GB2487072A

GB2487072A - Method of detecting damage to a wind turbine component during transport

Info

Publication number: GB2487072A
Application number: GB1100182.3A
Authority: GB
Inventors: Lars Glavind; Ib Svend Olesen
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2011-01-06
Filing date: 2011-01-06
Publication date: 2012-07-11
Also published as: GB201100182D0

Abstract

A method of detecting damage to a wind turbine component during transport comprises: mounting the wind turbine component on or in a transport unit; providing a first sensor for detecting damage to the wind turbine component by operatively monitoring a first physical parameter of the component during transport; connecting the first sensor to a power supply provided on or in the transport unit; operating the sensor during transport to monitor the first physical parameter of the wind turbine component and emit an output signal based on the value of the first physical parameter; receiving the output signal from the first sensor; and processing the output signal with a controller to detect changes to the value of the first physical parameter that are indicative of damage to the wind turbine component. The method may detect the first physical parameter going beyond a threshold value thereby indicating potential damage to the wind turbine blade. The sensor may detect deformation, temperature, acoustic emissions, weight, surface cracks or corrosion, or acceleration. A second sensor may be triggered to monitor a second physical parameter of the wind turbine component when the first physical parameter goes beyond the threshold. The first sensor may be a sensor embedded within the wind turbine component for sensing the same physical parameter during operation of the turbine.

Description

METHOD OF DETECTING DAMAGE TO A WIND TURBINE COMPONENT

DURING TRANSPORT

The present invention relates to a method of monitoring a wind turbine component during transport of the component, for example to the installation site, in order to detect damage to the component. The invention finds particular application in the detection of damage to wind turbine blade components during transport.

Wind turbines are formed of a number of separate components, including the tower, the nacelle, the hub and the blades, which are typically assembled at the installation site.

The individual components must be transported in some way from the place of manufacture to the installation site, which may be in a remote location. At least part of the journey is likely to be over land, with the wind turbine component mounted on the back of a truck or train. A major concern during the transport of wind turbine components is the avoidance of damage to the component, which can reduce the lifetime of the component and at worst, may weaken the component such that it is incapable of withstanding the forces to which it may be subjected during operation of the turbine.

Damage can occur as a result of impact to the component either during the loading or unloading of the component, or during transportation, for example as a result of a collision or a sudden, sharp movement of the transport vehicle. In addition, there is the potential for damage to occur as a result of the component being subjected to sustained, high levels of strain or deformation during transportation. Certain types of components, such as wind turbine blades or blade portions, are likely to be subjected to relatively high loads simply as a result of supporting their own weight. In addition, forces will be exerted back on the * component by the transport unit on which the component is loaded or mounted: The magnitude of these forces will be affected by external factors such as the quality of the road surface or the quality of the driving of the transportation vehicle.

Continuous and high levels of vibration may also be a problem during transport, for example, in parts of the component that are positioned directly above the wheels of a transportation vehicle. Furthermore, extreme environmental conditions, such as extreme temperatures or humidity levels, may have an adverse effect on the integrity of the materials from which the component is formed.

A visual inspection of the component is typically carried out once the component reaches the installation site. However, whilst this visual method may detect certain types of damage which are apparent on the surface of the component, it is generally an ineffective way of detecting damage to the components, since often the damage may not be visible on the outside of the component. Furthermore, visual methods provide no way of identifying potential damage or weakness within a component, which may increase the likelihood of damage or malfunctioning of the component during operation. Based on a visual inspection alone, it is also typically not possible to identify the location or time at which the damage took place, which makes it difficult or impossible to determine responsibility or liability for the damage or to prevent similar damage occurring again.

It would therefore be desirable to provide a method for monitoring wind turbine components during transport, which enables damage to the component to be detected before the component is put into place on the turbine and may also enable the prevention of damage to subsequently transported components. It would also be desirable if such methods could enable the lifetime of the component to be predicted.

