Patent Publication Number: US-2007095793-A1

Title: Secondary arc chute and electrical switching apparatus incorporating same

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application is related to commonly assigned, concurrently filed U.S. patent application Ser. No. __/______, filed ______, 2005, entitled “Arc Plate with Runner, and Arc Chute and Electrical Switching Apparatus Incorporating Same” (Attorney Docket No. 03-EDP-086). 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates generally to electrical switching apparatus and, more particularly, to arc chutes of circuit breakers. The invention also relates to arc chutes for electrical switching apparatus and to electrical switching apparatus having arc chutes.  
      2. Background Information  
      Circuit breakers and other electrical switching apparatus (e.g., without limitation, circuit switching devices and other circuit interrupters such as contactors, motor starters, motor controllers and other load controllers) typically include a set of stationary electrical contacts and a set of moveable electrical contacts. The stationary and moveable contacts are in physical contact with one another when it is desired that the circuit breaker provide electrical current therethrough to a load. When it is desired to interrupt the circuit, however, the moveable contacts are moved away from the stationary contacts, thus removing the moveable contacts from physical contact with the stationary contacts and creating a space therebetween.  
      The movement of the moveable contacts away from the stationary contacts results in the formation of an electrical arc in the space between the contacts beginning at the time the contacts are initially separated. Such an arc is undesirable for a number of reasons. For one, it provides a pathway for current to flow through the circuit breaker to the load when it is desired to isolate the load from such current. Additionally, the electrical arc extending between the contacts often results in vaporization or sublimation of the contact material itself, eventually resulting in destruction or pitting of the moveable and stationary contacts. It is thus desired to eliminate any such arcs as soon as possible.  
      The moveable contact is typically mounted on an arm that is contained in a pivoting assembly which pivots the moveable contact away from the stationary contact. An arc chute is provided along the path of the arm to break up and dissipate such arcs. Such arc chutes typically include a plurality of spaced apart arc plates mounted in a wrapper. As the moveable contact is moved away from the stationary contact, the moveable contact moves past the ends of the arc plates, with the arc being magnetically urged toward and between the arc plates. The arc plates are electrically insulated from one another such that the arc is broken up and extinguished by the arc plates. Examples of arc chutes are disclosed in U.S. Pat. Nos. 6,703,576; 6,297,465; 5,818,003; and 4,546,336. Generally, in operation in an air circuit breaker, for example, the stack of arc plates divides-up the arc voltage in the circuit breaker in order to extinguish the arc and produce a current-limiting effect, thereby providing downstream protection. This cools the arc and splits the same into series arcs. Cooling, in turn, results from arc attachment to the arc plates. Arc cooling also depends on the gas flow over the plates (e.g., convection) and hot gas removal out of a vent in the circuit breaker housing.  
      Arc plate geometry, the number of plates within the arc chute, and other parameters, such as spacing between arc plates, have evolved over the years as attempts have been made to provide optimum arc dissipation. Additionally, many arc chute designs employ devices such as, for example, an arc horn, or other structure which is specifically designed to draw the arc into the arc chute. See, e.g., U.S. Pat. No. 6,417,474. An arc horn generally comprises an extension of an arc plate which is bent or otherwise directed toward the direction in which it is desired to coax the arc. Such devices are most often present on the first arc plate among the stack of arc plates in the arc chute, and are designed to draw the arc away from the separable contacts, upward into the other arc plates. However, the arc has a tendency to follow the inside edge of the arc chute adjacent the separable contacts which can cause heavy erosion of the arc plates and damage to the nearby separable contacts.  
      There is, therefore, room for improvement in arc chutes for electrical switching apparatus, and in electrical switching apparatus having arc chutes.  
     SUMMARY OF THE INVENTION  
      These needs and others are met by the present invention, which is directed to a secondary arc chute for an electrical switching apparatus.  
