Abstract:
A circuit breaker rotary contact arm is used within a plurality of single pole circuit breakers ganged together to form a single multi-pole circuit breaker. To provide uniform contact wear among the associated circuit breaker contacts, the rotor carrying the rotary contact arm pivot is slotted to automatically position the rotary contact arm to allow for changes in the contact geometry while maintaining constant contact compressive forces. The individual circuit breakers connect with the central operation mechanism by means of a single pin.

Description:
BACKGROUND OF THE INVENTION 
     U.S. Pat. No. 4,616,198 entitled “Contact Arrangement for a Current Limiting Circuit Breaker” describes the early use of a first and second pair of circuit breaker contacts arranged in series to substantially reduce the amount of current let-through upon the occurrence of an overcurrent condition. 
     When the contact pairs are arranged upon one movable rotary contact arm, such as described within U.S. Pat. No. 4,910,485 entitled “Multiple Circuit Breaker with Double Break Rotary Contact”, some means must be provided to insure that the opposing contact pairs exhibit the same contact pressure to reduce contact wear and erosion. 
     One arrangement for providing uniform contact wear is described within U.S. Pat. No. 4,649,247 entitled “Contact Assembly for Low-voltage Circuit Breakers with a Two-Arm Contact Lever”. This arrangement includes an elongated slot formed perpendicular to the contact travel to provide uniform contact closure force on both pairs of contacts. 
     U.S. Pat. No. 5,030,804 entitled “Contact Arrangement for Electrical Switching Devices” describes providing a pair of cylindrical plates on either side of the rotary contact arms and forming elongated slots within each of the cylindrical plates. 
     When the rotary contacts are used within a range of differing ampere-rated circuit breakers, the size of the contact arms varies in accordance with the ampere rating such that the accompanying cylindrical plates must be sized accordingly. 
     It would be economically advantageous to have a wide range of rotary contact circuit breakers having provision for reducing contact wear without having to stock and assemble a wide range of slotted cylindrical plates. 
     Accordingly, one purpose of the invention is to include means for reducing such contact wear in rotary contact circuit breakers over a wide range of ampere ratings with the smallest number of associated contact assembly components. 
     SUMMARY OF THE INVENTION 
     A circuit breaker rotary contact arm is used within a plurality of single pole circuit breakers ganged together to form a single multi-pole circuit breaker. To provide uniform contact wear among the associated circuit breaker contacts, the rotor carrying the rotary contact arm pivot is slotted to allow the contact arm to provide constant contact compressive forces. The central section of the contact arm is configured to position the contacts within defined CLOSED, BLOW OPEN and LOCK OPEN positions. Interconnection of the rotor assemblies with the operating mechanism is achieved by a single elongated pin. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a top perspective view of a multi-pole circuit breaker consisting of three single pole assemblies contained within a single circuit breaker housing; 
     FIG. 2 is an enlarged side view of one of the single pole assemblies within the circuit breaker of FIG. 1; 
     FIG. 3 is a top perspective view of the contact arrangement within the single pole assembly of FIG. 2; 
     FIG. 4 is a side plan view of the rotor used with the contact arrangement of FIG. 2; and 
     FIG. 5A is a side plan view of the single pole assembly of FIG. 2 depicting the contact arm in the CONTACTS CLOSED position; 
     FIG. 5B is a side plan view of the single pole assembly of FIG. 2 depicting the contact arm in the BLOWN OPEN position under intense overcurrent condition (short circuit current); 
     FIG. 5C is a side plan view of the single pole assembly of FIG. 2 depicting the contact arm in the LOCKED OPEN position; and 
     FIG. 5D is a side plan view of the single pole assembly of FIG. 2 depicting the contact arm the OPEN position due to the intervention of tripping devices associated to the circuit breaker. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A multi-pole circuit breaker  10  is shown in FIG. 1 consisting of a case  14  and cover  15  with an operating handle  16  projecting from the cover through an aperture  17 . The operating handle interacts with the circuit breaker operating mechanism  18  to control the ON and OFF positions of the central rotary contact arm  26 , and central rotary contact arm assembly  32  within the circuit breaker operating mechanism. A first rotary contact arm  22  and first rotary contact arm assembly  20  within a first pole  12 , on one side of the operating mechanism  18 , and a second rotary contact arm  24  and second rotary contact arm assembly  21  within a second pole  13 , on the opposite side of the operating mechanism move in unison to provide complete multi-pole circuit interruption. An elongated pin  38  interconnects the operating mechanism  18  with the first and second rotary contact arm assemblies  20 ,  21 . As described within the aforementioned U.S. Pat. No. 4,649,247, a rotor  25  interconnects each of the rotary contact arms  22 ,  24  with the corresponding pairs of fixed contacts  27 ,  28  and movable contacts  29 ,  30 . 
