Patent Publication Number: US-3876846-A

Title: Combination ground and test switch apparatus for pressurized-gas-insulated high voltage systems

Description:
United States Patent 1191 Graybill Apr. 8, 1975 [5 1 COMBINATION GROUND AND TEST 3.567.885 3/1971 Boersma 200/148 R SWITCH APPARATUS FOR 3.592.984 7/1971 Turgeon 200/148 R 3.665.135 5/1972 Boersma et a1 200/148 F PRESSURIZEDGAS&#39;INSULATED HIGH 3,778,574 12/1973 Clark 200/148 B VOLTAGE SYSTEMS Inventor: Howard W. Graybill, G reensburg.  
 l-T-E lmperial Corporation, Spring House, Pa.  
 Filed: Mar. 12, 1974 Appl. No.: 450.466  
  Related U.S. Application Data Continuation of Ser. No. 280999. Aug. 16. 1972.  
 Assignee:  
 Milliken 200/148 F Primary Eraminer-Robert S. Macon Attorney. Age/1!, or Firm-Ostrolenk, Faber, Gerb &amp; Soffen [57] ABSTRACT A combination ground and test switch apparatus for pressurized-gas-insulated high-voltage systems capable of selectively electrically grounding and/or testing through the use of a medium voltage electrical source selectively connectible to a system internal conductor which is completely surrounded by a grounded conductor and which is constantly maintained in a pressurized state.  
 7 Claims, 3 Drawing Figures COMBINATION GROUND AND TEST SWITC APPARATUS FOR PRESSURIZED-GAS-INSULATED HIGH VOLTAGE SYSTEMS This is a continuation of application Ser. No. 280,999, filed 16 Aug. 1972.  
  The present invention relates to pressurized gasinsulated high-voltage systems and more particularly to a novel combination ground and test switch apparatus for testing high-voltage conductors completely enclosed in grounded metal covers without the need for either depressurizing or removing the grounded covers.  
 BACKGROUND OF THE INVENTION In metal-enclosed pressurized-gas-insulated high voltage switchgear, of the type described in US. Pat. Nos. 3,546,356; 3,573,342; 3,643,003 and in pending application Ser. No. 234,811, filed Mar. 15, 1972, now abandoned, all of which have been assigned to the assignee of the present application, it is conventional that the high-voltage conductors be completely enclosed in grounded metal housings or covers at all points along the system. The advantages of this construction in both safety and reliability are obvious. There is, however, one decided disadvantage in that it is not convenient to gain access to the enclosed high-voltage conductor for low-voltage tests commonly performed on a routine basis such as, for example, resistance tests on circuit breaker contacts, power-factor tests on transformer insulation, and so forth.  
  Since it is desirable and even necessary to periodically measure the contact resistance of circuit breakers by the application of a known measured current across two terminals of the circuit breaker for the purpose of measuring the voltagedrop between the terminals, it is conventional in outdoor substation design that this can be readily accomplished by clipping the test leads on to the exposed high-voltage conductors at the upper ends of their bushings. However, this is not possible in metalenclosed pressurized systems since the high-voltage conductors are not exposed at any point along the system.  
 BRIEF DESCRIPTION OF THEINVENTION The present invention is characterized by providing a combination ground and test switch apparatus for pressurized-gas-insulated high-voltage systems and the like which maintains the integrity of the pressurized system and which may be selectively operated to provide either grounding or voltage testing without the need for either depressurizing or removal of any of the system grounded housings or covers.  
  The present invention comprises a housing joined to the grounded enclosure of a pressurized-gas-insulated high-voltage system and hermetically sealed thereto with an opening provided in the aforesaid grounded housing to provide communication between the interior of the switchgear and the housing affixed thereto. A reciprocally movable switch blade is mounted within said housing and is arranged to&#39;be moved to a closed position within the interior of the switchgear equipment for engageme&#39;ntwith a jaw structure which is surrounded by an electrostatic shield to reduce dielectric stresses within the switchgear. An operating mechanism which may be safely manipulated from the exterior of the housing is provided for moving the switch blade between its connected and disconnected positions. The end of&#39;the switch housing remote from the switchgear grounded housing is provided with a conductive terminal electrically insulated from the test switch housing and is electrically coupled to the movable blade by a flexible conductor which is provided so as to allow for free reciprocal movement of the switch blade without in any way affecting the integrity of the electrical connection therebetween. A conductive ground strap is normally coupled between the aforementioned terminal and the switchgear grounded housing to maintain the conductive components of the switch housing at ground potential during intervals when no tests are being performed. To perform the desired test, the conductive group strap is first removed and the switch blade is operated to the closed position to establish an electrical connection between the aforementioned terminal and the central conductor of the switchgear network. A medium voltage source may then be coupled to the aforementioned terminal for test purposes without the need for either depressurizing the switchgear equipment or removing any of its housings or covers.  
