Abstract:
A circuit breaker includes an elongated movable contact having a contact at one end thereof for flowing a current therethrough and the other end rotatably supported with a holder, and a protection cover made of an insulating material for covering and protecting a movable contact from short circuit and discharge. The protection cover is made of only the insulating material, covers the movable contact, and has elasticity to tightly hold the movable contact.

Description:
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT 
   The present invention relate to a circuit breaker such as a molded case circuit breaker or an earth leakage breaker having a movable contact opened by an electromagnetic repulsive force when a large current such as a short-circuit current flows. In particular, the present invention relates to a circuit breaker having a protection cover made of an insulating material that covers a movable contact to extinguish a contact arc generated when the contact opens. 
   A protection cover made of an insulating material for a movable contact in a conventional circuit breaker is disclosed in Patent Reference 1 or 2. According to Patent References 1 and 2, the insulating material is disposed near a contact of the movable contact to improve breaking capability. The insulating material having a shape to cover a periphery of the contact is fixed by clamping with a pin penetrating the contact and the insulating material. 
   Patent Reference 1: Japanese Patent Publication (Kokai) No. 57-130325 
   Patent Reference 2: Japanese Patent Publication (Kokai) No. 57-130329 
   In the circuit breakers disclosed in Patent References 1 and 2, when the protection cover made of the insulating material is disposed to cover the movable contact, the protection cover is pressed against the movable contact by clamping with the pin (or clamping with a bolt). Depending on the material and strength of the protection cover and the pin, the protection cover may break when the pin is clamped with an excessive stress. When the protection cover is loosely fixed and the protection cover is detached as the moving contact repeats opening and closing, the contact arc can not be extinguished upon an over-current, thereby damaging a wiring on a secondary side of the circuit breaker and a connection device. 
   Also, the arc may be spread through a metal member such as a pin and the like, thereby lowering current limiting capability. When the protection cover is damaged, the protection cover may fall off and obstruct a function of the circuit breaker, thereby damaging a wiring on a secondary side of the circuit breaker. 
   In view of the foregoing problems, an object of the present invention is to provide a circuit breaker in which a protection cover made of an insulating material covers a movable contact and is difficult to detach without other components causing an adverse effect such as spreading an arc, thereby preventing damage on a wiring on a secondary side of the circuit breaker and a connection device. 
   Further objects and advantages of the invention will be apparent from the following description of the invention. 
   SUMMARY OF THE INVENTION 
   To achieve the foregoing objects, according to a first aspect of the present invention, a circuit breaker includes an elongate plate-shaped movable contact having a contact at one end thereof for flowing a current therethrough and the other end rotatably supported with a holder, and a protection cover made of an insulating material for covering and protecting a movable contact from short circuit and discharge. The protection cover has a shape made of only the insulating material to cover the movable contact and elasticity to tightly hold the movable contact. 
   With this structure, the protection cover is formed of the insulating material only and incorporated in the movable contact without a metal member such as a pin as in a conventional breaker. Therefore, it is possible to eliminate a step of clamping a pin in the conventional breaker, thereby reducing manufacturing cost. The protection cover is incorporated in the movable contact without a metal member, thereby preventing an arc from spreading due to a metal material as in the conventional breaker and improving current limiting capability. 
   According to a second aspect of the present invention, in the circuit breaker in the first aspect, the movable contact may be provided with a through-hole penetrating through two lateral sides thereof or recess portions in the two lateral sides. Further, the protection cover may be provided with a protrusion for inserting in the through-hole or the recess portions. 
   With this structure, when the protection cover is incorporated in the movable contact, the protrusion is fitted into the through-hole or the recess portions, so that the protection cover does not shift from the movable contact and is held tightly. 
   According to a third aspect of the present invention, in the circuit breaker in one of the first and second aspects, the movable contact may be provided with a protrusion, and the protection cover may be provided with a recess portion for receiving the protrusion on the movable contact. 
   With this structure, when the protection cover is incorporated in the movable contact, the protrusion on the movable contact is fitted in the recess portion in the protection cover, so that the protection cover does not shift from the movable contact and is held tightly. When the third aspect is combined with the second aspect, the protrusions are fitted in the recess portions at separate positions, so that the protection cover is held tightly. 
   According to a fourth aspect of the present invention, in the circuit breaker in one of the first to third aspects, the protection cover has a shape such that a periphery thereof is supported by a holder when the protection cover is incorporated in the movable contact. 
   With this structure, the periphery of the protection cover corresponding to a holder arrangement part is supported by the holder. Therefore, even if the recess portions and protrusions are broken, the protection cover is not detached when the movable contact is opened and closed. 
