Patent Publication Number: US-2023154706-A1

Title: Toroidal encapsulation for high voltage vacuum interrupters

Description:
BACKGROUND 
     Field 
     The disclosed concept relates generally to a vacuum interrupter and, more particularly, to a vacuum interrupter having a toroidal portion at one or both ends that achieves higher dielectric levels and hence higher interruption levels. 
     Related Art 
     Vacuum interrupters include separable main contacts located within an insulated and hermetically sealed envelope that may be referred to as a vacuum chamber. The vacuum chamber typically includes, for example and without limitation, a number of cylinder-shaped sections of ceramics (e.g., without limitation, a number of tubular ceramic portions that are of a roughly cylindrical shape) for electrical insulation that are capped by a number of end members (e.g., without limitation, metal components, such as metal end plates; end caps; seal cups) to form an envelope in which a vacuum or a reduced pressure is drawn. The example ceramic section is typically cylindrical; however, other suitable cross-sectional shapes may be used. Two end members are typically employed. Where there are multiple ceramic sections, an internal center shield is disposed between the example ceramic sections. Some known vacuum interrupters also include encapsulation that is applied over an exterior surface thereof and that may be formed of a silicone material or other appropriate insulating materials. 
     Vacuum interrupters suffer from a number of shortcomings. For example, on vacuum interrupters used in typical high voltage applications, such as applications where line-to-line voltage ratings of 72 kV exist, the vacuum interrupter must be able to achieve a 350 kV Lightning Impulse Withstand Voltage (LIWV) rating, which has been achievable. However, on vacuum interrupters used in even higher voltage applications, such as in application where line-to-line voltage ratings of 84 kV exist, the vacuum interrupter must be able to achieve a 400 kV LIWV rating, which can be difficult to achieve. There is thus room for improvements in vacuum switching apparatus. 
     SUMMARY 
     These needs and others are met by embodiments of the invention, which are directed to an improved vacuum interrupter. 
     As one aspect of the disclosed and claimed concept, an improved vacuum interrupter is structured to interrupt electrical current to a protected portion of a circuit, the general nature of which can be stated as including an envelope that can be stated as including a cylinder that is insulative and a pair of end caps situated at opposite ends of the cylinder, the envelope having an interior region and having a reduced pressure within the interior region, a movable contact movably situated on the envelope and situated adjacent an end cap of the pair of end caps, a stationary contact situated on the envelope and situated adjacent another end cap of the pair of end caps, and a coating that is formed at least in part of an insulative material and that is situated on an exterior of the envelope, the coating can be stated as including a first portion situated on the cylinder and having a first thickness in a radial direction with respect to the cylinder, the coating further can be stated as including a second portion situated adjacent the end cap and having a second thickness greater than the first thickness in the radial direction. As employed herein, the expression “a number of” shall refer broadly to any non-zero quantity, including a quantity of one. 
     A toroidal-shaped encapsulation, such as may be made from silicone or other appropriate material, on the end sections of a vacuum interrupter (VI) that is used in a typically high voltage application, for example in an application involving line-to-line voltage ratings of 72 kV and above, effectively helps with achieving higher ratings of AC withstand voltage and passing high lightning impulse withstand voltage levels of 400 KV successfully. While silicone encapsulation on the VI is typically applied after all conditioning processes are complete, it can also be applied before conditioning to provide some processing benefits. The addition of a toroidal-shaped silicone encapsulation provides a number of enhancements on the VI: 
     very good protection of triple point junctions; 
     very good electric-field distribution to help mitigate surface flashovers wherein equipotential voltage lines spread out protecting the triple point junctions; 
     increased dielectric strength; 
     increased electrical permittivity; 
     added creepage length; 
     more margin on 400 kV LIWV ratings; 
     ability to pass high voltage levels no matter how the VI is installed in the mechanism, such as in GIS or compressed air etc.; 
     employment in designs involving pole-to-pole layout with safe insulating distances between VIs and the enclosure in 3-phase mechanism configurations; 
     the insulating medium is dry air, and the toroidal profile of silicone encapsulation will help space the distance for achieving 160 kV high potential and 400 kV LIWV; and 
     when applied before conditioning, protects the VI from through-ceramic dielectric breakdowns (punctures) during the conditioning process that cause leaks and scrap product during manufacturing. 
