Patent Publication Number: US-10332715-B2

Title: Fusion welding isolation mechanism for operation mechanism of circuit breaker

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of low-voltage electric apparatus, more particularly, relates to operation mechanism of switching electric apparatus. 
     2. The Related Art 
     A circuit breaker is a main switching electric apparatus which plays a protective role in a low-voltage power distribution network. The circuit breaker provides overload protection and short circuit protection for the network. A molded case circuit breaker is a type of the circuit breakers. A large capacity molded case circuit breaker refers to a circuit breaker with a rated current reaching or exceeding 800 A. Generally, such a circuit breaker has a three-pole and four-pole structure, namely the circuit breaker is provided with three or four groups of contacts, which correspond to a three-phase or four-phase circuit. An operation mechanism is in contact with all of the three or four groups of contacts. By operating the operation mechanism, the three or four groups of contacts can perform closing, opening or tripping at a same time. 
     In some cases, the contact may be subject to fusion welding. Fusion welding refers to that the moving contact and the static contact are melted due to high temperature, and therefore the moving contact and the static contact are fixed to each other and cannot be separated. As the operation mechanism is in linkage with the contact, when the moving contact and the static contact are subjected to fusion welding and cannot be separated, the operation mechanism cannot act as well. Fusion welding usually occurs when the circuit is conducted, so that the operation mechanism is locked at the closing position. At this time, if the operation mechanism is subjected to an opening operation by an external force, such as manual operation, the operation mechanism will be damaged. 
     SUMMARY 
     The present invention discloses a fusion welding isolation mechanism which can limit a stroke of an operation mechanism when a fusion welding occurs. 
     According to an embodiment of the present invention, a fusion welding isolation mechanism for operation mechanism of circuit breaker is disclosed. The operation mechanism of circuit breaker comprises: a tripping component, a left side plate component, a right side plate component, a latch component, a half shaft component, a lever component and a main shaft component. The tripping component, the latch component and the lever component are mounted between the left side plate component and the right side plate component, the half shaft component and the main shaft component penetrate through the left side plate component and the right side plate component and extend out of the left side plate component and the right side plate component. The tripping component, the latch component, the half shaft component, the lever component and the main shaft component move in linkage. The lever component and the main shaft component are provided with isolation devices for preventing an operation handle from an opening operation when a moving contact is subject to fusion welding. 
     According to an embodiment, the main shaft component comprises a main shaft with a plurality of cantilevers arranged thereon, a main shaft limiting piece is provided on the main shaft and a limiting block is provided on the main shaft limiting piece. 
     According to an embodiment, the lever component comprises a sheet metal bending piece, the sheet metal bending piece being bent to form a top wall and two side walls; a lever component spring is mounted on the sheet metal bending piece, the lever component spring is surrounded by the sheet metal bending piece, the sheet metal bending piece forms a shallow hook shaped extension part at a first end of the bottom of the two side walls. 
     According to an embodiment, the isolation devices comprise the limiting block on the main shaft limiting piece and the shallow hook shaped extension part on the sheet metal bending piece. 
     According to an embodiment, when a moving contact is subjected to fusion welding, the main shaft component in linkage with the moving contact is locked at the closing position and is not able to rotate; when the lever component rotates towards an opening direction under an external force, the limiting block on the main shaft liming piece is in contact with the shallow hook shaped extension portion on the sheet metal bending piece, so that the lever component is not able to reach the opening position. 
     According to an embodiment, when the external force disappears, the lever component spring generates a torque for driving the lever component to rotate towards a closing direction and reset. 
     The fusion welding isolation mechanism for operation mechanism of circuit breaker of the present invention can limit a rotation stroke of the operation mechanism towards an opening direction, so as to prevent the operation mechanism from being damaged by forced operation. After an external force disappears, the operation mechanism can reset to a closing position automatically. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features, natures, and advantages of the invention will be apparent by the following description of the embodiments incorporating the drawings, wherein, 
         FIG. 1  illustrates a structural diagram of an operation mechanism of circuit breaker using a fusion welding isolation mechanism according to an embodiment of the present invention. 
         FIG. 2 a    and  FIG. 2 b    illustrate a structural diagram of a tripping component of the operation mechanism of circuit breaker shown in  FIG. 1 . 
