Vacuum valve

Abstract

To reduce the electric field at high electric field points of a vacuum valve.SOLUTION: A vacuum valve according to an embodiment includes an insulating container having an opening, a vacuum container having a sealing metal fitting joined to the opening via a joint, a pair of electrodes detachably arranged opposite each other within the vacuum container, and an electric field mitigation shield arranged to cover the sealing metal fitting and the joint, and the electric field mitigation shield includes a conductive region containing a conductive resin and an insulating region containing an insulating resin arranged on at least a portion of the conductive region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION An embodiment of the present invention relates to a vacuum valve. [Background technology]

[0002] One method of mitigating high electric fields in areas with high electric fields is to use a metallic electric field mitigation shield. Vacuum valves equipped with this electric field mitigation shield are used in cubicle-type gas-insulated switchgear (C-GIS) that uses SF6 gas. Because SF6 gas is a greenhouse gas and its use is expected to be restricted in the future, C-GIS that use alternative gases instead of SF6 gas are being developed. Alternative gases include dry air, but its insulating performance is only about one-third that of SF6 gas. Other alternative gases often have inferior insulating performance compared to SF6 gas, making it difficult to achieve the same insulating performance (breakdown voltage) as SF6 gas using alternative gases alone. Therefore, the use of composite solid insulators has been considered. One such approach is to coat the surface of a metal electric field mitigation shield with a resin to improve its breakdown voltage. However, because the resin is a dissimilar material bonded to the metal electric field mitigation shield, stress occurs when the temperature rises due to the difference in the expansion coefficients of the materials, which reduces the adhesive strength and may lead to defects at the interface. In addition, special treatment of the metal surface may be necessary to increase adhesive strength.Furthermore, the electric field mitigation shield itself has a high electric field, and in models with high rated voltages, the electric field may penetrate the resin coating and cause insulation breakdown, so the surface electric field of the electric field mitigation shield must also be sufficiently reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-110012 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-182877 [Patent Document 3] Japanese Patent Application Laid-Open No. 2001-338557 [Patent Document 4] Japanese Patent Application Publication No. 2017-165811 Summary of the Invention [Problem to be solved by the invention]

[0004] An embodiment of the present invention aims to reduce the electric field at high electric field points in a vacuum interrupter. [Means for solving the problem]

[0005] According to one embodiment, a vacuum valve is provided which comprises an insulating container having an opening and a vacuum container having a sealing metal fitting joined to the opening via a joint, a pair of electrodes detachably arranged opposite each other within the vacuum container, and an electric field mitigation shield arranged to cover the sealing metal fitting and the joint, wherein the electric field mitigation shield includes a conductive region containing a conductive resin and an insulating region containing an insulating resin arranged on at least a portion of the conductive region. [Brief explanation of the drawings]

[0006] [Figure 1] 1 is a schematic cross-sectional view illustrating an example of a vacuum interrupter according to an embodiment. [Figure 2] 2 is a partially enlarged view showing a first example of the electric field mitigation shield used in FIG. 1. FIG. [Figure 3] 1. FIG. 4 is a partially enlarged view showing a second example of the electric field mitigation shield used in FIG. [Figure 4] 1. FIG. 4 is a partially enlarged view showing a third example of the electric field mitigation shield used in FIG. [Figure 5] FIG. 1 is a graph showing the relationship between CNF content and electrical conductivity. [Figure 6] FIG. 1 is a graph showing the relationship between CNF content and relative dielectric constant. [Figure 7] FIG. 1 is a graph showing the relationship between the BTO content and the relative dielectric constant. DETAILED DESCRIPTION OF THE INVENTION

[0007] The vacuum interrupter according to the embodiment includes an insulating container having an opening, a vacuum container having a sealing metal fitting joined to the opening via a joint, a pair of electrodes detachably arranged opposite each other within the vacuum container, and an electric field mitigation shield provided to cover the sealing metal fitting and the joint. The electric field mitigation shield includes a conductive region containing a conductive resin and an insulating region containing an insulating resin provided on at least a portion of the conductive region.