According to the invention there is provided a method of detecting damage to a wind turbine component during transport, the method comprising the steps of: mounting the wind turbine component on or in a transport unit; providing a first sensor for detecting damage to the wind turbine component by operatively monitoring a first physical parameter of the component during transport; connecting the first sensor to a power supply on the transport unit; operating the first sensor during transport to monitor the first physical parameter of the wind turbine component and emit an output signal based on the value of the first physical parameter; receiving the output signal from the first sensor; and processing the output signal with a controller to detect changes to the value of the first physical parameter that are indicative of damage to the wind turbine component.

The term first physical parameter' is used to refer to a physical parameter of the wind turbine component which varies as a result of forces exerted on the component and changes in a predictable way as a result of damage to the blade. Examples of the first physical parameter are described below in more detail and include but are not limited to deformation of the component and local temperature of the component.

The method of the present invention provides an effective way of monitoring a wind turbine component during the period in which the component is being transported. This increases the traceability of the component and provides an improved way of detecting damage to the component or adverse conditions to which the component has been subjected during transportation which may increase the likelihood of subsequent damage to the component. Information and data that is collected about the parameters of the component during transport may also be useful in reviewing and potentially adapting features of the transportation process such as the transport route, the transport vehicle or the manner in which the component is mounted, or in detecting any abnormalities in the transport process.

The method of the present invention is suitable for use in conjunction with a wide variety of sensors, which can be used to monitor a wide variety of physical parameters of the component during transport, as set out in more detail below. The physical parameter to be monitored using the method of the present invention can be selected depending upon the type of journey, the likely conditions during transportation and the most likely types of damage to occur to the component. All of the necessary apparatus for operating the first sensor and receiving and analysing data from the first sensor can conveniently be provided in situ on or in the transport unit and in some cases, would already be incorporated within the transport unit for other purposes.

The first sensor must be connected to a power supply which is being transported along with the component on the transport unit. The power source may be provided within the transport unit, such as a mains electricity source or a battery. Alternatively, the power supply may be provided within the wind turbine component, for example as part of the first sensor device, or may be mounted on the transport unit in proximity to the component. In most cases, the receiver and the controller will also require connection to a power supply during operation, which may be the same power supply as that to which the first sensor is connected, or a different power supply. The sensor system may be adapted to work continuously during the time period over which the component is transported, or may be adapted to work intermittently or in response to a particular set of conditions.

Preferred methods according to the present invention further comprise the step of determining a threshold value for the first physical parameter and detecting when the value of the first physical parameter goes beyond the threshold value, thereby indicating potential damage to the blade. Such methods can effectively be used to detect when a physical parameter changes significantly from its expected value under normal conditions to a value which is sufficiently high (or low) that damage to the component is to be expected. For example, levels of deformation above a certain threshold value are likely to adversely affect the mechanical integrity of the component and may result in a certain amount of damage to the component. Similarly, values of temperature above a certain level are likely to be indicative of an abnormal event such as a cracking of the component.

Detection of values of the first physical parameter beyond the threshold value may provide a direct indication of damage, for example in the case of a crack detection sensor, or may simply provide an indication that there is an increased likelihood that damage has occurred, so that the component can be tested further, repaired or replaced rather than being put into place on the turbine.

In some cases, it may be appropriate to determine a maximum threshold value such that values of the first parameter above the threshold value are indicative of damage to the component. This will be the case, for example, when deformation is monitored. Conversely, in other cases, it may be more appropriate to determine a minimum threshold value such that values of the first parameter below the threshold value are indicative of damage. This may be the case, for example, when temperature is monitored in order to detect damage due to extreme, low temperatures.

The first sensor may be operated to emit an output signal only when the value of the first physical parameter goes beyond the threshold value. Alternatively, the first sensor may emit a continuous output signal and changes to the first physical parameter beyond the threshold value may instead be detected by the controller. For example, the controller can be programmed to compare the measured values of the first physical parameter against a preset threshold value and generate a warning when the threshold value is exceeded. In some cases, the warning may advantageously be used to provide the driver of the transport unit with an immediate indication that there may be damage to the component, so that measures can be taken to prevent the damage from worsening during further transport.

Alternatively or in addition, the warning may be stored so that it can provide an immediate indication of actual or potential damage when the component arrives at the installation site.

