Abstract:
A slipring assembly comprises a slipring module having at least one slipring track, which is in electrical contact with at least one slipring brush. The slipring module comprises an isolating body holding the at least one slipring track. Furthermore a cooling element is embedded into or attached to the slipring module to remove heat from the slipring module and to increase the temperature of the at least one slipring track. This allows decreasing the temperature of the slipring module to increase the maximum transferable power and lifetime.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of pending International Application No. PCT/EP2015/056612 filed Mar. 26, 2015 which designates the United States and claims priority from the European Application No. 14161942.9 filed on Mar. 27, 2014. The disclosure of each of the above-identified patent documents is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The invention relates to an electrical power transfer device such as a slipring or rotary joint. Sliprings are used to transfer electrical power between rotating parts of machines such as wind power plants, CT scanners or electrical generators. There a brush, mainly comprising electrically conductive material such as a metal or carbon is sliding on a rotating cylindrical track of conductive material, called the sliding track. Common materials for such tracks are steel, bronze or brass, sometimes being gold or silver-plated. At least one or a plurality of sliding tracks is held by an insulating material forming a module. Modules may have a shape of a disc or of a cylinder. 
         [0004]    2. Description of Relevant Art 
         [0005]    In the European patent application EP 0 662 736 A1 a slipring is disclosed which comprises of a plurality of wires of conductive material which are sliding in a V-groove of a sliding track of further conductive material. Due to the galvanic contact between the wires and the sliding track electric current can be transferred between the two parts rotating against each other. 
         [0006]    The international patent application publication WO 2012/028992 discloses problems arising due to high heat developing under rotation of a slipring while transferring high currents. It further discloses a solution to handle high temperatures within the slipring by selecting specific materials. 
         [0007]    The U.S. Pat. No. 4,849,586 discloses a slip ring based on a planar conductive plate, which has a heater located near such a planar conductive plate to prevent condensed water from freezing. 
         [0008]    GB 2 461 533 A discloses a method for estimating and controlling of wear in wind turbine slip ring brushes by measuring the slip ring temperature and the wind turbine nacelle humidity. 
         [0009]    A heated slipring module is disclosed in EP 2 696 449 A1 which prevents the sliding track from icing and moisture on the surface, which would decrease isolation. Various transmission systems. 
       SUMMARY 
       [0010]    The embodiments of the present invention provide a slipring with enhanced current transfer capabilities in an increased temperature range, especially if the available space is limited. 
         [0011]    In contradistinction, in a first embodiment of the invention, a cooling element is integrated into a slipring module. Preferably, this cooling element is embedded into the slipring module or attached to the module. Most preferably, it is attached to the surface of the slipring module, preferably attached to the side opposite of the slipring tracks, most preferably attached to the inner surface of the slipring module. Due to the cooling, the temperature of the module and/or the sliding tracks may be decreased which leads to a higher current capability of the module and the whole slipring. Tests have shown that system wear increases at high temperatures (especially if operated above 100° C.). Any liquid lubrication (if used) can be subjected to significant vaporization (since vapor pressure increases). In addition, if temperature becomes too high, design components under stress can fail or creep and/or unacceptable shape changes can occur due to different thermal expansion. 
         [0012]    The cooling element preferably is a Peltier element or a heat pipe. It may also be a heat sink or a pipe containing a liquid or cooling agent. The cooling element transfers heat from the slipring module to environment. The cooling element may further be connected to a heat sink for a better heat dissipation to the environment. Such a heat sink may be a large metal part, preferably with fins. 
         [0013]    In one embodiment, the cooling element comprises a liquid cooling system. It may be fed by a cooling liquid, which may be water or any cooling agent. Sometimes, in complex slipring systems, sliprings are combined with at least one liquid media rotary joint for transporting a liquid between the rotating parts. Often, the transported liquid used therein is water or any other cooling agent. This liquid may also be used in the cooling element for cooling the module. Therefore, the rotating part of the liquid media rotary joint may be connected to the cooling element. There may also be a heat exchanger, which may also be a heat pipe and which couples a local cooling liquid feeding the cooling element to the transported liquid. 
         [0014]    The flow of the cooling liquid through the pipe can be either active (by a pump) or passive by convection of the liquid or liquid vaporizing on the hot side of the pipe and condensing on the cold side of the pipe (heat pipe). 
         [0015]    Preferably, cooling of the slipring module is controlled by a temperature controller or a cooling controller. Most preferably, a temperature controller switches cooling on if the temperature exceeds a threshold value and/or it controls the cooling element such that there is a constant temperature value at the slipring module and/or track. The controller may control a liquid pump or the current through a Peltier element. A major advantage of cooling the slipring module is the comparatively low power consumption as cooling is only applied to the portion of the slipring, where it is required. A cooling controller may feed a cooling liquid into cooling pipe to cool the module. The controller may comprise a Peltier element, a heat pump, a heat sink or any other means for cooling the liquid. It is further preferred, if the controller comprises a pump for generation a cooling liquid flow through the pipe. 
