CA2933943A1

CA2933943A1 - Wind turbine rotor blade with an electrical heating device

Info

Publication number: CA2933943A1
Application number: CA2933943A
Authority: CA
Inventors: Danela Jacob; Ines Runge; Konrad Sachse
Original assignee: Nordex Energy SE and Co KG
Current assignee: Nordex Energy SE and Co KG
Priority date: 2015-06-26
Filing date: 2016-06-23
Publication date: 2016-12-26
Also published as: EP3109465A1; ES2704099T3; DK3109465T3; EP3109465B1

Abstract

A wind turbine rotor blade with an electrical heating device for heating a surface region of the wind turbine rotor blade and a temperature sensor, wherein the electrical heating device is designed so that, while the heating device is operating, a maximum temperature is achieved in a section of the surface region close to the blade root in which the temperature sensor is arranged.

Description

Wind Turbine Rotor Blade with an Electrical Heating Device This application claims priority based on European Patent Application 15 174 151.9 entitled "WIND TURBINE ROTOR BLADE WITH AN ELECTRICAL HEATING
DEVICE" filed June 26, 2015, which is herein incorporated by reference.
The invention relates to a wind turbine rotor blade with an electrical heating device for heating a surface region of the wind turbine rotor blade, and a temperature sensor. By supplying electrical energy to the electrical heating device, existing ice on the rotor blade can be removed, and/or imminent icing can be prevented. To control the supply of energy, a wind turbine equipped with the wind turbine rotor blade can have a control which is connected to the temperature sensor so that a current temperature can be monitored.
A wind turbine rotor blade with an electrical heating device is known from the document WO 2012/164167 Al, the heating device having a heating mat which extends in the longitudinal direction of the rotor blade which is supplied through special electrical connections with electrical heating current that flows through the heating mat in the longitudinal direction of the rotor blade.
A wind turbine rotor blade with an electrical heating element is known from the document EP 2 738 383 Al and also has a heating mat with a flow in the longitudinal direction. The width of the heating mat varies along its length to achieve area output adapted to the required heating output.
A wind turbine rotor blade with an electrical heating device is known from the document WO 2014/023734 Al, the electrical heating device having a plurality of heating circuits with a sinusoidal, wavy or zigzag running path. By varying an amplitude and/or a wavelength of the heating circuits, an area output of the heating device can be sectionally varied.

- 2 -A wind turbine rotor blade with an electrical heating device is known from the document EP 2 843 228 Al and has heating elements substantially transverse to a longitudinal direction of the rotor blade through which an electrical heating current flows. The heating elements have electrically conductive fiber bundles with a length that can be varied relative to a length of the relevant heating element by means of different curved arrangements in order to be able to influence an area output.
A particular difficulty in operating such heating devices is to establish a sufficient temperature differential relative to the environment throughout the relevant surface region in order to reliably achieve the desired effect without inappropriately high energy consumption and/or local overheating occurring. If the temperature exceeds a specific maximum value depending on the employed materials, permanent, possibly irreparable damage to the rotor blade may quickly occur.
Known electrical heating devices for wind turbine rotor blades counteract this difficulty with a plurality of temperature sensors that are arranged in different regions of the heating device in order to monitor the temperature over a large area. In so doing, generally at least one temperature sensor is arranged close to the blade tip where a relatively large heat output requirement exists due to the particularly high flow speeds, and a high surface output is accordingly available, which is associated with a particularly high risk of overheating.
The arrangement of temperature sensors close to the blade tip is, however, also associated with particular disadvantages. On the one hand, the electrical conductors extending close to the blade tip that are required to operate the temperature sensor can increase the risk of damaging the rotor blade from lightning and necessitate involved lightning protection measures. On the other hand, the region close to the blade tip is no longer accessible from the inside after the production of the rotor blade.
Repairs can only be performed from the outside for which special service openings must be created in the rotor blade. Any servicing or repair of a temperature sensor close to the blade tip is therefore associated with very high costs.

