Abstract:
Methods for making and using vacuum switching devices are disclosed. A vacuum switching device has an operating rod for actuating a movable electrical contact within the device. The operating rod may be a hollow epoxy glass tube with an electrical sensor disposed within it, and there may be an elastomeric polymer filling compound disposed within the tube and encasing the sensor. The operating rod may be attached to the movable electrical contact on one end by a steel end-fitting that has been press-fit into the tube and secured with at least one cross pin. In this way, a very secure electromechanical connection may be made between the operating rod and the rest of the vacuum switching device, and the sensor is protected from shock associated with the operation of the device. Moreover, the vacuum switching device is compact and easy to construct.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 10/359,275, filed Feb. 6, 2003, which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This description relates to high voltage switchgear. 
     BACKGROUND 
     Conventional vacuum fault interrupters provide high voltage fault interruption. Such a vacuum fault interrupter, which also may be referred to as a vacuum interrupter, generally includes a stationary electrode assembly having an electrical contact, and a movable electrode assembly having its own electrical contact and arranged on a common longitudinal axis with respect to the stationary electrode assembly. The movable electrode assembly generally moves along the common longitudinal axis such that the electrical contacts come into and out of contact with one another. In this way, a vacuum interrupter placed in a current path can be used to interrupt excessively high current and thereby prevent damage to an external circuit. 
     To determine when to move the electrical contacts out of contact with one another, conventional vacuum interrupters often use some type of current and/or voltage-sensing device. 
     SUMMARY 
     In one general aspect, a vacuum switching device includes a vacuum assembly. Switching contacts are disposed within the vacuum assembly, and one of the switching contacts is a switching contact that is movable along an axis. The vacuum switching device also includes a rod disposed along the axis and operable to actuate movement of the movable switching contact along the axis, and a sensor disposed within the rod and encapsulated by a filling compound. 
     Implementations may include one or more of the following features. For example, the filling compound may be made of an elastomeric polymer compound. The sensor may include a resistive element, and the rod may include a radially-wound epoxy glass tube. 
     A metallic fitting may be press-fit into an end of the rod and connected to the sensor, and a cross pin may be inserted through the rod and the metallic fitting to hold the metallic fitting in place. In this implementation, a conductive guard sleeve may be electrically connected to the metallic fitting by the cross pin. Further, the metallic fitting may be grounded, so that the conductive guard sleeve is also grounded. Also, a voltage-sensing resistor may be electrically connected to the metallic end fitting via a pin socket assembly. 
     The rod may be encased in a ribbed silicone sleeve, and the device may include a vacuum fault interrupter. 
     In another general aspect, an operating rod for a vacuum switching device may be made by inserting a sensor into a hollow tube, connecting a first portion of the sensor to a first end fitting attached to a first end of the tube, connecting a second portion of the sensor to an electrical connection extending outside of the tube, and filling the tube with a filling compound. 
     Implementations may include one or more of the following features. For example, the filling compound may be an elastomeric polymer compound. 
     In inserting a sensor, a resistive element may be threaded through a length of the hollow tube. One end of the resistive element may be attached to a pin socket assembly attached to the first end fitting. 
     Also in inserting a sensor, at least one hole may be drilled through a portion of the tube near the first end of the tube, the first end fitting may be press-fit into the first end of the tube, and a pin may be inserted through the hole and into the first end fitting. 
     A ribbed rubber skirt may be pulled over the operating rod. The tube may be a radially-wound epoxy glass tube. 