In certain embodiments of the present invention, a second sensor is provided for operatively monitoring a second physical parameter of the wind turbine component, wherein the detection of a value of the first physical parameter beyond the threshold value triggers the second sensor to begin monitoring the second physical parameter. The second physical parameter may be the same as the first physical parameter, or may be different.

In methods of this type using a second sensor, the first sensor is typically used to continuously monitor the first physical parameter of the component and detect a change from normal to abnormal conditions as a result of damage to the component, Le. to identify that damage has occurred. The second sensor is then triggered, for example, to provide more accurate measurement of the same physical parameter or a different physical parameter. Once the occurrence of damage has been identified by the first sensor, the second sensor may be used to provide additional or more detailed information or data about the severity, location or propagation of the damage. In one example, the second sensor is a CCD camera which is used to visually monitor the component upon detection of abnormal conditions by the first sensor.

Preferably, the wind turbine component is provided with an embedded or integrated first sensor, for monitoring a physical parameter within the material forming the wind turbine component. Typically, such a first sensor would be integrated or embedded within the component during manufacture of the component, for example, a suitable sensor may be incorporated into a composite, moulded wind turbine component such as a blade during the -5-.

moulding process. The embedding of certain types of sensors within a wind turbine component is a well known process which is used for the incorporation of sensors intended for monitoring the component during operation of the turbine. In particular, it is well known to embed fibre optic sensors within composite components such as blades.

The first sensor may be embedded a small distance underneath the surface of the component in order to monitor a physical parameter of the surface of the component. This arrangement may be suitable, for example, for detecting surface damage such as corrosion or cracking. Alternatively, the first sensor may be embedded deeper within the material of the component in order to monitor a physical parameter within the interior of the component.

This arrangement may be suitable, for example, for measuring strain within the component for the purposes of detecting damage within the components, such as delamination or * cracking.

Advantageously, the embedded or integrated sensor for monitoring a physical parameter during transport of the component may be an existing sensor that has been incorporated within the component for the purposes of monitoring the same physical parameter during operation of the turbine. This is particularly convenient and efficient, both from a cost and a processing perspective, since it means that it is not necessary to incorporate an additional sensor into the component. Instead, the method of the present invention can be carried out using the existing sensors within the component. The additional apparatus that is required to operate the first sensor within the blade component during transport, such as the power supply and a suitable receiver for receiving the output signal from the first sensor, can readily be provided within the transport unit or may in fact already be present within the transport unit or the component.

In other preferred embodiments, the first sensor used in methods according to the invention may be mounted on an inner or outer surface of the wind turbine component for monitoring a physical parameter of the surface of the component. For example, the first sensor may be provided for operatively monitoring the strain at the surface, bending of the component or temperature or humidity at the surface.

In some cases, it may be possible to mount the first sensor or a component thereof adjacent or proximate the component for monitoring a physical parameter of the component which does not require the first sensor to be in direct contact with the component. This arrangement may be suitable, for example, where the first sensor is operative to monitor temperature at the component surface or to detect acoustic waves released from the component as described in more detail below.

In preferred embodiments, the first sensor used to monitor the component in methods according to the present invention is a strain or deformation sensor used to monitor a type of strain or deformation of the component during transport. The strain or deformation sensor may be embedded within the component, or may be mounted on the surface, as described above. Suitable sensors may be operated to monitor strain, bending or twisting of the component in one or more directions. For example, in the case of a wind turbine blade, the embedded sensor may be used to monitor edgewise or flapwise bending of the blade.

The wind turbine component will be subjected to various forces during transportation which will lead to strain within the component. For example, certain types of component may be subjected to a relatively high amount of sustained loading due to their own weight and/or due to deformation or bending of the component caused by the movement of the component on the transport unit during transport. In addition, the component may be subjected to sudden, high levels of strain as a result of, for example, an impact or a sharp acceleration or deceleration of the transport unit. In many cases where damage occurs to the component as a result of high levels of strain during transport, the damage will not be visible and therefore would not be detected during a visual quality control. However, the is method of the present invention can be used to monitor and record strain or deformation levels of the component throughout the transportation process so that components that have been subjected to undesirably high levels of strain can be detected and appropriate action taken.

