The invention relates to a grounding system for a concrete structure, the grounding system comprising an electrically conductive mounting element and a grounding de- vice for casting into the concrete structure. A method for arranging the grounding sys tem in the concrete structure is described as well.

The prior art and the drawbacks thereof

Offshore wind turbines are particularly prone to lightning strikes, and, therefore, solu tions that reduce the risk of damage by possible lightning strikes are sought. One precaution is turbine platforms made of concrete, on which railings are formed from an electrically non-conductive material, preferably a composite material. On the turbine platform various electric components may be installed, for example navigation lights, sign lights and antennas. A known and commonly used method for grounding on concrete structures is the use of a ground wire. A first end of the ground wire is attached to a reinforcing element in the concrete structure, whereas a free second end of the ground wire extends out of the concrete structure, whereupon the free end is attached to the electric component or a cable rack, for example by the use of a screw connection.

A substantial drawback of the prior art is that the ground wire is prone to corrosion. This problem is particularly large offshore because of moist and salty air. A ground wire that extends on the exterior of the concrete structure, for example in an arc, may also function as an electric antenna which may give interference in electric equipment and apparatuses, referred to as EMC in technical language.

The invention has for its object to remedy or reduce at least one of the drawbacks of the prior art or at least provide a useful alternative to the prior art. The object is achieved through the features that are specified in the description below and in the claims that follow.

General description of the invention

The invention is defined by the independent claims. The dependent claims define ad vantageous embodiments of the invention.

In a first aspect, the invention relates more specifically to a grounding system for a concrete structure, the grounding system comprising a mounting element and a grounding device. The grounding device comprises: i) an electrically conductive mounting bracket with a first coupling face for a mounting element and at least one cast-in portion for casting into the concrete structure; and ii) an electrically conductive grounding element which, in a first end portion, is at tached in an electrically conductive manner to a second coupling face of the mounting bracket and, in a fixing portion, is arranged for electrically conductive coupling to a reinforcing element of the concrete structure, the grounding element and the second coupling face being arranged to be covered by the concrete structure. The mounting element is attached in an electrically conductive manner to the mounting bracket.

The first coupling face may be an outer coupling face. By outer may be understood a face or a side facing away from the concrete structure. The second coupling face may be an inner coupling face. By inner may be understood herein a face or a side facing inwards in the concrete structure.

The mounting element may be attached to the mounting bracket via the screw con nection.

An effect of the mounting element being attached to the mounting bracket in an elec trically conductive manner is that an electrically conductive connection may be formed between the reinforcing element and the mounting element so that an external ground cable may be avoided. The electrically conductive mounting element may be used as grounding for an electric element on the outside of the concrete structure. The electric element may be a cable, for example.

As mentioned introductorily, it is known that an external ground cable may function as an antenna and give interference in electric equipment and apparatuses, referred to as EMC in technical language. By establishing a cable-less grounding system as described herein, this problem can be eliminated.

The system may comprise a mounting device for an electric component, wherein the mounting device rests in an electrically conductive manner against the mounting ele ment. The mounting device may rest in an electrically conductive manner against the mounting bracket. The mounting device may be a cable rack.

An effect of this is that the mounting device may be used as a grounding element without the use of a ground cable.

An effect of the mounting device being a cable rack is that the cable rack may house electrical cables and, at the same time, protect the cables against electric interference, known as a Faraday cage in technical language. The cable rack may also include a function as a protective plate, known as a kick plate in technical language. A further effect is that electric components that are installed in proximity to the cable rack may use the cable rack as a grounding point.

The mounting element may be a post bracket.

An effect of the electrically conductive element being a post bracket is that the post bracket may both be used for housing a portion of a post, for example a railing post, and function as a grounding point for an electric element. The post bracket may be arranged to house an end portion of the railing post. The post bracket may have a length such that a cable rack can be mounted in an electrically conductive manner to the post bracket. The post may be formed of a electrical non-conductive material and form part of a railing.

The electrically conductive mounting element may include at least one elongated cut out for a screw, wherein the at least one elongated cut-out is arranged perpendicularly to a longitudinal axis of the mounting element.

The effect of the elongated hole is that a post positioned in the electrically conductive mounting element may be rotated axially around the longitudinal axis of the mounting element in order thereby to get a correct positioning relative to adjacent elements. If the concrete structure is ellipsoidal and provided with a plurality of mounting elements along a perimeter of the concrete structure, it may be necessary to adjust the axial position on the post, which is possible when the screw hole is elongated.