     The shape of the toroidal profiles of the insulation member, made of silicone in the depicted exemplary embodiment, that are situated at both ends of the envelope of the vacuum interrupter and that are integrated with the silicone coating that overlies the envelope of the VI helps achieving higher dielectric levels. The toroidal shape is created in a way to encompass and protect the triple point junctions which are formed of the conductor, ceramic, and the silicone insulator. The radii of the hemispheres peak or have an apex along the junction planes to enable the high field gradients, as depicted by equipotential lines, to move away from the triple junctions. Electric field gradients, as depicted by equipotential lines, are advantageously pushed generally in a radial direction from the standpoint of the cylinder of the VI envelope to advantageously drive corona, discharge, and external flashovers during very high voltage dielectric tests. Such electric fields in the vicinity of the triple junctions are mitigated very well and this helps with preventing destructive dielectric breakdown through ceramic, and avoids the causing of any leaks, which advantageously improve the overall high voltage performance of the VI. The advantageous deflection by the toroidal silicone profiles of the disclosed and claimed concept of the equipotential lines takes place at these critical triple junctions, and the toroidal shape profile plays an advantageous role in enhancing the VI performance. 
     The silicone material itself from which the toroidal profiles are formed is formulated to be of a high relative permittivity. It is noted that the relative permittivity, or dielectric constant, of a material is its (absolute) permittivity expressed as a ratio relative to the permittivity of a vacuum. In the depicted exemplary embodiment, the insulative silicone material from which the coating over the VI, and including the toroidal profiles at the ends, has a relative permittivity that is in a range of about 2.7 to 5 and, more particularly, may have a relative permittivity that is about 3.5. Molding a metallic film or sheath that is embedded into the toroidal profiles further helps to mitigate the high field gradients at the triple junctions. Coating in outer surface of the toroidal profiles with a metallic covering in the form of a coating or layer around the toroidal profiles also contributes to mitigate the high field gradients at the triple junctions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full understanding of the disclosed concept can be gained from the following Description when read in conjunction with the accompanying drawings in which: 
         FIG.  1    is a sectional view of an improved vacuum interrupter in accordance with a first embodiment of the disclosed and claimed concept in an OPEN state; 
         FIG.  2    is view similar to  FIG.  1   , except depicting the vacuum interrupter in a CLOSED state; 
         FIG.  3    is a depiction of equipotential electric field lines in a prior art vacuum interrupter showing equipotential electric field lines wrapping around the triple junctions and increasing the stresses at these locations; 
         FIG.  4    is a view depicting equipotential electric field lines of the improved vacuum interrupter of  FIG.  1    showing the equipotential electric field lines deflecting away at the triple junctions to help resolve the high field gradients; 
         FIG.  5    is a sectional view of an improved vacuum interrupter in accordance with a second embodiment of the disclosed and claimed concept in an OPEN state; and 
         FIG.  6    is a sectional view of a metallic components of the second embodiment depicted as being sectioned along a different section than that depicted in  FIG.  5   . 
     
    
    
     Similar numerals refer to similar parts throughout the Specification. 
     DESCRIPTION 
     An improved vacuum interrupter (VI)  4  in accordance with a first embodiment of the disclosed and claimed concept is depicted generally in  FIGS.  1  and  2   . The exemplary vacuum interrupter  4  includes an envelope  8  that can be said to include a cylinder  12  and to further include a pair of end caps that are indicated at the numerals  16 A and  16 B. The envelope  8  has an interior region  18  having a reduced pressure or a vacuum formed therein. 
     The cylinder  12  is formed of an insulative material, such as a ceramic or other appropriate material, and thus is itself insulative. While the cylinder  12  is depicted herein as being of a hollow cylindrical shape and as having both a radial direction and a longitudinal direction with respect thereto, it is understood that in other embodiments the cylinder  12  can be of a rectangular or other cross-sectional shape and as still having a radial direction and a longitudinal direction without departing from the spirit of the disclosed concept. 
