Abstract:
The movable conductors of a three phase isolation switch are incorporated into the electrically insulative molded shaft, thereby mechanically supporting them and isolating them from the metal axle of the shaft. Movable contacts on the ends of each movable conductor are angularly spaced by α degrees, where α is less than  180 ° and is  90 ° in the exemplary embodiment. A common fixed load contact is located angularly between, and spaced α degrees from, both the fixed line and ground contacts so that the shaft is rotated only α degrees between a first, closed position, in which the movable conductors connect the fixed load contact for each phase to the corresponding fixed line contact, and a second, grounded position, where the fixed load contact of each phase is connected by the movable conductor to the corresponding fixed ground contact.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates generally to the distribution of electric power and particularly to apparatus that operates an isolation switch in coordination with a circuit breaker with which it is used.  
           [0003]    2. Background Information  
           [0004]    The feeder circuits in an electric power distribution system are connected to a power source through power circuit breakers which provide protection and can isolate the feeder lines for maintenance. An isolation switch can be used in combination with the power circuit breaker to ground the feeder to assure that it is safe to work on. Where the isolation switch is provided on the line side of the circuit breaker, it is important that the circuit breaker be open when the isolation switch is being switched to the grounded position. The circuit breaker can then be reclosed to ground the feeder line for maintenance. It is important, therefore, to coordinate the operation of the isolation switch with that of the circuit breaker.  
           [0005]    Ideally, the isolation switch is located adjacent the power conductors at the rear of the circuit breaker. In addition, multiple circuit breakers can be stacked one on a top of another and side-by-side in a switch gear assembly. Thus, little room is available for operating the isolation switches from the front of the switch gear assembly.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an object of the present invention to provide apparatus for coordinating the operation of an isolation switch with that of a circuit breaker with which it is used.  
           [0007]    It is another object of the invention to provide apparatus for operating an isolation switch that is located behind a circuit breaker and for mechanically interlocking the operation of the isolation switch with the operation of the circuit breaker.  
           [0008]    Thus, the present invention is directed to apparatus for operating an isolation switch in coordination with a circuit breaker comprising a drive assembly that includes a driven member and a drive coupling coupling the isolation switch to the driven member for movement of the isolation switch between open, isolated and grounded positions with movement of the driven member between corresponding positions. The apparatus further includes an interlock assembly that interlocks movement of the driven member with the condition of the circuit breaker. More particularly, the interlock assembly includes an interlock member having a lock position in which the interlock member prevents movement of the driven member, and therefore, the isolation switch and an unlock position in which the driven member is free to move. The interlock assembly further includes an interlock coupler coupling the interlock member to the circuit breaker for movement of the interlock member to the lock position when the circuit breaker is closed and to the unlock position when the circuit breaker is in the open condition.  
           [0009]    The drive assembly can further include a driving member moving the driven member between the closed, isolated, and open positions, and the interlock assembly can include a blocking member that blocks access to the driving member when the interlock member is in the lock position.  
           [0010]    The driving member can move the driven member along a reciprocal path in which case the interlock assembly includes a mount mounting the interlock member for movement into the reciprocal path of the driven member in the lock position to prevent movement of the driven member. The interlock member can have edges formed by fingers that prevent the reciprocal movement of the driven member. Where the reciprocal path is linear, the interlock member is mounted for pivotal movement into and out of the lock position about a pivot axis substantially parallel to the linear path. In this case also, the driving member can be a threaded shaft on which the driven member is threaded for the reciprocal movement along the linear path.  
           [0011]    The drive coupling can comprise cables connecting the driven member to the isolation switch. A position indicator can be provided such as a pointer carried by the cable for movement relative to a stationary legend indicating switch position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    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:  
         [0013]    [0013]FIG. 1 is an isometric view of apparatus in accordance with the invention for operating an isolation switch in coordination with circuit breaker operation shown with the isolation switch in the closed position and the interlock in the lock position.  
         [0014]    [0014]FIG. 2 is a partial isometric view of the drive/interlock unit of the invention shown with the isolation switch in the isolated position and the interlock in the lock position.  
         [0015]    [0015]FIG. 3 is an isometric view of the drive/interlock unit with the isolation switch in the grounded position and the interlock in the unlock position.  
