Abstract:
There is disclosed a door assembly for use on an electric switch housing which is virtually arc proof. The door assembly includes a rectangular frame with a door pivotally connected to one side of the frame by an elongated piano type hinge. A multi-latch door lock secures the door to the frame by providing a plurality of locking latch points along three sides of the door and door frame. The multi-latch door lock is operated from a single handle to operate the lock between its locked and unlocked conditions. A fail safe mechanism is provided to automatically cut off the flow of current in the electric switch when the door is opened.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from U.S. provisional patent application No. 61/484,820 filed May 11, 2011, the entirety of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The invention relates generally to door assemblies for use with high voltage electric switches. 
     BACKGROUND OF THE INVENTION 
     Medium voltage interrupting devices (circuit breakers, switches, fuses) and associated equipment (instrument transformers, bus bars, L.A., etc) are contained in switchgear housings which consist of a large steel box divided in separate compartments. Lockable arc-resistant doors are provided in front of the medium voltage compartments. The arc-resistant doors are designed and tested to provide the highest possible degree of protection to personnel standing in front of the doors against the effects of an short circuit arc occurring in atmospheric air within the medium voltage compartment. 
     The short circuit current can reach values of thousands of amperes and the can cause a powerful explosion which can blow of the doors, eject outside hot gases and particles that can injure or kill personnel close to the switchgear enclosure. 
     To prevent injuries the switchgear enclosures are made as arc-proof as possible. The door accessing the medium voltage compartment is the point of weakness. To overcome the possibility of short circuit by-products escaping through the door of the switchgear housing, the door is made of thick steel and usually bolted closed by a plurality of bolts along the periphery of the door. While this is effective in closing off the door and securing it from a high short circuit arc, it makes accessing the inside of the compartment very difficult since a great deal of time will be required to unbolt the door to open it. 
     Ordinary door locks as used on standard or high security doors are much more convenient to use. These doors&#39; locking system generally comprise a handle portion which is coupled to one or more door latches which engage one or more corresponding keepers in the door frame. Turning or moving the door handle generally causes the latch, or latches, to disengage their respective keepers, unlocking the door and allowing the user to open the door. While this standard type of door lock is quit convenient to use, it is generally not suitable for use with medium voltage switchgear enclosures. Standard door locks of this type do not provide the security required by high current short circuits arcs up to 63 kA, and will generally result in the door being blown off the housing in the event of a high current arc. An improved door assembly but which is as secure and arc-proof as a bolted door is therefore required. 
     SUMMARY OF THE INVENTION 
     In accordance with one aspect of the present invention, there is provided an arc proof door assemble for use with medium voltage equipment contained within a switchgear enclosure. The door is designed and tested to withstand the transient pressure and the thermal effects of an internal arcing fault and remain closed and latched. The multi point latching elements on three sides of the door periphery are moved between locked and un-locked position by a rotary handle (180 degree rotation). On the fourth side of the door, there is a piano continuous steel hinge (⅜″ diameter pin, and ⅛″ steel flaps). The operating handle has a cam that when rotated moves the locking elements 1.25″ between closed and locked positions. 
     The door assembly includes a frame having opposite first and second sides, opposite third and fourth sides and a central opening, each side of the frame having a length. A door is provided which is dimensioned and configured to close off the central opening, the door having opposite first and second sides and opposite third and fourth sides, the first side of the door being hinged to the first side of the frame, the door having an inside surface facing towards the opening and an outside surface facing away from the opening, each side of the door having a length. The door assembly further includes a lock mechanism for releasably locking the door when the door is in a closed position, the lock mechanism including first, second and third elongated movable lock members extending along the lengths of the second, third and fourth sides of the door, respectively, said first, second and third elongated movable lock members engaging corresponding first, second and third stationary lock members extending along the lengths of the second, third and fourth sides of the frame, respectively, the first, second and third movable lock members each being movable between a locked position wherein the movable lock member locks with its respective stationary lock member, and an unlocked position wherein the movable lock member disengages from is respective stationary lock member. The lock mechanism further includes first and second link arms movably mounted to the door, the first link arm coupling the first and second movable lock members together and the second link arm coupling the second and third movable lock members together, the link arms and movable lock members being configured such that moving one of the movable lock members between its locked and unlocked positions causes the remaining movable lock arms to move between their locked and unlocked positions simultaneously. Finally, the door assembly includes a handle mounted to the outside surface of the door, the handle being operatively coupled to one of the movable lock members to enable a user to move the movable lock member between its locked and unlocked position. 
