Electric field relaxation structure, vacuum valve, method for manufacturing electric field relaxation structure, and method for manufacturing vacuum valve

Abstract

This electric field relaxation structure is provided with: a ceramic insulator (2); a ceramic layer (6) that is laminated on the ceramic insulator (2), includes zinc oxide, and has a nonlinear voltage-resistance characteristic; and an insulating layer (7) that is laminated on the ceramic layer (6). Thus, the current-carrying area is not limited, and peeling due to heat generation can be suppressed.

Description

Electric field relaxation structure, vacuum interrupter, method of manufacturing electric field relaxation structure, and method of manufacturing vacuum interrupter

[0001] The present disclosure relates to an electric field relaxation structure, a vacuum interrupter, a method for manufacturing an electric field relaxation structure, and a method for manufacturing a vacuum interrupter.

[0002] Insulation design is carried out for devices with high electric field areas. The electric field is a major consideration, and the device is designed to keep the electric field for the applied voltage below the allowable value. If the structure has a margin for the electric field compared to the allowable value, the insulation distance can be further shortened, making it possible to further miniaturize the device. Therefore, reducing the electric field is a means of miniaturizing the device.

[0003] A known method for mitigating the electric field is to place a voltage nonlinear resistance material in the high electric field area. For example, in Patent Document 1, a composite material made of a compound (resin) of ZnO or SiC (ceramic voltage nonlinear resistance material filler) is applied to the inner or outer surface of the insulating container of a vacuum interrupter to improve the electric potential distribution.

[0004] Japanese Utility Model Application Publication No. 60-75940

[0005] In Patent Document 1, the current flows only through the ZnO or SiC filler, which limits the current-carrying area, which can lead to a localized increase in current density, generating heat and potentially causing peeling due to differences in thermal expansion.

[0006] The present disclosure has been made in view of the above, and aims to provide an electric field relaxation structure that does not limit the current-carrying area and can suppress peeling due to heat generation.

[0007] In order to solve the above-mentioned problems and achieve the objectives, the electric field relaxation structure of the present disclosure comprises a ceramic insulator, a ceramic layer having voltage nonlinear resistance characteristics containing zinc oxide laminated on the ceramic insulator, and an insulating layer laminated on the ceramic layer.

[0008] The electric field relaxation structure of the present disclosure has the advantage that the current-carrying area is not limited and peeling due to heat generation can be suppressed.

[0009] 4 is a cross-sectional view showing the layer structure of the electric field relaxation structure according to the first embodiment; FIG. 5 is a diagram showing the relationship between the electric field and current characteristics of the varistor according to the first embodiment; FIG. 6 is a diagram showing a method for manufacturing a ceramic layer having voltage nonlinear resistance characteristics of the electric field relaxation structure according to the first embodiment; FIG. 7 is a cross-sectional view showing the layer structure of the electric field relaxation structure according to the second embodiment; FIG. 8 is a cross-sectional view showing the layer structure of a modified electric field relaxation structure according to the second embodiment;

[0010] An electric field relaxation structure, a vacuum interrupter, a method for manufacturing an electric field relaxation structure, and a method for manufacturing a vacuum interrupter according to embodiments will be described in detail below with reference to the drawings.

[0011] 1 is a cross-sectional view showing the layer configuration of an electric field relaxation structure according to embodiment 1. The electric field relaxation structure includes a ceramic insulator 2, a ceramic layer 6 having voltage nonlinear resistance characteristics, and an insulating layer 7. In this electric field relaxation structure, the ceramic layer 6 is stacked on the ceramic insulator 2, and the insulating layer 7 is stacked on the ceramic layer 6.

[0012] The voltage-nonlinear resistor realized by the ceramic layer 6 has the property of becoming an insulator when a low electric field is applied and a conductor when a high electric field is applied, and is a material that reversibly exhibits an insulator and a conductor across a threshold electric field. Therefore, voltage-nonlinear resistors do not follow Ohm's law and are called varistors. Figure 2 shows the relationship between the electric field and current characteristics of the varistor according to the first embodiment. As shown in Figure 2, the varistor has electrical characteristics in which its resistance changes across a threshold electric field Ec beyond the low electric field region, and current flows rapidly in an electric field region above the threshold electric field Ec. A varistor is a material primarily composed of zinc oxide, with trace amounts of several minor components added, and then fired. A varistor is a material whose performance, such as the magnitude of the threshold electric field Ec and the volume resistance when insulator, can be controlled by its composition.