[0008] According to the embodiment, by using a conductive resin instead of metal for the conductive region of the electric field mitigation shield and an insulating resin for the insulating region, it is possible to obtain an electric field mitigation shield in which the conductive region and the insulating region have sufficient adhesive strength and are less likely to develop defects such as peeling, and no special treatment is required for bonding the conductive region and the insulating region. By using such an electric field mitigation shield, it is possible to mitigate the electric field in high-electric-field areas of the vacuum interrupter.

[0009] Hereinafter, embodiments will be described with reference to the drawings. The disclosure is merely an example, and appropriate modifications that are easily conceivable by those skilled in the art while maintaining the gist of the invention are naturally included within the scope of the present invention. Furthermore, in order to clarify the explanation, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in this specification and each drawing, elements similar to those described above with reference to the previous drawings may be designated by the same reference numerals, and detailed descriptions may be omitted as appropriate.

[0010] FIG. 1 is a schematic cross-sectional view showing an example of a vacuum interrupter according to an embodiment. As shown in the figure, the vacuum interrupter 105 includes a vacuum vessel 100 having openings 10a, 10b at both ends and a cylindrical ceramic vessel 10 serving as an insulating vessel made of, for example, alumina porcelain, a fixed sealing metal fitting 11 joined to one opening 10a via a joint 31, and a movable sealing metal fitting 12 joined to the other opening 10b via a joint 32, and a vacuum is maintained within the vacuum vessel 100. A central opening is provided in the fixed sealing metal fitting 11, through which a fixed current-carrying shaft 13 is fixedly passed. A fixed contact 14 is fixed to the end of the fixed current-carrying shaft 13 within the ceramic vessel 10. A movable contact 15, which faces the fixed contact 14 and forms a pair of separable contacts, is fixed to the end of a movable current-carrying shaft 16 that movably passes through a central opening provided in the movable sealing metal fitting 12. The portion of this movable current-carrying shaft 16 closer to the movable sealing metal fitting 12 than the central portion extends outside the ceramic container 10, and a freely expandable cylindrical bellows 17 is disposed in this portion to provide an airtight seal. A free end 101 of the bellows 17 is sealed to the central portion of the movable current-carrying shaft 16, and a fixed end 102 is sealed to the central opening of the movable sealing metal fitting 12. A cylindrical arc shield 18 is provided around the fixed contact 14 and the movable current-carrying shaft 16. The arc shield is a conductor and can be made of a metal material such as stainless steel.

[0011] The vacuum interrupter 105 further includes, for example, a bowl-shaped fixed electric field reduction shield 19-1 provided around the fixed sealing metal fitting 11, which forms the outer periphery of the vacuum vessel 100. The fixed electric field reduction shield 19-1 is fixed to the fixed current-carrying shaft 13 and spaced apart from the vacuum vessel 100 and its components, such as the fixed sealing metal fitting 11 and the ceramic vessel 10. The vacuum interrupter 105 may also include a bowl-shaped movable electric field reduction shield 20-1 provided around the movable sealing metal fitting 12. The movable electric field reduction shield 20-1 is fixed to the movable current-carrying shaft 16 and spaced apart from the vacuum vessel 100 and its components, such as the movable sealing metal fitting 12 and the ceramic vessel 10. An insulating atmosphere may be provided around the vacuum vessel 100, in which the fixed electric field reduction shield 19-1 and the movable electric field reduction shield 20-1 are provided.

[0012] FIG. 2 is a partially enlarged view showing a first example of the electric field mitigation shield used in FIG. As shown in the figure, the electric field reduction shield 19-1 of the first example has a conductive region 19b containing a conductive resin and an insulating region 19a containing an insulating resin provided on at least a portion of the surface of the conductive region 19b. Here, the conductive region 19b is the main body of the fixed-side electric field reduction shield 19-1 and has a similar bowl shape. A surface layer containing an insulating resin is provided as the insulating region 19a from the outer surface 19b-1 of the conductive region 19b to the inner surface (inner side) 19b-2 of the trunk portion. The conductive region 19b is exposed on the inner surface 19b-3 of the waist portion of the conductive region 19b.