         FIG. 3 a    illustrates a structural diagram of a left side plate component and a latch component of the operation mechanism of circuit breaker shown in  FIG. 1 . 
         FIG. 3 b    illustrates a structural diagram of the left side plate component and the latch component from another perspective. 
         FIG. 4 a    illustrates a structural diagram of a latch component according to a first embodiment. 
         FIG. 4 b    illustrates a structural diagram of a latch component according to a second embodiment. 
         FIG. 5  illustrates a structural diagram of a right side plate component of the operation mechanism of circuit breaker as shown in  FIG. 1 . 
         FIG. 6 a    and  FIG. 6 b    illustrate a structural diagram of a lever component of the operation mechanism of circuit breaker as shown in  FIG. 1 . 
         FIG. 7 a    and  FIG. 7 b    illustrate a structural diagram of a main shaft component of the operation mechanism of circuit breaker as shown in  FIG. 1 . 
         FIG. 8  illustrates an assembly structural diagram of an operation mechanism as shown in  FIG. 1  and a circuit breaker. 
         FIG. 9  illustrates an assembly structural diagram of an operation mechanism as shown in  FIG. 1  and a circuit breaker. 
         FIG. 10 a    and  FIG. 10 b    illustrate a closing process of a moving contact driving by the operation mechanism as shown in  FIG. 1 . 
         FIG. 11 a    and  FIG. 11 b    illustrate an opening process of a moving contact driving by the operation mechanism as shown in  FIG. 1 . 
         FIG. 12 a    and  FIG. 12 b    illustrate a structural diagram of the operation mechanism according to an embodiment of the present invention with a fusion welding isolation indication. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     As shown in  FIG. 1 ,  FIG. 1  illustrates a structural diagram of an operation mechanism of circuit breaker according to an embodiment of the present invention. The operation mechanism  107  comprises: a tripping component  100 , a left side plate component  101 , a latch component  102 , a half shaft component  103 , a right side plate component  104 , a lever component  105  and a main shaft component  106 . 
       FIG. 2 a    and  FIG. 2 b    illustrate a structural diagram of a tripping component. As shown in  FIG. 2 a    and  FIG. 2 b   , the tripping component  100  comprises a tripping buckle  204 . A first hole  207  is provided at a first end of the tripping buckle  204 , and a rotation shaft  208  is riveted in the first hole  207 . A pin hole is provided at the middle of the tripping buckle  204 , a pin  203  passes through the pin hole to rivet an upper connection rod  201  to the tripping buckle  204 . A limiting hole is formed at a position close to the pin hole, and a limiting pin  205  is riveted in the limiting hole.  FIG. 2 a    illustrates a structure after the limiting pin  205  is riveted, therefore the limiting hole is shielded. The position of the limiting hole is the position of the limiting pin  205 . A second end of the tripping buckle  204  is hook shaped, a first inclined surface  256  is formed on an inner side of the hook, and a second inclined surface  253  is formed on an outer side of the hook. It should be noticed that, although the second inclined surface  253  is called “an inclined surface”, it is actually an arc surface, or at least comprises an arc surface in part. An upper end of the upper connection rod  201  is riveted to the tripping buckle  204 . A pin hole is provided in the middle of the upper connection rod  201 , a pin  203  passes through the pin hole to rivet the lower connection rod  202  to the upper connection rod  201 . A connection hole  236  is provided at a bottom end of the upper connection rod  201 . As shown in  FIG. 2 b   , a connection hole  283  is provided at an upper end of the lower connection rod  202 . A pin passes through the connection hole  283  to rivet the lower connection rod  202  to the upper connection rod  201 . A connection hole  282  is provided at a bottom end of the lower connection rod  202 . 
