Electro-thermal heating elements

The present invention relates to an Electro-Thermal Heating element for a wind turbine blade comprising an electrically conductive resistive material; two active busbars for supplying electrical power to the electrically conductive resistive material; and at least one dummy busbar at a predetermined spacing between the two active busbars on the electrically conductive resistive material. The present invention is also directed to a method of repair of the Electro-Thermal Heating Element.

The present invention is directed to Electro-Thermal Heating (ETH) Elements and, in particular, to the repair of Electro-Thermal Heating Elements.

BACKGROUND

Wind turbines generate electrical power from wind energy and can be situated on land or off-shore. Wind turbines situated in cold climates can suffer from icing events where ice may be formed on the surface of the wind turbine blades due to freezing water on the cold surface. The accumulation of ice on the surface of a blade can result in undesirable consequences. For example, a change in the profile of the wind turbine blades due to the accumulation of ice may reduce the speed of rotation of the wind turbine. As a result, the wind turbine may operate below optimal efficiency which degrades the performance of the wind turbine. Also, the additional weight of the accumulating ice on the wind turbine blades may cause fatigue and stress failures of the blades.

Therefore, there is a need to be able to prevent or reduce the effects of icing on the blades of a wind turbine in order to prevent damage to the blades and also to increase the performance of a wind turbine.

Various systems and methods have been described to either, or both, to de-ice (e.g. remove ice accumulated) a wind turbine or to provide anti-icing (e.g. prevent ice from accumulating) for a wind turbine.

For example, it is known to attach ETH elements to the wind turbine blades which, when supplied with electrical power, generate heat to increase the surface temperature of the surface of the blade. Such ETH elements may be used for either or both of anti-icing or de-icing of the wind turbine blade.

However, if the blade surface or structure is damaged which subsequently causes damage to the embedded ETH element then it is difficult to make a repair to the embedded ETH element without further damaging the ETH element or having to replace the entire ETH element within the blade structure.

The present invention seeks to address, at least in part, the problems and disadvantages described hereinabove and to seek to provide an improved method of repair of an ETH element embedded in a wind turbine blade and an improved ETH element.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided an Electro-Thermal Heating element for a wind turbine blade comprising: an electrically conductive resistive material; two active busbars for supplying electrical power to the electrically conductive resistive material; and at least one dummy busbar at a predetermined spacing between the two active busbars on the electrically conductive resistive material.

The present invention advantageously provides an Electro-Thermal Heating (ETH) element with dummy busbars at predetermined spacings so that a repair of the ETH element can be achieved in a more effective manner.

The Electro-Thermal Heating element may further comprise a new section of electrically conductive resistive material connected to a first dummy busbar and a further busbar, wherein the new section of electrically conductive resistive material replaces a damaged section of electrically conductive resistive material that is removed from the Electro-Thermal Heating element. The further busbar may be a second dummy busbar or one of the two active busbars.

The Electro-Thermal Heating element may further comprise at least one new busbar attached to one or both of the first dummy busbar and the further busbar. According to a second aspect of the present invention there is provided a method of repairing an Electro-Thermal Heating element; the Electro-Thermal Heating element being embedded in laminate layers of a wind turbine blade structure and the method comprising: an electrically conductive resistive material; two active busbars for supplying electrical power to the electrically conductive resistive material; and at least one dummy busbar at a predetermined spacing on the electrically conductive resistive material between the two active busbars; the method of repairing the Electro-Thermal Heating element comprising: determining a location of damage to a section of electrically conductive resistive material; determining a position of a first dummy busbar and a further busbar adjacent to the location of the damaged section of electrically conductive resistive material; removing the laminate layers of the blade structure at the location of the damaged section of electrically conductive resistive material between the adjacent busbars; removing the damaged section of electrically conductive resistive material; attaching a new section of electrically conductive resistive material wherein the new section of electrically conductive resistive material makes electrical contact with the adjacent busbars; and replacing the laminate layers of the blade structure over the new section of electrically conductive resistive material.

