Abstract:
A circuit interrupter including a housing having an internal cavity. The internal cavity includes a space at a first end thereof, and includes an internal wall extending from the space to a second end of the housing. A vacuum interrupter is disposed in the space. The vacuum interrupter has at least one movable contact for contacting at least one stationary contact. An operating rod extends through the cavity, and is operable to move the moveable contact At least one baffle is fixed to the operating rod, and disposed in the cavity. In a preferred embodiment, at least one step is formed in the wall. The step separates a first internal wall section from a second internal wall section, and the first internal wall section is closer to the space than the second internal wall section.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS  
         [0001]    Not Applicable  
         STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH  
         [0002]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0003]    The field of invention is electrical circuit interrupters, and more particularly to a dry high voltage circuit interrupter having an increased strike distance.  
           [0004]    High voltage circuit interrupters are used to selectively interrupt the flow of electrical current through a circuit. As used herein, the term “high voltage” means a voltage greater than 1,000 volts. Two types of high voltage circuit are generally in use, dry high voltage circuit interrupter and wet high voltage circuit interrupters. The primary difference between the two high voltage circuit interrupters is that the wet type is filled with oil, or some other dielectric fluid, which can leak.  
           [0005]    Dry high voltage circuit interrupters typically include a vacuum interrupter encapsulated in an epoxy housing mounted to a frame. The vacuum interrupter includes a pair of electrodes, one being stationary and the other movable between an open position and a closed position to open and close the circuit. The movable electrode is typically mounted on the end of an operating rod which moves the moveable electrode between the open and closed positions.  
           [0006]    The operating rod typically extends from the vacuum interrupter to engage an actuating mechanism mounted in the frame. The operating rod is insulated from the electrode to prevent the operating rod from conducting high voltage electrically energy from the electrode to the frame.  
           [0007]    The housing typically includes an internal cavity for supporting the vacuum interrupter and operating rod. The shape of the internal cavity must also be designed to prevent high voltage energy from bridging the gap between the vacuum interrupter and the frame. The high voltage energy can bridge the gap by “tracking” along the internal wall of the cavity formed in the housing, or by striking the frame directly through the cavity.  
           [0008]    Tracking is a phenomena resulting from contamination or condensation forming on the internal cavity walls which allows electrical charges to creep along the surface of the internal cavity wall from a high potential at the vacuum interrupter to the frame which is at ground potential. Tracking can be minimized by increasing the distance the electrical charge must creep before reaching the frame. Typically, increasing the distance between the vacuum interrupter and the frame requires increasing the overall height of the circuit interrupter to increase the distance between the vacuum interrupter and the frame. Unfortunately, a larger, that is taller, circuit interrupter is not always desirable.  
           [0009]    In one known dry high voltage circuit interrupter disclosed in U.S. Pat. No. 5,747,765, a vacuum interrupter is disposed in an upper end of an internal cavity formed in the housing. The housing is mounted to a frame, and the internal cavity is open to the frame. Convolutions formed in the internal wall of the cavity increases the length of the internal wall between the vacuum interrupter and the frame to minimize tracking.  
           [0010]    Providing convolutions minimizes the problems associated with tracking and allows a shorter circuit interrupter. Unfortunately, the shorter circuit interrupter increases the chance for a direct strike between the vacuum interrupter and the frame because of the shorter physical distance between the two components. Accordingly, a need exists to minimize direct strikes between the vacuum interrupter and the frame.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention provides a circuit interrupter including a housing having an internal cavity. The internal cavity includes a space at a first end thereof, and includes an internal wall extending from the space to a second end of the housing. A vacuum interrupter is disposed in the space. The vacuum interrupter has at least one movable contact for contacting at least one stationary contact. An operating rod extends through the cavity, and is operable to move the moveable contact At least one baffle is fixed to the operating rod, and disposed in the cavity. In a preferred embodiment, at least one step is formed in the wall. The step separates a first internal wall section from a second internal wall section, and the first internal wall section is closer to the space than the second internal wall section.  
