Patent Publication Number: US-9431184-B2

Title: Circuit breaker

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     Pursuant to 35 U.S.C. §119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application Nos. 10-2013-0134330, filed on Nov. 6, 2013 and 10-2013-0134332, filed on Nov. 6, 2013, the contents of which are all hereby incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a circuit breaker, and more particularly, to a circuit breaker, which is capable of enhancing the breaking speed of a fault current. 
     2. Description of the Conventional Art 
     As is well known in the art, a circuit breaker is an electrical device which is installed between a power supply and a load in order to protect load side equipments and electric lines in the event of an abnormal situation such as a fault current (short-circuit, large scale current by a ground fault) which may occur in an electric circuit. 
       FIG. 1  illustrates a circuit breaker in accordance with the conventional art. As shown in  FIG. 1 , the circuit breaker in accordance with the conventional art comprises a vacuum interrupter  10  including a fixed contact  14  and a movable contact  16 , a driving mechanism or a driving unit  20  (hereinafter, referred to as a driving unit  20 ) configured to drive the movable contact  16  of the vacuum interrupter  10  to be brought into contact and separated from the fixed contact  14 , and a power transmission unit  30  disposed between the driving unit  20  and the vacuum interrupter  10  and configured to transmit a driving force of the driving unit  20  to the movable contact  16 . 
     The vacuum interrupter  10  includes a vacuum container  12  for maintaining a vacuum condition therein, the fixed contact  14  disposed within one side of the vacuum container  12 , and the movable contact  16  configured to move between a closing position where it contacts the fixed contact  14  and an opening position (trip position) where it is spaced from the fixed contact  14  within the vacuum container  12 . 
     One of the fixed contact  14  and the movable contact  16  is connected to a main line  17  and the other is connected to a load  18 . 
     The driving unit  20 , though not shown in the drawings specifically, but as is well known in the art, includes a main shaft  22  disposed to be rotatable between the closing position and the opening position, a plurality of springs (for instance, a closing spring and an opening spring, not shown) configured to generate a driving force to cause the main shaft  22  to promptly rotate between the closing position and the opening position, and a plurality of links  24  coupled together to transmit the driving force to the main shaft  24 . 
     An over-current relay (not shown) is provided next to the driving unit  20  which detects a fault current and outputs a trip signal to break a conduction of a large scaled current. 
     A trip mechanism module or a trip unit  40  (hereinafter, referred to as a trip unit) is provided at one side of the driving unit  20 . The trip unit  40  is configured to generate a mechanical operation force and transmit the mechanical operation force to the driving unit  20  when a trip signal is output from the over-current relay. 
     The trip unit  40  includes a trip lever  41  disposed at one side of one of the plurality of links  24  so as to be rotatable between a restricting position where the one of the plurality of links  24  is restricted from being moved toward the trip position, and a releasing position where the one of the plurality of links  24  are allowed to turn to the trip position; and a solenoid  50  configured to rotate the trip lever  41  to the releasing position. 
     The solenoid  50  includes a main body  51  and an operation rod  62  configured to protrude and retract from/into the main body  51 . 
     The main body  51 , though not shown specifically in the drawings, includes a coil that generates a magnetic force when a power is applied thereto, a yoke that forms a magnetic path, a fixed core that forms a magnetic path together with the yoke, a movable core disposed to be brought into contact with and separable from the fixed core, and a restoration spring to return the movable core to its initial position. 
     The operation rod  62  is configured to have one end connected to the movable core and another end protruded to outside of the main body  51 . 
     The power transmission unit  30  includes a driving arm  32  coupled to the main shaft  22  and protruded in a radius direction, a first link  34  connected to the movable contact  16  and configured to move the movable contact  16  between the closing position and the opening position, and a second link  36  having one end connected to the driving arm  32  and another end connected to the first link  34 . 
     Under such a configuration, a power is applied to a coil of the solenoid  50  by an opening signal and a trip signal. Once the power is applied to the coil of the solenoid  50 , a magnetic force is generated and the magnetic force flows through the yoke and the fixed core. At this moment, the movable core moves in a direction that a magnetic resistance becomes smaller. The operational rod  62  is moved to protrude from the main body  51  when a power is applied to the coil of the solenoid  50 . When the operational rod  62  is moved to protrude from the main body, the trip lever  41  is rotated to a releasing position. 
     Once the trip lever  41  is rotated to the releasing position, the main shaft  22  of the driving unit  20  is rotated to an opening position (trip position), and the driving force of the main shaft  22  is transmitted to the movable contact  16  by the power transmission unit  30 , thereby breaking a current flow between the fixed contact  14  and the movable contact  16 . 
     In such a conventional circuit breaker, however, when a trip signal is output according to detection of a fault current by the over-current relay, a power is applied to the coil of the solenoid to generate a magnetic force, and then the operation rod  62  is moved to release the trip lever  41 , thereby requiring a relatively long time to perform such an operation in sequence. Thus, it is difficult to reduce time taken to break a fault current by separating the movable contact  16  from the fixed contact  14  after the over-current relay outputs a trip signal. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a circuit breaker, which is capable of promptly breaking a fault current. 
     Another object of the present invention is to provide a circuit breaker, which is capable of restraining a time delay when transferring a trip signal. 
     It is a further object of the present invention to provide a circuit breaker, which is capable of breaking a fault current within 1.5 cycles after a trip signal is transmitted. 
     It is a still further object of the present invention to provide a circuit breaker, which is capable of restraining generation of an operation delay of a driving unit. 
     To achieve these and other advantages and in accordance with the purpose of this specification, as embodied and broadly described herein, there is provided a circuit breaker, including a vacuum interrupter including a fixed contact and a movable contact; a driving unit including a main shaft rotatable between a closing position where the movable contact contacts the fixed contact and an opening position where the movable contact is separated from the fixed contact, and a plurality of links interlocked with the main shaft, and configured to supply a driving force to open and close the vacuum interrupter; a power transmission unit disposed between the driving unit and the vacuum interrupter and configured to transmit a driving force of the driving unit to the movable contact; an over-current relay configured to detect a fault current and to output a trip signal to break a large-scaled current conduction; a trip unit disposed at one side of the driving unit and configured to generate and transmit a mechanical operation force to the driving unit when a trip signal is output from the over-current relay; and a Thomson drive including a Thomson coil and a repulsive plate configured to be spaced from the Thomson coil by an electromagnetic repulsive force when a power is applied to the Thomson coil, and configured to be connected to the power transmission unit to rotate the main shaft to an opening position by a movement of the repulsive plate when a power is applied to the Thomson coil, or configured to be provided at the trip unit to transmit the trip signal to the trip unit by a movement of the repulsive plate when a power is applied to the Thomson coil. 