The further busbar may be a second dummy busbar or one of the two active busbars.

The method may further comprise attaching at least one new busbar to one or both of the first dummy busbar and the further busbar.

Attaching or connecting the new section of ETH element and/or new busbars may be via one or more of adhesive, stitching, and staples.

EMBODIMENTS

FIG.1shows a schematic of a typical wind turbine10which includes embodiments of wind turbine blades19according to the present invention. The wind turbine10is mounted on a base12which may be onshore foundations or off-shore platforms or foundations. The wind turbine includes a tower14having a number of tower sections. A nacelle16is located and attached to the top of tower14. A wind turbine rotor, connected to the nacelle16, includes a hub18and at least one wind turbine blade19, where inFIG.1three wind turbine blades are shown although any number of wind turbine blades19may be present depending on the design and implementation of the wind turbine10. The wind turbine blades19are connected to the hub18which in turn is connected to the nacelle16through a low speed shaft which extends out of the front of the nacelle16.

With reference toFIG.2, Electro-Thermal Heating (ETH) elements201may be embedded within the blade202structure between laminate layers of the blade structure and are therefore contained within the blade202. If the ETH element201suffers damage then it is very difficult to access the ETH element201within the blade202in order to replace or repair the ETH element201.

The ETH elements201are typically formed from a lightweight layer of conductive material, for example, between 3 grams per meter squared to 50 grams per meter squared, with two busbars203positioned at opposite sides or ends of the ETH element201, to provide the connection for the supply of electrical power. The busbars may be positioned in the blade chordwise or spanwise directions on the ETH elements.

Conventionally, if the laminate layers of the blade are damaged and require a repair then the standard repair procedure would be to grind away the laminate layers that are damaged, or to grind down to the damaged area, and the damaged laminate layers replaced with new materials.

However, as mentioned hereinabove, the ETH elements are formed of a lightweight layer of conductive material and so the standard blade repair procedure would not be suitable as it would be difficult to accurately grind down to the ETH element layer without further damaging the ETH element. Furthermore, even if one could accurately and carefully grind down to the damaged section of ETH element then by simply replacing the damaged area with a new section of ETH element would provide a poor electrical connection between the existing ETH element and the new ETH element replacement section.

One strategy to repair the ETH element could be to remove the entire ETH element which has a damaged section. This would require grinding away and removing the blade laminate layers and the ETH element layer between the two busbars that connect the ETH element to the power supply. If the entire ETH element was removed between the two busbars then the new replacement ETH element section would have a good electrical connection to the busbars. However, this strategy has the disadvantage that the entire ETH element has to be removed which requires a large amount of grinding as ETH elements may be several meters in length and/or width.

A further strategy to repair the ETH element according to one or more of the embodiments of the present invention will now be described with reference toFIG.3.

An ETH element301comprises at least one additional “dummy” busbar302positioned between two active busbars303on the ETH element301. A dummy busbar302is an extra busbar that serves no real purpose during the normal operation of the ETH element301but can be utilized if the ETH element301is damaged and needs repairing. In contrast, the active busbars303provide the connection to the power supply and are always in use during the operation of the ETH element301.

InFIG.3, there are four extra dummy busbars302ato302dpositioned between the two active busbars303. Each of the dummy busbars302ato302dis positioned at predetermined locations on the ETH element301. For example, the dummy busbars302ato302dmay be spaced every 500 millimeters (mm), 1000 mm, or any other suitable predetermined spacing on the ETH element301between the active busbars303.

As will be appreciated, there may be any number of dummy busbars302at any suitable predetermined spacing or position on the ETH element301for the purpose of the present invention.

