Abstract:
An encapsulated vacuum interrupter with grounded end cup and drive rod is disclosed. The double break vacuum interrupter includes a first contact system including an annular stationary contact which is engaged by a primary moving contact with the moving contact drive rod extending through the primary moving contact and through the opening of the annular stationary contact. A second contact system includes a secondary moving contact placed on the end of the moving contact rod, which engages and operates a floating contact, which moves along the same axis. A mechanical adjustment system is provided for the floating contact. A coaxial moving contact drive rod system is provided. With the encapsulated vacuum interrupter, the lower portion of the vacuum envelope is insulated from the current path, which allows for the elimination of the long internal cavity in the encapsulation as the lower end cup of the vacuum envelope may be grounded.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This is a continuation-in-part patent application taking priority from nonprovisional application Ser. No. 13/012,176 filed on Jan. 24, 2011 now U.S. Pat. No. 8,471,166. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of high voltage vacuum switches and circuit interrupting devices and more particularly to an encapsulated vacuum interrupter with a grounded lower end-cup and drive rod, which allows an actuating mechanism to be mounted in close proximity to the vacuum module. 
     2. Discussion of Prior Art 
     Encapsulated vacuum switchgear is used to interrupt and control the flow of power through high voltage distribution circuits. As used here, the term “high voltage” refers to a voltage greater than 1000 volts. The encapsulated vacuum switchgear typically includes a vacuum interrupter encapsulated in an epoxy housing mounted to a cabinet or tank for the operating mechanism. The vacuum interrupter includes a pair of contacts, one stationary and one movable between an open and closed position to open and close the electrical circuit. The movable contact is typically mounted on the end of a drive rod, which moves the movable contact between the open and closed position. 
     The operating rod typically extends from the vacuum interrupter to engage an actuating mechanism mounted in an external cabinet or tank. The portion of the operating rod extending from the vacuum interrupter is insulated to prevent the flow of high voltage electrical energy from the vacuum interrupter to the actuating mechanism cabinet. The actuating cabinet of the actuating mechanism is usually grounded. 
     The epoxy housing typically includes an internal cavity for supporting the vacuum interrupter and the operating rod. The shape of the internal cavity must be designed to prevent high voltage electrical energy from bridging the gap between the vacuum interrupter and the actuating mechanism cabinet. The high voltage energy will bridge the gap by either “tracking” along the internal wall of the cavity formed in the housing or by striking the actuating mechanism cabinet directly through the cavity. 
     Tracking is a phenomena resulting from contamination or moisture forming on the internal cavity walls which allows electrical current to creep along the surface of the internal cavity wall from the high potential of the vacuum interrupter to the grounded actuating mechanism cabinet. The electrical current results in heating which over time will degrade the electrical insulating properties of the epoxy insulation and can result in eventual failure. Tracking can be minimized by increasing the distance that the electrical current must creep to reach the grounded actuating mechanism cabinet. Increasing the distance from the vacuum interrupter to the actuating mechanism frame results in a large switchgear device, which is undesirable as it adds cost and requires more space for installation. 
     U.S. Pat. Nos. 4,568,804; 5,452,172; 6,747,234; 6,828,521 B2; 6,888,086 B2; 7,488,916 B2 and U.S. Pat Application Publication 2006/0231529 A1 disclose several prior art methods of encapsulation that utilize a cavity. These devices utilize techniques such as insulating foam, convoluted cavity walls or semi-conductive coatings to reduce voltage stress or baffles and insulating plugs to increase the path over which current must track down the walls of the cavity. All of these devices are attempts to deal with the high voltage stresses within the internal cavity and they still result in switchgear that is unnecessarily large and still subject to dielectric breakdown of the cavity over time. 
     U.S. Pat. Nos. 3,471,669, 4,618,749, 5,206,616 and 7,239,490 B2 disclose devices that that have an actuating mechanism in close proximity or in direct contact with the vacuum interrupter. This renders the actuating mechanism at or near same potential as the end of the vacuum interrupter from which the operating rod exits. Such devices must then be fully encapsulated and protected by a grounded metal casing or mounted within another device that has a grounded metal casing to protect the operator from exposure to high voltage. Another device which actually has an exposed electrically hot mechanism housing is demonstrated by U.S. Pat. Nos. 6,753,493 B2 and 6,794,596 B2. This device is meant to be operated in a manner similar to an expulsion fuse and therefore must always be operated by an insulated hook stick in order to prevent the operator from contacting high voltage. 
     U.S. Pat. No. 6,723,940 B1 discloses a device that utilizes SF6 gas within the internal cavity and depends on the fact that SF6 gas has a higher dielectric strength than air to reduce the size of the internal cavity. However, SF6 gas insulated switchgear can leak over time and SF6 gas has been know to adversely affect the environment as it can affect the ozone layer. 
