MOVING INTERRUPTER GAP SHIELD

Abstract: The movable nozzle (95) of a puffer circuit interrupter (15-17) has a coaxial cylindrical shield (110) connected to its downstream end and the main movable contacts (89) connected to its upstream end. The shield (110) is electrically connected to the stationary contact terminal (44). The movable contact ring (89) and coaxial shield (110) at the upstream end of the nozzle (95) define a well shielded open gap when the interrupter gap opens.

Description: MOVING INTERRUPTER GAP SHIELD BACKGROUND OF THE INVENTION This invention relates puffer circuit interrupters, and more specifically relates to a novel gap shield carried by the movable nozzle of such a circuit interrupter. Puffer circuit interrupters are subject to large electrical stress in the interrupter gap during arc interruption operation and after arc interruption is completed. High stress in this region requires large and heavier movable parts for the interrupter, and carefully controlled design margins. SUMMARY OF THE INVENTION In accordance with the present invention, electric field stress in the arc gap region is reduced by providing a conductive shield that moves with the main interrupter nozzle and is electrically attached to the stationary contact assembly. The shield provides an improved electrical shape in the gap region when the interrupter is more than 1/2 open. The improvement increases until the interrupter is fully open. The geometry allows the moving cylinder and the stationary finger contacts to be of larger diameter than would otherwise be possible, a desirable condition for current transfer and internal interrupter gas volume. The ultimate effect is to allow reduction in the overall interrupter size for a given voltage rating without sacrificing the dielectric withstand capability. The electrical connection to the stationary side of the interrupter can be accomplished in several ways. A separate sliding, low friction contact spring can be used to form a direct connection as the shield slides through the main current contacts. A flexible wire connection is also possible. This electrical connection is important to keep the shield at the same electrical potential as the stationary contacts and eliminates any possibility of local arcing at the shield-stationary contact interface and improves the effectiveness of the moving shield. This improvement can be used at any voltage or interruption current rating. Preferably, the shield is made from aluminum to minimize weight but other materials, metallic and non-metallic, are possible. Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is an elevational view of a prior art three-pole circuit breaker employing gas buffer type interrupters. Figure 2 is a side view of the circuit breaker of Figure 1. Figure 3 is a partial cross-sectional view and partial schematic view of one pole unit of Figures 1 and 2. Figure 4 is a partial cross sectional and partial schematic view of a novel interrupter assembly in which the interrupter is slidably mounted within an adapter assembly supported at one end of an entrance conductor. Figure 5 is an enlarged view of portions of Figure 4, to highlight the structure of the slip-through interruptermounting. Figure 6 is a further enlargement of Figure 5 to further display the novel slip-through feature of the interrupter assembly. Figure 7 is a cross-section, similar to that of Figure 6, but emphasizing the structure of a novel gas mixing plate fixed to the moving baffle. Figure 8 is a view, similar to that of Figures 6 and 7, further emphasizing a novel moving electrostatic shield structure secured to the movable baffle and showing the interrupter gap in an open position above the contact center line, and in the closed position below the contact center line. DETAILED DESCRIPTION OF THE INVENTION A prior art circuit breaker, employing puffer interrupters, is shown in Figures 1,2 and 3. Figures 1 and 2 show a three-pole circuit breaker having entrance bushing insulators 10,11 and 12 for each respective phase (Figure 1) and three corresponding exit bushing insulators of which only one, bushing 13, is shown in Figure 2. The circuit breaker is a dead tank circuit breaker, and has three horizontal puffer interrupter assemblies 15,16 and 17 (Figure 1), each of which is associated with a corresponding pair of exit and entrance bushings. The interrupter assemblies, bushings and an operating mechanism 10, which simultaneously operates each of the interrupters, are mounted on a frame mounting 19, shown in Figures 1 and 2. Figure 3 is a view, partly in cross-section, of interrupter 15 and bushings 10 and 13 of Figures 2 and 3. Bushings 10 and 13 have current transformers 20 and 21, respectively. Entrance bushing 10 has a central conductor 22 which supports the interrupter assembly 23 within conductive tank 24. The right-hand end of assembly 23 is fixed to an insulator tube 25, through which a linearly movable operating rod 26 extends, which operates movable contact 27 between its open and closed positions, in the