     In filling the tube with the filling compound, the filling compound may be injected through the silicone rubber skirt and into the tube. Further, filling the tube with the filling compound may also include drilling a hole in the tube near the second end of the tube, standing the tube with the first end facing in a downward direction, and injecting the filling compound at a point near the first end, such that air displaced by the filling compound is removed from the tube through the hole. In this implementation, the hole may be used to facilitate formation of the electrical connection to the second portion of the sensor. 
     According to another general aspect, an operating rod for use in a vacuum switching device includes a radially-wound, epoxy glass tube, a sensor extending through a length of the tube, and a filling compound within the tube and encasing the sensor. 
     Implementations may include one or more of the following features. For example, a silicone sleeve may encase a first portion of the operating rod, and a grounded guard sleeve may be around a second portion of the operating rod. 
     The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is an illustration of a vacuum switching device. 
         FIG. 2  is an illustration of an operating rod for use with the vacuum switching device of  FIG. 1 . 
         FIG. 3  is a more detailed illustration of a portion of the operating rod of  FIG. 2 . 
         FIG. 4  is an illustration of a body of the operating rod of  FIG. 2 . 
         FIG. 5  is an illustration of the operating rod of  FIG. 2  including an exterior rubber skirt. 
         FIG. 6  is a flow chart illustrating methods for making the operating rod of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a vacuum switching device including a vacuum interrupter  105  that may be used to protect an external circuit (not shown) from excessively high current is illustrated. The vacuum interrupter  105  includes a stationary terminal rod  110  that is connected to an upper contact terminal  115 . The upper contact terminal  115  allows a connection of the vacuum interrupter  105  to the external circuit. 
     The vacuum fault interrupter  105  is affixed to an operating rod  120  that is contained within a dielectric-filled cavity  125  (dielectric, not shown, may be gaseous or liquid) and extends through an opening  130 . The operating rod  120  is connected to an external device (not shown) operable to cause axial movement thereof and to a movable electrical contact assembly  135  so as to move a movable electrical contact of the assembly  135  into or out of contact with a stationary electrical contact within the vacuum interrupter  105  (interior of vacuum interrupter not shown). 
     The movable electrical contact assembly  135  is instrumental in actuating a movement of an electrical contact within vacuum interrupter  105  to thereby interrupt a flow of current within vacuum interrupter  105 . 
     A current interchange assembly  140  permits current flow between the moving electrical contact assembly  135  and a stationary conductor  145 . In general, the assembly facilitates current flow between two points and may include, for example, a roller contact, a sliding contact, or a flexible connector. 
     A compliant material  150 , which may be, for example, a silicone sleeve, encases the vacuum interrupter  105 . In one implementation, the compliant material  150  is adhered to the vacuum interrupter  105  by, for example, a silane-based adhesive such as SILQUEST A-1100 silane (that is, gamma-aminopropyl triethoxysilane). A rigid encapsulation material  155 , which may be, for example, an epoxy encapsulation material, is used to enclose the whole of the vacuum switching device of  FIG. 1 . 
     In one implementation, operating rod  120  is manufactured from a tube made from a high-rigidity, insulating, polymeric material. The polymeric-material tube may be a filament-wound, epoxy glass reinforced tube (i.e., a fiberglass tube), having an internal cavity. Space within this internal cavity may be used to hold one or more resistors, which may then be used as a resistive, high-voltage sensor. Around such resistors, a low viscosity, liquid polymer compound may be injected, and subsequently cured to assume a stable polymer state. In this implementation, one end of one of the resistors may be connected to the moving contact assembly  135 . An end of another one of the resistors (or the same resistor) may be connected to a highly flexible wire  160 , and through this wire to a parallel connection of an overvoltage protection device  165  and a low-arm resistor  170 . Thus, in this implementation, the sensor output voltage Vout measured across the low-arm resistor  170  is equal to: 
     
