Patent Publication Number: US-2016248304-A1

Title: System and method for cooling or cleaning a slip ring assembly of a generator

Description:
FIELD OF THE INVENTION 
     The present disclosure relates generally to wind turbines, and more particularly to systems and methods for cooling wind turbine generators, particularly the slip ring compartment of the generator. 
     BACKGROUND OF THE INVENTION 
     Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The nacelle includes a rotor coupled to the gearbox and to the generator. The rotor and the gearbox are mounted on a bedplate support frame located within the nacelle. More specifically, in many wind turbines, the gearbox is mounted to the bedplate via one or more torque supports or arms. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid. 
     In some instances, the generator of the wind turbine may be a doubly fed induction generator (DFIG), which supplies electrical current to a rotor winding by way of slip rings. The current is typically applied to the slip rings via brushes mounted on a fixed conducting ring. Ordinarily, the slip rings in such systems are at low voltage. Some high voltage systems also employ slip rings for such purposes as power transfer. See, in this regard, U.S. Pat. No. 3,471,708 to Rauhut for a rotary transformer for coupling multiphase systems having a small frequency difference. 
     The carbon brushes typically utilized in such generators wear with use over time. In addition, sticking in brush holders caused by carbon dust build up and swelling may lead to arcing and catastrophic failure of the collector ring. Further, operative elements in such generators can become quite hot due to electrical losses and mechanical friction. Wear to the brushes, as well as excessive heat in the collector ring department may cause generator failures. Such failures result in turbine down time, which means a loss in revenue stream for turbine owners in addition to the cost for replacing failed hardware. 
     In view of the aforementioned, systems and methods which provide cooling and/or cleaning to the slip ring compartment to enhance overall operation of the turbine would be desired in the art. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, the present disclosure is directed to a generator assembly for a wind turbine. The generator assembly includes a rotor assembly having rotor windings which rotates about a rotatable shaft, a stator having stator windings, a slip ring assembly, and a conduit assembly. The slip ring assembly is configured to apply current to the rotor assembly and is at least partially enclosed in a slip ring compartment. In addition, the slip ring assembly includes an electrically conductive slip ring mounted to the rotatable shaft and a fixed conductive ring assembly having slip-ring contacting members mounted thereon. The conduit assembly is configured to direct fluid into the slip ring compartment so as to cool or clean the slip ring compartment. Further, the conduit assembly extends from a first end to a second end. More specifically, the first end is configured at or before an inlet of the generator assembly and the second end is configured with the slip ring compartment. 
     In one embodiment, the generator assembly also includes a generator housing configured to at least partially enclose the rotor assembly and the stator. In addition, the generator assembly may also include a generator heat exchanger and a fan, both being configured to control a temperature of the generator housing. As such, in particular embodiments, the conduit assembly may be configured at or before an inlet of the generator heat exchanger and after the fan such that the fan directs the cooling fluid through the conduit assembly, i.e. prior to becoming heat soaked. 
     In certain embodiments, the conduit assembly may include a plurality of conduit members arranged between the first end and the second end. Further, the conduit assembly may also include one or more straight conduit members, bent conduit members, and/or curved conduit members arranged from the first end to the second end so as to direct fluid from the inlet of the generator assembly to the slip ring compartment. In addition, the conduit assembly may also include one or more support brackets configured to support and/or mount the one or more conduit members to an exterior surface of the generator housing. 
     In particular embodiments, the slip-ring contacting members may include brushes, e.g. carbon brushes. In still additional embodiments, the fluid may include ambient air. 
     In another aspect, the present disclosure is directed to a system for cooling or cleaning a slip ring assembly of a generator. The slip ring assembly is at least partially enclosed in a slip ring compartment and contains an electrically conductive slip ring mounted to a rotatable shaft and a fixed conductive ring assembly having slip-ring contacting members mounted thereon. As such, the system includes a conduit assembly configured to direct fluid into the slip ring compartment so as to cool or clean the slip ring assembly. In addition, the conduit assembly extends from a first end to a second end. More specifically, the first end is configured at or before an inlet of the generator, whereas the second end is configured with the slip ring compartment. It should be understood that the system may be further configured with any of the additional features as described herein. 
     In yet another aspect, the present disclosure is directed to a method for cooling or cleaning a slip ring assembly of a generator. The slip ring assembly is at least partially enclosed in a slip ring compartment and contains an electrically conductive slip ring mounted to a rotatable shaft and a fixed conductive ring assembly having slip-ring contacting members mounted thereon. As such, the method includes installing a conduit assembly having a first end and second end onto the generator. More specifically, the method includes installing the first end of the conduit assembly at or before an inlet of the generator and the second end at the slip ring compartment. Further, the method includes directing a fluid through the conduit assembly from the inlet of the generator to the slip ring compartment. 