In particularly preferred embodiments of the present invention, the wind turbine component is provided with an embedded sensor comprising an arrangement of optical fibres. Methods using such optical fibre arrangements include the steps of inputhng a light signal into the one or more optical fibres from a suitable light source; receiving light that has transmitted or reflected along the one or more optical fibres using a suitable optical detector; and processing the received light to determine the monitored parameter of the wind turbine component.

Various arrangements of optical fibres for the measurement of strain and deformation in wind turbine components, such as wind turbine blades, are well known. Some known types of optical fibre sensor systems detect changes in the light transmitted through the optical fibre and received at the opposite end to the light source, such as changes in wavelength, intensity or polarisation of the light, which indicate a change in the optical fibre, such as length, arising as a result of strain or deformation of the component on or in which the optical fibre has been mounted. Other systems detect changes in the light reflected back through the optical fibre towards the light source.

In certain embodiments, the method according to the invention may use a Fibre Bragg Grating (FBG) sensor. A FBG sensor is an optical fibre in which an optical grating is formed. The grating itself is typically a periodic variation in the refractive index of the fibre, tuned to reflect a particular wavelength of light. The part of the optical fibre having the grating is attached to the region of the wind turbine component where the strain is to be measured. It is attached in such a way that any deformation or strain experienced by the component is transmitted to the fibre and to the grating. Deformation and strain causes the spacing of the grating to change, and causes a detectable change in the wavelength of light reflected back by the grating. Various arrangements are known for inserting light into the FBG sensors and for extracting and analysing the output.

In alternative embodiments, the method according to the invention may use a long period grating (LPG) sensor. Such sensors enable bend to be measured directly. LPG sensors generally have a grating with a period much larger than the wavelength of the operating light source. Thus, in contrast to FBG sensors, LPG sensors do not produce * reflected light but serve as spectrally selective absorbers. The grating couples light traveling in a guided mode to a non-guided or cladding mode. The light coupled in these non-guided modes interacts with surface defects on the optical fibre and is rapidly attenuated, which results in resonance loss in the transmission spectrum, from which bend may be calculated.

In alternative methods according to the invention, a temperature sensor may be used to monitor the temperature of different parts of the component in order to detect local changes in temperature which are indicative of increased strain within the component, or the release or energy due to damage to the component, such as cracking. A temperature sensor, such as a thermocouple, may be provided on or within the component in order to provide actual temperature measurements. Alternatively, some methods according to the invention may use thermal imaging methods to detect local hot spots' in the component, for example, using an infrared camera. By identifying areas of increased local temperature in the component, the presence and position of defects or high areas of stress can be identified.

Methods according to the invention may also use a first sensor which monitors acoustic emissions from the component in order to identify acoustic or stress waves that are emitted during the occurrence of damage to the component. For example, acoustic waves will be detected upon the cracking, delamination, deformation or crushing of the component, or upon an impact, which enable the damage to be detected and the position of the damage to be identified. A microphone may be mounted on or adjacent the component in order to detect audible sounds resulting from, for example, cracking or delamination of the component or a collision of the component with an external object. Other types of sensor, such as piezoelectric sensors, may be mounted on the surface of the component to detect acoustic or stress wave activity.

As a further alternative to the sensors described above, methods according to the present invention may use a first sensor for monitoring the weight or load of the wind turbine component, or a part thereof. Certain changes to the weight or load of the wind turbine component may be indicative of a part breaking off from the component, or coming loose.

In further alternative embodiments of the present invention, the first sensor may be an accelerometer or G-sensor mounted on or in the wind turbine component in order to measure the vibration of the component during transport, wherein the output signal from the first sensor is processed to detect values of acceleration above a threshold value thereby indicating potential damage to the component.

10. The wind turbine component will be subjected to a certain amount of strain during transport as a result of vibration of the component, for example, arising from an uneven road surface or from vibration of the transport unit on which the component is mounted.

Relatively high levels of strain for sustained periods during the transportation of the component may affect the lifetime of the component, or may cause damage such as is cracking or delamination. It is therefore desirable to detect high levels of vibration and take all possible measures to minimise the vibration during transport, for example by providing additional damping means on the transport unit, or by avoiding the use of roads or tracks having a particularly uneven surface.

