Method and control system for lifting a wind turbine component

Abstract

Disclosed herein is a method for moving a wind turbine component (101) of a wind turbine between a ground level and a desired position on the wind turbine using a crane (100). The method includes determining a first maximum load capacity (4) for the crane (100) with the lifting hook located at a first distance (7, 17) from the boom tip, and determining a second maximum load capacity (4) for the crane (100) with the lifting hook located at a second distance (7, 17) from the boom tip. The first and second maximum load capacities are determined by taking into account both boom arm (102) position and the distance (7, 17) between the lifting hook and the boom tip. The method further includes operating the crane (100) to move the component from ground level to the desired position, taking into account the first and second maximum load capacities. In this way, larger loads can be lifted safely in comparison to the prior art (1, 10, 20).

Description

[0001] METHOD AND CONTROL SYSTEM FOR LIFTING A WIND TURBINE COMPONENT

[0002] Technical Field

[0003] The current disclosure relates to cranes for lifting wind turbine components for example tower sections, blades, gearboxes and nacelles. In particular, this disclosure relates to methods for lifting the wind turbine components from the ground to a desired position using a tower mounted crane.

[0004] Background

[0005] Wind turbines are used to generate electricity from the wind. They typically comprise a rotor, which is connected to a generator, and a tower that supports the rotor and generator at a height above the ground. The rotor is typically made up of several blades, which are mounted to a hub. The hub is connected to a gearbox, which in turn is connected to the generator.

[0006] The installation and maintenance of these components at the top of the wind turbine tower can be a challenging and dangerous task. Cranes used for this process may be ground based or tower mounted. Tower mounted cranes are typically mounted near the top of the wind turbine tower and are used to lift and move the components to and from the turbine. Tower mounted cranes may for example be self-hoisting cranes or self-climbing cranes.

[0007] WO 2011 / 050812 A1 (Liftra ApS) discloses a self-hoisting crane adapted to be mounted on a crane base mounted on the nacelle of a wind turbine. The selfhoisting crane is lifted to the nacelle by means of a winch placed on ground which pulls two wires extending upwards from the winch to the nacelle and then back down to the crane. When the crane arrives at the nacelle of the wind turbine, the crane is mounted on a crane base mounted to the nacelle. In its mounted position on the nacelle, the crane may be used for lifting heavy parts by means of the same wires that were used for lifting the crane itself, and by operating the winch on ground. The self-hoisting crane may be used for servicing and replacement of the wind turbine components located in the wind turbine nacelle.

[0008] Other forms of tower-mounted cranes are also available in the art. In certain prior art embodiments, a small crane mounted to the nacelle is used to lift a medium sized crane to the nacelle which is then used to hoist a larger crane to the nacelle. The larger crane is then mounted to the nacelle via a crane mounting fixture arranged in the nacelle. In other cases, self-climbing cranes are provided which climb up the tower. Such self-climbing cranes can be used to build the tower itself. An example of a self-climbing crane is disclosed in applicants co-pending application published as WO2020 / 234435.

[0009] The advantage of using a tower mounted crane is that it eliminates the need for large mobile cranes or large independent cranes constructed / arranged beside the wind turbine during installing and / or servicing a wind turbine. In this way substantial savings may be achieved when performing these tasks.

[0010] A critical tool used in the operation of any crane, is a load chart. Load charts provide information about the crane’s capacity to lift and move different loads at various configurations and under different environmental conditions.

[0011] It remains a problem to provide improved methods for using the full capacity of cranes for lifting wind turbine components.

[0012] Summary of the Invention

[0013] Accordingly, in various embodiments of the method and system disclosed herein, the use of the crane’s lifting capacity can be optimized by taking into account that the actual maximum load capacity of the crane is different for different configurations of the crane. It is known in the prior art that the further the tip of the crane is extended away from the crane base, the lower the lift capacity of the crane will be. Likewise, it is known that the slew angle, or angle of the boom about a vertical axis, will also have an effect on the lifting capacity. Hence, prior art load charts take these configuration parameters into consideration. A lifting operation can therefore be planned based on the known maximum lifting capacity of the crane in the different configurations.

