Patent Publication Number: US-2012025539-A1

Title: Cooling device for electrical device and method of cooling an electrical device

Description:
BACKGROUND OF THE INVENTION 
     The subject matter described herein relates to cooling an electrical device, and in particular, a heat transfer element for cooling a magnetic inductor. 
     One type of electrical device includes an inductor, which is a passive electrical component that stores energy in a magnetic field created by electric current passing through the inductor. The inductor includes a conductive coil of material (e.g., wire or foil) wrapped around a core of air or a ferromagnetic material (magnetic core). Passing electrical current through the conductive coil generates a magnetic flux Φ m  that is conducted in the core and that is proportional to the current. 
     The inductor is characterized by a high permeability (for example μ m  (&gt;1000)) and therefore a low magnetic resistance (for example R m ˜1/(μ m  μ)). High permittivity material, however, is sensitive to temperature, pressure, voltage and frequency. Further, magnetic energy that is stored in an inductive component is proportional to the square of the magnetic flux Φ m  and indirectly proportional to the permeability of the material μ m . Thus, a good magnetic inductor could result in low energy storage. 
     To minimize these sensitivities and shortcomings, one or more air gaps are inserted in the inductor. In some known inductors, the air gaps are filled with a gap material. Gap material includes material such as paper, nylon or glass. Inserting air gaps in the inductor, however, facilitates the magnetic flux leaving the magnetic core while crossing the air gap. In crossing the air gap, the flux fringes out. The fraction of the total magnetic flux Φ m  that fringes out is known as fringing flux Φ m,fring . 
     The inductor may experience energy loss attributed to the fluctuating magnetic field, such as eddy loss currents and hysteresis loss. This energy loss is known as core losses. The core losses are caused by the non-linear hysteresis-afflicted interrelationship between the exciting magnetic voltage and the flux density of the magnetic circuit. Due to the alternating flux in the magnetic material, eddy currents are induced in the magnetic core. The intensity of the eddy currents, and therefore, the eddy current losses depend on the electrical conductivity of the core material. Further, the inherent resistance of coils converts a portion of electrical current flowing through the coils into thermal energy, causing a loss of inductive quality. This loss is known as coil loss. Any electrically conductive material in the area of fringing flux will exhibit high power loss. 
     The coil and core losses are generated within the inductor as heat. The build up of heat due to coil losses and core losses may reduce performance of the inductor, and lead to failure of the electrical device. To reduce the eddy current losses, some known conductors include laminations to reduce the electrical conductivity of the magnetic core. 
     Known conductors also apply a liquid-cooled heat sink to the magnetic core. The material of the heat sink is commonly a thermal conductor to facilitate heat transfer between the core and the heat-sink. Close to the air gaps, the alternating fringing flux Φ m,fring  enters and penetrates the heat sinks. Generally, a material that has good thermal conducting properties is also a good electrical conductor. As noted, flux penetrating an electrical conducting compound causes eddy current losses. Thus, eddy losses occur in the heat sink near or about the air gaps. Accordingly, the inductor loses energy while the cooling liquid is heated up by the losses originating from the inductor. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a cooling device is provided for cooling an electrical device having an air gap. The cooling device includes a heat transfer element coupled to a core of the electrical device. The heat transfer element includes a first material to facilitate transferring heat out of the core. The cooling device further includes an electrical insulator coupled to the heat transfer element. The insulator includes a second material to facilitate flow of magnetic flux across the air gap. 
     In another aspect, an electrical device is provided. The electrical device includes a magnetic core having an air gap, a conductive coil and a cooling device. The cooling device includes a heat transfer element coupled to a core of the electrical device. The heat transfer element includes a first material to facilitate transferring heat out of the core. The cooling device further includes an electrical insulator coupled to the heat transfer element. The insulator includes a second material to facilitate flow of magnetic flux across the air gap. 