     The circuit breaker may further include a control unit configured to apply a power to the Thomson coil when a trip signal is output from the over-current relay; and an unlatch unit disposed at one side of one of the plurality of links and configured to be rotatable between a restricting position where the driving unit is restricted from being rotated to the opening position and a releasing position where the driving unit is rotated from the restricting position so that the driving unit is rotated to the opening position when the main shaft is rotated to the opening position by the Thomson drive 
     The Thomson drive may be connected to the power transmission unit, the trip unit may be disposed at one side of an unlatch unit and configured to rotate the unlatch unit to a releasing position when the opening signal is applied; and. 
     The unlatch unit may include an operation pin configured to contact one of the links; a first trip latch including the operation pin and configured to be rotatable so that the operation pin may be rotated to the restricting position and the releasing position; a first trip latch spring configured to apply an elastic force to the operation pin so as to be in contact with the one of the links; a second trip latch disposed to be relative-rotatable with respect to the first trip latch and having one side contacting the operation pin; and a second trip latch spring having one end supported by the first trip latch and another end elastically supporting the second trip latch in a contacting manner. 
     The trip unit may include a trip lever disposed to contact the second trip latch and configured to restrict the first trip latch and the second trip latch from being rotated to a releasing position; and a solenoid disposed at one side of the trip lever and configured to rotate the trip lever to the releasing position where the first trip latch and the second trip latch are rotatable to the releasing position. 
     The power transmission unit may include a driving arm having one end connected to the main shaft and another end protruded in a radius direction; a first link connected to the movable contact and configured to be rotatable between a closing position where the movable contact contacts the fixed contact and an opening position where the movable contact is spaced from the fixed contact; and 
     a second link having one end connected to the driving arm and another end connected to the first link. 
     The repulsive plate may include a connection rod extended from the Thomson coil in a penetrating manner and connected to the power transmission unit. 
     The connection rod may be connected to a connection region between the first link and the second link. 
     The connection rod may be connected to the first link. 
     The first link may be provided with a compression spring configured to apply an elastic force to the movable contact so as to be in contact with the fixed contact at a predetermined pressure, and the connection rod may be connected to a connection region between the first link and the push rod. 
     The connection rod may be connected to a connection region between the driving arm and the second link 
     The Thomson drive may be provided at the trip unit. The trip unit may include a trip latch disposed to be rotatable between a restricting position where one of the links is restricted to be rotated to the closing position by contacting with the one of the plurality of links that rotate the main shaft to the closing position and a releasing position where the one of the links is allowed to rotate to the closing position; and a trip lever disposed at one side of the trip latch and configured to restrict or release the trip latch to rotate to the releasing position, and the Thomson drive may include a signal transmission actuator. The signal transmission actuator may include a Thomson coil disposed at one side of the trip lever; and a repulsive plate disposed at one side of the Thomson coil and configured to move the trip lever to the releasing position when a power is applied to the Thomson coil. 
     The power transmission unit may include a driving arm connected to the main shaft; a first link disposed at one side of the movable contact and configured to move the movable contact to the closing position and the opening position; and a second link having one end connected to the driving arm and another end connected to the first link. 
     The Thomson drive may further include a Thomson coil disposed at one side of the power transmission unit; and an acceleration actuator including a repulsive plate configured to move the power transmission unit to the opening position by being spaced from the Thomson coil by an electromagnetic repulsive force generated when a power is applied to the Thomson coil. 
     The repulsive plate of the acceleration actuator may include a connection rod passing through and extended from the Thomson coil in a penetrating manner. 
     The connection rod may be connected to one of the connection region between the first link and the second link, the connection region between the driving arm and the second link, and the first link. 
     The first link may be connected to the push rod having one end connected to the movable contact, and the connection rod may be connected to the connection region between the first link and the push rod. 
     The repulsive plate may include an operation rod which is protruded toward the trip lever. 
     The circuit breaker of the present invention may further include a housing configured to accommodate therein the Thomson coil and the repulsive plate. 
     The repulsive plate may include a guide rod which is protruded in a moving direction, and the housing may include a guide slot configured to guide movement of the guide rod. 
     The circuit breaker of the present invention may further include a control unit configured to control that a power to be applied to the Thomson coil when a trip signal is output from the over-current relay, and wherein the control unit may control a power to be applied to the acceleration actuator when a predetermined time passes after a power has been applied to the signal transmission actuator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  illustrates a circuit breaker in accordance with the conventional art; 
         FIG. 2  is a perspective view illustrating a circuit breaker according to an embodiment of the present invention; 
         FIG. 3  is a side view illustrating the circuit breaker of  FIG. 2 ; 
         FIG. 4  is an enlarged view illustrating a driving unit of  FIG. 3 ; 
         FIG. 5  is a block diagram illustrating a control procedure of the circuit breaker of  FIG. 2 ; 
         FIGS. 6 through 8  are views illustrating an operation of an unlatch unit; 
         FIGS. 9 through 12  are views illustrating an operation of a trip unit and the unlatch unit when an opening signal is input; 
         FIGS. 13 and 14  are views illustrating another embodiment of the circuit breaker of  FIG. 2 ; 
         FIG. 15  is an enlarged view illustrating a solenoid of  FIG. 3 ; 
         FIG. 16  is a side view illustrating a circuit breaker according to an embodiment of the present invention; 
         FIG. 17  is an enlarged view illustrating a signal transmission actuator of  FIG. 16 ; 
         FIG. 18  is a view illustrating an operation of the signal transmission actuator of  FIG. 17 ; 
         FIG. 19  is a block diagram illustrating a control procedure of the circuit breaker of  FIG. 16 ; 
         FIG. 20  is a side view illustrating a circuit breaker according to another embodiment of the present invention; 
         FIG. 21  is a block diagram illustrating a control procedure of the circuit breaker of  FIG. 20 ; and 
         FIGS. 22 and 23  are views illustrating another embodiment of an acceleration actuator of  FIG. 20 , respectively. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, a preferred embodiment of a circuit breaker according to the present invention will now be described in detail with reference to the accompanying drawings. 
