Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D80/00—Details, components or accessories not provided for in groups F03D1/00 - F03D17/00
  • F03D80/30—Lightning protection
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F03—MACHINES OR ENGINES FOR LIQUIDS; WIND, SPRING, OR WEIGHT MOTORS; PRODUCING MECHANICAL POWER OR A REACTIVE PROPULSIVE THRUST, NOT OTHERWISE PROVIDED FOR
  • F03D—WIND MOTORS
  • F03D80/00—Details, components or accessories not provided for in groups F03D1/00 - F03D17/00
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/72—Wind turbines with rotation axis in wind direction

Definitions

• the invention concerns a device for overvoltage protection in a wind turbine comprising a drive shaft that is arranged so as to operatively connect one or a plurality of rotor blades to a generator.
• Wind power plants generally consist of a tower with a wind turbine, which converts wind energy into electrical energy.
• the wind turbine comprises rotor blades, which connect to a shaft that is connected to an electrical generator.
• the rotor blades transfer forces from the wind striking the blades to the shaft, and a generator can be caused to rotate thereby.
• SE, B, 429 279 describes a previously known overvoltage protection for a wind turbine.
• the bearings and the generator are insulated from the rotor shaft by means of a coating of insulating material.
• Each bearing lies in abutment with a bearing seat of high insulating capacity, which is fitted to the rotor shaft.
• the generator shaft is equipped with insulating material in an area that connects to the rotor shaft.
• a lightning discharge is conducted from the wind turbine via a spark discharge gap between a stationary and a moving part.
• One disadvantage of this known solution is that it imposes heavy loads on the connections between the shaft and its insulating layer, e.g. in connection with emergency braking, since the kinetic mass of the generator is substantial. There is a major risk that the insulating material will be torn away from the shaft.
• the device for overvoltage protection in a wind turbine comprises a drive shaft made of composite material, which consists mainly of carbon fiber composite.
• the drive shaft has a longitudinally through-passing cavity.
• a connector to a hub connecting the rotor blades is arranged so as to be introduced into one end of the cavity.
• a coupling to the generator is arranged to be introduced into the second end.
• the cavity is surrounded by a layer of fiberglass composite that is integrally realized with the carbon fiber composite, which fiberglass composite is arranged so as to electrically insulate the connector and the coupling from the carbon fiber composite of the drive shaft.
• the drive shaft is connected to ground.
• the drive shaft is arranged so as to rotate in at least two bearings. These bearings lie in abutment with the drive shaft via a layer of fiberglass composite that is integrated with the carbon fiber composite.
• a slipring is arranged so as to conduct currents from the drive shaft to ground.
• the thickness of the fiberglass composite may account for 2 - 10% of the thickness of the entire composite structure. Because each respective layer of fiberglass composite can be relatively thin in relation to the carbon fiber composite, the properties that render the carbon fiber composite suitable for use in large drive shafts are retained, while satisfactory insulation of the electrically conductive carbon fiber composite is achieved at the same time.
• a thin layer of fiberglass composite is realized on the respective short sides of the drive shaft, so that each respective end of the drive shaft is electrically insulated.
• a metallic guide is integrated with the hub.
• a slipring lies in abutment with the metallic guide, whereby currents in the hub are conducted to ground.
• an insulating layer is arranged between the metallic guide and a bearing adjacent thereto to prevent currents from being able to pass through the bearings.
• Figure 1 provides a schematic side view of a wind power plant.
• Figure 2 provides a schematic view of a coupling between the rotor hub of the wind power plant and a generator.
• Figure 3 shows another example of a coupling between a rotor hub and a generator.
• Reference number 1 in Figure 1 generally designates a wind power plant consisting of a tower 2, a housing 3 arranged at the top of the tower, and a wind turbine arranged in the housing 3.
• the tower 2 is secured to a surface, either on land or at sea.
• the parts of the wind turbine that are essential to the invention are shown in Figure 2.
• the rotor blades 12 are operatively connected to a generator 9 so that a torque applied to the rotor blades 12 is converted into electrical current in the generator.
• the rotor blades 12 are securely fastened to a drive shaft 7 in the wind turbine via a hub 4.
• a connector 5 connects the hub 4 to the drive shaft 7 in such a way that, when the rotor blades 12 begin to rotate, the rotational motion is also imparted to the drive shaft 7.
• a coupling 10 connects the generator 9 to the drive shaft 7. The rotational motion is thereby transferred from the drive shaft 7 to the generator 9, which converts the rotational energy of the shaft into electrical energy.
• the way in which the generator 9 is constructed is not the object of this invention. What is essential is that the drive shaft 7 has an operative connection to the generator 9 via a coupling 10, which may constitute a part of the generator 9 in an embodiment.
• the drive shaft 7 consists of a cylindrical body with a longitudinally through-passing cavity. In large wind turbines it is advantageous, from a weight standpoint, to allow the cavity to be through-passing and to have the greatest possible diameter, since this results in substantially lower weight.
• the main part of the drive shaft 7 consists of a core of carbon fiber composite 7a.
• the fiber composite material is composed of a plastic base reinforced with carbon fiber threads.
