Abstract:
A switchboard applied with a bushing-type current transformer includes a terminal bushing inserted from a front direction, a switchboard terminal coupled to the terminal bushing, a metering current transformer bushing inserted from a front direction and inserted into the terminal bushing while wrapping the switchboard terminal, and a metering current transformer disposed outside the metering current transformer bushing and assembled or disassembled at a front surface through a circuit breaker chamber. Thus, the switchboard applied with a bushing-type current transformer has an advantage of having a high degree of internal space utilization or capable of being made to be compact.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Patent Application No. 10-2014-0172444, filed on Dec. 3, 2014, the contents of which are all hereby incorporated by reference herein in its entirety. 
       BACKGROUND 
       [0002]    The present disclosure relates to a switchboard and, more specifically, to a switchboard to which a bushing-type current transformer having a metering current transformer and a metering current transformer bushing is applied. 
         [0003]    Generally, a switchboard is a device used in monitoring, controlling, and protecting an electric power system, several electric devices such as a circuit breaker and a current transformer are accommodated in the switchboard to operate or control a power plant and a substation and to operate a motor. 
         [0004]    From among the electric devices accommodated in the switchboard, maintenance is able to be performed on those mounted on the front surface portion thereof from a direction of the front surface thereof, but maintenance is difficult to be performed on those mounted on a rear surface portion thereof unless a maintenance space having a particular or larger portion is ensured between the rear surface portion of the switchboard and a rear surface wall or a worker enters the switchboard through the front surface portion thereof. 
         [0005]      FIG. 1  is a view illustrating a structure of compartments of a switchboard according to related arts when a circuit breaker is located at a test position,  FIG. 2  is a view illustrating a structure of compartments of a switchboard according to related arts when a circuit breaker is located at an operation position, and  FIG. 3  is a perspective view illustrating the inside of a circuit breaker chamber and the inside of a voltage transformer chamber of a switchboard according to related arts. 
         [0006]    A switchboard applies a voltage and electric current while accommodating several sorts of devices therein and detects abnormality when a fault voltage or current occurs thereby blocking a circuit breaker or providing information to other control devices. 
         [0007]    A plurality of compartments are provided in a switchboard so that spaces for accommodating the devices may be defined for each use, and each of the compartments should have shielding and insulating functions that are prescribed under laws and regulations. 
         [0008]    The compartments of a switchboard may include a circuit breaker chamber  1  for accommodating a circuit breaker  6 , a cable chamber  2  into which a input/output bus or a cable is introduced, a bus bar chamber  3  through which a bus bar passes, a voltage transformer chamber  4  for accommodating a metering voltage transformer, and a low voltage device chamber  5  for accommodating a low voltage device. 
         [0009]    Here, each of the compartments, frames, and electric devices or internal components in the compartments are generally coupled to each other through a coupling technique using bolts. 
         [0010]    Electric devices accommodated in a switchboard include a circuit breaker  6 , a metering voltage transformer  7 , a metering current transformer  8 , a bus bar chamber bus bar  9 , a cable chamber bus bar  10 , a metering voltage transformer bus bar  11 , a switchboard terminal  12  that is coupled to a bus bar and may be connected to the circuit breaker, a circuit breaker tulip-type terminal  13 , and a input/output handle  14  transferring a circuit breaker body. 
         [0011]    In the switchboard, as illustrated in  FIG. 1 , when the circuit breaker  6  is accommodated at a test position in the circuit breaker chamber  1 , an electric current is not applied between a power supply and a load. On the other hand, in the switchboard, as illustrated in  FIG. 2 , when the circuit breaker  6  is located at an operation position, an electric current and voltage may be applied between a power supply and a load, and thus an electric current may be connected or disconnected by the circuit breaker. 
         [0012]    The circuit breaker  6  is moved to a test position or an operation position by a input/output handle  14 . 
         [0013]    When the metering voltage transformer  7  is accommodated in the testing position, a voltage is not detected, as illustrated in  FIG. 1 . When located at the operation position, the metering voltage transformer  7  may detect a voltage by contacting a switchboard terminal  15  coupled to the metering voltage transformer bus bar  11 , as illustrated in  FIG. 2 . 
         [0014]    A method of moving the metering voltage transformer  7  to the test position or operation position may be the same as the method of moving the circuit breaker. 
