Abstract:
A modular arc chamber assembly suitable for use in a cassette assembly in a circuit breaker comprising: an electrically insulative first side member, an electrically insulative second side member; a plurality of plates disposed between said first and second side members and arranged in a stacked spaced-apart relationship, and an arc runner plate disposed at one end and between the first and second side members capable of directing an arc to an arc dissipating chute comprised of the plurality of arc plates.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to an arc chamber, and more particularly, to a modular arc chamber assembly for a circuit breaker.  
           [0002]    Circuit breakers are one of a variety of overcurrent protective devices used for circuit protection and isolation. The basic function of a circuit breaker is to provide electrical system protection whenever an electrical abnormality occurs in any part of the system. In a circuit breaker, current enters the system from a power line. The current passes through a strap to a stationary contact fixed on the strap and then to a movable contact. The movable contact is fixedly attached to an arm, and the arm is mounted to a rotor. As long as the stationary and movable contacts are in physical contact, current passes from the stationary contact to the movable contact and out of the circuit breaker to downline electrical devices.  
           [0003]    In the event of an overcurrent condition (e.g., a short circuit), extremely high electromagnetic forces are generated. These electromagnetic forces repel the movable contact away from the stationary contact. Because the movable contact is fixedly attached to a rotating arm, the arm pivots and physically separates the stationary and movable contacts thus blowing open (tripping) the circuit. Upon separation of the contacts and blowing open the circuit, an arcing condition occurs. It is desirable to suppress the resultant arc in order to minimize the energy that the breaker sees, thus minimizing breaker damage. The typical method of suppressing the arc is to direct it into an arc chute, which is generally a series of metal plates that dissipate the energy of the arc. This arc chute is situated proximate to the stationary contact point of the circuit.  
           [0004]    Such arc chute assemblies consist of a plurality of metallic chute plates that are held in a stacked, spaced-apart relationship by side panels that are fabricated from electrically non-conductive material. Retention of the chute plates between the side panels is usually achieved by providing the plates with small protrusions that are slipped into a series of radiused notches in the side panels.  
           [0005]    An arc runner is used to direct the arc to the arc chute. The arc runner substantially covers the exposed area of the stationary contact disposed on the strap. Blowing a circuit open thus resulting in an arc causes tremendous stress to the parts of the system. Since the arc runner provides a pathway for the arc to follow to the arc chute, it is subject to intensely high temperatures. The construction of an arc runner, and especially its manner of securement to the strap, is critical to reliable dissipation of an arc.  
           [0006]    Conventional methods of securing an arc runner to a load or line strap increase the costs of manufacturing a circuit breaker because of the hardware involved. The arc runner is typically screwed onto the strap, as described in U.S. Pat. No. 5,877,467 entitled “Circuit Breaker Current Limiting Arc Runner”. Similarly, U.S. Pat. No. 5,075,520 entitled “Contact Member for Electrical Switching Devices” describes an arc runner having one end inserted into a groove in a block and then having the arc runner secured to the block by a screw. The use of a screw in the fastening operation adds the cost of an extra piece of hardware to the manufacturing process.  
           [0007]    Bolts are also used to secure an arc runner to a strap. For example, U.S. Pat. No. 4,229,630 entitled “Circuit Breaker Utilizing Improved Arc Chambers” describes using a pair of bolts that extend through openings in an arc runner to secure the arc runner to a stationary contact. Another method of securing an arc runner to a strap includes the use of rivets, as discussed in U.S. Pat. No. 4,771,140 entitled “Circuit Interrupter”, wherein a single rivet pierces the body of an arc runner and a stationary conductor to firmly connect the arc runner to the stationary conductor. Bolts and rivets add the cost of an extra piece of hardware to the manufacturing process in the same way that screws do.  
           [0008]    Brazing, or Welding, as discussed in U.S. Pat. No. 5,818,003 entitled “Electric Switch with Arc Chute, Radially Converging Arc Splitter Plates, and Movable and Stationary Arc Runners”, provides a further option for securing an arc runner to a strap, wherein the strap is directly welded to a D-shaped arc runner. Although brazing and welding do not introduce an additional discrete component into the manufacturing process, they do contribute to the expenses associated with the finished product.  
