Sensor, arrangement and system

Abstract

The present invention relates to a sensor (120) for indicating the presence of water and / or ice at a surface of a structure. The sensor (120) comprises: an electrical power source (122), a first conductive element (124) connected to a first pole of the power source (122), and a second conductive element (126) connected to a second pole of the power source (122), wherein the first conductive element (124) and the second conductive element (126) are arranged with a mutual distance (d) between them at the surface (210); wherein the sensor (120) is configured to: indicate the presence of water and / or ice at the surface (210) when an electrical current ( / ) flows between the first conductive element (124) and the second conductive element (126). The invention also relates to an arrangement (100) comprising such a sensor and a system (300) comprising such an arrangement (100).

Description

[0001] SENSOR, ARRANGEMENT AND SYSTEM

[0002] The present invention relates to a sensor for indicating the presence of water and / or ice at a surface of a structure. The invention also relates to an arrangement comprising such a sensor and a system comprising such an arrangement.

[0003] Background

[0004] Wind turbines are used to extract energy from wind. Wind energy is a renewable energy source and is part of the energy transition from fossil-based energy sources to renewable energy sources in order to achieve set climate goals.

[0005] A common type of wind turbine is the type that has horizontal axis wind turbines comprising three blades which are also called wings. Icing of blades or wings can occur under certain meteorological conditions where the combination of temperature, humidity and wind are considered to be the most important parameters. Ice formation on blades leads to reduced efficiency of the wind turbine and also constitutes a safety risk in the event of so-called ice drift.

[0006] To reduce the risk of ice formation, de-icing systems are most often used which can be arranged to heat the blades and thereby reduce the formation of ice on the blades. De-icing systems can also be of the type that includes heat-emitting panels which are powered by electric current.

[0007] Summary

[0008] An object of the present invention is to provide a solution that has advantages over the prior art.

[0009] A further object of the present invention is to provide an energy-saving and simple solution for indicating the presence of water and / or ice at a surface of a structure.

[0010] According to a first aspect of the invention, the above object is achieved by a sensor comprising: an electrical power source, a first conductive element connected to a first pole of the power source, and a second conductive element connected to a second pole of the power source, wherein the first conductive element and the second conductive element are arranged with a mutual distance between them at the surface; wherein the sensor is configured to: indicate the presence of water and / or ice at the surface when an electrical current flows between the first conductive element and the second conductive element.

[0011] The indication may also refer to the presence of snow and high humidity. Snow during phase transformation becomes water which is conductive. High humidity allows a current to flow between the first conductive element and the second conductive element.

[0012] A structure can refer to a physical structure and can be understood as a physical construction or a physical object, which means that the surface is also a physical surface belonging to the structure, construction or object. A current source can also be understood as a voltage source as they can be considered reciprocal.

[0013] According to one embodiment of the sensor, the sensor comprises a heat source at which the first conductive element and the second conductive element are arranged; wherein the heat source is configured to: heat the surface of the structure at the first conductive element and the second conductive element for at least a period of time.

[0014] Thus, ice and snow formed between the conductive elements can be phase transformed into water.

[0015] According to one embodiment of the sensor, the heat source is configured to: heat the surface at the first conductive element and the second conductive element such that ice formed between the first conductive element and the second conductive element is at least partially phase transformed into water.

[0016] According to one embodiment of the sensor, the sensor is configured to: indicate the presence of ice at the surface when an electrical current flows between the first conductive element and the second conductive element when the heat source has heated the surface. According to one embodiment of the sensor, the sensor is configured to: indicate the non-presence of ice at the surface when an electrical current does not flow between the first conductive element and the second conductive element when the heat source has heated the surface.

[0017] According to one embodiment of the sensor, the heat source is configured to: heat the surface at the first conductive element and the second conductive element with a periodicity.

[0018] This provides a regularity for when ice formation can be detected at the surface due to the phase transformation from ice to water when the surface is heated by the heat source.