         [0015]    Referring to  FIG. 3 , side surface frames  16  are symmetrically disposed at both sides of the circuit breaker chamber  1  and voltage transformer chamber  4 . A top plate rear surface  17 , a top plate front surface  18 , a middle base  19 , and a bottom plate  20  are coupled to the side surface frames  16  from top to bottom. At a side of a rear surface, an upper rear plate  21 , a middle rear plate  22 , and a lower rear plate  23  are coupled to pillar frames  24  disposed at left and right sides. A circuit breaker chamber bushing terminal  26  and a voltage transformer chamber bushing terminal  27  are coupled to each of the rear plates  21 ,  22 , and  23  and the pillar frames  24 , and a circuit breaker chamber shutter  28  and a voltage transformer chamber shutter  29  are fixed to the pillar frames  24  in front of each of the bushing terminals. These shutters  28  and  29  are opened by a unit connected thereto when the circuit breaker  6  and metering voltage transformer  7  move to the operation position. 
         [0016]    One or more front doors  28   a ,  28   b , and  28   c  may be disposed at the switchboard. The front doors  28   a ,  28   b , and  28   c  may include a low voltage device chamber door  28   a , a circuit breaker chamber door  28   b , and a voltage transformer chamber door  28   c . A hinge shaft is disposed at one side of each of the front doors  28   a ,  28   b , and  28   c , and a handle and a locking unit are disposed at the other side thereof, so that the doors may be opened and closed. The front doors  28   a ,  28   b , and  28   c  are usually provided so as to manage devices that require much maintenance or front-side maintenance, such as a circuit breaker, a voltage transformer, and a low voltage device that need to be input and output. 
         [0017]    Rear doors  29   a  and  29   b  are mounted on the rear surface of the switchboard, and usually provided so as to enable to perform maintenance on the metering current transformer and the like that are difficult to be disposed in the front surface portion thereof. Here, a space needed for maintenance should be ensured to open the rear doors  29   a  and  29   b.    
         [0018]    For example, a device attached to the cable chamber  2  or bus bar chamber  3  is shaped such that maintenance may be performed only through the rear surface thereof, and therefore a work space for maintenance should be ensured at the rear surface of the switchboard. 
         [0019]    That is, in a switchboard installation space, a front side pathway for the maintenance of a device disposed at a front surface portion with respect to the switchboard and a rear side work space for the maintenance of a device disposed at a rear surface portion should be respectively ensured. 
         [0020]    However, a switchboard according to related arts may require a large installation space to ensure both a front side pathway and a rear side work space, and the installation thereof may be difficult when a space for installing a switchboard is limited. 
       SUMMARY 
       [0021]    Embodiments provide a switchboard having a high degree of internal space utilization or capable of being made to be compact. 
         [0022]    Embodiments also provide a switchboard by which a part of components disposed in the switchboard easily enters and exits. 
         [0023]    Embodiments also provide a switchboard by which the insulating function of components disposed in the switchboard is improved. 
         [0024]    In one embodiment, a switchboard applied with a bushing-type current transformer includes: a terminal bushing inserted from a front direction; a switchboard terminal coupled to the terminal bushing; a metering current transformer bushing inserted from a front direction, and inserted into the terminal bushing while wrapping the switchboard terminal; and a metering current transformer disposed outside the metering current transformer bushing and assembled or disassembled at a front surface through a circuit breaker chamber. 
         [0025]    A terminal bushing mounter at which the terminal bushing may be installed may be provided inside at least one of a bus bar chamber and a cable chamber. 
         [0026]    A current transformer mounter at which the metering current transformer may be installed may be provided on a rear plate of the circuit breaker chamber. 
         [0027]    The metering current transformer bushing may include: a head portion; a protrusion portion protruding from the head portion and provided in a flange shape; and a body portion extending from the protrusion portion. 
         [0028]    Wrinkles may be formed on the outer circumferential surface of at least one of the head portion and body portion. 
         [0029]    The switchboard may further include a stress control sealed member disposed at the body portion. 
         [0030]    A section in which the stress control sealed member is installed may be longer than a section in which the metering current transformer is installed. 
         [0031]    An inner supporting portion supporting an end of the switchboard terminal may be provided in the body portion. 
         [0032]    The switchboard terminal may be spaced without contacting the metering current transformer bushing excluding the inner supporting portion. 
         [0033]    A ring conductor portion may be disposed at a front surface portion of the body portion. 
         [0034]    An earthing member may be coupled to the ring conductor portion, and the earthing member may contact the switchboard terminal. The earthing member may be made of a leaf spring. 
         [0035]    A semi-conductive layer may be disposed on the outer circumferential surface of the body portion. 
         [0036]    The semi-conductive layer may be connected to a frame of the switchboard. 
         [0037]    A base plate forming a lower portion of the circuit breaker chamber may be made of a module that may be separated from the switchboard. 
         [0038]    The switchboard may further include a voltage transformer body input into or output from a voltage transformer chamber and a voltage transformer bus bar installed in a bus bar chamber or a cable chamber, wherein a voltage transformer terminal of the voltage transformer body may be directly connected to the voltage transformer bus bar through a contacting technique. 