           [0009]    In most conventional circuit breaker designs, a lower arc runner is brazed to the fixed contact strap and a top arc runner is snapped into the cassette molding. The disadvantage of this design is that the upper arc runner could conceivably be installed improperly or forgotten entirely. Also, as mentioned, brazing the lower arc runner to the fixed contact strap adds manufacturing costs and complexity.  
           [0010]    In addition to the costs of the hardware used to fasten the arc runner to the strap, tools are required. Automated assembly systems and automated welders are usually expensive to install and run. Furthermore, the maintenance for these systems is costly, and the use of such systems often poses reliability concerns. Hand-held tools such as wrenches and screwdrivers, on the other hand, are far less expensive. The use of small hand-held tools may, however, increase the time required for assembly of an arc runner to a load strap because machine assembly is usually faster than hand assembly is. An increase in the time required for assembly using hand-held tools is becoming cost prohibitive. Furthermore, hand-held tools, because of their size, frequently tend to be misplaced and need to be replaced on a regular basis. Constant replacement of even the most inexpensive tools can be a limiting factor.  
           [0011]    Circuit breaker design, and more particularly, cassette design should enable the efficient and proper positioning of the various components, such as the rotor and arc chute assemblies, into the cassette. For example, care must be taken to ensure that an arc chute assembly is correctly positioned into the cassette. This ensures proper rotation of the moveable contact arm as well as the proper spacing between the moveable contact and the plate closest to the moveable contact. Improper installation of an arc chute assembly into a cassette half piece will require disassembly and reassembly of the cassette. Such disassembly and reassembly is time consuming and can increase the production cost of the circuit breaker.  
         BRIEF SUMMARY OF THE INVENTION  
         [0012]    The above discussed and other drawbacks and deficiencies are overcome or alleviated by a modular arc chamber assembly suitable for use in a cassette assembly in a circuit breaker comprising: an electrically insulative first side member, an electrically insulative second side member; a plurality of plates disposed between said first and second side members and arranged in a stacked spaced-apart relationship, and an arc runner plate disposed at one end and between the first and second side members capable of directing an arc to an arc dissipating chute comprised of the plurality of arc plates.  
           [0013]    The above-discussed and other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0015]    [0015]FIG. 1 is a front perspective view of a circuit breaker rotary cassette assembly;  
         [0016]    [0016]FIG. 2 is a front perspective view of a first electrically insulative cassette half piece of the cassette assembly;  
         [0017]    [0017]FIG. 3 is a view of a first electrically insulative cassette half piece of the cassette assembly showing the arc chamber recesses and retention features;  
         [0018]    [0018]FIG. 4 is a view of a second electrically insulative cassette half piece of a cassette assembly showing the arc chamber recesses and retention features;  
         [0019]    [0019]FIG. 5 is a top view of a preferred embodiment of a modular arc chamber assembly employed in the electrically insulative cassette half pieces of FIGS. 2 and 3;  
         [0020]    [0020]FIG. 6 is a front perspective view of an arc chamber assembly of FIG. 4 employed in the electrically insulative cassette half pieces of FIGS. 2 and 3;  
         [0021]    [0021]FIG. 7 is a side view of an arc side member employed in the modular arc chamber assembly of FIG. 4;  
         [0022]    [0022]FIG. 8 is a front perspective view of a preferred embodiment of a modular arc chamber assembly employed in a cassette assembly; and  
         [0023]    [0023]FIG. 9 is a view of a preferred embodiment of a modular arc chamber assembly employed in a cassette assembly. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0024]    Referring to FIG. 1, a rotary contact assembly  12  in a circuit breaker cassette assembly  10  is shown in a first electrically insulative cassette half piece  14  intermediate a line-side contact strap  16 , load-side contact strap  18  and associated arc chambers  20 ′,  22 ′. Line-side contact strap  16  is electrically connected to line-side wiring (not shown) in an electrical distribution circuit, and load-side contact strap  18  is electrically connected to load-side wiring (not shown) via a lug (not shown) or some device such as a bimetallic element or current sensor (not shown). Electrically insulative shields  24 ,  26  separate load-side contact strap  18  and line-side contact strap  16  from the associated arc chamber assemblies  20 ,  22  respectively. Although a single rotary contact assembly  12  is shown, it is understood that a separate rotary contact assembly  12  is employed within each pole of a multi-pole circuit breaker and operates in a similar manner.  