[0019] According to one embodiment of the sensor, the periodicity is between 60s - 600s, or between 120s - 480s, or between 120s - 300s, or between 120s - 240s.

[0020] This provides suitable intervals in which it can be checked whether or not ice formation has occurred at the surface, or whether there is a risk of ice formation at the surface.

[0021] According to one embodiment of the sensor, the heat source is configured to: heat the surface with a temperature higher than 1QC, or higher than 2QC, or higher than 3QC, or higher than 4QC, or higher than 5QC, or higher than 6QC, or higher than 7- C, or higher than 8QC, or higher than 9QC, or higher than 10QC.

[0022] According to one embodiment of the sensor, the heat source is configured to be supplied with a pulsed direct current or an alternating current for heating the surface.

[0023] Pulsed direct current and alternating current are suitable current types for these types of applications.

[0024] According to one embodiment of the sensor, the heat source is part of a heating mat of an arrangement for heating the surface. Thus, an integrated solution can be provided where the heat source and the heating mat form a common unit which is both simple and inexpensive to implement.

[0025] According to one embodiment of the sensor, the mutual distance between the first conductive element and the second conductive element is less than 1 mm, or less than 2 mm, or less than 3 mm, or less than 4 mm, or less than 5 mm, or less than 7 mm, or less than 10 mm, or less than 15 mm.

[0026] This provides suitable mutual distances between the conductive elements suitable for various applications.

[0027] According to one embodiment of the sensor, a gap between the first conductive element and the second conductive element comprises a dielectric.

[0028] Various types of dielectrics may occur, one example of which is gas such as air.

[0029] According to one embodiment of the sensor, the gap between the first conductive element and the second conductive element forms a depression or recess.

[0030] This provides a depression / sink where ice / water can accumulate.

[0031] According to one embodiment of the sensor, the sensor comprises means for attaching the sensor to the surface.

[0032] According to one embodiment of the sensor, the first conductive element and the second conductive element are partially depressed in the structure in use.

[0033] According to one embodiment of the sensor, the sensor is configured to: indicate the presence or absence of water or ice at the surface when the electrical current is greater than a current threshold and / or when a resistance between the first pole and the second pole of the current source is less than a resistance threshold. Thus, current measurement of the sensor can be used to indicate the presence or absence of water or ice. Resistance measurement of the sensor can also be used to indicate the presence or absence of water or ice.

[0034] According to one embodiment of the sensor, the sensor is configured to: provide a sensor signal indicating the presence or absence of water and / or ice at the surface.

[0035] According to one embodiment of the sensor, the sensor is connected to a supply circuit or control circuit for a heating mat of an arrangement and is configured to act as a switch for activating / deactivating the heating mat.

[0036] According to a second aspect of the invention, the above object is achieved with an arrangement for heating a surface of a structure, the arrangement comprising: at least one heating mat configured to be attached to the surface and to heat the surface upon activation; a sensor according to embodiments of the invention; wherein the arrangement is configured to: activate the heating mat to heat the surface of the structure when the sensor indicates the presence of water and / or ice at the surface.

[0037] The present arrangement provides an energy-saving solution for detecting ice formation on a surface and de-icing it compared to conventional solutions as the heating mat only needs to be activated when necessary, i.e. when there is an indication that ice formation has occurred on the surface or when there is a risk of ice formation on the surface. Thus, the energy costs for generating heat can be significantly reduced compared to conventional solutions. Furthermore, the present arrangement is cheap to implement compared to conventional solutions as the arrangement has low complexity and few components and parts.

[0038] According to one embodiment of the arrangement, the arrangement is configured to: deactivate the heating mat when the sensor indicates the non-presence of water and / or ice at the surface. This provides a mechanism for turning off the heating mat when there is no longer a need for heating the surface.

[0039] According to an embodiment of the arrangement, the arrangement is configured to: further activate or deactivate the heating mat based on an air temperature at the surface.

[0040] According to one embodiment of the arrangement, the sensor is connected to a supply circuit or control circuit for the heating mat and configured to act as a switch for activating / deactivating the heating mat.