     In accordance with the invention, the central rotary contact arm assembly  32  is depicted in FIG. 2 to show the positional arrangement between the rotor  25  intermediate a lower or load strap  23  and an upper or line strap  31  and the associated arc chutes  33 ,  34 . The first rotary contact arm assembly  20  and second rotary contact arm assembly  21  of FIG. 1 are not shown herein but are mirror image of the central rotary contact arm assembly  32  and operate in a similar manner. The arc chutes  33 ,  34  are similar to that described within U.S. Pat. No. 4,375,021 entitled “Rapid Electric Arc Extinguishing Assembly in Circuit-Breaking Devices Such as Electric Circuit Breakers”. The central rotary contact arm  26  moves in unison with the rotor  25  that, in turn, connects with the circuit breaker operating mechanism by means of the elongated pin  38  to movable contacts  29 ,  30  from fixed contacts  27 , 28 . The clevis  35  consisting of the extending sidearms  36 ,  37  attach the rotor  25  with the circuit breaker operating mechanism  18  and the operating handle  16  of FIG. 1 to allow both automatic as well as manual intervention for opening and closing the circuit breaker contacts  27 - 30 . The rotor  25  is supported within the side walls  52  by means of trunnion  51 . 
     FIG. 3 shows a cross sectional view of rotor  25 . The half of rotor  25  shown in FIG. 3 includes an outer face  60 , an inner face  62 , and a perimeter  64 . Outer face  60  includes a groove  66  disposed thereon. Groove  66  has a length equal to the diameter of rotor  25  and a depth that is less than the distance between the inner and outer faces  62 ,  60 . Inner face  62  includes protrusions  68 ,  70  extending therefrom and positioned along the periphery of rotor  25 . 
     Perimeter  64  includes diametrically opposed slots  53 ,  54 , which extend from said groove to said inner face and from perimeter toward the axis of rotor  25 . Slot  53  accepts one end of a pin  43 . Slot  54  accepts one end of a pin  44 . Pins  43 ,  44  extend from slots  53 ,  54 , respectively, to corresponding slots in the half of rotor  25  not shown. Slots  53 ,  54 , and the corresponding slots on the half of rotor  25  not shown, are sized to prevent the translational movement of pins  43 ,  44  in all directions but the radial direction with respect to rotor  25 . Pins  43 ,  44  include rollers  45 ,  46 , respectively, disposed along a center length thereof. Groove  64  accepts an extension spring  41  that extends from pin  43  to pin  44 . Similarly, an extension spring  42  extends from pin  43  to pin  44  and is positioned on the opposite side of rotor  25 . 
     FIG. 3 also shows rotary contact arm  26  positioned between protrusions  68 ,  70  of rotor  25  and between the line and load straps  23 ,  31 . Rotary contact arm  26  includes a central region  26 A, with the upper and lower portions of central region forming camming surfaces  48 ,  49 ,  50 . Rotary contact arm  26  further includes a pivot pin  39 , which extends from both sides of central region  26 A. 
     Pins  43 ,  44  extend across the top and bottom of central region  26 A, respectively. Rollers  45 ,  46  are urged onto camming surfaces  48 ,  49 ,  50  of central region  26 A by the force of springs  41 ,  42 , which act to draw pins  43 ,  44 , and their rollers  45 ,  46 , towards each other. Rollers  45 ,  46  prevent uneven wear of camming surfaces  48 ,  49 ,  50 . The positional relationship between rollers  45 ,  46  and the central region  26 A of rotor  26  to avoid uneven wear is an important feature of the invention and will be described below with reference to FIGS. 5A-5D. 