     In a further aspect, a method of cooling an electrical device is provided. The method includes disposing a conductive coil around a magnetic core having an air gap. The method also includes disposing a heat transfer element between the core and the coil to facilitate heat transfer out of the core. An electrical insulator is disposed between the air gap and said coil, wherein the electrical insulator is configured to facilitate current flow through the core. The heat transfer element and electrical insulator are coupled together. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an exemplary electrical device. 
         FIG. 2  is a perspective view of a core of an inductor of the electrical device of  FIG. 1  having an air gap disposed therein. 
         FIG. 3  is an exaggerated, partial cross sectional view of an exemplary cooling device coupled to the core. 
         FIG. 4  is an exaggerated, partial cross sectional view of another exemplary cooling device coupled to the core. 
         FIG. 5  is a flowchart of an exemplary method for use in manufacturing the cooling device of  FIG. 3 . 
         FIG. 6  is a schematic view of a wind turbine. 
         FIG. 7  is a partial sectional view of a generator of the wind turbine of  FIG. 6  that may use the exemplary cooling device. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Various electronic devices benefit from the use of magnetic circuits. The cooling device described herein facilitates heat transfer and electrical conductivity for the magnetic circuit. Heat may degrade the performance of an inductor of the electrical device, or may cause degradation and premature failure of the device. Accordingly, the cooling device and method described herein remove thermal energy from the core of the conductor while reducing eddy current losses and magnetizing losses across air gaps of the core. 
       FIG. 1  illustrates a perspective view of an exemplary electrical device  5 . Electrical device  5  herein relates to any shape and application of a magnetic circuit such as, but not limited to, conductors, transformers, galvanic isolation and inductors. For illustrative purposes, the electrical device described will be in the form of an inductor  10 . Configurations and the design of the exemplary inductor  10  may vary based on specific applications. For example, inductor  10  may include a single conductive coil disposed about a single magnetic core. In other embodiments, inductor  10  may include multiple conductive coils, each wound about a portion of the magnetic core. The design of inductor  10  may be varied to meet specific applications and the desired performance. 
     In the exemplary embodiment, inductor  10  includes a magnetic core  12 , conductive coils  14 , and a cooling device  16 . Conductive coils  14  surround the magnetic core  12 , with cooling device  16  orientated in a cooperative relationship with conductive coil  14  and magnetic core  12 . Conductive coil  14  includes various features for use within the inductor  10 . In one embodiment, conductive coil  14  includes material disposed about a central region  18 . Central region  18  includes an opening configured to accommodate at least a portion of magnetic core  12 . Further, central region  18  provides a location to orientate cooling device  16 . Conductive coil  14  includes a variety of materials such as, but not limited to, copper, aluminum or steel windings. 
       FIG. 2  illustrates a perspective view of core  12 . In the exemplary embodiment, core  12  includes a “figure-eight” shaped geometry. In this configuration, each leg  20  of magnetic core  12  may be surrounded by conductive coil  14 . The geometry of magnetic core  12  includes other configurations depending on the application. For example, other configurations of magnetic core  12  include “I”, “C,” “E,” toroidal, planar, or pot shaped geometries. Magnetic core  12  may also include a geometry formed from a combination of shapes. For example, the figure-eight shape shown in  FIG. 2  may include an “I” shaped piece and an “E” shaped piece, or two “E” shaped pieces, combined to form single magnetic core  12 . 
     Core  12  includes at least one air gap  22  disposed within core  12 . Air gap  22  includes any void of material or equivalent filler of nonmagnetic material within core  12 . The gap material facilitates keeping the distance between the adjacent core parts constant and facilitates a stable design and operation for inductor  10 . The gap material includes materials such as nylon, paper, glass, and any nonmagnetic material immune to saturation. 
     Magnetic core  12  includes various materials suitable for use in inductor  10 . In the exemplary embodiment, core  12  includes a metal material. In one embodiment, magnetic core  12  includes metals such as, but not limited to, copper, aluminum, iron or steel. In other embodiments, core  12  includes various materials such as iron alloyed with silicon, carbonyl iron and ferrite ceramics. Further, various forming techniques, such as laminations and the like, may be utilized to form magnetic core  12 . 