- 3 -Against this background, it is the object of the invention to provide a wind turbine rotor blade with an electrical heating device that can be operated reliably and safely without a temperature sensor close to the blade tip.
This object is achieved by the wind turbine rotor blade with the features of claim 1.
Advantageous embodiments are specified in the subsequent dependent claims.
The wind turbine rotor blade has an electrical heating device for heating a surface region of the wind turbine rotor blade and a temperature sensor, wherein the electrical heating device is designed so that, while the heating device is operating, a maximum temperature is achieved in a section of the surface region close to the blade root in which the temperature sensor is arranged.
The heatable surface region can extend over a part of the overall surface of the wind turbine rotor blade, in particular over a longitudinal section of the rotor blade which extends from a middle radial position to near a blade tip, or up to the blade tip. The middle radial position can be arranged at a distance from a blade root, in particular in a region of approximately 30% to approximately 70% of a radius of a rotor equipped with a wind turbine rotor blade, as normally measured starting from a rotary axis of the rotor.
The heatable surface region can in particular enclose an airfoil leading edge in the relevant longitudinal section of the rotor blade. It can extend from the airfoil leading edge in the direction of flow to the rear up to an airfoil trailing edge, or terminate at a distance therefrom on the pressure side and on the suction side, for example in a region between 10% and 90% of an airfoil cord measured from the airfoil leading edge.
An energy supply for the electrical heating device can be controlled with a control that for example is arranged outside of the wind turbine rotor blade, for example in a rotor hub, or in a nacelle of a wind turbine equipped with a wind turbine rotor blade. In the simplest case, the control can offer a way to shut the heating device off and on. Also possible is a control or regulation of the electrical output that is infinitely variable or is provided with two or more output levels. The temperature sensor is connected to the

- 4 -control so that the energy supply can be controlled with regard to a temperature detected by the temperature sensor.
According to the invention, the temperature sensor is arranged in a section of the surface region close to the blade root. This means a section that is located at a significant distance from the blade tip, or respectively from a blade-tip-side the end of the heatable surface region. The section close to the blade root can be at a distance from the blade root as well as from a blade-root-side end of the heatable surface region. It is, however, close enough to the blade root so that any required maintenance work in the area of the temperature sensor is easier to do than in the case of the usual arrangement of a temperature sensor close to the blade tip.
In the section close to the blade root, a plurality of temperature sensors can optionally be arranged, in particular to continue obtaining informative data when a temperature sensor malfunctions. Outside of the section close to the blade root, in particular in a region close to the blade tip, the wind turbine rotor blade preferably does not have a temperature sensor.
According to the invention, the electrical heating device is designed so that when the heating device is operating, a maximum temperature is achieved in the section of the surface region close to the blade root. The temperature distribution which arises during the operation of the wind turbine rotor blade in the heatable surface region depends on several influencing factors. Of relevance are the local heat supply from the electrical heating device which depends on the area output of the heating device, i.e., on the thermal output emitted, or electrical power consumed, per surface unit in the relevant region, as well as the local heat dissipation which depends on the local flow conditions, in particular the inflow speed of the surrounding air and the thermal conductivity and thermal capacity of the rotor blade itself. These influencing factors can be determined by computation or experiment and considered in the design of the electrical heating device.
Generally, a temperature that is as even as possible in the heatable surface region is always sought, and the output capacity of the heating device is selected so that a desired =

