Patent Publication Number: US-10770248-B2

Title: Molded case circuit breaker

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Pursuant to 35 U.S.C. § 119(a), this application claims the benefit of earlier filing date and right of priority to Korean Application No. 10-2018-0054443, filed on May 11, 2018, the contents of which is incorporated by reference herein in its entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present disclosure relates to a molded case circuit breaker, and more particularly, to a contact unit of a molded case circuit breaker. 
     2. Description of the Conventional Art 
     In general, a molded case circuit breaker (MCCB) is an electric device that automatically shuts off a circuit during an overload condition or a short-circuit accident to protect the circuit and load. 
     The molded case circuit breaker includes a terminal unit capable of being connected to a power source or a load, a contact unit including a fixed contact and a movable contact brought into contact with or separated from the fixed contact to connect or disconnect a circuit, a switching mechanism that moves the movable contact to provide power required for the switching of the circuit, a trip unit that senses an overcurrent or a short-circuit current flowing on the circuit to induce a trip operation of the switching mechanism, and an arc-extinguishing unit for extinguishing an arc generated when an abnormal current is interrupted, and the like. 
       FIG. 1  illustrates an internal structural view of a molded case circuit breaker according to the related art. A molded case circuit breaker according to the related art includes a fixed contact  1  and a movable contact  2  constituting a contact unit provided to connect or disconnect a circuit transmitted from a power source side to a load side within a case  9  formed of an insulating material, a switching mechanism unit  4  that provides power capable of rotating the movable contact  2 , an arc-extinguishing unit  3  provided to extinguish an arc generated when a fault current is interrupted, and a trip unit  5  that detects an abnormal current to trip the switching mechanism, and the like. 
     When a fault current flows in the circuit, a trip operation is carried out to separate the movable contact  2  from the fixed contact  1  to disconnect the flow of the current, and an arc is generated between the contactors  1 ,  2 . At this time, the magnitude (intensity) of the arc is proportional to the magnitude of the current. An arc is a discharge in which gas in the air instantaneously reaches a plasma state by a voltage, and the arc center temperature reaches 8,000-12,000° C. and has an explosive expansion pressure. As a result, it has characteristics in that the contactors  1 ,  2  are melted and consumed, and neighboring parts are deteriorated and destroyed, and thus the continuity or non-continuity of the arc greatly affects the performance and durability of the circuit breaker. Therefore, the arc must be quickly interrupted, extinguished and discharged from the arc-extinguishing unit  3 . 
     In this manner, in a molded case circuit breaker, an operation of processing an arc is a main purpose in interrupting a fault current to protect a product, a load and a line and directly affects the performance of the circuit breaker. 
       FIGS. 2 and 3  illustrate a base assembly of a molded case circuit breaker according to the related art. The base assembly includes a contact unit and an arc-extinguishing unit.  FIG. 2  shows a conduction state, and  FIG. 3  shows an interruption state. 
     The movable contact  2  is coupled to a shaft  6  rotated by receiving a force of the switching mechanism unit  4  to rotate, and a contact unit at which a fixed contact of the fixed contact  1  and a movable contact of the movable contact  2  are brought into contact with each other is disposed inside a lateral plate of the arc-extinguishing unit  3 . 
     An arc-extinguishing device mainly used in the arc-extinguishing unit  3  of the circuit breaker is a cold cathode type extinguishing chamber using a metal plate. The arc-extinguishing unit  3  is formed by vertically arranging grids  3   b  made of metal plates having a V-shaped groove between a pair of lateral plates  3   a  typically spaced apart from each other at appropriate intervals. When the contactors  1 ,  2  are open to generate an arc (A) during interruption, the arc moves from the lateral plates  3   a  to the grids  3   b . The arc is cooled by the grids  3   b  and divided into short arcs between the respective grids  3   b  to increase the arc voltage and reduce the current. Furthermore, a case internal pressure rises due to extinguishable gas generated in an insulating plate (not shown) constituting the arc-extinguishing unit  3  to compress the arc to a high pressure and suppress the release of free electrons, thereby rapidly extinguishing the arc (A) and restoring the gap voltage. 