     Side plate components comprise the left side plate component  101  and the right side plate component  104 . The left side plate component  101  and the right side plate component  104  have symmetrical structures. As shown in  FIG. 1 , the tripping component  100 , the latch component  102 , the half shaft component  103 , the lever component  105  and the main shaft component  106  are disposed between the left side plate component  101  and the right side plate component  104 . And, the tripping component  102 , the half shaft component  103 , the lever component  105  and two ends of the main shaft component  106  are mounted on the left side plate component  101  and the right side plate component  104 .  FIG. 3 a    and  FIG. 3 b    illustrate the structure of the left side plate component.  FIG. 3 a    and  FIG. 3 b    illustrate the structure of the left side plate component from different perspectives. As shown in the drawings, the left side plate component  101  comprises a left side plate  209 . Bending holes  210  are formed in the bottom of the left side plate  209  at positions close to the two ends. The bending hole  210  comprises an extension plate perpendicular to the side plate  209  and a hole opened on the extension plate. A nut  211  is riveted on the bending hole  210 . The bending hole  210  and the nut  211  are used to install the operation mechanism  107  onto the circuit breaker. A mounting hole  212  is provided in the middle of the left side plate  209  at a position close to the bottom. The mounting hole  212  is used for mounting a rotation shaft  213 . The rotation shaft  213  is the rotation axis of the lever component  105 . The lever component  105  rotates about the rotation shaft  213 . As shown in  FIG. 3 b   , the rotation shaft  213  is a short shaft. An end cap is provided on the end of the rotation shaft  213  which is facing to an inner side of the left side plate  209 . A mounting hole  215  is provided on the left side plate  209  at a position close to the top of a second end. A rotation shaft  207 , which is the rotation shaft of the tripping component  102 , is mounted in the mounting hole  215 , so that the tripping component  102  is mounted onto the left side plate  101 . A half shaft hole  226  is provided on the left side plate  209  at a position close to the bottom the second end. The half shaft hole  226  is used to assemble the half shaft component  103 . A semi-circular notch  299  is provided on the left side plate  209  at a position close to the bottom of a first end. The notch  299  is used to accommodate the main shaft component  106 . A mounting hole  290  is provided above the notch  299 , and is used for fixing a screw of the main shaft component  106 . A tripping mounting hole  280  is provided on the left side plate  209  at a position close to the top of the first end. The tripping mounting hole  280  is used to accommodate a rotation shaft  208  of the tripping component  102 . 
       FIG. 5  illustrates the structure of the right side plate component. The right side plate component  104  has a structure that is symmetrical to that of the left side plate component  101 . A right side plate  309  is provided with the following structures which are symmetric to those of the left side plate  209 : bending holes  310 , a nut  311 , a mounting hole  312  for mounting the rotation shaft  213 , a mounting hole  315  for mounting the rotation shaft  217  of the tripping component  102 , a half shaft hole  227  for assembling the half shaft component  103 , a semi-circular notch  399  for accommodating the main shaft component  106 , a mounting hole  291  for fixing a screw of the main shaft component  106  and a tripping mounting hole  281  for accommodating the rotation shaft  208  of the tripping component  102 . 
     The latch component  102  comprises a sheet metal piece  219 , a positioning shaft  220 , a bearing  221 , a latch component spring  222  and a rotation shaft  217 . The structure of the latch component is shown in  FIG. 3 a    and  FIG. 3 b    and mainly shown in  FIG. 3   b.  It should be noticed that, for the purpose of illustrating the mounting structure of the latch component  102  more clearly,  FIG. 3 a    and  FIG. 3 b    illustrate the structure of the side plate component  101  and the latch component  102  from two different perspectives. In the perspective of  FIG. 3 b   , the mounting structure of the latch component is illustrated more clearly.  FIG. 4 a    illustrates the structure of the sheet metal piece  219 , the positioning shaft  220  and the bearing  221  of the latch component. The sheet metal piece  219  comprises two sheet metal sheets with identical shapes, and the two sheet metal sheets are arranged with a certain gap. Two positioning shafts  220  fix the two sheet metal sheets to form the sheet metal piece  219 . The bearing  221  is disposed between the two sheet metal sheets, each of two ends of the bearing  221  are mounted on one sheet metal sheet respectively. The bearing  221  is positioned between the two positioning shafts  220 . A shaft hole is provided on an upper end of the sheet metal piece  219 . The sheet metal piece  219  is mounted on the rotation shaft  217  through the shaft hole, and the sheet metal piece  219  can rotate about the rotation shaft  217 . The latch component spring  222  is fit on the rotation shaft  217 , and is also disposed between the two sheet metal sheets. The bearing  221  cooperates with the second inclined surface  253  of the tripping component  100 , so that the latch component  102  can limit the tripping component  100 .  FIG. 4 b    illustrates the structure of a latch component according to another embodiment. According to the structure shown in  FIG. 4 b   , the sheet metal piece  219 A comprises two sheet metal sheets with different shapes. A bending foot is provided on one sheet metal sheet, while the other sheet metal sheet is not provided with a bending foot. Both sheet metal sheets are provided with holes for the rotation shaft  217  to penetrate through. The two sheet metal sheets are arranged with a certain gap. The two sheet metal sheets are connected to each other via a sheet-shaped part instead of a positioning shaft. In other words, the sheet metal piece  219 A is a single element with the sheet-shaped part and two sheet metal sheets connected by the sheet-shaped part. A bearing  221 A is disposed between the two sheet metal sheets. 
