surface. The method also includes applying a plurality of strengthening elements within the external grooves so as to extend along the span length of the blade. An outer surface material layer is deposited in fluid form to cover the external surface and the plurality of strengthening elements. The method then includes curing the shell core sections, the strengthening elements, and the outer surface material layer to produce a final consolidated part defining the blade.
As set forth above with respect to the local manufacturing system, the method may include additional features and steps in other aspects. For example, the method can also include applying tension to the plurality of strengthening elements and maintaining the tension through the steps of deposition the outer surface material layer and curing. The method may also include applying a differing density per area of the strengthening elements on different portions of the external surface of the shell core sections, such as a higher density in the sparcap regions adjacent a reinforcement web within the blade being manufactured. The method of may preferably further comprise forming the outer surface material layer by additive manufacturing. This may include depositing uncured material on the shell core sections and on the strengthening elements. Deposited, uncured material may thereby envelop the strengthening elements. The method may further comprise consolidating together the plurality of strengthening elements and the outer surface material layer by curing of the outer surface material layer. The method preferably further includes manufacturing the shell core sections from raw material proximate to the site of installation. In one aspect, this may be done by moulding the shell core sections in at least one mould, while in another aspect, this may be done by additive manufacturing. The methods of the invention described herein minimize the costs needed for human labor in making wind turbine blades as well as the transport costs associated with moving the blades to the final installation sites for wind turbines.
Various additional features and advantages of the invention will become more apparent to those of ordinary skill in the art upon review of the following detailed description of one or more illustrative embodiments taken in conjunction with the accompanying drawings. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the general description given above and the detailed description given below, serve to explain the one or more embodiments of the invention.
With reference to
With reference to
According to embodiments of the invention, one or more of the wind turbine blades 22 shown in
With continued reference to
The wind turbine 10 may be included among a collection of similar wind turbines belonging to a wind farm or wind park (not shown) that serves as a power generating plant connected by transmission lines with a power grid, such as a three-phase alternating current (AC) power grid. The power grid generally consists of a network of power stations, transmission circuits, and substations coupled by a network of transmission lines that transmit the power to loads in the form of end users and other customers of electrical utilities. Under normal circumstances, the electrical energy is supplied from the generator 18 to the power grid as known in the art.
As noted above, localized wind flow causes the blades 22 to activate rotation of the rotor 16. To this end, air flowing over the wind turbine blade 22 produces lift between a suction surface 28 and a pressure surface 30 of the wind turbine blade 22 to cause the rotor 16 to rotate. As is understood in fluid dynamics, air flowing over the wind turbine blade 22 forms a boundary layer that may separate from the outer surface of the wind turbine blade 22 between a leading edge 32 of the wind turbine blade 22 and a trailing edge 34 of the wind turbine blade 22, depending on air speed, geometry (e.g., angle of attack), or other factors. The leading edge 32 and the trailing edge 34 may extend from a root region 36 of the wind turbine blade 22 including a root end 38, at which location the wind turbine blade 22 is secured to the rotor 16, to a tip region 40 including a tip 42 of the wind turbine blade 22. A mid span region 44 extends between the root region 36 and the tip region 40. These various regions of the blade 22 are schematically shown most clearly in
One selected shell core section 26 is shown in
With continued reference to
As set forth in further detail below, the external grooves 58 are configured to be aligned with similar sets of external grooves 58 such that these external grooves 58 can receive elongated strengthening elements 62 (not shown until
In this embodiment, the shell core section 26 includes opposing ends 64 in the length direction defined by the sidewall 50. The opposing ends 64 are generally open because of the tubular structure defined by the shell core section 26, and this allows for the fully assembled wind turbine blade 22 to have an elongated interior space defined by each of the hollow spaces 52 brought into alignment when opposing ends 64 of the shell core section 26 are placed in abutting end-to-end contact with adjacent shell core sections 26. Although the opposing ends 64 are shown in the embodiment of
It is known that large wind turbine blades 22 often need internal reinforcement to help the outer shell carry the loads applied by the environmental wind. Accordingly, the shell core section 26 of
As shown by the different cross-hatchings visible in
Regardless of the specific material(s) chosen for the shell core sections 26 and associated elements, these shell core sections 26 are sized small enough to allow for easy transport to a site of a blade manufacturing system 24, if required, which may be positioned proximate to the site of installation for the wind turbine 10. Alternatively, the shell core sections 26 can be made by a shell section manufacturing station included in a local manufacturing system 24, in some embodiments. The transport of the smaller shell core sections 26 or the raw materials needed to make the shell core sections 26 to remote locations where a wind turbine 10 is to be installed is less complex and expensive than transport of fully pre-assembled or finalized blades to the same remote locations, so the various embodiments of this invention provide advantages over conventional manufacturing designs and processes.