       FIG. 3  is an exaggerated, partial cross sectional view of exemplary cooling device  16  coupled to core  12 . Cooling device  16  includes a heat transfer element  24  and an electrical insulator  26 . Heat transfer element  24  couples to core  12  at portions  28  orientated on opposite sides of air gap  22 . In the exemplary embodiment, a surface  30  of heat transfer element  24  is generally shaped to provide contact between core portion  28  and heat transfer element  24 . Contact between surface  30  of heat transfer element  24  and core portion  28  facilitates efficient transfer of thermal energy between core  12  and heat transfer element  24 . Thus, heat from core  12  is more efficiently removed by heat transfer element  24 . 
     Heat transfer element  24  includes other configurations such as, but not limited to, heat fins, heat exchangers and cooling tubes. Heat transfer element  24  includes any configuration that facilitates transferring heat out of and away from core  12 . 
     Heat transfer element  24  includes a first material  32  wherein the composition of first material  32  includes a thermally conductive material. First material  32  facilitates heat transfer out of core  12 . In the exemplary embodiment, first material  32  facilitates transferring heat generated as a result of core losses and coil losses. First material  32  includes materials such as, but not limited to, metals, plastics and composites. More specifically, first material  32  includes materials such as aluminum, copper, conductive plastics and conductive composites. First material  32  may also include any material that facilitates heat transfer out of core  12 . 
     Insulator  26  is coupled to at least one of core  12 , air gap  22  and the heat transfer element  24 . Electrical insulator  26  facilitates flow of magnetic flux  34  across air gap  22  and through core  12 . Electrical insulator  26  also facilitates reducing eddy current losses and magnetizing losses  36  emanating from air gap  22 . In the exemplary embodiment, electrical insulator  26  couples to portions  28  of core  12 . Core portions  28  are orientated on opposite sides of air gap  22 . Additionally, electrical insulator  26  couples to heat transfer element  24  near opposing sides of air gap  22 . In this orientation, electrical insulator  26  is located about air gap  22  and between portions  28  of heat transfer element  24 . 
     In one embodiment, a fastener  38  thermally couples insulator  26  to heat transfer element  24 . In the exemplary embodiment, fastener  38  includes a thermal adhesive. Fastener  38  may include any connection that facilitates connecting electrical insulator  26  to heat transfer element  24 . 
     Electrical insulator  26  includes a second material  40  including an electrically insulating material having low conductivity and high resistivity characteristics. In the exemplary embodiment, the composition of second material  40  is different than the composition of first material  32 . Second material  40  facilitates flow of magnetic flux  34  across air gap  22  and through core  12 . Second material  40  facilitates reducing eddy current losses and reducing magnetizing losses  36  emanating from air gap  22 . The second material  40  includes materials such as, but not limited to, plastic, glass and silicone. Second material  40  may include any material that facilitates flow of magnetic flux  34  within core  12  and reduces core losses and coil losses. 
     During one mode of operation of inductor  10 , current is passed through conductive coils  14 . In response, magnetic flux  34  is generated and conducted within core  12 . Heat transfer element  24  transfers heat generated by coils  14  and heat generated in response to eddy current losses and magnetizing losses  36 . The low conductivity and high resistivity of insulator  26  opposes magnetic flux  34  leaving air gap  22  and reduces losses emanating from air gap  22 . 