well-known manner. Exit insulator 13 has a central conductor 30 which is connected to the stationary contact assembly 31 which is suitably supported within tank 24. An insulator tube 32 extends between the stationary and movable contact assemblies 31 and 23, respectively. The interior volume of tank 24 and insulators 10 and 13 is filled with a dielectric gas, such sulfur hexafluoride (SF6) at ambient pressure. During operation of the contacts of interrupter assemblies 23 and 31, a piston which moves with the movable contact compresses the SF6 gas and forces it through the arc drawn between the separating contacts to cool and extinguish the arc. The gas also acts to provide an excellent insulator between the conductive parts within housing 15 and the wall of tank 24. SLIP THROUGH INTERRUPTER STRUCTURE There is next described, particularly with respect to Figures 4,5 and 6, the novel"slip-through"mounting for the interrupter structure which simplifies the installation and removal of the interrupter from the housing and which improves the overall conductivity of the interrupter, minimizes bushing insulator spacing and maximizes manufacturing tolerances. In the prior art interrupters of Figures 1,2 and 3, relatively long support insulators 10 and 13 are required and they must be carefully aligned to permit low friction motion for the interrupter during its operation. The current path between the ends of the bushing conductors 22 and 30 is also necessarily relatively long, resulting in higher electrical resistance in the path and thus higher temperature rises, limiting the continuous current carrying ability of a given size interrupter. The novel interrupter support structure shown in Figures 4,5 and 6 improves these undesired features of the prior art interrupter of Figures 1,2 and 3. Figures 4,5 and 6 show one pole 40 of an interrupter structure and its internal structure. The pole has a vertically disposed entrance insulator 41 and a horizontally disposed exit insulator 42, which have entrance and exit conductors 43 and 44, respectively. The tank entrances at insulators 41 and 42 are also provided with current transformers 50 and 51, respectively, as shown. A metal support tank 53 has a horizontal body portion 54, a vertical tubular portion 55 and a horizontal tubular portion 56. Insulators 41 and 42 are bolted to the ends of tank portions 55 and 56, respectively. Tank 53 is filled with SF6 at a pressure, for example, of about 4 atmospheres. An operating mechanism housing 57 (Figure 4) contains an operating lever 58 for operating the interrupter contacts to be described. In accordance with an important feature of the novel structure of Figures 4,5 and 6, a hollow conductive adapter 60 is bolted to the end of entrance conductor 43 and has a conductive ring which surrounds and slidably supports the moving conductive cylinder 61 of the interrupter moving contact assembly 62. A ring-shaped guide bearing 65 (Figure 6) is contained within the inner diameter of hollow adapter 60 and ensures low friction sliding of the moving cylinder 61 along its axis and along the axis of tank 54, and reduces the generation of conductive particles. A ring-shaped groove 66 (Figure 6) acts as a particle trap or low field region in which conductive particles will remain trapped once reaching the groove 66. Current is transferred from adapter 60 to conductive sleeve 61 by a plurality of suitable sliding transfer contacts 69 (Figure 6) which encircle the sleeve 61. A plastic insulation rod adapter 70, which is mounted on the inside wall of housing 54 is connected to the adapter 60 to provide added lateral support to the adapter 70. The upper end of rod 70 is connected by a slide fit to an opening in adapter 60. The bottom of rod 70 is glued, or otherwise fixed, to an opening in tank 53. Adapter 60 limits the bending motion of the entrance conductor 43 which might be caused by side loads during sliding movement of the interrupter moving cylinder 61. The stationary contact assembly 79 in Figures 4,5 and 6 is connected to and supported from the end of exit conductor 44 and includes stationary arcing contact rod 80, a conductive enlarged housing 81 (Figures 4,5 and 7), and stationary contact fingers, including flexible fingers 83 and 84 (Figure 6). A conductive electrostatic shield 85 encloses contact fingers 83-84. The movable contact assembly in Figures 4,5 and 6 includes the movable conductive cylinder 61, main contact ring 89, movable operating rod 90, connected to cylinder 61 by flange 92, the movable arcing contact fingers 93 and 94, and insulation nozzle 95. Operating rod 90 has radial openings therethrough, such as openings 90a and 90b. A stationary piston 96 is held in the annular space between axially movable rod 90 and sleeve 61 during device operation, as shown in Figure 8. Piston 96 is fixed to piston support assembly 97 which, in turn, is supported from small, flexible insulation support rods 98 and 99 (Figure 4) which are connected from the end of housing 54 to openings within ring 100 at the end of assembly 