     As shown in  FIG. 1 , the half shaft component  103  comprises a half shaft  223 . Two ends of the half shaft  223  are installed in the half shaft hole  226  on the side plate  209  of the left side plate component  101  and the half shaft hole  227  on the side plate  309  of the right side plate component  104  respectively. Two fault receivers are provided on the half shaft component  103 , that is, a first fault receiver  224  and a second fault receiver  225 . The first fault receiver  224  and the second fault receiver  225  are both located between the left side plate component  101  and the right side plate component  104 . The first fault receiver  224  is arranged close to an inner side of the side plate of the left side plate component  101 , and the second fault receiver  225  is arranged close to an inner side of the side plate of the right side plate component  104 . The half shaft component  103  and the latch component  102  form a two-level latch of the operation mechanism. 
       FIG. 6 a    and  FIG. 6 b    illustrate the structure of the lever component. The lever component  105  comprises a sheet metal bending piece  228 , which is bent to form a top wall and two side walls. The top wall and the two side walls form a semi-surrounding structure. A mounting shaft  229  is riveted to the top wall of the sheet metal bending piece  228 , and is used for mounting an operation handle  230 . Mounting grooves  233  are provided on the metal plate bending piece  228  at junctions of each side wall and the top wall. A spring mounting shaft  232  is mounted between the two mounting grooves  233 . A top end of a lever component spring  231  is connected to the spring mounting shaft  232 . According to the illustrated embodiment, two lever component springs  231  are arranged in parallel. The lever component spring  231  is surrounded by the sheet metal bending piece  228 . A connection hole  234  is provided on a bottom end of the lever component spring  231 . The connection hole  234  is aligned with the connection hole  236  at the bottom end of the upper connection rod  201 . A connection shaft  235  penetrates through the connection hole  234  and the connection hole  236 , so that the lever component spring  231  is connected with the upper connection rod  201  of the tripping component  100 , and the lever component  105  is in linkage with the tripping component  101 . The sheet metal bending piece  228  forms a shallow hook shaped extension part  258  at a first end of the bottom of the two side walls. The shallow hook shaped extension part  258  has a shape similar to a “boot”. The shallow hook shaped extension part  258  limits the rotation of the lever component. Semi-circular notches  241  are formed in the bottom of the two side walls of the sheet metal bending piece  228  at a position close to a second end. The semi-circular notches  241  are used for accommodating the rotation shaft  213 . The lever component  105  rotates about the rotation shaft  213 . 
       FIG. 7 a    and  FIG. 7 b    illustrate the structure of the main shaft component. The main shaft component  106  comprises a main shaft  237 , and a plurality of cantilevers  238  are arranged on the main shaft  237 . According to an embodiment, the plurality of cantilevers  238  are welded on the main shaft  237 . The plurality of cantilevers  238  correspond to moving contact components with a plurality of poles respectively, in other words, correspond to multi-phase circuits. Each cantilever  238  is provided with a connection hole. A pair of main shaft limiting pieces  239 ,  240  is provided on the main shaft  237 . The pair of main shaft limiting pieces  239 ,  240  is arranged on two sides of one of the plurality of cantilevers  238 , and, the positions of the main shaft limiting pieces  239  and  240  on the main shaft  237  are symmetric relative to the cantilever  238 . The main shaft limiting pieces  239  and  240  correspond to one phase of the multi-phase circuit. Bent limiting blocks  259  are provided on ends of the main shaft limiting pieces  239  and  240 . The bent limiting block  259  can be matched with the shallow hook shaped extension part  258  with a “boot” shape on the sheet metal bending piece  228 , so that and a rotation range of the lever component  105  is limited by using the main shaft component  106 .  FIG. 7 b    discloses a mounting accessory of the main shaft component. The mounting accessory includes two portions: a first portion  242  and a second portion  243 . The first portion  242  and the second portion  243  are on a single element. A circular hole is formed in the first portion  242 , and the diameter of the hole is matched with the diameter of the main shaft  237 . The main shaft  237  penetrates through the hole. The second portion  243  is located above the first portion  242 , and a screw hole is formed on the second portion  243 . The left side plate component  101  and the right side plate component  104  are mounted with a mounting accessory respectively. The holes on the first portion  242  are aligned with the semi-circular notches  299  or  399  respectively, so as to accommodate the main shaft  237 . The screw holes on the second portion  243  are aligned with the mounting hole  290  or the mounting hole  291  respectively. A screw penetrates through the mounting hole and the screw hole, so that the mounting accessory and the main shaft are mounted onto the left side plate component and the right side plate component. 