One preferred embodiment of the present invention provides a method for detecting cracking, delamination or corrosion at the surface of the component using a system of fibre optics embedded at or adjacent the surface. Such arrangements can advantageously be used to provide an early warning of cracking, delamination or corrosion, so that appropriate measures can be taken to prevent the damage from worsening. Upon initial cracking, delamination or corrosion of the surface, at least one optical fibre becomes exposed at the surface of the component, thereby altering the transmission or reflective properties of the fibre, as detected by a suitable receiver. As the damage worsens, for example due to propagation of the crack or further corrosion, the at least one optical fibre at the surface will eventually break or corrode itself, so that the transmission of light through the fibre is terminated. This event can also be detected by a suitable light detector or receiver. In some examples, parallel networks of fibres may be provided, which break sequentially as the damage spreads from the surface into the component.

In one example, the optical fibres of the first sensor are doped with a material which releases light at a particular wavelength upon exposure to external light when the surface of the component cracks or is corroded to reveal the embedded optical fibre. Suitable optical fibres may be doped with a fluorescent material, or a scintillation material. The material is preferably excited by light at a wavelength present in ambient daylight, such as visible light, infrared or ultraviolet, or by ionising radiation present in the environment. The fluorescence or other light emitted from the fibres can be detected using a suitable light detector or receiver in order to detect that the damage has occurred and determine the location of the damage.

s A single sensor may be incorporated into the wind turbine component in order to monitor a specific parameter at a specific location. The location is preferably selected so that the sensor monitors a location at which the risk of damage is considered to be highest.

However, in many cases it will be desirable to incorporate one or more additional sensors into the wind turbine component. The additional sensors may also be used to carry out methods according to the invention, or may be used for the monitoring of parameters for reasons other than to detect damage.

* A plurality of the same type of sensor, including the first sensor, may be provided in order to monitor the same physical parameter at different positions on or in the wind turbine component so that damage at those different positions can be detected. This may be advantageous if there is likely to be considerable variation in the parameter depending upon where the measurement is taken, or if the location of damage is unpredictable. For example, a number of strain sensors may be embedded in order to monitor the strain level at different positions within the component.

A combination of different types of sensors may also be provided, in order to independently monitor a number of different physical parameters of the component during transport using methods according to the invention, or to detect different types of damage to the component. For example, one or more strain sensors could be used to monitor strain in a component, whilst a temperature sensor is used to independently monitor the temperature at the surface of the component. In another example, the first sensor is used to detect cracks at the surface of the component, whilst the second sensor is used to detect deformation of the component. Any additional sensors may be connected to the same power supply, receiver and/or controller as the first sensor, or different apparatus for operating each sensor may alternatively be provided.

In some cases, the output of the first sensor may vary depending on the local conditions at the sensor, such as temperature or humidity. One or more additional sensors may be used in order to operatively monitor the local conditions, such as temperature and humidity, in the region of the first sensor so that the output signal from the first sensor can be adjusted or compensated to take into account the variation in conditions.

In preferred embodiments of the present invention, the method further comprises the step of monitoring the location of the transport unit. comprising monitoring the location of the transport unit and processing the output signal from the sensor to determine the first physical parameter of the wind turbine component as a function of location and to thereby detect the location at which any damage to the component occurred.

Suitable devices for establishing location are commonly available and could be readily incorporated into the transport unit. For example, suitable devices include GPS (Global Positioning System) devices using satellite positioning systems, or GSM (Global System for Mobile Communications) devices providing mobile phone localisation using telecommunication network systems. Such devices allow for the location of the transport unit to be tracked and recorded so that the exact location of any damage to the component can be established. Specific regions in which the component is subjected to high levels of strain or deformation, for example due to an uneven road surface, can also be identified and if necessary, an alternative route can be selected for the transport of subsequent components, based on this information.

In addition or alternatively to the monitoring of the location of the transport unit, methods according to the invention may further comprise the step of monitoring the first physical parameter of the wind turbine component as a function of time whereby the time at which any damage occurred to the component can be determined.