     Another interrupting device uses an external air insulated drive rod to eliminate the cavity as demonstrated in U.S. Pat. No. 6,946,614 B2. This design is more complex than those that utilize an internal cavity and quite large due to the clearances required in air. 
     Still another device utilizes a vacuum interrupter with an internal ceramic contact rod to operate a cantilever beam moving contact and electrically isolate the lower end cup of the vacuum interrupter. This type of device, which is disclosed by U.S. Pat. Nos. 3,178,542 and 5,387,772 does eliminate the need for the internal cavity in the encapsulation and does result in a more compact switchgear unit. However, the ceramic contact rod is exposed to the impact stresses created during closing and the tensile loads created when breaking contact welds upon opening and is therefore subject to breakage. 
     While the aforementioned prior art arrangements may be suitable for their intended use in accordance with their respective defined applications, as discussed hereinbefore, it would be desirable to provide an encapsulated vacuum interrupter with a grounded lower end-cup and actuating rod. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is the principal object of the present invention to provide an encapsulated vacuum interrupter module with a grounded lower end cup and drive rod to allow the elimination of the need for an elongated cavity in the encapsulation, so that the actuator may be installed in close proximity to the vacuum module. 
     This patent application hereby incorporates in its entirety, U.S. patent application Ser. No. 13/012,176 to Glaser. The double break contact structure is required as this eliminates the need for a current exchange on the moving contact drive rod, which allows the lower end-cup of the vacuum interrupter to be electrically isolated or grounded. In the practice of the invention, the primary contact system has an annular stationary contact, which is engaged by a disc shaped moving contact. Both contacts are preferably fabricated of a copper-tungsten material, if the interrupter is designed for switching duty or a chromium-copper material, if the interrupter is designed to interrupt fault currents. The contacts may be of the butt style, transverse magnetic field or axial magnetic field designs as used in prior art. The base of the stationary contact is supported between two tubular insulators, which are preferably made of ceramic and form the main portion of the interrupter housing. One of these insulators contains the first contact system. The end of this insulator is closed off by an end cup preferably fabricated from stainless steel or monel, which has an opening for the moving contact rod and insulating system. A bellows preferably fabricated from stainless steel is connected from the inner diameter of the lower end cup to an annular moving internal insulator to allow motion of the moving internal insulator relative to the end cup and to seal the vacuum envelope. The annular moving internal insulator is preferably fabricated from ceramic. The other end of the moving internal insulator is connected to an internal end cup and a moving shield, which prevents vapors created during the interruption process from contacting the moving internal insulator. The moving shield is preferably fabricated from stainless steel and the internal end cup is preferably fabricated from stainless steel or monel. The internal end cup is attached to a contact rod, which has steel reinforcing rod. The contact rod is preferably fabricated from copper and the reinforcing rod is preferably fabricated from stainless steel. The reinforcing rod has a threaded portion that extends beyond a lower end of the moving contact rod to facilitate the connection of a capacitive voltage divider contact drive rod. The capacitive voltage divider contact drive rod is attached to the reinforcing rod, after brazing of the vacuum envelope. In this way, the capacitive voltage divider contact rod directly drives the moving contact rod, which eliminates the application of excessive forces to the moving internal ceramic insulator to protect it from breakage. The moving contact rod is attached to the disc shaped moving contact for the primary contact system. The moving contact rod also extends through the moving contact disc and annular stationary contact into the region of the second insulator. A second moving contact disc is mounted on the end of the moving rod and is engaged by a floating contact disc, mounted on a floating contact rod. The second moving contact disc and the floating contact disc are preferably fabricated from copper-tungsten or chromium-copper material and the floating contact rod is preferably fabricated from copper with a stainless steel reinforcing rod. The floating contact rod is mounted on the other end of the second insulator using a bellows and end-cup arrangement to allow sealing and free motion of the floating contact disc. The floating contact disc is driven by the motion of the second moving contact, which is directly coupled to the first contact system. 
     A mechanism is mounted on the end cup that supports the floating contact and allows the tolerance accumulation of the components to be adjusted out and the floating contact positioned so that the second moving contact and floating contact can be close just before the primary contacts. The mechanism also has the capability of controlling the range of motion of the floating contact so that it may be contacted by the second moving contact at approximately the same time the primary contacts close. 
     The mechanism includes an annular housing with two long slots along the main axis placed 180 degrees apart. The length of these slots is preferably the sum of the diameter of the holes in the adjuster described below plus the full range of tolerance accumulation of all parts that determine the spacing between the primary and secondary contacts. 