     As shown in  FIG. 1 ,  FIG. 2 a   ,  FIG. 2 b   ,  FIG. 3 a   ,  FIG. 3 b   ,  FIG. 4 a   ,  FIG. 4 b   ,  FIG. 5 ,  FIG. 6 a   ,  FIG. 6 b   ,  FIG. 7 a    and  FIG. 7 b   , the tripping component  100 , the left side plate component  101 , the latch component  102 , the half shaft component  103 , the right side plate component  104 , the lever component  105  and the main shaft component  106  assemble as follows to form the operation mechanism  107 . Two ends of the rotation shaft  208  of the tripping component  100  are mounted on the tripping mounting hole  280  of the left side plate component  101  (located on the left side plate  209 ) and the tripping mounting hole  281  of the right side plate component  104  (located on the right side plate  309 ) respectively. The semi-circular notches  241  in the bottom of the two side walls of the sheet metal bending piece  228  of the lever component  105  are respectively erected on the rotation shafts  213  of the left side plate component  101  and the right side plate component  104 . As described above, the rotation shafts  213  are short shafts. Two rotation shafts  213  are mounted on the left side plate  209  and the right side plate  309  respectively. An end cap is provided on the end of the rotation shaft  213  facing to an inner side. The diameter of the end cap is larger than that of the rotation shaft. The end cap is used for horizontally limiting the side wall of the sheet metal bending piece  228 . The connection hole  234  in the bottom of the lever component spring  231  of the lever component  105  is aligned with the connection hole  236  at the lower end of the upper connection rod  201 . The connection shaft  235  penetrates through the connection hole  234  and the connection hole  236 , so that the lever component spring  231  is connected with the upper connection rod  201 . The main shaft  237  of the main shaft component  106  passes through the holes on the first portions  242  of the two mounting accessories, so that the main shaft  237  is connected to the two mounting accessories. The main shaft  237  is placed in the semi-circular notch  299  of the left side plate component  101  (located on the left side plate  209 ) and the semi-circular notch  399  of the right side plate component  104  (located on the right side plate  309 ). The screw holes in the second portions  243  of the two mounting accessories align with the mounting hole  290  on the left side plate component  101  (located on the left side plate  209 ) and the mounting hole  291  on the right side plate component  104  (located on the right side plate  309 ) respectively. Screws pass through the screw holes in the second portions  243  of the two mounting accessories and the mounting holes  290 ,  291 , so that the mounting accessories are fixed on the left side plate component and the right side plate component, then the main shaft component  106  is assembled to the left side plate component  101  and the right side plate component  104 . One of the cantilevers  238  of the main shaft component  106  is connected to the lower connection rod  202  of the tripping component  100 . The connection hole on the cantilever  238  is connected with the connection hole  282  at the lower end of the lower connecting rod  202  through a pin shaft  246  (the pin shaft  246  is shown in  FIG. 11 ), so that a connection rod structure is formed and the main shaft component  106  is connected with the tripping assembly  100 . For a multi-phase circuit with a multi-pole structure, the main shaft component  106  is provided with a plurality of cantilevers  238  and each cantilever  238  corresponds to one pole. The operation mechanism  107  is mounted on the structure of one pole. The cantilever  238  corresponding to the pole is connected with the lower connection rod in the tripping component of the operation mechanism. For the fixing of the left side plate component  101  and the right side plate component  104 , in addition to the rotation shaft  217  of the latch component  102 , another fixing shaft  247  is provided on the other end of the latch component  102 . The fixing shaft  247  also penetrates through the holes in the left side plate component and the right side plate component and is fixed by screws. The fixing shaft  247  and the rotation shaft  217  are used for connecting the left side plate component  101  and the right side plate component  104 . 