  It is therefore one object of the present invention to provide a novel test switch assembly and housing adapted for selectively and simply performing tests upon the internal high-voltage conductor of metalenclosed pressurized-gas-insulated high-voltage switchgear while avoidingthe need for either depressurizing the switchgear network or removing any of its housings or covers.  
 BRIEF DESCRIPTION OF THE FIGURES The above, as well as other objects of the present invention will become apparent when reading the accompanying description and drawings in which:  
  FIG. 1 shows an elevational sectional view of a ground and test switch assembly embodying the principles of the present invention.  
  FIG. 2 shows a sectional view of the assembly of FIG. 1 looking in the direction of arrows 2-2.  
  FIG. 3 shows a sectional view of the assembly of FIG. 1 looking in the direction of arrows 3-3.  
 DETAILED DESCRIPTION OF THE FIGURES Copending application Ser. No. 234,811 discloses a metal-enclosed pressurized-gas-insulated high-voltage circuit breaker in which the high-voltage conductors are completely enclosed in grounded metal covers at all points. In equipment of this type as well as other components of such a switchgear and/or power distribution and transmission network it becomes desirable and even necessary at periodic intervals to measure the contact resistance of the circuit breakers as well as other components, by application of a known measured current from one terminal of the breaker to the other in order to measure the voltage drop between terminals. Since the central conductors are metal-enclosed within conductive pressurized housings at all point, it is an object of the present invention to provide an assembly 10 of the type shown in FIGS. 13 to perform the necessary test procedures without the need for depressurizing the system or removing any portion of the enclosure to gain access to the high voltage conductor. In pressurized gas systems of this type, it is further necessary to provide means for grounding the internal high-voltage conductor to provide complete safety for personnel at such times when it becomes necessary to open the enclosure and gain access to internal partsfor inspection, maintenance or repair. Grounding or earthing switches, which establish a good metal connection between the internal conductor and the grounded metal enclosure are well known in the art. Such grounding switches must be capable of carrying the full ground fault current capability of the electrical system at the point of connection without being damaged or destroyed. The assembly of FIGS. 1-3, which combines the functions of a grounding switch with those of a test switch, may be adapted for use in establishing an electrical connection with an internal conductor 11 which is energized at a high voltage in normal usage. The grounded metal enclosure 12 serves as the means for retaining the pressurized insulating gas within the hollow space 13 between the conductor 11 and the grounded enclosure 12. Suitable insulators or spacers formed of a solid material and described in detail in US. Pat. No. 3,573,341, for example, act to maintain appropriate spacing and centering of conductor 11 relative to its associated grounded housing 12.  
  The test switch assembly 10, which may be selectively electrically connected with the switchgear highvoltage conductor 11, comprises a hollowsubstantially cylindrical shaped housing 14 secured by weldments 14a and 14b to internal flanges 15 and 16, respectively. A disc-shaped member 17 formed of a suitable insulating material such as phenolic or epoxy, forms the outer end of the ground and test switch housing and is joined to internal flange 15 by fastening means 18 arranged at spaced intervals about the periphery of the disc. Synthetic resilient O-rings 19 serve to seal and hermetically join disc 17 to the flange 15 of the housing. Disc 17 is provided with a centrally located opening 17a for receiving a copper terminal 20 which is preferably ccmented in place to prevent gas leakage. A fastening nut 21 threadedly engages the threaded portion of terminal 20 along the exterior of disc .17, while a fastening nut 22 threadedly engages the opposite threaded portion of terminal 20 for securing the end terminal 23a ofa flexible metallic conductor 23 arranged in an undulating fashion, as can best be seen in FIG. 1. The opposite end terminal 23b of flexible conductive cable 23 is secured to a clevis assembly 24 by fastening means 25,25. The clevis assembly is secured to the left-hand end of a switch blade 26 which is mounted for reciprocating action under control of a crank member 27 arranged to pivot about an actuating shaft 7, which shaft is provided with a polygonal-shaped cross-section, as shown best in FIG. I, for. mating with an opening 27a of similar shape provided within insulating crank 27. Crank 27 is a bifurcated member having a pair of spaced parallel arms 27b and 270 (note especially FIG. 3) which arms are provided with suitable openings for receiving a pin 28 secured between arms 27b and 270 by cotter pins 29,29. The clevis assembly is provided with an elongated vertically aligned slot 24a adapted to slidably receive pin 28. Bifurcated crank arm 27 is adapted to move between the solid line representation of FIG. 1 to the dotted line representation 27. During such movement, pin 28 traverses an arcuate path represented by dotted line 28a. As a result of this movement, the clevis assembly 24 is moved from the solid line representation of FIG. 1, to the dotted line representation 24&#39; thereby causing switch blade 26 to move from the solid line representation of FIG. 1 to the dotted line representation 26, Due to the flexible characteristics of cable 23, the cable is free to become elongated as shown by dotted line representation 23 in FIG. 1 so as to freely permit the clevis assembly and switch blade to move toward the engaged or connected position for test purposes, as will be more fully described.  
