Patent Publication Number: US-2019180932-A1

Title: Core for current transformer

Description:
TECHNICAL FIELD 
     The present disclosure relates to a core for a current transformer, and more particularly, to a core mounted on a current transformer installed in a transmission line or a distribution line for power acquisition and current sensing using a magnetic induction phenomenon. 
     BACKGROUND ART 
     Recently, various types of magnetic induction power supply devices have been developed as the interest in a power supply method using a magnetic induction phenomenon is increasing. 
     The magnetic induction type power supply device includes a current transformer installed in a power line through which a large-capacity current flows, such as a transmission line, a distribution line, and the like. The magnetic induction type power supply device converts the power obtained by the magnetic induction phenomenon in the current transformer into DC to supply it to the load. 
     At this time, the current transformer is configured to include a core that surrounds the power line and a coil wound around the core for power acquisition through the magnetic induction phenomenon. 
     For example, referring to  FIG. 1 , the conventional core for the current transformer  10  has an upper core  12  and a lower core  14  formed in the same shape. At this time, there is a problem in that since the upper core  12  and the lower core  14  are formed with bent portions having an angle of about 90 degrees, the stress region on a magnetic path is generated, thereby reducing the permeability. 
     In addition, the conventional core for the current transformer  10  has a problem in that the inductance reduces due to the reduction in the permeability, thereby reducing the power acquisition efficiency when it is mounted on the current transformer. 
     Meanwhile, referring to  FIG. 2 , the conventional core for the current transformer  10  is configured to include the upper core  12  and the lower core  14  in a semi-cylindrical shape. At this time, since the conventional core for the current transformer  10  directly winds a coil  20  around one of the upper core  12  and the lower core  14 , the number of turns of the coil  20  reduces, thereby reducing the inductance. 
     In addition, the conventional core for the current transformer  10  has a problem in that the power acquisition efficiency is reduced when it is mounted on the current transformer due to the reduction in the inductance. 
     DISCLOSURE 
     Technical Problem 
     The present disclosure is intended to solve the problems, and an object of the present disclosure is to provide a core for a current transformer, which forms the upper core in a round shape, and is disposed at a position lower than the center of the power line in which both ends of the upper core are received, thereby minimizing the stress of the magnetic path and enhancing the magnetic induction efficiency by increasing the permeability. 
     Technical Solution 
     For achieving the object, a core for a current transformer according to an embodiment of the present disclosure includes an upper core curved in a semi-circular shape to have a receiving groove formed therein, and having both ends extended downwards to be disposed to be spaced apart from each other, and a lower core disposed on the lower portion of the upper core, and having both ends extended upwards to be disposed to face both ends of the upper core. 
     The upper core includes an upper base curved in a semi-circular shape; a first upper extension portion extended in a straight-line shape in the direction of the lower core from the upper base; and a second upper extension portion spaced apart from the first upper extension portion, and extended in a straight-line shape in the direction of the lower core from the upper base. 
     The upper base may have an upper receiving groove in a semi-cylindrical shape formed on the lower end thereof and a lower receiving groove in a hexahedral shape may be formed between the first upper extension portion and the second upper extension portion. At this time, the first upper extension portion and the second upper extension portion may be disposed in parallel with each other. 
     Both ends of the upper core may be disposed at a position lower than the center of a power line received in the receiving groove, and the receiving groove may receive all the cross sections of the power line. 
     The lower core may include a lower base; a first lower extension portion extended in the direction of the upper core from the lower base; and a second lower extension portion spaced apart from the first lower extension portion, and extended in the direction of the upper core from the lower base. 
     The lower base may be curved in a semi-circular shape, or may be formed in a hexahedral shape. At this time, the first lower extension portion may be formed to extend from one side portion of the lower base in the direction of the upper core, the second lower extension portion may be formed to extend from the other side portion of the lower base in the direction of the upper core, and the first lower extension portion and the second lower extension portion may be disposed in parallel with each other. 
     Advantageous Effects 
     According to the present disclosure, it is possible to form the extended portions at both ends of the base in a round shape, thereby reducing the stress region of the magnetic path as compared with the conventional cores for the current transformer. 
     In addition, it is possible to minimize the stress region of the magnetic path instead of reducing the volume as compared with the conventional cores for the current transformer, thereby increasing the inductance and the permeability equal to or greater than those of the conventional core for the current transformer. 
     In addition, it is possible to increase the inductance and the permeability as compared with the conventional core for the current transformer, thereby increasing the power acquisition efficiency when it is installed in the current transformer. 
     In addition, it is possible to increase the magnetic path length as compared with the conventional core for the current transformer to increase the permeability, thereby increasing the power acquisition efficiency when it is installed in the current transformer. 
     In addition, it is possible to form the receiving groove in a round shape in the upper core so that the power line is received adjacent to the outer circumference of the receiving groove, thereby forming the power line to be relatively small in size as compared with the conventional core for the current transformer spaced apart from the outer circumference of the receiving groove. 
     In addition, it is possible to constitute the lower core greater than the conventional core for the current transformer when it is manufactured to have the same size as that of the conventional core for the current transformer, thereby increasing the size of the mountable bobbin, and increasing the number of turnable turns of the bobbin. 
     In addition, it is possible to increase the size of mountable bobbin and increase the number of turnable turns, thereby increasing the inductance as compared with the conventional core for the current transformer to increase the power acquisition efficiency when it is installed in the current transformer. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIGS. 1 and 2  are diagrams for explaining the conventional core for the current transformer. 
         FIG. 3  is a diagram for explaining a core for a current transformer according to an embodiment of the present disclosure. 
         FIG. 4  is a diagram for explaining an upper core of  FIG. 3 . 
         FIGS. 5 and 6  are diagrams for explaining a lower core of  FIG. 3 . 
         FIGS. 7 to 9  are diagrams for explaining by comparing the core for the current transformer according to an embodiment of the present disclosure with the conventional core for the current transformer. 
         FIGS. 10 to 13  are diagrams for explaining a method for manufacturing the core for the current transformer according to an embodiment of the present disclosure. 
         FIGS. 14 and 15  are diagrams for explaining the current transformer in which the core for the current transformer according to an embodiment of the present disclosure is installed. 
     
