Abstract:
An automatically operating interlock device prevents connection of an electrical device within a cabinet unless the cabinet door is closed. The interlock is particularly useful for circuit breakers contained within arc resistant cabinets. The interlock includes a spring-biased brake bar controlling the position of a brake. The brake bar is biased so that it pulls the brake against one of the wheels of the circuit breaker, thereby preventing movement of the circuit breaker towards its rear, connected position. Closing the door causes the door to push against the brake bar, thereby causing the brake bar to pivot the brake away from the wheel. The circuit breaker may then be moved rearward towards this connected position.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to automatic lockout mechanisms for electrical equipment containers. More specifically, the invention relates to a system for preventing connection of electrical equipment within a cabinet unless the cabinet door is closed.  
           [0003]    2. Description of the Related Art  
           [0004]    Electrical equipment such as circuit breakers is typically housed within containers designed to prohibit access to the equipment at times when servicing the equipment would be unsafe. A circuit breaker for medium voltage applications will typically include male and female connectors for disconnecting the circuit breaker from the circuit prior to opening the circuit breaker&#39;s container. Additionally, it is generally considered desirable to house such circuit breakers within an arc resistant container. To qualify as arc resistant, the door of the circuit breaker must be closed before the circuit breaker can be connected.  
           [0005]    One example of a system for preventing access to a fuse box while the fuses are connected to the circuit is described in U.S. Pat. No. 5,757,260, issued to J. E. Smith et al. on May 26, 1998. This patent describes a pivoting rod blocking rotation of the door&#39;s handle when the box containing the fuses is not fully retracted from the circuit. When the box if fully retracted, a pin on the carriage roller engages a camming surface on the rod, disengaging the rod from the door handle mechanism and permitting the door to be opened. Additionally, a slider prevents access to the threaded rod of the levering in mechanism when the door&#39;s handle is rotated away from the locked position, thereby securing the carriage in the retracted position. An interlock acting on the carriage itself, instead of the levering in mechanism, may exhibit greater reliability.  
           [0006]    Therefore, there is a need for an automatically operating interlock for electrical cabinets wherein the lockout mechanism is controlled by the position of the door itself instead of the door handle. Additionally, there is a need for an interlock mechanism that is simpler, easier to manufacture, and more reliable than presently available interlock systems.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is an automatically operating interlock for electrical cabinets, such as arc resistant circuit breaker cabinets. The interlock prevents connecting the circuit breaker or other electrical equipment within the cabinet unless the cabinet door is closed.  
           [0008]    A typical circuit breaker for medium voltage applications is mounted on a carriage that is movable between a forward, disengaged position and a rearward, engaged position within the cabinet containing the circuit breaker. At least one pair of quick disconnects terminating in finger clusters protrudes from the rear of the circuit breaker, being dimensioned and configured to engage a pair of stabs at the rear of the circuit breaker&#39;s cabinet when the circuit breaker is in the rearward position, thereby connecting the circuit breaker to the protected circuit. A typical medium voltage circuit breaker will use three pairs of mating stab/quick disconnect combinations. When the circuit breaker is moved to its forward position, the finger clusters are withdrawn from the quick disconnects, thereby disconnecting the circuit breaker from the circuit.  
           [0009]    Moving the circuit breaker from one position to the other is accomplished by means of a threaded rod extending from the front to the rear of the cabinet. A levering in block engages the threaded rod so that rotation of the threaded rod pushes the levering in block either forward or rearward. The levering in block is secured to the carriage, so that rotation of the threaded rod thereby moves the carriage forward or backward. This process is known as levering in.  
           [0010]    The interlock includes a spring-biased brake bar controlling the position of a pivotally mounted brake. The brake bar extends from the cabinet door to a position adjacent one of the wheels of the circuit breaker when the circuit breaker is in its forward, disconnected position. The rear end of the brake bar is pivotally secured to the brake. The brake is in turn pivotally secured to the cabinet floor, also adjacent to the circuit breaker&#39;s wheel when the circuit breaker is in the forward position. The brake bar is biased to pull the brake against the wheel, thereby preventing movement of the circuit breaker. The front end of the brake bar is dimensioned and configured to abut the cabinet door when the door is closed. Closing the cabinet door pushes the brake bar rearward, thereby rotating the brake away from the wheel. The circuit breaker may then be moved from its forward, disconnected position to the rearward, connected position using the normal levering in procedure.  
           [0011]    It is therefore an aspect of the present invention to provide an automatically operating interlock for electrical cabinets, preventing equipment within the cabinet from moving from a forward, disconnected position to a rearward, connected position unless the cabinet door is closed.  
           [0012]    It is another aspect of the present invention to provide an automatically operating interlock for electrical cabinets that is actuated by the position of the cabinet door.  
           [0013]    It is a further aspect of the present invention to provide an automatically operating interlock locking the rotation of the rollers for the equipment within the cabinet unless the cabinet door is closed.  
           [0014]    It is another aspect of the present invention to provide a brake that is biased towards the rollers of electrical equipment within a cabinet unless the cabinet door is closed.  