       
         
           
             
               
                 
                   
                     V 
                     out 
                   
                   = 
                   
                     
                       
                         V 
                         
                           i 
                           ⁢ 
                           
                               
                           
                           ⁢ 
                           n 
                         
                       
                       × 
                       
                         R 
                         
                           low 
                           - 
                           arm 
                         
                       
                     
                     
                       
                         R 
                         
                           low 
                           - 
                           arm 
                         
                       
                       + 
                       
                         R 
                         
                           operating 
                           - 
                           rod 
                         
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     In this way, a reliable, low-cost, easily-manufactured voltage sensor may be incorporated into the operating rod  120 . Moreover, the elastic nature of the polymer compound greatly reduces an effect of mechanical impacts on the voltage sensors that result from motion and impacts associated with operation of operating rod  120 . Details of the structure, operation, and assembly of the operating rod  120  are discussed below. 
       FIG. 2  is an illustration of one implementation of operating rod  120 . In  FIG. 2 , a epoxy glass tube  205  is shown to house a first resistor  210  and a second resistor  215 , the two resistors being connected by connector  220 . Connector  220  may be, for example, a conventional wire connection, a pin socket assembly (discussed in more detail with respect to  FIG. 3 ), or any other type of suitable connector. 
     A first fitting  225  and a second fitting  230  are metal pieces pre-fabricated to securely cap tube  205  while helping to provide an electrical contact to interior components of tube  205  and provide electrical connection to an outer conductive sleeve  245  (discussed below) through cross pins  235 . Fittings  225  and  230  may be composed of, for example, steel. In one implementation, steel fittings  225  and  230  are knurled and press-fitted into the epoxy glass tube  205 . The steel fittings  225  and  230  are further affixed to the tube  205  by inserting cross pins  235  through corresponding holes drilled in the tube  205  and fittings  225  and  230 , as shown. 
     Such a process of press-fitting the steel fittings  225  and  230  into the inner diameter of the epoxy glass tube  205 , and subsequent addition of cross pins  235  through the epoxy glass tube and end fittings, provides a high degree of mechanical strength at the connection of the steel fittings  225  and  230  to the epoxy glass tube  205 . Such a strong and reliable mechanical joint is capable of transferring high impact forces from the steel fittings  225  and  230  to the epoxy glass tube  205 , where such forces are expected due to the operation of the vacuum interrupter  105 , as outlined above. 
     Moreover, the steel fittings  225  and  230  may be machined and pre-threaded for easy and reliable assembly to, respectively, the moving electrical contact assembly  135  (see  FIG. 1 ) at the end of steel fitting  225  and the vacuum interrupter operating mechanism on the end of steel fitting  230 . Thus, by directly connecting one end of resistor  210  to steel fitting  225  using, for example, a pin socket assembly  240 , a direct connection between resistor  210  and stationary conductor  145  (see  FIG. 1 ) is obtained simply by threading steel fitting  225  into a corresponding portion of the moving electrical contact assembly  135 . In this way, an electrical contact is established which brings a high-voltage potential present on the stationary conductor  145  through the steel fitting  225  to the high-voltage resistor  210 . 
     At the other end of epoxy glass tube  205 , an electrical connection is made between a resistor lead  250  and a high elasticity wire  255 . This connection may be made prior to inserting the resistor assembly into the epoxy glass tube  205 , by means of, for example, a solder connection or a crimped splice connector. The highly elastic wire  255  is used to bring the voltage signal out of the epoxy glass tube through a slot (not shown) machined in the inner diameter of conductive sleeve  245 . Fitting  230  is typically mechanically and electrically connected to a grounded mechanism linkage. Since sleeve  245  is electrically connected to fitting  230  through pins  235 , sleeve  245  is thus electrically grounded as well. Alternatively, a separate ground lead (high elasticity wire) may be used to provide this ground connection. 
     Free space remaining within a cavity of epoxy glass tube  205  (that is, between the epoxy glass tube  205  and the resistors  210  and  215 ) is filled with an elastomeric compound  260 . Compound  260  remains elastic over a relatively wide temperature range (for example, −50 to +100° C.), possesses high dielectric properties (for example, &gt;400 volts/mil), and is cured to a high degree so as to have few, if any, voids. Compound  260  provides damping for mechanical/shock energy transferred through operating rod  120 , and provides excellent bonding to all encapsulated parts, in particular, the epoxy glass tube  205  and the high-voltage resistors  210  and  215 . 
       FIG. 3  is a more detailed illustration of steel fitting  225 , including an illustration of pin socket assembly  240 . Specifically, pin socket assembly  240  is pressure-fitted to form an integral part of the steel fitting  225 . As discussed in more detail below, pin socket  240  is used to establish good electrical contact between the steel fitting  225  and the high-voltage resistor  210 . Moreover, use of pin socket assembly  240  simplifies assembly procedures, and provides sufficient elasticity (that is, in particular, freedom of movement for resistor  210 ) during a high mechanical impact operation of operating rod  120 . 