[0013] The ceramic layer 6, which is the voltage nonlinear resistor in the first embodiment, is manufactured as follows. First, zinc oxide powder, the main raw material, is weighed. Next, bismuth oxide, antimony oxide, chromium oxide, nickel oxide, manganese oxide, cobalt oxide, and silicon oxide are added as secondary ingredients so that the total amount of the zinc oxide powder is 100 mol %, and the resulting mixture is crushed and mixed using water. A binder to bond the raw materials together and a dispersant to uniformly disperse the raw materials are added. For example, the raw materials may be 96.5 mol % zinc oxide powder, 0.5 mol % bismuth oxide, 0.5 mol % antimony oxide, 0.5 mol % chromium oxide, 0.5 mol % nickel oxide, 0.5 mol % manganese oxide, 0.5 mol % cobalt oxide, and 0.5 mol % silicon oxide. It is recommended that the raw materials be crushed and mixed uniformly to achieve the same average particle size.

[0014] The mixed material is then sprayed into a high-temperature atmosphere of 100° C. or higher to spray-dry the raw materials, thereby obtaining spherical granules 1 in which raw materials such as zinc oxide, bismuth oxide, antimony oxide, chromium oxide, nickel oxide, manganese oxide, cobalt oxide, and silicon oxide are uniformly aggregated.

[0015] Next, the ceramic insulator 2 and the spherical granules 1 are integrated using a mold. FIG. 3 is a diagram showing a method for manufacturing a ceramic layer 6 having voltage nonlinear resistance characteristics in an electric field relaxation structure according to the first embodiment. As shown in FIG. 3, for example, a mold composed of a die 3, an upper punch 4, and a lower punch 5 is used. First, the ceramic insulator 2 is placed on the lower punch 5 of the mold, and the spherical granules 1 are poured onto the ceramic insulator 2. Next, the upper punch 4 is lowered to apply pressure, thereby forming the spherical granules 1 into a compact. This integrates the ceramic insulator 2 and the compact. Then, by firing, as described below, a ceramic layer 6 having voltage nonlinear resistance characteristics is obtained.

[0016] As the ceramic insulator 2, various ceramics such as aluminum oxide, titanium oxide, chromium oxide, silicon oxide, glass, silicon nitride, silicon carbide, zirconium dioxide, mullite, stearite, forsterite, cordierite, and aluminum nitride can be used, but aluminum oxide is preferable from the viewpoint of cost. In this case, if the ceramic insulator 2 is a material having an uneven surface, a higher adhesion to the ceramic layer 6 can be obtained due to the anchor effect. Thereafter, the ceramic insulator 2 and the ceramic layer 6 having voltage nonlinear resistance characteristics are fired in an integrated state at a temperature of 1000°C or higher, whereby the ceramic layer 6 having voltage nonlinear resistance characteristics can be produced from the compact.

[0017] The insulating layer 7 can be made of various insulating materials such as resin, ceramic, and glass.

[0018] As described above, in the first embodiment, the voltage nonlinear resistor is made of only ceramic and does not contain resin, so that the current-carrying area is not limited, and peeling due to heat generation can be suppressed.

[0019] 4 is a cross-sectional view showing the layer structure of an electric field relaxation structure according to embodiment 2. In embodiment 2, a glass layer 8 is provided between the ceramic insulator 2 and the ceramic layer 6 having voltage-nonlinear resistance characteristics, thereby improving the adhesion between the ceramic insulator 2 and the ceramic layer 6 having voltage-nonlinear resistance characteristics.

[0020] The glass layer 8 acts as an adhesive that connects the ceramic insulator 2 and the ceramic layer 6 having voltage nonlinear resistance characteristics, thereby improving adhesion. For example, by using a ceramic insulator 2 that has a glass layer 8 on its surface in advance and carrying out the manufacturing method described with reference to FIG. 3, the electric field relaxation structure shown in FIG. 4 is created.

[0021] FIG. 5 is a cross-sectional view showing the layer structure of a modified example of the electric field relaxation structure according to the second embodiment. The compact is in a state where pressure is applied to spherical granules 1, and voids exist between the spherical granules 1. Firing expels the voids to the outside, resulting in a dense structure. Therefore, when a ceramic insulator 2 having a glass layer 8 between the ceramic insulator 2 and the ceramic layer 6 having voltage-nonlinear resistance characteristics is used, the glass layer 8 can penetrate into the voids, as shown in FIG. 5, and after firing, an interface layer 9 can be formed in which the glass contained in the glass layer 8 and the ceramic contained in the ceramic layer 6 having voltage-nonlinear resistance characteristics coexist.