         [0016]    [0016]FIG. 4 is a partial isometric view of the drive/interlock unit shown with the isolation switch in the close position and the interlock in the unlock position.  
         [0017]    [0017]FIG. 5 is a front view of the drive/interlock unit in which the position indicator illustrates the isolation switch in the closed position and the drive mechanism indicates that the interlock is in the unlock position.  
         [0018]    [0018]FIG. 6 is similar to FIG. 5 illustrating the isolation switch in the isolated position and with the interlock in the lock position. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0019]    As shown in FIG. 1, apparatus in the form of a drive/interlock unit  1  operates an isolation switch  3  in coordination with a power circuit breaker  5 . As is common, the power circuit breaker  5  has an output  7  which indicates the open and closed position of the circuit breaker contacts. An auxiliary trip bar  9  on the side of the power circuit breaker  5  holds the breaker in the tripped open position when actuated.  
         [0020]    The isolation switch  3  may be of the type described in commonly owned U.S. patent application Ser. No. 10/241,122, filed on Sep. 11, 2002. This switch  3  has a shaft  11  carrying a moveable conductor  13  for each phase. A set of terminals  15  is connected by buses (not shown) to corresponding terminals (not shown) on the back of the circuit breaker  5 . A second set of terminals  17  is connected to a power source (not shown). An additional set of terminals (not shown) underneath the isolation switch  3  are connected to ground. Rotation of the shaft  11  selectively connects the circuit breaker  5  to the source or ground. In a third, intermediate position in which the moving conductors are between the terminals, the circuit breaker is isolated. Thus, the shaft  11  of the isolation switch  3  is reciprocally rotatable between a closed position, an isolated position, and a grounded position.  
         [0021]    As the isolation switch  3  is located behind the circuit breaker  5 , the drive/interlock unit  1  allows the switch to be manually operated from a position in front of the circuit breaker  5 . Referring also to FIGS. 2-4, this drive/interlock unit  1  includes a drive assembly  19  and interlock assembly  21 , both mounted on a support platform  23 . The drive assembly  19  includes a driving member in the form of a threaded shaft  25  journaled in bearings  27  supported by L-shaped brackets  29  mounted on a support platform  23 . A driven member  31  is threaded on the threaded shaft  25  for reciprocal movement along a linear path  33 . One end (the forward end)  35  of the threaded shaft is provided with a drive connection in the form of a hex head  37 . This hex head  37  can be accessed through an opening  39  and a front panel  41 . See FIGS. 2 and 3. The hex head  37  can be engaged by a tool (not shown) to rotate the shaft  25  and thereby reciprocate the driven member  31  along the linear path  33 .  
         [0022]    The drive assembly  19  also includes a drive coupling  43  coupling the driven member  31  to the shaft  11  of the isolation switch. The drive coupling  43  includes a first cable  45  connected at one end to a flange  47  on the driven member and which passes around a pair of guide pulleys  49  and is connected through a connector  51  to a lever  53  secured to the one end of the shaft  11 . A second cable  55  is connected to another flange  47  on the opposite side of the driven member  31  and passes around a second pair of guide pulleys  57  to reverse its direction and then passes over a third pair of guide pulleys  59  and is secured by another connector  51  to a second lever  53  on the opposite end of the switch shaft  11 . This second lever  53  is diametrically opposite the first lever so that when the driven member  31  moves upward and to the right as shown in FIG. 1 along the threaded shaft  25 , the second cable  55  rotates the shaft  11  counterclockwise as viewed in FIG. 1. As can be appreciated from viewing FIG. 1, when the driven member  31  moves down and to the left to the position shown, the first cable  45  rotates the shaft  11  clockwise.  
         [0023]    Operation of the isolation switch needs to be coordinated with operation of the circuit breaker. This coordination requires that the following conditions be met:  
         [0024]    1. If the circuit breaker is closed, then the switch cannot change positions.  
         [0025]    2. If the switch is between positions, then the circuit breaker must remain open/trip free.  
         [0026]    3. If the switch is in any one of its three positions, then the circuit breaker position can be open or closed or open/trip free.  