     The vacuum interrupter  4  further includes a movable contact  20  and a stationary contact  24 . The movable contact  20  is movably situated on the envelope  8  and extends outwardly through an opening formed in the end cap  16 A while retaining the reduced pressure within the interior region  18 . The stationary contact  24  is stationary with respect to the envelope  8  and extends outwardly through an opening formed in the end cap  16 B. The movable contact  20  is movable with respect to the envelope  8  to cause the vacuum interrupter  4  to be movable between an OPEN state, such as is depicted generally in  FIG.  1   , wherein the movable and stationary contacts  20  and  24  are electrically disconnected from one another, and a CLOSED state, such as depicted generally in  FIG.  2   , wherein the movable and stationary contacts  20  and  24  are electrically connected with one another. In an understood fashion, the movable and stationary contacts  20  and  24  are electrically connectable with a protected portion of a circuit. 
     The end caps  16 A and  16 B can each be generally characterized as including a planar portion  28  and a cylindrical portion  32 , wherein the cylindrical portion  32  protrudes from a perimeter of the planar portion  28 . The cylindrical portion  32  abuts an end of the cylinder  12  at a junction  36 . The cylindrical portions  32  of the end caps  16 A and  16 B each form one of the junctions  36 , which are disposed at opposite ends of the cylinder  12 . 
     The vacuum interrupter  4  further includes a coating  40  that is formed of an insulative material and that is formed on an exterior of the envelope  8 . The coating  40  can be said to include a first portion  44  that is formed generally on an exterior surface of the cylinder  12  and a pair of second portions that are indicated at the numerals  48 A and  48 B that are formed generally on the end caps  16 A and  16 B and on the end regions of the cylinder  12  where the junctions  36  are situated. 
     As can be understood from  FIG.  1   , for example, the first portion  44  is of a first thickness  52  as measured in a radial direction  56  with respect to the cylinder  12 . The first thickness  52  is of a substantially unvarying dimension in a region of the coating  40  that extends generally between the second portions  48 A and  48 B. In other embodiments, the first portion  44  or the second portions  48 A and  48 B may have an encapsulated shape that additionally includes ribs or watersheds along this length. The benefits of toroidal encapsulation can also be applied here, as long as the substantially largest diameter of the insulation is applied at the triple junctions at both ends as described herein. 
     In contrast to the first portion  44 , the second portions  48 A and  48 B are each of a toroidal profile, meaning that they each have an arcuate outer surface  64  and a second thickness  60 A and  60 B as measured in the radial direction  56  that varies along a longitudinal direction  70  with respect to the cylinder  12 . The aforementioned ribs or watersheds that may exist along the first portion  44  would be smaller than the toroidal shapes at the second ends  48 A and  48 B. 
     Moreover, it can be seen from  FIGS.  1  and  2    that the second portions  48 A and  48 B each have an apex  68 , which can be referred to as a region of relatively greatest thickness, at a location along the longitudinal direction  70  that is adjacent in the radial direction  56  the corresponding junction  36 . In the depicted exemplary embodiment, each apex  68  is situated at a location along the longitudinal direction  70  to be substantially aligned in the radial direction  56  with the junction  36  of the corresponding end of the envelope  8 . The longitudinal direction can also be seen as being parallel and/or coaxial with an axis that includes the axially-aligned movable and stationary contacts  20  and  24 . 
     In the depicted exemplary embodiment, the coating  40  is formed of a single molding of a silicone insulation material having a high relative permittivity that is in a range of about 2.7 to 5 and, more particularly, may have a relative permittivity that is about 3.5. Such high relative permittivity advantageously deflects electric fields away from the junctions  36 , which are the triple junctions of the vacuum interrupter  4 . For instance,  FIG.  3    depicts at the letter X a previous vacuum interrupter that is formed without the first and second portions  48 A and  48 B and that includes an end cap B having a triple junction C.  FIG.  3    also depicts a set of equipotential field lines at the numeral A, with one of the equipotential field lines A also being designated with AA that can be seen in  FIG.  3    to be extending at least partially across the end cap B in a direction generally toward where the stationary contact would be. This is undesirable and is alleviated by the disclosed and claimed concept. 