       FIG. 4  illustrates another exemplary embodiment of a cooling device  42  having a heat transfer element  44  and insulator  46 . Heat transfer element  44  includes at least one body  48  having channels  50  sized and orientated to circulate a cooling fluid  52  through heat transfer element  44 . Body  48  couples to core  12  on opposite sides of air gap  22 . The circulation of cooling fluid  52  facilitates removing heat from heat transfer element  44 ; and, thus, promotes heat exchange between heat transfer element  44  and components of inductor  10 . Body  48  includes a coolant inlet  54  configured to receive cooling fluid  52  from an external source, such as a fluid pump (not shown.) Body  48  further includes a coolant outlet  56  configured to discharge cooling fluid  52  to an external source, such as a reservoir (not shown.) In the exemplary embodiment, cooling fluid  52  includes a liquid such as a water based liquid or oil. Cooling fluid  52  includes any gas or liquid capable of being passed through heat transfer element  44  and including thermal properties beneficial to absorbing heat from body  48  of heat transfer element  44 . 
     Electrical insulator  46  includes another body  58  sized and orientated to couple with channel  50 . Body  58  also couples core  12 . Body  58  includes an electrically insulating material having low conductivity and high resistivity characteristics. Composition of the material of insulator  46  is different than the composition of channel  50  and/or cooling fluid  52 . Material of insulator  46  facilitates flow of magnetic flux  34  across air gap  22  and through core  12  while reducing eddy current losses and magnetizing losses  36  from air gap  22 . Further, insulator  46  facilitates flow of cooling fluid  52  in the area across air gap  22  while insulator  46  will experience minimal or no power loss due to flux  34 . 
     In the exemplary embodiment, body  58  includes a hose  60 . A fastener  62  couples hose  60  to channel  50 . In the exemplary embodiment, fastener  38  includes at least one valve with associated fittings (not shown) to facilitate coupling hose  60  to channel  50 . Fastener  62  includes any connector that facilitates connection between hose  60  and channel  50 . 
     Hose  60  has an internal diameter in the range between about 6 mm and about 13 mm. Hose  60  includes materials such as, but not limited to, rubber and plastic. Hose  60  includes any sizing, orientation and composition that facilitate flow of cooling fluid  52  from, and back into, channel  50 . Hose  60  also includes any sizing, orientation and composition that facilitate flow of magnetic flux  34  within core  12  and reduce eddy current losses and magnetizing losses  36  from air gap  22 . 
     During operation, cooling fluid  52  enters channels  50  via coolant inlet  54  and flows through channels  50  internal to heat transfer element  44 . After flowing through channels  50 , fluid  52  flows into hose  60  via open fastener  62 . Fluid  52  flows through hose  60  and re-enters the channel via another fastener  62 . Fluid  52  exits channel  50  via heat transfer outlet  56 . The circulation of cooling fluid  52  through heat transfer element  44  provides for an increased rate transfer of thermal energy from other components of inductor  10 , such as conductive coils  14  and core  12 . The material of hose  60  facilitates flow of magnetic flux  34  across air gap  22  and facilitates reducing core and coil losses from air gap  22 . Further, hose  60  facilitates flow of cooling fluid  52  in the area across air gap  22  while insulator  46  will experience minimal or no power loss due to flux  34 . 
       FIG. 5  illustrates a flowchart of an exemplary method for use in manufacturing the electrical device  5  of  FIG. 1 . In the exemplary embodiment, any or all of the manufacturing processes can be performed on a new assembly of an electrical device or integrated with an existing electrical device. Initially, core  12  is provided  510  having at least one air gap  22 . A conduit coil  14  is disposed  520  around core  12 . Next, heat transfer element  24  is disposed  530  between core  12  and coil  14 . Insulator  26  is disposed  540  between air gap  22  and coil  14 . Insulator  26  is then coupled  550  to heat transfer element  24 . 
     The cooling device  16  may have a variety of shapes, sizes, orientations and compositions to facilitate removing heat from components of the inductor, including the magnetic core  12  and the conductive coil  14 . The cooling device  16  may also have a variety of shapes, sizes, orientations and compositions to facilitate magnetic flux flow across the air gap  22  and through the core  12  while reducing core and coil losses from the air gap. 