         [0027]    The interlock assembly  21  coordinates the operation of the isolation switch  3  with the condition of the circuit breaker  5 . The interlock assembly  21  includes an interlock member in the form of a plate  61 . The plate  61  is mounted for movement into and out of the linear path  33  followed by a projection or boss  63  on the driven member  31 . This is accomplished by mounting the interlock plate  61  on a pivot shaft  65  mounted parallel to the threaded shaft  25  so that the interlock plate pivots into and out of the linear path  33  followed by the boss  63 . The interlock plate  61  has a pair of fingers  67  and  69  projecting laterally from the pivot shaft  65  with the side edges of these fingers forming abutment surfaces. The fingers  67  and  69  are sized and spaced such that the interlock plate  61  can only be rotated into the linear path  33  of the boss  63  and, therefore, the driven member  31  when the latter is in one of the closed, isolated and grounded positions.  
         [0028]    Referring again to FIG. 1, the interlock assembly also includes an interlock coupler formed by a pair of push-pull cables  71  and  73  each connected at one end to the interlock plate  61 . The push-pull cable  71  has its other end connected to the output  7  of the circuit breaker  5 . When the circuit breaker  5  is in the closed condition, the push-pull cable  71  rotates the interlock plate  61  into the path  33  of the boss  63  on the driven member  31 . With the circuit breaker closed and, therefore, the interlock plate member  61  in the lock position as shown in FIG. 1, the position of the isolation switch  3  cannot be changed thus, as shown in FIG. 1 with the isolation switch closed, a first abutment surface  75  on the outside of the finger  67  prevents movement of the driven member. Similarly, with the isolation switch  3  in the isolated position as shown in FIG. 2, the facing edges on the fingers  67  and  69  form a second abutment surface  77  and third abutment surface  79  which prevent movement of the driven member. With the isolation switch in the grounded position shown in FIG. 3, the outer edge on the finger  69  forms a fourth abutment surface  81  that blocks movement of the driven member  31 .  
         [0029]    In order to change the position of the isolation switch  3 , the circuit breaker must be in the open condition so that the interlock plate  61  is rotated to the unlock position out of the path  33  of the boss  63  as shown in FIG. 4. Rotation of the interlock plate  61  to the unlock position causes the second push-pull cable  73  to actuate the auxiliary trip lever  9  on the circuit breaker  5  to hold the circuit breaker in the tripped open position so that it cannot be closed while the position of the isolation switch is being changed.  
         [0030]    The interlock assembly  21  also includes a blocking member in a form of a lever  83  on the end of the pivot shaft  65  which is at least in partial axial alignment with the hex head  37  thereby blocking access to the hex head when the interlock plate  61  is in the lock position as shown in FIG. 2. Therefore, in order to change the position of the isolation switch, the lever  83  must be rotated out of alignment with the hex head, but this only occurs when the circuit breaker is open so that the interlock plate  61  is rotated to the unlock position as can be seen in FIG. 4. A guide pin  85  on the free end of the lever  83  rides in a slot  87  in the panel  41  to stabilize the lever  83 . As a further precaution, a hinged access door  89  can be secured over the opening  39  as shown in FIG. 1 and held in place by lock (not shown) through the hasp  91 .  
         [0031]    As the isolation switch is located behind the drive/interlock unit  1  and the circuit breaker  5 , a position indicator  93  is provided so that the operator is able to determine at any time the position of the isolation switch. This position indicator  93  includes a pointer  95  inscribed on a bracket  97  carried by the cable  55  as can be seen in FIG. 3. The position indicator  93  also includes a legend  99  provided on the face plate  41  adjacent slots  101  in the face plate  41  at the positions assumed by the pointer  95  for the closed, isolated and grounded positions of the isolation switch  3 . The legend  99  includes a fixed pointer  103  at each of these positions and a representation  105 ,  107  and  109  of the closed, isolated and grounded position of the isolation switch. Additional slots  111  reveal the position of the moveable pointer  95 , and therefore, the position of the isolation switch during transition between the closed, isolated and grounded positions. FIG. 5 illustrates the condition of the position indicator  93  with the isolation switch in the closed position and the interlock member in the unlock position as shown in FIG. 4. FIG. 6 illustrates the condition of position indicator  93  with the isolation switch in the isolated position as shown in FIG. 2 with the interlock member in the lock position as indicated by the position of the locking lever  83  preventing access to the hex nut  37  of the drive unit.  
         [0032]    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.