A mounting device for an electric component may rest in an electrically conductive manner against the mounting element.

By the grounding element being attached in an electrically conductive manner to the inner coupling face of the mounting bracket, the mounting bracket and the first cou- pling face of the mounting bracket may function as an external grounding point for the concrete structure. Thereby, elements that need grounding may be connected directly to the mounting bracket.

By electrically conductive is meant in this connection that the grounding element is formed from an electrically conductive material. The term electrically conductive is, in this connection, equivalent to current-carrying.

A grounding device, for a concrete structure, is also described, the grounding device comprising a current-carrying mounting bracket with a first coupling face for a mount ing element and at least one cast-in portion for casting into the concrete structure, and a grounding element which, in a fixing portion, is arranged for current-carrying connection to a reinforcing element in the concrete structure. In a first end portion, the grounding element is attached in a current-carrying manner to a second coupling face of the mounting bracket, and the grounding element and the second coupling face are arranged to be covered by the concrete structure. By current-carrying is meant, in this connection, that the grounding element is formed from an electrically conductive material.

In a preferred embodiment, the mounting bracket may be formed from stainless met al. The mounting bracket may be a profile. The profile may be formed of a plate with one or more bends. The profile may comprise a centre portion, the centre portion con stituting a coupling portion. The first coupling face may be an outside of the coupling portion. The second coupling face may be an inside of the coupling portion. The cast-in portion may include a plurality of cut-outs so that concrete may flow through the cut outs so that the mounting bracket is cast into the concrete structure. In an advanta geous embodiment, the mounting bracket includes two cast-in portions positioned on either side of the coupling portion.

Between the coupling portion and the cast-in portion, there may be an angle equal to or larger than 90 degrees. In one exemplary embodiment, the angle may be 120 de grees.

The first end portion of the grounding element may be attached to the second coupling face by means of heat treatment, for example welding. The advantage of welding is that a strong electrically conductive connection is formed.

The first end portion of the grounding element may, alternatively or additionally, be attached to the second coupling face via a screw connection. The effect of the screw connection is that the securing of the grounding element to the mounting bracket may be done using elements that are normally parts of an ordinary mounting bracket as an ordinary mounting bracket typically has a nut on the inside for receiving a screw. The screw may be arranged to attach the mounting bracket to a formwork element.

When the grounding element is attached to the coupling portion, the grounding ele ment will typically project perpendicularly from the coupling portion, which makes the grounding device space-consuming. The screw connection makes it possible to store and transport the grounding element and the coupling portion separately. Thereby, the grounding element and the coupling portion can be stacked in a way that gives maximum space utilization.

A further effect of the screw connection is that, in a simple way, it is possible to com bine different mounting brackets and different grounding elements, depending on the structure in which the grounding element is to be arranged. For example, one type of grounding element may be used for different mounting brackets, or vice versa.

The grounding element may be an electrically conductive rail.

The effect of the grounding element being an electrically conductive rail is that the grounding element may project rigidly from the coupling portion and provide a correct and repeating position relative to the mounting bracket.

The rail may have an elasticity that makes it possible to clamp the rail against at least one reinforcing element. The rail may be flexible so that the rail may be placed alter nately over and under a plurality of concrete irons lying in a common plane. Thereby, a plurality of electrically conductive contact points between the rail and the reinforce ment may be achieved.

In comparison, a cable typically has a little or no elasticity and will therefore not be able to provide a corresponding clamping to that of the rail against the reinforcing el ement. When the concrete structure is being cast, it is therefore likely that a cable will move relative to the reinforcing elements so that there will be no contact between the cable and the reinforcing element.

The grounding device may include a clamp for attaching the grounding element to the reinforcement.

The effect of the clamp is that a secure and electrically conductive connection may be provided between the grounding element and the reinforcing element, even if the grounding element has a deviating or wrong position relative to the reinforcing ele ment.

Another effect is that the clamp can hold the grounding element in electrically conduc tive contact with the reinforcing element when the grounding element and/or the rein forcing element is subjected to strain during casting, for example by concrete that is being added forcing the grounding element and/or the reinforcing element down wards.

