Abstract:
The present invention provides a motor control cam having a relief channel adjacent to the switch lever notch. The relief channel extends generally circumferentially from said switch lever notch under the second, wide diameter portion of the cam surface. In this configuration, when the switch lever is in the switch lever notch and a counter rotation of the cam occurs, the switch lever enters the relief channel and does not impact against the cam. As such, the switch lever is not damaged or moved out of adjustment by a counter rotation of the cam.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a medium voltage switchgear having a circuit breaker, the circuit breaker having a charging motor actuated by a control switch with a switch lever, the switch lever engaging a control cam having a relief channel. 
   2. Background Information 
   A medium voltage switchgear typically comprises a switching mechanism housed in an enclosure. The switching mechanism, typically a circuit breaker, includes separable contacts for each phase and a common spring operated closing and tripping device. This device includes one or more opening springs which separates the contacts and a pair of closing springs which close the contacts and charge the opening spring. The separable contacts are closed by releasing the energy stored in the closing springs through activation of a closing trigger mechanism. This can be done manually or remotely through a solenoid. An electronic trip circuit monitors the load currents and actuates an opening trigger mechanism through an opening solenoid if the current exceeds certain current-time characteristics. The closing springs are charged manually by a lever arm through a ratchet coupling, or, more preferably, by a motor. 
   The motor is coupled to a crank shaft. The crank shaft is further coupled to the closing springs, the opening springs and a pole shaft. The pole shaft is coupled to the contacts. In operation, the motor rotates the crank shaft to charge the closing springs. When the closing springs are released, the closing springs cause the crank shaft to rotate and this motion is transferred to the pole shaft which closes the contacts. At this point, the closing springs are typically recharged so that the circuit breaker may be closed again after being tripped. 
   The motor may be controlled by a motor control switch mounted adjacent to the crank shaft. The motor control switch includes a switch lever that contacts a motor control cam. The motor control cam is fixedly coupled to the crank shaft and has a cam surface with a first, reduced diameter portion and a second, wide diameter portion. Each portion of the cam surface extends about 180 degrees about the motor control cam. At one boundary between the first, reduced diameter portion and the second, wide diameter portion is a switch lever notch. The switch lever notch is, essentially, a radial edge on the cam surface. When the switch lever is in contact with the first, reduced diameter portion, the motor control switch does not actuate, that is, turn on, the motor. When the switch lever is in contact with the second, wide diameter portion, the motor control switch actuates the motor. The motor control cam is coupled to the crank shaft so that when the closing springs are charged, the switch lever is disposed in the switch lever notch and at the beginning of the first, reduced diameter portion. Thus, when the closing springs are charged, the motor is not actuated. When the closing springs are released, the crank shaft rotates about 180 degrees so that the switch lever is disposed on the second, wide diameter portion. Accordingly, after the closing springs are released, the motor is actuated causing the crank shaft to rotate and charge the closing springs. When the closing springs are charged, the crank shaft has rotated about 180 degrees and the switch lever falls into the switch lever notch, causing the motor to stop. During these operations, the crank shaft, and therefore the motor control cam, are intended to rotate in a single direction. 
   The disadvantage to this configuration is that various tolerances in the circuit breaker components, wear and tear, and other factors may allow the crank shaft to counter-rotate. That is, the crank shaft, and therefore the motor control cam, may rotate in the opposite direction. Thus, because the switch lever notch is, essentially, a radial edge on the cam surface, counter rotation of the motor control cam may cause the radial edge of the switch lever notch to impact the switch lever. This impact may damage the switch lever or move the switch lever out of the optimal position. 
   There is, therefore, a need for a motor control cam structured to not impact the switch lever during a counter rotation of the crank shaft. 
   There is a further need for a motor control cam that may be incorporated into existing circuit breakers. 
   SUMMARY OF THE INVENTION 
   These needs, and others, are met by the present invention which provides a motor control cam having a relief channel adjacent to the switch lever notch. The relief channel extends generally circumferentially from said switch lever notch under the second, wide diameter portion of the cam surface. In this configuration, when the switch lever is in the switch lever notch and a counter rotation of the cam occurs, the switch lever enters the relief channel and does not impact against the cam. As such, the switch lever is not damaged or moved out of adjustment by a counter rotation of the cam. Such a cam may be easily incorporated into existing circuit breakers. 

