Patent Publication Number: US-8525054-B2

Title: Discharge mechanism for circuit breaker

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to a mechanism for a circuit breaker. In particular, the subject matter disclosed herein relates to a mechanism coupled to the circuit breaker that opens a contact arm structure and discharges the stored energy the mechanism springs prior to the circuit breaker being installed or removed from service. 
     Air circuit breakers are commonly used in electrical distribution systems. A typical air circuit breaker comprises an assembly of components for connecting an electrical power source to a consumer of electrical power called a load. The electric circuit the circuit breaker is connected to is referred to herein as the protected electric circuit. The components are referred to as a main contact assembly. In this assembly, a main contact is typically either opened, interrupting a path for power to travel from the source to the load, or closed, providing a path for power to travel from the source to the load. In a particular type of circuit breaker, referred to as an air circuit breaker, the force necessary to open or close the main contact assembly is provided by an arrangement of compression springs. When the compression springs discharge, they exert a force that provides the energy needed to open or close the main contacts. Compression springs that provide a force to close the main contacts are often called closing springs. Compression springs that provide a force to open the main contacts are often referred to as contact springs. 
     The air circuit breakers may be installed in several different configurations. The simplest method is typically referred to as a “fixed breaker” where the installer mounts the air circuit breaker and utilizes hardware, such as bolts for example, to couple the air circuit breaker to the source and load electrical conduits. In this instance, when maintenance or repair is required, the hardware coupling the breaker must be removed before the maintenance or repairs can be performed. 
     Alternatively, the air circuit breaker may be mounted within a mechanism referred to as a drawout. A drawout is a device well known in the art that holds and carries the air circuit breaker into and out of contact with electrical connections for the source and load. To remove the air circuit breaker from service, the drawout automatically disconnects the circuit breaker from the electrical circuit and moves it into a position for servicing. 
     In the drawout installation, it is desirable to disconnect the circuit breaker from the protected electrical circuit and to discharge the energy in the compression springs prior to initiating the service work. Issues sometimes arise when retrofitting an older drawout unit with a newer model circuit breaker since interlocks mounted in the drawout unit to discharge the compression springs may not be compatible with the new circuit breaker. 
     While existing circuit breakers are suitable for their intended purposes, there still remains a need for improvements particularly regarding the operation of the circuit breaker and the discharging of the circuit breaker compression springs to allow the servicing of the circuit breaker in a variety of applications. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a circuit breaker is provided. The circuit breaker includes a base with a cross shaft operably coupled thereto. The cross shaft being rotatable between a first position and a second position. A first linkage is coupled to the base and arranged transverse to the cross shaft, the first linkage being rotatable between a third position and a fourth position. A second linkage is operably coupled to the first linkage, the second linkage translating between a fifth position and a sixth position in response to the first linkage rotating between the third position and the fourth position. A cam surface is operably coupled between the cross shaft and the first linkage. An opening latch shaft is coupled between said second linkage and a contact arm assembly, wherein the opening latch shaft moves the contact arm assembly from a closed position to an open position in response to the second linkage translating between the fifth position and the sixth position. 
     According to another aspect of the invention, a circuit breaker is provided having a housing. A base is coupled to the housing. A contact structure is movable between a closed position and an open position and is disposed within the housing. An opening latch shaft is operably coupled to the contact structure. A mechanism is provided that includes a cross shaft operably coupled to the base, the cross shaft rotating between a first position and a second position in response to movement of the circuit breaker. A first linkage is rotationally coupled to the base and arranged transverse to the cross shaft, the first linkage movable between a third position and a fourth position. A cam surface is disposed between the cross shaft and the first linkage, the cam surface moving between a fifth position and a sixth position when the cross shaft rotates between the first position and the second position. A second linkage is coupled between the opening latch shaft and the first linkage, wherein the second linkage translates between a seventh position and an eighth position in response to the first linkage moving between the third position and the fourth position. Wherein the contact structure moves from the closed position to the open position in response to the second linkage translating between the seventh position and the eighth position. 