[0041] This provides a low-complexity solution for activating / deactivating the heating mat, which can be implemented with simple electrical components, for example.

[0042] According to one embodiment of the arrangement, the arrangement comprises: a control device configured to activate or deactivate the heating mat upon receipt of a sensor signal from the sensor.

[0043] This provides a solution where a control algorithm of varying complexity can be implemented in the control device for activating / deactivating the heating mat. Furthermore, other functions can also be implemented in the control algorithm.

[0044] According to a third aspect of the invention, the above object is achieved with a system comprising: an arrangement according to any embodiment of the invention; and a structure with a surface.

[0045] According to one embodiment of the system, the heating mat is attached to or at the surface of the structure.

[0046] According to one embodiment of the arrangement, the structure is one of a blade of a wind turbine, a dam gate in a hydroelectric power plant, or a stretcher. Further advantages and embodiments of the invention will become apparent from the following detailed description.

[0047] Brief figure description

[0048] The following figures are intended to show embodiments of the invention, wherein:

[0049] Fig. 1 shows a sensor according to embodiments of the invention;

[0050] Fig. 2 shows an arrangement seen in top view according to embodiments of the invention;

[0051] Fig. 3 shows an arrangement where the sensor also functions as a switch, seen in top view, according to embodiments of the invention;

[0052] Fig. 4 shows an arrangement comprising a heater, seen in top view, according to embodiments of the invention;

[0053] Fig. 5 shows conductive elements at a surface of a structure, seen in cross- sectional side view, according to embodiments of the invention;

[0054] Fig. 6 shows conductive elements at a surface of a structure, seen in top view, according to embodiments of the invention; and

[0055] Fig. 7 illustrates a system comprising an arrangement and a structure according to embodiments of the invention.

[0056] Detailed description of the invention

[0057] Fig. 1 shows a sensor 120 according to embodiments of the invention. As shown, the sensor 120 includes an electrical power source 122, a first conductive element 124 connected to a first pole of the power source 122, and a second conductive element 126 connected to a second pole of the power source 122. The first conductive element 124 and the second conductive element 126 are arranged with a mutual distance d between them at or on the surface 210. The sensor 120 is configured to indicate the presence of water and / or ice at the surface 210 when an electrical current / flows between the first conductive element 124 and the second conductive element 126.

[0058] As mentioned, the sensor 120 includes an electrical current / voltage source 122, a first conductive element 124 which is connected to a first pole of the current source 122 via a first conductive conductor L1 , and a second conductive element 126 which is connected to a second pole of the current source 122 via a second conductive conductor L2. The conductive conductors L1 , L2 electrically connect the conductive elements 124, 126 with the respective poles of the current source 122. The poles of the current / voltage source 210 can be defined as the negative and positive poles, respectively. Depending on the polarity, a direct current will either move from the plus pole to the minus pole or in the opposite direction in the sensor 120. A non-limiting example of the direction of current is illustrated in the figure with an arrow and “ / ” which refers to electrical current. Thus, the power source 122 is configured to provide an electrical current that can travel in the sensor 120 between the poles under certain conditions.

[0059] Furthermore, the first conductive element 124 and the second conductive element 126 are arranged with a mutual distance d between them at the surface 210 of the structure 200 as shown in the figures. A mutual distance means that the conductive elements 124, 126 are not in galvanic contact with each other but that a space or gap exists between them. The mutual distance d can be understood as a distance from one surface of the first conductive element 124 to another surface of the second conductive element 126. Said surfaces of the conductive elements 124, 126 can refer to the surfaces of the conductive elements 124, 126 that are spatially closest to each other.

[0060] Furthermore, the sensor 120 may be arranged to indicate the presence or absence of water or ice at the surface 210 when the electric current / is greater than a current threshold value and / or when a resistance R between the first pole and the second pole of the current source 122 is less than a resistance threshold value. Thus, threshold values may be used to detect the presence or absence of water or ice at the surface 210.