- 5 -temperature differential relative to the environment can be achieved everywhere.
Deviations from this ideal are scarcely avoidable in practice. On one hand, they result from an incomplete consideration of the cited influential factors and/or a consideration subject to imprecisions, and on the other hand, they result from production tolerances and dynamic effects before a thermal equilibrium is achieved.
The inventors have realized that the temperature monitoring required for reliable and safe operation of the electrical heating device can be significantly simplified when a section of the surface region close to the blade root is specified in the design of the electrical heating device in which a maximum temperature shall be reached. If the temperature sensor is then arranged in this section, overheating throughout the heatable surface region can be avoided.
In designing the electrical heating device, the area output in the section close to the blade root can be rated so that the temperature differential to the environment achievable at that location can be for example at least 0.5 K, 1 K, 2 K, or 5 K higher than at the sections of the surface region adjacent to the section close to the blade root. The area output required for this can be determined by calculation or experiment.
In one embodiment, the electrical heating device has a heating mat consisting of an electrically conductive material, a blade-root-side electrical connection to a blade-root-side end of the heating mat, and a blade-tip-side electrical connection to a blade-tip-side end of the heating mat so that an electrical heating current substantially flows in a longitudinal direction of the wind turbine rotor blade. The heating mat has an electrically conductive material such as plies or fabric consisting of an electrically conductive fiber material, in particular consisting of carbon fibers. Due to the cited arrangement of the electrical connections, the heating current flows substantially in the longitudinal direction through the entire heating mat so that the same current flows through each longitudinal section in the heating mat. The overall heat output provided by the heating mat is determined by the electrical properties of the heating mat and by the energy supply. The effective heat output in a specific longitudinal section of the heating mat depends on the heating current and the voltage drop occurring over the relevant =

- 6 -longitudinal section. If the relevant longitudinal section has a relatively high electrical resistance (i.e., particularly in comparison to other longitudinal sections of the heating mat), the voltage drop and hence the heat output increases. This can generate an elevated area output in the relevant longitudinal section. The width of the heating mat in the longitudinal section also has an influence on the area output. It is therefore possible to vary the area output of the heating mat so that a region of maximum temperature relative to the entire heating mat is created in the section close to the blade root.
In one embodiment, the heating mat has an outer longitudinal section that extends from the blade-tip-side end of the heating mat to a first middle radial position, and an inner longitudinal section that extends from a second middle radial position to the blade-root-side end of the heating mat, wherein the section close to the blade root is arranged in the inner longitudinal section. As usual, the term "radial position" refers to the distance from the rotary axis of a rotor equipped with the wind turbine rotor blade. The inner and outer longitudinal section can be directly adjacent to each other. In this case, the first middle radial position and second middle radial position coincide. They can, however, also be arranged at a distance from each other; in this case, the first middle radial position is arranged closer to the blade tip than the second middle radial position, and the heating mat has a transitional section between the two radial positions. The inner and outer longitudinal section can be provided with different electrical properties or with a different arrangement to adapt the area output of the heating mat to the required heating output, and to ensure that the maximum temperature is reached in the section close to the blade root. The section close to the blade root is arranged in the inner longitudinal section. It can extend over the entire longitudinal section, or only over a part thereof.
In one embodiment, the inner longitudinal section has a smaller width than the outer longitudinal section. Due to the smaller width, the inner longitudinal section has a greater electrical resistance per length which increases the area output in the inner longitudinal section relative to the outer longitudinal section. This can help the maximum temperature in the section close to the blade root to be reached within the inner longitudinal section.
Also possible is an arrangement of the inner longitudinal section of the heating mat over a lesser width while the overall cross-section is unchanged. In this case, the area output

- 7 -in the inner longitudinal section also increases, although not due to a greater electrical resistance, but rather to a reduction of the area within which the heat output is emitted.
In one embodiment, the outer longitudinal section has a uniform width. The area output provided by the heating mat is therefore substantially constant over the outer longitudinal section.
In one embodiment, the outer longitudinal section is trapezoidal. In particular, a width of the outer longitudinal section can decrease toward the blade tip. This increases the electrical resistance, the voltage drop and electrical heat output toward the blade tip which brings about an adaptation to the required heat output.
In one embodiment, the inner longitudinal section has a length within a section of 0.5 m to 5 m. On the one hand, this section of length causes an informative temperature to form in the inner longitudinal section; on the other hand, an unnecessarily high energy requirement from generating a maximum temperature over an unnecessarily large area is avoided.
In one embodiment, the inner longitudinal section has a uniform width. This can help generate a uniform, maximum temperature in the section close to the blade root.
In one embodiment, the electrical heating device has two of the heating mats which are arranged so that they overlap each other in an overlapping region running along an airfoil leading edge of the wind turbine rotor blade. Such an overlapping region can be created with just two heating mats, as well as with a suitable combination of three or more heating mats which at least partially overlap in the region of the airfoil leading edge. In the overlapping region, the area outputs of the two heating mats add up so that the heat output region of the airfoil leading edge is increased as needed.
In one embodiment, the section close to the blade root is arranged in the overlapping region. Even in an overlapping arrangement, it therefore lies within a region in which a maximum temperature is achieved.