[0014] However, prior art methods do not take into account the vertical position of the lifting hook. Modern cranes have become so large, that the weight of the lifting hook and wires is a significant load parameter. When the lifting hook is in the bottom most position, then there is a very large amount of wire arranged between the tip of the crane and the lifting hook. The weight of this wire needs to be accounted for when planning the lifting operation. In contrast, when the lifting hook is all the way up, then there is very little wire arranged between the tip of the crane and the lifting hook. Hence, the wire weight contributes very little to the loading of the crane in the upper position of the lifting hook.

[0015] Likewise, the wind loading in prior art load charts is also provided as a single measurement taken near the top of the wind turbine. However, it is typically the case that the wind will be lower near the bottom of the wind turbine tower than the top of the wind turbine tower. Hence, the load capacity based on the wind measured near the top of the tower will also be dependent on the position of the lifting hook.

[0016] Accordingly, the present invention provides for a method for moving a wind turbine component of a wind turbine between ground level and a desired position on the wind turbine using a crane having a boom arm with a boom base and a boom tip, a lifting hook and a lifting wire arranged between the lifting hook and the boom tip, the method comprising the steps of:

[0017] - determining a first maximum load capacity for the crane with the lifting hook located at a first distance from the boom tip, said first maximum load capacity being determined by taking into account both boom arm position and the first distance between the lifting hook and the boom tip;

[0018] - determining a second maximum load capacity for the crane with the lifting hook located at a second distance from the boom tip, said second maximum load capacity being determined by taking into account both boom arm position and the second distance between the lifting hook and the boom tip; and - operating the crane to move the wind turbine component between ground level and the desired position, taking into account the first and second maximum load capacities.

[0019] It should be noted that in this specification, the term “lifting hook” should be interpreted broadly. In certain cases, the lifting wire is connected to a load via a connecting element, other than a hook, but the functionality is the same. For example, a shackle, a quick connector, etc. Likewise, it should be noted that in most modern crane systems, the lifting wire is not just a wire running from the boom tip to the lifting hook in a single pass, but rather, the lifting wire is arranged in multiple loops passing over multiple sheaves at the boom tip and the lifting hook to increase the lifting power of the crane.

[0020] Since wind turbine towers can be up to 200m or more in height, the lifting wire, typically made from steel or another strong material, adds a considerable weight to the system. This is especially true when considering the number of passes the lifting wire makes between the boom tip and the lifting hook. The closer to the tip of the crane the lifted wind turbine component is, i.e. the higher the wind turbine component is off the ground, the less weight the lifting wire adds to the total weight of the system. By taking this change in the weight of the suspended lifting wire into account when calculating the load capacities, the maximum load capacity of the crane at a particular boom position will increase as the distance between the lifting hook and the tip of the boom decreases. As the weight of the suspended lifting wire will be dependent on the distance between the boom tip and the lifting hook, the maximum lifting capacity can therefore be determined by considering the distance between the lifting hook and the boom tip.

[0021] As such, considering the maximum load capacity of the crane at different boom arm position and the distance of the lifting hook from the boom tip, provides very valuable information to the crane operator and allows the cranes lifting capacity to be more fully utilized. This allows, for example, the operator to start lifting a higher load near crane tower and then moving the boom tip away from the crane tower as the load moves vertically, since the weight of the lifting wire decreases as the load moves vertically, thereby increasing the maximum load capacity of the crane. In this manner, the present method allows the operator to lift heavier loads when compared to prior art methods.

[0022] Furthermore, it can be mentioned that in situations where taglines are used to control the position of the wind turbine component being lifted, when the wind turbine component is close to the ground, the length of the taglines will be low and therefore the weight of the taglines on the load will also be low. Likewise, when the load is close to the ground, the taglines will be arranged at a roughly horizontal angle and the vertical component of the force applied by the taglines on the load will be relatively small. However, when the load is close to the top, the contribution of the weight of the taglines on the load and the vertical component of the force applied by the taglines on the load will increase. Hence, the loading due to the taglines will be high when the load is at the top of the crane and lower when the load is close to the ground. Hence, taking the effect of the weight of the lifting wire onto the maximum lifting capacity of the crane into consideration during the lifting operation, will also help in working more flexibly with taglines.