     More specifically,  FIG.  4    depicts at the numeral  72  a set of equipotential field lines extending from a portion of the vacuum interrupter  4 . As can be seen in  FIG.  4   , the first portion  48 A advantageously deflects the electric fields, as represented by the equipotential field lines  72 , so that they do not flash over the end cap  16 A and thus advantageously resist damage to the triple junction that can be said to exist at the junction  36 . The same advantages are provided by the second portion  48 B and with respect to the end cap  16 B. This advantageously enables the vacuum interrupter  4  to be used in relatively higher voltage applications than the vacuum interrupter X of  FIG.  3   . 
     An improved vacuum interrupter  104  in accordance with a second embodiment of the disclosed and claimed concept is depicted generally in in  FIG.  5   . The vacuum interrupter  104  is similar to the vacuum interrupter  4  in that the vacuum interrupter  104  includes an envelope  108  having an insulative cylinder  112  and a pair of end caps  116 A and  116 B that meet the cylinder  112  at a pair of junctions  136 , and having a reduced pressure therein. The envelope  108  likewise includes a coating  140  having a first portion  144  and a pair of second portions  148 A and  148 B that are likewise of a toroidal shape. However, the second portions  148 A and  148 B each additionally have a metallic component indicated at the numerals  150 A and  150 B in addition to the silicone insulative material that forms the second portions  148 A and  148 B. 
     As with the coating  40  of the vacuum interrupter  4 , the first portion  144  is of a first thickness  152  in a radial direction  156  with respect to the cylinder  112  that is of a substantially unvarying dimension between the first and second portions  148 A and  148 B. As noted elsewhere herein, however, the first portion  144  again can include ribs or watersheds along this length that are smaller than the end toroids. The second portions  148 A and  148 B each have a second thickness  168  and  160 B, respectively, as measured in the radial direction  156  that varies along a longitudinal direction  170  with respect to the cylinder  112 . As before, the first and second portions  148 A and  148 B are each situated along the longitudinal direction  170  to each have an apex  168  that is adjacent in the radial direction  156  the corresponding junction  136  and which, in the depicted exemplary embodiment, is substantially aligned with the junction  136  in the radial direction  156 . The second portions  148 A and  148 B each have an outer surface  164  that is of an arcuate shape and which, in the depicted exemplary embodiment, is of a toroidal profile. 
     The metallic components  150 A and  150 B of the exemplary vacuum interrupter  104  each include a metallic body  176  that is depicted in  FIGS.  5  and  6    and that is embedded in the silicone material of each of the second portions  148 A and  148 B. Each metallic body  176  is generally ring-shaped and extends about the cylindrical portion of each end cap  116 A and  116 B, and at least a portion of the metallic body  176  is disposed generally between the junction  136  and the apex  168  of the corresponding second portion  148 A and  148 B. In the depicted exemplary embodiment, the metallic components  150 A and  150 B each further include a metallic covering  180  that is in the form of a metallic coating that is situated on the outer surface  164  of the silicone material of each of the second portions  148 A and  148 B. It is understood that in other embodiments the metallic components  150 A and  150 B might include either the metallic body  176  or the metallic covering  180 , or both, without departing from the spirit of the instant disclosure. 
     The metallic body  176  and the metallic covering  180  each advantageously assist in further dispersing the electric fields away from the end caps  116 A and  116 B and away from the junctions  136 , which further assists in protecting the vacuum interrupter  104  from flashover and from a breakdown of the vacuum interrupter  104 . This is advantageous because it enables the vacuum interrupter  104  to be used in various high-voltage applications without a risk of breakdown. It is further advantageous, but not required, that the metallic covering be nonmagnetic to prevent eddy current heating during conduction through the VI in its closed state. Other benefits will be apparent. 
     While specific embodiments of the disclosed concept have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limiting as to the scope of the disclosed concept which is to be given the full breadth of the claims appended and any and all equivalents thereof.