     In another embodiment, the method includes directing the fluid through the conduit assembly via an existing fan of the generator. It should be understood that the method may further include any additional steps and/or features as described herein. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  illustrates a perspective view of one embodiment of a wind turbine according to one embodiment of the present disclosure; 
         FIG. 2  illustrates a perspective view of a simplified, internal view of one embodiment of a nacelle of a wind turbine according to the present disclosure; 
         FIG. 3  illustrates a cross-sectional, internal view of one embodiment of a generator of a wind turbine according to the present disclosure; 
         FIG. 4  illustrates a perspective, external view of one embodiment of a system for cooling or cleaning the slip ring compartment of a generator of a wind turbine according to the present disclosure; 
         FIG. 5  illustrates a side view of one embodiment of a system for cooling or cleaning the slip ring assembly of a generator of a wind turbine according to the present disclosure; 
         FIG. 6  illustrates an end view of one embodiment of a system for cooling or cleaning the slip ring assembly of a generator of a wind turbine according to the present disclosure; and 
         FIG. 7  illustrates a flow diagram of one embodiment of a method for cooling or cleaning the slip ring assembly of a generator of a wind turbine according to the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     Generally, the present disclosure is directed to systems and methods for cooling or cleaning a slip ring assembly of a generator of a wind turbine. The slip ring assembly is enclosed in a slip ring compartment and contains an electrically conductive slip ring mounted to a rotatable shaft and a fixed conductive ring assembly having slip-ring contacting members mounted thereon. Accordingly, the system includes a conduit assembly configured to direct ambient air into the slip ring compartment so as to cool or clean the slip ring compartment. More specifically, a first end of the conduit assembly is configured at or before an inlet of the generator, whereas the second end is configured at the slip ring compartment. As such, the conduit assembly takes air from the front inlet of the generator and bypasses the rotor/stator assembly so as to direct cool air directly to the slip ring compartment to eliminate heat-soaked cooling air use. 
     The present disclosure provides many advantages not present in the prior art. For example, the system of the present disclosure improves the wear rate of the slip-ring contacting members (e.g. carbon brushes) as well as mitigates sticking in brush holders caused by carbon dust build up and swelling. Sticking brushes can lead to arcing and catastrophic failure of the collector ring, therefore, improved cooling leads to improved slip ring operation and brush life. As such, the down time of the units due to failed brushes is reduced and brush life is increased. In addition, maintenance intervals and costs are reduced. Further, in certain embodiments, the system and method of the present disclosure uses existing generator components, e.g. the generator fan, therefore system costs are relatively inexpensive. 
     Referring now to the drawings,  FIG. 1  illustrates a perspective view of one embodiment of a wind turbine  10  according to the present disclosure. As shown, the wind turbine  10  generally includes a tower  12  extending from a support surface  14 , a nacelle  16  mounted on the tower  12 , and a rotor  18  coupled to the nacelle  16 . The rotor  18  includes a rotatable hub  20  and at least one rotor blade  22  coupled to and extending outwardly from the hub  20 . For example, in the illustrated embodiment, the rotor  18  includes three rotor blades  22 . However, in an alternative embodiment, the rotor  18  may include more or less than three rotor blades  22 . Each rotor blade  22  may be spaced about the hub  20  to facilitate rotating the rotor  18  to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub  20  may be rotatably coupled to an electric generator  24  ( FIG. 2 ) positioned within the nacelle  16  to permit electrical energy to be produced. 
     The wind turbine  10  may also include a wind turbine controller  26  centralized within the nacelle  16 . However, in other embodiments, the controller  26  may be located within any other component of the wind turbine  10  or at a location outside the wind turbine  10 . Further, the controller  26  may be communicatively coupled to any number of the components of the wind turbine  10  in order to control the components. As such, the controller  26  may include a computer or other suitable processing unit. Thus, in several embodiments, the controller  26  may include suitable computer-readable instructions that, when implemented, configure the controller  26  to perform various different functions, such as receiving, transmitting and/or executing wind turbine control signals. 