         [0039]    A voltage transformer cradle may be provided at the voltage transformer chamber, a voltage transformer cradle bushing may be disposed at the voltage transformer cradle, and the voltage transformer bus bar may be input into a rear portion of the voltage transformer cradle bushing. When the voltage transformer body is input to an operation position, the voltage terminal may be directly connected to the voltage transformer bus bar by being input into a front portion of the voltage transformer cradle bushing while not contacting the voltage transformer cradle bushing. 
         [0040]    In another embodiment, a switchboard applied with a bushing-type current transformer includes: a casing having a front opening portion and a circuit breaker chamber including a circuit breaker disposed therein; a terminal bushing mounter disposed in the casing; a terminal bushing inserted into the terminal bushing mounter from a front portion of the terminal bushing mounter; a switchboard terminal coupled to the terminal bushing; a metering current transformer bushing inserted into a circuit breaker chamber rear plate forming the circuit breaker chamber, wrapping the switchboard terminal, and having a part inserted into the terminal bushing; a current transformer mounter disposed at the circuit breaker chamber rear plate; and a metering current transformer inserted into the current transformer mounter in a front portion of the current transformer mounter and assembled or disassembled by passing through the circuit breaker chamber. 
         [0041]    The switchboard applied with a bushing-type current transformer may further include: a stress control sealed member disposed in the metering current transformer bushing; a ring conductor portion disposed at the metering current transformer bushing to be connected to the stress control sealed member; an earthing member coupled to the ring conductor portion and contacting the switchboard terminal to form an earth circuit; and a semi-conductive layer disposed at the outer surface of the metering current transformer bushing and earth-connected. 
         [0042]    A base plate forming a lower portion of the circuit breaker chamber may be made of a module capable of being separated from the switchboard. 
         [0043]    The casing may be partitioned into: a voltage transformer chamber having a voltage transformer disposed therein; a bus bar chamber through which a bus bar passes; and a cable chamber which a input/output bus or a cable enters. The switchboard applied with a bushing-type current transformer may further include: a voltage transformer body input into or output from the voltage transformer chamber; and a voltage transformer bus bar disposed in at least one of the bus bar chamber and cable chamber. A voltage transformer terminal of the voltage transformer body may be directly connected to the voltage transformer bus bar through a contacting technique. 
         [0044]    A voltage transformer cradle may be provided at the voltage transformer chamber, a voltage transformer cradle bushing may be disposed at the voltage transformer cradle, and the voltage transformer bus bar may be input into a rear portion of the voltage transformer cradle bushing. When the voltage transformer body is input to an operation position, the voltage terminal may be directly connected to the voltage transformer bus bar by being input into a front portion of the voltage transformer cradle bushing while not contacting the voltage transformer cradle bushing. 
         [0045]    The switchboard applied with a bushing-type current transformer according to an embodiment has an advantage of easily attaching and detaching a metering current transformer because the metering current transformer may be backwardly mounted or forwardly removed. 
         [0046]    Moreover, a separate work space for attaching and detaching the metering current transformer needs not to be provided in an internal rear space of the internal space of the switchboard, so that the switch may have a higher degree of internal space utilization or may be made to be compact. 
         [0047]    In addition, the metering current transformer has an advantage of being easily attached and detached even when a space between the rear surface of the switchboard and a structure disposed in a rear of the switchboard is narrow. 
         [0048]    Furthermore, the stress control sealed member is disposed in the metering current transformer bushing, and the semi-conductive layer is provided outside the metering current transformer bushing, so that a dielectric breakdown phenomenon may be minimized. 
         [0049]    Still more, the base plate of the circuit breaker chamber is made of the module capable of being separated and removed, and the circuit breaker chamber and voltage transformer chamber may be connected when the base plate of the circuit breaker chamber is removed, so that maintenance may be easily performed on the switchboard. 
         [0050]    Even more, the voltage transformer terminal is directly connected to the voltage transformer bus bar through a contacting technique, so that the voltage transformer cradle may be easily separated. 
         [0051]    Much more, the voltage transformer terminal is not in contact with the voltage transformer cradle bushing, so that an insulating function is improved. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0052]      FIG. 1  is a view illustrating a structure of compartments of a switchboard according to related arts when a circuit breaker is located at a test position. 
           [0053]      FIG. 2  is a view illustrating a structure of compartments of a switchboard according to related arts when a circuit breaker is located at an operation position. 
           [0054]      FIG. 3  is a perspective view illustrating the inside of a circuit breaker chamber and the inside of a voltage transformer chamber of a switchboard according to related arts. 
           [0055]      FIG. 4  is a cross-sectional view of a switchboard according to an embodiment when a circuit breaker and a voltage transformer of the switchboard are located at a test position. 