     The mechanism has the capability of adjusting out the tolerance build-up in the system. The housing also has an internal thread to allow the insertion of the adjuster. The moving contact rod for the floating contact has a cross-hole placed in a position to allow the adjuster move through its required range within the housing. A fixture pin placed in a through hole in the contact rod of the floating contact and passes through both slots formed through the housing. In this manner, when the interrupter is processed through a brazing cycle, the relationship between the contact rod and housing is established and the housing can also be used as a bellows anti-twist device. After the interrupter is brazed, the fixture pin is removed and an annular adjuster with external thread is screwed into the housing. The adjuster has six holes spaced 60 degrees apart, perpendicular to the main axis and of a diameter that is calculated to provide a small amount of over travel (approximately 1/32 inch) to accommodate any erosion or compression of the primary contacts due to interruption duty and repeated impact upon closing. The adjuster also has a counter-bore into which a compression spring or series of Bellville washers may be inserted. With the primary contacts held together, the adjuster is rotated so that the bottoms of the holes are below the cross-hole in the moving contact rod by the planned contact wear allowance. The multiple holes in the adjuster allow for a finer adjustment in determining this setting. Once the adjustment is complete, a pin is inserted, so that it passes through the housing, contact rod and adjuster and is secured with retaining rings at both ends. A compression spring or a series of Bellville type washers of appropriate design provide the required contact pressure for the secondary contacts and return force for the floating contact is placed in the counter-bore of the adjuster and is secured in place with a threaded cap. This forces the pin through the contact rod to the lower portion of the adjuster cross-holes and establishes the setting so the secondary contacts engage at approximately the same time as the moving contacts. 
     A portion of the moving contact rod extends through the cap and captures the compression springs to which a flexible lead or other current exchange method (garter springs, multi-lam current transfer devices or the like) may be attached. As the primary contact rod moves to the closed position, it can be seen that the secondary contacts will engage just before the primary moving contact engages the stationary contact. No current exchange is needed for the main contact rod as electric current flows from the stationary contact of the primary contact set to the moving contact, up the contact rod and through the secondary contacts and out the top terminal of the interrupter. As noted above, a capacitive voltage divider contact drive rod is connected to the threaded portion of the contact rod reinforcement. This drive rod includes an epoxy glass tube into which is inserted a system of capacitors and resistors which form a capacitive voltage divider to balance the voltage between the two contact systems as to provide more efficient interruption of the electric current. The capacitive voltage divider also serves to grade the voltage uniformly to ground. The capacitive voltage divider drive rod is positioned along the axis of the module and is coaxial with respect to the internal insulators and all internal contact structures. Epoxy is used to fill the gap between the external contact drive rod and the inner diameter of the internal insulator for improved dielectric performance. The capacitive voltage divider drive rod is used to connect to the drive mechanism for the encapsulated vacuum module. The lower end of the capacitive voltage divider drive rod as well as the lower end cup of the vacuum module are isolated from the main current path and may be grounded, eliminating the need for the elongated cavity required in prior art encapsulations. 
     The vacuum switch or interrupter above is prepared for encapsulation by the addition of a housing over the upper portion of the vacuum module which prevents the encapsulation material from contacting the moving components of the adjuster mechanism. The housing includes a metallic cylinder with a top fabricated from an insulating material. Portions of the housing are held in place by screws that engage insulators, which are secured to studs that are brazed to the end-cup of the interrupter. A flexible lead transfers current from floating contact rod to a terminal, which extends from a top of the housing. A terminal rod extends from the stationary contact. This configuration may be encapsulated using the various techniques established in prior art. Because the lower end cup on the vacuum module and the lower portion of the capacitive voltage divider drive rod are grounded, the encapsulation may be mounted directly to a drive mechanism and housing without concern about possible dielectric failure of the internal cavity in prior art encapsulations. 
     In another embodiment of the double break vacuum switch, the space formerly occupied by the internal cavity may be utilized to install an actuator within the encapsulation. The actuator has a flange at the bottom that allows it to be mounted onto a shoulder formed in the cavity in the encapsulation described above. In this way if issues arise during manufacture or use, the actuator may be replaced or salvaged, resulting in reduced scrap costs. When the actuator mechanism is mounted in the encapsulation, an extension rod and adapter is threaded onto the capacitive voltage divider drive rod to allow tolerance accumulation to be adjusted out, so that a slot in the adapter can be made to align with a cross hole in the portion of the plunger that extends below the drive mechanism. The extension rod and adapter also serve to place the vacuum module and actuator at ground potential. A flanged cover preferably fabricated from steel is placed over the end of the plunger that contains a contact pressure spring within and engages an external opening spring with the flanged portion. The cover has a cross-hole there through; so that it may be lined up with the slot in the adapter and the cross-hole in the plunger. A pin is placed through these three components and also through a pair of external linkages. The linkages extend down from the drive mechanism and also extend down to a chamber that contains a manual operating handle, contact position indicator, counter, electronic control board for a drive mechanism and electrolytic capacitors to energize the opening and closing coils. These items are contained in a housing attached to the lower portion of the encapsulation. The configuration described above eliminates the dielectric problems with the cavity under the vacuum module in prior art encapsulations resulting in a much more compact and cost effective switchgear unit. 