[0061] According to embodiments of the invention, the sensor 120 is configured to provide a sensor signal S indicating the presence or absence of water and / or ice at the surface 210. This sensor signal S may, for example, be sent to a controller for processing and used in a control algorithm to control a heating mat or other application. The sensor signal S may be generated and sent by a controller 170 of the sensor 120.

[0062] Fig. 2 shows an arrangement 100, seen in top view, comprising a control device 160 according to embodiments of the invention. The arrangement 100 further comprises one or more heating mats 110 configured to be attached to a surface 210 of a structure 200 (see Fig. 7) and to heat the surface 210 when activated. The heating mat 1 10 may be an electric heating mat 1 10 that is driven by an electric current to generate heat. Thus, the heating mat 1 10 may comprise a conductive mesh encapsulated or arranged in an electrically insulating layer. The conductive mesh may consist of copper or other suitable conductor with an insulating surface layer.

[0063] The supply current to the heating mat 1 10 can be provided by a power source which is not shown in the figure. For fastening the heating mat 1 10 to the surface 210, the heating mat 1 10 includes suitable fastening means such as screws, bolts, glue, varnish, and / or various known hardening methods and techniques that allow the heating mat 1 10 to be attached or fixed to the surface 210. With hardening methods and techniques, the heating mat 1 10 can be fully or partially integrated into the surface 210 or the structure 200. The arrangement 100 further includes at least one sensor 120 according to embodiments of the invention.

[0064] The arrangement 100 is, according to embodiments of the invention, configured to activate, i.e. turn on, the heating mat 1 10 for heating the surface 210 of the structure 200 when an electrical current / flows between the first conductive element 124 and the second conductive element 126 of the sensor 120 or when a sensor signal S from the sensor 120 indicates the presence of water and / or ice at the surface 210 as illustrated in the figure.

[0065] Since the gap g between the first conductive element 124 and the second conductive element 126 consists of a non-conductive substance or medium, i.e. a dielectric (dialectic material), no current will flow in the sensor 120 unless a conductive / conductive material ends up or is placed between the conductive elements 124, 126. For example, when said dielectric is air and the distance d between the conductive elements 124, 126 is suitably dimensioned, no current will flow between the conductive elements 124, 126 and thus also not in the sensor 120. However, if a conductive substance or material ends up or is formed in the gap g corresponding to the distance d between the conductive elements 124, 126, a current will flow in the sensor 120 between the poles of the current source 122 and thus also via the conductive elements 124, 126. This can happen, for example, when water ends up or is formed between the conductive elements 124, 126, as water is electrically conductive unlike air. Even air with high humidity can cause a current to flow between the conductive elements 124, 126, which means that the sensor 120 can also indicate the presence of air with high humidity.

[0066] Detection of a current / flowing in the sensor 120 can be done with a conventional current detection circuit which can be included in the control unit 170. Thus, the arrangement 100 or the sensor 120 can include a current detection circuit configured to detect whether a current flows in the sensor 120 according to embodiments of the invention. The current / referred to can also be called a detection current as the current indicates that there is a conductive material between the conductive elements 124, 126 and which thereby breaks the electrical insulation of said dielectric. Thus, it is detected whether there is a conductive material between the conductive elements 124, 126.

[0067] In a similar manner as for activating the heating mat 1 10, the arrangement 100 according to embodiments of the invention is configured to deactivate the heating mat 1 10 when an electrical current / no longer flows between the first conductive element 124 and the second conductive element 126. Said current detection circuit may also be configured to detect or signal when a current no longer flows in the sensor 120, for example through a sensor signal S.

[0068] In order to control the heating mat 110 more precisely, current measurement and / or resistance measurement of the sensor 120 can also be used to activate the heating mat 100. Values from current measurement and / or resistance measurement can in this regard be compared against suitable threshold values. Methods for current measurement and resistance measurement can be carried out according to known technology. The sensor signal S can also include current measurement values and / or resistance measurement values.