           [0056]      FIG. 5  is a cross-sectional view of a switchboard according to an embodiment when a circuit breaker and a voltage transformer of the switchboard are located at an operation position. 
           [0057]      FIG. 6  is an enlarged cross-sectional view illustrating a terminal bushing, a switchboard terminal, a metering current transformer bushing, and a metering current transformer. 
           [0058]      FIG. 7  is a perspective view illustrating the inside of a switchboard according to an embodiment. 
           [0059]      FIG. 8  is a side view illustrating the inside of a switchboard according to an embodiment. 
           [0060]      FIG. 9  is a rear perspective view illustrating a terminal bushing of a switchboard according to an embodiment. 
           [0061]      FIG. 10  is a front perspective view illustrating a terminal bushing of a switchboard according to an embodiment. 
           [0062]      FIG. 11  is a perspective view illustrating a metering current transformer bushing of a switchboard according to an embodiment. 
           [0063]      FIG. 12  is a partial cut-away perspective view illustrating the metering current transformer bushing of  FIG. 11 . 
           [0064]      FIG. 13  is a perspective view illustrating a bushing-type current transformer of a switchboard according to an embodiment. 
           [0065]      FIG. 14  is a partial cut-away perspective view illustrating a state in which a metering current transformer is coupled to a metering current transformer bushing of a switchboard according to an embodiment. 
           [0066]      FIG. 15  is a perspective view illustrating a base plate of a circuit breaker chamber of a switchboard according to an embodiment. 
           [0067]      FIG. 16  is a perspective view illustrating the inside of a switchboard according to an embodiment when a circuit breaker and a voltage transformer are input into a switchboard according to an embodiment. 
           [0068]      FIG. 17  is a perspective view illustrating a state in which a voltage transformer and a voltage transformer cradle are output from a switchboard according to an embodiment. 
           [0069]      FIG. 18  is a perspective view illustrating a voltage transformer body, a voltage transformer cradle, a voltage transformer bus bar, and a transferring cart of a switchboard according to an embodiment. 
           [0070]      FIG. 19  is a perspective view illustrating a voltage transformer body and a transferring cart of a switchboard according to an embodiment. 
           [0071]      FIG. 20  is a perspective view illustrating a voltage transformer cradle and a voltage transformer bus bar of a switchboard according to an embodiment. 
           [0072]      FIG. 21  is a cross-sectional view of the cradle bushing illustrated in  FIG. 20 . 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0073]    Hereinafter, reference will be made to the embodiments of the present disclosure with reference to accompanying drawings, the reference as a detailed description enabling the disclosure to be easily worked by a person of ordinary skill in the art to which the present disclosure pertains but not meaning that technical ideas and categories of the present disclosure are restricted thereby. 
         [0074]    A switchboard applied with a bushing-type current transformer according to an embodiment will be described below with reference to the drawings. 
         [0075]    A switchboard applied with a bushing-type current transformer may include: a terminal bushing  41  inserted from a front direction; a switchboard terminal  42  coupled to the terminal bushing  41 ; a metering current transformer bushing  31  inserted from a front direction and inserted into the terminal bushing  41  while wrapping the switchboard terminal  42 ; and a metering current transformer  40  disposed outside the metering current transformer bushing  31 . The metering current transformer bushing  31  may be assembled or disassembled at a front surface through a circuit breaker chamber  30 . 
         [0076]    Hereinafter, the switchboard applied with a bushing-type current transformer will be simply referred to as a switchboard, for convenience. 
         [0077]    The switchboard may be partitioned into a plurality of compartments. The plurality of compartments may include a circuit breaker chamber  30  capable of accommodating a circuit breaker  90 , a low voltage device chamber  50  for accommodating a low voltage device, a voltage transformer chamber  60  for accommodating a metering voltage transformer, a bus bar chamber  70  through which a bus bar passes, and a cable chamber  80  which a input/output bus or a cable enters. The switchboard may be partitioned into the circuit breaker chamber  30 , a low voltage a device chamber  50 , a voltage transformer chamber  60 , a bus bar chamber  70 , and a cable chamber  80 . 
         [0078]    The switchboard, as illustrated in  FIGS. 16 and 17 , may include a casing  100  forming the outer appearance thereof. The casing  100  may have a front opening portion, and several components in the switchboard may enter and exit through the front opening portion. 
         [0079]    The casing  100  may be made of an assembly of at least two members. If necessary, at least a part of the casing  100  may be configured as a door that is opened and closed. The casing  100  may include a lower body, a rear body, a pair of side bodies, and an upper body. At least one of the lower body, rear body, side bodies, and upper body may be made of an assembly of a plurality of members. 