     The rotor  25  is shown in FIG. 4 relative to the line strap  23  and load strap  31 , central rotary contact arm  26  and contacts  27 - 30  to help describe the manner in which the fixed contacts  27 ,  28  remain in close abutment with the movable contacts  29 ,  30  in counter-relation to contact erosion and wear. As shown earlier, a pair of extension springs, one of which is shown at  42 , extend between opposing top and bottom pins  43 ,  44  that are positioned within slots  53 , 54  in the rotor  25 . An elongated slot  47  is disposed in rotor  25 . Elongated slot  47  accepts pivot pin  39  pivotally secure the rotary contact arm  26  within the rotor  25 . Slot  47  is elongated in a direction parallel to springs  41  and  42 . Because aperture  47  is elongated, the rotary contact arm  26  can move in the direction of the elongation. The “floating” relationship between the operating pivot pin  39  and the contact closing springs  41 ,  42  allows the springs to force the movable contacts  29 ,  30  into tight abutment with the associated fixed contacts  27 ,  28  as indicated in phantom to compensate for contact wear and erosion. 
     The enhanced contact separation and control provided by the rotor  25  is best seen by now referring to FIGS. 5A-5D rotary contact arm  26  and contact pairs  27  and  30 ,  28  and  29  move from the CONTACTS CLOSED, to BLOWN OPEN, to LOCKED OPEN and OPEN positions indicated therein. As previously described, the central region  26 A of rotary contact arm  26  includes camming surfaces  48 ,  49 ,  50 . Rollers  45 ,  46  are urged onto camming surfaces  48 ,  49 ,  50  by the force of springs  41 ,  42 , which act to draw the two rollers  45 ,  46  towards each other. Rollers  45 ,  46  transmit the force of springs  41 ,  42  to camming surfaces  48 ,  49 ,  50  in a direction normal to the surfaces. Camming surfaces  48 ,  49 ,  50 , are shaped to affect the direction of this force. In the CONTACTS CLOSED condition indicated in FIG. 5A, the lines of force created by springs  41 ,  42  and through rollers  45 ,  46  to camming surfaces  48  are indicated by the arrows  A  and  A ′. In the CONTACTS CLOSED condition, the forces in the directions A and A′ create a moment about pivot  39  that rotates contact arm  26  in the clockwise direction and forces contact pairs  27  and  30 ,  28  and  29  together. In the BLOWN OPEN condition, when the central rotary contact arm  26  is magnetically “blown” in the counter-clockwise direction under intense overcurrent conditions, the rollers are positioned on the second camming surfaces  49  formed on the central region as indicated in FIG.  5 B. During the BLOWN OPEN condition, the lines of force created by springs  41 ,  42  and through rollers  45 ,  46  to rotary contact arm  26  are indicated by the arrows  B  and  B ′. The lines of force B and B′, which control the opening of the central rotary contact arm  26  under an intense overcurrent condition, is dictated by the shape of the second camming surfaces  49 . Devices suited for selectivity will employ second camming surfaces  49  that produces lines of force B 1  and B 1 ′. Whereas, devices suited for rapid opening will employ second camming surfaces  49  that produces lines of force B 2  and B 2 ′. Upon complete contact separation, by further rotation of the rotary contact arm  26  in the counter-clockwise direction to the LOCKED OPEN condition shown in FIG. 5C, rollers  45 ,  46  become trapped within grooved camming surfaces  50  In the LOCKED OPEN condition, the lines of force created by springs  41 ,  42  and through rollers  45  and  46  to central rotary contact arm  26  are indicated by the arrows  C  and  C ′ to prevent the central rotary contact arm  26  from rotating back to the CONTACTS CLOSED condition. FIG. 5D shows contact arm  26  in the OPEN position due to the intervention of tripping devices associated with the circuit breaker. Tripping of the circuit breaker operating mechanism causes the rotor  25  and the rollers  45 ,  46  to rotate in a counter-clockwise direction until the rollers  45 ,  46  engage the camming surfaces  48 , and protrusions  68 ,  70  abut against rotary contact arm  26 , placing the central rotary contact arm  26  in the OPEN condition. The central rotary contact arm  26  remains in the OPEN condition, depicted in FIG. 5D, until the operating handle  16 , described earlier in FIG. 1, is first rotated to the contact opening to reset the operating mechanism, and then to contact closure, as viewed in FIG. 1, to reset the operating mechanism and return the rotary contact arm to the CLOSED condition shown in FIG.  5 A. 
     A rotary contact arm assembly for circuit breaker having a wide range of ampere ratings has herein been described. Contact wear and erosion along with rotary contact arm control facility and mechanism interconnect means was illustrated by use of a limited number of components to reduce component cost as well as assembly time.