  Internal flange 16 which forms part of the test equipment housing is mechanically and electrically joined to a cylindrical-shaped section 31 joined to the switchgear grounded conductive housing 12 by a weldment, as shown at 32, and having a flange portion 31a joined to internal flange 16 by fastening members 33 arranged at spaced intervals around the periphery of flange 31a. Flexible resilient synthetic O-rings 34 provide for airtight joining between flanges 31a and 16 when fastening members 33 are appropriately tightened.  
  An insulating guide bearing 35 has a flange portion 35a joined to the inner portion of flange 16 by fastening means 36 arranged at spaced intervals around flange portion 35a. Guide bearing 35 has a central opening 35b whose interior surface is provided with a low friction liner 37 which may, for example, be Teflon. Guide bearing 35 acts to guide the movement of switch blade 26 so as to prevent any movement thereof transverse to the longitudinal axis 26a of switch blade 26. In addition thereto, a pair of guide rods 39 and 40 are mounted within the interior of the test switch housing with their opposite ends being mounted within suitable diametrically opposed openings 15a-15b and 16a-l6b provided in flanges l5 and 16, respectively. Clevis assembly 24 is provided with two wing portions 24b and 24c each having an opening 24d and 24e, respectively, for slidably receiving guide rods 39 and 40 to guide the linear movement of the clevis assembly and prevent any twisting movement thereof.  
  As shown best in FIGS. 1 and 2, the grounded conductive enclosure 12 is provided with an opening 12a to facilitate the free reciprocating movement of switch blade 26. The hollow interior of the grounded test switch housing is filled with an insulating gas maintained at the same pressure as the gas inside the main enclosure or housing 12. Guide bearing member 35 is provided with an opening 35b to permit the pressurized gas to move freely between the switchgear and test switch enclosures so as to maintain and equalize the pressure within the two enclosures. The three major components of the housing, namely the cylindrical enclosure 14, disc member 17 and tube and flange mem-.  
 Under normal conditions, a conductive ground strap 39&#39; is connected between conductive terminal 20 and tube and flange member 31, as shown best in FIG. 1. A first end of the strap is mechanically secured to terminal 20 by means of fastening nuts 40 and 41, while the opposite end thereof is coupled to flange portion 31a by fastening member 33&#39;. In the arrangement shown in FIG. 1, it can be seen that the entire ground and test switch assembly is maintained at ground potential, i.e., the potential of grounded conductive housing 12. In order to ground the internal conductor 1, shaft 7 is rotated in the direction shown by arrow A in FIG. 1 to move switch blade 26 into the dotted line position 26&#39; so as to engage a tulip-type jaw contact assembly 42 comprised of a plurality of contact fingers 42a arranged at spaced intervals in a radial fashion and having spring members 42b urging the contact fingers into engagement with tubular projection 11a secured to conductor 11 by fastening means 43 and to selectively engage the free end of switch blade 26 when it occupies the dotted line position 26. Conductive member 44 comprises an electrostatic shield having a smooth exterior surface andan external radius of sufficient dimension so as to prevent the development of internal corona at the operating voltage and so as to reduce flashover voltage due to the concentration of dielectric stress which might otherwise occur at sharp points or edges on the high-voltage parts. The electrostatic shield &#39;44 is provided with asuitable opening 440 to permit the free reciprocating movement of switch blade 26.  
  in order to ground internal conductor 11, shaft 30 is rotated in the direction shown by arrow A&#39;of FIG. I to move switch blade 26 into engagement with the contact assembly 42. When it is desired to connect any test device having a voltage of up to l0kV (relative to ground potential) to the internal conductor, the grounding strap 39&#39; is removed and the lead of the test device (not shown for purposes of simplicity) is connected to terminal by removing and reapplying the fastening nuts 40 and 41. The bifurcated crank member 27, as was previously described, is formed of a suitable insulatingmaterial to permit movement of the switch blade into and/or out of engagement with central high-voltage conductor 11 without endangering operating personnel.  
  It can be seen from the foregoing description that the present invention provides a novel grounding and test switch structure for use with metal-enclosed pressurized-gas-insulated high-voltage switchgear and the like wherein grounding of the internal high-voltage conductor and removal of the ground therefrom may be simply and safely performed through the operation of an externally accessible operating mechanism. In addition thereto, the assembly facilitates the application of highcurrent medium voltage electrical sources to the internal conductor for test and maintenance purposes without the need for either depressurizing the switchgear network or removal of any housings or covers.employed therein.  
  Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.  
 What is claimed is:  
  1. For use in a metal-enclosed pressurized-gasinsulated high-voltage switchgear system, a doublepurpose grounding and test switch assembly capable of grounding a high-voltage internal conductor and of permitting a non-grounded electrical connection to the internal conductor for test purposes, said assembly comprising:  
 a grounded conductive housing completely surrounding said internal conductor and having an opening provided therein;  
 a switch housing mechanically and electrically connected to said grounded conductive housing and having an opening at a first end thereof whereby the pressurized interior of the grounded conductive housing communicates with the interior of said switch housing to maintain an equalized gas pressure therebetween;  
 a reciprocating conductive switch blade;  
 guide means mounted within saidswitch housing for guiding said conductive switch blade to move along a substantially linear path and through the grounded conductive housing opening;  
 the internal conductor including a jaw blade structure;  
 drive means mounted within said switch housing for moving said conductive switch blade from a first position whereby its free end is disengaged from the jaw contact structure to a second position whereby the free end of said conductive switch blade electrically engages the jaw structure;  
 a terminal mounted to the free end of said switch housing remote, from the grounded conductive housing and electrically insulated therefrom;  
 flexible conductive cable means positioned within said switch housing and electrically connected between said terminal and the end of said conductive switch blade remote from the jaw structure for permitting free reciprocating movement of said conductive switch blade while maintaining the integrity of a conductive electric path between said terminal and said conductive switch blade;  
 said guide means including means for electrically insulating said conductive switch blade from the grounded conductive housing and said switch housing;  
 said drive means including an actuating shaft having one end thereof extending outwardly from said switch housing to provide for movement of said conductive switch blade from and to a position exterior of said switch housing; said terminal being selectively connected to ground potential or to test equipment.  
  2. The device of claim 1 further comprising a conductive strap selectively connectible between said terminal and said switch housing for maintaining said conductive switch blade at the voltage level of said grounded conductive housing.  
  3. The device of claim 1 wherein said drive means further comprises a crank arm formed of an insulating material coupled to said operating shaft for pivoting said crank arm about said operating shaft when said shaft is rotated;  
 a clevis assembly coupled to the end of said conductive switch blade remote from the internal conductor;  
 means for coupling the free end of said crank arm to said clevis assembly.  
  4. The apparatus of claim 3 wherein said drive means is further comprised of means for providing an airtight seal in the region where said operating shaft protrudes from said switch housing to prevent the escape of the pressurized gas contained therein.  
  5. For use in a metal-enclosed pressurized gasinsulated high-voltage switchgear system, a doublepurpose ground and test switch assembly capable of grounding a high-voltage internal conductor and of permitting a non-grounded electrical connection to the internal conductor for test purposes in which a grounded conductive housing surrounds the internal conductor and has an opening provided therein;  
 a switch housing mechanically and electrically connected to said grounded conductive housing and having an opening communicating with the opening of the grounded conductive housing whereby the pressurized interior of the grounded conductive housing communicates with the pressurized inte: rior of said switch housing to maintain an equalized gas pressure therebetween;  
 a conductive switch blade;  
 drive means for moving said conductive switch blade from a first position whereby its free end is electrically disengaged from the internal conductor to a second position whereby the free end of said conductive switch blade electrically engages the internal conductor;  
 an electrical terminal mounted on said switch housing and electrically insulated from said switch housing;  
 conductive means positioned within said switch housing and electrically connected between said electrical terminal and said conductive switch blade and permitting free movement of. said conductive switch blade while maintaining the integrity of a conductive electric path between said electrical terminal and said conductive switch blade;  
 said conductive switch blade being electrically insulated from said grounded conductive housing and said switch housing;.  
 a conductive strap selectively connectible between said electrical terminal and ground potential for maintaining said conductive switch blade at the voltage level of said grounded conductive housing when said conductive strap is electrically connected to both said electrical terminal and ground potential;  
 said conductive strap designed to be removable to disconnect the electrical connection between said electrical terminal and ground potential to thereby permit a non-grounded electrical connection to be made from test equipment to the internal conductor through said electrical terminal and said conductive switch blade without the need to depressurize the switchgear system and without the need to remove either said switch housing or the grounded conductive housing.  
  6. The device of claim 5 wherein said switch housing and the grounded conductive housing are mechanically and electrically secured to each other so that they are both maintained at the same ground potential.  
  7. The device of claim 6 wherein said drive means moves a portion of said conductive switch blade through the opening of said switch housing and the opening of the grounded conductive housing to mechanically and electrically engage the internal conduc- IOI&#39;.