     A further ramification of the invention provides for the coaxial alignment of the primary and secondary contact systems as indicated in US Patent Application No. 13012176. In this case the primary moving contact is cup shaped and the moving contact rod extends through the primary moving contact just far enough so the face of the primary and secondary moving contacts lie in the same plane. The moving contact rod for the floating contact is extended far enough so it passes through the primary stationary contact to the point that the floating contact and the primary stationary contact lie in approximately the same plane. The adjustment mechanism described above would be utilized so that the floating contact and secondary moving contacts engage approximately 1/32 of an inch before the primary contacts. As state above, this allows for any wear of the primary contacts due to interruption duty or yielding of the contact rod due to repeated impact upon closing. The contacts again may be of the butt style, transverse magnetic field or axial magnetic field designs as used in prior art. Axial magnetic field contacts employed in this invention will actually produce a coaxial magnetic field and yield a more effective interruption due to the cancellation of magnetic fields outside the contact structure. The stationary contact may also have a cup shape to stabilize the arc at the outside contact ring and eliminate the expulsion of plasma from the interruption into the contact shield. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a vacuum interrupter with a grounded lower end cup and drive rod in accordance with the present invention. 
         FIG. 1   a  is an enlarged cross-sectional view of a bellows anti-twist housing of a vacuum interrupter with a grounded lower end cup and drive rod in accordance with the present invention. 
         FIG. 2  is a front view of a capacitor-resistor voltage divider of a vacuum interrupter with a grounded lower end cup and drive rod in accordance with the present invention. 
         FIG. 3  is a cross-sectional view of a vacuum interrupter with a grounded lower end cup and drive rod prepared for encapsulation in accordance with the present invention. 
         FIG. 4  is a cross sectional view of a two terminal encapsulated vacuum interrupter with a grounded lower end cup and drive rod in accordance with the present invention. 
         FIG. 5  is a cross-sectional view of a two terminal encapsulated vacuum interrupter with a grounded lower end cup and drive rod mounted on top of a housing containing an actuating mechanism in accordance with the present invention. 
         FIG. 6  is a cross-sectional view of a second embodiment of a two terminal encapsulated vacuum interrupter with grounded lower end cup and drive rod mounted to an actuator in accordance with the present invention. 
         FIG. 7  is a cross-sectional view of an actuator to be utilized with an encapsulated vacuum interrupter with a grounded lower end cup and drive rod in accordance with the present invention. 
         FIG. 8  is a cross-sectional view of a vacuum interrupter with a grounded lower end cup and drive rod modified to have a double break vacuum switch in accordance with the present invention. 
         FIG. 9  is a cross-sectional view of a vacuum interrupter with a grounded lower end cup and drive rod having a second modification of a contact structure in accordance with the present invention. 
         FIG. 10  is a cross-sectional view of a vacuum interrupter with a grounded lower end cup and drive rod having a third modification of a contact structure in accordance with the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The encapsulated vacuum interrupter with grounded lower end cup and drive rod utilizes a double break vacuum switch  1  shown in  FIG. 1 , which comprises a vacuum envelope  2 . The vacuum envelope  2  includes a pair of insulating cylinders  4 A and  4 B preferably made of alumina ceramic joined end-to-end by way of two triple point shields  6 A and  6 B preferably fabricated from stainless steel or monel and a stationary contact support ring  8  preferably fabricated from copper. A threaded hole in the stationary contact support ring  8  allows the attachment of a terminal rod  10  preferably fabricated from copper to facilitate electrical connection to the source line. The opposite ends of the ceramic cylinders are enclosed by two end cups  12 A and  12 B preferably fabricated from stainless steel or monel. A second set of triple point shields  14 A and  14 B are attached to the two end cups  12 A and  12 B. A generally tubular internal shield  16 A and  16 B preferably fabricated of stainless steel is provided within each insulating cylinder  4 A and  4 B, spaced from the interior wall and overlapping the triple point shields  6 A and  6 B to prevent any vaporized material from contacting the interior wall. 