         [0025]    Electrical transport through the circuit breaker interior proceeds from the line-side contact strap  16  to associated first fixed and first moveable contacts  28 ,  30  at one end of a movable contact arm  32 , to second fixed and second movable contacts  34 ,  36  at the opposite end thereof, to the associated load-side contact strap  18 . The movable contact arm  32  is arranged between two halves of a circular rotor  37 . Moveable contact arm  32  moves in unison with the rotor  37  upon manual articulation of the circuit breaker operating mechanism (not shown) to drive the first and second movable contacts  30 ,  36  between CLOSED and OPEN (depicted in FIG. 1) positions.  
         [0026]    In an exemplary embodiment, modular arc chamber assemblies  20 ,  22  are positioned in the first electrically insulative cassette half piece  14  adjacent the respective pairs of first fixed and first moveable contacts  28 ,  30  and second fixed and second moveable contacts  34 ,  36 . The first and second movable contacts  30 ,  36  and moveable contact arm  32  move through a passageway provided by arc plates intermediately disposed on modular arc chamber assemblies (not shown)  20 ,  22  in order to engage and disengage the respective first and second fixed contacts  28 ,  34 . Each modular arc chamber assembly  20 ,  22  is adapted to interrupt and extinguish the arc which forms when a circuit breaker is tripped and the first and second moveable contacts  30 ,  36  are suddenly separated from the first and second fixed contacts  28 ,  34 .  
         [0027]    Referring to FIGS. 2 and 3, the first electrically insulative cassette half piece  14  is shown. First electrically insulative cassette half piece  14  has an inner surface  52  having a rotor recess  56  also formed on the inner surface  52 . Arc chambers  20 ′,  22 ′ (shown in phantom) are disposed on either side of the rotor recess  56 . FIG. 3 shows load-side and line-side contact strap recesses  67 ,  69  that are also formed on the inner surface  52  proximate arc chamber recesses  58 ,  60 . Arc chamber recesses  58 ,  60  are substantially rectangular with each having defined complementary pockets (e.g., recesses)  64 ,  66  respectively to more clearly define a recessed pocket in which to position a modular arc chamber assembly  20 ,  22 . It should also be noted that defined complementary pockets  64 ,  66  are positioned and oriented to the load-side and line-side contact strap recesses  67 ,  69 .  
         [0028]    Referring to FIG. 4, a second electrically insulative cassette half piece  71  is shown prior to attaching with the first electrically insulative cassette half piece  14  (FIG. 3) to form a complete enclosure. Second electrically insulative cassette half piece  71  has an inner surface  52 . Second electrically insulative cassette half piece  71  is attached to the first electrically insulative cassette half piece  14  (FIG. 3) by suitable mechanical fastening means. A rotor recess  56  is also formed on the inner surface  52 . Load-side and line-side contact strap recesses  67 ,  69  are also formed on the inner surface  52  proximate the arc chamber recesses  58 ,  60  clearly defining a pocket in which to position a modular arc chamber assembly. It should be noted that a pocket is clearly defined with defined complementary pockets  64 ,  66  as part of the arc chamber recesses  58 ,  60 .  