By monitoring at least one of the location and time of the transport unit so that the time or place at which any damage occurred to the component can be determined, the traceability of the component can be greatly improved. Any patterns in damage to the components over distance or time can be detected so that necessary changes can be made to the transport and logistics of the component. Responsibility and liability for any damage can also more readily be ascertained.

During transportation of the component using methods according to the present invention, the output signal from the first sensor is received by a suitable receiver or detector and the signal is then processed by the controller in order to determine the value of the first physical parameter of the component. An appropriate receiver and connection between the sensor and the receiver will be provided according to the type of output signal generated by the sensor. The first sensor may generate an electrical signal, an optical signal, a radio signal or another type of electromagnetic or magnetic signal during use.

The output signal may be transmitted to a local receiver provided within the transport unit using a suitable arrangement of wires, fibres or cables. Alternatively, the output signal may be wirelessly transmitted from the first sensor and received by a receiver or detector which is provided in a separate location within the transport unit, or remotely from the transport unit.

In one preferred embodiment, the output signal is wirelessly transmitted and can be received by a receiver provided within another transport unit within the same convoy as the -11-.

transport unit carrying the monitored component. This may provide transport units further back in the convoy with a warning of potentially undesirable conditions ahead so that subsequent transport units can be stopped or diverted before damage to further components is caused.

The output signal from the sensor is received by any suitable means and then sent to the controller for processing. The controller may be integrated with the receiver, or may be a separate component which is connected to the receiver with suitable wires or cables, or using a wireless connection. The controller is preferably a type of portable computer which can be readily incorporated within the transport unit. The information or data providing information about the measured parameter may be stored within the controller or associated hardware, so that it can be analysed at the end of the journey. In some cases, methods according to the present invention may additionally further comprise the step of outputting one or more control signals from the controller based on the measured physical parameter of the wind turbine component.

The control signal may be used to provide information to the driver of the transport unit, so that he can monitor the component and if necessary, adjust the loading of the component and/or the way in which the transport unit is driven. Alternatively or in addition, in some cases the control signal may be used directly to control a device within the component, or the transport unit, for example, to adjust the damping of the component, or to control the temperature of the component. In certain cases, the control signal may be transmitted to a different location, such as to other transport units within a convoy, as an alternative or in addition to the transmission of the output signal, as described above, and for similar purposes.

* The method of the present invention is suitable for monitoring any type of wind turbine component but finds particular application in monitoring composite wind turbine components, in particular, wind turbine blade components including blade shells and blade spars. In the transport of wind turbine blade components, it is particularly desirable to monitor the strain and deformation of the components during transport so that any damage or potential weakness in the blade component can be identified before the blades are subjected to further loading during operation of the turbine.

The method of the present invention is suitable for use in conjunction with a variety of types of transport unit, including but not limited to lorries, trucks, carts, trains, trailers, boats and barges. The component is mounted' on the transport unit, where the term mounted' is to be interpreted broadly as including any arrangement for transporting the component using the transport unit. For example, the component may be mounted on the transport unit, in or within the transport unit, or the first component may be connected to the transport unit by suitable means, or it may form a part of the transport unit.

The invention wilt now be further described, by way of example only, and with reference to the accompanying figures in which: Figure 1 is a front view of a horizontal axis wind turbine; and Figure 2 is a schematic view of a wind turbine blade mounted on a lorry for transportation and incorporating a sensor system for detecting damage to the blade during transport; and Figure 3 is a schematic view of a wind turbine blade incorporating an alternative sensor system for detecting damage to the blade during transport.

Figure 1 illustrates a wind turbine 1, comprising a wind turbine tower 2 on which a wind turbine nacelle 3 is mounted. A wind turbine rotor 4 comprising three turbine blades 5 attached to a central hub 6 is mounted on the turbine. The wind turbine illustrated in Figure 1 may be a small model intended for domestic or light utility usage, or for example may be a large model, such as those that are suitable for use in large scale electricity generation on a wind farm. In the latter case, the diameter of the rotor may be as large as 100 metres or more.