     A primary contact system  11  includes an annular stationary contact support  18  preferably made of copper and attached to the stationary contact support ring  8 . An annular stationary contact  20  preferably made of copper tungsten is attached to the lower end of the stationary contact support  18 . The stationary contact support  18  is engaged by an annular moving contact  22  also preferably made of copper tungsten. The moving contact  22  is attached to a disc shaped moving contact support  24  preferably made from copper, reinforced by a moving contact reinforcement cone  26  preferably made from stainless steel with both being attached to a moving contact rod  28  preferably made from copper. The moving contact rod  28  is reinforced by a reinforcing rod  30  preferably fabricated of stainless steel and the end of the reinforcing rod  30  is threaded and extends beyond the lower end of the moving contact rod  28 . An end cup  32  preferably made from stainless steel or monel and a tubular shield  34  preferably fabricated of stainless steel is attached to the end of the contact rod  28  and centered over the protruding reinforcing rod  30 . A tubular moving internal insulator  36  preferably made from alumina ceramic is attached to the end cup  32 . The opposite end of the moving insulator is attached to a bellows  38  preferably made from stainless steel, which is sealingly attached to the inside diameter of the end cup  12 A. A second tubular shield  40  preferably made from stainless steel is also attached to the inside of end cup  12 A. The shields  34  and  40  protect the outside diameter of the moving internal insulator  36  from deposition of conductive metallic vapors that would reduce its insulating properties and protects the bellows  38  from damage. In order to drive the contact rod  28 , a capacitive voltage divider contact rod  202 , described in detail below, is attached to the reinforcing rod  30 . The end of the capacitive voltage divider contact rod  202  connected to a stud is equipped with a threaded adapter  210  preferably made from steel to allow attachment to the stud. With reference  FIGS. 5-6 , the opposite end of the capacitive voltage divider contact rod  202  is equipped with a threaded adapter  224  to allow attachment to an actuator mechanism  402  or  500  described below. Once the capacitive voltage divider contact rod  202  is tightened onto reinforcing rod  30 , the space between the capacitive voltage divider contact rod  202  and the inner diameter of the moving internal insulator  36  is filled with epoxy  42  for improved dielectric performance. It is critical that the filling operation for epoxy  42  is controlled so that no epoxy  42  is deposited on the bellows  38 . A bellows anti-twist housing  43  preferably fabricated from stainless steel is attached to the opposite side of end cup  12 A and is centered by the circular depression formed in the end cup  12 A. The bellows anti-twist housing  43  is indexed to the moving contact rod  202  by a pin  45  preferably made from nickel plated hardened steel, which passes through a cross-hole  226  in the capacitive voltage divider contact rod  202  and slides in a slot  49  in the bellows anti-twist housing  43 . Two threaded holes  47  are formed into the bellows anti-twist housing  43  to facilitate the attachment of a housing  126  described below. 
     The double break vacuum switch requires a capacitor-resistor voltage divider  207  to distribute the voltage equally between the two contact gaps during interruption and to grade the high voltage to zero in the region of the lower end-cup  12 A so that the end-cup  12 A and a connected actuator mechanism  402  or  500  may be grounded; as shown in  FIG. 2 , which is provided by an capacitive voltage divider contact rod  202 . Capacitive voltage divider contact rod  202  preferably includes a filament wound epoxy glass insulating tube  204  of sufficient diameter to allow the insertion of a 500 pf 30 kV disc capacitor  206  connected in parallel with a 20 Meg-ohm 2 watt carbon resistor  208 . A sufficient number of these capacitor-resistor units are connected in series on the inside of the insulating tube  204  to withstand the impulse voltage requirements of the voltage rating that the vacuum switchgear is designed for. The capacitor-resistor units are connected to a top of the insulating tube  204  with an adapter  210  preferably made from steel, which is pinned to the insulating tube  204  with roll pins or groove pins  214 A and  214 B preferably made from steel and preferably has a tin plated brass terminal  216 A attached with a tin plated steel screw  218 A to allow connection of one end of a capacitor-resistor network  207 . The lengths of the insulating cylinder  4 A and the internal insulator  36  are designed so that the lower portion of the capacitor-resistor network  207  rests in the area of the bellows  38  and the end-cup  12 A. In this way the voltage stress will be graded to near zero in the area of the end-cup  12 A as the lower portion of the capacitor resistor network  207  is grounded via its connection to the actuating mechanism  402  or  500 . The insulating tube  204  is filled with an epoxy  220  to improve dielectric characteristics. A preferable steel adapter  224  is pinned to the other end of the insulating tube  204  with roll pins or groove pins  222 A and  222 B preferably made from steel and has a preferably tin plated brass terminal  216 B attached with a tin plated steel screw  218 B to allow connection of the lower portion of the capacitor-resistor network  207 . The adapter  224  includes a cross-hole  226  to allow insertion of a pin  45  to index with the slot  49  in the bellows anti-twist housing  43 , described previously. However, the capacitor-resistor voltage divider  207  would not be necessary when used with voltages lower than about 17 KV. A space in the insulating tube  204  created by the removal of the capacitor-resistor network  207  would be filled with the epoxy  220  to prevent arcing therein. 
     Referring back to  FIG. 1  the second contact system  13  includes an extension of moving contact rod  28 , which passes through the moving contact support  18 . The aforementioned extension is attached to a preferable disc-shaped copper moving contact support  44  and a moving contact disc  46  preferably made from copper tungsten, which together form a second moving contact  39 . The second moving contact  39  engages a floating contact  41 , which includes a floating contact disc  48  preferably made from copper-tungsten and a preferable disc-shaped copper floating contact support  50 . The floating contact support  50  is attached to a floating contact rod  52  preferably made from copper, which is reinforced by a reinforcing rod  54  preferably made from stainless steel and sealingly passed through end cup  12 B and triple point shield  14 B by a preferable stainless steel bellows  56 . The bellows  56  is protected from damage by vaporized material by a preferable stainless steel bellows shield  58 . A mechanism housing  60  preferably made from stainless steel is attached to the opposite side of end cup  12 B and is centered by a circular depression formed in the end cup  12 B. The mechanism housing  60  is indexed to the floating contact rod  52  by a preferable nickel plated hardened steel pin  62 , which passes through a cross-hole  64  in the floating contact rod  52  and slides in a slot  66  in the bellows mechanism housing  60 . During the brazing cycle for the vacuum switch, pin  62  is replaced by a preferable stainless steel fixture pin to assure the alignment of the parts. 
