Abstract:
A draw-out arrangement for molded case circuit breakers is disclosed. A circuit breaker plug-in system generally comprises a plug-in base to which the draw-out mechanism is secured. The base includes a right plate and a left plate. A circuit breaker is movable between the right plate and the left plate and is retractably connected to the plug-in base by the action of the draw-out mechanism. The draw-out mechanism of the present invention includes a shaft connecting the right plate to the left plate which provides rigidity to the system and balances the circuit breaker during movement. When a crank is inserted into the draw out mechanism and used to rotate a lead screw connected therein, a rider positioned about the lead screw is prevented from rotating due to being sandwiched between a pair of plates. Movement is thereby translated into linear motion which is used to move the circuit breaker into or out of engagement with the plug-in base.

Description:
CROSS REVERENCE TO RELATED APPLICATION ross Reference To Related Applications  
       [0001]    This application is based upon, and claims the benefit of, United States Provisional Patent Application No. 60/190,299 filed on Mar. 17, 2000, which is herein incorporated by reference in its entirety. 
     
    
     
       BACKGROUND OF INVENTION  
         [0002]    This invention relates to a draw-out unit for electrical switchgear cabinets.  
           [0003]    More specifically, this invention relates to a draw-out unit for mounting a molded case circuit breaker in a switchgear cabinet.  
           [0004]    The use of switchgears in electrical distribution systems is well known. The switchgear houses a plurality of draw-out units, with each draw-out unit housing one or more switching devices, such as motor controllers and circuit breakers, releasably interconnected to one or more busbars. Periodically, the draw-out units are removed from the switchgear to allow for maintenance of equipment. The switching devices within the draw-out units make electrical contact with the busbars through a plurality of clip connectors, which extend from the draw-out unit. Each clip connector is electrically connected to an electrical conductor for connection to the switching devices of the switchgear. As the draw-out unit is inserted into the switchgear, the busbar slides between the two contact arms, and the contact arms frictionally engage the busbar.  
           [0005]    Two types of draw out systems are prevalent. The first type of system uses two levers, one connected on each side of a breaker, and both the levers have to be moved simultaneously. This requires use of both hand and skill for using the system. This system cannot be used when the panel (in which the breaker is enclosed) door is closed. A second type of system is operated by a crank mounted on one side of the breaker, or at the bottom portion of the breaker. This system can be operated by one hand, but has other disadvantages. The system with crank on one side uses bulky plastic components (for support to its mechanism) and makes the draw out system bulky. When the crank system is mounted at the bottom it interferes with the termination of cables, as a result of which, the cables must be terminated only at the rear. Furthermore, this second type of draw-out system cannot be added on to an existing breaker.  
           [0006]    One such draw-out mechanism is described in U. S. Pat. No. 4,743,715 issued May 10, 1988. These mechanisms have discrete positions for testing, installing and removing the circuit breaker. The positions may be referred to as CONNECT, DISCONNECT and TEST. In the CONNECT position the circuit breaker can be closed, opened or tripped. In the DISCONNECT position the circuit breaker is in the trip position and the draw-out mechanism can be locked to prevent access to the circuit breaker. The third position is TEST, wherein the circuit breaker is disconnected from the main circuit. In the TEST position the circuit breaker can be closed, opened or tripped in order to check internal and external accessories such as auxiliary switches, shunt trip and under voltage and secondary circuits. However, draw-out mechanisms with a “test” position relate to air circuit breakers (ACB&#39;s), which are large in size. Because these draw-out mechanisms are larger in size, they also tend to be costly to produce.  
         SUMMARY OF INVENTION  
         [0007]    The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a circuit breaker plug-in system. In an exemplary embodiment of the invention, the circuit breaker plug-in system has a plug-in base with a left plate and a right plate, a draw-out mechanism secured to the plug-in base and having a shaft connecting the right plate to the left plate, the draw-out mechanism further including a main unit held adjacent the right plate, and, a plug-in circuit breaker retractably connected to the plug-in base by action of the draw-out mechanism, the circuit breaker movably positioned between the left plate and the main unit.  