[0069] Thus, the arrangement 100 according to embodiments of the invention is configured to activate the heating mat 1 10 to heat the surface 210 when the electrical current / is greater than a current threshold value ITHI . Thus, the arrangement 100 or the sensor 120 includes a current measurement circuit configured to measure a magnitude of the current flowing in the sensor 120 according to embodiments of the invention. The current measurement circuit may be fully or partially integrated with the current detection circuit and may be included in the control unit 170.

[0070] Furthermore, the arrangement 100 according to embodiments of the invention is configured to activate the heating mat 1 10 for heating the surface 210 when a resistance of the sensor 120 is less than a resistance threshold value RTHI . Thus, the arrangement 100 includes a resistance measurement circuit configured to measure a magnitude of the resistance of the sensor 120 according to embodiments of the invention. The resistance measurement circuit may be included in the control unit 170. Air temperature should also be taken into account when controlling the heating mat 1 10, which is why the arrangement 100 may be configured to activate or deactivate the heating mat 1 10 further based on an air temperature at the surface 210. The air temperature may be provided by one or more temperature sensors suitably placed on or at the surface. These are not shown, however.

[0071] It should be noted that in a corresponding manner the heating mat 1 10 can also be deactivated, i.e. switched off, by current measurement and / or resistance measurement. Threshold values can also be used for deactivation. For this purpose, other threshold values are used than those used for activation of the heating mat 1 10. If threshold values for activation are referred to as first threshold values, threshold values for deactivation can be referred to as second threshold values. Thus, the arrangement 100 can be configured to deactivate the heating mat 1 10 based on other current threshold values ITH2 and / or other resistance threshold values RTH2.

[0072] The values of the first and second thresholds can be determined theoretically and / or by practical testing and calibration. According to embodiments of the invention, the first current threshold is greater than the second current threshold, and further, the first resistance threshold is less than the second resistance threshold.

[0073] Generally speaking, the sensitivity of the sensor 120 for detecting ice or risk of ice formation at the surface 210 can be determined by the values of the parameters d, ITHI and RTHI all depending on the application to be implemented. By adjusting the values of said parameters d, ITHI and RTHI the detection sensitivity and the activation sensitivity can be determined. Similarly, the deactivation sensitivity can also be determined by adjusting the values of the second current threshold value ITH2 and / or the second resistance threshold value RTH2.

[0074] In the embodiment shown in Fig. 2, the arrangement 100 further comprises a control device 160 configured to activate / deactivate the heating mat 1 10 upon receipt of a sensor signal S from the sensor 120. The sensor signal S may be a suitable information-carrying signal according to established communication protocols and standards. The control device 160 may activate / deactivate the heating mat by sending suitable control signals to the heating mat 1 10 through a control line 162 shown by an arrow of dashes and dots. The control device 160 may include one or more processors, memories, communication interfaces, control interfaces, etc. which are configured to cooperate so that the control device 160 can perform its functions, i.e. control of various parts of the arrangement 100. The sensor 120 may also include a control device.

[0075] Fig. 3 shows an arrangement 100, seen in top view, where the sensor 120 also functions as a switch according to embodiments of the invention. This embodiment differs from that shown in Fig. 1 in that the sensor 120 is directly connected to a supply circuit 150 for the heating mat 1 10 via a control line 128 and is thus configured to act as a switch for activating / deactivating the heating mat 1 10 via the supply circuit 150 for the heating mat 1 10. When it is detected that a current / is moving between the conductive elements 124, 126, a switch that is connected to or is part of the supply circuit 150 or the sensor 120 itself can be turned on so that the supply circuit 150 supplies the heating mat 1 10 with a supply current via a supply line 152. Correspondingly, the switch can be turned off when there is no longer a current between the conductive elements 124, 126 so that no supply current is delivered to the heating mat 1 10. The switch can thus close or open the supply circuit for the heating mat 1 10. The supply current allows the heating mat 110 to generate heat.