     An operating mechanism for floating contacts  15  includes the mechanism housing  60  into which is threaded a preferable brass adjuster  68 . The mechanism housing  60  has two slots  66  located at opposite sides around its circumference. The adjuster  68  has six holes  70  equally spaced around its perimeter, so that the pin  62  can be inserted into any opposite facing pair of holes  70  during an adjustment process. When threading the adjuster  68  into the mechanism housing  60 , the pin  62  is withdrawn from the mechanism housing  60 . The adjuster  68  is positioned, so that the center of one pair of holes  70  line-up with the center of the cross-hole  64  in the floating contact rod  52  and the top of the pair of holes  70  are preferably 0.031 inch above cross-hole  64 . During the adjustment, both the first and second set of contacts must be closed. The pin  62  is then inserted back through the mechanism housing  60 , the adjuster  68  and the floating contact rod  52 . The pin  62  is held in place by a preferable pair of steel retaining rings  61 A and  61 B and a pair of steel washers  63 A and  63 B. A compression spring  72  preferably made of music wire is inserted into a counter-bore in the adjuster  68  and a preferable threaded nickel plated steel spring retainer  74  is tightened. This forces the pin  64  to the bottom of the pair of holes  70 . The diameter of the pair of holes  70  in the adjuster is preferably 0.062 larger than the diameter of the cross hole in floating contact rod  52  to provide for an allowance for contact wear. The slots  66  in the mechanism housing  60  have a minimum length equal to the tolerance build-up between the location of the cross-hole  64  in floating contact rod  52  and the end of the moving contact disc  46  plus the diameter of the holes  70  in the adjuster  68 . This allows the adjuster  68  to be able to be adjusted through the full range of possible locations of cross-hole  64 . 
     In order to facilitate encapsulation, a module  100  is created by placing a protective enclosure  101  over the mechanism  15  at the top end of the vacuum envelope  2  as shown in  FIG. 3 . The mechanism includes a preferable aluminum external mechanism housing  102  and a cover  104  which may be made of an insulating material such as GP01 or GP03 fiberglass or G10 epoxy glass. A preferable pair of stainless steel studs  106 A and  106 B is attached to the outside surface of end cup  12 B. An insulating stringer  108 A and  108 B preferably made of filament wound epoxy glass is threaded onto each stud  106 A and  106 B and a preferable stainless steel screw  110 A and  110 B is threaded into the opposite end of each stringer  108 A and  108 B to retain the cover  104  and the external housing  102 . A split-clamp connector  112  preferably made of copper is tightened onto the end of floating contact rod  52  using a bolt  114  and nut  116 . Preferably, a pair of highly flexible multi-stranded copper conductors  118 A and  118 B are crimped to a preferable copper split clamp connector  112  and to a terminal connector  120 . The terminal connector  120  is threaded onto the lower portion of a source terminal  122  and secured with a jam nut  124 , creating a current exchange between the floating contact rod  52  and the source terminal  122 . The opposite end of the vacuum envelope  2  is prepared for encapsulation by the installation of a housing  126  preferably fabricated from a thermoset plastic over the bellows anti-twist housing  43  and securing with a pair of stainless steel bolts  128 A and  128 B. 
     There are several examples of prior art, which show the encapsulation of vacuum modules.  FIG. 4  indicates one possible way of encapsulating the aforementioned vacuum module as demonstrated by U.S. Pat. No. 5,917,167. In this case, the module  100  is encased in a preferable silicone rubber tube  302  and cast in an epoxy encapsulation  304 . The result is a two terminal encapsulation  300  with a source terminal  306  and a load terminal  308 . The encapsulation  300  is then mounted on top of a housing  400  preferably made of steel, which contains the actuating mechanism  402  as shown in  FIG. 5 . 