[0023] In some embodiments, the crane is a tower mounted crane, for example a selfhoisting crane or a self-climbing crane. Tower mounted cranes may be more susceptible to environmental factors such as wind speed than ground based cranes which may for example be constructed on a concrete pad next to the wind turbine. Therefore, it is particularly important for tower mounted cranes to make full use of a change in maximum load capacity as a function of height.

[0024] In some embodiments, each of the maximum load capacities are calculated / obtained before initiating the lift of the wind turbine component. Accordingly, this makes it possible for the crane operator to proactively plan the lifting procedure. This may entail for example starting the lifting procedure with the wind turbine component close to the tower, and then extending the boom of the crane during the lift, as the maximum load capacities indicates that the reach of the crane can be extended as the wind turbine component moves higher towards the crane. In various embodiments, one or more of the load capacities are calculated during the lift of the wind turbine component, i.e. after the wind turbine component has left the ground. This has the advantage that any changes in environmental conditions during the lift can be accounted for dynamically. For example, a change in wind speed during the lift may mean that a lift that was deemed safe at the outset, now has a load exceeding the maximum safe capacity of the crane at the new wind speed. By calculating load capacities based on the changing environmental parameters during the lift, the changing environmental parameters can be taken into account.

[0025] In some embodiments, the maximum load capacity for the crane at a further height above the ground is also determined / obtained / calculated. By calculating or determining the maximum load capacities for a number of heights and a number of boom arm positions, it is possible to optimise the lift path of the wind turbine component.

[0026] In some embodiments, the method also includes obtaining the maximum load capacities for the crane at different boom positions with the lifting hook located at a additional different distances from the boom tip.

[0027] In some embodiments, the boom arm position is specified by the reach of the boom of the crane and / or the slew angle of the crane. The operator of the crane has control over the reach of the crane, as well as the slew angle of the crane. As the wind turbine component is lifted higher, the maximum load capacity increases for a given reach of the crane, i.e. the higher the wind turbine component is lifted, the further away from the wind turbine tower a wind turbine component of a given weight can be lifted. By giving this information to the operator of the crane, the lift path can be optimized.

[0028] In some embodiments, the step of determining the first and second maximum load capacities takes into account the wind speed at the first and second distances of the lifting hook from the boom tip. In some embodiments, the wind speed is measured using an anemometer placed at the top of the wind turbine tower. In general, the wind speed will typically be the strongest at the top of the tower, and therefore using the measured wind speed at the top of the tower for obtaining the maximum load capacity will be a sufficient proxy value that can be used as a maximum wind speed for the entire height of the tower. However, by understanding that the wind speed will be higher at the top of the tower than at the bottom of the tower, a more optimal lifting operation can be performed. For example, when the lifting hook is located close to the ground, a lower wind speed will be present, but a higher lifting wire weight will be present. In contrast at a higher position of the lifting hook, a higher wind speed will be present, but a lower lifting wire weight will be present. Hence these two factors can be used to compensate for each other allowing a lifting operation to take place which would otherwise not have been possible had traditional load charts and wind speed safety measures been followed.

[0029] In some embodiments, the wind speed is estimated based on force measurements on the crane. In particular, in embodiments in which one or more of the load capacities are calculated during the lift of the wind turbine component, force measurements on the crane can give better estimates of the actual wind speed at the current height of the lifted wind turbine component. The force measurements may measure sideways forces on the crane, for example via force measurements at different load points on the crane. These measurements can give detailed information about the sideways load being applied to the crane by the load being lifted. If the type of load being lifting is known, then the identified forces can be compared to expected forces to find the effect of the wind on the lifting operation.