   
     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 side elevational view with some parts cut away with a typical medium voltage circuit breaker in accordance with the invention shown in the disconnected position. 
       FIG. 2  is a front elevational view of a typical circuit breaker as seen in  FIG. 1  with the cover removed. 
       FIG. 3  is a partial side view of a circuit breaker. 
       FIG. 4  is a detailed side view of a portion of the charging mechanism. 
       FIG. 5  is an isometric view of the charging mechanism shown in  FIG. 4 . 
       FIG. 6   a  is a sectional view taken along the line  6 — 6  in  FIG. 2  shown with the breaker in the open position and the closing springs discharged. 
       FIG. 6   b  is similar to  FIG. 6   a  but showing the breaker closed with the closing springs charged. 
       FIG. 7   a  is a sectional view taken along the line  7 — 7  in  FIG. 2  showing the breaker open and the closing spring discharged. 
       FIG. 7   b  is similar to  FIG. 7   a  but showing the breaker in the open position and the closing springs charged. 
       FIG. 7   c  is similar to  FIGS. 7   a  and  7   b  but showing the breaker closed and the closing springs discharged. 
       FIG. 8  is a side view of the motor control cam having a relief channel. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   As shown in  FIGS. 1 and 2 , a switch gear apparatus  10  includes a cabinet or enclosure  13  for enclosing a circuit breaker  15 . The exemplary circuit breaker  15  is, preferably, a draw-out three-phase vacuum circuit interrupter having controls on a front panel  17  for manually operating the circuit breaker  15 . The circuit breaker  15  has wheels  19  which engage rails  21  for inserting the circuit breaker  15  into and removing the circuit breaker  15  from the enclosure  13 . The enclosure  13  includes at least one line terminal  27  and at least one load terminal  29 . The circuit breaker  15  includes at least one line terminal  23  and at least one load terminal  25 . Typically, the switch gear apparatus  10  has three circuit breaker line and load terminals  23 ,  25  and three corresponding enclosure line and load terminals  27 ,  29 . The circuit breaker line and load terminals  23 ,  25  are positioned to engage, and be electrically coupled to, the enclosure line and load terminals  27 ,  29 . Movement of the circuit breaker  15  along the rails  21  also effects connection and disconnection of circuit breaker line and load terminals  23 ,  25  with the enclosure line and load terminals  27 ,  29 . While a medium voltage vacuum interrupter is shown for the circuit breaker  15 , the invention is also applicable for use with air circuit breakers. 
   The circuit breaker  15  has a front low voltage section  31  adjacent to the front panel  17  and a rear high voltage section  33  containing a vacuum interrupter  35  for each phase. The low and high voltage sections  31 ,  33  are electrically insulated from each other by upper and lower insulators  37 ,  39 . Within each vacuum interrupter  35 , a pair of separable contacts  40  including a stationary contact  41  and a moveable contact  43  are provided. The contacts  40  are operated between the open position (shown) and a closed position by a linkage  45  which includes a bell crank  47  (shown schematically) pivoted at pivot point  49  and an insulated push rod  51  extending into the low voltage section  31 . 
   An operating mechanism  53  for opening and closing the separable contacts  40  through the linkage  45  is contained in the low voltage section  31 . This operating mechanism  53  has a number of driven parts  54  which include a pole shaft  55  which is rotatably journaled in side walls  57 ,  59  of a housing  61  ( FIG. 2 ). A pole arm  63  ( FIG. 1 ) for each phase projects laterally from the pole shaft  55  and is pivotally connected to the associated push rod  51  so that rotation of the pole shaft  55  simultaneously opens or closes the separable contacts  40  of each pole. The pole shaft  55  is rotated counter-clockwise as viewed in  FIG. 1  to open the contacts  40  by an opening spring  65  in the form of a helical tension spring connected at one end to an upper portion of the housing  61  of the low voltage section  31  and at the other end to a lever arm  67  mounted on the pole shaft  55 . 