     In operation, the encapsulated vacuum interrupter  300  would be coupled via capacitive voltage divider contact rod  202  to an actuating mechanism  402 . The closing stroke of the mechanism  402  and capacitive voltage divider contact rod  202  would drive the moving contact rod  28  upward. Because the moving internal insulator  36  is coupled to the moving contact rod  28  by the end cup  32 , the moving internal insulator  36  moves in unison with the moving contact rod  28 . In this way, the capacitive voltage divider contact rod  202  directly drives the moving contact rod  28  which eliminates the application of excessive impact forces to the moving internal ceramic insulator  36  to protect it from breakage when the contacts close. Because of the aforementioned adjustment of the mechanism adjuster  68 , when the spring  72  is installed, the pin  62  is forced to the bottom of the pair of holes  70  which causes the floating contact rod  52  to be pushed forward 0.031 inch. This causes the second set of contacts  46  and  48  to engage slightly in advance of the first set of contacts  20  and  22 . As the moving contact rod  28  continues its closing stroke, the floating contact rod  52  is driven upward resulting in the pin  62  moving upward in hole  70  and compressing spring  72 . The closing stroke is completed when moving contact rod  28  is driven to the point that the first set of contacts  20  and  22  mate, which results in the pin  62  being centered in the hole  70 . At this point, the electric current flows from the source terminal  306  through the first set and second of contacts and directly out the load terminal  308 . 
     Upon initiation of the opening stroke, the moving contact rod  28  moves downward causing the first set of contacts  20  and  22  to immediately part and initiate an arc. Because the moving internal insulator  36  is coupled to the moving contact rod  28  by the end cup  32 , the moving internal insulator  36  again moves in unison with the moving contact rod  28 . In this way, the capacitive voltage divider contact rod  202  directly drives the moving contact rod  28 , which eliminates the application of excessive tensile weld breaking forces to the moving internal ceramic insulator  36  to protect it from breakage when the contacts open. The energy stored in the spring  72  forces the floating contact rod  52  downward maintaining contact through the second set of contacts  46  and  48  for the first 0.031 inch of contact travel until the pin  62  is driven to the bottom of pair of holes  70 . At this point, floating contact rod  52  is no longer able to follow the moving contact rod  28  downward and the second set of contacts  46  and  48  begin to part initiating a second arc. The capacitor-resistor network  207  contained in capacitive voltage divider contact rod  202  acts to distribute the voltage evenly across the two contact gaps resulting in an efficient interruption of the arc as the moving contact rod  28  completes its opening stroke and provides the full open gap for the first and second sets of contacts. Because the first and second sets of contacts are electrically connected in series, this results in a double break of the arc when the contacts open allowing the vacuum interrupter to be utilized at elevated voltages. The fact that pair of holes  70  are 0.062 larger than the pin allows +/−0.031 for wear of the contacts which may be unequally distributed between the first and second set of contacts. 
     With reference to  FIG. 6 , another embodiment of the encapsulated vacuum interrupter with grounded lower end cup and drive rod, an actuator  500  may be mounted in a space formerly occupied by an internal cavity to provide compact switchgear with the vacuum module and actuator within the same encapsulation. Because a lower end of the vacuum switch module  100  as well as the actuator  500  are at ground potential, the cavity formerly used to provide dielectric clearance can now be used to house actuator  500  as well as the other components necessary for the operation of the complete switchgear unit. To accomplish this, an enlarged chamber  502  is formed below the encapsulated vacuum module to allow for installation of the actuator  500 . U.S. Pat. No. 6,009,615 provides an example of a bi-stable magnetic actuator, which would be preferred to be applied as the actuator  500 . The actuator  500  would be provided with a plurality of mounting feet  504  at the lower end. This allows the mounting feet  504  to be attached to a shoulder  506  cast into the internal cavity of an encapsulation  503  utilizing a preferable plurality of steel bolts  508  threaded into a plurality of cast in threaded inserts  510 . 
     With reference to  FIG. 7 , the actuator  500  contains a preferable laminated steel frame  512  divided into two sections  514  and  516 , which serve as the magnetic circuit. A pair of permanent magnets  518 A and  518 B is attached to the portion of the magnetic circuit that separates the two sections  514  and  516 . The permanent magnets  518 A and  518 B are preferably attached to the frame  512  with industrial adhesive in a way that the south pole for both magnets is oriented toward a center of the frame  512  and the north pole of both magnets is oriented toward an outside of the frame  512 . A closing coil  520  is placed in chamber  516  and an opening coil  522  is placed in chamber  514  of the frame  512 . Preferably, a “400 series” stainless steel plunger  524  is disposed within the open space of frame  512  and permanent magnets  518 A and  518 B in such a way that it can move from end to end within frame  512 . The plunger  524  has a bore through its full length to allow for insertion of a preferable stainless steel extension drive rod  526  for connection to the capacitive voltage divider contact rod  202 . The plunger  524  also has a necked portion  527  that extends through the lower end of frame  512  and contains a cross hole  528  to provide an attachment means to a preferable nickel plated steel threaded adjuster  530  attached to the extension drive rod  526 . The adjuster  530  contains a slot  534  with a length designed to provide the desired contact pressure plus over travel distance. The threaded adjuster  530  is adjusted so that an upper edge of the slot  534  in the threaded adjuster  530  is preferably 1/32 inch above the top of the cross hole  528  in the neck  527  of plunger  524  when the primary contacts of the vacuum module  100  and the plunger  524  are in the closed position. An opening spring  536  is slid over the neck  527  of plunger  524  and a contact pressure spring  538  is placed into the bore of plunger  524 . A preferable steel retaining cap  540  is pushed onto the neck  527  of the plunger  524  to the point that a cross-hole  542  in the retaining cap  540  lines up with the cross hole  528  in the neck  527  of plunger  524  and the slot  534  in threaded adjuster  530 . A preferable nickel plated hardened steel pin  544  is inserted through cross-holes  542  and  528  and the slot  534  to secure these parts. When actuator  500  moves to the closed position, the movement of pin  544  in the slot  534  allows the retaining cap  540  to compress the contact pressure spring  538 , providing contact pressure through adjuster  530  and extension drive rod  526  to the closed first and second contacts of vacuum module  100 . An optional pair of linkages  546 A and  546 B may also be added to each side of the pin  544 , which is retained by washers  548 A and  548 B and retaining rings  550 A and  550 B. The use of the optional linkages  546 A and  546 B is dependent on the final design of the switchgear unit as described below. 