   As described above, according to the present invention, the protection cover made of the insulating material covers the movable contact and is difficult to detach without other components causing an adverse effect such as spreading an arc, thereby preventing damage on a wiring on a secondary side of the circuit breaker and a connection device. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a longitudinal sectional view showing essential parts at a central pole section of a three-pole circuit breaker according to an embodiment of the present invention; 
       FIGS. 2(   a ) and  2 ( b ) are views showing a structure of a protection cover of the circuit breaker according to the embodiment, wherein  FIG. 2(   a ) is a plan view showing the structure of the protection cover, and  FIG. 2(   b ) is a sectional view of the protection cover taken along line  2 ( b )— 2 ( b ) in  FIG. 2(   a ); 
       FIGS. 3(   a ) and  3 ( b ) are views showing the structure of the protection cover of the circuit breaker according to the embodiment, wherein  FIG. 3(   a ) is a side view showing a movable contact, and  FIG. 3(   b ) is a plan view thereof; 
       FIG. 4  is a view showing a state where the protection cover is incorporated in the movable contact of the circuit breaker according to the embodiment; and 
       FIGS. 5(   a ) and  5 ( b ) are views showing a state where the movable contact incorporated in the protection cover of the circuit breaker is incorporated in a holder according to the embodiment, wherein  FIG. 5(   a ) is a plan view thereof, and  FIG. 5(   b ) is a sectional view taken along line  5 ( b )— 5 ( b ) in  FIG. 5(   a ). 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 
     FIG. 1  is a longitudinal sectional view showing essential parts at a central pole section of a three-pole circuit breaker according to an embodiment of the present invention. In the circuit breaker shown in  FIG. 1 , a breaking unit is disposed in an insulating container formed of a case  1  and a cover  2 , and includes a fixed contact  3  fixed to the case  1  and an elongate plate-shaped movable contact  5  driven to open and close by an opening/closing mechanism  4 . An arc extinguish chamber  6  is installed in the breaking unit. 
     FIG. 1  shows the breaking unit at the central pole section, and the insulating container is divided into three-phase spaces by phase partitions and a breaking unit corresponding to each phase is housed in each space. The fixed contact  3  has a power-side terminal  3   a  integrally formed at one end and a fixed contact  7  at the other end. 
   The movable contact  5  having a movable contact  8  that moves in contact with and away from the fixed contact  7  is rotatably supported on the case  1  via a holder  9  made of an insulating material, and is driven to open and close by the opening/closing mechanism  4 , using an opening/closing axis (not shown) integrated with the holder  9  as a support point. The arc extinguish chamber  6  has a structure such that plural grids  11  made of a magnetic material are vertically stacked and supported at proper intervals on a pair of left and right sidewalls (supporting member sidewalls)  10  of a supporting member made of an insulating material. The grid  11  has a U-shape provided with a cut-out to pass the movable contact  5  when the movable contact  5  is driven. 
   An arc gas emission port  12  is provided ahead of the breaking unit. The arc gas emission port  12  is closed by a protection board  13  made of an insulating material to prevent entry of foreign matter. The protection board  13  is fixed by having both sides of its base part inserted between the supporting member sidewall  10  and the fixed contact  3 . Meanwhile, a protection cover  14  made of a molded insulating material to cover the movable contact  5  is provided between the breaking unit and the opening/closing mechanism  4 . 
   Arc gas generated at the time of breaking contains molten metals generated from the contacts  7  and  8 , the fixed contact  3 , the movable contact  5 , the grids  11 , and the like. However, the partitions interrupt the movement of the arc gas to the opening/closing mechanism  4  and thus prevent the molten metals contained in the arc gas from being scattered and attached to the opening/closing mechanism  4  and its peripheral part. 
   In the embodiment, the circuit breaker having the structure as described above is characterized by the structure of the protection cover  14  made of an insulating material covering the movable contact  5  and the structure of the movable contact  5  for attaching the protection cover  14 . 
     FIG. 2(   a ) is a plan view showing the structure of the protection cover  14 .  FIG. 2(   b ) is a sectional view showing a section of the protection cover  14  taken along line  2 ( b )— 2 ( b ) in  FIG. 2(   a ). As shown in  FIG. 2 , the protection cover  14  has an elongate U-shape to hold both lateral sides of the movable contact  5  from the lower side and thus cover the movable contact  5 , so that the contact of the elongate plate-shaped movable contact  5  having a predetermined width is exposed. On the parallel inner sidewalls near the distal end of this U-shape, protrusions  14   a  are provided. On the outer sidewall corresponding to the intermediate part of the movable contact  5 , a recess portion  14   b  is provided. The width between the parallel sidewalls from the vicinity of the part where the recess portion  14   b  is provided to the proximal end is broader than the width on the distal end side. The sidewall parts having the broader width between them are to be fitted with the parallel inner walls of the holder  9  (described later). The elongate U-shaped protection cover  14  is made of a thermoplastic insulating material such as plastics and has elasticity to tightly hold the movable contact  5  from below and maintain this state by itself. 