      As one aspect of the invention, a secondary arc chute is provided for an electrical switching apparatus. The electrical switching apparatus includes a housing, a pair of separable contacts enclosed within the housing, and a primary arc chute disposed proximate the separable contacts in order to attract an arc generated by the separable contacts. The primary arc chute has a first end including an arc horn, and a second end. The secondary arc chute comprises: a chute member including a first portion structured to be disposed at or about the arc horn of the primary arc chute, and a second portion, wherein the chute member is structured to provide an extension of the primary arc chute in order to facilitate drawing the arc away from the separable contacts, to cool and dissipate the arc, and to ground the arc into the housing of the electrical switching apparatus.  
      The first portion of the chute member may comprise a hook structured to attract the arc. The hook may include a tip structured to be disposed proximate the arc horn at or about the first end of the primary arc chute. The tip of the hook may comprise a first arc runner extension and the second portion of the chute member may include a second arc runner extension wherein the first and second arc runner extensions are structured to attract the arc from the arc horn. The second portion of the chute member may also include a pair of opposing tab extensions which extend generally vertically from the second portion wherein the pair of opposing tab extensions are structured to be disposed proximate the arc horn of the primary arc chute in order to further attract and dissipate the arc.  
      The chute member may comprise a single-piece chute member. The single-piece chute member may be made from a metallic material and may include a number of bends. The chute member may also be made from a magnetic material, such as for example, without limitation, nickel-plated steel.  
      As another aspect of the invention, an electrical switching apparatus comprises: a housing; separable contacts enclosed within the housing; an operating mechanism structured to open and close the separable contacts; a primary arc chute disposed proximate the separable contacts in order to attract an arc generated by the separable contacts, the primary arc chute including an end; and a secondary arc chute comprising: a chute member including a first portion disposed at or about the end of the primary arc chute, and a second portion, the first portion of the chute member being structured to draw the arc out of the primary arc chute and away from the separable contacts, the second portion of the chute member being structured to ground the arc into the housing of the electrical switching apparatus.  
      The end of the primary arc chute may include an arc horn and the first portion of the chute member may include a hook disposed proximate the arc horn at or about the end of the primary arc chute. The secondary arc chute may be coupled to the housing of the electrical switching apparatus. More specifically, the second portion of the chute member may include an opening and the secondary arc chute may further include at least one fastener inserted through the opening in order to secure the chute member to the housing. Alternatively, the secondary arc chute may be coupled to the primary arc chute.  
      The secondary arc chute may have a surface area and the chute member includes a number of surface area enlarging mechanisms selected from the group consisting of openings, hooks, tab extensions, fms, and a combination of openings, hooks, tab extensions and fms, wherein the surface area enlarging mechanisms are structured to enlarge the surface area of the secondary arc chute in order to further attract, dissipate and cool the arc. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:  
       FIG. 1  is a vertical elevational view of an arc chute of a molded case circuit breaker employing arc plates;  
       FIG. 2  is an isometric view of one of the arc plates of  FIG. 1 ;  
       FIG. 3  is an isometric view of a secondary arc chute in accordance with the present invention;  
       FIG. 4  is a vertical elevational view of the secondary arc chute of  FIG. 3  as employed in a molded case circuit breaker along with the arc chute of  FIG. 1 ; and  
       FIG. 5  is a vertical elevational view of the secondary arc chute and portions of the molded case circuit breaker of  FIG. 4 , with all but one arc plate of the arc chute removed. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      For purposes of illustration, the invention will be described as applied to the arc chute of a molded case circuit breaker, although it will become apparent that it could also be applied to a wide variety of electrical switching apparatus (e.g., without limitation, circuit switching devices and other circuit interrupters such as contactors, motor starters, motor controllers and other load controllers) having an arc chute with a plurality of arc plates.  
      Directional phrases used herein, such as, for example, left, right, top, bottom, front, back and derivatives thereof, relate to the orientation of the elements shown in the drawings and are not limiting upon the claims unless expressly recited therein.  
      As employed herein, the term “fastener” refers to any suitable connecting or tightening mechanism expressly including, but not limited to, screws, bolts and the combinations of bolts and nuts (e.g., without limitation, lock nuts) and bolts, washers and nuts.  