     As shown in  FIG. 8  and  FIG. 9 , the assembly structure of the operation mechanism  107  and the circuit breaker  108  is illustrated.  FIG. 8  and  FIG. 9  illustrate the structure of the circuit breaker without a lid. As shown in  FIG. 8  and  FIG. 9 , the circuit breaker  108  includes a base  109  and a middle cover  159 . According to the illustrated embodiment, the circuit breaker  108  is a multi-pole circuit breaker with multi-pole moving contacts  110  corresponding to multi-phase circuits. The operation mechanism  107  is mounted on one moving contact corresponding to one pole. The screw  249  is matched with the nut  211  on the left side plate component  101  and the right side plate component  104  of the operation mechanism, so that the left side plate component  101  and the right side plate component  104  are fixed on the middle cover  159 , then the operation mechanism  107  is mounted on a moving contact of one pole. The multi-pole moving contacts  110  are respectively connected to the corresponding cantilevers  238  of the main shaft component  106  through the pin shafts  250 , and the moving contact  110  of each pole is connected to a cantilever  238  corresponding to the moving contact  110 . The pin shaft  250  is fixed in a connection hole on the cantilever  238 . As shown in  FIG. 7 a   , two connection holes are provided on each cantilever  238 . The upper connection hole is used for connecting with the tripping component, and the lower connection hole is used for connecting with the moving contact. The operation handle  230  is mounted on the lever component  105 , and more specifically, the operation handle  230  is mounted on the mounting shaft  229 . 
       FIG. 10 a    and  FIG. 10 b    illustrate a closing process of a moving contact driving by the operation mechanism described above.  FIG. 10 a    mainly illustrates the closing process of the operation mechanism.  FIG. 10 b    illustrates the closing process of the moving contact driven by the operation mechanism. When performing the closing process, the second inclined surface  253  formed on the outer side of the hook shaped tail end of the tripping buckle  204  of the tripping component  100  is pressed by the bearing  221  and is limited by the bearing  221 . The sheet metal piece  219  of the latch component  102  is limited by the half shaft  223  of the half shaft component  103 . The lever component  105  rotates anticlockwise about the rotation shaft  213  under an action of human force, for example, the operation handle  230  is pushed by human force to drive the lever component to rotate. According to the embodiment shown in  FIG. 10 a    and  FIG. 10 b   , the closing direction in the drawings is indicated by arrows, the lever component rotates anticlockwise. When the lever component  105  is driven to rotate anticlockwise, the lever component spring  231  drives the upper connection rod  201  to rotate by taking the pin shaft  203  as a rotation shaft. The upper connection rod  201  rotates clockwise about the pin shaft  203 . The upper connection rod  201  drives the lower connection rod  202  to move. The lower connection rod  202  drives the cantilever  238  of the main shaft component  106  (the cantilever  238  is connected with the tripping component  100 ) through the pin shaft  246 . The cantilever  238  further drives the main shaft  237  to rotate about an axis  106 A of the main shaft  237  clockwise. The rotation of the main shaft  237  drives other cantilevers  238  to move in linkage. The respective cantilevers  238  drive the respective moving contacts  110  through the pin shafts  250  to complete the closing process. The respective moving contacts  110  rotate anticlockwise about respective rotation centers  255 . Back to  FIG. 2 a   , a limit position of a clockwise rotation of the upper connection rod  201  is limited by the limiting pin  205 . When the upper connection rod  201  rotates to be in contact with the limiting pin  205 , the upper connection rod  201  does not rotate any further. Then, after the closing process is completed, the upper connection rod  201  is limited by a limiting pin  205 . 