[0030] In some embodiments, the step of determining the first maximum load capacity includes the step of obtaining a first load chart for the crane associated with the lifting hook being located at the first distance from the boom tip, the first load chart comprising information about maximum load capacities for the crane at different reaches and / or slew angles of the crane when the lifting hook is located at said first distance from the boom tip, the step of determining the second maximum load capacity includes obtaining a second load chart for the crane associated with the lifting hook being located at the second distance from the boom tip, the second load chart comprising information about maximum load capacities for the crane at different reaches and / or slew angles of the crane when the lifting hook is located at said second distance from the boom tip, and the first and second load charts being different.

[0031] Accordingly, a plurality of different load charts can be used to obtain the load capacities at various lifting hook distance from the boom tip. Moreover, the load capacities can be determined corresponding to the slew angles of the boom and / or reach of the boom tip from each load chart to determine the maximum load capacities.

[0032] In some embodiments, the step of determining the first maximum load capacity includes calculating the first maximum load capacity using a model of the crane where the first distance of the lifting hook from the boom tip and the boom arm position are used as input to the model, and the step of determining the second maximum load capacity includes calculating the second maximum load capacity using the model of the crane with the second distance of the lifting hook from the boom tip and the boom arm position as input to the model.

[0033] Accordingly, the maximum load capacities corresponding to one or more distances of the lifting hook from the boom tip can be determined by using values of the distance of the lifting hook from the boom tip together with the boom arm position.

[0034] In some embodiments, the model may be stored in a processor to facilitate the determination of the maximum load capacity of the crane in real time in different positions and configurations.

[0035] Moreover, in some embodiments, parameters related to distance of the lifting hook from the boom tip and the boom arm position (i.e., slew angle and / or reach of the boom) are determined using suitable sensors, and the processor calculates the maximum load capacities accordingly. In some embodiments, a user or an operator of the crane may input the distance of the lifting hook from the boom tip and the position of the boom arm manually into the model to determine the maximum load capacity.

[0036] In some embodiments, the model may be trained using a dataset.

[0037] In some embodiments, the model is adapted to provide a load chart based on the distance of the lifting hook from the boom tip and the operator / user determines the maximum load capacity from the load chart. The load chart can also provide the maximum load capacity based on the slew angle and / or reach of the boom.

[0038] In some embodiments, the wind speed is also used as an input into the model to generate the load charts. In some embodiments, the model includes an equation or a function for calculating the maximum load capacity of the crane depending on the distance of the lifting hook from the boom tip and the boom arm position.

[0039] According to another aspect, disclosed herein is a control system for a wind turbine tower mounted crane, the control system comprising a memory for storing program instructions and a processor for executing the program instructions, wherein the program instructions comprise computer code for determining a maximum load capacity for the crane, where the maximum load capacity is calculated based on the boom position and the distance of the lifting hook from the boom tip. In another embodiment, the control system is arranged to provide load charts for the crane at a plurality of heights above the ground.

[0040] The information needed to determine the load charts / maximum load capacities may be manually input by the user, or may in some embodiments be automatically generated. For example, information about the wind speed at the top of the wind turbine tower, may be sent through a wired or wireless connection to the control system, from an anemometer placed at the top of the turbine. Alternatively, or in addition, information about the load balance or force measurements on the crane can give detailed information about the stress the crane experiences from the given load. This information may also be automatically sent through the wired or wireless connection to the control system. In some embodiments, the control system further provides real-time feedback on maximum load capacities to the crane operator. If for example the wind suddenly increases as the wind turbine component is lifted, by giving real-time information to the crane operator as he is lifting, the operator is able to change the trajectory of the lift, or pause or abort the lift if the load limits are in danger of being exceeded.

[0041] In some embodiments, the real-time feedback comprises an alarm signal. The alarm signal may be in the form of visual notification or a sound notification, so that the control system makes the operator aware that safety limits are in danger of being exceeded.