    
    
     BEST MODE 
     Hereinafter, the most preferred embodiment of the present disclosure will be described with reference to the accompanying drawings so that those skilled in the art to which the present disclosure pertains may easily practice the technical spirit of the present disclosure. First, in adding reference numerals to the components in each drawing, it is to be noted that the same components are denoted by the same reference numerals even though they are illustrated in different drawings. In addition, in the following description of the present disclosure, a detailed description of relevant known configurations or functions will be omitted when it is determined to obscure the subject matter of the present disclosure. 
     Referring to  FIG. 3 , a core for a current transformer  100  is configured to include an upper core  120  in which a power line  200  is received and a lower core  140  in which a bobbin  300 , around which a coil  320  is wound, is installed. 
     The upper core  120  is disposed on the upper portion of the lower core  140 , and has a receiving groove  124  in which the power line  200  is received formed therein. At this time, the upper core  120  is curved in a semicircular shape at the center thereof, and is formed in a shape surrounding a part of the circumference of an electric wire (e.g., ∩ shape). Therefore, the upper core  120  minimizes the spacing between the power line  200  and the core. 
     At this time, when the power line  200  is received in the receiving groove  124  of the upper core  120 , both ends of the upper core  120  are disposed at a position lower than the center of the power line  200  (i.e., a position further adjacent to the lower core  140 ). Therefore, the power line  200  is fully received in the receiving groove  124  formed in the upper core  120 . 
     For example, referring to  FIG. 4 , the upper core  120  is configured to include an upper base  121 , a first upper extension portion  122 , and a second upper extension portion  123 . Hereinafter, although it has been described by separating the upper core  120  into the upper base  121  to the second upper extension  123  in order to easily explain the shape of the upper core  120 , the upper core  120  is integrally formed. 
     The upper base  121  is formed in a semi-cylindrical shape. The cross section of the upper base  121  may be formed in a rectangular shape. The upper base  121  has an upper receiving groove  125  in a semi-cylindrical shape in which the power line  200  is received formed therein. That is, the upper base  121  is curved in a semicircular shape to form the upper receiving groove  125  in a semi-cylindrical shape. At this time, the upper receiving groove  125  receives a part of the power line  200  (i.e., a part of the cross section of the power line  200 ). 
     The first upper extension portion  122  is formed to extend from one end of the upper base  121  downwards (i.e., toward the lower core  140 ). At this time, the first upper extension portion  122  is formed to extend in a straight-line shape. The first upper extension portion  122  may be formed in a hexahedral shape whose cross section is formed in the same shape as the cross section of the upper base  121 . 
     The second upper extension portion  123  is formed to extend from the other end of the upper base  121  downwards (i.e., toward the lower core  140 ). At this time, the second upper extension portion  123  is formed to extend in a straight-line shape. The second upper extension portion  123  may be formed in a hexahedral shape whose cross section is formed in the same shape as the cross section of the upper base  121 . Herein, the second upper extension portion  123  may be disposed in parallel with the first upper extension portion  122 . 
     Meanwhile, as the first upper extension portion  122  and the second upper extension portion  123  extend from both ends of the upper base  121  to be spaced apart from each other, a lower receiving groove  126  in a predetermined shape (e.g., a rectangular parallelepiped shape) is formed between the first upper extension portion  122  and the second upper extension portion  123 . At this time, the lower receiving groove  126  receives the remaining portion of the power line  200  excluding the portion received in the upper receiving groove  125 . 
     Therefore, the upper core  120  has the receiving groove  124  having a structure in which the groove in a rectangular parallelepiped shape is coupled to the lower portion of the groove in a semi-cylindrical shape formed on the upper portion thereof. At this time, half of the power line  200  may be received in the upper portion of the receiving groove  124  (i.e., the groove in a semi-cylindrical shape) with respect to the cross section thereof, and the other half of the power line  200  may be received in the lower portion thereof (i.e., the groove in a rectangular parallelepiped shape). 