         [0080]    The casing  100  may have a circuit breaker chamber  30  capable of accommodating a circuit breaker  90  therein. The casing  100  may have a low voltage device chamber  50  accommodating a low voltage device therein. The casing  100  may have a voltage transformer chamber  60  accommodating a metering voltage transformer therein. The casing  100  may have a bus bar chamber  70  through which a bus bar passes. The casing  100  may have a cable chamber  80  which an input/output bus or a cable enters. 
         [0081]    A front surface portion of the casing  100  may be opened, and the front opening portion may be disposed at a front portion of the casing  100 . The front opening portion may be opened in forward and backward directions at the front portion of the casing  100 . 
         [0082]    The switchboard may include at least one front door opening and closing the front opening portion. At least one front door, as illustrated in  FIGS. 16 and 17 , may include a circuit breaker chamber door  30   b  opening and closing the circuit breaker chamber  30  and a voltage transformer chamber door  60   b  opening and closing the voltage transformer chamber  60 . At least one front door may further include a low voltage device chamber door (not indicated by a reference numeral) opening and closing the low voltage device chamber  50 . 
         [0083]    The insides of the circuit breaker chamber  30 , the voltage transformer chamber  60 , and the low voltage device chamber  50  may be seen when the front door is opened. 
         [0084]    The metering current transformer  40  may have a hollow portion wrapping a part of the metering current transformer bushing  31 , and may be disposed outside the metering current transformer bushing  31 . A part of the metering current transformer bushing  31  may be inserted into the hollow portion of the metering current transformer  40 . 
         [0085]    The metering current transformer  40  may be mounted from a front position toward a rear direction when mounted on the switchboard, and may be removed from a rear position toward a front direction when separated from the switchboard. That is, the metering current transformer  40  may be attached and detached in forward and backward directions. 
         [0086]    The switchboard may include a terminal bushing mounter  71  on which the terminal bushing  41  is mounted. The terminal bushing mounter  71  may be disposed inside at least one of the bus bar chamber  70  and cable chamber  80 . The terminal bushing  41  may be disposed at the terminal bushing mounter  71  and supported on the terminal bushing mounter  71 . The terminal bushing mounter  71  may be connected to a rear plate  30   a  of the circuit breaker chamber  30 . A horizontal supporting rod  72  may be provided in a lower portion of the terminal bushing mounter  71 . 
         [0087]    The rear plate  30   a  of the circuit breaker chamber  30  may make the circuit breaker chamber  30  partitioned from another space in a rear portion side thereof, and the terminal bushing mounter  71  may make the position of the terminal bushing  41  maintained, while being supported on the rear plate  30   a  of the circuit breaker chamber  30 . The rear plate  30   a  of the circuit breaker chamber  30  may form a rear portion of the circuit breaker chamber  30 , and the rear late  30   a  of the circuit breaker chamber  30  may partition the circuit breaker chamber  30  disposed at the front thereof and the bus bar chamber  70  disposed at the rear thereof. The rear plate  30  of the circuit breaker chamber  30  may be lengthily disposed in upper and lower directions in the casing  100 . 
         [0088]    The terminal bushing  41 , as illustrated in  FIGS. 9 and 10 , may be provided in a box shape having one open side. The terminal bushing  41  may be coupled to the terminal bushing mounter  71  with a flange  41   a  disposed at one side thereof. The terminal bushing  41  may be inserted into the terminal bushing mounter  71  from a front direction. 
         [0089]    The terminal bushing mounter  71  may be disposed in the rear of the rear plate  30   a  of the circuit breaker chamber  30 . 
         [0090]    A terminal bushing through-hole in which the terminal bushing  41  is inserted may be defined in the terminal bushing mounter  71 . The flange  41   a  may be caught around the terminal bushing through-hole when the terminal bushing  41  is mounted on the terminal bushing mounter  71 , and the insertion of the terminal bushing  41  may be completed when the flange  41   a  is caught by the terminal bushing mounter  71 . The terminal bushing  41  may be supported on the terminal bushing mounter  71  by being mounted on the terminal bushing mounter  71 . 
         [0091]    The switchboard terminal  42  may be lengthwise provided in forward and backward directions and include: a power supply side bus bar contacting portion connected to a power supply side bus bar  45  to be described below; and a metering current transformer bushing contacting portion supported by contacting the metering current transformer bushing  40 . Hereinafter, the power supply side bus bar contacting portion will be described as being termed one end  42   a  of the switchboard terminal  42 , and the metering current transformer bushing contacting portion will be described as being termed the other end  42   b  of the switchboard terminal  42 . 
         [0092]    One end  42   a  of the switchboard terminal  42  may penetrate through the terminal bushing  41 , and one end  42   a  penetrating through the terminal bushing  41  contacts the power supply side bus bar  45 , so that the switchboard terminal  42  is connected to the power supply side bus bar  45 . 
