Abstract:
An electrically powered, fast acting transfer switch utilizes a single action solenoid that, alternately, through a mechanical assembly, moves the handle of one electric power switch between OFF and ON positions. A coupling including a rigid strap operates the handle of a second electric power switch oppositely between ON and OFF positions. The mechanical assembly includes an electromagnet drive plate to which the electromagnet of the solenoid is secured and an armature drive plate carrying the solenoid armature. A latch mechanism alternately holds one drive plate and then the other stationary so that the electromagnet and armature alternately move to effect reciprocal movement of the handle of the one electric power switch, and through the rigid strap, the handle of the second electric power switch.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to switches for electric power distribution systems and, more particularly, to electrically powered operators for interlocking the operation of a pair of switches, such as those in a transfer switch.  
           [0003]    2. Background Information  
           [0004]    Transfer switches commonly used to connect alternate power sources to a load, including networks, utilize a pair of switches each connecting one of the sources to the load. In order to prevent connecting unsynchronized sources together, the operation of the two switches is coordinated, typically by a mechanical interlock, so that only one switch at a time can be turned ON. In many instances, it is desirable to operate the transfer switch remotely. Typically, electric motors have been used to operate the interlocks on transfer switches. The motor powered interlocks operate relatively slowly so that there is a noticeable dead period between the time that one of the switches is turned OFF and the other is turned ON. It is desirable to minimize this dead period while assuring that the two switches are never both ON at the same time.  
           [0005]    U.S. Pat. No. 4,553,115 describes a solenoid powered operator for a single, molded case circuit breaker. This device operates the circuit breaker handle rapidly each time the solenoid is energized. It would be desirable to be able to operate the pair of switches in a transfer switch at a similar rapid rate, thereby reducing the interval in which the load is unenergized.  
           [0006]    There is a need, therefore, for an improved operator for the switches of a transfer switch which allows the transfer to be made more rapidly.  
         SUMMARY OF THE INVENTION  
         [0007]    This need, and others, are satisfied by the invention which is directed to a fast acting, electrically powered operator for a pair of electric power switches and to a transfer switch incorporating this operator. The switches of a transfer switch are mounted end to end with their handles oppositely reciprocable in a common plane between OFF and ON positions. The electrically powered operator comprises a solenoid, and a mechanical assembly coupling the solenoid to the handle of the first switch for reciprocating the handle between the ON and OFF positions on successive actuations of the solenoid. A coupling comprising an elongated member couples the handle of the second switch to the handle of the first switch for movement therewith to reciprocate the handle of the second switch between the OFF position and the ON position opposite to the ON position and OFF position of the handle of the first switch.  
           [0008]    The solenoid is a single action solenoid having an electromagnet and an armature movable relative to the electromagnet. The mechanical assembly includes a first drive member coupled to the electromagnet and a second drive member coupled to the armature. A latch mechanism reciprocates between a first latch position in which the first drive member is held fixed and the second drive member moves upon actuation of the single action solenoid, and a second latch position in which the second drive member is held fixed and the first drive member moves upon actuation of the single action solenoid. A first yoke engages the first handle to reciprocate the first handle between the ON and OFF positions on successive actuations of the single action solenoid through alternate engagement by one and then the other of the first and second drive members. The first yoke engages and toggles the toggle mechanism as the first handle reciprocates between the ON and OFF positions. The elongated member of the coupling is coupled to the first yoke. A second yoke connects the elongated member to the second handle. The coupling includes a guide mounted on the second switch guiding the reciprocal movement of the elongated member and maintaining the second yoke in engagement with the second handle. The mechanical assembly includes a frame mounted on the first switch and within which the first and second drive members reciprocate. The frame includes a guide in the form of a slot for guiding reciprocal movement of the elongated member and maintaining the elongated member in engagement with the first handle through the first yoke.  