     As shown in  FIGS. 2 and 3 , a circuit breaker according to an embodiment of the present invention may include a vacuum interrupter  110  including a fixed contact  114  and a movable contact  116 ; a driving unit  130  including a main shaft rotatable between a closing position where the movable contact  116  contacts the fixed contact  114  and an opening position where the movable contact  116  is separated from the fixed contact  114  and a plurality of links  134  interlocked with the main shaft  132 , and configured to supply a driving force to open and close the vacuum interrupter  110 ; a power transmission unit  150  disposed between the driving unit  130  and the vacuum interrupter  110  and configured to transmit a driving force of the driving unit  130  to the movable contact  116 ; a Thomson drive  170  connected to the power transmission unit  150  and configured to rotate the main shaft  132  to the opening position when a power is applied; and an unlatch unit  190  disposed at one side of one of the plurality of links  134  and configured to be rotatable between a restricting position where the driving unit  130  is restricted to rotate to the opening position and a releasing position where the driving unit  130  is rotated from the restricting position so that the driving unit  130  is rotated to the opening position when the main shaft  132  is rotated to the opening position by the Thomson drive  170 . 
     The vacuum interrupters  110  may be disposed to be spaced from each other by phases (e.g., R, S and T phases). 
     In the embodiment of the present invention, it is exemplarily described that three vacuum interrupters  110  are spaced apart from each other in a horizontal direction. 
     Each of the vacuum interrupters  110  may include a vacuum container  112 , a fixed contact  114  disposed within the vacuum container  112 , and a movable contact  116  disposed within the vacuum container  112  to be in contact with and separable from the fixed contact  114 . One of the fixed contact  114  and the movable contact  116  may be connected to a main power line  117  and the other may be connected to a load  118 . 
     A push rod  122  may be extendedly connected to the movable contact  116  in a lengthwise direction. 
     The push rod  122  may be provided with a compression spring  124  that applies an elastic force to the movable contact  116  so as to contact the fixed contact  114  at a predetermined pressure. 
     The driving unit  130 , configured to provide a driving force to move the movable contact  116  toward the fixed contact  114 , may be disposed at one side of the vacuum interrupter  110 . 
     As shown in  FIG. 4 , the driving unit  130  may include a main shaft  132  configured to be rotatable between a closing position where the movable contact  114  contacts the fixed contact  116  and an opening position where the movable contact  116  is separated from the fixed contact  114 , and a plurality of links  134  interlocked with the main shaft  132 . 
     The driving unit  130 , though not shown in the drawings in detail, may include a plurality of springs (for instance, a closing spring and an opening spring) providing an elastic force to rotate the main shaft  132  to the closing position and the opening position, respectively. 
     The power transmission unit  150  may be provided between the driving unit  130  and the vacuum interrupter  110  to transmit the driving force from the driving unit  130  to the movable contact  116 . 
     The power transmission unit  150  may include a driving arm  152  having one end connected to the main shaft  132  and another end protruded in a radius direction; a first link  154  configured to be rotatable between a closing position where the movable contact  116  contacts the fixed contact  114  and an opening position where the movable contact  116  is separated from the fixed contact  114 ; and a second link  156  having one end connected to the driving arm  152  and another end connected to the first link  154 . 
     The first link  154  may be connected to a lower end of the push rod  122  so as to be relatively movable. 
     The first link  154  may be configured to rotate up and down centering around a pivot shaft  155  provided at one end thereof. 
     The Thomson drive  170  may be provided to rotate the main shaft  132  to the opening position. 
     The Thomson drive  170  may include a Thomson coil  172  disposed at a lower side of the power transmission unit  150 ; and a repulsive plate  176  disposed below the Thomson coil  172  and configured to move to be spaced from the Thomson coil  172  by an electromagnetic repulsive force generated when a power is applied to the Thomson coil  172  to rotate the main shaft  132  to an opening position. 
     The Thomson coil  172  and the repulsive plate  176  may be configured to have a delay time of 0.5 milliseconds (ms) until the repulsive plate  175  starts to move upon applying a power to the Thomson coil  172 . Under such a configuration, it is possible to remarkably reduce an operation time (about more than 9.5 ms) when compared with the conventional one in which 10 ms were required to get the operation rod to start to move upon applying a power to the solenoid. 
     The Thomson coil  172  may be configured to have a disk shape. 
     The Thomson coil  172  may have a through-hole  174  at the central portion thereof. 
     The repulsive plate  176  may be configured to have a disk shape. 
     The Thomson drive  170 , as is well known in the art, may be configured in such that an eddy current to generate an electromagnetic repulsive force together with the Thomson coil  172  may be generated by the repulsive plate  176  when a power is applied to the Thomson coil  172 . Under such a configuration, the repulsive plate  176  can be promptly separated from the Thomson coil  172  by the electromagnetic repulsive force generated between the Thomson coil  172  and the repulsive plate  176  when a power is applied to the Thomson coil  172 . 
     The repulsive plate  176  may include a connection rod  177  that penetrates through the Thomson coil  172  to thus be connected to the power transmission unit  150 . 
     As shown in  FIG. 3 , the connection rod  177  may be connected to the first link  154 . 
     More specifically, the connection rod  177  may be relative-movably connected to a connection region between the first link  154  and the push rod  122 . 
     Here, the connection rod  177  may be configured as one or a plurality of parts (rods) connected with each other. 
     The connection rod  177  may be connected to the first link  154  so as to be relative-movable. 
     Here, as shown in  FIG. 13 , the connection rod  177  may be connected to a connection region between the first link  154  and the second link  156 . In this case, the stroke of the repulsive plate  176  may be increased when compared with the embodiment of  FIG. 3 , whereas the output (driving force) can be reduced, thereby reducing electric power consumption. 
     Further, as shown in  FIG. 14 , the connection rod  177  may be connected to a connection region between the driving arm  152  and the second link  156 . In this case, the output and the stroke may be appropriately adjusted. 
     Meanwhile, the driving unit  130  may include an unlatch unit  190  that rotates the main shaft  132  to the opening position when a power is applied to the Thomson drive  170 . 