     According to yet another aspect of the invention, a method of operating a circuit breaker is provided. The method includes rotating a cross shaft coupled to the circuit breaker. A cam surface is moved from a first position to a second position in response to rotation of the cross shaft. A first linkage is rotated from a third position to a fourth position with the cam surface. A second linkage is translated from a fifth position to a sixth position with the first linkage. A set of contacts is opened with the second linkage when the first linkage is in the fourth position. Wherein the cross shaft rotates in response to a movement of the circuit breaker between and installed and a withdrawn position. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a side plan view of a circuit breaker in accordance with an embodiment of the invention; 
         FIG. 2  is a side plan view of a discharge mechanism for the circuit breaker of  FIG. 1  in a first position; 
         FIG. 3  is a side plan view of the discharge mechanism of  FIG. 2  in a second position; 
         FIG. 4  is a perspective view of the discharge mechanism of  FIG. 2 ; 
         FIG. 5  is a side plan view of a discharge mechanism for the circuit breaker of  FIG. 1  in accordance with another embodiment of the invention; 
         FIG. 6  is a perspective view of the discharge mechanism of  FIG. 5 . 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a circuit breaker  20  in the open position. The circuit breaker  20  includes a main mechanism (not shown) arranged within a housing  23 . The circuit breaker  20  further includes a racking cassette base  48  disposed on one end of the housing  23 . The main mechanism is coupled to a lay shaft assembly  22  that rotates in response to the main mechanism being moved between an on and off position. The lay shaft assembly is coupled to a contact arm coupler  24  through a pin  26 . The contact arm coupler  24  as illustrated in  FIG. 1  is in a open position and will transfer energy from the main mechanism compression springs (closing springs)  27  that is necessary to close a contact arm assembly  28 . The contact arm assembly  28  is mounted in the circuit breaker  20  to pivot about a pin  30  to move between a closed and open position. 
     It should be appreciated that the contact arm assembly  28  is illustrated in the exemplary embodiment as a single component. However, the contact arm  32  may be comprised of multiple contact arms each coupled to the contact arm coupler  24 . Further, the exemplary embodiment illustrates the circuit breaker  20  has a single contact arm or what is commonly referred to as a “pole.” Each pole of a circuit breaker carries electrical current for a single electrical phase. In a “multi-pole” circuit breaker the circuit breaker will have several poles, typically three or four, each carrying a different phase of electricity through the circuit breaker  20 . Each of the poles is individually connected to the lay shaft assembly  22  through a separate contact arm coupler  24 . 
     The contact arm assembly  28  includes an arm  32  having a movable contact  34  and an arcing contact mounted to one end. A flexible, electrically conductive strap, made from braided copper cable for example, is attached to the opposite end of the arm. The strap electrically couples the contact arm  32  to a conductor  40  that allows electrical current to flow through the circuit breaker  20 . The electrical current flows through the contact arm assembly  32  and exits via movable contact  34  and into the protected electric circuit. The current then passes through stationary contact  42  and into conductor  44  where it is transmitted to the protected electric circuit and load. 
     During normal operation of the circuit breaker  20 , the operator may desire to remove electrical power from a circuit. To accomplish this, the main mechanism is activated, by a handle for example, causing the lay shaft assembly  22  to rotate to an open position as illustrated in  FIG. 1 . The rotational movement of the lay shaft assembly  22  is translated into motion of the contact arm coupler  24  causing the contact arm assembly  28  to rotate about pivot  30 . This rotation by the contact arm assembly  28  results in the movable contact  34  separating from the stationary contact  42  and the halting of electrical current flow through the protected electrical circuit. To re-initiate flow of electrical power to the protected electrical circuit, the operator reverses the main mechanism, by moving a handle for example, causing the lay shaft assembly  22  to rotate back to a closed position. 
     In typical air circuit breakers, the main mechanism will have a closing latch shaft assembly  36  that is used to hold the closing latch linkage (not shown) and a tripping or opening shaft assembly  38  that holds an opening latch linkage (not shown). The rotation of the closing latch shaft assembly  36  will cause the release of the closing latch linkage further causing to release the energy stored in the closing springs  27 . This energy will be utilized to close the contact system against the contact springs  50  during the normal closing operation. During the normal closing operation the opening shaft assembly  38  will hold the opening latch linkages. Similarly under normal conditions, the rotation of opening shaft assembly in the anticlockwise direction will cause the opening latch to be unlatched and linkages will collapse allowing the contact springs  50  to open the circuit breaker contacts. 