     With the foregoing in view, and other advantages as will become apparent to those skilled in the art to which this invention relates as this specification proceeds, the invention is herein described by reference to the accompanying drawings forming a part hereof, which includes a description of the preferred typical embodiment of the principles of the present invention. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a door assembly made in accordance with the present invention with the door in its open position. 
         FIG. 2  is a front view of the outside of the door assembly made in accordance with the present invention with the door in its closed position. 
         FIG. 3  is a side view of the door assembly shown in  FIG. 2 . 
         FIG. 4  is a back view of the door assembly shown in  FIG. 2  showing the back side of the door portion. 
         FIG. 5  is a cross sectional view taken along line A-A of  FIG. 2 . 
         FIG. 6  is a cross sectional view of the interlock fail safe portion of the present invention in its locked state. 
         FIG. 7  is a cross sectional view of the interlock fail safe portion of the present invention in its unlocked state. 
     
    
    
     In the drawings like characters of reference indicate corresponding parts in the different figures. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIGS. 1 and 2 , an arc proof door assembly made in accordance with the present invention is shown generally as item  10  and includes door frame  12  and a door  14  pivotally connected to the door frame. Door frame  12  has an opening  16  and door  14  is dimensioned to close off opening  16  when the door is in its closed position as shown in  FIG. 2 . Door frame  12  has opposite sides  20  and  24  and opposite sides  22  and  26 . Likewise, door  14  has opposite sides  28  and  32  and opposite sides  30  and  34 . Side  28  of door  14  is pivotally connected to side  20  of door frame  12  by elongated piano type hinge  36  which extends along the entire length of sides  20  and  28  permitting the door to swing freely between its open position as shown in  FIG. 1  to its closed position shown in  FIG. 2 . In order to ensure that the door remains securely hinged to the frame during a high energy arc, hinge  36  must be quite robust. It has been discovered that if hinge  36  has a ⅜ inch pin and ⅛ inch steel flaps, then it will be sufficiently robust to withstand a high energy arc and ensure that the hinge keeps the door secure to the frame. 
     Door  14  can be releasably locked to door frame  12  by means of a plurality of movable locking elements positioned along the periphery of door  14  which couple to corresponding stationary locking elements positioned along the frame. In particular, each of sides  22 ,  24  and  26  of frame  12  is provided with an elongated row of hooked fingers  38  which are dimensioned to pass through apertures  40  on door  14  which are formed in an elongated row along the edges of sides  30 ,  32  and  34 . Hooked fingers  38  form a row of stationary locking elements which extend along the lengths of sides  22 ,  24  and  26  of the frame. Apertures  40  are positioned in elongated rows along sides  30 ,  32  and  34  such that the apertures receive fingers  38  when door  14  is placed in its closed position and the fingers project from outside surface  18  of the door. Movable lock members  42 ,  44  and  46  are provided on sides  30 ,  32  and  34  of door  14 , respectively. 
     Each of the movable lock members are slidingly mounted to outside surface  18  of door  14  by means of bolts  54  mounted within elongated slots  52 . Each of the movable lock members have a row of openings  48  which are dimensioned and configured to receive hooked fingers  38 . Each movable lock member is movable between an unlocked position as shown in  FIG. 1  and a locked position as shown in  FIG. 2 . When the movable lock members are in their unlocked position, each aperture  48  in the movable lock member is coaxially aligned with aperture  40  in the underlying portion of door  14  to enable hooked fingers  38  to pass through both apertures  40  and apertures  48  without the hooked fingers engaging the movable lock member. When movable lock members  42 ,  44  and  46  are in their unlocked position, it is possible to close door  14  to completely close off opening  16  since fingers  38  will pass through apertures  40  and  48  and sides  22 ,  24  and  26  of frame  12  can closely abut sides  30 ,  32  and  34  of door  14 . When the door is in its closed position, movable lock members  42 ,  44  and  46  can then be moved from their unlocked position to their locked position simply by sliding them. 
     Referring now to  FIG. 5 , the operation of each of the movable lock members will now be discussed with reference to movable lock member  42 . It will be appreciated that each of the movable lock members operates in the same way. When the movable lock members are moved into their locked position when door  14  is closed, the movable lock members are positioned such that they engage hooked fingers  38 . In particular, when the movable lock member (in this case item  42 ) is placed in its locked position, edges  56  of the movable lock member are positioned underneath hook  58  of hooked fingers  38 . Side  22  of frame  12  is thereby locked onto door  14  by the positioning of the movable lock member  42  which prevents the door from being opened by partially obscuring aperture  40  preventing hooked portion  58  from passing through the aperture. Hooked fingers  38  on side  22  of frame  12  and movable lock member  42  act as a multi-latch lock providing many locking points along the length of side  22 . This makes for a very strong and secure lock. 