       FIG. 11 a    and  FIG. 11 b    illustrate an opening process of a moving contact driving by the operation mechanism described above.  FIG. 11 a    mainly illustrates the opening process of the operation mechanism.  FIG. 11 b    illustrates the opening process of the moving contact driven by the operation mechanism. When performing the opening process, the lever component  105  rotates clockwise about the rotation shaft  213  under an action of human force, for example, the operation handle  230  is pushed by human force to drive the lever component to rotate. According to the embodiment shown in  FIG. 11 a    and  FIG. 11 b   , the opening direction in the drawings is indicated by arrows, the lever component rotates clockwise. When the lever component  105  is driven to rotate clockwise, the lever component spring  231  drives the upper connection rod  201  to rotate by taking the pin shaft  203  as a rotation shaft. The upper connection rod  201  rotates anticlockwise about the pin shaft  203 . The upper connection rod  201  drives the lower connection rod  202  to move. The lower connection rod  202  drives the cantilever  238  of the main shaft component  106  (the cantilever  238  is connected with the tripping component  100 ) through the pin shaft  246 . The cantilever  238  further drives the main shaft  237  to rotate about the axis  106 A of the main shaft  237  anticlockwise. The rotation of the main shaft  237  drives other cantilevers  238  to move in linkage. The respective cantilevers  238  drive the respective moving contacts  110  through the pin shafts  250  to complete the opening process. The respective moving contacts  110  rotate clockwise about respective rotation centers  255 . As shown in  FIG. 7 a   , a limit position of an anticlockwise rotation of the main shaft  237  is limited by the main shaft limiting pieces  239 ,  240  and the fixing shaft  247 . As shown in  FIG. 11 a    and  FIG. 11 b   , when the main shaft limiting pieces  239 ,  240  are in contact with the fixing shaft  247 , the main shaft component does not rotate any further. 
       FIG. 12 a    and  FIG. 12 b    illustrate a structural diagram of the operation mechanism according to an embodiment of the present invention with a fusion welding isolation indication.  FIG. 12 a    mainly illustrates the structure of the operation mechanism during the fusion welding isolation indication.  FIG. 12 b    illustrates the structure of the operation mechanism and the moving contact during the fusion welding isolation indication. When a moving contact  110  in the multi-pole moving contact is subjected to fusion welding, the moving contact  110  is fixed to the static contact  188  due to fusion welding and cannot rotate about the rotation center  255 . The main shaft component  106  is in linkage with the moving contact  110 , so that the main shaft component  106  cannot rotate about the rotation center  106   a  when the moving contact is fusion welded, in other words, the main shaft component  106  is locked at the closing position. At the moment, if the lever component  105  is operated manually to open, the mechanism is easy to be damaged because the main shaft component  106  is locked. In order to avoid such a situation, the operation mechanism of the invention is provided with an isolation protection function directing to the fusion welding situation. The isolation protection function is implemented by a limiting block  259  on the ends of the main shaft limiting piece  239 ,  240  and the shallow hook shaped extension part  258  with a “boot” shape on the sheet metal bending piece  228 . As shown in  FIG. 12 a    and  FIG. 12 b   , when a fusion welding occurs, if the operation handle  230  is operated manually to rotate clockwise for an opening action, after the lever component  105  rotates clockwise for a certain angle, the limiting block  259  will be in contact with the shallow hook shaped extension portion  258  with a “boot” shape, so that the lever component  105  cannot rotate anymore and cannot reach the opening position. When the manual operation disappears, a torque exists under the action of the lever component spring  231 . A force arm of the torque is L 1 . The lever component spring  231  generates the torque through the force arm L 1  and drives the lever component  105  to rotate anticlockwise about the rotation shaft  213  to return to the closing position. The direction indicated by an arrow in  FIG. 12 a    is the direction when the lever component  105  automatically resets under the action of the torque, the direction is anticlockwise rotation. 
     The fusion welding isolation mechanism for operation mechanism of circuit breaker of the present invention can limit a rotation stroke of the operation mechanism towards an opening direction, so as to prevent the operation mechanism from being damaged by forced operation. After an external force disappears, the operation mechanism can reset to a closing position automatically. 
     The above embodiments are provided to those skilled in the art to realize or use the invention, under the condition that various modifications or changes being made by those skilled in the art without departing the spirit and principle of the invention, the above embodiments may be modified and changed variously, therefore the protection scope of the invention is not limited by the above embodiments, rather, it should conform to the maximum scope of the innovative features mentioned in the Claims.