     As described above, the molded case circuit breaker according to the related art induces, extends and cools an arc (A) generated between the fixed contact and the movable contact to the grids  3   b  during an interruption operation due to the occurrence of a fault current to extinguish the arc, and such a sequential opening mechanism provides a possibility that the movable contact and the fixed contact are exposed to the arc for a long time during an arc interruption operation to cause damage and destroy insulation around the shaft. As a result, interruption performance may decrease to cause a temperature rise. 
     SUMMARY OF THE INVENTION 
     The present disclosure has been made to solve the above-mentioned problems, and an object of the present disclosure is to provide a molded case circuit breaker for effectively extinguishing an arc generated at a contact unit during interruption. 
     Another object of the present disclosure is to provide a molded case circuit breaker for improving insulation performance around a shaft assembly. 
     A molded case circuit breaker according to an embodiment of the present disclosure may include a fixed contact; a movable contact rotatably provided on a shaft body to be brought into contact with or separated from the fixed contact; and an insulating barrier that enters between the fixed contact and the movable contact during interruption, wherein the insulating barrier is coupled to the movable contact to rotate along a circumferential surface of a shaft body. 
     Here, an end portion of the insulating barrier may be coupled to the movable contact and the other end portion thereof may form a free end. 
     Furthermore, a guide portion that guides the other end portion of the insulating barrier may be protruded on part of a base mold provided with the shaft body. 
     Furthermore, the guide portion may include a pair of protrusion portions spaced apart from each other. 
     Furthermore a fitting groove may be formed on a rear surface of the movable contact, and one end portion of the insulating barrier may be fitted and coupled to the fitting groove by a fixing pin. 
     Furthermore, the insulating barrier may be formed of a flexible material and disposed in a shape of surrounding an outer circumferential surface of the shaft body. 
     Furthermore, a circumferential groove-shaped plate groove may be formed on the shaft body, and a contact plate sliding along the plate groove may be provided in the plate groove. 
     Furthermore, the plate groove may be formed smaller than a radius of an outer circumferential surface of the shaft body. 
     Furthermore, an elastic member providing an elastic force in a direction in which the contact plate is brought into contact with the movable contact may be provided in a pin insertion groove of the shaft body. 
     Furthermore, the insulating barrier may include a cover portion covering an opening portion of the shaft body and an arc interrupting portion extended to one end of the cover portion. 
     In addition, a mover insertion hole into which the movable contact can be inserted may be formed on the cover portion. 
     According to a molded case circuit breaker according to an embodiment of the present disclosure, when a fault current is interrupted, an insulating barrier may enter between the fixed contact and the movable contact to cut off an arc in advance. As a result, the arc transferred to the arc-extinguishing unit is reduced to rapidly perform an arc interruption operation and reduce damage to neighboring parts. 
     Furthermore, the insulating barrier is coupled to the movable contact to operate together with the movable contact, and thus applied not only to general fault current interruption but also to cold current interruption. 
     In addition, the insulating barrier covers an opening portion of the shaft assembly, and thus insulating performance to an inside of the shaft assembly is improved. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       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 embodiments of the invention and together with the description serve to explain the principles of the invention. 
       In the drawings: 
         FIG. 1  is an internal structural view illustrating a molded case circuit breaker according to the related art; 
         FIGS. 2 and 3  are internal structural views illustrating a base assembly of a molded case circuit breaker according to the related art, wherein  FIG. 2  shows a conduction state, and  FIG. 3  shows an interruption state; 
         FIG. 4  is an internal structural view illustrating a molded case circuit breaker according to an embodiment of the present disclosure; 
         FIG. 5  is a perspective view of a shaft assembly in  FIG. 4 ; 
         FIGS. 6 through 8  are perspective views of a base assembly of a molded case circuit breaker according to an embodiment of the present disclosure, in which an interruption process is shown, wherein  FIGS. 6 through 8  show a conduction state, an interruption operation progress state, and an interruption complete state, respectively; 
         FIG. 9  is a perspective view of a base assembly of a molded case circuit breaker according to an embodiment of the present disclosure, in which a cold current interruption state is shown; 
         FIG. 10  is a perspective view illustrating a shaft assembly of a molded case circuit breaker according to another embodiment of the present disclosure; 
         FIGS. 11 and 12  are perspective views illustrating a shaft assembly of a molded case circuit breaker according to still another embodiment of the present disclosure, wherein  FIG. 12  illustrates a state in which an insulating barrier is separated in  FIG. 11 ; 
         FIGS. 13 and 14  show an interruption operation during cold current interruption in the embodiment of  FIG. 10 , wherein  FIG. 13  shows a conduction state, and  FIG. 14  shows an interruption state; and 
         FIG. 15  is a cross-sectional view illustrating an insulating barrier according to still another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Hereinafter, preferred embodiments of the present disclosure will be described with reference to the accompanying drawings, which are intended to describe the present disclosure in detail to allow a person skilled in the art to easily carry out the invention, but not to mean that the technical concept and scope of the present disclosure are limited thereto. 