• the plastic is, e.g. an epoxy plastic, vinylester plastic or polyester plastic. This material provides a number of desirable properties, in that such material is light, very strong, and rigid.
• an inner layer of fiber glass composite 7b is integrally realized with the carbon fiber composite along the inside diameter of the drive shaft 7 so that the inner layer of the fiberglass composite 7b delimits the cavity.
• the fiberglass composite is an electrically insulating material, and the drive shaft 7 is insulated from the inner cavity thereby.
• the core of the carbon fiber composite 7a and the respective layers 7b and 7c of fiber glass composite consist of a plurality of thin layers of composite material arranged on top of one another - often with different fiber orientations - which are joined in an autoclave press to produce an integrated structure.
• the integrated layer of fiberglass composite comprises a part of the drive shaft 7 and thus contributes to bearing the load on the shaft.
• a metallic hub 4 connects the rotor blades 12 to the drive shaft by means of a connector 5, which is realized in one piece with the hub 4, or connected thereto in some other way.
• the connector 5 holds the hub 4 to the drive shaft 7 by means of a press-fit.
• the joint 13 between the connector 5 and the drive shaft 7 can also consist of other types of joints, such as adhesive joints or bolt joints, as shown in Figure 3.
• the connector 5 connects the hub 4 to the drive shaft 7 in such a way that, when the hub 4 begins to rotate, the rotational motion is also imparted to the drive shaft 7. In its mounted state, the connector 5 lies in abutment with the insulating inner layer of fiberglass composite 7b.
• the hub 4 also comprises a guide 6, which is either realized in one piece with the hub 4 or constitutes a separate part that is mounted on the hub 4.
• the guide 6 extends from the hub 4 on the outside of the drive shaft 7 and includes a wall that is designed so as to surround, with play, the drive shaft 7 along a portion of the length of the drive shaft 7.
• the guide 6 is intended to hold the hub 4 in position relative to the drive shaft 7, and to permit its unimpeded rotation.
• Bearings 8 are arranged along the length of the drive shaft 7, which bearings 8 hold the drive shaft 7 in its position, and in which bearings the drive shaft 7 rotates, hi the embodiment shown in Figure 2, a first bearing 8 can surround the guide 6 of the hub 4, which guide is thereby caused to rotate in the bearing.
• a second bearing 8 surrounds the drive shaft 7 itself at a point nearer to the generator 9. The bearings and, above all, the bearing surfaces are sensitive to heavy currents, which makes it necessary to protect these surfaces from the heavy currents that can arise in connection with a lightning discharge.
• An electrically insulating layer of, preferably, fiberglass composite is arranged between each respective bearing 8 and the part against which that bearing lies in abutment.
• an insulating outer layer of fiberglass composite 7c is integrally realized with the carbon fiber composite on the outside of the drive shaft 7 so that the drive shaft wholly or partly exhibits an outside layer of fiber glass composite.
• the bearings are thereby insulated from those surfaces that could potentially be electrically conductive.
• the inner layer of fiberglass composite 7b of the drive shaft insulates the generator 9 connected at the end from any current passing via the electrically conductive carbon fiber composite. To ensure that no current path into the generator 9 can arise, there is no contact between the coupling 10 to the generator 9 and the drive shaft 7. This is achieved by means of an air gap or beveling at the end surface on the drive shaft 7. It is also possible to coat the two end surfaces of the drive shaft 7 with fiberglass composite so that the entire drive shaft 7 becomes electrically insulated, despite its core of electrically conductive carbon fiber composite. Because the drive shaft 7 consists of fiber composite, the joint described in Swedish patent application SE0103610-2 "Device and method for a drive shaft" can be used.
• a slipring 11 can lie in abutment with the mechanical guide 6.
• the slipring 11 connects to a ground potential and thus constitutes the natural current path for a current entering via the rotor blades 12.
• a lightning discharge is described below in connection with the embodiment shown in Figure 2.
• a current path arises via the rotor blades 12 and into the hub 4 of the wind turbine.
• the electrical current is conducted via the guide 6 and the slipring 11, which constitute the easiest path for the current to follow to ground.
• contact is present only between the inner layer of fiberglass composite 7b on the drive shaft 7 and the generator 9. This prevents any type of current path from continuing on into the generator 9.
• Figure 3 shows a wind turbine where the hub 4 is securely fastened to the drive shaft by means of a bolt joint 13.
• the bolts in this case are electrically conductive, and a current path could consequently arise in the carbon fiber composite.
• This current is however diverted via a slipring 11, which can lie in abutment with a portion of the carbon fiber core 7a in the drive shaft 7.
• the figure does not show the insulating layers that should be present in direct connection to each bearing 8 to further decrease the risk that the current path will propagate through the bearings.

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• Engineering & Computer Science (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Wind Motors (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 2001
  • 2001-11-21 SE SE0103872A patent/SE518617C2/sv not_active IP Right Cessation
• 2002
  • 2002-11-04 EP EP02780245A patent/EP1461531A1/en not_active Withdrawn
  • 2002-11-04 WO PCT/SE2002/001997 patent/WO2003054389A1/en not_active Application Discontinuation
  • 2002-11-04 AU AU2002343314A patent/AU2002343314A1/en not_active Abandoned

Non-Patent Citations (1)

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