[0076] Fig. 4 shows a sensor 120 including a heat source 140 seen from above according to further embodiments of the invention. The first conductive element 124 and the second conductive element 126 are in these embodiments located at or on a heat source 140. According to this embodiment, the sensor 120 is configured to heat the surface 210 of the structure 200 at the first conductive element 124 and the second conductive element 126 by means of the heat source 140 for at least a period of time. More specifically, the surface 210 at the first conductive element 124 and the second conductive element 126 is heated so that any ice and snow that has formed between the first conductive element 124 and the second conductive element 126 is at least converted to water, i.e. so that a phase transformation from ice to water occurs. This results in a non-conductive substance, i.e. ice and snow, being converted to a conductive substance, i.e. water. It is noted that not all of the ice or snow between the conductive elements needs to be converted to ice for an electrical current to flow between the conductive elements, but it is usually sufficient for some of the ice to melt for the current to flow between them.

[0077] It is suitable to heat the surface 210 at the first conductive element 124 and the second conductive element 126 with a certain periodicity for regular phase transformation from ice / snow to water if ice / snow has formed at the conductive elements 124, 126. The periodicity can be varied but according to embodiments the periodicity is something between 60s - 600s, or between 120s - 480s, or between 120s - 300s, or between 120s - 240s depending on the application.

[0078] The heat source 140 is intended to heat the surface 210 to a temperature such that any ice / snow on the surface 210 between the conductive elements melts completely or partially. Depending on physical parameters, this temperature may vary. According to embodiments of the invention, the heat source 140 is configured to heat the surface 210 to a temperature that is greater than 1 - C, or greater than 2QC, or greater than 3QC, or greater than 4QC, or greater than 5QC, or greater than 6QC, or greater than 7- C, or greater than 8QC, or greater than 9QC, or greater than 10QC.

[0079] The present sensor 120 is, according to embodiments of the invention, configured to indicate the presence of ice / snow at the surface 210 when an electrical current / flows between the first conductive element 124 and the second conductive element 126 when the heat source 140 has heated the surface 210, and to indicate the nonpresence of ice / snow at the surface 210 when an electrical current / does not flow between the first conductive element 124 and the second conductive element 126 when the heat source 140 has heated the surface 210. These indications can be made with a sensor signal S. Ice also refers to frost and hoarfrost. Regarding implementation aspects of the electric heat source 140, there are different solutions. According to one solution, the heat source 140 can consist of an independent and standalone heating unit that can be controlled by the control unit 170. According to another solution, the heat source 140 can be fully or partially integrated with the heating mat 1 10 of the arrangement 100. The heat source 140 can be supplied with a pulsed direct current or an alternating current for heating the surface 210 by generating heat at the surface 210. However, pure direct current can also be used to operate the heat source 140. The heating mat 110 can also be supplied with a pulsed direct current or an alternating current. Furthermore, the heat source 140 and the heating mat 1 10 can share a power supply circuit or have separate power supply circuits. According to one embodiment, the area of the heat source 140 is smaller than the area of the heating mat 110. According to a further embodiment, the area of the heat source 140 is larger than an area covered by the conductive elements 124, 126 on the surface 210.

[0080] It is further noted that the control device 160 of the arrangement 100 can also control the heat source 140 by means of a control line 164. However, the heat source can also be controlled by the control unit 170 of the sensor 120 as previously mentioned. The control of the heat source 140 includes at least activating and deactivating the heat source 140. The temperature level of the heat source 140 is also controlled.

[0081] Fig. 5 shows the conductive elements 124, 126 at a surface 210 of a structure 200, seen in a side cross-sectional view, according to embodiments of the invention. The conductive elements 124, 126 have a portion which is partially disposed above the surface 210 and a portion which is integral with the structure 200 in the example. However, the conductive elements 124, 126 may also be fully integral with the structure 200 such that the top of the conductive elements 124, 126 is substantially flush with the surface 210. Thus, the first conductive element 124 and the second conductive element 126 are fully or partially submerged in the structure 200 when used according to embodiments of the invention.