     A molded case circuit breaker according to each embodiment of the present disclosure will be described in detail with reference to the drawings. 
       FIG. 4  is an internal structural view illustrating a molded case circuit breaker according to an embodiment of the present disclosure, and  FIG. 5  is a perspective view of a shaft assembly in  FIG. 4 .  FIGS. 6 through 8  are perspective views of a base assembly of a molded case circuit breaker according to an embodiment of the present disclosure, in which an interruption process is shown.  FIGS. 6 through 8  show a conduction state, an interruption operation progress state, and an interruption complete state, respectively. 
     A molded case circuit breaker according to an embodiment of the present disclosure includes fixed contacts  120 ,  121 ; a movable contact  140  rotatably provided on a shaft body  131  to be brought into contact with or separated from the fixed contacts  120 ,  121 ; and an insulating barrier  150  entering between the fixed contacts  120 ,  121  and the movable contact  140  during interruption, and the insulating barrier  150  is coupled to the movable contact rotate along a circumferential surface of the shaft body  131 . 
     First, the molded case circuit breaker  100  in a first embodiment will be described. 
     A case  101  accommodates and supports the components of the molded case circuit breaker. The case  101  is formed in a substantially box shape. A handle  103  is exposed on an upper surface of the case  101 . The handle  103  operates a switching mechanism  102  by a user&#39;s manual operation force. 
     Terminal portions  108 ,  109  capable of being connected to a power source or a load are provided on front and rear surfaces of the case  101 . The terminal portions  108 ,  109  are provided for each phase (or for each pole). For example, in the case of a three-phase four-pole molded case circuit breaker, four terminal portions may be provided on the power source side and the load side, respectively. 
     Fixed contacts  120 ,  121  are fixedly provided inside the case  101 . The fixed contacts  120 ,  121  are connected to the terminal portions  108 ,  109 , respectively. In the case of a double molded case circuit breaker, the fixed contacts  120 ,  121  are provided on a power source side and a load side thereof, respectively. In other words, a power source side fixed contact  120  and a load side fixed contact tip  121  are provided. At this time, the power source side fixed contact  120  may be directly connected to or integrally formed with the power source side terminal portion  108 . The load side fixed contact tip  121  may be connected to the load side terminal portion  109  through a trip mechanism (particularly, a heater  111 ). 
     In the vicinity of the contact unit (fixed contact and movable contact), an arc-extinguishing unit (arc-extinguishing device)  105  is provided to extinguish an arc generated during interruption. In the case of a double molded case circuit breaker (double circuit breaker), the arc-extinguishing units  105  are provided on a power source side and a load side thereof, respectively. The arc-extinguishing unit  105  may be configured with a pair of side walls  105   a  and a plurality of grids  105   b  coupled to the side walls  105   a  at predetermined intervals. 
     A trip unit  110  that detects an abnormal current flowing through a circuit and tripping the switching mechanism is provided in a part of the case  101 . The trip portion  110  is usually provided on the load side. The trip unit  110  may include a heater  111  connected to the load side terminal unit  109 , a bimetal  112  coupled to the heater  111  to sense heat so as to be bent according to the amount of heat, a magnet and an amateur  114  provided around the heater  111 , a crossbar  115  provided to rotate by the contact of the bimetal  112  and the armature  113 , and a shooter  116  restrained or released by the rotation of the crossbar  115  to restrain or release a nail (not shown) of the switching mechanism  102 . Typically, the bimetal  112  is bent by heat generated from the heater  111  to rotate the crossbar  115  so as to operate the switching mechanism  102  during small current delay interruption, and the crossbar  115  rotates while the armature  114  is sucked by a magnetic force excited in the magnet  113  to operate the switching mechanism  102  during a large current during large current instant interruption. 