For larger models, the wind turbines are typically assembled at the operation site and the tower, nacelle, hub and blades will all be transported to the site separately. Figure 2 provides a schematic illustration of one of the wind turbine blades 5 mounted on the back of a truck 10 for transportation.

The blade 5 incorporates a sensor arrangement 10 comprising a plurality of Fibre Bragg Grating sensors 12 for monitoring strain in different positions along the blade 5. The sensor arrangement comprises a light emitting device 14, such as an LED, laser, halogen or metal halide source, a light collecting measuring device 16, such as a photo-sensor, and an optical fibre 18 with an optical grating. The light emitting device 14 is connected to one end of the optical fibre 18 to input light into the fibre, and the light measuring device 16 is connected to the other end to receive light transmitted along the fibre. A controller (not shown) is connected to both the light emitting device and light measuring device, by connections, such as wires or cables.

The optical fibre 18 runs along the length of the wind turbine blade 5 with the FBG sensors 12 spaced apart along the length of the blade. The optical fibre 18 has been incorporated within the composite material forming the outer shell during moulding of the blade so that the optical fibre is embedded within the shell. The light source 14 and the light collecting measuring device 16 are provided within a mounting box on the transport unit.

The FBG sensors 12 are primarily adapted for use in the monitoring of strain in the blade during operation of the wind turbine but may be similarly operated during transport.

The blade is mounted on the trailer unit 22 of the truck 20 shown in Figure 2 using conventional loading methods. The truck is steered and powered by the front cab 24, in which the controller is located. In order to monitor the strain within the blade 5 during transport, the FBG sensors 12 are connected to the mains power supply (12V/24V) already provided on the truck.

In operation, the light emitting device 14 inputs broadband, white light into the optical fibre 18. The FBG strain sensor arrangement operates by detecting changes in the wavelength of the light reflected along the optical fibre 18 by the optical grating. Any deformation of the wind turbine blade within which the portion of the optical fibre * incorporating the optical grating is embedded will cause a change in the spacing of the optical grating and a resultant change in the wavelength of the reflected light.

When the optical fibre 18 is in an unstrained state, the wavelength of the light received at the input to the light detector is determined. This wavelength may be considered a zero or a rest value for the purposes of calibrating the sensor.

The controller comprises a memory for storing the wavelength output received from the light collecting measuring device. An analyser, such as a processor, is provided within the controller to analyse the wavelength variation and determine a value for the strain to which the blade is being subjected. Once the blade arrives at its destination, an operator can review the strain measurements from the journey and look for any particularly high levels of strain which might indicate that some damage has occurred to the blade during transport.

The operator can additionally use the strain measurements to predict the lifetime of the * blade.

The transport unit is further equipped with a GPS system (not shown) which tracks the location of the transport unit and feeds the information to the controller, so that the controller can determine the variation of strain as a function of position and detect the location at which any damage occurs.

Figure 3 illustrates a wind turbine blade 30 incorporating an alternative sensor arrangement 32 for detecting cracks at the surface of the blade during transport on a transport unit similar to that shown in Figure 2.

The sensor arrangement 32 comprises a plurality of optical fibres 34 embedded within the blade shell, underneath the surface and extending around the perimeter of the blade. The plurality of optical fibres 34 are in a parallel arrangement to each other and to the surface of the blade and are spaced apart by a small distance from each other, with the first optical fibre being embedded immediately underneath the surface of the blade shell and the other optical fibres being embedded successively deeper within the blade shell. Four parallel optical fibres are shown schematically in Figure 4 but a higher number may be provided.

As in the sensor arrangement shown in Figure 2, the arrangement 32 of Figure 3 additionally comprises a light emitting device 36, such as an LED, laser, halogen or metal halide source and a light collecting measuring device 38, such as a photo-sensor. The light emitting device 36 is connected to one end of each of the optical fibres 34 to input light into the fibres, and the light measuring device 38 is connected to the other ends to receive light transmitted along the fibres. A controller (not shown) is connected to both the light emitting device and light measuring device, by connections, such as wires or cables.