     Referring back to  FIG. 6 , an aluminum or stainless steel enclosure  600  is mounted to the lower end of the encapsulation  503  to contain the remaining components required to complete the switchgear assembly. In this case, a pair of capacitors  610 A and  610 B and an actuator circuit board assembly  612  may be mounted on a top surface of a preferable aluminum enclosure  600 , so that they fit in the cavity below the actuator  500 . The enclosure  600  is attached to a lower end of the encapsulation  503  using a plurality of preferable stainless steel bolts  614  threaded into a plurality of cast in threaded inserts  616 . An elastomer “o” ring seal  618  is provided to prevent moisture ingress at this point. The linkages  540 A and  540 B extend from the actuator into the enclosure  600  so that a manual operating means (not shown) as know in prior art may be provided for the completed switchgear unit. A space  619  is also provided in the enclosure for an operations counter, contact position indicator and a receptacle to allow connection of an external control. These items are well known in prior art and need not be shown. The lower portion of the enclosure  600  is closed off by an aluminum cover plate  620 , which is held in place by a plurality of preferable stainless steel bolts  622 . An elastomer “o” ring seal  624  is provided at this point to prevent the ingress of moisture. A mounting bracket  626  preferably made of galvanized steel is provided for the completed switchgear unit and is held in place by a pair of preferable stainless steel bolts  628 A and  628 B. 
     In still another embodiment of the encapsulated vacuum interrupter with grounded end cup and drive rod  1 ′, the contact structures may be modified as shown in U.S. patent application Ser. No. 13/012,176. A first modification of the double break vacuum switch with grounded end cup and contact rod  1 ′ is shown in  FIG. 8 . In this case, the length of the moving contact rod  28 ′ is reduced and the length of floating contact rod  52 ′ is increased so both the first and second sets of contacts part in the same plane. This embodiment eliminates the passage of the moving contact rod  28 ′ through the arc zone of the first set of contacts. 
       FIG. 9  shows a second modification of the contact structure of the encapsulated vacuum interrupter with grounded end cup and drive rod  1 ″. The annular stationary contact  20 ″, the annular moving contact  22 ″, the moving contact disc  46 ″ and the floating contact  48 ″ are preferably fabricated from copper chromium instead of copper tungsten utilizing any of the transverse or axial magnetic field contact structures shown in prior art.  FIG. 9  shows one possible axial magnetic field contact structure as demonstrated by U.S. Pat. Nos. 4,871,888 and 6,867,385, and US Pat App No. 2006/0016787, which are hereby incorporated into this application by reference in their entirety. The double break vacuum switch  1 ″ includes contact rods  28 ″,  52 ″. The revised contact structures convert the contacts  20 ″,  22 ″,  46 ″ and  48 ″ from switching duty to fault interrupting duty and results in a double break vacuum interrupter. Preferably, stainless steel reinforcing tubes  702 ″ and  704 ″ are provided to support the inside diameter of contacts  20 ″ and  22 ″. 
       FIG. 10  illustrates a third modification of the contact structure of the encapsulated vacuum interrupter with grounded end cup and drive rod  1 ′ utilizing coplanar axial magnetic field contacts. In this case, the length of the moving contact rod  28 ″′ is reduced and the length of the floating contact rod  52 ″′ is increased, so both sets of axial magnetic field contacts  20 ″′,  22 ″′,  46 ″′ and  48 ″′ are in the same plane. In this embodiment the fields are coaxial and the interruption would benefit from the fact that in a coaxial electrical system, the fields of the two conductors cancel outside the enclosing conductor so that the effect outside magnetic fields is shielded from the central conductor. Stainless steel reinforcing tubes  702 ″′ and  704 ″′ are provided to support the inside diameter of contacts  20 ″′ and  22 ″′. 
     While particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the true spirit and scope of the invention.