A further effect is that the clamp may provide an electrically conductive contact with the reinforcing element preventing slurry from penetrating between the grounding element and the reinforcing element.

The clamp may be displaceable in the longitudinal direction of the grounding element.

The effect of the clamp being displaceable in the longitudinal direction of the ground ing element is that the clamp can provide a secure and electrically conductive connec tion between the grounding element and the reinforcing element by varying distance between the mounting bracket and the reinforcing element.

The clamp may be displaceable along a slot in the electrically conductive rail. The ef fect of the slot is that a large contact surface is achieved between the clamp, the rail and the reinforcing element.

The clamp may include a screw connection. The effect of the screw connection is that the clamp can easily be attached in a simple way by the use of simple tools. The screw connection may include a locking screw so that the clamp can be attached with just one tool, for example a spanner.

In a second aspect, the invention relates more specifically to a concrete structure for a wind turbine, the concrete structure including a grounding system in accordance with the first aspect of the invention.

The effect of the concrete structure including the grounding system is that the ground ing on the wind turbine can be protected against corrosion as components belonging to the grounding system are protected and hidden by the concrete structure.

The concrete structure may be a platform for the wind turbine.

Wind turbines may comprise a platform under the turbine itself, also known as a tur- bine platform. The platform may be a platform for service personnel. On the platform, various electric components may be mounted, for example navigation lights, sign lights and antennas.

The platform being formed from concrete, the risk of lightning strikes is reduced. However, the electric components will be prone to lightning strikes and overvoltage, which places great demands on grounding of the electric components. In a concrete structure, it is known to connect one or more reinforcing elements to ground. By providing the concrete structure with the grounding system that is described herein, a concrete platform for a wind turbine can be provided with a secure grounding while, at the same time, the grounding is hidden in the concrete structure.

The concrete structure may be positioned offshore.

Wind turbines that are positioned offshore have a higher risk of lightning strikes than wind turbines on land. A concrete platform including the grounding system that is de scribed herein is therefore particularly well suited for an installation offshore.

In a further aspect, the invention relates to a method for arranging a grounding sys tem in accordance with the first aspect of the invention in a concrete structure, the method comprising the steps of:

• positioning the mounting bracket on an inside of a formwork element for the concrete structure in such a way that the first coupling face of the mounting bracket is resting against a portion of the formwork element;

• screwing the mounting bracket to the formwork element with a screw, the first end portion of the grounding element being positioned between the inside of the mounting bracket and the nut;

• attaching the fixing portion of the grounding element to the reinforcement;

• adding concrete on the inside of the formwork element so that the reinforce ment, the grounding element and the nut are covered by the concrete; and

• removing the screw.

The method may further include the steps of:

• screwing a mounting element to the first coupling face of the mounting brack et; and screwing a mounting device for an electric component to the mounting bracket.

In what follows, an example of a preferred embodiment is described, which is visual ized in the accompanying drawings, in which:

Figure 1 shows the grounding device in perspective;

Figure 2 shows the grounding device in its individual components, from above;

Figure 3 shows the grounding device from above and attached to a formwork element;

Figure 4 shows the grounding device in a concrete structure in perspective;

Figure 5 shows how an electric voltage is carried through a system for grounding an electric element of the concrete structure; and

Figure 6 shows a concrete structure including the grounding device.

Figures 1 and 2 show a grounding device 1 for a concrete structure 9 (figures 3-6), the grounding device 1 comprising an electrically conductive mounting bracket 10 with a first coupling face 101 for a mounting element 5 (figures 4 and 5) and at least one cast-in portion 12 for casting into the concrete structure 9, and a grounding element 2 which, in a fixing portion 21, is arranged for electrically conductive connection to a reinforcing element 91 of the concrete structure 9. The grounding element 2 is at tached in an electrically conductive manner in a first end portion 22 to a second cou pling face 102 belonging to the mounting bracket 10, and the grounding element 2 and the second coupling face 102 are arranged to be covered by the concrete struc ture 9.