         [0016]    In a further embodiment, there is a temperature sensor embedded into a slipring module. 
         [0017]    A further aspect is a thermal management system, which comprises a cooling element and a heating element. An exemplary heating element is disclosed in EP 2 696 449 A1 which is included herein by reference in its entirety. Such a thermal management system may heat the slipring module, if its temperature is under a lower limit and it may cool the slipring module, if its temperature is above an upper limit. 
         [0018]    Another embodiment relates to a slipring assembly, including a slipring module with an isolating body with at least one slipring track and at least one brush, which is in electrical contact with at least one slipring track. 
         [0019]    Tests on a large number of sliprings have shown that the current capacity of slipring tracks can be increased by lowering temperatures. This also reduces contact noise and wear of the sliding brushes. Specifically carbon brushes have shown to be sensitive to an extremely dry environment. Due to the cooling, the temperature can be increased and the relative humidity can be increased, which significantly increases lifetime. Furthermore, high temperatures lead to a degradation of electrical isolation of the brushes and the module, which may cause sparking and damaging of the parts. 
         [0020]    Furthermore, the thermal capacity of the brush block is significantly higher than the thermal capacity of the brushes. Therefore cooling the brush block will often result in cooling the brushes. 
         [0021]    An inventive method comprises the steps of cooling a slipring module by transporting heat from the slipring module by a cooling element. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]    In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings. 
           [0023]      FIG. 1  shows a preferred embodiment. 
           [0024]      FIG. 2  shows another view of a preferred embodiment. 
           [0025]      FIG. 3  shows a controller connected to a slipring module. 
           [0026]      FIG. 4  shows a further embodiment. 
           [0027]      FIG. 5  shows a further embodiment in a sectional view. 
           [0028]      FIG. 6  shows another embodiment in a sectional view. 
           [0029]      FIG. 7  shows a direct track cooling. 
           [0030]      FIG. 8  shows a side view of a general slipring assembly. 
           [0031]      FIG. 9  shows a top view of a general slipring assembly. 
           [0032]      FIG. 10  shows a slipring housing. 
       
    
    
       [0033]    While the invention can be modified without changing its scope and take alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims. 
       DETAILED DESCRIPTION 
       [0034]    In  FIG. 1 , a sectional view of a preferred embodiment is shown. A slipring module  10  has at least one slipring track  17 , which is held by insulating body  13 , which may rotate around rotating axis  14 . Preferably, the slipring track  17  is embedded or molded into insulating body  13 . Furthermore, a cooling element  60  is integrated into the body  13 . Preferably, the cooling element is a pipe through which a coolant flows. It may have an inlet  61  and an outlet  62 . Preferably, the cooling element  60  is isolated from the slip ring track  17 . Most preferably, the pipe is of a plastic material. It is further preferred, if the cooling element  60  is arranged in close proximity to the slipring track  17  and most preferably in a good thermal contact to slipring track  17 . In a further preferred embodiment, the insulating body  13  comprises a thermally conductive material to improve heat transfer from cooling element  60  to slipring track  17 . The cooling element  60  may be a single pipe or a plurality of pipes. 
         [0035]    In  FIG. 2 , another view of a preferred embodiment is shown. Here the slipring module is cut parallel to the rotation axis  14 . Besides first track  17  there is a second track  18  and a third track  19 . In this embodiment, the cooling element is a pipe forming a spiral, which is embedded into the isolating body  13  below the three slipring tracks. Instead of the spiral shaped pipe, also a plurality of pipes may be used. Furthermore a tube or any other kind of cavity such as e.g. a drilled or molded hole may be used. 
         [0036]    In  FIG. 3 , a cooling controller  80  is shown. This controller is connected to cooling element  60  to control the temperature of the cooling element and/or slipring track  17 . The controller feeds a cooling liquid into cooling pipe  60  to cool the module. The controller may comprise a Peltier element, a heat pump, a heat sink or any other means for cooling the liquid. It is further preferred, if the controller comprises a pump for generation a cooling liquid flow through the pipe. This cooling liquid flow and/or temperature may be controlled by using at least one sensor or by an external control signal. There may be a temperature sensor  81  to provide information about the temperature of the slipring module and/or the slipring tracks to the controller  80 . Preferably, the temperature sensor is embedded into the insulating body  13  of the slipring module. It may also be thermally connected to at least one slipring track to provide a precise temperature measurement. Furthermore, there may be a plurality of temperature sensors to provide temperature information of different locations. There may also be a humidity sensor  82  providing humidity information to the controller  80 . Preferably, this humidity sensor is at the surface of slipring module  10 . Either the humidity sensor may be a standard capacitive humidity sensor or it may be a conductivity sensor measuring the conductivity on the surface of slipring module  10 . For measuring conductivity, there may be some electrodes within this surface of slipring module  10 . In an alternative embodiment the conductivity and/or isolation between slipring tracks, most preferably between neighboring slipring tracks, may be measured. Based on the information from the humidity sensor, cooling may be reduced or suspended to prevent condensation at the module surface, which would degrade isolation. The cooling controller may also be enabled to deliver heat to the slipring module if the temperature of the slipring module falls below a lower temperature limit. 