           [0008]    The main unit of the draw-out mechanism further preferably comprises a slider plate adjacent the right plate of the plug-in base, a guide plate positioned parallel to the slider plate, a lead screw held between the slider plate and the guide plate, a rider threadably connected to the lead screw, a first cam plate positioned between the rider and the guide plate, and a flat plate positioned between the rider and the slider plate. The shaft passes through the first cam plate and is connected to the flat plate on a first end of the shaft. The draw-out mechanism further comprises a second cam plate positioned on a second end of the shaft. Rotation of the lead screw imparts linear motion to the rider, and linear motion of the rider imparts rotation to the first cam plate and flat plate, which in turn imparts rotation to the shaft and second cam plate. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0009]    Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0010]    [0010]FIG. 1 is a three dimensional perspective view of a molded case circuit breaker in a draw out mechanism;  
         [0011]    [0011]FIG. 2 is a three dimensional perspective view of a molded case circuit breaker;  
         [0012]    [0012]FIG. 3 is a three dimensional perspective view of a draw out mechanism for a molded case circuit breaker;  
         [0013]    [0013]FIG. 4 is another three dimensional perspective view, from a different angle than that shown in FIG. 3, of a draw out mechanism for a molded case circuit breaker; and  
         [0014]    [0014]FIG. 5 is a cam plate for the draw out mechanism of FIGS. 3 and 4. 
     
    
     DETAILED DESCRIPTION  
       [0015]    Referring to FIG. 1, a circuit breaker plug-in system is shown generally at  100 . The circuit breaker plug-in system  100  generally comprises a plug-in base  200  to which a draw out mechanism  400  is secured. The draw-out mechanism  400  is connected to an electrical distribution circuit (not shown) at clip connectors which receive plug-in contacts  308  of the circuit breaker  300 . A circuit breaker  300  is retractably connected to the plug-in base  200  by the action of the draw out mechanism  400 .  
         [0016]    [0016]FIG. 2 shows the circuit breaker  300  disengaged from the plug-in base  200  and FIG. 3 shows the draw out mechanism  400  divorced from the plug-in base  200 . The plug-in base  200  and draw out mechanism  400  form a rigid and guided draw-out system for guiding the circuit breaker  300  in and out of the circuit breaker plug-in system  100 . On one side of the plug-in base  200  a left plate  202  including a guide slot  206  is secured to the plug-in base  200 . On the opposite side of the plug-in base  200  a right plate  204  including a guide slot  206  is secured to the plug-in base  200 . The right plate  204  holds the draw out mechanism  400  between the right plate  204  and the circuit breaker  300 , while the left plate  202  is coupled to the right plate  204  through a shaft  424  (not shown in FIG. 1). The left plate  202  provides rigidity and balances the circuit breaker  300  while the circuit breaker  300  is being moved in or out of the circuit breaker plug-in system  100 .  
         [0017]    In FIG. 2 the circuit breaker  300 , having a right side  301  and a left side  299 , is shown to include three plug-in moveable contacts  308  which may engage with stationary contacts on the plug-in base  200  when the circuit breaker  300  is moved into engagement with the plug-in base  200 . The circuit breaker  300  preferably has a plurality of shaped profiles  310  (indents) in which a plurality of wedges  306  can be slidably engaged. A pair of support plates  302  are affixed to the circuit breaker  300  on either side thereof by, for instance, a set of screws  312 , inserted through the support plates  302  and fastened on the wedges  306 . The support plates  302  and the wedges  306  are thus captively secured to the circuit breaker  300 . The support plates  302  have a pair of riveted guide pins  304  for guiding the circuit breaker  300  onto the left plate  202  and right plate  204  along the guide slot  206 .  
         [0018]    As shown in FIGS. 3 and 4, the draw out mechanism  400  includes a main unit  401  held adjacent the right plate  204 . The draw out mechanism  400  comprises a lead screw  410  capable of being rotably coupled to a crank  402  (shown in FIG. 1 detached from the lead screw  410  and held in a storage slot). The lead screw  410  may include a sleeve portion (again as shown in FIG. 1) for accepting the crank  402 . The crank  402  and lead screw  410  in combination extend essentially the full depth of the draw-out mechanism  400  from front to back. When the lead screw  410  is rotated by way of the crank  402  linear motion is imparted to a rider  418  threadably connected to the lead screw  410 . This linear motion is directed along the screw axis, which is parallel to the axis indicated at X. The rider  418  is restricted from rotating by being held between a cam plate  426  (first cam plate) and a flat plate  416  disposed on one end of a shaft  424 . The rider  418  includes a protrusion  419  which is coupled to a first slot  428  in the first cam plate  426  whereby linear motion of the rider  418  rotates the first cam plate  426  (and the flat plate  416 ) with a shaft  424  connected thereto. The lead screw  410  is contained in the draw out mechanism  400  by a bush  420  and split pin  422 . The rotation of the cam plate  426  and shaft  424  rotates a cam plate  426  (a second cam plate) disposed on the opposite end of the shaft  424  at the opposite side of the circuit breaker  300 . The shaft  424  is supported and pivoted inside holes provided on the left plate  202  and right plate  204  and is free to rotate about the axis of the shaft  424 . A first slot  428  and second slot  430  in the cam plate  426  engage the rider  418  and guide pins  304  on the support plate  302 . The first slot  428  and second slot  430  have a profile operative to transmit the operating force from the rider  418  to the circuit breaker  300  with high efficiency.  