      As employed herein, the statement that two or more parts are “coupled” together shall mean that the parts are joined together either directly or joined through one or more intermediate parts.  
      As employed herein, the term “secondary” shall refer to a component which is structured to assist, supplement or otherwise improve upon the functionality of one or more primary components. For example, the secondary arc chute disclosed herein is intended to be used in combination with the existing primary arc chute in order to supplement (i.e., improve) the arc cooling and dissipating capabilities of the same.  
      As employed herein, the term “number” shall mean one or more than one (i.e., a plurality).  
      Referring to the figures, an electrical switching apparatus, such as a molded case circuit breaker  2 , in accordance with aspects of the invention includes a housing  4 , separable contacts  6  enclosed within the housing  4 , and an operating mechanism  8  which is structured to open and close the separable contacts  6  and to trip open the separable contacts  6  in response to a trip condition (e.g., without limitation, an overcurrent condition, an overload condition, an undervoltage condition, or a relatively high level short circuit or fault condition), as is well known. For simplicity of illustration, the separable contacts  6  and operating mechanism  8  are shown in simplified form in  FIG. 1 . An arc chute  10  is disposed adjacent to the separable contacts  6  in order to attract and dissipate an arc which is generated by the separable contacts  6 , when opened.  
      As shown in  FIG. 1 , the arc chute  10  generally comprises a support structure  12 ,  14  which holds a plurality of arc plates  30 ,  30 ′,  30 ″ in a spaced, stacked relation proximate the separable contacts  6 . At least some of the arc plates  30 ,  30 ′ include a first end  34 ,  34 ′ which is disposed generally proximate the separable contacts  6 , and a second end  36 ,  36 ′ which is disposed distal from the separable contacts  6 . At least one of the arc plates  30 ,  30 ′ includes an integral arc runner  46 ,  46 ′ which is structured to draw the aforementioned arc into the arc chute  10  and toward the second ends  36 ,  36 ′ of the arc plates  30 ,  30 ′. In this manner, the arc chute  10  of the invention functions not only to draw the arc into the arc chute  10 , as is conventionally known, but further to attract such arc to the back (e.g., toward second ends  36 ,  36 ′ of arc plates  30 ,  30 ′) of the arc chute  10 , thereby directing the arc as far away from the separable contacts  6  as possible in order to avoid arc damage to the separable contacts  6  and to reduce arc plate erosion.  
      In the example of  FIG. 1 , the arc chute  10  includes an arc horn  20  and nine arc plates  30 ,  30 ′  30 ″ supported by the support structure which comprises a pair of opposing side walls  12 ,  14  (side wall  12  has been substantially cut away in  FIG. 1  to show internal structures of arc chute  10 ). The opposing side walls  12 ,  14  have openings or slots  22 ,  24  structured to receive corresponding first and second protrusions  42 ,  42 ′ ( FIG. 1 ),  44 ,  44 ′ ( FIG. 4 ) which protrude laterally from the first and second sides  38 ,  38 ′ ( FIG. 1 ),  40 ,  40 ′ ( FIG. 4 ) of the arc plates  30 ,  30 ′ (best shown in  FIG. 2 ). Included among the nine arc plates in the example of  FIG. 1 , are one first arc plate  30 , five second arc plates  30 ′, and three third arc plates  30 ″. The second arc plates  30 ′ are generally disposed towards the first end  16  or top (from the perspective of  FIG. 1 ) of the arc chute  10 , while the third arc plates  30 ″ are generally disposed towards the second end  18  or bottom, as shown. The exemplary first arc plate  30  constitutes the fourth arc plate up from the bottom (from the perspective of  FIG. 1 ) or second end  18  of the arc chute  10 , and is disposed intermediate the second and third arc plates  30 ′,  30 ″. It will be appreciated, however, that any suitable number of each type of arc plate  30 ,  30 ′,  30 ″ could be employed in any suitable arc chute configuration other than the configuration shown and described with respect to the example of  FIG. 1 .  