     Referring now to  FIGS. 3 and 4 , it is important that all of the movable lock members move between their locked and unlocked positions simultaneously to allow for the proper operation of the door lock. Each of the movable lock members are linked to its adjacent movable lock member by a link arm which permits all three movable members to move together when one of the movable lock members is moved. Handle portion  50  is mounted to movable lock member  44  and projects from outside surface  18  of door  14  to enable a user to grasp the handle portion and move lock member  44 . Movable lock member  44  is coupled to movable lock members  42  and  46  by pivoting link arms  60  and  62 , respectively. Link arm  60  is pivotally mounted to inside surface  19  of door  14  by pivotal connection  64 . Link arms  60  is an “L” shaped members having two arms joined at an apex, the link arm being pivotally connected to the door at the link arm&#39;s apex. Link arm  60  is pivotally connected to a different movable lock member at the end of each arm through slots  66  and  68 . End  70  of link arm  60  is pivotally coupled to movable lock member  42  on the other side of door  14  via link bolt  74  passing through slot  66 . Likewise, end  72  of link arm  60  is pivotally coupled to movable lock member  44  via link bolt  76  passing through slot  68 . Moving movable lock member  44  causes a corresponding movement in link arm  60  which in turn causes movable lock member  42  to move by the same distance in a perpendicular direction to lock member  44 . Movable lock member  44  is coupled to movable lock member  46  via pivoting link arm  62  in an identical fashion as with link arm  60 . Hence, all three movable lock members are coupled together by link arms  60  and  62  such that moving one movable lock member causes a simultaneous perpendicular movement of the other two link arms. 
     Referring back to  FIGS. 1 and 2 , handle portion  50  is movable between a locked position as seen in  FIG. 2  and an unlocked position as shown in  FIG. 1 . Lock  70  is configured to lock handle  50  to door  14  when the handle is in its locked position and when movable lock member  44  is in its locked position. Lock  70  is configured such that when the lock is engaged, handle  50  cannot be moved and; therefore, movable lock member  44  cannot be moved and door  14  cannot be opened. Lock  70  can take the form of any suitable key operated lock, even a padlock. 
     Referring now to  FIGS. 6 and 7 , the door assembly is provided with a failsafe mechanism which ensures that the switch housed inside the switch housing is opened and current shut off when door  14  is opened. The interlock failsafe mechanism  80  includes a pivot arm  84  mounted to the inside surface of door  14  with a biasing spring  86  in the middle. One end of arm  84  is mounted to a locking pin  82  which is dimensioned and configured to pass through an aperture passing through door  14  and movable lock member  46 . The opposite end of arm  84  is provided with member  88  which is configured to couple to breaker  90  which operates the electric switch (not shown). When the arm is placed in its locked position as shown in  FIG. 6 , locking pin  82  prevents movable lock member  46  from moving into its unlocked position, thereby preventing door  14  from being opened. Spring  86  biases arm  84  towards its locked position. When locking pin  82  is unlocked and pushed inwardly the arm is placed in its unlocked position (see  FIG. 7 ) and movable lock member  46  is free to move into its unlocked position, permitting the door to be opened. When arm  84  is positioned into its unlocked position, member  88  engages breaker  90  to shut the current off. In this way, it is not possible to open door  14  while current is flowing. Locking pin  82  is preferably a lockable pin which can be locked in the position shown in  FIG. 6  by means of a key (not shown). Suitable locking pins are available on the market which can be used. 
     The present invention has several advantages over the prior art. In particular, the elongated multi-latch lock formed along the edges of the door forms a very secure and strong means of securing the door closed. All sides of the door are secured directly to the door frame by a multi-point attachment mechanism; namely, a piano lock in the case of side  28  and a multi latch lock in the case of sides  30 ,  32  and  34 . Since all sides of the door are secured to the frame directly, door  14  is as secure to frame  12  as if it were mounted by a plurality of bolts. However, since all movable lock members are coupled to a single handle, it is possible to unlock the door by simply moving one handle. This makes it quick and easy to unlock and open the door while at the same time providing a door which is very secure. 
     A specific embodiment of the present invention has been disclosed; however, several variations of the disclosed embodiment could be envisioned as within the scope of this invention. It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.