     The lower core  140  is disposed at the lower portion of the upper core  120 , and has both ends in contact with both ends of the upper core  120 . The lower core  140  is formed in a shape of rotating the upper core  120  by 180 degrees (e.g., U shape). At this time, a bobbin  300  having a coil  320  wound around at least one end of both ends of the lower core  140  is mounted. Herein, the bobbin  300  is mounted on the lower core  140  as one end of the lower core  140  passes through the groove formed in the bobbin  300 . 
     For example, referring to  FIG. 5 , the lower core  140  is configured to include a lower base  142 , a first lower extension portion  144 , and a second lower extension portion  146 . Hereinafter, although it has been described by separating the lower core  140  into the lower base  142  to the second lower extension portion  146  in order to easily explain the shape of the lower core  140 , the lower core  140  is integrally formed. 
     The lower base  142  is formed in a semi-cylindrical shape. At this time, the cross section of the lower base  142  may be formed in a rectangular shape. That is, the lower base  142  is curved in a semicircular shape to be formed in a semi-cylindrical shape. 
     The first lower extension portion  144  is formed to extend from one end of the lower base  142  upwards (i.e., toward the upper core  120 ). At this time, the first lower extension portion  144  may be formed in a hexahedral shape whose cross section is formed in the same shape as the cross section of the lower base  142 . The cross section of the first lower extension portion  144  may be formed in the same shape as the cross section of the upper core  120 . 
     The second lower extension portion  146  is formed to extend from the other end of the lower base  142  upwards (i.e., toward the upper core  120 ). At this time, the second lower extension portion  146  may be formed in a hexahedral shape whose cross section is formed in the same shape as the cross section of the lower base  142 . The cross section of the second lower extension portion  146  may be formed in the same shape as the cross section of the upper core  120 . Herein, the second lower extension portion  146  may be disposed in parallel with the first lower extension portion  144 . 
     As illustrated in  FIG. 5 , when the core for the current transformer  100  mounts the bobbin  300  on the lower core  140  formed in a U shape, the spacing is generated between the lower core  140  and the bobbin  300 , thereby reducing an adhesion rate between the lower core  140  and the bobbin  300 . 
     In addition, since the core for the current transformer  100  may not mount the bobbin  300  on the round portion (i.e., the lower base  142 ) when mounting the bobbin  300  on the lower core  140  formed in a U shape, the size of the bobbin  300  that may be mounted on the lower core  140  is reduced, and the number of turns of the coil  320  is reduced due to the reduction in the size of the bobbin  300 . 
     Therefore, the inductance of the core for the current transformer  100  reduces, thereby reducing the output voltage (i.e., the voltage obtained from the power line  200 ). 
     Therefore, the lower core  140  may form the core disposed on the lower portion thereof (i.e., the lower base  142 ) in a hexahedral shape so that the direction of the lower portion thereof may be formed in a straight-line shape. That is, the core for the current transformer  100  may form the lower portion of the lower core  140  in a straight-line shape, thereby increasing the size of the bobbin  300  that may be mounted on the lower core  140 , and increasing the number of turns of the coil  320  due to the increase in the size of the bobbin  300 . 
     Therefore, the inductance of the core for the current transformer  100  increases, thereby increasing the output voltage (i.e. the voltage obtained from the power line  200 ). 
     For example, referring to  FIG. 6 , the lower core  140  may include the lower base  142  to the second lower extension portion  146 , and may be formed in a ‘⊏’ shape. 
     The lower base  142  is formed in a rectangular parallelepiped shape. At this time, the first lower extension portion  144  and the second lower extension portion  146  may be formed at both ends of the lower base  142 , or the first lower extension portion  144  and the second lower extension portion  146  may be formed at both ends of one surface thereof. 
     The first lower extension portion  144  is formed to extend from one end of one surface of the lower base  142  upwards (i.e., toward the upper core  120 ). The first lower extension portion  144  may also be formed to extend from one end portion of the lower base  142 . At this time, the first lower extension portion  144  is formed in a hexahedral shape whose cross section is formed in the same shape as the cross section of one end of the upper core  120 . 
