Abstract:
In some embodiments, a cooling device of a power transformer is presented and, more particularly, to a cooling device of a power transformer which may include a heat pipe and a heat sink to improve cooling performance, and to attenuate noise by eliminating a cooling fan.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Korean Patent Application No. 10-2015-0086804, filed on Jun. 18, 2015, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Technical Field 
     The present disclosure relates to a cooling device of a power transformer and, more particularly, to a cooling device of a power transformer which is provided with a heat pipe and a heat sink to improve cooling performance, and attenuates noise by eliminating a cooling fan. 
     2. Description of the Related Art 
     In general, a power transformer is configured in a power system, and plays an important role in transmitting power supplied from a power plant to the customer side by stepping-up/stepping-down. In particular, to reduce power loss, ultra high voltage transformers are widely used. 
     The power transformer includes a tank called a cabinet, a bushing, and many accessory components including a conservator. In addition, a core for forming a magnetic circuit and coils wound around the core are provided in the power transformer. 
     An example of the power transformers described above is a hydraulic (oil) power transformer. The hydraulic power transformer is provided with a cooling duct defined by a spacer to insulate and cool the coils, and an oil (insulating oil) flowing through the cooling duct is introduced into the hydraulic power transformer. 
       FIG. 1  is a perspective view illustrating a support structure of a hydraulic power transformer according to the prior art. The illustrated hydraulic power transformer, which is a 3-phase power transformer, includes three coils  2  arranged on a core  1  in series. The power transformer support structure according to the prior art includes a pair of bed frames  3  disposed on a floor in parallel, a lower frame  4  placed on the bed frames  3  to be perpendicular to the bed frames  3 , an upper frame  5  placed on the coils  2  in the direction of arrangement of the lower frame  4 , and spacers  6  interposed between the upper and lower frames  4  and  5  and the coils  2 . 
     When a current is applied to the power transformer to increase or decrease the voltage, heat is generated due to loss occurring in the core  1  or the coils  2 . The generated heat is transferred to the insulating oil circulating through the power transformer. When the temperature in the insulating oil increases, the internal pressure of the power transformer also increases. Thereby, such overheat and increase of power may result in explosion of the power transformer and deterioration of the insulating oil, which causes damage to insulation. 
     To address these problems, a radiator (not shown) and cooling fan (not shown) are disposed at the exterior of the power transformer such that heat generated in the power transformer and transferred to the insulating oil is dissipated through the radiator. That is, the insulating oil circulating through a cooling duct inside the coils is sent to the radiator to discharge heat to the outside, and the insulating oil which is cooled through the radiator re-enters the cooling duct to absorb heat generated from the coils. A conventional power transformer provided with a radiator and a cooling fan as described above is disclosed in US Patent Application Publication No. 20120249275A1 (titled “Insulation for Power Transformers”). 
     However, as cooling devices such as the radiator and cooling fan are provided to the exterior of the power transformer, the occupied space significantly increases, and loud noise occurs during operation of the cooling fan. 
     BRIEF SUMMARY 
     It is an aspect of some embodiments of the present disclosure to provide a cooling device of a power transformer which attenuates noise without causing degradation of cooling performance. 
     In accordance with one aspect of some embodiments of the present disclosure, a cooling device of a power transformer includes: an upper frame and a lower frame; a core installed or disposed between the upper frame and the lower frame; a coil wound around a leg portion of the core; a plurality of radial spacers formed of plates and interposed between coil sections horizontally dividing the coil; a heat pipe supported by the plurality of radial spacers and installed or disposed inside and outside the core and the coil; a heat sink coupled to an upper portion of the heat pipe and exposed to an upper portion of the coil; and a fractionating column interposed between the heat sink and the heat pipe, one end of the fractionating column being provided with one conduit and connected to the heat sink, and the other end of the fractionating column being provided with a plurality of conduits and connected to the heat pipe. 
     Herein, each of the radial spacers may be provided with a plurality of through holes, and the heat pipe is inserted into the through holes. 