97. Support rods 98 and 99 are sufficiently flexible to permit the interrupter assembly to move up and down slightly as operating mechanism lever 58 rotates to move the contacts between their engaged and disengaged positions. Furthermore, since rods 98 and 99 are thin, parallel rods, the cool gas in the space surrounding the rods can flow through or be sucked through openings in the piston 97 and axially along the interrupter interior when they are opened, to provide additional cool gas in the interruption region. Prior art support cylinders prevented the use of gas in this support volume and, indeed, would prevent the necessary displacement of the axis of the interrupter during contact operation. Stationary piston 96 has a plurality of axially directed openings 96a and 96b therethrough which are closed by an appropriate spring biased valve plate 96c. Similarly, flange 92 has a plurality of openings 92a, 92b which are closed by an appropriately spring biased plate 92c. When the interrupter is closed, as shown in Figure 6, a current path extends from entrance conductor 43, adapter 60, transfer contacts 70, moving conductive cylinder or sleeve 61, main contact ring 89, stationary contacts 8384, housing 85 and exit conductor 44. To open the interrupter, operating rod 90 is moved to the left, and the conductive cylinder 61, also moves left. Contact ring 89 disconnects from contacts 83 and 84 and, subsequently, an arc is drawn between arcing contact 93 and stationary arcing contact rod 80. As cylinder 61 moves to the left, insulation nozzle 95 also moves to the left. The gas trapped between the stationary piston 96 and the moving cylinder 91 is compressed and flows through flow holes 90a and 90b in rod 90, and through the interior of assembly 62 and into and through the arc region. Since adapter 70 supports the interrupter assembly 62, the entire assembly floats with and is guided by adapter 70, allowing the insulating supports to ground to be very small and flexible. The main support for the entire interruption is provided by the entrance and exit insulators 41 and 42. Furthermore, manufacturing tolerances are large because of the self-guiding characteristics of the design. That is, the support structure allows centering and alignment of relatively out-of-tolerance parts without wear or high friction during operation. This novel geometry eliminates the need for large and expensive insulators to support the stationary piston assembly and across the interrupter gap region. The laterally flexible stationary contact assembly is guided and supported by the main nozzle 95 that bridges the gap. The result is a simpler assembly with fewer parts and a better usage of the interrupting gas within the tank. This gas is used for electrical insulation of the high voltage parts from the ground potential of the tank wall and the gas is also used for interruption of the arcs generated in the circuit breaker during its operation. The ideal situation is to have all of the gas cycled through the interrupter as it repeatedly operates to keep the gas in the interruption region cool and relatively pure. The novel design shown in Figures 4,5 and 6 largely achieves this goal by elimination of any insulation support that tends to block free gas flow throughout the tank interior. Less total gas can then be used. The assembly of the circuit breaker is simplified because the entire assembled interrupter, the entrance insulator assembly 41, and the exit insulator assembly 44 are fully assembled outside of the tank 53 as subassemblies. They are then simply inserted into the tank 53 with no required adjustments or assembly inside the tank. This reduces required labor and allows a small tank to be used because there is no need to work inside the tank 53. This geometry also allows the current transfer length in the interrupter to be very short compared to designs now in use. Also, the main contacts 89 are all on relatively large diameters because they are on the outside diameter of the components instead of the inside. This reduces the resistance of the current path, reduces the temperature rise of the parts, and allows smaller parts for a given rated current. This geometry also shortens the entire circuit breaker pole assembly by allowing the insulators (or bushings) to be closer together. A 90 arrangement is shown because this is the optimum geometry to minimize tank length and number of parts. Other entrance geometries are possible. SHIELD RING ON MAIN NOZZLE Figure 7 shows the interrupter of Figure 6 and the same identifying numeral identifies the same parts. Figure 7 shows a shield ring 110 which is fixed to the downstream end of nozzle 95. Shield ring 110 is electrically connected to the ring of stationary contacts 83-84 by sliding low friction springs 111 and 112 which contact conductive cylinder 113, which is connected to contact fingers 83-84. When the contacts open, the field stress in the open interruption gap will be applied between movable contact 89 which has a ring shape and shield 110. This will lower the