[0042] In some embodiments, the wind turbine component is one of a section of the wind turbine tower, a rotor, a hub, a blade, a nacelle, a gearbox or a generator

[0043] It should be emphasized that the term "comprises / comprising / comprised of" when used in this specification is taken to specify the presence of stated features, integers, steps or components but does not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0044] Brief description of the drawings

[0045] In the following, the invention will be described in greater detail with reference to embodiments shown by the enclosed figures. It should be emphasized that the embodiments shown are used for example purposes only and should not be used to limit the scope of the invention.

[0046] Fig. 1 shows an embodiment of a prior art type wind turbine crane load chart.

[0047] Fig. 2 a)-c) shows embodiments of wind turbine crane load charts according to the current invention.

[0048] Fig. 3 shows a perspective view of a self-climbing crane lifting a tower section of a wind turbine. Fig. 4 shows a perspective view of a self-climbing crane installing a nacelle on a wind turbine tower.

[0049] Fig. 5 shows a perspective view of a self-climbing crane installing a wind turbine blade on a wind turbine hub.

[0050] Detailed description

[0051] Fig. 1 shows a prior art version of a load chart 1. This example shows a load chart for a tower mounted crane calculated at a max peak wind speed of 14 m / s. Here the maximum load capacity is shown as a function of the reach 2 of the crane and the slew angle 3. The reach is defined as the horizontal distance between the base of the boom arm and the lifting wire. The slew angle is defined as the rotation angle of the boom arm about a vertical axis passing through the base of the boom arm. The height of the load above the ground is not considered for these prior art load charts. Furthermore, a load chart is provided for the maximum allowed peak wind speed, for which a safe lift can be accomplished.

[0052] However, for modern cranes that are mounted on a very large wind turbine tower, the weight of the wires of the crane that extend from a tip end of the boom arm to the lifting hook becomes significant and affects the load carrying capacity of the crane.

[0053] To take this into consideration, figure 2a shows a first crane load chart, generally designated by reference numeral 1 , according to an embodiment of the disclosure. As shown, the first crane load chart 1 comprises information about the maximum load capacity 4 as a function of the reach 2 of the boom of the crane and the slew angle 3 of the crane. In this particular example, the input used to calculate the first load chart include a first crane mounting height 5, for example, 200m from a mounting surface, a first wind speed 6 at the first crane mounting height which is taken as 14m / s and a first hook distance 7 of a lifting hook from the boom tip that corresponds to 200m. Therefore, the first load chart 1 provides details of maximum load lifting capacities of the crane for various combinations of the boom reach and slew angle when the lifting hook of the crane is positioned close to the ground. It should be noted that the lifting hook’s height from the ground is inversely proportional to the distance between the lifting hook and the tip of the crane boom (i.e., boom tip). In the load charts in the figures the term “Hook height (from the crane tip)” is used. This should be understood as the distance between the lifting hook and the crane tip (i.e., boom tip).

[0054] FIG. 2b depicts a second load chart 10 again having information about the maximum load capacity 4 as a function of the reach 2 of the boom of the crane and the slew angle 3 of the crane. The second load chart 10 is determined / obtained / calculated at the first crane mounting height 5, the first wind speed 6 at the first crane mounting height 5 and a second hook distance 17 from the crane tip / boom tip that corresponds to 30m. Therefore, the second load chart 10 provides details of maximum load lifting capacities of the crane for various combinations of the boom reach 2 and slew angles 3 when the lifting hook of the crane is arranged 170m above the ground level.

[0055] In this example, the maximum load capacity, determined from the second load chart 10, for a reach 2 of 5m and a slew angle 3 of 30 degrees is 60t when the lifting hook height 7 is 170m from the ground. However, it can be seen from the first load chart 1 that for a reach 2 of 5m and a slew angle 3 of 30 degrees, the maximum load capacity of the crane is only 51t for the first hook height 17 i.e., at ground level. Accordingly, the crane can lift a maximum load of 511 at the ground level with the reach of 5m and slew angle of 30 degrees. However, as can be seen from the first load chart 1, for a reach of 2m and a slew angle of 30 degrees, the maximum load capacity of the crane is 811 for the first hook height. This means that the operator can safely take for example, a load of 60t, and start the lift close to the wind turbine tower. As the load is lifted, the boom of the crane can be extended, such that at a height of 170m above the ground, the reach of the crane is 5m.