           [0012]    A general objective of the present invention is to increase the through-air strike distance between the vacuum interrupter and frame without increasing the overall height of the circuit interrupter. This objective is accomplished by providing a baffle in the cavity formed in the housing which blocks the most direct through-air path inside the housing between the vacuum interrupter and the frame.  
           [0013]    The foregoing and other objectives and advantages of the invention will appear from the following description. In the description, reference is made to the accompanying drawings which form a part hereof, and in which there is shown by way of illustration a preferred embodiment of the invention. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    [0014]FIG. 1 is a cross sectional view of a high voltage circuit interrupter incorporating the present invention;  
         [0015]    [0015]FIG. 2 is a detailed cross sectional view of the high voltage circuit interrupter of FIG. 1;  
         [0016]    [0016]FIG. 3 is a detailed cross sectional view of an second embodiment of a high voltage circuit interrupter incorporating the invention;  
         [0017]    [0017]FIG. 4 is a detailed cross sectional view of an third embodiment of a high voltage circuit interrupter incorporating the invention;  
         [0018]    [0018]FIG. 5 is an exploded cross sectional view of the high voltage circuit interrupter of FIG. 4;  
         [0019]    [0019]FIG. 6 is a cross sectional view of a fourth embodiment of a high voltage circuit interrupter incorporating the present invention; and  
         [0020]    [0020]FIG. 7 is a cross sectional view of a fifth embodiment of a high voltage circuit interrupter incorporating the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]    As shown in FIGS. 1 and 2, a dry high voltage circuit interrupter  10  includes a vacuum interrupter  12  disposed in an internal cavity  14  formed in a housing  16 . The housing  16  is fixed to a base  18  having an operating mechanism  20  which axially drives an operating rod  22  to operate the vacuum interrupter  12 . A baffle  24  fixed to the operating rod  22  increases the through-air strike distance between the vacuum interrupter  12  and the base  18 .  
         [0022]    The housing  16  is, preferably, formed from molded epoxy, and, has a top  26 , bottom  28 , and sides  30  joining the top  26  and bottom  28 . As is known in the art, fins  32  extend radially from the housing sides  30  to increase the creep distance on the housing exterior surface  34 . The internal cavity  14  formed in the housing  16  is, preferably, open to the housing bottom  28 , and encapsulates the vacuum interrupter  12  in an internal cavity upper space  36 . Threaded inserts  38  can be molded into the housing bottom  28  for fixing the housing  16  to the base  18  using bolts (not shown).  
         [0023]    The internal cavity  14  has an inwardly facing internal wall  40  extending downwardly from the space  36  toward the base  18 , and has a circular cross-section. Preferably, upper and lower steps  42 ,  44  formed in the internal wall  40  divides the internal wall  40  into three internal wall sections: an upper internal wall section  46 , an intermediate internal wall section  48 , and a lower internal wall section  50 . Although an internal cavity  14  having a circular cross-section is disclosed, the cross section can be any shape, such as polygonal, elliptical, and the like without departing from the scope of the invention.  
         [0024]    Each wall section  46 ,  48 ,  50  defines an internal cavity portion  52 ,  54 ,  56  having a different constant diameter. Preferably, the diameter of the cavity portion  52  defined by the upper internal wall section  46  is less than the diameter of the cavity portion  54  defined by the intermediate internal wall section  48  which is less than the diameter of the cavity portion  56  defined by the lower internal wall section  50 . Of course, each cavity portion  52 ,  54 ,  56  can having a diameter which varies along the internal wall  40 , such as to form a frustoconical shaped cavity portion without departing from the scope of the present invention.  
         [0025]    The upper step  42  has a downwardly facing surface  58  formed in the internal wall  40  which divides the internal wall  40  into the upper internal wall section  46  and the intermediate internal wall section  48 . The step  42  includes a radially inner edge  60  joined to the upper internal wall section  46  and a radially outer edge  62  joined to the intermediate wall internal wall section  48 .  
