Abstract:
A wind power installation includes a nacelle, and energy conversion system for converting wind power into electric energy. The energy conversion system includes a heat-generating source which is disposed in the nacelle and constructed to include a closed primary cooling system using air for dissipating generated heat. Further provided is an open secondary cooling system which uses ambient air for cooling heated air from the primary cooling system.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS  
       [0001]     This application is a division of prior filed copending U.S. application Ser. No. 11/042,836, filed Jan. 24, 2005, which in turn is a continuation of prior filed PCT International application no. PCT/DE2003/002355, filed Jul. 11, 2003, which designated the United States and on which priority is claimed under 35 U.S.C. §120, and which claims the priority of German Patent Application, Serial No. 102 33 947.3, filed Jul. 25, 2002, pursuant to 35 U.S.C. 119(a)-(d). 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates, in general, to a wind power plant, and more particularly to a wind power installation of a type having a generator disposed in a nacelle and including a cooling circuit, and a turbine with at least one rotor blade.  
         [0003]     Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.  
         [0004]     Typically, a wind power plant has a rotor blade which is rotatable around a horizontal axis and pivotable around a vertical axis to turn the rotor blade in appropriate alignment to the wind. The rotor blade is rotated by wind velocity at speed depending on diameter and shape of the rotor blade and its pitch to drive a generator, so that wind power is converted into electric energy. The conversion of energy normally results in energy loss in the form of heat. This heat loss applies in both the conversion of kinetic energy of wind into electric energy in the generator of a wind power plant as well for the electrical feeding of energy, generated by the wind power plant, into an electric power supply network. This heat loss takes place also in other electrical components, in particular the electronic power equipments, such as e.g. inverter or transformer. Also other components of the wind power plant heat up such as gears, bearings or control units like, e.g., hydraulic systems or similar control and regulation units, which adjust the rotor blades or turn the wind power plant towards the wind.  
         [0005]     The heat loss amounts hereby to 5 to 7% of the installed nominal output. Heretofore, the heat loss has been dissipated into the environment by using fans which pull in cold air from outside to cool the corresponding component, e.g., the generator. The heated air is then discharged again to the outside. This is disadvantageous especially when the outside air is humid or has a high salt content particularly in coastal regions, and the components to be cooled are then exposed to this humid and salty air.  
         [0006]     German patent publication no. DE 198 02 574 A1 describes a wind power installation having a generator which is cooled by an air stream produced by low pressure at a mouth of a rotor blade. This low pressure results in a pressure drop between each mouth of a rotor blade and an opening on a rotor blade distal side of the nacelle. As a consequence, ambient air is drawn in at the opening in opposition to the actual wind direction and flows via the flow path through the nacelle and through the interior of a rotor blade toward the mouth of this rotor blade. The provision of such a closed circulating ventilation is disadvantageous and, especially when located off-shore, results air with high salt content being aspirated. Moreover, noise is generated by the mouths at the rotor blades.  
         [0007]     German patent publication no. DE 199 47 915 A1 describes a cooling system for cooling heat-generating structures in particular of a wind power plant, using a chimney effect of heated air to cool the structures in the foot region of the tower and also in a top area of the nacelle. It is hereby disadvantageous that the tower cross section is already formed with channels. Moreover, also a closed circulating ventilation system is involved here which is susceptible to penetration of dirt and humidity and thus is unsuitable for carrying out a reliable operation.  
         [0008]     U.S. patent publication no. 2001/0035651 describes a wind power generating device in which lost energy of the generator is dissipated to the ambient air by direct heat conduction to the outer skin of the nacelle which is provided with ribs for surface enlargement. This cooling system is however able to dissipate only little heat energy.  
         [0009]     It would therefore be desirable and advantageous to provide an improved wind power installation which obviates prior art shortcomings and is reliable in operation even for off-shore operation, without experiencing breakdown or maintenance works as a result of contaminated or salty cooling air.  
       SUMMARY OF THE INVENTION  
       [0010]     According to one aspect of the present invention, a wind power installation includes a nacelle, energy conversion means for converting wind power into electric energy, said energy conversion means including a heat-generating source disposed in the nacelle and constructed to include a closed primary cooling system using air for dissipating generated heat, and an open secondary cooling system using ambient air for cooling heated air from the primary cooling system.  