     The first lower extension portion  144  is formed in a hexahedral shape. The first lower extension portion  144  has one end coupled to one end of the lower base  142  or has one end portion of one surface coupled to one end of the lower base  142  or one end portion of one surface thereof. The first lower extension portion  144  has the other end (i.e., one end disposed upwards) in contact with one end of the upper core  120 . 
     The second lower extension portion  146  is formed to extend from the other end portion of one surface of the lower base  142  upwards (i.e., toward the upper core  120 ). The second lower extension portion  146  may also be formed to extend from the other end portion of the lower base  142  upwards. At this time, the second lower extension portion  146  is formed in a hexahedral shape whose cross section is formed in the same shape as the cross section of the other end of the upper core  120 . 
     The second lower extension portion  146  is formed in a hexahedral shape. The second lower extension portion  146  has one end coupled to the other end of the lower base  142  or the other end portion of one surface thereof, or has one end portion of one surface thereof coupled to the other end of the lower base  142  or the other end portion of one surface thereof. The second lower extension portion  146  has the other end (i.e., one end disposed upwards) in contact with the other end of the upper core  120 . 
     As described above, the core for the current transformer  100  forms the core (i.e., the lower base  142 ) disposed at the lower portion of the lower core  140  in a hexahedral shape so that the lower portion of the lower core  140  is formed in a straight-line shape, thereby increasing the size of the bobbin  300  that is mountable on the lower core  140  as compared with the core for the current transformer  100  having the lower portion of the lower core  140  formed in a round shape, and increasing the number of turns of the coil  320  due to the increase in the size of the bobbin  300 . 
     Therefore, the inductance of the core for the current transformer  100  increases, thereby increasing the output voltage (i.e., the voltage obtained from the power line  200 ). 
     Referring to  FIG. 7 , the core for the current transformer  100  according to an embodiment of the present disclosure has a volume smaller than that of the conventional core for the current transformer  100 . At this time, since the inductance of the core is proportional to the volume, the core for the current transformer  100  according to an embodiment of the present disclosure has the inductance smaller than the conventional core for the current transformer  100 . 
     However, in the conventional core for the current transformer  100 , the upper core  120  is bent to generate the stress region  400  of the magnetic path, thereby reducing the permeability. 
     In contrast, in the core for the current transformer  100  according to an embodiment of the present disclosure, the upper core  120  is formed in a round shape, thereby reducing the stress region  400  of the magnetic path as compared with the conventional core for the current transformer  100 . 
     At this time, since the increase in the stress region  400  of the magnetic core causes the inductance and the permeability of the core to be reduced, the core for the current transformer  100  according to an embodiment of the present disclosure has a reduced volume but minimizes the stress region  400  of the magnetic path, thereby increasing the inductance and the permeability equal to or greater than the conventional core for the current transformer  100 . 
     In addition, the inductor and the permeability of the core for the current transformer  100  according to an embodiment of the present disclosure are increased as compared with the conventional core for the current transformer  100 , thereby increasing the power acquisition efficiency when it is installed in the current transformer. 
     Referring to  FIG. 8 , when the size, the permeability, and the number of turns is the same, the core for the current transformer  100  according to an embodiment of the present disclosure has the increased magnetic path length  500  as compared with the conventional core for the current transformer  100 . 
     That is, the upper core  120  has the upper core  120  formed in a round shape, thereby reducing the inner diameter and the outer diameter thereof as compared with the conventional core for the current transformer  100  when they are manufactured in the same size. At this time, as in Equation 1, the magnetic path length  500  applies the inner diameter and the outer diameter of the core as a factor, thereby increasing the magnetic path length  500  when the inner diameter and the outer diameter reduce. 
     