[0022] The configuration shown in Figure 5 allows for even stronger adhesion between the ceramic insulator 2 and the ceramic layer 6 having voltage-nonlinear resistance characteristics. This layer configuration can be created by slowing down the firing rate of the ceramic layer 6 having voltage-nonlinear resistance characteristics, softening the glass before firing the compact, and allowing the glass to penetrate into the gaps in the compact. From the perspective of permeability of the glass layer 8, a porosity of 20% or more is desirable. Furthermore, from the perspective of handling the compact, a porosity of 80% or less is desirable. The porosity can be determined, for example, by calculating the bulk density from the weight and apparent volume of the compact, and then calculating the ratio of the calculated bulk density to the true density after firing.

[0023] Thus, according to embodiment 2, a glass layer 8 is provided between the ceramic insulator 2 and the ceramic layer 6 having voltage-nonlinear resistance characteristics, or an interface layer 9 is provided in which the glass contained in the glass layer 8 and the ceramic contained in the ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, thereby making the adhesion between the ceramic insulator 2 and the ceramic layer 6 having voltage-nonlinear resistance characteristics stronger.

[0024] 6 is a cross-sectional view showing the layer configuration of an electric field relaxation structure according to embodiment 3. Methods for forming the insulating layer 7 include a first method in which the insulating layer 7 is newly formed after the ceramic layer 6 having voltage-nonlinear resistance characteristics is formed, and a second method in which the insulating layer 7 is formed simultaneously with the formation of the ceramic layer 6 having voltage-nonlinear resistance characteristics.

[0025] In the first method, after firing the ceramic layer 6 having voltage nonlinear resistance characteristics, a resin can be applied to the surface by spraying or brushing and then cured to form the insulating layer 7. Alternatively, a glass paste can be applied by spraying and the glass can be fired to form the insulating layer 7 made of glass.

[0026] In the second method, after forming a compact from the spherical granules 1, a precursor material for the insulating layer 7 is applied to the top surface of the compact, and the precursor and the compact are reacted to form the insulating layer 7. The precursor material is a paste made by mixing bismuth oxide, antimony oxide, and / or silicon oxide with an organic material. The insulating layer 7 is formed by firing the compact to form the ceramic layer 6 having voltage-nonlinear resistance characteristics, resulting in a reaction between the compact and the precursor. When the firing temperature exceeds 1100°C, the reaction between the compact and the precursor becomes more active, resulting in an interface layer 10 in which the insulator contained in the insulating layer 7 and the ceramic contained in the ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, as shown in FIG. 6 . This interface layer 10 strengthens the adhesion between the ceramic layer 6 having voltage-nonlinear resistance characteristics and the insulating layer 7, making them less likely to peel off.

[0027] 7 is a cross-sectional view showing a layer structure of a modified example of the electric field relaxation structure according to the third embodiment. In the electric field relaxation structure of FIG. 7, the insulating layer 7 has a two-layer structure consisting of an insulating layer 71 and an insulating layer 72. The insulating layer 71 and the insulating layer 72 are made of different materials. One of the insulating layer 71 and the insulating layer 72 contains Zn. ２ SiO ４ or Zn ７ Sb ２ O １２ If the structure includes the above, the insulating properties can be further improved, and the adhesion between the ceramic layer 6 having voltage nonlinear resistance properties and the insulating layer 7 becomes stronger.

[0028] Thus, according to embodiment 3, an interface layer 10 is provided between the ceramic layer 6 having voltage-nonlinear resistance characteristics and the insulating layer 7, in which the insulator contained in the insulating layer 7 and the ceramic contained in the ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, thereby making the adhesion between the ceramic layer 6 having voltage-nonlinear resistance characteristics and the insulating layer 7 stronger.