   The operating mechanism  53  also includes a pair of helical tension closing springs  69 ,  71  each of which is connected at its upper end to the housing  61  and at its lower end through a spring link  73 ,  75  to an eccentric pivot  77 ,  79  on a spring crank  81 ,  83 , respectively. The spring cranks  81 ,  83  are mounted on opposite ends of a crank shaft  85  rotatably supported between a pair of spaced supports  87 ,  89 . Fixed on the crank shaft  85  between the supports  87 ,  89  is a closing cam  91  which includes a notch  93  in the peripheral cam surface thereof (see  FIGS. 7   a–c ). 
   The crank shaft  85  is rotated to extend or charge the two closing springs  69 ,  71  by a charging mechanism  200 . As shown in  FIG. 2 , the charging mechanism  200  includes a motor  202 , preferably electric, having a motor shaft  204 , and a drive eccentric  206 . As further shown in  FIGS. 3–5 , the charging mechanism  200  further includes at least one charge pawl  208 , at least one hold pawl  209  a ratchet wheel  210 , at least one charging plate  211 , at least one drive lever  213 , a motor control cam  212  having a switch lever notch  214  with a relief channel  216  ( FIG. 8 ), and a motor control switch  218  having a switch lever  220 . The switch lever  220  is, preferably, a rectangular beam  221  having a diameter thickness between about 0.031 and 0.062 inch, and more preferably about 0.040 inch. The motor shaft  204  extends in a direction generally parallel to the crank shaft  85 . The drive eccentric  206  is coupled to the motor shaft  204 . The ratchet wheel  210  is fixedly mounted to freely rotate about the crank shaft  85  within rotational boundaries set by an integral detent  223  and at least one charging plate  211 . The at least one charging plate  211  is fixedly mounted to the crank shaft  85 . The charge pawl  208  is coupled to at least one drive lever  213 , which in turn freely rotates about the crank shaft  85 . The drive gear eccentric  206  is structured to operatively engage the ratchet wheel  210  through at least one drive lever  213  so that, when the motor  202  is energized, the crank shaft  85  is rotated counterclockwise as shown by the arrows in  FIGS. 7   a–c . That is, rotation of the motor shaft  204  is transferred to the crank shaft  85  via the linking of the drive eccentric  206 , the charge pawl  208 , at least one drive lever  213 , and the ratchet wheel  210 . Reverse rotation of the crank shaft  85  is substantially limited by the at least hold one pawl  209  which is coupled to the housing  61  and also structured to engage the ratchet wheel  210 . 
   The motor control cam  212  is also fixedly coupled to the crank shaft  85 . The motor control switch  218  is coupled to the housing  61  adjacent to the motor control cam  212 . The motor control switch lever  220  extends toward and engages the cam surface of the motor control cam  212 . The motor control switch  218  is electrically coupled to the motor  202  and provides a control signal thereto. That is, the motor control switch  218  is structured to selectively actuate the motor  202  in response to the position of the switch lever  220 . The switch lever  220  is structured to engage the motor control cam  212  and move in response to the changing diameter of the motor control cam  212 . The motor control cam  212  includes a first, reduced diameter portion  230 , and a second, wide diameter portion  232 . The switch lever notch  214  is located at one boundary between the first, reduced diameter portion  230 , and the second, wide diameter portion  232 . The motor control switch  218  is structured to provide an actuation signal to the motor  202  when the motor control switch lever  220  engages the second, wide diameter portion  232  of the motor control cam  212 . When the motor control switch lever  220  engages the first, reduced diameter portion  230  of the motor control cam  212  the motor  202  is not actuated. 
   Alternatively, as is known, the crank shaft  85  can be manually rotated to charge the closing springs  69 ,  71  by a charging lever (not shown) which engages the charging mechanism  200 . The closing springs  69 ,  71  are retained in the charged condition and released by a first, closing spring release  99  (see  FIGS. 6   a  and  b ) which includes a closing spring release latch  101  pivotally connected on a shaft  103 . This closing spring release latch  101  has a latch surface  105  which is engaged by a latch roller  107  supported between a pair of roller support arms  109  fixed to the crank shaft  85 . 