electrical stress in the gap after it is more than about 1/2 open. More specifically, lowering electrical stress in the open gap region allows smaller components to be used and can provide greater design margins. This applies to the arc interruption and to the dielectric withstand of the gap after interruption is completed. However, there are limits to this stress reduction process when the several other geometric requirements of an interrupter are met also. An improvement on these limits is possible by providing the conductive shield 110 which moves with the main interrupter nozzle 95 and is electrically attached to the stationary contact assembly. The shield 110 provides an improved electrical shape in the gap region when the interrupter is more than 1/2 open. The improvement increases until the interrupter is fully open. This geometry also allows the moving cylinder 61 and the stationary finger contacts 83-84 to be of larger diameter than would otherwise be possible, a desirable condition for current transfer and internal interrupter gas volume. The ultimate effect is to allow reduction in the overall interrupter size for a given voltage rating without sacrificing the dielectric withstand capability. The electrical connection to the stationary side can be accomplished several ways. Figure 7 shows a separate sliding, low resistance contact spring and a direct connection as the shield slides through the main current contacts. A flexible wire 120 which will slidably contact cylinder 113 when the contacts open may also be used. This electrical connection is important to keep the shield at the same electrical potential as the stationary contacts (Figure 8). This eliminates any possibility of local arcing at the shield-stationary contact interface and improves the effectiveness of the moving shield 110. This improvement can be used at any voltage or interruption current rating. Preferably, the shield is made from aluminum to minimize weight but other materials, metallic and non-metallic, are possible. Another version of the shield is shown in Figure 8 as two part shield 120-121 where shield portion 121 contains the sliding contacts 111-112. The lower half of Figure 8 shows the shielded fully open gap which improves electrical stress across the open gap. MOVING GAS MIXING PLATE Figures 7 and 8 show a novel mixing plate 130 spaced from and bolted to the moving shield 110/120 and movable with baffle 95. Plate 130 is preferably a round disk which may or may not have a central opening 131, as in Figure 8. Plate 130 is of any high temperature resistant material, for example, steel. Plate 130 has the function of causing hot gas from the interruption gap during circuit interruption to flow turbulently into the mixing volume within housing 81 to mix with cool gas, before the gas reaches other areas within the interrupter housing which is subject to high voltage stress. More specifically, the arc is generated in the breaker interrupter during opening and successful interruption of the current flow depends largely upon a rapid flow of cool gas (SF6) through the arc. The heated gas leaving the interrupter main gap area, coming out of the main nozzle 95, must be cooled before it is allowed to flow into a region of voltage stress. This cooling is often accomplished by the use of a stationary mixing plate, the hot gas forcing past and around the plate becoming a turbulent flow and causing good mixing with cooler gas in its path. This operation requires a relatively large volume of cool gas in the flow path that is inside the main interrupter body 53. A large, unused volume is thus needed that generally serves no other purpose. The mixing plate of the invention permits use of a smaller gas volume, and thus a smaller interrupter structure. In operation, the main nozzle and plate 130 move with the interrupter cylinder 61 as it is opened. Therefore, a significant volume is vacated by the nozzle assembly into which cool gas will be drawn. The heated gas from the arc region will begin to flow out of the nozzle from the mid-stroke of the interrupter and will mix with the now larger cool gas volume created. Turbulent mixing will be improved because the cool gas is already in motion due to the drawing-in action and mixing will be more complete. This reduces surface erosion of parts of the interrupter interior, caused by the flow of the hot gas if not cooled evenly and quickly. The assembly of the interrupter with a moving plate 130 is also easier than one using a stationary plate design. The moving plate 130 attaches directly to the moving nozzle assembly 95 which is assembled on a bench in production or during field maintenance. A stationary plate is often attached deep in the interrupter, difficult to access, inspect, and replace. The plate shape is usually of a round disk, with or without a center hole, and is sized to obtain the correct flow and turbulence. Other shapes are possible depending upon the specific interrupter design and gas flow requirements. Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.