         [0011]     It will be appreciated by persons skilled in the art that cooling by means of the primary cooling circuit should not be limited to the generator only but also includes other electrical equipments such as converters or slip-ring members of the generator.  
         [0012]     By separating the primary cooling circuit from the secondary cooling circuit, a wind power installation in accordance with the present invention can be erected at any site, irrespective of adverse outer conditions. In other words, the wind power installation can also be built offshore where humid and salty air is prevalent because the primary cooling circuit is encapsulated or enclosed internally and a sufficient cooling action of the nacelle can be realized using the wind. The air velocity about the nacelle is dependent on wind strength, whereby the relationship between wind strength and generator output and thus also generator losses is proportional.  
         [0013]     Suitably, the nacelle is constructed as secondary air cooler so as to realize an air-air cooler.  
         [0014]     According to another feature of the present invention, the secondary air cooler may be constructed in the form of a heat exchanger which is designed as tube bundle and secured to the nacelle or forming part of the nacelle. Suitably, the tube bundle is disposed in an upper portion about the nacelle. Heated air produced by the generator or other electrical components connected to the primary cooling circuit rises or is forced by fans into the interstices between the tube bundles and cooled there by wind flowing through the tube bundles. The cooled air of the primary cooling circuit is flowed back through natural convection or by a further fan for cooling the generator or other electrical components disposed in the nacelle. The arrangement of the tube bundle on the nacelle ensures an alignment of the tubes of the tube bundle in parallel relationship to a wind direction so as to provide a sufficient cooling action by wind velocities and sufficient passage of air through the tube bundle. The tube bundle forms the heat exchanger between the primary and secondary circuits.  
         [0015]     To provide a particularly efficient heat transfer, the tubes may be formed with surface-enlarging structures.  
         [0016]     According to another feature of the present invention, the secondary cooler has an inlet and an outlet, wherein the inlet or the outlet of the secondary cooler is disposed on the nacelle at a location which has enhanced flow dynamics.  
         [0017]     According to another feature of the present invention, air of the primary cooling circuit exits the nacelle via tubes. Suitably, the nacelle may be constructed such as to resemble a handle-shaped object when viewed in wind direction. Accordingly, the primary cooling circuit may have at least one handle-shaped tubular member on the nacelle, with ambient air, i.e. wind, freely flowing about the handle-shaped tubular member and defining the secondary cooling circuit. Suitably, the tubes have at least one outlet provided in the upper portion of the nacelle, and at least one inlet preferably disposed in the lower portion of the nacelle so as to enable a natural convection of air of the primary cooling circuit. To assist the natural convection, fans, in particular axial fans, may be provided.  
         [0018]     According to another feature of the present invention, the tubular member may have a first port, disposed in an upper portion of the nacelle for receiving heated air from the heat-generating source, and a second port, disposed at a location below the outlet, for returning cooled air into the nacelle. Suitably, a fan may be provided for assisting a circulation of air through the tubular member  
         [0019]     Compared with facilities operating with air-water cooling systems, a wind power installation according to the present invention has the advantage of being compact, substantially maintenance-free and reliable operation, without any need for preparing coolants in great amounts. As a result, costs are low. Compared to wind power plants with closed circulating ventilation in particular of the generators, a wind power installation according to the present invention is less likely to breakdown as a result of humid or salty air.  
         [0020]     The outgoing heated air of the primary cooling circuit can be used to heat the nacelle, rotor blades, in particular during the cold season. Condensate formations on electrical equipment and ice build up on the rotor blades are thereby eliminated. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0021]     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which:  
         [0022]      FIG. 1  is a longitudinal section of one embodiment of a wind power installation according to the present invention;  
         [0023]      FIG. 2  is a cross section of the wind power installation of  FIG. 1 ;  
         [0024]      FIG. 3  is a longitudinal section of another embodiment of a wind power installation according to the present invention; and  
         [0025]      FIG. 4  is a cross section of the wind power installation of  FIG. 3 .  
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0026]     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted.  