[0013] The rim portion 19-1a of the electric field mitigation shield 19-1 extends further toward the fixed contact 14 than the joint 31 between the fixed sealing metal fitting 11 and the opening of the ceramic container 10 so as to fully cover the triple junction 30 at the joint 31. Here, the triple junction 30 is, for example, a triple point of the ceramic of the ceramic container 10, the metal of the fixed sealing metal fitting 11, and the insulator of the insulating atmosphere, and creates a relatively high electric field, which can be the starting point of dielectric breakdown.

[0014] In this way, by including resin in the conductive region 19b and insulating region 19a of the electric field mitigation shield 19-1, stress caused by temperature increases and other factors is reduced. Furthermore, since the same resin material is used, the two regions are well-matched, providing sufficient adhesive strength, making it possible to obtain an electric field mitigation shield that is less prone to defects such as peeling between the conductive and insulating regions. Furthermore, there are no defects at the adhesive interface, and no special adhesive processing is required. In this way, by covering the triple junction 30, which is subject to a high electric field, with the electric field mitigation shield 19-1, the electric field at the high-electric field portion of the vacuum interrupter 105 can be mitigated.

[0015] In addition, the electric field mitigation shield 20-1 has a conductive region 20b containing a conductive resin and an insulating region 20a containing an insulating resin provided on at least a portion of the surface of the conductive region 20b, and can mitigate the electric field at high electric field locations of the vacuum valve 105 in the same manner as the electric field mitigation shield 19-1.

[0016] To maintain an insulating atmosphere, the vacuum vessel 100 equipped with the fixed electric field mitigation shield 19-1 and the movable electric field mitigation shield 20-1 can be housed in a case (not shown). Examples of insulating atmospheres include insulating gases such as SF6 gas and dry air. Dry air can be used to avoid the use of greenhouse gases. A high dielectric constant region containing a high dielectric constant resin may be further provided between the conductive region and the insulating region.

[0017] FIG. 3 shows a partially enlarged view of a second example of the electric field mitigation shield used in FIG. As shown in the figure, electric field reduction shield 19-2 of the second example has a configuration similar to that of the first example shown in Figure 2, except that it has conductive region 19b containing a conductive resin, insulating region 19a containing an insulating resin provided on at least a portion of the surface of conductive region 19b, and high-dielectric-constant region 19c containing a high-dielectric-constant resin provided between conductive region 19b and insulating region 19a. High-dielectric-constant region 19c is provided from outer surface 19b-1 to inner surface 19b-2 of conductive region 19b, similar to insulating region 19a, and conductive region 19b is exposed on inner surface 19b-3 of the waist portion of conductive region 19b.

[0018] According to the second example of the electric field mitigation shield, by further arranging high-dielectric-constant region 19c, which contains a high-dielectric-constant resin with a higher dielectric constant than the insulating resin of insulating region 19a, between conductive region 19b and insulating region 19a, it is possible to further reduce the electric field on the surface of the conductive resin, reducing the possibility of dielectric breakdown through the coated resin, maintaining good adhesive strength between conductive region 19b and insulating region 19a, and reducing the occurrence of defects such as peeling. Use of the second example of the electric field mitigation shield can sufficiently mitigate the electric field in high-field areas of the vacuum interrupter.

[0019] The conductive resin may have a conductivity of 10^-1 S / m or more. Preferably, the conductivity of the conductive resin may be 10^-1 S / m to 10^4 S / m. Furthermore, the insulating resin may have a conductivity of 10^-10 S / m or less. The high dielectric constant resin has a higher dielectric constant than the insulating resin, and can have insulating properties, and can have a conductivity of 10^-8 S / m or less.

[0020] The insulating resin and the conductive resin may be selected so as to chemically bond with each other, and the high dielectric constant resin may be selected so as to chemically bond with the insulating resin and the conductive resin. Examples of resins that chemically bond include thermosetting resins such as epoxy resin, phenolic resin, melamine resin, urea resin, polyurethane resin, unsaturated polyester resin, polyimide resin, and silicone resin, as well as resins that harden through a chemical reaction caused by ultraviolet light (light energy), such as epoxy and acrylic resins. Using resins that chemically bond to each other makes them easier to blend together during bonding, resulting in good adhesive strength.

[0021] Resins that do not chemically bond can also be used, and examples of such resins include thermoplastic resins such as polyethylene, polyvinyl chloride, polypropylene, polystyrene, ABS resin, PMMA (acrylic) resin, PET resin, polyacetal, polyether ether ketone, fluororesin, polycarbonate, nylon, engineering plastics, and super engineering plastics.

[0022] Furthermore, the insulating resin and the conductive resin can have similar main chains. By using resins having similar main chains, even when resins that do not chemically bond are used, they can easily blend with each other during bonding, and sufficient adhesive strength can be obtained. Furthermore, the main chains of the high dielectric constant resin, the main chains of the insulating resin, and the main chains of the conductive resin can be similar to each other. By using resins that chemically bond and resins having similar main chains, they can easily blend with each other during bonding, and sufficient adhesive strength can be obtained.

[0023] The insulating resin, conductive resin, and high dielectric constant resin can be made into a composite material containing a base material containing an insulating resin material and a conductive particle component dispersed in the base material. The conductive particles may be, for example, conductive fibrous particles, which have a small particle diameter and a long length, a fibrous aspect ratio, and can be arranged so as to be randomly oriented and dispersed in the high-dielectric-constant resin.

[0024] The conductive fibrous particles may be those having a conductivity comparable to that of metals and made up of a six-membered carbon ring network, taking into consideration dispersion in hydrophobic liquids such as resins. Examples of materials composed of a six-membered carbon ring network include carbon nanotubes, carbon nanofibers, carbon microfibers, and graphene. Furthermore, carbon nanofibers can be used as materials composed of a six-membered carbon ring network. Carbon nanofibers have a larger diameter than carbon nanotubes, about several hundred nanometers.

[0025] The conductive fibrous particles used in the embodiment can have a volume resistivity of 10^-1 Ωcm or less. The conductive fibrous particles 2 used in the embodiment can have a particle diameter of 100 nm to 10 μm, a length of 1 μm to 100 μm, and an aspect ratio (length to particle diameter) of 1.25 to 100. When the conductive fibrous particles 2 have the above sizes, the effect of increasing the relative dielectric constant can be sufficiently obtained, and the particles can be made less likely to aggregate with each other. The resin in which the conductive fibrous particles are dispersed can be, for example, an epoxy resin, etc. When the resin is an epoxy resin, a polyetheramine can be used as a curing agent.

[0026] In addition, in order to increase the dielectric constant of high dielectric constant resin, there are methods of filling it with high dielectric constant inorganic particles (non-conductive particles) or metal particles such as silver. Examples of inorganic particles with a high dielectric constant include barium titanate (BTO), strontium titanate, titanium oxide, aluminum oxide, barium magnesium niobate, barium neodymium titanate, and zirconia. When high-dielectric-constant inorganic particles are used, the loading tends to be higher than when conductive fibrous particles are used. When metal particles are used, the surface area of ​​the metal particles facing each other is smaller than that of conductive fibrous particles, so the loading also tends to be higher than that of conductive fibrous particles.

[0027] In addition to the high-dielectric inorganic particles and metal particles, non-conductive particles can be added to change various properties, such as mechanical, thermal, and resin fluidity. Examples of materials that can be used to improve mechanical properties include crushed silica, spherical silica, rubber particles, aluminum oxide, and magnesium oxide. To adjust the resin's fluidity (viscosity), dispersing fine silica particles of several tens of nanometers to several micrometers contributes to an increase in viscosity, while dispersing spherical silica particles exceeding 10 micrometers can lower the viscosity compared to dispersing the same amount of crushed silica. To improve thermal properties, examples of materials that can be used include boron nitride, aluminum nitride, silicon nitride, and silicon carbide, which improve thermal conductivity.

[0028] The non-conductive particles can have a volume resistivity of 10^10 Ωcm or more. The conductivity of the conductive resin can be set to, for example, a range of 10^5 to 10^9 S / m, which is similar to that of metals. However, if the conductivity of the resin (approximately 10^-20 S / m) is increased to the above range, a considerable amount of conductive particles will tend to be filled, which may increase the viscosity of the resin and make it difficult to handle. Furthermore, since the conductive resin used in the embodiment is not used on a path through which current flows, a conductivity in the range of 10^-1 to 10^4 S / m is considered sufficient to achieve the effect of electric field relaxation.

[0029] FIG. 4 shows a partially enlarged view of a third example of the electric field mitigation shield used in FIG. As shown in the figure, the electric field mitigation shield 19-3 of the third example is a variation of the electric field mitigation shield 19-2 of the second example, and the conductive region, high-permittivity region, and insulating region are not clearly separated. For example, the torso region has a conductive region 19e containing a conductive resin, a high-permittivity region 19f containing a high-permittivity resin and provided outside the conductive region 19e, and an insulating region 19d containing an insulating resin and provided outside the high-permittivity region 19f. The conductivity continuously decreases from the conductive region 19e through the high-permittivity region 19f to the insulating region 19d. The waist region has a conductive region 19e-1, a high-permittivity region 19f-1 provided outside the conductive region 19e-1, and an insulating region 19d-1 containing an insulating resin and provided outside the high-permittivity region 19f-1. The conductivity continuously decreases from the conductive region 19e-1 through the high-permittivity region 19f-1 to the insulating region 19d-1.

[0030] Even in cases where the conductivity decreases continuously from the conductive region through the high dielectric constant region to the insulating region, as in electric field mitigation shield 19-3, as in electric field mitigation shield 19-2, good adhesive strength is maintained between conductive regions 19e, 19e-1, high dielectric constant regions 19f, 19f-1, and insulating regions 19d, 19d-1, reducing the occurrence of defects such as peeling, and adequately mitigating the electric field in high electric field areas of the vacuum interrupter.

[0031] The high-dielectric resin, insulating resin, and conductive resin can be resins having the same main chain. The high-dielectric resin and the conductive resin can contain the same conductive particles. In this case, the conductive particle component in the electric field reduction shield can have a concentration gradient from the conductive region to the insulating region. The conductive fibrous particles described above can be used as the conductive particles. Furthermore, as necessary, high-dielectric inorganic particles, etc., can be used as in the second example.

[0032] Example 1 The following experiment was carried out to measure the electrical conductivity of resins that can be used in the electric field mitigation shield according to the embodiment. The resin base was bisphenol A and the curing agent was polyetheramine. The conductive particles were carbon nanofibers (CNF) with a diameter of 200-800 nm and a length of 1-20 μm. A planetary mixer was used to mix the base resin and curing agent and to disperse the CNF. First, the base resin and CNF were mixed, and then the curing agent was added and mixed. After all the ingredients were mixed, the mixture was poured into a mold and heated at 60°C for approximately 3 hours to harden. After that, it was removed from the mold and a cured epoxy resin containing CNF was created.

[0033] Cured resins were prepared in the same manner by varying the CNF content in the resin. The electrical conductivity of each of the obtained cured epoxy resin products was measured. FIG. 5 shows a graph illustrating the relationship between CNF content and electrical conductivity. As shown, the graph in Figure 5 plots the measured conductivity values ​​for CNF contents of 1, 3, and 5% by volume. As a result, it was found that the conductivity of the cured epoxy resin containing 5% by volume of CNF was 1.14*10^-8 S / m, which is significantly higher than the conductivity of 10^-13 S / m of epoxy resin (insulating resin) without CNF mixed in. By further increasing the CNF loading amount, epoxy resin containing CNF can be made to have the desired conductivity as a conductive resin.