         [0026]    The lower step  44  also has a downwardly facing surface  64  formed in the internal wall  40  to separate the intermediate internal wall section  48  from the lower internal wall section  50 . The step  44  includes a radially inner edge  66  joined to the intermediate internal wall section  48  and a radially outer edge  68  joined to the lower internal wall section  50 . Although two steps are shown, one or more steps can be provided without departing from the scope of the present invention. Advantageously, each step  42 ,  44  increases the through-air distance and the distance an electrical charge must creep before reaching the base  18 . In addition, although steps  42 ,  44  having a downwardly facing surface which is substantially perpendicular to the internal wall is shown, the downwardly facing surface can define an angle relative to the internal wall, such as by providing an angled internal wall, an angled surface, or both, without departing from the scope of the present invention.  
         [0027]    The vacuum interrupter  12  is, preferably, encapsulated in the upper space  36  of the internal cavity  14 , and includes a casing  70  which encloses a pair of electrodes (not shown), one being stationary and the other movable between an open position and a closed position to open and close the circuit. A terminal  72  extending out of the housing top  26  is electrically connected to the stationary electrode, and another terminal  74  extending out of the housing side  30  is electrically connected to the moveable electrode. Any commercially available vacuum interrupter which can be encapsulated in the housing can be used without departing from the scope of the present invention.  
         [0028]    The base  18  is fixed to the housing bottom  28 , using methods known in the art, such as bolting, and houses the operating mechanism  20 . The operating mechanism  20 , can be any commercially available operating mechanism, which can axially drive an operating rod to operate the vacuum interrupter.  
         [0029]    The operating rod  22  extends through the internal cavity  14 , and is operatively connected to the operating mechanism  20  and the vacuum interrupter  12 . The operating mechanism axially moves the operating rod  22  to move the moveable electrode relative to the stationary electrode in the vacuum interrupter  12  to selectively open or close the circuit, and thus interrupt the flow of electricity between the terminals  72 ,  74 . Preferably, the operating rod  22  is formed from a dielectric material, such as an epoxy, and the like, so as not to conduct electricity between the vacuum interrupter  12  and the operating mechanism  20 .  
         [0030]    The baffle  24  is formed as an integral part of the operating rod  20  from the same type of material as the operating rod  24  to increase the through-air strike distance  78  of the dry high voltage circuit interrupter  10  over the straight line path  80  from the vacuum interrupter  12  to the base  18 . Preferably, the baffle  24  is disc-shaped, and extends radially from the operating rod  22  toward the intermediate internal wall section  48 . Most preferably, the radial outer edge  82  of the baffle  24  extends past the inner edge  60  of the upper step  42  to further increase the through-air strike distance  78  of the dry high voltage circuit interrupter  10 . Although forming the baffle  24  as an integral part of the operating rod  22  is disclosed, the baffle  24  can be fixed to the operating rod  22 , such as by adhesive bonding, interference fit, and the like, without departing from the scope of the invention.  
         [0031]    In a second embodiment shown in FIG. 3, a dry high voltage circuit interrupter  100  has a housing  102  which includes a downwardly extending convolution  104  formed in a cavity internal wall  106 . The convolution  104  forms a downwardly opening annular groove  108  between upper and intermediate internal wall sections  110 ,  112 . A ring  114  extending upwardly from a baffle  116  fixed to an operating rod  118  is received in the groove  108  to further increase the through-air strike distance of the dry high voltage circuit interrupter  100  over the straight line path. Preferably, the ring  114  is formed as an integral part of the baffle  116  from the same material as the baffle  116 . However, the ring  114  can be formed as a separate piece and fixed to the baffle  116  using methods known in the art, such as adhesive bonding, without departing from the scope of the present invention.  