[0056] Accordingly, a plurality of load charts can be determined / obtained / calculated for a plurality of hook heights from the ground for the crane and used to control the lifting operation of the crane based on the plurality of load charts. In an embodiment, a wind speed may also be used as an input for determining the load chart. For example, FIG. 2c depicts a load chart, for example, a third load chart 20. The third load chart 20 is determined / obtained / calculated at the first crane mounting height 5, a second wind speed 26 at the first crane mounting height 5 and the second hook height 17 from the crane tip i.e., boom tip that corresponds to 200m. Therefore, the third load chart 20 provides details of maximum load lifting capacities of the crane for various combinations of the boom reach 2 and slew angles 3 when the lifting hook of the crane is arranged at 170m above the ground level when the wind speed at the crane mounting height is 7m / s.

[0057] Consequently, by consulting load charts that are determined for various configurations or parameters related to the crane, as well as environmental factors such as wind speed and wind speed direction related to the crane slew angle, it is possible to make better use of the capacity of the crane.

[0058] Although, load charts are shown and contemplated to determine the maximum load capacity of the crane corresponding to a slew angle, a reach, a hook height, a wind speed, it may be appreciated that an operating system of the crane may include a model that allows the operator of the crane to determine a maximum load capacity of the crane based on the slew angle, the reach, the hook height, and other potential parameters, for example the wind speed and / or direction. In some embodiments, the model may provide a load chart to the operator corresponding to the hook height and the wind speed, having information about the maximum load capacity for each of the various combinations of the reach and the slew angle of the crane. In some embodiments, the model may include one or more equations or functions to determine the maximum load capacity of the crane. In such a case, the operator may input a hook height and a wind speed, and the model may determine the maximum lift capacity of the crane corresponding to the hook height and the wind speed for a minimum or optimum reach and minimum or optimum slew angle. However, it may be appreciated that a model may use a desired reach and / or a slew angle as the input for determining the corresponding load capacity.

[0059] These input parameters may be manually input by, for example, the crane operator into a computer system for calculating the load charts. Alternatively, the input parameters may be directly transmitted to the computer system by measurement equipment. For example, the wind speed at the crane mounting height may be measured directly by an anemometer placed on top of the wind turbine, and transmit the current wind speed through either a wired or wireless connection to the computer system.

[0060] Fig. 3 shows an example of a tower mounted crane 100 in the process of lifting a wind turbine component 101. In this instance, the wind turbine component 101 is a tower section of the wind turbine. The shown crane 100 is a self-climbing crane, comprising a boom arm 102, lifting wire 103 and clamps 104 for attaching the crane to the wind turbine tower. As will be appreciated, the distance from the ground to the installation height of the tower section, is substantially lower than the full height of the wind turbine tower. In this case, the lifting capacity of the crane is quite high, as the amount of wire between the crane tip / boom tip and the lifting hook is quite low. In addition, the tower section is lifted close to the existing tower, and at a low slew angle, hence, the lifting capacity of the crane is fine, as can be seen from the example load charts of fig. 2a to 2c.