         [0027]     Turning now to the drawing, and in particular to  FIG. 1 , there is shown a longitudinal section of one embodiment of a wind power installation according to the present invention, including a nacelle  2  which is supported by an unillustrated tower. The nacelle  2  supports at least one rotor blade which is rotatable around a horizontal axis by wind velocity to drive a generator, so that wind power is converted into electric energy. Besides the generator, the nacelle  2  accommodates also other heat-generating electrical components, e.g. converter or slip-ring member of the generator. For sake of simplicity, reference numeral  1  is used in  FIG. 1  to generally indicate a heat-generating source  1 . Although not shown in detail, the generator as heat source  1  has a laminated stator core and laminated rotor core, whereby the laminations of the stator and/or the rotor are traversed in a manner known per se by radial and/or axial ventilation channels defining a closed primary cooling circuit. Furthermore, the air of the primary cooling circuit may flow through the air gap of the generator.  
         [0028]     The nacelle  2  further accommodates above the heat source  1  a system of tube bundles  6 . Currently preferred is the arrangement of the system of tube bundles  6  upon the top surface of the nacelle  2 . Wind for driving the rotor blade on the nacelle  2  flows through the tube bundles  6  in axial direction and enters the system of tube bundles  6  via an inlet, as indicated by arrow  4 , and exits the tube bundles  6  through outlet, as indicated by arrow  5  to thereby define an open secondary cooling circuit. The tube bundles  6  act as heat exchanger between the inlet  4  and outlet  5  to transfer heat from air, circulating in the closed primary cooling circuit of the heat source  1 , to wind sweeping through the system of tube bundles  6 . The heated air from the heat source  1  enters the system of tube bundles  6  via an outlet  7 , is cooled there and flowed back through convection and/or a fan  8  to the heat source  1 . Reference numeral  10  designates the transition zones between the primary cooling circuit and the secondary cooling circuit realized by the heat exchanger in the form of tube bundles  6 .  
         [0029]      FIG. 2  shows a cross section of the wind power installation and depicts in more detail the arrangement of the tube bundles  6  in the nacelle  2 . The tubes of the tube bundles  6  have a cylindrical configuration and are suitably formed with unillustrated surface-enlarging structures to enhance the cooling efficiency. Examples of such surface-enlarging structures may include ribs or fins. The nacelle  2  is constructed for rotational movement to properly align the rotor blade or blades of the wind power installation in relation to the wind direction and thus to enable an alignment of the tube bundles  6  in axis-parallel relationship to the wind direction. As a result, the air throughput through the tube bundles  6  is increased and the cooling efficiency is improved.  
         [0030]     Referring now to  FIG. 3 , there is shown a longitudinal section of another embodiment of a wind power installation according to the present invention. Parts corresponding with those in  FIG. 1  are denoted by identical reference numerals and not explained again. The description below will center on the differences between the embodiments. In this embodiment, the outlet  7  of the primary cooling circuit is constructed in the form of a handle-shaped, tubular member  9  (see  FIG. 4 ) which projects from the outlet  7  to an area outside the nacelle  2  and is returned for connection to the primary cooling circuit of the heat source  1  via an inlet  3 . The heat transfer of the primary cooing circuit takes also place by natural convection and/or fan  8 . The tubular members  9  may be assembled on site from single parts.  
         [0031]      FIG. 4  shows a cross section of the wind power installation of  FIG. 3  and depicts in detail the basic arrangement of the tube system of the primary cooling circuit of the heat source  1  with its tubes extending in wind direction and suitably formed with surface-enlarging structures (not shown). The convection of heated air in the primary cooling circuit can be facilitated by disposing the outlet  7  in the upper portion of the nacelle  2  and by disposing the inlet  3  below the outlet  7  in midsection or lower portion of the nacelle  2 .  
         [0032]     A wind power installation according to the present invention has the following advantages: There is no need for an intermediate water circuit, including of the air-water cooler of the generator. The provision of an air-air cooler outside the heat source  1  allows the creation of more space in the tight nacelle  2 . Operation is significantly safer compared to conventional systems while at the same time maintenance work can be reduced. There is no need for a cooling water supply and for a cooling water preparation and supervision. The energy consumption of the secondary devices such as, e.g., water pumps or monitoring devices, is reduced. The heated air of the primary cooling circuit may also be used to heat the nacelle  2  or even the rotor blades so as to prevent problems relating to ice buildup during the cold winter months. Suitably, fans are hereby provided to realize a proper air circulation.  
         [0033]     Compared to wind power installations with closed circulating ventilation, the wind power installation according to the present invention is also safer to operate as no humid air or salty air is conducted into the operating space of the electrical components or equipments.  
         [0034]     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated.