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.
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.
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:
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.
A full understanding of the disclosed concept can be gained from the following Description when read in conjunction with the accompanying drawings in which:
Similar numerals refer to similar parts throughout the Specification.
An improved vacuum interrupter (VI) 4 in accordance with a first embodiment of the disclosed and claimed concept is depicted generally in
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 16A 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 16B. 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
The end caps 16A and 16B 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 16A and 16B 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 48A and 48B that are formed generally on the end caps 16A and 16B and on the end regions of the cylinder 12 where the junctions 36 are situated.
As can be understood from
In contrast to the first portion 44, the second portions 48A and 48B are each of a toroidal profile, meaning that they each have an arcuate outer surface 64 and a second thickness 60A and 60B 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 48A and 48B.
Moreover, it can be seen from
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,
More specifically,
An improved vacuum interrupter 104 in accordance with a second embodiment of the disclosed and claimed concept is depicted generally in in
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 148A and 148B. 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 148A and 148B each have a second thickness 168 and 160B, 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 148A and 148B 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 148A and 148B 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 150A and 150B of the exemplary vacuum interrupter 104 each include a metallic body 176 that is depicted in
The metallic body 176 and the metallic covering 180 each advantageously assist in further dispersing the electric fields away from the end caps 116A and 116B 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.
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Entry |
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Translation of JP2014182876 (Original document published Sep. 29, 2014) (Year: 2014). |
European Patent Office, “International Search Report and Written Opinion” for corresponding International (PCT) Patent Application No. PCT/EP2022/025506, dated Feb. 15, 2023, 19 pp. |
Number | Date | Country | |
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20230154706 A1 | May 2023 | US |