[0061] Turning now to fig. 4, a perspective view of a self-climbing crane installing a nacelle on a wind turbine tower is shown. The weight of the nacelle on modern wind turbines may be large, for example 100 tonnes, and it must be installed at the top of the wind turbine tower, at the maximum height. Accordingly, a method according to an example embodiment of the current invention is used for lifting the nacelle to the top of the tower. Taking for example a situation with a 200m high tower, and a wind speed of 14m / s, the method at a first step determines a maximum load capacity of the crane at the ground level and determines one or more suitable configurations of the crane using the first load chart 1 as illustrated in Fig. 2a, the nacelle lift should start close to the tower, i.e. with a low reach, and with a slew angle as close to 0 degrees as possible. For example, the lift of the nacelle is started with the reach being less than 4m and a slew angle between 0 degrees and 20 degrees. As the nacelle is lifted above the ground and moved upwardly by retracting the wires on the winch drum, the weight of the wires decreases, and hence a different load chart may be used to facilitate a movement of the crane to a new configuration. For example, the method includes obtaining another load chart, for example, the second load chart 10, when the lifting hook reaches a certain height above the ground, for example, 170m, from the ground. At this position, the second load chart 10 is used to determine maximum load capacity of the crane and various available configurations of the crane for lifting the weight of 100 tonne. As can be seen from the second load chart, the crane can be operated safely with a reach of 5m and slew angle of 30 degrees. In this manner, the crane can be controlled based on the applicable load charts at various heights of the hook position to control lifting of the load and lifting of relatively larger weight as compared to the situation where the lifting operation is controlled based on single load chart.

[0062] Fig. 5 shows another view of a tower mounted crane 100 lifting a wind turbine component 101 , in this case a blade for the wind turbine. As can be seen from the figure, the boom arm 102 of the crane is extended a distance x from the vertical position. This distance x is also referred to as the reach 2 of the crane. Also illustrated in figure 5 is the slew angle 0. The weight of typical wind turbine blades may be on the order of up to 70t. Taking again the example from fig. 2a and 2b with a wind speed of 14 m / s, lifting a wind turbine blade with a weight of 70t, the lifting operation should start with a low reach of the crane boom, since the weight of the blade as well as the added weight of the lifting wire, means that the total load is at a maximum when starting the lift. As the blade is lifted, the cable weight is gradually reduced, which means that the total load can be increased. This allows the operator to extend the boom of the crane further, i.e., the reach can be increased as the blade is lifted towards its intended position. If the prior art load chart were used, then this operation might not have been possible, since the prior art load charts do not take the reduction in weight of the wires as the load moves upwardly into consideration.

[0063] It may be appreciated that the method may be performed by an operator of the crane by determining a plurality of maximum load capacities corresponding to a plurality of distances of the lifting hook from a ground, for example, a first maximum load capacity and a second maximum load capacity at a first position of the lifting hook and a second position of the lifting hook. For so doing, the operator can access a plurality of load charts. In some embodiments, the load charts may be stored inside a memory in the form a model, and a controller of the crane may provide the applicable load chart to the operator via a display based on input corresponding to crane mounting height, hook height, and the wind speed. In some embodiments, the operator may manually access the load charts stored inside the memory via the user interface.

[0064] In some embodiments, the crane may include suitable sensors to determine various input parameters during lifting of the load, and provides the applicable load charts i.e. , maximum load capacity of the crane at various hook heights. For example, the crane may include a wind speed sensor to monitor a wind speed at the crane mounting height and / or the hook height and obtain the load chart at the particular hook height and the wind speed. In some embodiments, the crane may include a detector to detect the extension of the wires from the tip of the crane and determines a hook height to obtain an associated load chart. In some embodiments, the memory may include a model for the crane that facilitates a determination, by a processor, of a plurality of load charts corresponding to a plurality of hook heights and / or determination of a maximum load capacity associated with an input hook height. In some embodiments, the model may use wind speed as one of the inputs to obtain load chart and / or maximum load capacity of the crane at a hook height. In some embodiments, the processor may calculate the maximum load capacity at a desired distance of the lifting hook from the boom tip directly using the equations or functions of the model without having to access or use a specific load chart.

[0065] Furthermore, in some embodiments, the crane may include a stress sensor to determine a stress or a load on the base of the crane and generate an alert when the stress / load on the base of the crane is above the maximum load capacity of the crane for the operating configuration of the crane. A processor may determine the maximum load capacity of the crane based on the hook height, the reach, the slew angle and the wind speed. In an embodiment, the alert may be a visual alert and / or an audio alert. In some embodiments, the processor is configured to control the boom of the crane or prompt the operator of the crane to control the boom of the crane when the load on the crane reaches the maximum load capacity of the crane and may operate the boom to adjust the slew angle and / or reach of the crane such that the load / stress becomes lower than the maximum load capacity. In some embodiments, the processor could continuously calculate the maximum load capacities and prevent the operator of the crane from moving the load into a not allowed position.