The shell core sections 26 may be formed in various methods, each of which could be used at a shell section manufacturing station. A shell manufacturing station may be established at a site remote from a blade manufacturing system 24. Optionally, a shell manufacturing station may be included in a blade manufacturing system 24. Each of the shell core sections 26 may be formed by additive manufacturing (also referred to as 3D printing) in some embodiments. To this end, the additive manufacturing may include a layering process, such as VAT photopolymerization, stereo lithography (SL), digital light processing (DLP), selective laser sintering (SLS), selective laser melting (SLM), electron beam melting (EBM), binder jetting, material jetting, direct metal layer sintering (DMLS), or fused deposition modeling (FDM). These processes utilize computer controlled deposition of individual layers of material based on a computer model of a part. The deposited layers are based on discrete cross sections of the model as determined by slicing the model into a finite number of individual model layers. Each model layer is then reproduced by depositing a layer of material from a 3D printer. By constructing each layer, one layer on a preceding layer, the computer model of the part is used to manufacture a real part, in this case, the plurality of shell core sections 26 needed to assemble the wind turbine blade 22. The additive manufacturing process can utilize different materials as noted above to generate each of the sidewall 50, web 66, and web flanges 68. Moreover, any design changes to the desired profile or components making the blade 22 can be easily implemented when using additive manufacturing because the computer model can be changed, with the printing process following suit automatically. Consequently, the shell section manufacturing station may include a 3D printer in these embodiments, or the shell core sections 26 could be 3D printed in this manner and then transported from a centralized manufacturing site to the blade manufacturing system 24 at a blade assembly site, which may be a local site.
Alternatively, the shell core sections 26 are formed by moulding in other embodiments of the invention. In this regard, the shell section manufacturing station may include at least one mould configured to form the shell core sections 26. The moulding process for blade components is well understood in the art and includes, at a minimum, a lay-up or deposit of raw material (e.g., a polymer type material, a composite material, etc.) into a shaped surface defined by the mould, and then curing and/or consolidation of the part at the mould. In one example, two moulds are used to construct two halves of the finished part, in this case the shell core section 26, and then the two halves of the finished part are coupled together by adhesives or the like. However, more or fewer moulds can be used to generate each shell core section 26. The moulding process can utilize different materials as noted above to generate each of the sidewall 50, web 66, and web flanges 68. The shell core sections 26 that have been formed by moulding can then be supplied directly to the blade manufacturing system 24. Therefore, in aspects, the blade manufacturing system 24 includes a shell core section supply station. Alternatively, the shell core sections 26 that have been formed by moulding can then be transported from a centralized manufacturing site for further processing at a local manufacturing system 24. The shell core sections may be introduced into the blade assembly process at a blade manufacture system 24 via a shell core section supply station.
While 3D printing processes and moulding techniques are described herein, other manufacturing techniques (e.g., manual build, etc.) may be used to manufacture the shell core sections 26. However, the embodiments described above advantageously limit or remove the need for significant manual labor in manufacturing and supplying the shell core sections 26 for further assembly steps to be performed at e.g. a local manufacturing system 24.
Further details of a blade manufacturing system 24 and corresponding methods for making the wind turbine blades 22 are shown in
The strengthening elements 62 are designed to transfer loads across the plurality of the shell core sections 26, such as bending loads and tensile loads caused by wind when the finalized blade 22 is in use at the wind turbine 10. The application of the strengthening elements 62 is therefore typically done along a substantial majority (or all) of the span length of the blade 22, and the strengthening elements 62 help couple the separately-formed shell core sections 26 to one another. The strengthening elements 62 thereby define load pathways or “highways” for loads on the wind turbine blade 22 to be transferred and carried by an entirety of the blade 22 rather than causing fatigue and stress along only localized portions of the blade 22.