[0082] Generally speaking, the sensor 120 may include means for attaching the sensor 120 to the surface 210. These means may be the same as those for attaching the heating mat 1 10 to the surface 210, such as screws, bolts, glue, varnish, and / or various known curing methods and techniques that allow the sensor 120 to be attached or fixed to the surface 210.

[0083] It is noted as previously mentioned that a gap g is formed between the first conductive element 124 and the second conductive element 126. The gap g may form a recess or more generally a volume between the conductive elements 124, 126 to hold water / ice. However, there need not be a recess in the gap g . As previously mentioned, the gap g between the first conductive element 124 and the second conductive element 126 comprises a dielectric, such as air.

[0084] The distance d between the first conductive element 124 and the second conductive element 126 affects how easily a current / starts to flow in the sensor 120. It can be noted that if the distance d is very short and the voltage between the conductive elements 124, 126 is large, there is an imminent risk of an electrical flashover even if the gap g between the conductive elements 124, 126 is filled with a dielectric. This should be avoided as false indication of ice formation may then occur and the components of the sensor 120 may be damaged by the electrical flashover. According to embodiments of the invention, the distance d is less than 1 mm, or less than 2 mm, or less than 3 mm, or less than 4 mm, or less than 5 mm, or less than 7 mm, or less than 10 mm, or less than 15 mm.

[0085] Fig. 6 shows the conductive elements 124, 126 on a surface 210 of a structure 200 seen in top view according to further embodiments of the invention. It is thus understood that the conductive elements 124, 126 may have varying shapes and consist of one or more constituent conductive parts or sub-elements to form a conductive element that covers a portion of the surface 210. In Fig. 6, each of the conductive elements 124, 126 has a plurality of parts shaped like fingers which are arranged in parallel and wrapped around each other in a simplified meander shape. The area of the meander shapes will cover the portion of the surface 210 to be monitored.

[0086] Fig. 7 illustrates a system 300 comprising an arrangement 100 according to embodiments of the invention. Furthermore, the system 300 comprises a structure 200 having a surface 210 at which unwanted ice formation may occur. The structure 200 may be any suitable structure where a risk of unwanted ice formation may occur. Examples of such structures are a blade of a wind turbine, a dam gate in a hydroelectric power plant, a stretcher or any other suitable physical structure.

[0087] In the example where the structure 200 is a blade of a wind turbine, the heating mat 1 10 according to embodiments of the invention may be attached to the so-called “leading edge ” of the blade. Thus, the heating mat 1 10 is configured to heat the “leading edge ” when activated according to such embodiments.

[0088] Finally, it is understood that the present invention is not limited to the above-described embodiments but includes and relates to all embodiments within the scope of the independent patent claim.

Claims

CLAIMS1 . A sensor (120) for indicating the presence of water and / or ice at a surface (210) of a structure (200), the sensor (120) comprising: an electrical power source (122), a first conductive element (124) connected to a first pole of the power source (122), and a second conductive element (126) connected to a second pole of the power source (122), the first conductive element (124) and the second conductive element (126) being arranged with a mutual distance (d) between them at the surface (210); the sensor (120) being configured to: indicate the presence of water and / or ice at the surface (210) when an electrical current ( / ) flows between the first conductive element (124) and the second conductive element (126).

2. The sensor (120) according to claim 1 , comprising a heat source (140) at which the first conductive element (124) and the second conductive element (126) are disposed; wherein the heat source (140) is configured to: heat the surface (210) of the structure (200) at the first conductive element (124) and the second conductive element (126) for at least one time period.

3. The sensor (120) according to claim 2, wherein the heat source (140) is configured to: heat the surface (210) at the first conductive element (124) and the second conductive element (126) such that ice formed between the first conductive element (124) and the second conductive element (126) is at least partially phase transformed to water.

4. The sensor (120) according to claim 2 or 3, wherein the sensor (120) is configured to: indicate the presence of ice at the surface (210) when an electrical current ( / ) flows between the first conductive element (124) and the second conductive element (126) when the heat source (140) has heated the surface (210).