     The circuit breaker  20  may be mounted in several different configurations. The two most common are a “fixed” breaker installation and a drawout installation. In the fixed breaker installation, conductors  40 ,  44  are mechanically fastened to the protected electrical circuit. In a drawout installation, the circuit breaker  20  is installed on a drawout mechanism. The drawout mechanism includes further assemblies that are well known in the art for moving the circuit breaker  20  into and out of connection with the protected electrical circuits. Typically, the drawout mechanism will include mechanical linkages that move the circuit breaker  20  when activated by service or installation personnel. 
     It is desirable to have the circuit breaker main mechanism springs  27  in the discharged position when maintenance and service operations are being performed. It is further desirable to have the circuit breaker  20  automatically discharge the main mechanism springs  27  during removal or insertion of the circuit breaker  20 . The exemplary embodiment illustrates with two methods by which the main mechanism springs  27  can be discharged. One is a manual mode and other is an automatic mode. The manual mode is used mostly in “fixed” breaker installations. The automatic mode is applicable to a drawout installation. exemplary spring discharge mechanism  46  that includes such features is illustrated in  FIGS. 1-4 . 
     In the exemplary embodiment, the spring discharge mechanism  46  is mounted on one end of the circuit breaker  20  to the racking cassette base  48 . As will be discussed in more detail herein, advantages are gained by mounting the spring discharge mechanism to the circuit breaker  20 , rather than to a drawout mechanism. By mounting the discharge mechanism to the circuit breaker  20 , incompatibilities between the circuit breaker and the drawout unit may be avoided. Thus, by mounting the spring discharge mechanism  46  to the circuit breaker  20 , the spring discharge mechanism  46  may operate in a variety of styles or types of drawout mechanism arrangements, which provides cost and manufacturing advantages. 
     The spring discharge mechanism  46  includes a cross shaft  52  that rotates in the direction indicated by arrow  54  in response to the circuit breaker  20  being moved into or withdrawn from a drawout installation. In the exemplary embodiment, the cross shaft  52  is movable between a first position ( FIG. 2 ) and a second position ( FIG. 3 ) in response to the movement of the circuit breaker  20 . A cam member  56  is disposed on one end of the cross shaft  52 . The cam member  56  is coupled to the cross shaft  52  such that the cam member  56  rotates in response to the rotation of the cross shaft  52 . A cam surface  58  projects from one side of the cam member  56 . It should be appreciated that the cam member  56  and the cam surface  58  move between a first position and a second position in response to the movement of the circuit breaker  20 . In another embodiment, the cam surface  58  is integrated into the cross shaft  52 . 
     A pivot linkage  60  is mounted to the racking cassette base  48  by a bracket  62  and a pivot pin  64 . In the exemplary embodiment, the pivot linkage  60  is arranged transverse to the cross shaft  52 . The pivot linkage  60  is arranged to rotate about the pivot pin  64  are indicated by the arrow  70 . The pivot linkage  60  has a first arm  66  that extends on one side of the pivot pin  64 . In one embodiment, the first arm  66  is disposed at an angle relative to the plane of the racking cassette base  48 . On an end distal from the pivot pin  64 , a roller pin  68  is coupled to the first arm  66 . The pivot linkage  60  also includes a second arm  72  that extends opposite the first arm  66 . In one embodiment, a plurality of standoffs  74  are arranged on opposite sides of the second arm  72 . The standoffs  74  are spaced apart to define a gap slightly larger than the width of the pivot linkage  60 . The standoffs  74  provide a means for maintaining the pivot linkage  60  in a desired alignment and may prevent damage or displacement of the pivot linkage during shipping, installation and operation. 
     On an end of the second arm  72  distal from the pivot pin  64 , an activator roller  76  is coupled to the second arm  72 . The activator roller  76  is arranged adjacent a discharge lever  78 . In the exemplary embodiment, the pivot linkage  60  is arranged such that the center of gravity of the pivot linkage  60  is disposed on the second arm  72  such that the roller pin  68  is biased against the cam surface  58 . This provides advantages in reliability since the springs or other biasing members are not utilized to maintain the roller pin  68  in contact with the cam surface  58 . 