     In addition, the plurality of through holes may be formed in a shape of a slit, wherein the heat pipe may include a plurality of heat pipes inserted into the through holes in parallel. 
     The through holes may be spaced from each other, wherein the heat pipe may include a plurality of heat pipes installed or disposed through the through holes and spaced from each other. 
     The cooling device may further include a plurality of axial spacers interposed between coil segments of the coil configuring sections in a radial direction. 
     The heat pipe may be inserted into an axial hole formed in the axial spacers. 
     The heat sink may be fixed to the upper frame. 
     The heat sink may include a plurality of heat sinks, the plurality of heat sinks being disposed circumferentially. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view illustrating a hydraulic power transformer according to the prior art. 
         FIG. 2  is a perspective view illustrating a power transformer according to an embodiment of the present disclosure. 
         FIG. 3  is a lateral cross-sectional view illustrating a power transformer according to an embodiment of the present disclosure. 
         FIG. 4  is a partial cross-sectional view taken along line A-A in  FIG. 3 . 
         FIGS. 5 and 6  are plan views illustrating a radial spacer according to an embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. It should be understood that the present disclosure is not limited to the following embodiments, and that the embodiments are provided for illustrative purposes only. The scope of the disclosure should be defined only by the accompanying claims and equivalents thereof. 
       FIG. 2  is a perspective view illustrating a power transformer according to an embodiment of the present disclosure, and  FIG. 3  is a lateral cross-sectional view illustrating a power transformer according to an embodiment of the present disclosure.  FIG. 4  is a partial cross-sectional view taken along line A-A in  FIG. 3 .  FIGS. 5 and 6  are plan views illustrating a radial spacer according to an embodiment of the present disclosure. 
     Hereinafter, a cooling device of a power transformer according to embodiments of the present disclosure will be described in detail with reference to the drawings. 
     According to an embodiment of the present disclosure, a cooling device of a power transformer includes an upper frame  10 , a lower frame  15 , a core  20  disposed between the upper frame  10  and the lower frame  15 , coils  30  and  40  wound around a leg portion  22 , a plurality of radial spacers  55  formed of plates and interposed between coil sections  41 ,  42 , . . . horizontally dividing the coils  30  and  40 , a heat pipe  60  supported by the radial spacers  55  and disposed inside and outside the core  20  and the coils  30  and  40 , and a heat sink  65  coupled to an upper portion of the heat pipe  60  and exposed to an upper portion of the coils  30  and  40 . 
     The lower frame  15  is disposed at the center of a base frame  16  such that the lower frame  15  is arranged perpendicular to the base frame  16 . The lower frame  15  may be as long as to accommodate all the 3-phase coils. 
     The lower frame  15  may be formed of section shape steel. 
     For example, the lower frame  15  may include a pair of square bracket-shaped channels. The square bracket-shaped channels may be symmetrically disposed on the base frame  16 . 
     The upper frame  10  is disposed at the upper portion of the coils  30  and  40  such that the upper frame  10  is arranged in the same direction as the lower frame  15 . 
     The upper frame  10  may include a pair of square bracket-shaped channels. 
     The core  20  is disposed between the upper frame  10  and the lower frame  15 . 
     The core  20  may include an upper core  21 , a lower core  23 , and the leg portion  22  formed between the upper core  21  and the lower core  23 , wherein the upper core  21  and lower core  23  are arranged in the horizontal direction. 
     Herein, a plurality of leg portions  20  may be used according to the number of phases. For example, for a 3-phase circuit, three leg portions  22  may be used. 
     The core  20  may be seated on the base frame  16  with the upper core  21  fixedly supported by the upper frame  10  and the lower core  23  fixedly supported by the lower frame  15 . 
     The core  20  may be formed of a material such as a grain oriented silicon steel sheet which is fabricated according to a cold rolling technique. The core  20  may be surrounded by an insulating tape including excellent thermal and mechanical properties, and anticorrosive coating may be applied to the surface of the core  20  to protect the core  20 . 