[0066] Although, the manual control of the crane based on the plurality of load charts and / or the plurality of maximum load capacity for the plurality of hook heights is described earlier. It may be appreciated that control system may automatically control the crane, for example, the reach and slew angle of the boom based on the model and input received from the hook height sensor, the crane mounting sensor, slew angle sensor, boom reach sensor etc. to safely lift the load.

[0067] It is to be noted that the figures and the above description have shown the example embodiments in a simple and schematic manner. Many of the specific mechanical details have not been shown since the person skilled in the art should be familiar with these details and they would just unnecessarily complicate this description.

Claims

Claims1. A method for moving a wind turbine component of a wind turbine between ground level and a desired position on the wind turbine using a crane having a boom arm with a boom base and a boom tip, a lifting hook and a lifting wire arranged between the lifting hook and the boom tip, the method comprising the steps of: a. determining a first maximum load capacity for the crane with the lifting hook located at a first distance from the boom tip, said first maximum load capacity being determined by taking into account both boom arm position and the first distance between the lifting hook and the boom tip; b. determining a second maximum load capacity for the crane with the lifting hook located at a second distance from the boom tip, said second maximum load capacity being determined by taking into account both boom arm position and the second distance between the lifting hook and the boom tip; and c. operating the crane to move the wind turbine component between ground level and the desired position, taking into account the first and second maximum load capacities.

2. The method according to claim 1 , characterized in that a. the step of determining the first maximum load capacity includes the step of obtaining a first load chart for the crane associated with the lifting hook being located at the first distance from the boom tip, the first load chart comprising information about maximum load capacities for the crane at different reaches and / or slew angles of the crane when the lifting hook is located at said first distance from the boom tip, b. in that the step of determining the second maximum load capacity includes the step of obtaining a second load chart for the crane associated with the lifting hook being located at the second distance from the boom tip, the second load chart comprising information about maximum load capacities for the crane at different reaches and / or slew angles of the crane when the lifting hook is located at said second distance from the boom tip, andc. in that said first and second load charts are different.

3. The method according to claim 1, characterized in that a. the step of determining the first maximum load capacity includes calculating the first maximum load capacity using a model of the crane where the first distance of the lifting hook from the boom tip and the boom arm position are used as input to the model and the maximum load capacity is the output of the model, and b. in that the step of determining the second maximum load capacity includes calculating the second maximum load capacity using the model of the crane with the second distance of the lifting hook from the boom tip and the boom arm position as input to the model.

4. The method according to claim 3, characterized in that the model includes an equation or a function for calculating the maximum load capacity of the crane depending on the distance of the lifting hook from the boom tip and the boom arm position.

5. The method according to any one of claims 1 to 4, characterized in that the step of determining the first and second maximum load capacities takes into account the weight of the lifting wire arranged between the boom tip and the lifting hook at the first and second distances of the lifting hook from the boom tip.

6. The method according to any one of the preceding claims, characterized in that the method further comprises the steps of determining the maximum load capacities for the crane at different boom positions with the lifting hook located at a different distance from the boom tip than the first and second distances.

7. The method according to any one of the preceding claims, characterized in that the maximum load capacities are obtained with the lifting hook located at different distances from the boom tip before initiating the movement of the wind turbine component.

8. The method according to any one of claims 1 to 6 characterized in that each of the first, second or further maximum load capacities are calculated during the movement of the wind turbine component.

9. The method according to any of the preceding claims, characterized in that the step of determining the maximum load capacities takes into account the wind speed at the first and second distances of the lifting hook from the boom tip.

10. A control system for a wind turbine tower mounted crane, the control system comprising a memory for storing program instructions and a processor for executing the program instructions, wherein the program instructions comprise computer code for determining a maximum load capacity for the crane, where the maximum load capacity is calculated based on the boom position and the distance of the lifting hook from the boom tip.

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