     The unlatch unit  190  may include an operation pin  192  that contacts the one link  136 ; a first trip latch  194  including the operation pin  192  at one side and configured to be rotatable so that the operation pin  192  may be moved to a restricting position and a releasing position, respectively; a first trip latch spring  197  configured to apply an elastic force to the operation pin  192  to contact the one link  136 ; a second trip latch  201  disposed to be relative-movable with respect to the first trip latch  194  and having one end contacting the operation pin  192 ; and a second trip latch spring  206  having one end supported by the first trip latch  194  and another end elastically supporting the second trip latch  201  in a contacting manner. 
     Here, the one link  136  may be one of the links  134  that are provided at one side of the main shaft  132  and rotate the main shaft  132  to an opening position. 
     An operation pin accommodating recess  137  configured to accommodate therein a part of the operation pin  192  may be formed at an upper portion of the one link  136 . 
     The trip latch  194  may be disposed so as to be rotatable at an upper portion of the one link  136 . 
     The first trip latch spring  197 , configured to apply an elastic force to the operation pin  192  to contact the one link  136 , may be provided at one side of the first trip latch  194 . 
     The first trip latch spring  197  may be implemented as a tension spring. 
     The operation pin  192  may be provided at one side of the pivot shaft  195  of the first trip latch  194 . 
     The second trip latch  201  may be provided at one side of the first trip latch  194  so as to be relative-movable. 
     A pivot shaft  204  of the second trip latch  201  may be provided at the first trip latch  194  so as to be spaced from the pivot shaft  195  of the first trip latch  194  and an upper portion of the operation pin  195 . 
     The second trip latch  201  may include a recess portion  203  recessed in correspondence to the shape of the operation pin  192 . 
     The second trip latch  201  may include a trip lever contact portion  202  which is formed to protrude and configured to contact a trip lever  231  (refer to  FIGS. 11 and 12 ). 
     The second trip latch spring  206  may be provided between the first trip latch  194  and the second trip latch  201  to elastically support the second trip latch  201  toward the first trip latch  194 . 
     The second trip latch spring  206  may be configured such that one end thereof (a lower end in the drawings) is supported by the first latch  194  and another end (an upper end in the drawings) is supported by the second trip latch  201 . 
     The second trip latch spring  201  may be provided in plurality in number. 
     In this embodiment of the present invention, the second trip latch springs  201  are exemplarily shown in two, but may be one or three or more. 
     The first trip latch  194  may include a second trip latch spring support portion  196  to support a lower end of the second trip latch spring  206 . 
     The second trip latch spring support portion  196  may be formed to protrude from the surface of the first trip latch  194  toward the second trip latch  201 . 
     The second trip latch  201  may include a second trip latch spring accommodating portion  205  to accommodate therein and support an upper end of the second latch spring  206 . 
     The second trip latch spring accommodating portion  205  may be formed to be in an upper-recessed manner. 
     The trip unit  230 , configured to rotate the unlatch unit  190  to a releasing position when an opening signal is applied, may be provided at one side of the unlatch unit  190 . 
     The trip unit  230  may include a trip lever  231  that contacts the second trip latch  201  and restrains the first trip latch  194  and the second trip latch  201  from being rotated to the releasing position; and a solenoid  250  disposed at one side of the trip lever  231  and configured to rotate the trip lever  231  to the releasing position where the first trip latch  194  and the second trip latch  201  are rotated to the releasing position. 
     The solenoid  250  may include a main body  251  and an operation rod  262  protruded and retractable from/into the main body  251 . 
     As shown in  FIG. 15 , the main body  251  may include a coil  252  generating a magnetic force upon applying a power thereto, a yoke  254  and a fixed core  256  forming a magnetic path, a movable core  258  disposed to be close to and separable from the fixed core  256 , an operation rod  262  connected to the movable core  256  so as to be movable together with the movable core  256 , and a restoration spring  260  to return the movable core  258  to an initial position. 
     The fixed core  256  and the movable core  258  may be disposed within the coil  252 . 
     The fixed core  256  may include a through-hole through which the operation rod  262  passes. 
     The trip lever  231  may be configured to rotate centering around a pivot shaft  235  provided at one side of the second trip latch  201 . 
     The trip lever  231  may be configured to be rotatable between the restricting position where the second trip latch  201  is restricted from being rotated to the releasing position and the releasing position where the second trip latch  201  is allowed to rotate to the releasing position. 
     A second trip latch contact portion  233  configured to contact the second trip latch  201  may be formed at one side of the trip lever  231 . More specifically, the trip lever contact portion  202  contacts the second trip latch contact portion  231 , so that rotation of the first trip latch  194  to the opening position can be restricted. 
     The trip lever  231  may be configured such that the second trip latch contact portion  233  contacts the second trip latch  201  to restrict rotation of the second trip latch  201  in the restricting position, and the second trip latch contact portion  233  is spaced from the second trip latch  201  to allow rotation of the second trip latch  201  and the first trip latch  194  to the releasing position. 
     A restraining lever  240 , configured to restrain the trip lever  231  from being rotated to the releasing position, may be provided at one side of the trip lever  231 . 
     The restraining lever  240  may be configured to be rotatable between a restricting position where one end of the restraining lever  240  contacts the trip lever  231  to restrain rotation of the trip lever  231  and a releasing position where one end of the restraining lever  240  is spaced from the trip lever  231  to allow rotation of the trip lever  231 . 
     Another end of the restraining lever  240  may be configured to cooperate with the operation rod  262  of the solenoid  250 . 
     The restraining lever  240  may be configured such that one end thereof which has contacted the trip lever  231  is separated from the trip lever  231  when the operation rod  262  of the solenoid  250  is protruded, so that the trip lever  231  may rotate to a releasing position. 
     Here, though not shown in detail in the drawings, the trip lever  231  may be configured to rotate to the releasing position by a trip lever spring. 
     Further, the restraining lever  240  may be configured as a plurality of levers which are coupled to be interlocked with each other. 
     Further, in this embodiment of the present invention, it is exemplarily described that the restraining lever  240  is disposed between the solenoid  250  and the trip lever  231 , but the solenoid  250  may be configured to directly restrain or release the restraint of the trip lever  231 . 
     Meanwhile, the circuit breaker in accordance with this embodiment of the present invention, may include a control unit  270  which contains a control program and is implemented as a microcomputer. 
     As shown in  FIG. 5 , an over-current relay  272 , configured to detect a fault current and output a trip signal to break a large-scaled current conduction, may be connected to the control unit  270  in a communicable manner. 