         [0032]    In a third embodiment shown in FIGS. 4 and 5, a dry high voltage circuit interrupter  200  has a housing  202  which includes a first baffle  204 , such as disclosed in the first embodiment, and a second baffle  206  extending inwardly from a cavity internal wall  208 . The second baffle  206  overlaps the first baffle  204  to further increase the through-air strike distance  210  of the dry high voltage circuit interrupter  200 . Preferably, the first baffle  204  is interposed between a vacuum interrupter  212  and the second baffle  206  to simplify assembly. However, the second baffle  206  can be interposed between the vacuum interrupter  212  and the first baffle  204  without departing from the scope of the invention.  
         [0033]    The second baffle  206  can be formed as an integral part of the internal wall  208 , or formed as a separate part and be fixed to the wall  208 . One method for fixing the second baffle  206  to the internal wall  208  is to bond an outwardly extending edge  214  of the second baffle  206  to the internal wall  208 . A lip  216  extending upwardly from the second baffle outer edge  214  can be formed to provide a large bonding surface for adhesively bonding the second baffle  206  to the wall  208 . Alternatively, the lip  216  can be received in a annular downwardly opening groove  218  formed in the internal wall  208  which is filled with an adhesive to bond the second baffle  206  to the internal wall  208 .  
         [0034]    Another method for providing a second baffle in the cavity includes a new method for forming the cavity in the housing. As shown in FIG. 6, a dry high voltage circuit interrupter  300  includes a housing  302  formed around a cylindrical insert  304  formed from a dielectric material, wherein the insert  304  extends from a vacuum interrupter  306  to a housing bottom  308 . The insert  304  forms cavity internal wall  310 , and includes a second baffle  312  extending inwardly and formed as an integral part of the internal wall  310 . Of course, the insert  304  can include steps, convolutions, sections having different diameters, and comprise multiple parts to accommodate the terminal extending through the housing side or simplify assembly without departing from the scope of the present invention.  
         [0035]    In a preferred embodiment disclosed in FIG. 7, a housing  416  is formed from a first epoxy  413  which encapsulates a vacuum interrupter  412 , and a second epoxy  415  which encapsulates the first epoxy and defines the internal cavity  414 , as is known in the art. As described above in the first embodiment, the housing  416  is fixed to a base  418 .  
         [0036]    An operating rod  422  extends through the internal cavity  414 , and is operatively connected to the vacuum interrupter  412  and an operating mechanism  420  disposed in the base  418 . As in the above embodiments, the operating rod  422  is preferably formed from a dielectric material, or an assembly containing a dielectric material, so as not to conduct electricity between the vacuum interrupter  412  and the operating mechanism  420 .  
         [0037]    A baffle  424 , such as disclosed in the above embodiments, is formed as an integral part of the operating rod  420  which overlaps with a second baffle  413  extending inwardly toward the operating rod  422 . In this embodiment the second baffle  413  is a disc supported by the base  418  which simplifies assembly. Although a disc is disclosed, the second baffle can be any shape which provides a barrier between the vacuum interrupter  412  and the operating mechanism  420 .  
         [0038]    In this embodiment, the base  418  includes a lip  419  which supports the second baffle  413 . Advantageously, the second baffle  413  is sandwiched between the base  418  and housing  416  to secure the second baffle  413  in place. As result, a means for attaching the second baffle  413  to the housing  416  or base  418  is not required. Although an attachment means is not required, means for attaching the second baffle  413  to the housing  416  and/or base  418  can be provided without departing from the scope of the invention. For example, the second baffle  413  can be attached to the housing bottom  428  using methods known in the art, such as adhesives, bolting, welding, and the like, and the lip  419  can be eliminated, such that the second baffle  413  is not supported by the base  418 .  
         [0039]    While there have been shown and described what is at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention defined by the appended claims. For example, the present invention is described with reference to a dry high voltage circuit interrupter, however, the invention can be incorporated into a wet high voltage circuit breaker without departing from the scope of the invention.