   With the circuit breaker  15  open and the closing springs  69 ,  71  discharged as shown in  FIG. 6   a , operation of the charging mechanism  200  causes the crank shaft  85  to rotate in a counterclockwise direction as shown by the arrow. This causes the eccentric pivots  77 ,  79  to move downward thereby extending the closing springs  69 ,  71 . Just after the eccentric pivots  77 ,  79  carry the lines of action of the closing springs  69 ,  71  through the center of the crank shaft  85 , the closing latch roller  107  engages the latch surface  105  on the closing spring release latch  101 . The tendency of the closing spring  69 ,  71  to continue the rotation in the clockwise direction is blocked by the engagement of an extension  111  on the release latch  101  with a fixed pin  113 . 
   The release latch  101  is operated by a release lever  115  pivotally connected at one end to an arm  117  on the pole shaft  55 . The other end of the release lever  115  rests on a close clapper  119 . The close clapper  119 , in turn, is pivotally supported on a bracket  121  which also supports a close solenoid  123 . Rotation of the close clapper  119  counterclockwise in  FIG. 6   a  about a pivot axis  125 , either manually by pressing on the lower end of the clapper  119 , or automatically by energization of the close solenoid  123 , causes clockwise rotation of the release lever  115 . The release lever  115  engages a projection  128  on the close spring release latch  101  which is rotated clockwise until the close latch roller  107  slips off of the latch surface  105 . This permits the closing springs  69 ,  71  to rapidly rotate the crank shaft  85 . This results in rotation of the pole shaft  55  to close the separable contacts  40  of the circuit breaker  15 . The force generated by two closings springs  69 ,  71  is required as they not only operate the mechanism  53  to close the separable contacts  40 , but they also charge the opening spring  65 . With the circuit breaker  15  closed as shown in  FIG. 6   b , the release lever  115  is lowered so that if the closing springs  69 ,  71  are recharged (as shown), the release lever  115  will not engage the closing spring release latch  101  and thus the closing springs  69 ,  71  cannot be discharged. The closing springs  69 ,  71  maintain the circuit breaker  15  ready for a recharge should the circuit breaker  15  trip open. 
   As shown in  FIGS. 7   a – 7   c , the operating mechanism  53  also includes a coupling mechanism  127  for coupling the crank shaft  85  to the pole shaft  55 . This coupling mechanism  127  includes a pair of parallel main links  129  each pivotally connected at one end to the pole shaft  55  through a crank arm  131  and rotatably supporting a main link roller  133  between their free ends. This main link roller  133  engages the peripheral surface of the closing cam  91  which, as the crank shaft  85  rotates, pushes on the main links  129  to rotate the pole shaft  55  through the eccentricity in the cam  91  surface. Opening spring release mechanism  135  includes a banana link  137  pivoted at one end on a common axis  125  with the main roller link  133  and at the other end to one end of a hatchet  139 . The hatchet  139  is mounted on a fixed pivot pin  141  and has a free curved end  143  forming a latch edge  145 . Opening spring release mechanism  135  also includes a trip lever  147  fixed to a rotatable trip lever “D” shaft  149 . The trip lever  147  rests on the upper end of an opening clapper  151  pivotally supported at second pivot point  153  by a bracket  155  on which is mounted an opening solenoid  157 . A trip latch reset spring  159  connected to this bracket  155 , biases the hatchet  139  clockwise as shown in  FIG. 7   a  to the hatchet  139  position as shown in  FIGS. 7   b  and  7   c  wherein the latch edge  145  is engaged by the D shaft  149 . 
     FIGS. 7   a–c  illustrate the coupling of the crank shaft  85  to the pole shaft  55  to close the circuit breaker  15  and tripping of the opening spring release mechanism  135  to open the circuit breaker  15 .  FIG. 7   a  illustrates the position of the parts with the circuit breaker  15  open and the closing springs  69 ,  71  discharged. As can be seen, the push rod  51  is retracted so that the separable contacts  40  are open. The sequence is initiated by operation of the charging mechanism  200  to rotate the crank shaft  85  in the counterclockwise direction to charge the closing springs  69 ,  71  in the manner described above. The trip latch reset spring  159  biases the main link roller  133  against the peripheral caming surface of the closing cam  91  until it falls into the notch  93  with the closing springs  69 ,  71  latched in the charged condition. This permits the trip latch reset spring  159  to rotate the hatchet  139  clockwise to the latched position in which the latch edge  145  is engaged by the D shaft  149  as shown in  FIG. 7   b . When the closing spring release  99  is actuated, the closing springs  69 ,  71  rapidly rotate the crank shaft  85  in the manner described above with reference to  FIGS. 6   a  and  6   b . The increasing effective diameter of the closing cam  91  produced by the eccentricity of the cam  91  surface, pushes the main links  129  downward and to the position shown in  FIG. 7   c . This rotates the pole shaft  55  in the counterclockwise direction to drive the push rod  51  to the left to close the separable contacts  40  while, as can be seen in  FIG. 7   c , the hatchet  139  remains engaged by the D shaft  149 . 