         [0019]    Continuing in FIGS. 3 and 4, the rider  418  also moves a slider plate  414  linearly which in turn rotates a position indicator  412 . The position indicator  412  is operative to rotate between distinct positions. The positions, which are viewable through a view window  432  in a front cover  404  of the draw out mechanism  400 , indicate the positions of the circuit breaker  300  with respect to the plug-in base  200 . The positions may be identified for example, as ENGAGED, ISOLATED and WITHDRAWN. Graphics (not shown) indicative of these positions may be provided on the position indicator  412  such that only one graphic per position is visible through the view window  432  at a time.  
         [0020]    The slider plate  414  is also guided in the right plate  204  by means of two pins riveted thereto, thereby ensuring that the motion of the slider plate  414  matches that of the rider  418 . A guide plate  436  including a slot  438  fitted on the right plate  204  holds the guide pins  304  of the support plate  302  in the slotted profile of the guide plate  436 . This ensures linear motion of the circuit breaker  300  proportional to that of the slider plate  414 . The guide plate  436  includes a top portion  437  having a hole  435  which locates the lead screw  410  and has provision for holding the crank  402  when the crank  402  is not in use. The opposing end of the lead screw  410  is held captive to the right plate  204  with a bush  420  and split pin  422 .  
         [0021]    The slider plate  414  is also linked to a locking mechanism  434  that provides a facility to lock the circuit breaker  300  in the ISOLATED position.  
         [0022]    The right plate  204  provides a plurality of features and is so designed that these features can be accessed through a single cutout in the panel door when the circuit breaker  300  is installed inside a panel. Thus the crank  402  may be stored and an access hole  440  is provided for insertion of the crank  402  during draw out operation.  
         [0023]    Figure locks  476  are optional features provided as part of the draw out mechanism. Two such locks can be fitted in the holes  478  provided on the right support plate  204  and front cover  404  as shown in FIG. 1. The locks  476  are preferably fitted from inside using threads available on the body of the locks and are tightened by a nut that fits on these threads. They are operated by a key which may be inserted through holes  478 .  
         [0024]    This draw out arrangement also provides appropriate motions to the circuit breaker  300  so as to cause opening of the circuit breaker  300  through the use of a trip arrangement in between the plug-in base  200  and the circuit breaker  300 . This draw out arrangement is designed to facilitate installation thereof and use on the circuit breaker  300  with the plug-in base  200  even if the plug-in base  200  and circuit breaker  300  are supplied separately.  
         [0025]    [0025]FIG. 5 depicts the cam plate  426  including the first slot  428  and the second slot  430 . The cam plate  426  is preferably a flat plate  448  composed of a stamped steel component. The flat plate  448  has a periphery  458  defined by a first side  450 , a second side  452 , a third side  454 , and a fourth side  456 . The first side  450  and third side  454  are preferably generally straight and parallel to each other. The second side  452  and fourth side  456 , on the other hand, include irregular peripheries including curvatures as shown. The first slot  428  is contained fully within the periphery  458  of the flat plate  448 . The first slot  428  includes a first end  462  located near an intersection of the third side  454  and fourth side  456 . The second end  464  of the first slot  428  is further from the third side  454  than the first end  462  is to the third side  454 . The second slot  430  includes a first end  466  which is open on the fourth side  456  and a second end  468  which is adjacent the second side  452 . The cam plate  426  further includes an aperture  460  sized for receiving the shaft  424 . The aperture  460  is preferably adjacent an intersection of the second side  452  and the third side  454 . The cam plate  426  further preferably includes rounded corners in its periphery  458  and the first slot  428 , second slot  430 , and aperture  460  further preferably include rounded ends.  
         [0026]    The plug-in base  200  and the draw-out mechanism  400  can be supplied as accessories. A customer already in possession of a circuit breaker can use these accessories, i.e. plug-in base  200  and draw-out mechanism  400 , to convert the breaker from a fixed type to a withdrawable type. This could be done by first fitting the support plates  302  on the breaker (e.g. breaker  300 ). Then, the draw-out mechanism  400  could be assembled on the plug-in base  200  and the breaker  300  fitted onto the draw-out mechanism  400  by sliding the guide pins  304  into the slots of the accessories, e.g. slots  206  in left plate  202  and right plate  204  attached to plug-in base  200  and slots  430  in draw-out mechanism  400 .  
         [0027]    While the 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 that the invention will include all embodiments failings within the scope of the appended claims.