           [0009]    The invention also embraces the fast acting, electrically powered operator for a pair of end mounted electric power switches. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    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:  
         [0011]    [0011]FIG. 1 is an isometric view of a transfer switch incorporating the invention;  
         [0012]    [0012]FIG. 2 is a side elevation view of a portion of the transfer switch of FIG. 1 showing the mechanical assembly with the associated switch in the OFF position;  
         [0013]    [0013]FIG. 3 is a horizontal section through the mechanical assembly shown in FIG. 2 taken along the line  3 - 3 ;  
         [0014]    [0014]FIG. 4 is a vertical section through FIG. 3 taken along the line  4 - 4 ;  
         [0015]    [0015]FIG. 5 is a simplified plan view illustrating that with the switch shown in FIGS. 2 and 3 in the OFF position, the other switch is in the ON position;  
         [0016]    [0016]FIG. 6 is a horizontal sectional view similar to FIG. 3 but with the associated switch in the ON position;  
         [0017]    [0017]FIG. 7 is a vertical section taken through the mechanical assembly in FIG. 6 along the line  7 - 7 ;  
         [0018]    [0018]FIG. 8 is an isometric view of the toggle mechanism which forms part of the mechanical assembly; and  
         [0019]    [0019]FIG. 9 is an isometric view of the electromagnet and armature drive plates that form part of the mechanical assembly of the transfer switch. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    [0020]FIG. 1 illustrates a transfer switch  1  which incorporates a pair of electric power switches  3  and  5 . These electric power switches  3  and  5  can be molded case switches, which are well known in the power distribution field. If overcurrent protection is desired, the switches  3  and  5  can be circuit breakers. Referring also to FIG. 5, the switches  3  and  5  have handles  7  and  9 , respectively, which move rectilinearly between ON and OFF positions, as is well known. The two switches  3  and  5  are mounted end to end, such as on a panel board  11 , with the handles  7  and  9  movable in a common plane. The switches  3  and  5  are oppositely oriented so that with the handles  7  and  9  turned in the same direction, one switch is ON and the other is OFF.  
         [0021]    Opposite rectilinear movement of the handles  7  and  9  is effected by an electrically powered operator  13 . Referring to FIGS. 2 through 4, the electrically powered operator  13  incorporates a single action solenoid  17  which includes an electromagnet  19  having a single electrical coil  21  wound on a magnetic core  23  and a generally T-shaped armature  25  that is movable with respect to and within the electromagnet  19 . The solenoid  17  is coupled to the handle  7  of the switch  3  by a mechanical assembly  26 . This mechanical assembly  26  includes a first drive member in the form or an electromagnet drive plate  27  that is secured to the electromagnet  19  and mounted for rectilinear movement along the axis of movement of the handle  7 . The armature  25  is secured to a second drive member in the form of an armature drive plate  29  that is also disposed for rectilinear movement along the axis of movement of the handle  7  but on the opposite side of the handle from the electromagnet drive plate  27 . The electromagnet drive plate  27  slides on a mounting plate or frame  31  and is contained by side flanges  33 , end flanges  35  and top flanges  37  formed by the mounting plate  31 . Referring to FIG. 9, the electromagnet drive plate  27  has a flat base section  27   a , upstanding side flanges  27   b  and horizontal terminal flanges  27   c  on which the electromagnetic is mounted. Offset end flanges  27   d  are aligned with the end flanges  35  on the mounting plate  31 .  
         [0022]    Similarly, the armature drive plate  29  slides on the mounting plate  31  and is contained by sides flanges  33 , end flanges  35  and top flanges  37 . The armature drive plate  29 , as shown in FIG. 9, has a flat base section  29   a , a vertical flange  29   b , a horizontal terminal flange  29   c  on which the armature is mounted and offset end flanges  29   d  aligned with end flanges  35  on the mounting plate  31 .  
         [0023]    The mounting plate  31  is secured to the top of the molded housing  41  of the switch  3  by fasteners  43 . The mounting plate  31  includes four rectangular latch slots  45  and a pair of latch pivot center apertures  47 . The mounting plate  31  also includes, at the center of each side, an integrally formed, upstanding spring bracket  49  each having a pair of integrally formed, inwardly bent rigid ears  51  for engaging the ends of four helical compression springs  53 . These helical compression springs  53  bear against offset end flanges  27   d  of the electromagnet drive plate  27  or the offset ends  29   d  of the armature drive plate  29 , as seen in FIGS.  2 - 4 , to bias the drive plates  27  and  29  to their limit positions.  
         [0024]    The mechanical assembly  26  incorporates a latch mechanism  55 . Referring also to FIG. 8, this latch mechanism  55  includes a first yoke  57  which comprises a base  59  having a transverse slot  61  in a bottom face  63  that seats on an escutcheon  65  on the molded housing  41  of the switch  3  surrounding the handle  7 . The yoke  57  has an upstanding collar  67  with a through aperture  69  in which the handle  7  is captured. As will be seen, the electromagnet drive plate  27  and the armature drive plate  29  bear against opposite sides of the yoke  57  to drive the handle  7  between the ON and OFF positions.  
         [0025]    Latch mechanism  55  also includes a pair of pivotable, bistable mechanical spring latches  71  configured to alternately engage and stop further movement of the electromagnet drive plate  27  and the armature drive plate  29 . Each of the spring latches  71  includes a latch arm  73  and a helical tension spring  75  stretched between the ends of the latch arm  73 . The latch arms  73  have stops  77  and  79  integrally formed at opposite ends that extend through the latch slots  45  in the mounting plate  31  and are configured to engage and stop the movement of the electromagnetic drive plate  27  and the armature drive plate  29 , respectively. The latch arms  73  are mounted for pivotable movement beneath the mounting plate  31  by pivot rivets  81  engaging the latch pivot apertures  47 .  