     The coils  30  and  40  are disposed to surround the core  20 . 
     The coils  30  and  40  may include a low voltage coil  30  and a high voltage coil  40 . The coils  30  and  40  may be disposed between the upper frame  10  and the lower frame  15 , and spaced from each other by a spacer  11 . 
     The low voltage coil  30  is disposed to surround the leg portion  20 . 
     The low voltage coil  30  may be formed by windings of a sheet conductor or line conductor. An insulation property may be provided to the surrounding of the low voltage coil  30  using, for example, a pre-preg insulated sheet. 
     The high voltage coil  40  is disposed outside the low voltage coil  30  to surround the low voltage coil  30 , while being spaced from the low voltage coil  30 . 
     That is, the high voltage coil  40  is formed to have an inner diameter greater than the outer diameter of the low voltage coil  30 . 
     In this case, a cooling duct  39  may be provided between the high voltage coil  40  and the low voltage coil  30 . Preferably, the high voltage coil  40  as well as the low voltage coil  30  is fabricated using a conductor including high electric conductivity. 
     Specifically, the low voltage coil  30  or high voltage coil  40  includes coil segments and coil sections. 
     Herein, the coil segments refer to arrangement of a plurality of walls in the radial direction, and the coil sections referred to arrangement of a plurality of layers in the vertical direction. 
     Hereinafter, the high voltage coil  40  will be described as an example. Referring to  FIGS. 3 and 4 , coil segments  40   a ,  40   b  and  40   c  may be formed by windings or stack of multiple coils or copper plates arranged in the form of walls. Herein, while three coil segments  40   a ,  40   b  and  40   c  are illustrated as being provided, this is simply illustrative. Any number of coil segments may be utilized. 
     Since a lot of heat is generated from the low voltage coil  30  or high voltage coil  40 , cooling ducts  38  and  39  are provided to dissipate heat. The cooling ducts  38  and  39  are provided in the low voltage coil  30  or high voltage coil  40  and between the coil segments  40   a ,  40   b  and  40   c . To form the cooling ducts  30  and  39 , a spacer is disposed. 
     Axial spacers  50 ,  50   a  and  50   b  are provided inside and outside the low voltage coil  30  or high voltage coil  40  and between the respective coil segments  40   a ,  40   b  and  40   c . The coil segments  40   a ,  40   b  and  40   c  are spaced from each other by the axial spacer  50 , and the cooling duct  38  is formed between the neighboring coil segments  40   a ,  40   b  and  40   c.    
     Herein, the axial spacers  50   a  and  50   b  disposed inside and outside the coils  30  and  40  have trapezoidal cross sections and are thus unseparably coupled to a radial spacer  55  which will be described later, to support the coils  30  and  40 . 
     The coil segments  40   a ,  40   b  and  40   c  configure multiple sections, forming multiple layers of walls in the radial direction. 
     The axial spacer  50   b  at the outer edge of the coil segments  40   a ,  40   b  and  40   c  may have the same shape as the axial spacer  50   a  at the inner edge of the coil segments and be disposed such that plane symmetry is formed between the axial spacer  50   b  and the axial spacer  50   a.    
     The coils  30  and  40  may be divided into coil sections  41 ,  42 , . . . which form layers arranged in the vertical direction. 
     Referring to  FIG. 3 , the coil sections  41 ,  42 , . . . are vertically spaced from each other by the radial spacer  55  to form layers. Groove portions  56  including a trapezoidal shape are formed on both sides of the radial spacer  55 . An axial spacer  50   a  at the inner edge and an axial spacer  50   b  at the outer edge are fixedly fitted into the groove portions  56 , respectively. The coil sections  41 ,  42 , . . . are spaced from each other by the radial spacer  55  and spaces are defined between the respective coil sections  41 ,  42 , . . . forming layers by the radial spacer  55 . 
     The radial spacer  55  may be formed of a rectangular plate. 