       
         
           
             
               
                 
                   le 
                   = 
                   
                     
                       π 
                        
                       
                         ( 
                         
                           OD 
                           - 
                           ID 
                         
                         ) 
                       
                     
                     
                       ln 
                        
                       
                         ( 
                         
                           OD 
                           ID 
                         
                         ) 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   1 
                 
               
             
           
         
       
     
     Herein, le is the magnetic path length, OD is the outer diameter, and ID is the inner diameter. 
     Meanwhile, the permeability of the core is expressed by the following Equation 2. At this time, the magnetic field  500  is disposed in the numerator of the permeability formula, such that the permeability  500  increases as the magnetic path length  500  increases. 
     
       
         
           
             
               
                 
                   
                     μ 
                     i 
                   
                   = 
                   
                     
                       L 
                       × 
                       le 
                     
                     
                       
                         μ 
                         0 
                       
                       × 
                       
                         N 
                         2 
                       
                       × 
                       Ae 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   2 
                 
               
             
           
         
       
     
     Herein, μ i  is the permeability, L is the inductance, le is the magnetic path length, μ 0  is the vacuum permeability, N is the number of turns of the coil and Ae is the cross sectional area of the core. 
     At this time, in the core for the current transformer  100  according to an embodiment of the present disclosure, the permeability is increased by about 20% to 32% as compared with the conventional core for the current transformer  100  in the same environment (the size, the permeability of the core itself, the number of turns, and the like). 
     Therefore, the core for the current transformer  100  according to an embodiment of the present disclosure has the increased permeability as compared with the conventional core for the current transformer  100 , thereby increasing the power acquisition efficiency when it is installed in the current transformer. 
     Referring to  FIG. 9 , the core for the current transformer  100  according to an embodiment of the present disclosure has the receiving groove  124  in a round shape formed in the upper core  120 , and the conventional core for the current transformer  100  has the receiving groove  124  in a rectangular shape in the upper core  120 . 
     At this time, in the core for the current transformer  100  according to an embodiment of the present disclosure, the power line  200  is received adjacent to the outer circumference of the receiving groove  124 , while the conventional core for the current transformer  100  has the power line  200  received spaced apart from the outer circumference of the receiving groove  124 . 
     Therefore, the core for the current transformer  100  according to an embodiment of the present disclosure may be formed in a relatively small size as compared with the conventional core for the current transformer  100 . That is, the core for the current transformer  100  according to an embodiment of the present disclosure has the power line  200  received by closely contacting with the receiving groove  124  in a round shape, thereby minimizing the length of the side portion thereof to be formed in a relatively small size as compared with the conventional core for the current transformer  100 . 
     Therefore, the core for the current transformer  100  according to an embodiment of the present disclosure may be composed of the lower core  140 , which is relatively large as compared with the conventional core for the current transformer  100  when they are manufactured in the same size. 