      A further understanding of the arc plates  30 ,  30 ′ in accordance with aspects of the invention will be had with reference to  FIG. 2 . For simplicity of disclosure, the structure of the second arc plates  30 ′, will first be described as shown in  FIG. 2 . Then, with reference to  FIG. 1 , differences between the second arc plate  30 ′ and first arc plate  30  will be discussed. In this regard, it will be appreciated that the first and second arc plates  30 ,  30 ′ are substantially similar in structure except for the fact that the arc runner  46  of first arc plate  30  includes at least one bend, as will be discussed herein.  
      In the example of  FIG. 2 , the arc plate  30 ′ comprises a plate member  32 ′ which is structured to be secured between the pair of opposing side walls  12 ,  14  ( FIG. 1 ) by way of the first and second protrusions  42 ′,  44 ′, as previously discussed. The first end  34 ′ of the arc plate  30 ′ which, when assembled within the arc chute  10  ( FIG. 1 ), is disposed generally proximate the separable contacts  6  ( FIG. 1 ), includes a notch or throat  35 ′. The throat  35 ′ is structured to accommodate the path of a moving arm carrying a moveable contact (not shown) of the separable contacts  6  ( FIG. 1 ). The second end  36 ′ of the plate member  32 ′ includes the aforementioned arc runner  46 ′ which comprises an integral protrusion, such as the tab extension  46 ′ shown. The exemplary integral tab extension  46 ′ includes a tapered portion  48 ′ which is structured to further attract the arc. More specifically, the arc plate  30 ′ is contemplated as being made from any known or suitable magnetic material, such as for example, without limitation, nickel-plated steel. Accordingly, the tapered portion  48 ′ of integral arc runner  46 ′ provides a location of consolidated magnetic flux which has a tendency to attract the arc toward it, and thus away from first end  34 ′, as desired.  
      Referring back to  FIG. 1 , it will be understood that the first arc plate  30  includes all of the foregoing structures (e.g., plate member  32 , tab extension  46 , and tapered portion  48 ) except the arc runner  46 ′. The arc runner  46  of the first arc plate  30 , however, is bent upward (from the perspective of  FIG. 1 ) in order to direct the arc toward the second end  36 ′ of the second arc plates  30 ′, which are substantially straight. Specifically, the plate member  32  includes a body portion  50  which lies in a plane  52 , and the integral tab extension arc runner  46  includes a bend  54  proximate the second end  36  in order that the tab extension  46  forms an angle  56  with respect to the plane  52 , as shown. The angle  56  is preferably between about 20 degrees and about 50 degrees with respect to the plane  52  of the body portion  50  of first arc plate  30 . However, it will be appreciated that any suitable angle, or alternative arc runner configuration (not shown), could be employed. For example, without limitation, the arc runner  46  could include more than one bend (not shown). It will also be appreciated that the integral tab extension which comprises the arc runner  46  of first arc plate  30  is slightly longer than the arc runner  46 ′ of second arc plates  30 ′, which are substantially straight. This added length, the exact amount of which is not meant to be limiting upon the invention, accounts for the bend  54  in first arc plate  30  while allowing the arc runner  46  thereof to be directed toward the second end  36 ′ of the adjacent second arc plate  30 ′, as shown in  FIG. 1 .  
      Accordingly, aspects of the present invention provide an arc chute  10  having arc plates  30 ,  30 ′ which effectively draw the arc into the chute to the location within the chute  10  most distal from the separable contacts  6 .  
       FIGS. 3, 4  and  5  show a secondary arc chute  70  for an electrical switching apparatus, such as the aforementioned circuit breaker  2 , in accordance with the invention. It will be appreciated that the secondary arc chute  70  may be used in combination with the aforementioned arc chute  10  having arc plates  30 ,  30 ′ or alternatively, with any known or suitable conventional arc chute (not shown). In either circumstance, the existing arc chute (e.g., arc chute  10 ) is the primary arc chute.  