         [0029]    Referring to FIGS. 5 and 6, a modular arc chamber assembly  22  for a circuit breaker is shown. The modular arc chamber assembly  22  includes a plurality of plates  68  (drawn in phantom lines in FIG. 5), a first side member  70  and a second side member  72 . The plurality of plates  68  are intermediate a first arc runner plate  80  at one end and a second arc runner plate  81  at the other end. The first arc runner plate  80  further includes a tab  88  extending and angled therefrom to facilitate guiding an arc into the chamber  22 ′. Typically, the plates  68  are metallic so as to induce magnetism thereby promoting arc movement into arc chamber assembly  22 . Each plate  68  and each arc runner plate  80 ,  81  have a protrusion  74  extending from each side thereof for coupling each plate  68  and each runner plate  80 ,  81  to side members  70 ,  72 , via an interference fit. Each plate  68  also includes a radiused notch  78  formed on one side thereof. The radiused notch  78  provides clearance for the contact arm  32  when the arc chute assembly  22  is mounted within the electrically insulative cassette half pieces  14 ,  71  (FIGS. 2 and 3). An exemplary embodiment includes a first arc runner plate  80  at one end of a modular arc chamber assembly and a second arc runner plate  81  at the other end that does not extend beyond side members  70 ,  82  (FIG. 6) of the modular arc chamber assembly second arc runner plate  81  and is in close proximity with either a load-side or a line-side contact strap  16 ,  18 . Arc runner plate  80  further includes a tab extending therefrom and angled to facilitate guidance of an arc into arc chamber assembly  22 .  
         [0030]    Referring to FIGS. 6 and 7, first and second side members  70 ,  72  have a plurality of slots  76  formed therethrough. Each protrusion  74  of the plates  68  and the runner plates  80 ,  81  are respectively inserted into a corresponding slot  76  formed in the first and second side members  70 ,  72 . The plates  68  are disposed in this manner between the first and second side members  70 ,  72  and are arranged in a stacked, spaced-apart relationship to each other. Second side member  72  is identical to first side member  70 . The first and second side members  70 ,  72  are assembled so as to be opposedly oriented to each other. First side member  70  has a defined portion (i.e., a protruding tab)  86  offsetly located and proximate arc runner plate  81  to facilitate assembly of an arc chamber assembly  22  into an arc chamber  22 ′. A defined portion  86  is similarly located along second side member  72 .  
         [0031]    Turning to FIG. 8, a second arc chamber assembly  20  comprises a plurality of plates  68  and third and fourth side members  82 ,  84 . Third and fourth side members  82 ,  84  are identical to first and second side members  70 ,  72 . Third and fourth side members  82 ,  84  are assembled so as to be opposedly oriented to each other. Third side member  82  has a defined portion  86  offsetly located and proximate to arc runner plate  81 . A defined portion  86  is similarly located along the fourth side member  84 . In an exemplary embodiment, a modular arc chamber assembly comprises two arc runner plates  80 ,  81  having arc runner plate  81  near the contact  28  making in close proximity with an edge of contact  28  and an edge of the first arc runner plate  81 . Arc runner plate  80  is disposed at an opposite end substantially parallel to plates  68  within the assembly  20  and further includes a tab  88  extending towards contact  36  to help direct an arc into assembly  20  to dissipate when circuit breaker  10  is in the OPEN position. Modular arc chamber assembly  22  would be similarly constructed.  
         [0032]    Referring to FIGS. 2, 3,  4  and  9 , the first modular arc chamber assembly  22  is correctly positioned into the first electrically insulative cassette half piece  14  by orienting and placing defined portion  86  of the first side member  70  into the first recess  60  having offset extension  66  of first electrically insulative cassette half piece  14 . Similarly, the second modular arc chamber assembly  20  is correctly positioned into the first electrically insulative cassette half piece  14  by orienting and placing defined portion  86  to fit into the second recess  58  having defined portion  86  of first electrically insulative cassette half piece  14 . It should be noted that the defined portion  86  provides only one orientation of the arc chamber assembly in order to fit within the recesses  58 ,  60  of cassette.  