     The core for the current transformer  100  according to an embodiment of the present disclosure largely forms the size of the lower core  140  as compared with the conventional core for the current transformer  100 , thereby increasing the size of the mountable bobbin  300  to increase the number of turnable turns. 
     In addition, the core for the current transformer  100  according to an embodiment of the present disclosure increases the inductance as compared with the conventional core for the current transformer  100  as the number of turnable turns increases. 
     In addition, the core for the current transformer  100  according to an embodiment of the present disclosure increases the power acquisition efficiency as compared with the conventional core for the current transformer  100  when it is mounted on the current transformer as the inductance increases. 
     Referring to  FIG. 10 , the core for the current transformer  100  according to an embodiment of the present disclosure is manufactured through the steps of winding a metal ribbon S 100 , inserting a mold S 200 , heat treating S 300 , impregnating S 400 , cutting S 500 , and processing a surface S 600 . Hereinafter, a method for manufacturing the upper core  120  and the lower core  140  having a structure in which an extension portion is formed in a core base  600  in a semi-cylindrical shape will be described as an example. 
     The winding the metal ribbon S 100  winds a metal ribbon having a predetermined thickness and width. For example, the winding the metal ribbon S 100  disposes two rollers to be spaced apart from each other, and winds the metal ribbon through the two rollers to manufacture the core base  600 . That is, the winding the metal ribbon S 100  manufactures the core base  600  through a rolling method. 
     Therefore, as illustrated in  FIG. 11 , the winding the metal ribbon S 100  manufactures the core base  600  in a rectangular parallelepiped shape having both ends formed in a semi-cylindrical shape. At this time, the receiving groove  124  in a rectangular parallelepiped shape having both ends formed in a semi-cylindrical shape is formed inside the core. 
     Of course, the winding the metal ribbon S 100  also winds the metal ribbon on the mold in a rectangular parallelepiped shape having both ends formed in a semi-cylindrical shape to manufacture the core base  600 . 
     The permeability of the core is reduced when an air gap is formed between the metal ribbons when the metal ribbon is wound in the winding the metal ribbon S 100 . 
     Therefore, the winding the metal ribbon S 100  winds the metal ribbon through the rolling to minimize the formation of the air gaps between the metal ribbons to prevent the permeability from being reduced, thereby preventing the characteristics of the core from being reduced. 
     The inserting the mold S 200  inserts the core base  600  manufactured in the winding the metal ribbon S 100  into the mold. Therefore, the core base  600  is prevented from being deformed during heat treatment and impregnation of the base core. 
     The heat treating S 300  heat-treats the core base  600  manufactured in the winding the metal ribbon S 100 . That is, the heat treating S 300  applies heat to the core base  600  so that the density of the core base  600  becomes uniform and the saturation induction characteristic is kept constant. 
     The impregnating S 400  impregnates the impregnation fluid into the heat-treated core base  600 . That is, the impregnating S 400  impregnates the impregnation fluid (e.g., varnish impregnation fluid) into the core base  600 , thereby minimizing the air gap of the core base  600 . 
     At this time, although it has been described that the impregnating S 400  is performed after the heat treating S 300 , the heat treating S 300  may also be performed after the impregnating S 400 . Herein, since the heat treating S 300  and the impregnating S 400  are processed through the conditions used in a general method for manufacturing the core, a detailed description thereof will be omitted. 
     As illustrated in  FIG. 12 , the cutting S 500  cuts the heat-treated and impregnated core base  600  to manufacture the upper core  120  and the lower core  140 . That is, the cutting S 500  cuts the core base  600  in a direction perpendicular to the winding direction. At this time, the cutting S 500  may cut the center of the core base  600  to manufacture the upper core  120  and the lower core  140  having the same size, or may cut the position shifted to one end of the core base  600  to manufacture the upper core  120  and the lower core  140  having different sizes from each other. 