         [0026]    The yoke  57  includes, at the laterally outward ends of the base  59 , latch camming surfaces  83  which engage and laterally deflect the tension springs  75  on the latch arms  73 . The latch arms  73  have two stable positions. In the first stable position, shown in FIG. 3, the latch arms  73  are rotated so that the stops  77  are in position to engage and limit the movement of the electromagnet drive plate  27 . In the second stable position, the latch arms  73  are rotated to the positions, shown in FIG. 6, where the stops  79  are rotated inward to form stops for and set the limit of travel of the armature drive plate  29 . The bistable latch arms  73  rapidly transfer between the two stable positions by movement of the camming surfaces  83  on the base  59  of the yoke  57  from one side to the other of the pivot axes of the latch arms  73  as the yoke  57  is alternately driven by the drive plates  27  and  29 .  
         [0027]    The electrically powered operator  13  further includes a coupling  85  which couples the handle  9  of the second electric power switch  5  to the handle  7  of the first switch  3 . This coupling  85  includes an elongated member, such as the flat strap  87  which has a first opening  89  sized to engage the collar  67  on the first yoke  57 . A second opening  91  in the strap  87  is positioned and sized to engage the collar  93  on a second yoke  95  which engages the second handle  9  on the second switch  5 . This second yoke  95  also engages and slides along an escutcheon (not shown) on the molded housing  97  of the second switch  5 . The same part can be used for the yoke  95  as the yoke  57  to reduce the parts count, although the camming surfaces  83  are not utilized on the second yoke  95 .  
         [0028]    Referring to FIG. 1, the flat strap  87  extends through a slot  99  in the flange  29   b  of the armature drive plate  29  which serves as a guide for the strap  87  and prevents it from lifting up off of the collar  67  on the yoke  57 . A bracket  107  integrally formed on mounting plate  109  on the second switch  5  holds the strap  87  down and in engagement with the collar  93  of the second yoke  95 .  
         [0029]    The operation of the transfer switch  1  is as follows:  
         [0030]    Prior to energization of the single action solenoid  17 , the electromagnet drive plate  27  and the armature drive plate  29  are biased by the helical compression springs  53  to their outermost limit positions against the end flanges  35  of the mounting plate  31 . If the first handle  7  is in the OFF position, as shown in FIGS.  2 - 4 , the armature drive plate  29  is in engagement with the yoke  57  through slot  29   e  in the base  29   a . At the same time, the second handle  9  of the second switch  5  is in the ON position, as shown in FIG. 5 as, it will be recalled, they are oppositely oriented end to end. Upon actuation of the single action solenoid  17 , the electromagnet drive plate  27  is rapidly moved into engagement with the electromagnet drive plate stops  77  which restrict further movement of the electromagnet drive plate  27 . However, as the armature  25  is rapidly pulled into the coil  21 , the armature drive plate  29  slides along the mounting plate  31  resulting in the movement of the yoke  57  which, in turn, carries the handle  7  with it.  
         [0031]    As the handle  7  passes the toggle point of the switch  3 , it rapidly travels to the ON position bringing the yoke  57  with it. When the camming surfaces  83  on the yoke  57  pass the pivots  81  on the latch arms, the latch arms  73  rapidly toggle to the position, shown in FIGS. 6 and 7, wherein the stops  79  are in position to engage the armature drive plate  29 . As the handle  7  of the switch  3  moves to the ON position, the handle  9  of the second switch  5  is moved from the ON position to the OFF position. The operating mechanisms of the switches  3  and  5  are such that the switch  5  toggles OFF before the switch  3  is toggled ON so that there is a dead period in which both switches are OFF.  
         [0032]    The next time the solenoid  17  is energized and the armature  25  is pulled into the coil  21 , the armature drive plate  29  is restrained by the stops  79 . Hence, the electromagnet, in effect, moves toward the armature, thereby pulling the electromagnet drive plate  27  with it. This electromagnet drive plate  27  engages the yoke  57 , thereby pushing the handle  7  back toward the OFF position. Simultaneously, the strap  87  being in engagement with the collar  93  on the second yoke  95  moves the handle  9  of the second switch  5  toward the ON position. Again, the switch  3  toggles OFF before the switch  5  is toggled ON to provide an open switching transition. As the camming surfaces  83  on the first yoke  57  pass the pivot rivets  81 , the arms  73  toggle rapidly to rotate the stops  77  in position for engaging the electromagnet drive plate  27  the next time the solenoid  17  is energized.  
         [0033]    The solenoid  17  provides rapid operation of the transfer switch  1 . The mechanical assembly  26  allows a single action solenoid to be used, as the latch mechanism alternately reverses the single motion of the solenoid for turning the switches OFF and ON.  
         [0034]    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 the invention which is to be given the full breadth of the claims appended and any and all equivalents thereof.