Claims: WHAT IS CLAIMED IS : i./A shield structure for shielding the interruption gap of a puffer gas interrupter; said interrupter comprising, in combination: a stationary contact assembly; a movable contact assembly movable between an engaged and a disengaged position relative to said stationary contact assembly and defining an open interruption gap when in said disengaged position: said movable contact assembly having a cylindrical ring-shaped contact structure defining one side of said interruption gap; a movable cylindrical insulation nozzle for directing gas through said interruption gap during the movement of said movable contact assembly; said movable contact assembly being connected to the upstream end of said nozzle and movable therewith; said nozzle being disposed within said movable and stationary contact assemblies when they are engaged; and a contact shield ring connected to the downstream end of said nozzle and movable therewith and electrically connected to said stationary contact assembly whereby, when said movable contact assembly is fully open, said contact shield faces said cylindrical ring-shaped contact structure and defines therewith a shielded volume within said open interruption gap. 2. The device of claim 1 wherein said gas is SF6. 3. The device of claim 1 which further includes a housing which is concentric with the direction of motion of said movable contact assembly and contains said gas therein; said movable and stationary contact assemblies and said insulation nozzle being contained within said housing. 4. The device of claim 3 which includes sliding contact means for making sliding contact from said contact shield ring to said stationary contact assembly. 5. The device of claim 1 wherein said cylindrical ring-shaped contact structure, said contact shield and said nozzle are coaxial. 6. The device of claim 3 wherein said gas is SF6. 7. The device of claim 4 wherein said gas is SF6. 8. The device of claim 5 wherein said gas is SF6. 9. The device of claim 7 which further includes an elongated housing which is generally concentric with the axis of motion of said movable contact assembly and contains said gas therein; said movable and stationary contact assemblies and said insulation nozzle being contained within said housing. 10. The device of claim 8 which further includes an elongated housing which is generally concentric with the axis of motion of said movable contact assembly and contains said gas therein; said movable and stationary contact assemblies and said insulation nozzle being contained within said housing. 11. The device of claim 9 wherein said cylindrical ring-shaped contact structure, said contact shield and said nozzle are coaxial. 12. A movable baffle and contact structure for a puffer circuit interrupter; said movable baffle comprising an elongated movable insulation cylinder having an input gas end with a small gas flow central area and an output gas end with a larger area gas flow central area than that of said small area; a movable contact ring encircling the outer diameter of said nozzle at its said input end, and a shield ring insulated from said movable contact ring and coaxial with said nozzle and said shield ring and fixed to the output end of said nozzle. 13. The device of claim 12 which further includes sliding contact means extending from the outer diameter surface of said shield ring.

Inventors: KALTENEGGER KURT, MEYER JEFFRY R, STECHBARTH JOACHIM, KALTENEGGER, KURT, MEYER, JEFFRY, R., STECHBARTH, JOACHIM
Applicants: ABB POWER T & D CO, ABB POWER T & D COMPANY INC.
Application year: 1995
Main classification: H01H33
IPC codes: H01H33