5. The sensor (120) according to any one of claims 2 to 4, wherein the sensor (120) is configured to:indicate the non-presence of ice at the surface (210) when an electrical current ( / ) does not flow between the first conductive element (124) and the second conductive element (126) when the heat source (140) has heated the surface (210).

6. The sensor (120) according to any one of claims 2 to 5, wherein the heat source (140) is configured to: heat the surface (210) at the first conductive element (124) and the second conductive element (126) with a periodicity.

7. The sensor (120) according to claim 6, wherein the periodicity is between 60s - 600s, or between 120s - 480s, or between 120s - 300s, or between 120s - 240s.

8. The sensor (120) of any one of claims 2 to 7, wherein the heat source (140) is configured to: heat the surface (210) to a temperature greater than 1QC, or greater than 2QC, or greater than 3QC, or greater than 4QC, or greater than 5QC, or greater than 6QC, or greater than 7- C, or greater than 8QC, or greater than 9QC, or greater than 10QC.

9. The sensor (120) according to any one of claims 2 to 8, wherein the heat source (140) is part of a heating mat (1 10) of an arrangement (100) for heating the surface (210).

10. The sensor (120) according to any one of the preceding claims, wherein the mutual distance (d) between the first conductive element (124) and the second conductive element (126) is less than 1 mm, or less than 2 mm, or less than 3 mm, or less than 4 mm, or less than 5 mm, or less than 7 mm, or less than 10 mm, or less than 15 mm.1 1 . The sensor (120) according to any one of the preceding claims, wherein a gap (g) between the first conductive element (124) and the second conductive element (126) comprises a dielectric.

12. The sensor (120) of claim 1 1 , wherein the gap (g) between the first conductive element (124) and the second conductive element (126) forms a recess.

13. The sensor (120) according to any one of the preceding claims, comprising means for attaching the sensor (120) to the surface (210).

14. The sensor (120) of any preceding claim, wherein the first conductive element (124) and the second conductive element (126) are partially depressed in the structure (200) in use.

15. The sensor (120) according to any one of the preceding claims, configured to: indicate the presence or absence of water or ice at the surface (210) when the electric current ( / ) is greater than a current threshold and / or when a resistance (R) between the first pole and the second pole of the current source (122) is less than a resistance threshold.

16. The sensor (120) according to any one of the preceding claims, configured to: provide a sensor signal (S) indicating the presence or absence of water and / or ice at the surface (210).

17. An arrangement (100) for heating a surface (210) of a structure (200), the arrangement (100) comprising: at least one heating mat (1 10) configured to be attached to the surface (210) and to heat the surface (210) upon activation; a sensor (120) according to any one of the preceding claims; wherein the arrangement (100) is configured to: activate the heating mat (1 10) to heat the surface (210) of the structure (200) when the sensor (120) indicates the presence of water and / or ice at the surface (210).

18. The arrangement (100) according to claim 17, wherein the arrangement (100) is configured to: deactivate the heating mat (110) when the sensor (120) indicates the nonpresence of water and / or ice at the surface (210).

19. The arrangement (100) according to claim 17 or 18, wherein the arrangement (100) is configured to:further activate or deactivate the heating mat (1 10) based on an air temperature at the surface (210).

20. The arrangement (100) according to any one of claims 17 to 19, wherein the sensor (120) is connected to a supply circuit (150) or control circuit (150) for the heating mat (1 10) and configured to act as a switch for activating / deactivating the heating mat (1 10).

21. The arrangement (100) according to any one of claims 17 to 20, comprising: a control device (160) configured to activate or deactivate the heating mat (130) upon receipt of a sensor signal (S) from the sensor (120).

22. A system (300) comprising: an arrangement (100) according to any one of claims 17 to 21 ; and a structure (200) having a surface (210).

23. The system (300) according to claim 22, wherein the structure (200) is a blade of a wind turbine or a dam gate of a hydroelectric power plant.

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