     The control unit  270  may be configured to apply a power to the Thomson coil  172  when a trip signal is output from the over-current relay  272 . 
     A signal input unit  274 , configured to input a closing signal and/or an opening signal, may be connected to the control unit  270 . 
     The control unit  270  may be configured to control a power to be applied to the solenoid  250  when an opening signal is input. 
     Under such a configuration, when an opening signal is input by the signal input unit  274 , the control unit  270  may control a power to be applied to the coil  252  of the solenoid  250 . 
     When a power is applied to the coil  252  of the solenoid  250 , the operation rod  262  is protruded and thereby the restraining lever  240  is rotated. 
     As the restraining lever  240  rotates, the restraint of the trip lever  231  is released as shown in  FIG. 10 , and the trip lever  231  rotates to a releasing position. 
     By the rotation of the trip lever  231 , the first trip latch  194  is released from the restraint as shown in  FIG. 11 , and rotates counterclockwise centering around the pivot shaft  195 . Thus, the operation pin  192  is spaced from the one link  136 , and the one link  136  may be rotated counterclockwise as shown in  FIG. 12 , since the operation pin  192  is released from the restraint. 
     When the one link  136  is rotated counterclockwise, namely to the breaking position, the main shaft  132  can be rotated to a breaking position. 
     When the main shaft  132  is rotated to the breaking position, the driving arm  152  is rotated clockwise and the second link  156  and the first link  154  can be interlocked with each other. 
     The first link  154  moves the compression spring  124  and the push rod  122  to a breaking position, thereby the movable contact  116  is separated from the fixed contact  114  and is moved downward. By this consecutive movement of the elements, connection of the load  118  and the main power line  117  is released so that power supply to the load  118  can be stopped. 
     When a fault current is detected and a trip signal is output from the over-current relay  272 , the control unit  270  controls the Thomson drive  172  to be driven. 
     When a power is applied to the Thomson coil  272  by the control unit  270 , the repulsive plate  176  can be promptly moved in a direction to be spaced from the Thomson coil  172 . Here, it takes 0.5 ms from detecting a fault current by the over-current relay  272  to initiation of a movement of the repulsive plate  176 . Thus, the breaking time can be remarkably reduced (by 9.5 ms) when compared with the case where it takes 10 ms to initiate the trip operation of the trip lever  231  by the solenoid  250 . 
     More specifically, when a power is applied to the Thomson coil  172  and the repulsive plate  176  is moved to a trip position, the first link  154  can be rotated downward in the drawings. 
     By the rotation of the first link  154 , the second link  156  is moved downward, and thereby the driving arm  152  and the main shaft  132  can be rotated clockwise in the drawings. 
     When the main shaft  132  is rotated to the breaking position, the one link  136  can be rotated counterclockwise centering around the pivot shaft  138 , as shown in  FIG. 6 . 
     As the one of the links  136  rotates counterclockwise, the operation pin  192  is compressed upward as shown in  FIG. 7 , thereby the first trap latch  194  can be rotated counterclockwise centering around the pivot shaft  195 . 
     Here, the second trap latch spring  206  is compressed, and the first trap latch  194  and the second trap latch  201  are continuously rotated centering around the pivot shaft  204 , so that the trap lever contact portion  202  of the second trap latch  201  is moved from the trap lever  231  (substantially, the second trap lever contact portion  233 ) so as to be released from the restraint state by the trip lever  231 . 
     As the first trip latch  194  rotates counterclockwise centering around the pivot shaft  195 , the operation pin  192  is separated from the one link  136 , and the one link  136  is released from the restraint by the operation pin  192  to thus be rotatable to a breaking position. 
     Here, the Thomson drive  170  is provided to promptly release the unlatch unit  190 , and a driving force to substantially drive the movable contact  116  is generated by the driving unit  130  (an elastic force of the breaking spring) and is transmitted to the movable contact  116  by the power transmission unit  150 . 
     When the main shaft  132  is rotated to a breaking position, the driving arm  152  can be rotated clockwise in the drawing. By this operation, the second link  156  can be moved downward and the first link  154  can be rotated downward counterclockwise centering around the pivot shaft  155 . 
     As the first link  154  rotates counterclockwise, the compression spring  124  is elongated and the push rod  122  is moved downward in the drawings. Thus, the movable contact  116  is separated from the fixed contact  114  and then moved downward. As a result, the fault current can be promptly cut-off. 
     As described above in detail, the circuit breaker according to this embodiment of the present invention can complete a fault current cut-off operation within 1.5 cycles (25 ms) upon input of a trip signal by separating the movable contact  116  from the fixed contact  114  to break a fault current when the fault current is detected by the over-current relay  272 . More specifically, the circuit breaker according to this embodiment can complete a fault current cut-off operation within one cycle (16.7 ms) after outputting a trip signal irrespective of the position of the Thomson drive  170 . 
     Hereinafter, another embodiment of the present invention will be described with reference to  FIGS. 16 through 19 . 
     As shown in  FIGS. 16 through 19 , the circuit breaker according to another embodiment of the present invention may include a vacuum interrupter  110  including a fixed contact  114  and a movable contact  116 ; a driving unit  130  including a main shaft  132  configured to be rotatable between a closing position where the movable contact  115  contacts the fixed contact  114  and an opening position where the movable contact  115  is spaced from the fixed contact  114 , and a plurality of links  134  which are coupled to each other so as to rotate the main shaft  132  to the closing position and the opening position, respectively; a trip latch  295  configured to be rotatable between a restricting position where one of the links  134  is restricted to rotate to an opening position by contacting with the one of the links  134  and a releasing position where the one of the links  134  is allowed to rotate to the opening position; a trip lever  231  disposed at one side of the trip latch  295  and configured to restrict or release rotation of the trip latch  295  to the releasing position; and a signal transmission actuator  280  including a Thomson coil  281  disposed at one side of the trip lever  231  and a repulsive plate  291  configured to be separated from the Thomson coil  281  to move the trip lever  231  to the releasing position by an electromagnetic repulsive force generated when a power is applied to the Thomson coil  281 , and configured to transmit the trip signal to the trip lever  231 . 
     The vacuum interrupter  110  may be provided by each phase (for instance, R, S, and P phases) of power. 
     The vacuum interrupter  110  may include a vacuum container  112  maintaining a vacuum condition therein, a fixed contact  114  disposed within the vacuum container  112 , and a movable contact  116  disposed within the vacuum container  112  and configured to be in contact with and separable from the fixed contact  114 . 