[0034] Example 2 In the same manner as in Example 1, the CNF content in the resin was varied, and each cured epoxy resin material containing CNF was prepared in the same manner. The relative dielectric constant of each of the obtained cured epoxy resin products was measured at a measurement frequency of 100 kHz. FIG. 6 is a graph showing the relationship between the CNF content and the relative dielectric constant. As shown, the graph in FIG. 6 plots the measured values ​​of the relative dielectric constant when the CNF content is 1, 3, and 5% by volume. As a result, it was found that while the relative dielectric constant of epoxy resin without CNF is 4 (S / m), the relative dielectric constant of cured epoxy resin with a CNF content in the range of 1 to 5% by volume is sufficiently higher than that of epoxy resin. Furthermore, as shown in Figure 5, when the CNF content is 1 to 3%, the conductivity is 10^-8 S / m or less, providing sufficient insulation. Epoxy resins with a CNF content in the range of 1 to 3% by volume can be suitably used as high-dielectric-constant resins.

[0035] Example 3 Cured epoxy resin materials containing BTO were prepared in the same manner as in Example 1, except that 18, 30, 40, and 50 volume % of BTO were used instead of 1, 3, and 5 volume % of CNF. The relative dielectric constant of each of the obtained cured epoxy resin products was measured at a measurement frequency of 100 kHz. FIG. 7 is a graph showing the relationship between the BTO content and the relative dielectric constant.

[0036] As shown, the graph of FIG. 7 plots measured values ​​of the relative dielectric constant when the BTO content is 18, 30, 40, and 50% by volume.

[0037] As a result, it was found that while the relative dielectric constant of epoxy resin without BTO was 4 (S / m), the relative dielectric constant of cured epoxy resin with BTO content in the range of 18, 30, 40, and 50 volume % was significantly higher than that of epoxy resin.

[0038] In order to increase the dielectric constant of high-dielectric resins, BTO can be used as a high-dielectric inorganic particle, but it has been found that the amount of filling tends to be greater than when conductive fibrous particles are used.

[0039] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0040] 10...insulating container, 10a, 10b...opening, 31...joint, 11, 12...sealing metal fitting, 100...vacuum container, 14, 15...contact (electrode), 19-1, 19-2, 19-3, 20-1...electric field mitigation shield, 19a...insulating region, 19b...conductive region, 19c...high dielectric constant region, 31, 32...joint, 105...vacuum valve

Claims

1. a vacuum vessel having an insulating vessel having an opening and a sealing metal fitting joined to the opening via a joint; a pair of electrodes detachably disposed opposite each other within the vacuum vessel; an electric field mitigation shield provided to cover the sealing metal fitting and the joint, The electric field mitigation shield is a vacuum interrupter including a conductive region containing a conductive resin, and an insulating region containing an insulating resin provided on at least a portion of the conductive region.

2. 2. The vacuum interrupter according to claim 1, wherein the insulating resin is chemically bonded to the conductive resin.

3. 3. The vacuum interrupter according to claim 2, wherein the insulating resin has a main chain similar to that of the conductive resin.

4. 2. The vacuum interrupter according to claim 1, further comprising a high dielectric constant region containing a high dielectric constant resin between the conductive region and the insulating region.

5. 5. The vacuum interrupter according to claim 4, wherein the high-permittivity resin is chemically bonded to the insulating resin and the conductive resin.

6. 5. The vacuum interrupter according to claim 4, wherein the main chain of the high dielectric constant resin is the same as the main chain of the insulating resin and the main chain of the conductive resin.

7. 5. The vacuum interrupter according to claim 4, wherein the high dielectric constant resin comprises a base material containing an insulating resin and a conductive particle component dispersed in the base material.

8. 5. The vacuum interrupter according to claim 4, wherein the electric field mitigation shield has a conductivity that decreases continuously from the conductive region through the high dielectric constant region to the insulating region.

9. 2. The vacuum valve according to claim 1, wherein the electric field mitigation shield and the vacuum vessel are spaced apart from each other.

10. 2. The vacuum valve according to claim 1, wherein the vacuum vessel and the electric field mitigation shield are surrounded by an insulating atmosphere.

11. 11. The vacuum valve according to claim 10, wherein the insulating atmosphere is an insulating gas.

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