           [0015]    It is another aspect of the present invention to provide an automatically operating interlock mechanism for electrical cabinets including a spring biased brake bar controlled by the position of the cabinet door, and controlling the position of a brake.  
           [0016]    It is a further aspect of the present invention to provide an automatically operating interlock that is simpler, more reliable, and easier to manufacture than other interlocks.  
           [0017]    These and other aspects of the present invention will become apparent through the following description and drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a side cross sectional view of a circuit breaker cabinet showing the circuit breaker in its forward, disengaged position.  
         [0019]    [0019]FIG. 2 is a side cross sectional view of a circuit breaker cabinet showing the circuit breaker in its rearward, engaged position.  
         [0020]    [0020]FIG. 3 is a top view of a levering in mechanism for a circuit breaker.  
         [0021]    [0021]FIG. 4 is a top isometric view of a cabinet floor including an interlock of the present invention.  
         [0022]    [0022]FIG. 5 is an isometric view of the interlock according to the present invention, showing the interlock in the locked position.  
         [0023]    [0023]FIG. 6 is an isometric view of a brake for an interlock according to the present invention, showing the brake in the locked position.  
         [0024]    [0024]FIG. 7 is a top view of an interlock and circuit breaker wheel according to the present invention, showing the position of the brake bar and brake relative to the wheel in the locked position.  
         [0025]    [0025]FIG. 8 is an isometric view of an interlock according to the present invention, showing the brake in the unlocked position.  
         [0026]    [0026]FIG. 9 is an isometric view of a brake for an interlock of the present invention showing the brake in the unlocked position.  
         [0027]    [0027]FIG. 10 is a top view of an interlock and circuit breaker wheel, showing the position of the brake bar, brake, and wheel with the interlock in the unlocked position. 
     
    
       [0028]    Like reference numbers denote like elements throughout the drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The invention is an automatically operating interlock for electrical cabinets, preventing connection of the electrical equipment within the cabinet unless the cabinet door is closed. The preferred embodiment is particularly useful for circuit breakers within arc resistant cabinets.  
         [0030]    An interlock of the present invention is best understood through and explanation of a conventional medium voltage circuit breaker. Referring to FIGS. 1 and 2, a switchgear assembly  10  is illustrated. The switchgear  10  includes cabinet  12 , containing a circuit breaker  14 . The back  16  of the circuit breaker  14  includes means for electrical connection with a circuit, which are preferably at least one pair of quick disconnects  18 , with each quick disconnect  18  terminating with a plurality of contact fingers  20 . The cabinet&#39;s rear wall  22  includes means for connecting to the means for electrical connection of the circuit breaker to a circuit, which preferably include a pair of channels  24 , with each quick disconnect containing a primary contact or stab  26 . Quick disconnects  18  and contact fingers  20  are dimensioned and configured so that, when the quick disconnects  18  are inserted into the channels  24 , the contact fingers  20  are electrically connected to the primary contact  26 . A typical medium voltage circuit breaker will include a combination of three pairs of quick disconnects  18  and three corresponding pairs of channels  24 . The bottom  28  of circuit breaker  14  may include a plurality of rollers  30 , dimensioned and configured to permit the circuit breaker to move along the rails  32 , extending from the cabinet&#39;s rear  22  to the cabinet&#39;s front  34 . The circuit breaker  14  may also rest on rollers  36 , permitting the circuit breaker  14  to move within the cabinet  12 .  
         [0031]    Referring to FIG. 3, the cabinet  12  also includes means for moving the circuit breaker  14  between a rearward position and a forward position, preferably including a levering in pan assembly  38  which is secured to the bottom  40  of the cabinet  12 . The levering in pan assembly  38  includes a pan  42 , upon which the levering in assembly  44  is mounted. The levering in assembly  44  includes a front bearing block  46 , mounted to the front of pan  42 , and a rear-bearing block  48 , mounted to the rear of pan  42 . A drive screw  50  extends between the front bearing block  46  and rear-bearing block  48 , terminating in a tip  52 , dimensioned and configured to engage a crank. The tip  52  will typically be a hex drive. A levering in block  54  is thread mounted on the drive screw  50 , so that rotation of the drive screw  50  moves the levering in block  54  forward or rearward. The levering in block may also include forward stop  56 .  
         [0032]    In use, the circuit breaker  14  will typically be in the rearward, engaged position of FIG. 2, wherein the contact fingers  20  are electrically connected to the primary contacts  26 . In this position, power may be supplied through the circuit breaker to the protected circuit. When servicing the circuit breaker is desired, power is disconnected by opening the circuit breaker (using either controls on the exterior of the cabinet or remotely), and a crank (not shown and well known in the art) is secured to the hex drive  52  of drive screw  50 . The rotation of drive screw  50  moves levering in block  54  forward, thereby moving the circuit breaker  14  forward so that the quick disconnects  18  are brought out of engagement with the channels  24 . The circuit breaker  14  is now completely isolated from electrical power, as illustrated in FIG. 1. In this position, the door may be opened and the circuit breaker may be serviced safely. When service is complete, the crank is again secured to the hex drive  52  of drive screw  50  so that drive screw  50  may be rotated in the opposite direction, thereby moving the levering block  54  and circuit breaker  14  rearward. The quick disconnects  18  are thereby brought into engagement with the channels  24 , bringing the contact fingers  20  back into electrical contact with the primary contacts  26 .  