     The vacuum interrupter  110  may be configured such that one of the fixed contact  114  and the movable contact  116  is connected to a main power line  117  and the other is connected to a load  118 . Under such a configuration, the vacuum interrupter  110  can control power supply to the load  118  by the movement of the movable contact  116  and restrict conduction of a large-scaled current such as a fault current. 
     A push rod  122  may be connected to the movable contact  116  in a moving direction (lengthwise direction). 
     The push rod  122  may include a compression spring  124  for applying an elastic force to the movable contact  116  to contact the fixed contact  114  with a predetermined pressure. 
     The driving unit  130 , configured to generate a driving force to drive the movable contact  116 , may be disposed at one side of the vacuum interrupter  110 . 
     The driving unit  130  may include a main shaft  132  configured to be rotatable between a closing position where the fixed contact  114  and the movable contact  116  are in contact with each other and an opening position (trip position) where the movable contact  115  is spaced and separated from the fixed contact  114 , and a plurality of links  134  which are coupled to each other to rotate the main shaft  132  to the closing position and the opening position, respectively. Although not shown in the drawings, the driving unit  130  may include a closing spring to apply an elastic force to the main shaft  132  to rotate to the closing position, and an opening spring to apply an elastic force to the main shaft  132  to rotate to the opening position. 
     A power transmission unit  150 , configured to transmit a driving force to the vacuum interrupter  110 , may be provided between the driving unit  130  and the vacuum interrupter  110 . 
     The power transmission unit  150  may include a driving arm  152  having one end connected to the main shaft  132  and another end protruded in a radius direction, a first link  154  connected to the movable contact  116  and configured to be rotatable between the closing position and the opening position, and a second link  156  having one end connected to the driving arm  152  to be relative-movable and another end connected to the first link  154  to be relative-movable. 
     The first link  154  may be configured to rotate centering around a pivot shaft  155  connected thereto. 
     The first link  154  may be connected to the push rod  122  to be relative-movable. Under such a configuration, when the first link  154  rotates to a closing position, the push rod  122  is moved upward in the drawings, and the movable contact  116  is moved to a closing position. When the second link  156  is rotated to an opening position, the push rod  122  is moved downward in the drawings, and the movable contact  116  is movable to an opening position (trip position). 
     Meanwhile, the driving unit  130  may include a trip latch  295  which is configured to be rotatable between a restricting position where one of the plurality of links  134  is restricted to rotate to an opening position and a releasing position where the one of the plurality of links  134  is allowed to rotate to a closing position. 
     The trip latch  295  may be configured to be rotatable centering around a pivot shaft  297 . 
     The trip latch  295  may have a trip latch spring  298  configured to apply an elastic force to the trip latch  295 , at its one end. 
     A trip lever  231 , configured to restrict or release a rotation of the trip latch  295  to a releasing position, may be provided at one side of the trip latch  295 . 
     The trip latch  295  may include a trip lever contact portion  296 , at its one end, configured to contact the trip lever  231 . 
     The trip lever  231  may be configured to rotate centering around a pivot shaft  235  which is provided at one end thereof. 
     The trip lever  231  may include a trip latch contact portion  2237 , at its one end, configured to contact the trip latch  295 . 
     The trip lever  231  may include, at one side thereof, a cut-out portion  238  formed along a rotation direction of the trip latch contact portion  296 . 
     The cut-out portion  238  may be configured out of a rotational range of the trip lever contact portion  296 . Under such a configuration, restriction of the trip latch  295  can be released. 
     The cut-out portion  238  may be formed to correspond to a releasing position of the trip lever  231 . 
     More specifically, the trip lever  231  may be configured such that the trip latch contacting portion  237  contacts the trip lever contacting portion  296  to restrict the trip latch  295  from rotating to an opening position in a restricting position, and the cut-out portion  238  is rotated toward the trip lever contacting portion  296  to release the restriction of the trip latch  295  so that the trip latch  295  may be rotated to an opening position. 
     Meanwhile, a signal transmission actuator  280 , configured to transmit a trip signal to the trip lever  231 , may be disposed at one side of the trip lever  231 . 
     The signal transmission actuator  280  may include a Thomson coil  281  disposed at one side of the trip lever  231 , and a repulsive plate  291  configured to be separated from the Thomson coil  281  by an electromagnetic repulsive force generated when a power is applied thereto, and to move the trip lever  231  to the releasing position. 
     The signal transmission actuator  280  is a type of Thomson drive including the Thomson coil  281  and the repulsive plate  291 , which scarcely has a time delay (for instance, 0.5 ms) from power input to completion of the operation. The repulsive plate  291 , as described above, may be configured such that an eddy current may be generated for an electromagnetic repulsive force with respect to the Thomson coil  281  when a power is applied to the Thomson coil  281 . 
     The signal transmission actuator  280  may include a housing  301  having an accommodating space to accommodate therein the Thomson coil  281  and the repulsive plate  291 . 
     The Thomson coil  281  may be configured to have a through-hole  283  at a central portion thereof in a disk shape. 
     The repulsive plate  291  may include a repulsive plate body  292  of a disk shape, and an operation rod  293  protruded from the repulsive plate  292  in a moving direction. 
     The operation rod  293  may be configured to protrude toward the trip lever  231  and to press the trip lever  231  toward the releasing position. 
     The housing  301  may include a through-hole  302  through which the operation rod  293  passes. 
     The repulsive plate  291  may include a guide rod  294  protruded toward a moving direction. 
     The guide rod  294  may be provided to protrude in an opposite direction to the operation rod  293 . 
     The housing  301  may include a guide slot  303  configured to accommodate therein the guide rod  294  to be relative-movable and to guide movement of the guide rod  294 . 
     Meanwhile, the circuit breaker according to this embodiment of the present invention may include a control unit  270  containing a control program and implemented as a microprocessor. 
     As shown in  FIG. 19 , an over-current relay  272 , configured to detect a fault current and output a trip signal to break a large-scaled current conduction, may be connected to the control unit  279 . 
     The control unit  270  may be configured to control a power to be applied to the Thomson coil  281  so that the repulsive plate  291  may be operated, when a trip signal is output from the over-current relay  272 . 
     A signal input unit  274 , configured to input a closing signal and/or an opening signal, may be connected to the control unit  270 . 