      As shown in  FIG. 3 , the secondary arc chute  70  generally comprises a chute member  72  which, in the example shown, is a single-piece member made from any known or suitable metallic material. For example, like the aforementioned arc plates  30 ,  30 ′, the chute member  72  of the exemplary secondary arc chute  70  is contemplated as being made from a magnetic material, such as for example, without limitation, nickel-plated steel. The chute member  72  includes a first portion  74  structured to be disposed at or about the arc horn  20  ( FIGS. 4 and 5 ) at the first end  16  ( FIG. 4 ) of the primary arc chute  10  ( FIG. 4 ) and a second portion  76 .  
      The first portion  74  of the chute member  72  comprises a hook  78 . The hook  78  includes a tip  80  which forms a first arc runner extension  80  structured to be disposed proximate the arc horn  20 , as shown in  FIG. 4 . The second portion  76  of the chute member  72  includes a second arc runner extension  82 . The first and second arc runner extensions  80 ,  82  are structured to attract the arc from the arc horn  20  ( FIGS. 4 and 5 ) of the primary arc chute  10  in order to facilitate drawing the arc away from the separable contacts  6  ( FIG. 1 ) of the circuit breaker  2  ( FIG. 1 ). To further attract and dissipate the arc, the second portion  76  of the chute member  72  further includes a pair of opposing tab extensions  84 ,  86  which extend generally vertically from the second portion  76 , as shown. The chute member  72  includes a number of bends  88  in order to create, for example, the aforementioned hook  78 , second arc runner extension  82 , and opposing tab extensions  84 ,  86 . These structures, in addition to an opening  90  and pair of fins  94 , as shown, serve to provide areas of concentrated magnetic flux having a tendency to attract the arc, as desired. These features also constitute surface area enlarging mechanisms which are structured to enlarge the surface area of the secondary arc chute  70 . It will be appreciated that any suitable combination of surface area enlarging mechanisms  78 ,  84 ,  86 ,  90 ,  94  other than the hook  78 , tab extension  84 ,  86 , opening  90 , and configuration of fins  94  as shown, could be employed in order to further attract, dissipate and cool the arc.  
      As shown in  FIG. 4 , the secondary arc chute  70  is coupled to the housing  4  of the circuit breaker  2  and, although the exemplary secondary arc chute  70  is not coupled directly to the arc horn  20  of the primary arc chute  10  in the example shown, it will be appreciated that in other embodiments of the invention it could be so coupled without departing from the scope of the invention. In the example of  FIGS. 4 and 5 , the tip  80  of hook  78  and the tab extensions  84 ,  86  are disposed adjacent to, but are not touching the arc horn  20  (best shown in  FIG. 5 ). The exact spacing between these components is not meant to be a limiting aspect of the invention. The secondary arc chute  70  is coupled to the housing  4  by way of a fastener, such as the screw  92  (shown in hidden line drawing in  FIG. 4 ). The screw  92  is inserted through opening  90  (best shown in  FIG. 3 ) of the chute member  72  and suitably tightened, in order to secure the chute member  72  in the aforementioned configuration. It will, however, be appreciated that any known or suitable fastening mechanism (not shown) other than the exemplary screw  92 , could be employed. For example, without limitation, the chute member  72  could be adhered using any known or suitable adhesive or it could be coupled with an interlocking arrangement (not shown) with the housing. It will be appreciated, therefore, that the secondary arc chute  70  also functions to ground the arc into the housing  4 .  
      Accordingly, the secondary arc chute  70  of the invention provides a supplemental arc dissipating mechanism which attracts the arc and further facilitates drawing it away from the separable contacts  6  ( FIG. 1 ) of the circuit breaker  2  ( FIG. 1 ) while also providing a variety of surface area enlarging mechanisms (e.g., hook  78 , arc runner extensions  80 ,  82 , tab extensions  84 ,  86 , openings  90 , and fms  94  to attract, cool and dissipate the arc, as well as to ground the arc into the housing  4  of circuit breaker  2 .  
      While specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.