     The user&#39;s operation force is transferred to the switching mechanism  102  through the handle  103 . A pair of rotation pins  104  are provided on the switching mechanism  102  to transfer the power of the switching mechanism  102  to each phase. The rotation pin  104  is formed to have a length across all phases and provided in the shaft assembly (or mover assembly)  130 . 
     The shaft assembly  130  is provided. The shaft assembly  130  is provided with a rotation pin  104  passing therethrough. The shaft assembly  130  receives the switching power of the switching mechanism  102  by the rotation pin  104  to rotate. As the shaft assembly  130  rotates, the movable contact  140  also rotates to be brought into contact with or separated from the fixed contacts  120 ,  121 . 
     The shaft assembly  130  includes a shaft body  131 , a movable contact  140 , a shaft pin  165 , a spring  160 , a shaft insulating plate  137 , and an insulating barrier  150 . 
     The shaft body  131  is formed in a cylindrical shape. A shaft  132  is protruded on both flat side surfaces (disk surfaces) of the shaft body  131 . An opening portion  133  is formed through the shaft body  131  in a direction perpendicular to the direction of the shaft  132 . A pin mounting groove  134  into which the shaft pin  165  can be inserted and fixed is formed on an inner wall of the shaft body  131 . A mover seating groove  135  in which the movable contact  140  is inserted and seated in a normal state is formed at one side of the opening  133  A pair of pinholes  136  through which the rotation pin  104  can be inserted are formed in the shaft body  131  in parallel to a direction of the shaft  132 . 
     The movable contact  140  is inserted into the opening  133  of the shaft body  131 . The movable contact  140  is brought into contact with or separated from the fixed contacts  120 ,  121  while rotating with the shaft body  131  or independently in a counterclockwise or clockwise direction to conduct or cut off the line. 
     Movable contact tip  141  that can be brought into contact with the fixed contact tips  122 ,  123  of the fixed contacts  120 ,  121 , respectively, are provided at both end portions of the movable contact  140 . The Movable contact tip  141  may be made of a conductive and durable material such as a chrome-copper (Cr—Cu) alloy. 
     A fixing protrusion  142  capable of hanging one end of the spring  160  is protruded on a side surface of the movable contact  140 . One end of the spring  160  is fixed to the fixing protrusion  142 , and thus the movable contact  140  is subjected to a force that rotates in a counterclockwise direction in the drawing. Accordingly, the movable contact  140  maintains the state of being inserted into the mover seating groove  135  of the shaft body  131  by an elastic force of the spring  160 , unless an external force acts on the movable contact  140 . 
     The movable contact  140  rotates together with the shaft body  131  in the case of a general small current or large current interruption situation, but the movable contact  140  rotates independently by a sudden electromagnetic repulsion force during cold current interruption. In this case, the movable contact  140  comes into contact with the shaft pin  165  of the opening portion  133  to stop the rotation. An engaging groove (not shown) that can be brought into contact with the shaft pin  165  may be formed on a rear surface of the movable contact  140 . 
     A fitting groove  145  capable of fixing the insulating barrier  150  is formed on a rear surface of the movable contact  140 . 
     The rotation of the movable contact  140  may be divided into three cases. A first case is a case where the user operates the handle  103  to allow the switching mechanism  102  connected to the handle  103  to rotate the shaft assembly  130  (refer to  FIGS. 6 through 8 ) so that the movable contact  140  rotates together with the shaft body  131 . In other words, the movable contact  140  is restrained by a force of the spring  160  to move together with the shaft body  131 . In other words, in this case, the shaft assembly  130  moves the movable contact  140  and the shaft body  131  together. 
     A second case is a case where the operation of the trip unit  110  according to the detection of a fault current releases the restraint to the switching mechanism  102  so that the movable contact  140  rotates. while the shaft assembly  130  rotates (similarly, refer to  FIGS. 6 through 8 ). Even at this time, the movable contact  140  is restrained by a force of the spring  160  to move together with the shaft body  131 . 