As shown inFIG.3, an area of damage304has occurred to the ETH element301towards the centre of the ETH element301and the area of damage is located between two dummy busbars302band302c. In this example, the repair of the damaged area304comprises grinding away the blade surface that corresponds to an area between the two dummy busbars302b,302cthat are adjacent to, or either side of, the damaged area of ETH element301. The ETH element301is then removed between the adjacent dummy busbars302b,302cand replaced with a new section of ETH element305. The new section of ETH element305is connected to the two adjacent dummy busbars302b,302cso that the new section of ETH element305is operable to generate heat once the ETH element301is activated.

Alternatively, or additionally, and with reference toFIG.4, one or more new busbars401may be attached to the new section of ETH element402where the new busbars401are also attached to the existing busbars403. The one or more new busbars401may be attached to ensure a good electrical connection between the new section of ETH element402and the existing ETH element404. A new busbar401may be required in situations where the existing busbars403were damaged during the process of grinding through the blade laminate layers, the existing busbar403has not been completely exposed, and/or any resin on the existing busbars403has not been completely removed.

A more localized repair strategy is shown inFIG.5where, as withFIG.3, there are four dummy busbars502ato502dpositioned on the ETH element501at predetermined spacings between the two active busbars503.

In this example, instead of removing the entire section of ETH element501between the two adjacent dummy busbars502b,502cto the damaged area504of the ETH element501, a more localized section or area of the damaged ETH element is removed.

A new section of ETH element505is then laid to replace the removed damaged section and is connected to the dummy busbars.

As with the example given with reference toFIG.4, new busbars may be attached to the new section of ETH element where the new busbars are also attached to the existing dummy busbars.

In the above example, the damaged area of ETH element was between two dummy busbars. However, as will be appreciated, the damaged section of ETH element may occur between a dummy busbar and an active busbar towards either end of the ETH element. In this case, the same process of repairing the ETH element can be performed according to the examples ofFIGS.3to5, with the adjacent busbars to the damaged area being one active busbar and one dummy busbar.

The principle of the invention is also applicable for situations where the damage covers or impacts a dummy busbar, as shown inFIG.6. The ETH element601comprises 4 dummy busbars602ato602dwhich are spaced between to active busbars603. An area of damage604occurs in the ETH element601which impacts upon the dummy busbar602calong with a section of the ETH element601. In this example, the two adjacent busbars will be dummy busbars602band602d, and the process of repair follows that of the examples described in relation toFIGS.3to5. Therefore, a new section of ETH element605replaces the section of damaged ETH element and new busbars may be used to make a connection to the two dummy busbars602band602d. Additionally, the damaged busbar602cmay be replaced by a new dummy busbar by attaching the new dummy busbar to the new section of ETH element605at the same location as the damaged busbar602c.

Similarly, if the area of damage impacts an active busbar then the same principles of the invention are applicable as shown inFIG.7. The ETH element701comprises four dummy busbars702ato702dwhich are spaced between to active busbars703aand703b. An area of damage704occurs in the ETH element701which impacts upon the active busbar703aalong with a section of the ETH element701. In this example, the two adjacent busbars will be the active busbar703aand the dummy busbars702a, and the process of repair follows that of the examples described in relation toFIGS.3to5. Therefore, a new section of ETH element705replaces the section of damaged ETH element and a new busbar may be used to make a connection to the dummy busbars702a. Additionally, the damaged active busbar703awill be replaced by a new active busbar by attaching the new active busbar to the new section of ETH element705at the same location as the damaged active busbar703a.

In all of the examples described hereinabove, once the new section of ETH element is attached to the existing ETH element then the removed areas of the blade structure are replaced with new materials.

In the above examples, there were four dummy busbars, however, as will be appreciated there may be any number of dummy busbars, e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, and so on, positioned or located at predetermined positions and/or spacings on the ETH element. The number of dummy busbars is related to the design of the ETH element (e.g. the length of the ETH element) and the predetermined spacing for the dummy busbars on the ETH element.

The examples and embodiments described above are for example purposes only, and it will be appreciated that features of different embodiments or examples may be combined with one another. Embodiments of the present invention have been described, by way of example only, and many modifications or changes may be made to the embodiments and be within the scope of the apppended claims.