     The processing the surface S 600  processes both ends (i.e., cut surfaces) of the upper core  120  and the lower core  140  manufactured in the cutting S 500 . 
     As illustrated in  FIG. 13 , the cut surfaces of the upper core  120  and the lower core  140  cut in the cutting S 500  are formed so that their surfaces are rough. Therefore, a gap may be generated when the upper core  120  and the lower core  140  cut in the cutting S 500  are coupled. 
     At this time, when it is mounted in the current transformer in a state where the gap has been generated, the voltage acquisition efficiency is reduced by the gap generated between the cut surfaces when the upper core  120  and the lower core  140  are coupled. 
     Therefore, the processing the surface S 600  performs surface processing so that both end surfaces (i.e., cut surfaces) of the upper core  120  and the lower core  140  become the same. At this time, the processing the surface S 600  may process both cross sections of the upper core  120  and the lower core  140  through polishing. 
     Meanwhile, when the lower core  140  is composed of the lower base  142  in a rectangular parallelepiped shape and the extension portions, the first core base  600  having the receiving groove  124  in a rectangular parallelepiped shape formed inside the rectangular parallelepiped shape through the winding the metal ribbon S 100  and the above-described second core base  600  (see  FIG. 11 ) are manufactured, respectively. 
     Then, the first core base  600  and the second core base  600  are each processed and then cut S 500  through the inserting the mold S 200 , the heat treating S 300 , and the impregnating S 400  for each of the first core base  600  and the second core base  600 . 
     Then, after the processing the surface S 600  is performed on the cut core, one core cut in the first core base  600  is used as the lower core  140 , and one core cut in the second core base  600  is used as the upper core  120  to manufacture the core for the current transformer  100 . 
     Referring to  FIGS. 14 and 15 , a current transformer  700  is configured to include a main body housing  720  on which the lower core  140  is mounted, and a core housing  740  on which the upper core  120  is mounted. 
     A hinge member  760  is formed at one side of the main body housing  720  and the core housing  740  in order to easily receive a cable, and a fastening member  780  (e.g., groove formed with a thread) is formed at the other side thereof in order to easily align and fasten the upper core  120  and the lower core  140 . 
     The main body housing  720  may have the lower surface formed in a planar shape in order to fix the current transformer  700 , thereby occurring the waste of the mounting space, and reducing the alignment accuracy with the upper core  120  by detaching (moving) the lower core  140  by an external impact when the lower core  140  is formed in a round shape. 
     At this time, when the alignment accuracy between the upper core  120  and the lower core  140  is reduced, the power acquisition efficiency of the current transformer  700  is reduced. 
     Therefore, the lower core  140  formed in a planar shape may further enhance the power acquisition efficiency than the lower core  140  formed in a round shape. 
     In addition, when the lower core  140  formed in a round shape is mounted on the current transformer  700 , the waste in the mounting space may occur, while when the lower core  140  in a planar shape is mounted on the current transformer  700 , the waste of the mounting space may be minimized. 
     In addition, when the lower core  140  is formed in a planar shape, the size of the mountable bobbin  300  increase as compared with the lower core  140  in a round shape in which the bobbin  300  may not be mounted on the round portion thereof (i.e., the lower base  142 ), and the number of turns of the coil  320  increase due to the increase in the size of the bobbin  300 . 
     Therefore, the inductance of the core for the current transformer  100  increases, thereby increasing the output voltage of the current transformer  700  (i.e., the voltage obtained from the power line  200 ). 
     As described above, although preferred embodiments according to the present disclosure have been described, it is to be understood by those skilled in the art that they may be modified into various forms, and various modifications and changes thereof may be embodied by those skilled in the art without departing from the scope of the present disclosure.