The mounting bracket 10 is shown as a bent profile comprising a coupling portion 100 and two cast-in portions 12. The first coupling face 101 is positioned on a first side of the coupling portion 100. The second coupling face 102 is positioned on a second side of the coupling portion 100. The two fixing portions 12 are shown with an angle of 60 degrees between them, so that the angle between each of the cast-in portions and the coupling portion is 120 degrees, and are provided with a plurality of cut-outs 121 so that concrete can flow through the cut-outs 121 to give the mounting bracket 10 extra anchoring to the concrete structure. The grounding element 2 is shown as an electrically conductive rail, in which the fixing portion 21 is arranged perpendicularly to the first end portion 22, so that the first end portion 21 projects from the mounting bracket 10. The first end portion 22 rests against the second coupling face 102 of the mounting bracket 10 and is attached to the mounting bracket 10 with a screw connection 31.

The fixing portion 21 of the grounding element 2 includes a cut-out 210. The cut-out 210 makes it possible to displace a clamp 3 with a second screw connection 32 in the longitudinal direction of the fixing portion 21, so that the clamp 3 may be screwed to the grounding element 2 in different positions along the cut-out 210.

Figure 3 shows the grounding device 1 cast into the concrete structure 9 and attached to a formwork element 99. When the grounding device 1 is to be cast into the con crete structure 9, the mounting bracket 10 is positioned on an inside 990 of the form- work element 99 in such a way that the first coupling face 101 of the mounting brack et is resting against the inside of the formwork element 99 and the coupling face 101 will be flush with the outside of the concrete structure 9 when the formwork element 99 is removed.

The grounding device 1 is attached to the formwork element 99 with the first screw connection 31. A nut 311 belonging to the screw connection 31 is arranged for casting into the concrete structure 9. A first screw 310 is arranged to be unscrewed from the screw connection 31 after the nut 311 has been cast in and the formwork element 99 is removed.

Figure 4 shows a partially cut-away drawing of a system 1 for grounding an electric element (not shown) for the concrete structure 9. The system 1 comprises the grounding device 1 and an electrically conductive mounting element 5 arranged on the mounting bracket 10. The electrically conductive mounting element 5 is shown as a post bracket 5 arranged to house a portion of a railing post 6. The post bracket 5 is attached to the mounting bracket 10 via two screw connections 31 and attaches the railing post 6 to the post bracket 5 at the same time, an electrically conductive con nection being formed between the reinforcing element 91, the mounting bracket 10, the post bracket 5 and the screw connection. The railing post 6 shown in the figure is formed of an electrically non-conductive material, for example a composite.

A cable rack 55 is attached to an outside of the post bracket 5 via two screw connec tions 33, an electrically conductive connection being formed between the reinforcing element 91, the mounting bracket 10, the post bracket 5 and the cable rack 55.

Figure 5 shows how a ground loop G can be provided between the reinforcing element 91 and an outside of the concrete structure 9 via the grounding element 2, the mount- ing bracket 10 and the post bracket 5 and the cable rack 55. Because the cable rack 55 is connected to earth, an electric element (not shown) may be connected to earth by connecting the ground wire of the electric element to the cable rack 55. The cable rack 55 may house electrical cables and at the same time protect the electrical cables against electric interference by the cable rack forming a Faraday cage.

Figure 6 shows a concrete structure 9 for a wind turbine, the concrete structure 9 comprising a plurality of grounding devices 1, and a plurality of electric elements 7.

The plurality of grounding devices 1 are cast into the concrete structure 9 along the outer side of the concrete structure 9. The concrete structure 9 also comprises a plu- rality of electrically non-conductive mounting brackets (10X). The electrically non- conductive mounting brackets 10X are identical to the electrically conductive mounting bracket 10 but are not connected in an electrically conductive manner to any reinforc ing element 91.

Along the edge of the concrete structure 9, a plurality of cable racks 55 are installed. These house electrical wires for an electric installation 7. An electrical wire P may be passed through corresponding cut-outs in the cable rack 55, the mounting bracket 10 and the post bracket 5, in order thereby to be threaded inside the post bracket to the electric installation 7.

It should be noted that all the above-mentioned embodiments illustrate the invention, but do not limit it, and persons skilled in the art may construct many alternative em bodiments without departing from the scope of the attached claims. In the claims, reference numbers in brackets are not to be regarded as restrictive.

The use of the verb "to comprise" and its different forms does not exclude the pres ence of elements or steps that are not mentioned in the claims. The indefinite article "a" or "an" before an element does not exclude the presence of several such elements.

The fact that some features are indicated in mutually different dependent claims does not indicate that a combination of these features cannot be used with advantage.