     Referring now to  FIG. 2 , a simplified, internal view of one embodiment of the nacelle  16  of the wind turbine  10  shown in  FIG. 1  is illustrated. As shown, the generator assembly  24  may be coupled to the rotor  18  for producing electrical power from the rotational energy generated by the rotor  18 . For example, as shown in the illustrated embodiment, the rotor  18  may include a rotor shaft  34  coupled to the hub  20  for rotation therewith. The rotor shaft  34  may, in turn, be rotatably coupled to a generator shaft  36  of the generator  24  through a gearbox  38 . Further, the gearbox  38  is connected to a bedplate support frame  48  by one or more torque supports  50 . As is generally understood, the rotor shaft  34  provides a low speed, high torque input to the gearbox  38  in response to rotation of the rotor blades  22  and the hub  20 . The gearbox  38  then converts the low speed, high torque input to a high speed, low torque output to drive the generator shaft  36  and, thus, the generator  24 . 
     Each rotor blade  22  may also include a pitch adjustment mechanism  32  configured to rotate each rotor blade  22  about its pitch axis  28 , depending on the wind speed and/or wind direction. As such, pitching the blades  22  directly affects the power output of the generator  24 . More specifically, each pitch adjustment mechanism  32  may include a pitch drive motor  40  (e.g., any suitable electric, hydraulic, or pneumatic motor), a pitch drive gearbox  42 , and a pitch drive pinion  44 . In such embodiments, the pitch drive motor  40  may be coupled to the pitch drive gearbox  42  so that the pitch drive motor  40  imparts mechanical force to the pitch drive gearbox  42 . Similarly, the pitch drive gearbox  42  may be coupled to the pitch drive pinion  44  for rotation therewith. The pitch drive pinion  44  may, in turn, be in rotational engagement with a pitch bearing  46  coupled between the hub  20  and a corresponding rotor blade  22  such that rotation of the pitch drive pinion  44  causes rotation of the pitch bearing  46 . Thus, in such embodiments, rotation of the pitch drive motor  40  drives the pitch drive gearbox  42  and the pitch drive pinion  44 , thereby rotating the pitch bearing  46  and the rotor blade  22  about the pitch axis  28 . Similarly, the wind turbine  10  may include one or more yaw drive mechanisms  66  communicatively coupled to the controller  26 , with each yaw drive mechanism(s)  66  being configured to change the angle of the nacelle  16  relative to the wind (e.g., by engaging a yaw bearing  68  of the wind turbine  10 ). 
     Referring now to  FIG. 3 , a cross-sectional view of one embodiment of the generator assembly  24  according to the present disclosure is illustrated. For example, as shown, the generator  24  may be a doubly-fed induction generator (DFIG), although any other type of generator is within the scope and spirit of the invention as well. More specifically, the generator  24  includes a generator housing  25  that contains a rotor assembly  62  having rotor windings which rotates about the rotatable shaft  36  and a stator  64  having stator windings. Further, as shown, the rotor assembly  62  is operatively coupled with the stator  64 . More specifically, the rotor assembly  62  of the generator  24  is mechanically connected to the wind turbine  10  through the drive train system (i.e. the high and low speed shafts  34 ,  36 , bearings, and the gearbox  38 ). Moreover, the rotor assembly  62  is fed by bi-directional voltage-source converters. Thereby, the speed and torque of the generator  24  is regulated by controlling the rotor-side converter of the power converter (not shown). The stator  64  transfers power to the grid while the generator rotor  62  can handle power in both directions. The converter controls the rotor circuit current, frequency and phase angle shifts. Such induction generators are capable of operating at a wide slip range (typically ±30% of synchronous speed). As a result, DFIGs offer many advantages such as high energy yield, reduction in mechanical stresses and power fluctuations, and controllability of reactive power. 
     In addition, the generator assembly  24  may also include various cooling components configured to cool the components within the generator housing  25 . For example, as shown, the generator assembly  24  includes a generator heat exchanger  30  and/or a fan  52  within the generator housing  25 . Further, as indicated by the dotted lines, the fan  30  is configured to direct ambient air across the rotor assembly  62  and the stator  64 . In addition, the heat exchanger  30  is configured to control the temperature within the generator housing  25  so as to maintain the operating temperature of the rotor assembly  62  and the stator  64  within safe operating ranges. 