     The control unit  270  may be configured to control a power to be applied to the signal transmission actuator  280 , when an opening signal is input from the signal input unit  274 . 
     Under such a configuration, when a trip signal is output from the over-current relay  272 , the control unit  270  may control a power to be applied to the signal transmission actuator  280 . 
     When a power is applied to the Thomson coil  281  of the signal transmission actuator  280 , the repulsive plate  291  may be promptly moved so as to be spaced from the Thomson coil  281 , as shown in  FIG. 18 . 
     As the repulsive plate  291  moves, the operation rod  293  which is protruded toward the trip lever  231  presses the trip lever  231  so as to be rotated to a releasing position. 
     When the trip lever  231  is rotated to the releasing position, the cut-out portion  238  of the trip lever  231  turns toward the trip latch  295  so that the restriction of the trip latch  295  may be released. Thus, the one of the links  134  and the main shaft  132  may be rotated to a releasing position. 
     When the main shaft  132  is rotated to an opening position, a driving force of the driving unit  130  may be transmitted to the push rod  122  and the movable contact  116  via the driving arm  152 , the second link  156  and the first link  154 . 
     As described above in detail, the circuit breaker according to this embodiment of the present invention is capable of remarkably reducing breaking time (within 2 ms) taken to release the trip lever  231  by the signal transmission actuator  280 , after output of a trip signal from the over-current relay  272 . That is, it is possible to reduce more than 3 ms when compared with the conventional one which requires more than 5 ms until the trip lever  231  is released by the solenoid. 
     Hereinafter, another embodiment of the present invention will be described with reference to  FIGS. 20 through 23 . 
     For the sake of brief description with reference to the drawings, the same or equivalent components may be provided with the same or similar reference numbers, and description thereof will not be repeated. 
     As shown in  FIGS. 20 and 21 , a circuit breaker according to this embodiment of the present invention, may include a vacuum interrupter  110  including a fixed contact  114  and a movable contact  116 ; a driving unit  130  including a main shaft  132  rotatable between a closing position where the movable contact  116  contacts the fixed contact  114  and an opening position where the movable contact  116  is separated from the fixed contact  114   a , and a plurality of springs and links  134  coupled with each other so as to rotate the main shaft  132  to the closing position and the opening position, respectively; a power transmission unit  150  disposed between the driving unit  130  and the vacuum interrupter  110  to transmit a driving force of the driving unit  130  to the movable contact  116 ; an over-current relay  272  configured to detect a fault current and output a trip signal to break a large-scaled current conduction; a trip unit  230  disposed at one side of the driving unit  130  and configured to generate and transmit a mechanical operation force to the trip unit  230  when a trip signal is output from the over-current relay  272 ; and a Thomson drive  170  including Thomson coils  172  and  281 , and repulsive plates  176  and  291  configured to be spaced from the Thomson coils  172  and  281  by an electromagnetic repulsive force generated when a power is applied to the Thomson coils  172  and  281 , and connected to the power transmission unit  150  to rotate the main shaft  132  to an opening position by a movement of the repulsive plate  176  when a power is applied to the Thomson coil  172 , or disposed at the trip unit  230  to transmit the trip signal to the trip unit  230  by an electromagnetic repulsive force generated when a power is applied to the Thomson coils  172  and  281 . 
     The Thomson drive  170  may include one or both of an acceleration actuator  171  and a signal transmission actuator  280 . The acceleration actuator  171  includes the Thomson coil  172 , and a repulsive plate  176  configured to rotate the main shaft  172  to a releasing position by an electromagnetic repulsive force generated when a power is applied to the Thomson coil  172 . The signal transmission actuator  280  includes the Thomson coil  281 , and a repulsive plate  291  configured to transmit a trip signal to the trip unit  230  by an electromagnetic force generated when a power is applied to the Thomson coil  281 . 
     The power transmission unit  150 , configured to transmit a driving force of the driving unit  130  to the vacuum interrupter  110 , may be provided at one side of the driving unit  130 . 
     The power transmission unit  150  may include a driving arm  152 , a first link  154  and a second link  156 . 
     A trip unit  230  may be provided at one side of the driving unit  230 . 
     The trip unit  230  may include a trip latch  295  disposed to be rotatable between a restricting position where one of the plurality of links  134  is restricted to move to the restricting position by contacting with the main shaft  132  and a releasing position where the one of the links  134  is allowed to rotate to the opening position; a trip lever  231  disposed at one side of the trip latch  231  and configured to restrict or release the rotation of the trip latch  194  to the releasing position; a signal transmission actuator  280  including a Thomson coil  281  disposed at one side of the trip lever  231 , and a repulsive plate  291  configured to move the trip lever  231  to the releasing position while being spaced from the Thomson coil  281  by an electromagnetic force generated when a power is applied to the Thomson coil  281 , and configured to transmit a trip signal to the trip lever  231 . 
     The trip latch  295  may be provided at one side of the one of the links  134  of the driving unit  130 . 
     The trip lever  231 , configured to restrict or release rotation of the trip latch  295  to the opening position, may be provided at one side of the trip latch  295 . 
     The signal transmission actuator  280  may be provided at one side of the trip lever  231 . 
     The signal transmission actuator  280  may include the Thomson coil  281 , the repulsive plate  291  and the housing  301 . 
     The repulsive plate  291  may include an operation rod  293  and a guide rod  294 . 
     The housing  302  may include a guide slot  303  configured to guide the guide rod  294 . 
     Meanwhile, the circuit breaker according to this embodiment of the present invention may include the acceleration actuator  171  including the Thomson coil  172  disposed at one side of the power transmission unit  150 ; and the repulsive plate  176  configured to be spaced from the Thomson coil  172  by an electromagnetic repulsive force generated when a power is applied to the Thomson coil  172  and allow the driving unit  150  to promptly move to the opening position. 
     Here, the acceleration actuator  171  may include the Thomson coil  172  and the repulsive plate  176 , and the repulsive plate  176  is promptly moved to be spaced from the Thomson coil  172  by an electromagnetic repulsive force generated when a power is applied to the Thomson coil  172 , so that time delay (for instance, 0.5 ms) scarcely occurs from the application of power to the completion of operation. 
     The Thomson coil  172  may be configured to have a through-hole  174  at it central portion in a disk shape. 
     The Thomson coil  172  may be disposed at a lower portion of the first link  154 . 