   The circuit breaker  15  is opened manually by pressing on the lower end of the opening clapper  151 . In addition, the circuit breaker  15  can be opened automatically by actuation of the opening solenoid  157  which rotates the opening clapper  151  clockwise. The opening solenoid  157  is energized by an electronic trip unit in response to current which exceeds predetermined current/time characteristics. Alternatively, the opening solenoid  157  can be energized from a remote source to open the circuit breaker  15 . In any case, rotation of the opening clapper  151  in the clockwise direction rotates the open trip lever  147  and with it the D shaft  149 . The force generated by the charged opening spring  65  through the main links  129  and banana link  137  rotates the hatchet  139  counterclockwise past the D shaft  149 . This allows the opening spring  65  to rotate the pole shaft  55  to withdraw the push rods  51  and open the separable contacts  40  as the main link roller  133  rolls along the outer surface of the closing cam  91  to the position shown in  FIG. 7   a.    
   In each of the steps identified above wherein the operation of the charging mechanism  200  causes the crank shaft  85  to rotate, the motor  202  is actuated by the position of the motor control switch lever  220 . That is, the motor control cam  212  is coupled to the crank shaft  85  so that when the closing springs  69 ,  71  are fully charged, the motor control switch lever  220  moves from the second, wide diameter portion  232  of the motor control cam  212  into the switch lever notch  214 . In this configuration, the motor control switch lever  220  will be disposed on the first, reduced diameter portion  230  during normal operation of the circuit breaker  15  and when the closing springs  69 ,  71  are discharged during the charging of the opening spring  65 . The discharging of the closing springs  69 ,  71  causes the crank shaft  85  to rotate so that the motor control switch lever  220  is disposed on the second, wide diameter portion  232  of the motor control cam  212 . Thus, after the discharge of the closing springs  69 ,  71 , the motor  202  is actuated causing the closing springs  69 ,  71  to be charged once again. 
   As shown in  FIG. 8 , the motor control cam  212  has a generally disk-like body  250  with an outer edge  252 . The outer edge  252  is a cam surface  253  that has, as noted above, a first, reduced diameter portion  230  and a second, wide diameter portion  232 . The motor control cam body  250  has a central opening  254  sized to accommodate the crank shaft  85 . The switch lever notch  214  is a radial edge on the cam surface  253  delineating one boundary between the first, reduced diameter portion  230  and the second, wide diameter portion  232 . That is, the outer edge  252  changes between the first, reduced diameter portion  230  and the second, wide diameter portion  232  at, essentially, a single point. The switch lever notch  214  may, however, have a rounded distal tip  256  at the end of the second, wide diameter portion  232 . Between the distal tip  256  and the central opening  254  is the relief channel  216 . The relief channel  216  extends from the switch lever notch  214  generally circumferentially a distance, between about 0.362 and 0.460 inch, and more preferably about 0.411 inch, between the central opening  254  and the outer edge  252  and under the second, wide diameter portion  232 . The relief channel  216  has a radial width sized to accommodate the motor control switch lever  220 . Preferably, the relief channel  216  radial width is between about 0.146 and 0.166 inch, and more preferably about 0.156 inch. 
   The relief channel  216  on the motor control cam  212  allows for the counter-rotation of the motor control cam  212 . That is, while charging the charging mechanism  200 , the at least one holding pawl  209  substantially resists the counter-rotation of the crank shaft  85 , various tolerances within the operating mechanism  53  may allow the crank shaft  85  to rotate, slightly, in a reverse direction. When the crank shaft  85  counter-rotates, the motor control switch lever  220  moves into the relief channel  216  as opposed to abutting the switch lever notch  214 . In this configuration, the motor control switch lever  220  will not be damaged by counter-rotation of the motor control cam  212 . 
   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 invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.