         [0033]    An alternative embodiment is absent any defined portions  86  and defined complementary pockets  64 ,  66  to correctly position the arc chamber assemblies  22 ,  20 . It should be noted that if a cassette assembly does not include defined portions  86  and defined complementary pockets  64 ,  66  to facilitate positioning the arc chamber assemblies  22 ,  20  for example, then the radiused notches  78  (shown in FIGS. 5 and 8) in the plates  68  might be incorrectly positioned to face opposite the first and second moveable contacts  30 ,  36  and the first and second fixed  28 ,  34  contacts. If this were to occur, the moveable contact arm  32  would not be permitted to rotate when the circuit breaker is tripped due to a short circuit event. Also, the arc chamber assembly  22  could be placed upside down with respect to the first electrically insulative cassette half piece  14 . If this were to occur, there can be insufficient air space between the plate  68  that is closest to the first moveable contact  30  and the line-side contact strap  16 . The loss of a conducting plate in the arc chute assembly  22  can result in an insufficient arc quenching. Thus, defined portions  86  ensure the correct positioning of the arc chamber assemblies  22 ,  20  within the recesses  58 ,  60 . Furthermore, the inner surface  52  of an electrically insulative cassette half piece in a preferred embodiment includes a groove for top runner and) recesses formed therein for proper positioning.  
         [0034]    Referring now to FIGS. 2, 3,  4 ,  5 ,  6  and  7 , after the first and second arc chamber assemblies  22 ,  20  are properly assembled into the first electrically insulative cassette half piece  14 , the second electrically insulative cassette half piece  71  is placed over the first electrically insulative cassette half piece  14  to form a complete enclosure. As a result, defined portion  86  of the second side member  72  will be inserted into a third recess  64  of the second electrically insulative cassette half piece  60 . Defined portion  86  of the fourth side member  84  will likewise be inserted into the fourth recess  66  of the second electrically insulative cassette half piece  71 . Thus, the first and second arc chamber assemblies  22 ,  20  will be correctly positioned into the first and second electrically insulative cassette half pieces  14 ,  71 . Proper operation of the rotary contact arm assembly is achieved.  
         [0035]    The first, second, third and fourth side members  70 ,  72 ,  82 ,  84  have been heretofore described with defined portions  86  that are offsetly located. The advantage to this arrangement of the defined portion  86  along the respective ends of the side members  70 ,  72 ,  82 ,  84  is the cost savings attributed to forming one stamped pattern that can be used for all side members  70 ,  72 ,  82 ,  84  for both the first and second arc chamber assemblies  22 ,  20 .  
         [0036]    Since the first and second arc chamber assemblies  22 ,  20  are assembled prior to placement within the first electrically insulative cassette half piece  14 , correct positioning of the first and second arc chamber assemblies  22 ,  20  can also be achieved by using defined portions  86  on only the first and third side members  70 ,  82 . In this alternative embodiment, the second and fourth side members  72 ,  84  would have no defined portions  86 . However, this would require the manufacture of two structurally different side members. Further, defined portions  86  on the first and third side members  70 ,  82 , as well as second and fourth side members  72 ,  84 , can be located generally central as opposed to located offset along the edges of the respective side members. However, this would require additional time to consider the orientation of the notches  78  respective to the contact arm location and the manufacture of a third type of side member to accommodate the defined center portion arrangement.  
         [0037]    As described herein, a cassette assembly for rotary contact circuit breakers utilizing a first electrically insulative cassette half piece  14  and a second electrically insulative cassette half piece  71  are arranged to mate with each other to form an enclosure. The electrically insulative cassette half pieces  14 ,  71  include improper installation rejection features for the arc chamber assemblies  22 ,  20 . Therefore, the cassette assembly, as described herein, prevents such disassembly and reassembly that can be time consuming and increase the production cost of the circuit breaker. Furthermore, by incorporating at least one runner plate with an arc chute assembly, a brazing or welding step may be eliminated, or alternatively, a runner is less likely not to be installed, thereby reducing manufacturing costs and complexity.  
         [0038]    While this invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but rather that the invention will include all embodiments falling within the scope of the appended claims.