     The repulsive plate  176  may include the repulsive plate body  178  and the connection rod  177  protruded from the repulsive plate body  178 . 
     The connection rod  177  may be configured to be connected to the first link  154 . 
     For instance, the connection rod  177  may be connected to a connection region between the first link  154  and the push rod  122 . 
     The connection rod  177 , as shown in  FIG. 22 , may be connected to a connection region between the first link  154  and the second link  156 . 
     More specifically, the Thomson coil  172  may be disposed at a lower portion of the second link  156  along the moving direction, and the repulsive plate  176  may be disposed at a lower portion of the Thomson coil  172 . The connection rod  177  of the repulsive plate  176  may be connected to a connection region between the first link  154  and the second link  156  in a relative-movable manner after passing through the through-hole  174  of the Thomson coil  172 . 
     Further, the connection rod  177 , as shown in  FIG. 23 , may be connected to a connection section between the driving arm  152  and the second link  156 . 
     More specifically, the Thomson coil  172  may be disposed at an upper portion to the second link  156  along a moving direction thereof, and the repulsive plate  176  may be disposed at an upper portion of the Thomson coil  172 . The connection rod  177  of the repulsive plate  176  may be connected to a connection region between the driving arm  152  and the second link  156  in a rotatable manner after passing through the through-hole  174  of the Thomson coil  172 . 
     Meanwhile, the circuit breaker according to this embodiment of the present invention may include a control unit  270 , as shown in  FIG. 21 . 
     The over-current relay  272 , configured to detect a fault current and to output a trip signal to break a large-scaled current conduction, may be connected to the control unit  270  in a communicable manner. 
     A signal input unit  274 , configured to input an opening signal of the vacuum interrupter  110 , may be connected to the control unit  270  in a communicable manner. 
     The control unit  270  may be configured to control a power to be applied to the signal transmission actuator  280  when a trip signal is output from the over-current relay  272  and/or when an opening signal is input by the signal input unit  274 . 
     The control unit  270  may be configured to control a power to be applied to the acceleration actuator  171  when a trip signal is output by the over-current relay  272 . 
     The control unit  270  may be configured to control such that a power may be applied to the acceleration actuator  171  when the trip lever  231  is rotated to the releasing position after the trip signal has been output. 
     The control unit  270  may be configured to control a power to be applied to the acceleration actuator  171  when a predetermined time elapses after a trip signal has been output from the over-current relay  272 . 
     More specifically, for instance, the control unit  270  may be configured to control a power to be applied to the acceleration actuator  171  when 1.5˜2.5 ms elapses after a trip signal has been output from the over-current relay  272 . Thus, the main shaft  132  is first rotated to the opening position before releasing of the trip lever  231  so that relatively-movable elements (for instance, the main shaft  132 , the trip lever  231 , and the trip latch  295 ) may be protected from damage. 
     Under such a configuration, when a trip signal is output from the over-current relay  272 , the control unit  270  controls a power to be applied to the signal transmission actuator  280 . 
     When a power is applied to the Thomson coil  281  of the signal transmission actuator  280 , the repulsive plate  291  may be promptly moved so as to be spaced from the Thomson coil  281 . 
     As the repulsive plate  291  moves, the operation rod  293  which is protruded toward the trip lever  231  presses the trip lever  231  so that the trip lever  231  can be rotated to a releasing position. 
     Once the trip lever  231  is rotated to a releasing position, the cut-out portion  238  of the trip lever  231  turns toward the trip latch  295  so that the restriction of the trip latch  295  may be released. Thus, the one of the links  134  and the main shaft  231  may be rotated to a restricting position. 
     Meanwhile, the control unit  270  may control a power to be applied to the acceleration actuator  171  after the trip lever  231  has been rotated to the releasing position and a predetermined time (for instance, 1.5˜2.5 ms) has elapsed. 
     When a power is applied to the Thomson coil  172  of the acceleration actuator  171 , the repulsive plate  176  of the acceleration actuator  171  may be promptly moved so as to be spaced from the Thomson coil  172 . 
     As the repulsive plate  176  is moved, the first link  154 , the second link  156 , the driving arm  152 , and the main shaft  132 , which are connected to one another for interlocking, may be operated to promptly turn to the opening position. 
     As the first link  154  is rotated to the opening position, the push rod  122  is moved downward, and thus the movable contact  116  may be promptly separated to be spaced from the fixed contact  114 . 
     As described above in detail, the circuit breaker according to this embodiment of the present invention is capable of remarkably reducing breaking time (within 2 ms) more than 3 ms taken to release the trip lever  231  by the signal actuator  280 , after output of a trip signal from the over-current relay  272 , when compared with the conventional method in which more than 5 ms are required to release the trip lever  231  by the solenoid. 
     Further, in the conventional art, more than about 5 ms time delay is generated to rotate the main shaft  132  to the opening position by a driving force of the driving unit  130 , that is, an elastic force of the opening spring and the compression spring  124 , whereas the circuit breaker according to this embodiment of the present invention can reduce the time delay approximately by more than 3 ms since it is possible to rotate the main shaft  132  to the closing position by the acceleration actuator  171  within 2 ms. 
     As described above in detail, according to this embodiment of the present invention, the main shaft can be promptly rotated to the opening position by the interaction between the Thomson drive and the unlatch unit so that a fault current can be promptly cut-off within 1.5 cycles after output of a trip signal. 
     Further, by providing the signal transmission actuator including the Thomson coil and the repulsive plate, time delay is restricted by an electromagnetic repulsive force when a power is applied. Thus, a signal is promptly transmitted, thereby promptly breaking a fault current. 
     Further, by providing the signal transmission actuator including the Thomson coil and the repulsive plate, the main shaft and the power transmission unit are promptly moved to the breaking position by the acceleration actuator at the initial stage of the rotation to the breaking position of the main shaft. Thus, generation of time delay by the operation of the elastic force of the opening spring may be restrained, thereby promptly breaking a fault current. 
     Further, since a power is applied to the acceleration actuator after a power has been applied to the signal transmission actuator and a predetermined time has elapsed, a damage of the elements due to the driving force of the acceleration actuator can be restrained. 
     As the present features may be embodied in several forms without departing from the characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, unless otherwise specified, but rather should be construed broadly within its scope as defined in the appended claims, and therefore all changes and modifications that fall within the metes and bounds of the claims, or equivalents of such metes and bounds are therefore intended to be embraced by the appended claims.