     A third case is a case where when a large fault current such as a short-circuit current is generated, the movable contact  140  is separated from the fixed contacts  120 ,  121  and rotated by an electromagnetic repulsive force (so-called cold current interruption). At this time, the movable contact  140  rotates independently of the shaft body  131  in a separate manner. The movable contact  140  moves within the opening portion  133  of the shaft body  131 . When the movable contact  140  moves in a clockwise direction against an elastic force of the spring  160  due to a strong electromagnetic repulsive force,  120 ,  121 , the movable contact  140  moves out of the mover seat groove  135  and the movable contact  140  is separated from the fixed contact  140 . The movable contact  140  is separated from the fixed contacts  120 ,  121  and the movable contact  140  is fixed in contact with the shaft pin  165 . In other words, in this case (in the case of cold current interruption), in the shaft assembly  130  only the movable contact  140  independently moves while the shaft body  131  does not rotate. 
     The insulating barrier  150  is coupled to the movable contact  140 . The insulating barrier  150  is coupled to a rear surface of the movable contact  140 . One end of the insulating barrier  150  is coupled to a rear surface of the movable contact  140 , and the other end thereof forms a free end with no restraint. 
     The manner in which the insulating barrier  150  is coupled to the movable contact  140  may be achieved by a variety of known coupling methods such as bonding, welding, fitting coupling, and pin coupling. In the present embodiment, the insulating barrier  150  is pin-coupled to a rear surface of the movable contact  140  as an example. A state is illustrated in which a fitting groove  145  is formed on a rear surface of the movable contact  140 , and one end portion of the insulating barrier  150  is fitted and coupled to the fitting groove  145  by a fixing pin  166 . 
     Here, the fitting groove  145  has a circular portion having a larger diameter than the fixing pin  166  and an opening portion in which part of the circular portion is open when viewed from the side. A width of the opening portion is formed smaller than a diameter of the circular portion. Therefore, the fixing pin  166  has to be pushed in from a lateral side of the fitting groove  145  and does not deviate in a rear surface direction (opening portion direction). One end portion  151  of the insulating barrier  150  is inserted into the opening portion. 
     At this time, the one end portion  151  of the insulating barrier  150  may be coupled thereto in a state that the fixing pin  166  is rolled (wound). As a result, the coupling force is increased. 
     The insulating barrier  150  is made of a member made of an insulating material. For such an example, a teflon-based material or an insulating sheet such as Nomax may be used. The insulating barrier  150  is formed of a material having flexibility. A degree of the flexibility may be adjusted to such an extent that it can be bent by an external force. In other words, as long as an external force does not act, the insulating barrier  150  may maintain a shape of surrounding an outer circumferential surface of the shaft body  131 , and may be bent by being brought into contact with a guide portion  107  or the like. 
     The insulating barrier  150  may be formed in a plate shape. 
     The insulating barrier  150  is disposed in a shape of surrounding an outer circumferential surface of the shaft body  131  in a normal state (conduction state). At this time, the other end (free end)  152  of the insulating barrier  150  exists in a state of being slightly lifted up (spaced apart) from the shaft body  131  by the guide portion  107  (refer to  FIG. 6 ). 
     The insulating barrier  150  rotates together with the movable contact  140  during interruption. Accordingly, the insulating barrier  150  is guided by the guide portion  107  to enter the fixed contacts  120 ,  121  and the movable contact  140  from the other end  152  of the insulating barrier  150 . Therefore, an arc generated between the fixed contacts  120 ,  121  and the movable contact  140  during interruption is rapidly extinguished. 
     The insulating barrier  150  quickly enters at the time of interruption, and enters between the fixed contact tips  122 ,  123  and the Movable contact tip  141  before the movable contact  140  is fully open, thus performing the role of extinguishing an arc prior to arc extinguishing due to the arc-extinguishing unit  105 . A pair of shaft pins  165  are provided. The shaft pin  165  is inserted into the pin mounting groove  134 . 
     Two pairs of springs  160  are provided. Each pair of springs  160  is provided between each fixing protrusion  142  and each shaft pin  165 . One end of the spring  160  is fixed to the fixing protrusion  142  and the other end thereof is fixed to the shaft pin  165 . The movable contact  140  is in a state in contact with the mover seat groove  135  of the shaft body  131  due to a tensile force of the spring  160 . 