         [0033]    It becomes apparent from the above description that preventing the circuit breaker  14  from being moved rearward into its connected position unless the door  35  of the cabinet  12  is closed is desirable to prevent any possibility of injury to personnel servicing the circuit breaker  14 . The interlock of the present invention accomplishes this purpose.  
         [0034]    Referring to FIGS.  4 - 10 , an interlock  58  of the present invention is illustrated. The interlock  58  includes a spring-biased brake bar  60 , controlling a brake  62 . The interlock  58  is preferably mounted on the floor  40  of the cabinet  12 , with the brake  62  directly behind one of the rollers  30  or  36 .  
         [0035]    The brake  62  is best illustrated in FIGS. 6 and 9. The brake is dimensioned and configured to block the rotation of a roller  30  or  36  when the brake is in its engaged position. The brake  62  preferably includes a first end  64 , pivotally secured to the floor  40  of cabinet  12 . The brake&#39;s second end  66  preferably includes a surface  68 , dimensioned and configure to be wedged underneath the bottom of a roller  30  or  36 , thereby preventing rotation of the roller  30  or  36 . The brake  62  pivots between an engaged position (FIG. 6) and a disengaged position (FIG. 9).  
         [0036]    The brake bar  60  is best illustrated in FIGS. 5 and 8. The brake bar  60  preferably includes a rear end  70 , dimensioned and configured to control the movements of the brake  62  between its engaged and disengaged positions. The rear end  70  of brake bar  60  is preferably pivotally secured to the brake  62 , at point  72 , located between the brake&#39;s first end  64  and brake&#39;s second end  66 . The brake&#39;s front end  74  is dimensioned and configured to abut the door  35  of the cabinet  12  when the door  35  is in its closed position. The brake bar&#39;s front end  74  may include a tab  76  perpendicular to the brake bar  60  for this purpose. The brake bar  60  moves between a forward position (FIG. 5) wherein the brake  62  is held in its engaged position, and a rearward position (FIG. 8), wherein the brake  62  is held in its disengaged position. Means for permitting the brake bar  60  to move between these two positions preferably includes the bolt  78 , securing the brake bar  60  to the cabinet floor  40 , passing through the slots  80  within the brake bar  60 . Referring to FIGS. 7 and 10, the brake bar  60  is biased towards its forward position, preferably by the tension springs  82  connected between the bolts  80  secured to the floor  40 , and the bolts  84  secured to the brake bar  60 . Because the brake  62  is connected to the brake bar  60  at  72 , the brake  62  is thereby biased into its engaged position.  
         [0037]    When the circuit breaker  14  is in use, it will be in a position shown in FIG. 2. In this rearward, connected position, the door  35  will abut the tab  76  of the brake bar  60 , thereby pushing the brake bar  60  towards its rearward position. The brake bar  60  will thereby hold the brake  62  in its disengaged position, illustrated in FIGS.  8 - 10 .  
         [0038]    When the circuit breaker  14  must be serviced, it is first moved from the rearward connected position of FIG. 2 to the forward disconnected position of FIG. 1. This is accomplished by opening the breaker, and then securing a crank to the hex drive  52  of the drive screw  50  as described above, so that the drive screw  50  can be rotate to move the levering block  54  and circuit breaker  14  to the forward position of FIG. 1 within the cabinet  12 . At this point, the door  35  may safely be opened. Because the door  35  no longer abuts the tab  76  of the brake bar  60 , the brake bar  60  will move forward under the bias of springs  82 . The brake  62  will thereby move from the disengaged position of FIGS.  8 - 10  to the engaged position of FIGS.  5 - 7 . In the engaged position, the surface  68  of the brake  62  fits between the roller  30  and rail  32 , or alternatively between the roller  36  and cabinet floor  40 , depending on the position of the brake  62  within the cabinet  12 . The roller  30  or  36  is thereby prevented from moving rearward, thereby securing the circuit breaker  14  in its forward, disconnected position.  
         [0039]    When service to the circuit breaker is complete, the door  35  is closed, thereby causing the door  35  to push rearward on the tab  76  of the brake bar  60 . The brake bar  60  thereby moves the brake  62  from the engaged position of FIGS.  5 - 7  to the disengaged position of FIGS.  8 - 10 . The rollers  30  and  36  are now free to move. The crank may then be secured to the hex drive  52  of the drive screw  50 , so that the drive screw  50  can be rotated in the opposite direction, thereby moving the levering block  54  and circuit breaker  14  to the circuit breaker&#39;s rearward, connected position, illustrated in FIG. 2.  
         [0040]    While a specific embodiment of the invention has 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 appended claims and any and all equivalents thereof.