     Still referring to  FIG. 3 , the generator assembly  24  also includes a slip ring assembly  55  configured to apply current to the rotor assembly  62 . As shown, the slip ring assembly  55  is at least partially enclosed in a slip ring compartment  54  (or collector ring compartment). The slip ring compartment  54  also houses the associated slip-ring contacting members  60  that supply electrical current to the rotor  62  windings. More specifically, the slip ring assembly  55  includes an electrically conductive slip ring  56  mounted to the rotatable shaft  36  and a fixed conductive ring assembly  57  having slip-ring contacting members  60  mounted thereon. Further, the conductive slip ring  56  includes a slip ring body  59  and slip contact rings  58 . As such, current is typically applied to the slip contact rings  58  via the slip-ring contacting members  60  (e.g. carbon brushes) that are mounted on the fixed conductive ring assembly  57 . As mentioned, the brushes  60  can wear with use over time. In addition, dust from the worn brushes can accumulate and contaminate insulation surfaces, thereby causing undesirable effects within the slip ring compartment  54 . Moreover, operative elements in the DFIG  24  can overheat, thereby causing additional damage. 
     Accordingly, the present disclosure is directed to a system  70  for cooling and/or cleaning the slip ring assembly  55  to prevent the undesirable affects as described herein from occurring. For example, as shown in  FIGS. 4-6 , various views of one embodiment of the system  70  for cooling or cleaning the slip ring compartment  54  of the generator  24  according to the present disclosure are illustrated. More specifically,  FIG. 4  illustrates a perspective view of the system  70 ;  FIG. 5  illustrates a side view of the system  70 ; and  FIG. 6  illustrates an end view of the system  70  according to the present disclosure. As shown, the system  70  includes a conduit assembly  72  that is configured to direct fluid (e.g. ambient air) into the slip ring compartment  54  so as to cool or clean the slip ring assembly  55 . Further, the conduit assembly  72  extends from a first end  74  to a second end  75 . More specifically, the first end  74  is configured at or before an inlet of the generator  24 , whereas the second end  75  is configured at the slip ring compartment  54 . In addition, in certain embodiments, the conduit assembly  72  may be configured at or before an inlet of the generator heat exchanger  30  and after the fan  52  such that the fan  52  directs the cool air through the conduit assembly  72  directly to the slip ring assembly  55 , thus bypassing the rotor/stator assembly. 
     In certain embodiments, the conduit assembly  72  may include a plurality of conduit members  76  arranged between the first and second ends  74 ,  75 . In addition, the conduit assembly  72  may also include one or more support brackets  78  configured to support or mount one or more of the conduit members  76  to an exterior surface of the generator housing  25 . For example, as shown in  FIGS. 5 and 6 , the conduit assembly  72  includes a total of five conduit members  76  arranged from the first and second ends  74 ,  75 . In further embodiments, it should be understood that the conduit assembly  72  may include any number of conduit members  76 , including more than five or less than five. In addition, the conduit assembly  72  may include any one of or a combination of straight conduit members  76 , bent conduit members, and/or curved or arcuate conduit members  76  arranged from the first and second ends  74 ,  75 . As such, the conduit assembly  72  may easily direct fluid from the inlet of the generator  24  to the slip ring compartment  54  so as to bypass heat generator by the rotor assembly  62  and/or the stator  64 . 
     In additional embodiments, the conduit members  76  may have any suitable cross-sectional shape, including but not limited to square, rectangle, arcuate, trapezoidal, and/or similar. Further, the conduit members  76  may be constructed of any suitable material, including but not limited to galvanized steel, aluminum, and/or any other suitable sheet metal material. Still additional non-metal materials are within the spirit and scope of the invention as well. 
     Referring now to  FIG. 7 , a flow diagram of one embodiment of a method  100  for cooling or cleaning a slip ring assembly of a generator according to the present disclosure is illustrated. As mentioned, the slip ring assembly is at least partially enclosed in a slip ring compartment and has an electrically conductive slip ring mounted to a rotatable shaft and a fixed conductive ring assembly having slip-ring contacting members mounted thereon. At  102 , the method  100  includes installing a conduit assembly having a first end and second end onto the generator, the first end being installed at or before an inlet of the generator, the second end being installed at the slip ring compartment. At  104 , the method  100  includes directing a fluid, e.g. ambient air, through the conduit assembly from the inlet of the generator to the slip ring assembly. As such, cool air is directly delivered to the slip ring compartment  54  and bypasses the rotor/stator assembly, thereby eliminating heat-soaked air use. 
     Furthermore, the skilled artisan will recognize the interchangeability of various features from different embodiments. Similarly, the various method steps and features described, as well as other known equivalents for each such methods and feature, can be mixed and matched by one of ordinary skill in this art to construct additional systems and techniques in accordance with principles of this disclosure. Of course, it is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein. 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.