         [0093]    A current transformer mounter  43  is disposed at the rear plate  30   a  of the circuit breaker chamber  30 . The metering current transformer  40  may be disposed at the current transformer mounter  43 . The current transformer mounter  43  may be provided to contact the rear surface of the rear plate  30   a  of the circuit breaker chamber  30 . The current transformer mounter  43  may be spaced apart from the terminal bushing  41  in forward and backward directions. The current transformer mounter  43  may be provided in a hollow container body shape, and at least a part of the metering current transformer  40  may be inserted into the current transformer mounter  43 . A stopper by which the metering current transformer  40  is caught in a rear direction may be disposed at the rear end of the current transformer mounter  43 . When the metering current transformer  40  is mounted, a mounted position of the metering current transformer  40  may be discerned by being caught by the stopper disposed at the rear end of the current transformer mounter  43 . That is, the stopper of the current transformer mounter  43  may perform a function of discerning a mounted position of the current transformer mounter  43 . 
         [0094]    The metering current transformer bushing  31  may be disposed at the rear plate  30   a  of the circuit breaker chamber  30 . The metering current transformer bushing  31  may be inserted from the front of the rear plate  30   a  of the circuit breaker chamber  30 . A metering current transformer bushing through-hole in which the metering current transformer bushing  31  is inserted may be defined in the rear plate  30   a  of the circuit breaker chamber  30 . 
         [0095]    A protrusion portion  33  (refer to  FIGS. 10 and 11 ) protruding on the metering current transformer bushing  31  may be caught around the metering current transformer bushing through-hole when the metering current transformer bushing  31  is mounted on the rear plate  30   a  of the circuit breaker chamber  30 , and the insertion of the metering current transformer bushing  31  may be completed when the protrusion portion  33  is caught by the rear plate  30   a  of the circuit breaker chamber  30 . The metering current transformer bushing  31  may be supported on the rear plate  30   a  of the circuit breaker chamber  30  by being mounted on the rear plate  30   a  of the circuit breaker chamber  30 . 
         [0096]    Referring to  FIGS. 11 to 14 , the metering current transformer bushing  31  may be provided in a pipe shape having a flange overall. The metering current transformer bushing  31  may include a head portion, a protrusion portion  33 , and a body portion  34 . 
         [0097]    The head portion  32  is a portion in which the switchboard terminal  42  and a main circuit terminal  91  of the circuit breaker  90  may be inserted and coupled. The head portion  32  may be provided in a hollow container body shape. The head portion  32  may include an inner space in which a part of the switchboard terminal  42  and the main circuit terminal  91  are inserted, and the main circuit terminal  91  may contact the switchboard terminal  42  in the inner space. The head portion  32  may be a protector protecting the main circuit terminal  91  and a part of the switchboard terminal  42  together. Wrinkles may be formed on the outer circumferential surface of the head portion  32 . The wrinkles formed on the outer circumferential surface of the head portion  32  have an effect in increasing a creeping distance. 
         [0098]    The protrusion portion  33  is a portion capable of being supported on and coupled to the rear plate  30   a  of the circuit breaker chamber  30 . The protrusion portion  33  may be provided in a flange shape. The protrusion portion  33  may be provided to be larger than the head portion  32 . A worker may make the protrusion portion  33  coupled to the rear plate  30   a  of the circuit breaker chamber  30  through bolt assembly and the like, and the metering current transformer bushing  31  may be fixed by the protrusion portion  33 . The protrusion portion  33  may be coupled to be disposed in the front of the rear plate  30   a  of the circuit breaker chamber  30  so that assembly work can be performed in the circuit breaker chamber  30 . 
         [0099]    The body portion  34  may be provided to be smaller than the head portion  32 . The body portion  34  may have a hollow container body shape just like the head portion  32 . The body portion  34  may have a smaller diameter than the head portion  32 . The body portion  34  may extend from the protrusion portion  32 . The body portion  34  may have a shape protruding from the protrusion portion  32 . 
         [0100]    Wrinkles may be formed on the outer circumferential surface of the body portion  34 . The wrinkles may be formed on the overall outer circumferential surface of the body portion  34 , and may be formed on a part of the outer circumferential surface thereof as well. The wrinkles formed on the outer circumferential surface of the body portion  34  have an effect in increasing a creeping distance. 
         [0101]    A stress control sealed member  35  may be disposed inside the metering current transformer bushing  31 . The stress control sealed member  35  may be made of aluminum wire mesh and the like. The stress control sealed member  35  may be provided in a hollow container body shape or a ring shape. The stress control sealed member  35  may be disposed to be integrated with the metering current transformer bushing  31 . The stress control sealed member  35  is able to be disposed in the body portion  34 . A section in which the stress control sealed member  35  is disposed may be longer than a section in which the metering current transformer  40  is disposed, in the metering current transformer bushing  31 . A forward and backward direction length of the stress control sealed member  35  may be longer than a forward and backward direction length of the metering current transformer  40 . 