The feeders 74 on the creel 72 may be pre-loaded with a single elongate carbon fiber roving that defines a length equal to the total length of the external grooves 58 that the strengthening element 62 is to be applied in, which may be substantially the entire span length of the blade 22 as described above. The feeders 74 also hold a carbon fiber roving that has a gauge, or size/number of filaments, corresponding to the size of the associated external grooves 58, so as to substantially fill the external grooves 58 recessed from the external surface 56 defined by the remainder of the shell core sections 26. In this regard, while each of the feeders 74 is configured to apply the same size of strengthening element 62 when the size of the external grooves 58 is generally uniform, as shown in
In order to help maintain the strengthening elements 62 in position upon application into the external grooves 58, the local manufacturing system 24 of this embodiment further includes a tensioner positioned proximate to the creel 72. The tensioner applies tension to the plurality of strengthening elements 62 and maintains this tension through at least a portion of movement through the subsequent steps of blade assembly to be described below (deposit of a surface material layer and curing). For example, the tensioner may include one or more idler wheels or rollers that maintain the strengthening element 62 in a taut condition as it moves towards application in the corresponding external groove 58. Other types of known tension-applying devices can also be used in further embodiments.
It will be appreciated that the creel 72 and feeders 74 are configured to assemble the strengthening elements 62 and the plurality of shell core sections 26 without human action. This further automation of the blade assembly process reduces costs and potential delays that may result when using human resources in such manufacturing. Other than re-loading of the creel 72 with new feeders 74 pre-loaded with another set of strengthening elements 62, no maintenance is required when finishing the assembly of one wind turbine blade 22 and starting assembly of another wind turbine blade 22. Thus, the use of the creel 72 in the local manufacturing system 24 provides advantages over known methods and designs.
Following the step of application of the strengthening elements 62 at the creel 72, the assembly next moves to a deposition station 78 included in the blade manufacturing system 24 and shown in
Following the step of application of the outer surface material layer 82 at the deposition station 78, the assembly next moves to a curing station 86 included in the blade manufacturing system 24 and shown in
The various parts of the blade manufacturing system 24, including the creel 72, the deposition station 78, and the curing station 86, are shown as part of a continuous tube-like enclosure or housing structure in
A cross section taken transverse to the longitudinal axis 46 and through a portion of the finalized wind turbine blade 22 formed by the blade manufacturing system 24 of this invention is shown in
An alternative embodiment of the wind turbine blade 22 (numbered 122 in
The wind turbine blade 22 assembled by the automated manufacturing system 24 and methods of this invention address many of the shortcomings in the current process for wind turbine construction. To this end, the blade is manufactured with little to no human intervention and action required. As such, high costs associated with human labor are avoided. The blade manufacture process and apparatus described and defined herein allows a blade manufacture along the lines of an assembly process for pre-manufactured elements. Pre-manufactured sub-elements of a blade may easily be transported to the blade assembly site for final manufacture. The blade 22 may thereby advantageously be manufactured and finalized without necessitating long-distance transport of the finished item, which, in the context of public transportation infrastructure such as railways and roads is generally considered oversized, difficult and costly to transport. The manufacturing process and system described and defined herein may allow a blade 22 to be assembled or finalized proximate to a site of installation for the wind turbine 10, which can be remote and hard to access via normal transportation channels, especially in the ever-expanding footprint of wind energy production around the world. Furthermore, the local manufacturing system 24 and methods improve the efficiency of wind turbine construction while remaining adaptable for future changes in blade design. A blade manufacturing system 24 as mentioned herein may designate a small-scale manufacturing site. A local blade manufacturing system 24 as mentioned herein may in particular designate a small-scale manufacturing site. Such a local manufacturing system 24 may advantageously, optionally be located proximate to a wind turbine construction site. The term proximate may advantageously include a designation of a distance which does not require passage on public roads. The term proximate may advantageously designate a distance which does not require passage on public railway networks, public, and/or private and/or otherwise. The term proximate may advantageously designate a distance which does not require passage over public infrastructure networks. Preferably, a proximal location may advantageously be one which includes transportation only over a short distance, optionally outside of public roads. By way of example, a proximate location may advantageously lie within 100 km (62-miles) of a wind turbine site. By way of example, a proximate location may advantageously lie within 70 km (43.5 miles) of a wind turbine site. By way of example, a proximate location may advantageously lie within 50 km (31 miles) of a wind turbine site.
While the present invention has been illustrated by the description of various embodiments thereof, and while the embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Thus, the various features discussed herein may be used alone or in any combination, including with any type of single rotor or multi rotor wind turbine. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope of the invention as defined in the claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1721419.8 | Dec 2017 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DK2018/050360 | 12/13/2018 | WO | 00 |