     In the exemplary embodiment, the activator roller  76  is disposed with a gap between the activator roller  76  and a first end  80  of the discharge lever  78  when the spring discharge mechanism  46  is in the first position. The activator roller  76  contacts the discharge lever  78  as the spring discharge mechanism moves to the second position. The discharge lever  78  is coupled to the circuit breaker  20  to translate in the direction indicated by arrow  86  response to the rotational movement of the pivot linkage  60 . The discharge lever  78  includes a second end  82  that is disposed adjacent a trip latch activator lever  84 . The trip latch activator lever  84  is coupled to the opening shaft assembly  38  to cause the opening of the contact arm assembly  28  as discussed above. 
     The spring discharge mechanism  46  is arranged in the first position shown in  FIG. 1-2  when the circuit breaker  20  is not installed (or in the fully racked out position) and when the circuit breaker  20  is fully installed (e.g. connected to the conductors  40 ,  44 ). As discussed above, it is desirable to have the contact arm assembly  28  in the open position when the circuit breaker  20  is being installed or removed from the drawout installation. During installation or withdrawal of the circuit breaker  20 , the cross shaft  52  is configured to rotate from the first position to the second position. As the cross shaft  52  rotates, the cam member  56  and the cam surface  58  also rotate in the direction indicted by arrow  88 . Since the roller pin  68  is biased against the cam surface  58 , the rotation of the cam member  56  results in the rotation of the pivot linkage  60  as the roller pin  68  engages the cam surface  58 . 
     As the pivot linkages  60  rotates, the activator roller  76  moves in the direction indicated by arrow  90  into contact with the first end  80  of discharge lever  78 . As the pivot linkage  60  continues to rotate, the discharge lever  78  translates in the direction of the trip latch activator lever  84 , as indicated by arrow  92 , causing the trip latch activator to rotate the opening shaft assembly  38 . The rotation of the opening shaft assembly  38  results in the opening of the contact arm assembly  28 . As the circuit breaker  20  continues to be installed or withdrawn, the cross shaft  52  reverses direction and rotates back to the first position as indicated by arrow  94 . 
     Referring now to  FIGS. 5-6 , another embodiment of the spring discharge mechanism  46  is shown. In this embodiment, the cross shaft  52  is configured to rotate in response to the installation or withdrawal of the circuit breaker  20  from a drawout installation. A crank member  96  is coupled to rotate with the cross shaft  52 . The crank member  96  has a projection  98  on one side. On an end of the projection  98  that is distal from the cross shaft  52 , the crank member  96  couples to a coupler linkage  100 . In one embodiment, the spring discharge mechanism includes two coupler linkages  100  arranged on either side of the crank member  96 . The coupler linkage  100  is connected to the crank member  96  by a pin  102 . This connection allows the coupler linkage to simultaneously rotate and translate in response to the rotation of the cross shaft  52 . 
     On an opposite end of the coupler linkage  100  from the pin  102 , the coupler linkage  100  is coupled to a slider linkage  104  by a pin  106 . In one embodiment, one side of the slider linkage  104  is in contact with the racking cassette base  48  and transverse to the cross shaft  52 . The slider linkage further includes a cam surface  108  on a side opposite the racking cassette base  48 . It should be appreciated that the slider linkage  104  translates along the surface of the racking cassette base  48  in response to the rotation of the cross shaft  52  as indicated by the arrow  110 . 
     The spring discharge mechanism  46  further includes a pivot linkage  112 . The pivot linkage  112  rotates about a pin  114 . Adjacent the pin  114 , a roller  116  is coupled to the pivot linkage  112  adjacent the cam surface  108 . In one embodiment, the center of gravity of the pivot linkage  112  is arranged to bias the roller  116  towards the slider linkage  104 . The pivot linkage  112  further includes an activator roller  118  disposed at an end opposite pin  114 . The activator roller  118  is disposed adjacent to the first end  80  of discharge lever  78 . 
     When the circuit breaker  20  installed or withdrawn from a drawout installation, the cross shaft  52  rotates. The rotation of the cross shaft  52  results in the translation of the slider linkage  104  towards the cross shaft  52  via coupler linkage  100 . As the slider linkage  104  translates, the roller  116  engages the cam surface  108  causing the pivot linkage  112  to rotate. As the pivot linkage  112  rotates, the activator roller  118  contacts the first end  80  of the discharge lever  78 . The translation of the discharge lever  78  in response to the activator roller  118  activates the opening shaft assembly  38  as described herein. 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.