     The guide portion  107  is formed in part of the base mold  106  forming an outer shape of the base assembly. The guide portion  107  is provided adjacent to the shaft body  131  between the movable contact  140  and the fixed contacts  120 ,  121 . The guide portion  107  may be formed with a pair of protrusions spaced apart at a predetermined interval. At this time, a separation distance between the pair of protrusions is greater than a thickness of the insulating barrier  150 . The insulating barrier  150  may be inserted between the guide portions  107 . The guide portion  107  guides the movement of the insulating barrier  150 . 
     Referring to  FIGS. 6 through 8 , the operation of a molded case circuit breaker according to a first embodiment of the present disclosure will be described. 
       FIG. 6  shows a conduction state. The shaft assembly  130  is placed in a state of being rotated in a counterclockwise direction. In other words, the shaft body  131  and the movable contact  140  are placed in a state of being rotated in a counterclockwise direction. The movable contact  140  is brought into contact with the fixed contacts  120 ,  121  to conduct a circuit. The insulating barrier  150  is placed in a state of being wrapped around a circumferential surface of the shaft body  131 . The insulating barrier  150  closes the opening portion  133  of the shaft body  131  at least partly. The other end portion  152  of the insulating barrier  150  is placed on any one protrusion of the guide portion  107 . 
       FIG. 7  shows an interruption operation progress state. The rotation pin  104  rotates in a clockwise direction by the power of the switching mechanism  102  when a small or large current is interrupted. The rotation pin  104  rotates the shaft body  131  to allow the shaft assembly  130  to rotate in a single body. The movable contact  140  is divided into fixed contacts  120 ,  121 . As the movable contact  140  rotates, the insulating barrier  150  is guided by the guide portion  107  to enter the space between the fixed contact tips  122 ,  123  and the Movable contact tip  141  to suppress an arc (A) generated between the contact portions at an initial stage. The arc (A) is divided and interrupted by the insulating barrier  150 . 
       FIG. 8  shows an interruption complete state. The shaft assembly  130  rotates and the movable contact  140  is placed as far as possible away from the fixed contacts  120 ,  121 . The insulating barrier  150  enters between the guide portions  107  to completely cover the fixed contact tips  122 ,  123 . A residual arc that is not extinguished by the insulating barrier  150  in the arc (A) is induced to the grids  105   b  of the arc-extinguishing unit  105  to completely disappear. 
       FIG. 9  shows an operation during cold current interruption. In the normal state of  FIG. 6 , when a sharp electromagnetic repulsion force acts on the contact portions  122 ,  123 ,  141  due to a short-circuit current, the movable contact  140  is separated from the fixed contacts  120 ,  121  while the shaft body  131  is fixed. At this time, the insulating barrier  150  coupled to the movable contact  140  enters between the fixed contact tips  122 ,  123  and the Movable contact tip  141  to interrupt an arc. 
     A shaft assembly  230  according to another embodiment of the present disclosure is illustrated in  FIG. 10 . The shaft assembly  130  and other parts of the previous embodiment will be described. 
     In the present embodiment, a plate groove  236  is formed adjacent to a pin insertion groove  234  of the opening portion  233  in the shaft body  231 . The plate groove  236  may be formed along a circumferential surface of the shaft body  231 . In other words, the plate groove  236  may be formed to be slightly smaller than a radius of the outer peripheral surface of the shaft body  231 . One end of the plate groove  236  communicates with the pin insertion groove  234 . 
     A contact plate  270  is provided. The contact plate  270  is inserted into the plate groove  236  and formed to move in a sliding manner. In other words, the contact plate  270  may be formed as a flat plate. At this time, a cross-sectional area of the contact plate  270  may be formed with a curvature radius equal to a curvature radius of the plate groove  236 . 
     One side surface of the contact plate  270  may be brought into contact with or fitted into the fitting groove  245  of the movable contact  240 . The contact plate  270  may be pushed by the movable contact  240  to move. 
     An elastic member  275  is provided to transfer the contact plate  270  to a position in a normal state (a state of being brought into contact with the movable contact, a counterclockwise direction in the drawing). The elastic member  275  may support the other side surface of the contact plate  270 . The elastic member  275  may include a torsion spring. The elastic member  275  may be inserted into the pin mounting groove  234 . At this time, a center coil portion of the elastic member  275  may be fitted into the shaft pin  265 . The contact plate  270  receives a force by the elastic member  275  in a direction of being brought into contact with the movable contact  240 . 