         [0037]      FIG. 4  shows a further embodiment in a top view. A first slipring module  100  comprises at least a first sliding track  110 . The sliding tracks are held by an isolating body  120 . At least one cooling element  101 ,  102 ,  103 , is located within a plurality of holes in the isolating body  120 . Preferably, the cooling elements are spaced equally. Preferably, there are one, two, three or four cooling elements rods. Such a cooling element may comprise a part of a heat pipe, preferably the “hot” end of a heat pipe. 
         [0038]      FIG. 5  shows the embodiment of the previous figure in a sectional view. A blind hole  109  may be provided within the isolating body  120 . It may hold a cooling element  101  for cooling slipring tracks  110 ,  111 ,  112 ,  113  and  114 . Preferably, the cooling element is part of a heat pipe. The other end of the heat pipe may be thermally connected to a heat sink outside of the module. The cooling element  101  may have a pipe connector  108  for easy assembly and disassembly. 
         [0039]      FIG. 6  shows another embodiment in a sectional view. There may be at least one through hole  130  within the isolating body  120 . Within the through hole  130 , there may be a cooling element, which preferably is connected by connecting pipes  131 ,  132 . 
         [0040]      FIG. 7  shows a direct track cooling. Here a cooling element, preferably part of a heat pipe may be directly connected to a slipring track  141 . Preferably, it is connected by a thread  142 . This allows for a solid mechanical and heat conducting connection. 
         [0041]    In  FIG. 8 , a side view of a general slipring assembly is shown. Exemplarily there are three slipring modules  10 ,  15  and a liquid media rotary joint  16  mounted to a shaft  12 . The rotating part of the liquid media rotary joint may be connected to a cooling element to deliver cooling liquid to the cooling element. 
         [0042]    In  FIG. 9 , a top view of the general slipring assembly is shown. A slipring module  10  is held by a module support  11  and mounted to a shaft  12 . There is a plurality of contact brushes such as first contact brush  21  and second contact brush  22 , which are held and electrically contacted by brush holder  20 . The preferred contact brushes shown herein are wire brushes, formed by metal wires. Instead, carbon brushes may be used. The slipring assembly is enclosed by a slipring housing  30  having a plurality of sidewalls  40 . There may be a connecting space  50  for electrically connecting the slipring brushes, which may have a first cover  51 . Furthermore, the inner space  70  of the housing has a second cover  71 . 
         [0043]    In  FIG. 10 , a slipring housing is shown. The first cover  51  may be locked by a plurality of screws  52 . There may further be a housing of bearing  90  to enclose a bearing, which allows rotation between the modules and the brushes and a module connection case  91  for electrically connecting and contacting the module. This case may also contain a controller  80 . 
         [0044]    It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide a slipring or a rotary joint with integrated cooling. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims. 
       LIST OF REFERENCE NUMERALS 
       [0000]    
       
           10  slipring module 
           11  module support 
           12  shaft 
           13  isolating body 
           14  rotation axis 
           15  second slipring module 
           16  liquid media rotary joint 
           17  first track 
           18  second track 
           19  third track 
           20  brush holder 
           21  first brush 
           22  second brush 
           30  slipring housing 
           31  ceiling 
           40  sidewall 
           50  connecting space 
           51  first cover 
           52  screws 
           60  cooling element 
           61  cooling element inlet 
           62  cooling element outlet 
           63  cooling pipe 
           70  inner space of housing 
           71  second cover 
           80  controller 
           81  temperature sensor 
           82  humidity sensor 
           90  housing of bearing 
           91  module connection case 
           100  third slipring module 
           101  first cooling element 
           102  second cooling element 
           103  third cooling element 
           108  pipe connector 
           109  hole 
           110  first track 
           111  second track 
           112  third track 
           113  second track 
           114  third track 
           120  isolating body 
           130  through hole 
           131 ,  132  connecting pipes 
           140  cooling element 
           141  slipring track 
           142  thread