- 8 -In one embodiment, a width of the overlapping region perpendicular to a longitudinal axis of the rotor blade narrows toward the blade tip. Due to this measure, the heat output of the two heating mats is concentrated into a smaller area toward the blade tip which takes into account the increasing heat output requirement toward the blade tip.
The invention is explained in greater detail below based on an examplary embodiment shown in two figures. In the figures:
Fig. 1 shows a schematic, perspective representation of a wind turbine rotor blade according to the invention, Fig. 2 shows the electrical heating device of the wind turbine rotor blade from Fig.
1 in a schematic representation.
The wind turbine rotor blade 10 from Fig. 1 comprises a blade root 12, a blade tip 14, an airfoil trailing edge 16, an airfoil leading edge 18, a suction side 20 and a pressure side 22. Furthermore, it has an electrical heating device 24 that extends over a longitudinal section 26 which runs from a blade-root-side end 28 to a blade-tip-side end 30. The blade-tip-side end 30 is arranged close to the blade tip 14. The blade-root-side end 28 is located at a distance from the blade root 12 which for example lies within a range of 30%
to 70% of an overall length of the wind turbine rotor blade 10.
The electrical heating device 24 consists of two heating mats 36, 38 (see Fig.
2) consisting of an electrically conductive material which is connected to a first supply line 34 by an electrical connection arranged on the blade-root-side end 28, and which is connected to a second supply line 32 by an electrical connection arranged on the blade-tip-side end 30. The energy is supplied to the electrical heating device by the two supply lines 32, 34 and causes current to flow through the electrical heating device substantially in a longitudinal direction of the wind turbine rotor blade 10.
Details of the electrical heating device 24 are better discernible in Fig. 2 which shows a schematic representation of the electrical heating device 24 with a view of the dot-dashed airfoil leading edge 18. The electrical heating device 24 has a first heating mat 36 and a second heating mat 38 which can be distinguished by the hatching with different

- 9 -orientation. The two heating mats 36, 38 each extend from a blade-root-side end 28 to a blade-tip-side end 30.
Each of the two heating mats 36, 38 has three different longitudinal sections:
One outer longitudinal section 40 extends from the blade-tip-side end 30 to a first middle radial position 42. The outer longitudinal section 40 has a uniform first width 50 that extends over its entire length.
One inner longitudinal section 46 extends from a second middle radial position 44 to the blade-root-side end 28. It has a uniform second width 52 which is smaller than the first width 50. The first middle radial position 42 is arranged closer to the blade-tip-side end 30 than the second middle radial position 44. A transitional section 48 extends between the two middle radial positions in that the width of each of the two heating mats 36, 38 decreases from the first width 50 to the second width 52.
In an overlapping region 54 that extends over the entire length of the two heating mats 36, 38 and along the airfoil leading edge 18, the first heating mat 36 and second heating mat 38 are arranged to overlap each other. The width of this overlapping region 50 continuously increases from the blade-root-side end 28 to the blade-tip-side end 30.
Both heating mats 36, 38 possess an inner longitudinal section 46 which has a second width 52 which is smaller than the first width 50. The specific area heat output in the inner longitudinal section 46 is therefore greater than in the outer longitudinal section 40.
A section 56 of the heatable surface region close to the blade root is formed within the two inner longitudinal sections 46 and within the overlapping region 54 to reach a maximum temperature. Two temperature sensors 58 indicated by small circles are arranged in this section 56 close to the blade root which serve to monitor the maximum temperature which occurs there. Two temperature relays 60 are located in the region of the outer longitudinal sections 40, also within the overlapping region 54, and offer additional protection against overheating. They are arranged at a substantial distance from the blade tip.