The blade 30 is first mounted on the transport unit, as described above in relation to blade 5. In operation of the sensor arrangement 32 during transport, the light emitting device 36 inputs broadband, white light into the plurality of optical fibres 34. If a crack 40 occurs at the surface of the blade, as shown in Figure 3, the crack will typically propagate in a direction substantially perpendicular to the surface of the blade. The crack 40 will reach the uppermost optical fibre 38 first and will cause the optical fibre to break. The breakage of the optical fibre will be immediately detected since the optical fibre will no longer transmit any of the incident light and therefore no light will be received from that optical fibre at the light receiver 38. As the crack propagates down through the blade shell, the plurality of optical fibres will successively break and the breakage of each fibre will be detected as described above, by detecting a sudden break in the light transmission through each fibre.

The sensor arrangement 32 may be adapted to determine the location of the crack by using the light source 36 to provide a pulsed light source and by providing an additional * light receiver at the same end of the fibre as the light source. The time taken for the pulses of light to reflect back to the end of the optical fibre from the point of breakage can be measured and the controller can use this information to calculate the distance of the crack from the light source.

The blade 30 further comprises a microphone 42 within the blade which provides an additional means for detecting a crack in the blade. The microphone will also detect any cracking by detecting the audible sound generated upon cracking.

Claims

CLAIMS1. A method of detecting damage to a wind turbine component during transport, the method comprising the steps of: mounting the wind turbine component on or in a transport unit; providing a first sensor for detecting damage to the wind turbine component by operatively monitoring a first physical parameter of the component during transport; connecting the first sensor to a power supply provided on or in the transport unit; operating the sensor during transport to monitor the first physical parameter of the wind turbine component and emit an output signal based on the value of the first physical parameter; receiving the output signal from the first sensor; and processing the output signal with a controller to detect changes to the value of the first physical parameter that are indicative of damage to the wind turbine component.
2. A method according to claim I further comprising determining a threshold value for the first physical parameter and detecting when the value of the first physical parameter goes beyond the threshold value, thereby indicating potential damage to the blade.

2ci
3. A method according to claim 2 wherein the sensor is operated to emit an output signal only when the value of the first physical parameter goes beyond the threshold value.
4. A method according to claim 2 or 3 further comprising providing a second sensor for operatively monitoring a second physical parameter of the wind turbine component, wherein the detection of a value of the first physical parameter beyond the threshold value triggers the second sensor to begin monitoring the second physical parameter.
5. A method according to any preceding claim wherein the first sensor is embedded within the wind turbine component.
6. A method according to any preceding claim wherein the first sensor is operated during transport to monitor deformation of the wind turbine component and wherein the output signal from the first sensor is processed to detect changes in the deformation of the component causing potential damage to the component.
7. A method according to claim 6 wherein the first sensor for monitoring deformation comprises an optical fibre arrangement including one or more Fibre Bragg gratings or Long Period gratings.
8. A method according to any of claims I to 5 wherein the first sensor is operated during transport to monitor a physical parameter selected from: temperature, acoustic emission, or weight of the component or a part thereof and whereby the output signal from the first sensor is processed to detect changes in the parameter indicative of damage to the component.
9. A method according to any of claims I to 5 wherein the first sensor is an optical fibre sensor provided at or proximate the surface of the component and operative to detect cracks or corrosion at the surface.
10. A method according to any of claims I to 5 wherein the first sensor is an accelerometer or a G-sensor for operatively monitoring acceleration of the wind turbine component and wherein the output signal from the first sensor is processed to detect values of acceleration above a threshold value thereby indicating potential damage to the component.
11. A method according to any preceding claim further comprising monitoring the location of the transport unit and processing the output signal from the sensor to determine the value of the first physical parameter of the wind turbine component as a function of location and to thereby detect the location at which any damage to the component occurred.
12. A method according to any preceding claim further comprising monitoring the first physical parameter of the wind turbine component as a function of time whereby the time at which any damage occurred to the component can be determined.
13. A method according to any preceding claim further comprising outputting one or more control signals from the controller when damage to the component is detected.
14. A method according to any preceding claim comprising wirelessly transmitting the output signal from the sensor and receiving the output signal remotely from the transport unit.
15. A method according to any preceding claim for monitoring a wind turbine blade component during transport.