     The groove portions  56  may be formed on both sides of the radial spacer  55  in a longitudinal direction of the radial spacer  55  such that the axial spacer  50   a  at the inner edge and the axial spacer  50   b  at the outer edge can be fixedly coupled thereto. 
     As shown in  FIG. 5 , through holes  57  into which the heat pipe  60  can be inserted is formed at the center of the radial spacer  55 . Herein, the through holes  57  may be formed in the shape of slit. 
     The heat pipe  60  is inserted into the through holes  57  of the radial spacer  55 . 
     The heat pipe  60  is disposed in and supported by the radial spacer  55 . 
     A plurality of heat pipes  60  may be inserted into the through holes  57 . 
     In this case, the heat pipes  60  may be arranged in parallel, forming a pipe bundle. As multiple heat pipes  60  are disposed in the form of a pipe bundle, heat dissipation performance may be improved. 
       FIG. 6  shows another embodiment of the radial spacer  55 . In this embodiment, a plurality of circular through holes  58  spaced from each other is provided in the radial spacer  55 . As the through holes  58  are spaced from each other, the heat pipes  60  may be arranged spaced from each other. Thereby, heat dissipation performance may be improved. 
     Although not shown, axial holes (not shown) may be formed in the axial spacers  50   a  and  50   b  at the inner and outer edges, and the heat pipes  60  may be inserted into the axial holes. As the heat pipes  60  are disposed in the axial spacers  50   a  and  50   b  at the inner and outer edges, cooling performance may be further improved. 
     Insulating oil for cooling is caused to flow through the cooling ducts  38  and  39 . As the insulating oil flows upward, it may pass throughout all places where the cooling ducts  38  and  39  are formed. 
     When one side of a depressurized pipe containing liquid (operational fluid) such as water or alcohol is heated, the liquid is vaporized and moves to the opposite side. The vaporized fluid dissipate heat at the opposite side and changes to the liquid phase. Then, the fluid returns to the heating portion of the pipe according to a capillary phenomenon. As this procedure is implemented repeatedly, heat is transferred from the heating portion to the heat dissipation portion of the pipe. The heat pipes  60  are based on this principle. A wick, which is a core component for operation of the heat pipes, is an internal capillary structure to return the operational fluid in the liquid phase from a condenser to an evaporator. The wick has a shape of mesh or groove. The wick causes the capillary phenomenon according to surface tension of the liquid. 
     The heat absorption portion of the heat pipe  60  is positioned inside the coils  30  and  40 , and the heat dissipation portion of the heat pipe  60  is exposed at the upper portion of the coils  30  and  40 . That is, heat generated from the coils  30  and  40  moves to the upper portion of the heat pipe  60  and is then dissipated. The heat pipe  60  may formed of a material such as a copper that has a high thermal conductivity. 
     The heat sink  65  is coupled to the upper portion of the heat pipe  60 . The heat sink  65  may be formed of a material such as aluminum that has a high thermal conductivity and is inexpensive. 
     The heat sink  65  may be fixedly disposed on the upper frame  10 . Thereby, the heat sink  65  may be stably disposed, and thus dissipate heat from the upper frame  10  as well. 
     Herein, a plurality of heat sinks  65  may be provided and disposed circumferentially (see  FIG. 2 ). The heat sinks  65  may be connected to the heat pipes  60 . The heat sinks  65  may be arranged aligned with the positions of the radial spacers  55 , or disposed at positions covering all the radial spacers  55 . 
     A fractionating column  61  may be interposed between the heat sink  65  and the heat pipes  60 , wherein one end of the fractionating column  61  may be provided with one conduit and connected to the heat sink  65 , and the other end of the fractionating column may be provided with a plurality of conduits and connected to the heat pipes  60 . Thereby, a plurality of heat pipes  60  and one heat sink  65  may be configured. Accordingly, various configurations may be designed in consideration of the limited installation area of the heat sink  65 . 
     While an embodiment of cooling devices applied to the high voltage coil  40  has been described above, the description is also applicable to the low voltage coil  30 . 
     Although preferred embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the disclosure as disclosed in the accompanying claims.