     For example, in one embodiment, the cooling device includes a shape (not shown) configured to conform to curvatures of the conductive coils. The cooling device may be disposed within the conductive coil that has been formed prior to placement of the cooling device. In another embodiment, the conductive coil may conform to the shape of the cooling device. For instance, forming the conductive coil may include fixing the cooling devices in a position and subsequently wrapping the windings of the conductive coil about the cooling device. The generally shared interface at each end turn may promote contact of the conductive coil and the cooling device such that thermal energy may be more efficiently transferred between the conductive coil and the cooling device. For example, disposing the conductive coil and the cooling device such that they are proximate one another along the curved surface may reduce thermal resistance across the interface, and, thus, promote the transfer of thermal energy between the conductive coil and the cooling device. Thus, heat from the electrical device may be more efficiently removed by the cooling device. Conforming the shape of the cooling device to the core and/or the coil also facilitates flow of magnetic flux across the air gap and through the core while reducing core and coil losses emanating from the air gap. 
       FIG. 6  is a schematic view of an exemplary wind turbine  64  that includes a nacelle  66 .  FIG. 7  is a partial sectional view of nacelle  66  of exemplary wind turbine  64 . Various components of wind turbine  64  are positioned in a housing  67  of nacelle  66 . In the exemplary embodiment, rotor  68  includes three pitch assemblies  70 . Each pitch assembly  70  is coupled to an associated rotor blade  72  (shown in  FIG. 6 ), and modulates a pitch of associated rotor blade  72  about pitch axis  74 . Only one of three pitch assemblies  70  is shown in  FIG. 2 . 
     As shown in  FIG. 7 , rotor  68  is rotatably coupled to an electric generator  76  positioned within nacelle  66  via rotor shaft  78  (sometimes referred to as either a main shaft or a low speed shaft), a gearbox  80 , a high speed shaft  82 , and a coupling  84 . Rotation of rotor shaft  78  rotatably drives gearbox  80  that subsequently drives high speed shaft  82 . High speed shaft  82  rotatably drives generator  76  via coupling  84  and rotation of high speed shaft  82  facilitates production of electrical power by generator  76 . Gearbox  80  is supported by support  86  and generator  76  is supported by support  88 . 
     In the exemplary embodiment, generator  76  includes magnetic core  12  that facilitates energy conversion from rotating blades  72 . Cooling device  16  couples to core  12 . As discussed above, cooling device  16  facilitates heat transfer out of core  12  while facilitating flow of magnetic flux  34  through core  12 . Additionally, cooling device  16  facilitates reducing eddy current losses and magnetizing losses  36  from core  12 . Accordingly, cooling device  16  enables enhanced operation of generator  76 . In alternative embodiment, cooling device  42  couples to generator  76  to enable enhanced operation of generator  76 . 
     Cooling device can be integrated within new manufacture of electrical devices or within existing electrical devices. In one embodiment, the cooling device includes the electrical insulator that facilitates flow of magnetic flux across the air gap and through the conductor. The insulator also facilitates reducing core and coil losses emanating from the air gap. Additionally, the cooling device facilitates heat transfer out of the core and coils. 
     A technical effect of the cooling device described herein includes utilizing the insulator to facilitate flow of magnetic flux across the air gap and through the core. Another technical effect of the insulator includes reducing core and coil losses emanating from the air gap. A further technical effect of the cooling device includes utilizing the heat transfer element to transfer heat from the core. 
     Exemplary embodiments of the electrical devices, cooling device, and methods of manufacturing the cooling device are described above in detail. The electrical device, cooling device, and methods are not limited to the specific embodiments described herein, but rather, components of the electrical device and/or the cooling device and/or steps of the method may be utilized independently and separately from other components and/or steps described herein. For example, the cooling device and methods may also be used in combination with other electrical devices and methods, and are not limited to practice with only the electrical device as described herein. 
     Although specific features of various embodiments of the invention may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the invention, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     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 layers 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 have 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 language of the claims.