         [0102]    The metering current transformer bushing  31  may include an inner supporting portion  34   a  supporting the switchboard terminal  42 . The inner supporting portion  34   a  may be provided to protrude on the inner circumference of the metering current transformer bushing  31 . The inner supporting portion  34   a  may protrude along the inner circumferential surface of the body portion  34  in the body portion  34 . The inner supporting portion  34   a  supports the other end  42   b  of the switchboard terminal  42 . The other end  42   b  of the switchboard terminal  42  may be supported by contacting the inner supporting portion  34   a.    
         [0103]    The switchboard terminal  42  may be provided in a long rod shape. One end  42   a  of the switchboard terminal  42  may be coupled to the terminal bushing  41 , and the other end  42   b  of the switchboard terminal  42  may be supported on the inner supporting portion  34   a . The switchboard terminal  42  may be stably maintained overall. When the switchboard terminal  42  is inserted into the body portion  34 , a part other than being supported on the inner supporting portion  34   a  of the body portion  34  may be spaced apart from the metering current transformer bushing  31 . The front end of the switchboard terminal  42  protrudes into the head portion  32  to be connected to the main circuit terminal  91 . 
         [0104]    A ring conductor portion  36  may be disposed at the metering current transformer bushing  31 . The ring conductor portion  36  may be disposed at a front surface portion of the body portion  34 . The ring conductor portion  36  may be made of aluminum. The ring conductor portion  36  may be connected to the stress control sealed member  35 . 
         [0105]    An earthing member  37  may be coupled to the ring conductor portion  36 . The earthing member  37  may form an earth circuit by contacting the switchboard terminal  42 . The earthing member may be made of a leaf spring. 
         [0106]    A semi-conductive layer  38  may be disposed at the outer circumferential surface of the body portion  34 . The semi-conductive layer  38  may be provided to be painted with a semi-conductive material. 
         [0107]    The semi-conductive layer  38  may be satisfied with equipotentiality by being connected to a frame of the switchboard such as the rear plate  30   a  of the circuit breaker chamber  30  by a leading wire (not shown) and the like. A frame of the switchboard may be provided as a part of the casing  100  and disposed in the casing  100  separately from the casing  100  to serve as a supporter supporting several sorts of devices disposed at the switchboard. 
         [0108]    The inside of the metering current transformer  40  comes in contact with the switchboard terminal  42  by the stress control sealed member  35 , the outside of the metering current transformer  40  may be earthed by the semi-conductive layer  38 , and a dielectric breakdown phenomenon caused by the Corona phenomenon after long-term usage may be minimized. 
         [0109]    The metering current transformer  40  may be disposed at the metering current transformer bushing  31 . The metering current transformer  40  may be disposed at the body portion  34  of the metering current transformer bushing  31 . The metering current transformer  40  may be provided in a ring shape to be disposed at the outer circumferential surface of the metering current transformer bushing  31 . The metering current transformer  40  may be a bushing-type current transformer. 
         [0110]      FIG. 15  illustrates a base plate  39  of the circuit breaker chamber  30 . The base plate  39  may form a lower portion of the circuit breaker chamber  30  and an upper plate of a middle base of the switchboard. The base plate  39  may be horizontally disposed in the casing  100 . The base plate  39  may be made of a separate module capable of being separated from the circuit breaker chamber  30  and switchboard. 
         [0111]    The base plate  39  may be screwed to a middle base side plate  55   b  through a tapped hole  39   a  defined in a side surface thereof. When the base plate  39  is removed from the switchboard, the circuit breaker chamber  30  and voltage transformer chamber  60  may be connected, and a sufficient space needed for the maintenance of the switchboard may be ensured. Several sorts of devices disposed at a lower portion of a cradle may be provided at the base plate  39 . 
         [0112]    A middle base front surface plate  55   a  may be removed as well. The base plate  39  and middle base front surface plate  55   a  may be simultaneously removed, and the circuit breaker chamber  30  and voltage transformer chamber  60  are completely opened, so that a space capable of helping maintenance in an internal front direction of the casing  100  may be provided. 