- 10 -List of Reference Numbers Wind turbine rotor blade 12 Blade root 14 Blade tip 16 Airfoil trailing edge 18 Airfoil leading edge Suction side 22 Pressure side 24 Electrical heating device 26 Longitudinal section 28 Blade-root-side end Blade-tip-side end 32 Supply line, blade-tip-side connection 34 Supply line, blade-root-side connection 36 First heating mat 38 Second heating mat Outer longitudinal section 42 First middle radial position 44 Second middle radial position 46 Inner longitudinal section 48 Transitional section First width 52 Second width 54 Overlapping region 56 Section close to the blade root 58 Temperature sensor Temperature relay

Claims

1. A wind turbine rotor blade (10) with an electrical heating device (24) for heating a surface region of the wind turbine rotor blade (10) and a temperature sensor (58), characterized in that while the heating device (24) is operating, a maximum temperature is achieved in a section (56) of the surface region close to the blade root in which the temperature sensor (58) is arranged.

2. The wind turbine rotor blade (10) according to claim one, characterized in that the electrical heating device (24) has a heating mat (36, 38) consisting of an electrically conductive material, an electrical connection to a blade-root-side end (28) of the heating mat (36, 38), and an electrical connection to a blade-tip-side end (30) of the heating mat (36, 38) so that an electrical heating current basically flows in a longitudinal direction of the wind turbine rotor blade (10).

3. The wind turbine rotor blade (10) according to claim 2, characterized in that the heating mat (36, 38) has an outer longitudinal section (40) that extends from the blade-tip-side end (30) of the heating mat (36, 38) to a first middle radial position (42), and an inner longitudinal section (46) that extends from a second middle radial position (44) to the blade-root-side end (28) of the heating mat (36, 38), wherein the section (56) close to the blade root is arranged in the inner longitudinal section (46).

4. The wind turbine rotor blade (10) according to claim 3, characterized in that the inner longitudinal section (46) has a smaller width than the outer longitudinal section (40).

5. The wind turbine rotor blade (10) according to claim 3 or 4, characterized in that the outer longitudinal section (40) has a uniform width.

6. The wind turbine rotor blade (10) according to claim 3 or 4, characterized in that the outer longitudinal section (40) is trapezoidal.

7. The wind turbine rotor blade (10) according to one of claims 3 to 6, characterized in that the inner longitudinal section (46) has a length within a range of 0.5 m to 5 m.

8. The wind turbine rotor blade (10) according to one of claims 3 to 7, characterized in that the inner longitudinal section (46) has a uniform width.

9. The wind turbine rotor blade (10) according to one of claims 2 to 8, characterized in that the electrical heating device (24) has two of the heating mats (36, 38) which are arranged so that they overlap each other in an overlapping region (54) running along an airfoil leading edge (18) of the wind turbine rotor blade (10).

10. The wind turbine rotor blade (10) according to claim 9, characterized in that the section (56) close to the blade root is arranged in the overlapping region (54).

11. The wind turbine rotor blade (10) according to claim 9 or 10, characterized in that a width of the overlapping region (54) perpendicular to a longitudinal axis of the rotor blade (10) increases toward the blade tip (14).

12. The wind turbine rotor blade (10) according to one of claims 1 to 11, characterized in that the heatable surface region has a blade-root-side end and a blade-tip-side end, and the section (56) close to the blade root is arranged closer to the blade-root-side end than the blade-tip-side end.

13. The wind turbine rotor blade (10) according to one of claims 1 to 12, characterized in that an area output of the electrical heating device (24) in the section (56) close to the blade root is just as large or larger than in a section close to the blade tip.

14. The wind turbine rotor blade (10) according to one of claims 1 to 13, characterized in that an area output of the electrical heating device (24) in the section (56) close to the blade root reaches a local and/or absolute maximum.