     One end portion  251  of the insulating barrier  250  is coupled to the contact plate  270 . 
     The operation of the present embodiment is similar to that of the previous embodiment. The shaft assembly  230  rotates to allow the insulating barrier  250  to enter between the movable contact  240  and the fixed contacts  220 ,  121  so as to interrupt an arc in a preemptive manner during general interruption, and the movable contact  240  pushes the contact plate  270  to allow the insulating barrier  250  to enter between the movable contact  240  and the fixed contacts  220 ,  121  during cold current interruption. 
       FIG. 11  is a perspective view illustrating a shaft assembly of a molded case circuit breaker according to still another embodiment of the present disclosure.  FIG. 12  illustrates a state in which an insulating barrier  350  is separated in  FIG. 11 . 
     The other components (parts) of the shaft assembly  330  excluding the insulating barrier  350  in the present embodiment may be configured in the same manner as in the first embodiment. 
     The insulating barrier  350  may include a cover portion  351  and an arc interrupting portion  352  connected to a rear end of the cover portion  351 . Here, the cover portion  351  may be formed to have a size that completely covers the opening portion  333  of the shaft body  331 . In other words, a length of the cover portion  351  may be formed larger than that of an arc from the mover seating groove  335  to a rear end surface of the opening portion  333  on a circumferential surface of the shaft body  331 . Accordingly, the insulating barrier  350  completely covers the opening portion  333  of the shaft body  331 . 
     A mover insertion hole  353  is formed in the cover portion  351 . The movable contact  340  is exposed through the mover insertion hole  353  of the insulating barrier  350 . A fixing groove (not shown) may be formed in the movable contact  340  to fit the cover portion  351  thereinto. 
     The arc interrupting portion  352  enters between the fixed contacts  320 ,  321  and the movable contact  340  to interrupt an arc. 
     The operation of this embodiment is as follows. First, a typical interruption operation of a small or large current is similar to the first embodiment, and thus detailed description thereof will be omitted. 
       FIGS. 13 and 14  illustrate an interruption operation during cold current interruption in a molded case circuit breaker according to this embodiment.  FIG. 13  shows a conduction state, and  FIG. 14  shows an interruption state. 
     In a conduction state, the movable contact  340  is restrained by a force of the spring  360  to receive a counterclockwise force and thus in a state of being brought into contact with the fixed contacts  320 ,  321 . Here, the spring  360  is provided between the fixing protrusion  342  of the movable contact  340  and the shaft pin  365  of the shaft body  331  as described above. At this time, when a sharp electromagnetic repulsive force acts on the contact portions  322 ,  323 ,  341  due to a short-circuit current, the movable contact  340  is separated from the fixed contacts  320 ,  321  against a force of the spring  360  while the shaft body  331  is fixed. At this time, the arc interrupting portion of the insulating barrier  350  coupled to the movable contact  340  enters between the fixed contacts  322 ,  323  and the movable contact  341  to interrupt an arc. 
       FIG. 15  is a cross-sectional view illustrating an insulating barrier according to still another embodiment of the present disclosure. 
     For the insulating barrier  450  in this embodiment, the insulating barriers  350  of the previous embodiment are not divided into a pair but integrally connected. The cover portion  451  of the insulating barrier  150  is formed in a ring shape to cover an entire circumferential surface of the shaft body  131 . A mover insertion hole  453  is formed in the cover portion  451 . A part of the cover portion  451  is cut to form an arc interrupting portion  452 . 
     Since the insulating barrier  450  of this embodiment is integrally formed, it is not necessary to be restrained to the movable contact  340 . 
     The operation of this embodiment is the same as that of the previous embodiment, and thus detailed description thereof will be omitted. 
     The above-described embodiments, which are embodiments for implementing the present disclosure, are only illustrative and not limitative to the concept of the present invention, and the scope of the concept of the invention is not limited by those embodiments. In other words, the scope protected by the present disclosure should be construed by the accompanying claims, and all the technical concept within the equivalent scope of the invention should be construed to be included in the scope of the right of the present disclosure.