         [0113]    Referring to  FIGS. 16 to 21 , a voltage transformer cradle  61  may be disposed at the voltage transformer chamber  60 . The voltage transformer cradle  61  may be fixed and disposed to a lower plate  60   a  of the voltage transformer chamber  60  by bolts and the like. That is, when bolts fixing the voltage transformer cradle  61  are released, the voltage transformer cradle  61  may be separated from the switchboard.  FIG. 17  illustrates the inside of a switchboard having the voltage transformer cradle  61  removed therefrom. Here, the lower plate  60   a  of the voltage transformer chamber  60  may be disposed at a lower portion of the voltage transformer chamber  60 , and a top surface thereof may face the voltage transformer chamber  60 . 
         [0114]    A voltage transformer body  65  (a power transformer) is carried through a transferring cart  66  to be input into or output from the voltage transformer cradle  61 . 
         [0115]    A voltage transformer cradle shutter  63   a  and a voltage transformer cradle shutter assembly  63   b  may be provided at the voltage transformer cradle  61 . 
         [0116]    A voltage transformer cradle bushing is provided at the voltage transformer cradle  61 . 
         [0117]    A voltage transformer bus bar  67  may be input into a rear portion  62   b  of a voltage transformer cradle bushing  62 . When the voltage transformer body  65  is input to an operation position, a voltage transformer terminal  65   a  is directly connected to the voltage transformer bus bar  67  through a contacting technique by being input into a front portion  62   a  of the voltage transformer cradle bushing  62 . Here, an elastic member capable of having a contacting and pressing force may be provided at an end portion of the voltage transformer terminal  65   a.    
         [0118]    That is, the voltage transformer terminal  65   a  is directly connected to the voltage transformer bus bar  67  through a contacting technique without coupling with a cradle terminal or a connection bus bar. Accordingly, the voltage transformer cradle  61  is led out without separate removing work, so that the voltage transformer terminal  65   a  may be easily separated from the voltage transformer bus bar  67 . The voltage transformer terminal  65   a  is not in contact with the voltage transformer cradle bushing  62 , so that an insulating function may be improved. 
         [0119]    An example of a step of performing maintenance on a switchboard according to an embodiment will be described. 
         [0120]    First, a worker may open a circuit breaker chamber door  30   b  and led out a circuit breaker  90 . The circuit breaker  90  may be led out along with a circuit breaker transferring cart. The worker may remove a middle base front surface plate  55   a  and a circuit breaker chamber base plate  39 . In addition, the worker may separate and remove a voltage transformer cradle  61 . 
         [0121]    The worker may separate a metering current transformer bushing  31  from a rear plate  30   a  of a circuit breaker chamber  30  and remove the metering current transformer bushing  31  in a forward direction. Moreover, the worker may separate a metering current transformer  40  from a current transformer mounter  43  and remove the metering current transformer  40  in a forward direction. That is, both the metering current transformer bushing  31  and the metering current transformer  40  may be separated in a forward direction from installed positions thereof. 
         [0122]    When the middle base front surface plate  55   a  and circuit breaker chamber base plate  39  are removed, the circuit breaker chamber  30  is connected with a voltage transformer chamber  60 , and a space through which the worker may enter and exit may be sufficiently ensured in a casing  100 . The worker is able to easily enter the inside of the casing  100  in the front of the casing  100  and easily perform maintenance on each of components in the switchboard. 
         [0123]    When a switchboard applied with a bushing-type current transformer according to an embodiment is provided at a place in which a rear surface space of the switchboard is insufficient or a space between the rear surface of the switchboard and a rear wall is insufficient, a worker may perform maintenance by entering the switchboard through the front surface thereof. 
         [0124]    To this end, a terminal bushing is provided at a bus bar chamber and a cable chamber, and a metering current transformer capable of being separated in a front direction may be provided. In addition, a metering current transformer bushing capable of being separated in a front direction may be provided at a rear plate of a circuit breaker chamber. Moreover, a circuit breaker chamber base plate is made of a module capable of being separated and removed, so that the circuit breaker chamber is connected to a voltage transformer chamber to be opened together when the module is removed. 
         [0125]    Furthermore, a stress control sealed member is inserted into the metering current transformer bushing to be connected to a switchboard terminal. A semi-conductive layer is provided outside the metering current transformer bushing, and a part of the semi-conductive layer is connected to a switchboard frame and earthed, so that a dielectric breakdown phenomenon, the Corona phenomenon, and the like are prevented. 
         [0126]    Still more, a voltage transformer terminal is directly connected to a bus bar through a contacting technique, so that a voltage transformer cradle is easily separated. Here, the voltage transformer terminal is not in contact with a voltage transformer cradle bushing, so that an insulating function is improved. 
         [0127]    Although embodiments have been described with reference to a number of illustrative embodiments thereof, it should be understood that numerous other modifications and embodiments can be devised by those skilled in the art that will fall within the spirit and scope of the principles of this disclosure. More particularly, various variations and modifications are possible in the component parts and/or arrangements of the subject combination arrangement within the scope of the appended claims.