   Namely, the protection cover  14  is formed by two sidewalls  15   a  with the protrusions  14   a  and one recess portion  14   b , and first and second bridging portions  15   b ,  15   c  for connecting the side walls  15   a . The first and second bridging portions  15   b ,  15   c  are spaced apart from each other. 
     FIG. 3(   a ) is a side view schematically showing the movable contact  5 .  FIG. 3(   b ) is a plan view thereof. As shown in  FIG. 3(   a ), the movable contact  5  has an elongate plate-shape with a predetermined width. Near its distal end where the contact is provided, a through-hole  5   a  is provided to fit with the protrusions  14   a  of the protection cover  14 . On the outer sidewall in the intermediate part between the distal end and the proximal end, a protrusion  5   b  is provided to fit in the recess portion  14   b  of the protection cover  14 . Instead of the through-hole  5   a , recesses in which the protrusions  14   a  can fit may be provided on both lateral sides of the movable contact  5 . 
     FIG. 4  shows a state where the protection cover  14  is incorporated with the movable contact  5  having the above-described structure. In the case of such incorporation, the protection cover  14  is fitted with the movable contact  5  from below, with both lateral sides of the movable contact  5  being held between the sidewalls of the protection cover  14 . The protrusions  14   a  are fitted into the through-hole  5   a  and the recess portion  14   b  is fitted with the protrusion  5   b . Since the fitting is made in this manner at the separate positions on the lateral sides, the protection cover  14  is prevented from shifting vertically or horizontally from the movable contact  5 . Moreover, since the bottom side of the protection cover  14  abuts against the lower side of the movable contact  5 , the protection cover  14  does not shift upwardly. 
   The protection cover  14  is also fitted in the holder  9 , which rotatably supports the movable contact  5  on the case  1 , as shown in  FIGS. 5(   a ) and  5 ( b ).  FIG. 5(   a ) is a plan view showing a state where the movable contact  5  incorporated with the protection cover  14  is incorporated in the holder  9 .  FIG. 5(   b ) is a sectional view showing a section taken along line  5 ( b )— 5 ( b ) in  FIG. 5(   a ). At a part “c” shown in  FIG. 5(   a ), the width of the protection cover  14  is substantially equal to the spacing of the holder  9 . Because of its shape, the protection cover  14  is fitted in the holder  9  without any gap. Moreover, as the protection cover  14  is supported by the holder  9  at a part “d” shown in  FIG. 5(   b ), the protection cover  14  is prevented from being shifted by the opening/closing operation of the movable contact  5 . 
   Even if the fitting parts of the protrusions  14   a  with the through-hole  5   a  and the fitting part of the recess portion  14   b  with the protrusion  5   b  are broken, the protection cover  14  is fixed at the parts “c” and “d” and prevented from falling off the movable contact  5 . 
   According to the circuit breaker of this embodiment as described above, the protection cover  14  is made of an insulating material only and can be incorporated with the movable contact  5  without using any metal member such as a pin as in the conventional technique. Therefore, the pin clamping step, which is necessary in the conventional technique, can be eliminated and the manufacturing cost can be reduced accordingly. 
   Since no metal member is used in the structure related to the protection cover  14  and its incorporation with the movable contact  5 , the spread of an arc, which is caused by the use of a metal material as in the conventional technique, can be prevented and the current limiting capability can be thus improved. 
   Moreover, in the case of incorporating the protection cover  14  with the movable contact  5 , the sets of the recess portions and the protrusions to fit with each other are provided at the separate positions and the recess and protrusion of each set are fitted with each other. Accordingly, the protection cover  14  is prevented from shifting vertically or horizontally from the movable contact  5 . Furthermore, since the protection cover  14  is so shaped that the periphery of its proximal end is supported by the holder  9 , which rotatably supports the movable contact  5  on the circuit breaker case, shift or detachment of the protection cover  14  due to the opening/closing operation of the movable contact  5  is prevented. 
   Even when the fitting parts of the recesses and protrusions are broken, since the protection cover  14  is supported by the parallel inner walls and bottom side of the holder  9 , the protection cover  14  is prevented from being detached by the opening/closing operation of the movable contact  5 . 
   As these enable proper extinction of the contacts arc, damage to the wiring on the secondary side of the circuit breaker and the connection device can be prevented. 
   The disclosure of Japanese Patent Application No. 2004-172585, filed on Jun. 10, 2004, is incorporated in the application. 
   While the invention has been explained with reference to the specific embodiments of the invention, the explanation is illustrative and the invention is limited only by the appended claims.