       FIG. 4  is an illustration of epoxy glass tube  205 . As shown in  FIG. 4 , a hole  405  is drilled through one side of epoxy glass tube  205  to permit insertion of compound  260 . Similarly, a hole  410  is drilled through the opposite end of epoxy glass tube  205  for venting of air during filling of compound  260 , and to permit high elasticity wire  255  to exit an inner diameter of the epoxy glass tube  205 . 
       FIG. 5  is an illustration of epoxy glass tube  205  covered by a silicone rubber skirt  505 . As shown, circumferential ribs are included along the length of silicone rubber skirt  505  in order to increase the “creep distance” (length of insulating surface), and to thereby help prevent debilitating short circuits and generally improve dielectric properties of the tube  205  and associated elements. As shown in  FIG. 5 , the silicone rubber skirt  505  is affixed to the tube  205  using a room temperature vulcanizing (“RTV”) silicone rubber-based adhesive. 
     The grounded sleeve  245  provides a function of “guarding” or “shielding” of any leakage current which may flow over the surface of the silicone skirt  505 . This provides and maintains an accurate output of the voltage sensor, regardless of varying leakage current which may occur over surface of silicone skirt  505  (such as that expected during high humidity conditions or other deterioration of dielectric properties of silicone skirt  505  or its interface with the epoxy glass tube  205 ). The length of the sleeve  245  may be such that it covers the exit of elastic lead  255  and is able to conduct any leakage currents to ground. 
       FIG. 6  is a flow chart illustrating a procedure  600  for assembling operating rod  120 . First, epoxy glass tube  205  is cut and drilled in the manner illustrated in  FIG. 4  to form holes  405  and  410  ( 605 ). Subsequently, resistors  210  and  215  are assembled together with an elastic lead  255  and joined with steel fitting  225  and pin socket assembly  240  to form a sub-assembly ( 610 ). 
     The subassembly is inserted through a first end of the epoxy glass tube  205  and pushed through the length of the epoxy glass tube  205 , such that an end of elastic wire  255  is pulled through hole  410  at the other end of the epoxy glass tube  205 , and the steel fitting  225  is properly positioned at the first end ( 615 ). 
     Subsequently, the second steel fitting  230  is placed into the remaining end of the epoxy glass tube  205  ( 620 ). Next, the prefabricated steel fittings  225  and  230  are pressed into their respective ends of epoxy glass tube  205  ( 625 ). 
     The elastomeric compound  260  then is injected into the cavity of the epoxy glass tube  205  ( 630 ). In one technique, epoxy glass tube  205  is placed on its end, with steel fitting  225  on the bottom. By steadily injecting the polymer compound  260  into the lower end of epoxy glass tube  205  through hole  405 , air within the cavity of epoxy glass tube  205  is pushed in an upward direction by the rising polymer compound  260 . In this way, the cavity within epoxy glass tube  205  is completely filled. It should be understood that in this implementation, air being displaced by the rising polymer compound  260  is released through hole  410  in epoxy glass tube  205 . 
     Thereafter, the polymer compound  260  is allowed to cure ( 635 ). If the technique for inserting the polymer compound  260  just described is followed, epoxy glass tube  205  may be left in the described upright position for the curing process to occur. Epoxy glass tube  205  having end fittings  225  and  230  already press-fitted into its respective ends then has sleeve  245  assembled, and both ends of tube  205  are drilled as necessary to include pins  235  ( 640 ). Finally, the silicone rubber skirt  505  is pulled over the entire assembly associated with the epoxy glass tube  205  ( 645 ). 
     In the above-described technique, the elastomeric compound  260  may be, for example, PolyButadiene (synthetic rubber), such as DolPhon CB1120 manufactured by the John C. Dolph Company of Monmouth Junction, N.J. Other materials may be used as elastomeric compound  260 , such as silicone rubber, polyurethane, or silicone gel. 
     Implementations described above have various features. For example, the fact that the sensor is implemented within the operating rod  120 , as opposed to outside of the operating rod (perhaps contained within an encapsulation material) allows for overall reduced dimension and ease of assembly of the assembly shown in  FIG. 1 , relative to conventional vacuum interrupter assemblies. 
     As another example, the implementations are relatively low in cost. In particular, epoxy glass tube  205  is easy to manufacture and very inexpensive. When radially-wound, such a epoxy glass tube is nonetheless very strong and reliable during operations, and is also very light in weight (which may allow for faster operation). Moreover, the epoxy glass material of epoxy glass tube  205  is resistant to the types of mechanical and thermal shock typically encountered during operation of vacuum interrupter  105 . 
     Further resistance to mechanical shock during operation is provided by the elastomeric compound  260 . Such a compound also offers a very low coefficient of thermal expansion over a wide range of operating temperatures. With the impact strength and low weight just described, implementations enable high speed interrupter operation with reduced contact bounce, and therefore increase interrupter lifetime and reliability. Moreover, implementations described have a straight forward and easily-implemented manufacturing process, and a relatively small part count. Also, the elastomeric compound that carries the mechanical forces around the centrally positioned resistors  210  and  215  has a high degree of thermal matching with respect to the resistors. 
     Finally, it should be understood that, although the above description has largely been provided in terms of vacuum interrupters, the features described above may be equally applicable in any high-powered, vacuum-based switching device, and in various other settings, such as use of this type of operating rod in a fluid-filled cavity  125 . Possible fluids include insulating oil, SF6, and/or air. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. Accordingly, other implementations are within the scope of the following claims.