[0029] Fourth Embodiment Figure 8 is a cross-sectional view showing the layer configuration of an electric field relaxation structure according to a fourth embodiment. The electric field relaxation structure of Figure 8 includes a ceramic insulator 2, a glass layer 8, a ceramic layer 6 having voltage-nonlinear resistance characteristics, an interface layer 10 in which the insulating layer 7 and the ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, and an insulating layer 7. In this electric field relaxation structure, the glass layer 8, the ceramic layer 6, the interface layer 10, and the insulating layer 7 are stacked in this order on the ceramic insulator 2. The electric field relaxation structure of Figure 8 is produced by combining the manufacturing method of the electric field relaxation structure of Figure 4 and the manufacturing method of the electric field relaxation structure of Figure 6.

[0030] Fig. 9 is a cross-sectional view showing the layer structure of a modified example of the electric field relaxation structure according to the fourth embodiment. The electric field relaxation structure of Fig. 9 includes a ceramic insulator 2, a glass layer 8, a ceramic layer 6 having voltage-nonlinear resistance characteristics, an interface layer 10 in which an insulating layer 71 and a ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, and two-layer insulating layers 71 and 72. In this electric field relaxation structure, the glass layer 8, the ceramic layer 6, the interface layer 10, and the two-layer insulating layers 71 and 72 are sequentially stacked on the ceramic insulator 2. The electric field relaxation structure of Fig. 9 is fabricated by combining the manufacturing method of the electric field relaxation structure of Fig. 4, the manufacturing method of the electric field relaxation structure of Fig. 6, and the manufacturing method of the electric field relaxation structure of Fig. 7.

[0031] Fig. 10 is a cross-sectional view showing the layer structure of a modified example of the electric field relaxation structure according to the fourth embodiment. The electric field relaxation structure of Fig. 10 includes a ceramic insulator 2, a glass layer 8, an interface layer 9 in which the glass layer 8 and a ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, a ceramic layer 6 having voltage-nonlinear resistance characteristics, an interface layer 10 in which an insulating layer 7 and a ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, and an insulating layer 7. In this electric field relaxation structure, the glass layer 8, the interface layer 9, the ceramic layer 6, the interface layer 10, and the insulating layer 7 are sequentially stacked on the ceramic insulator 2. The electric field relaxation structure of Fig. 10 is fabricated by combining the manufacturing method of the electric field relaxation structure of Fig. 5 and the manufacturing method of the electric field relaxation structure of Fig. 6.

[0032] FIG. 11 is a cross-sectional view showing a layer structure of a modified example of the electric field relaxation structure according to the fourth embodiment. The electric field relaxation structure of FIG. 11 includes a ceramic insulator 2, a glass layer 8, an interface layer 9 in which the glass layer 8 and a ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, a ceramic layer 6 having voltage-nonlinear resistance characteristics, an interface layer 10 in which an insulating layer 71 and a ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, and two-layer insulating layers 71 and 72. In this electric field relaxation structure, the glass layer 8, the interface layer 9, the ceramic layer 6, the interface layer 10, and the two-layer insulating layers 71 and 72 are sequentially stacked on the ceramic insulator 2. The electric field relaxation structure of FIG. 11 is fabricated by combining the manufacturing methods of the electric field relaxation structure of FIG. 5, the electric field relaxation structure of FIG. 6, and the electric field relaxation structure of FIG. 7.

[0033] Fifth Embodiment In the fifth embodiment, a vacuum interrupter to which the above-described electric field relaxation structure is applied will be described. FIG. 12 is a cross-sectional view showing the configuration of a vacuum interrupter 11 according to the fifth embodiment. FIG. 12 shows the vacuum interrupter 11 in a closed state with its contacts closed. The vacuum interrupter 11 includes a fixed electrode 12, a movable electrode 13, a fixed contact 14, a movable contact 15, a bellows 16, a fixed end plate 17, a movable end plate 18, an arc shield 19, a ceramic insulator 21, and a ceramic insulator 22. The ceramic insulators 21 and 22 correspond to the ceramic insulator 2 in the first to fourth embodiments. The first electrode corresponds to the fixed electrode 12 and the fixed contact 14, and the second electrode corresponds to the movable electrode 13 and the movable contact 15.

[0034] The vacuum interrupter 11 comprises an arc shield 19, ceramic insulators 21, and ceramic insulators 22, which form, for example, a cylindrical vacuum insulating container. A fixed end plate 17 and a movable end plate 18 are sealed to circular openings at both ends of the vacuum insulating container. The fixed electrode 12 is fixed to the fixed end plate 17 by brazing, with the fixed electrode 12 passing through the fixed end plate 17. A fixed contact 14 is fixed to the end of the fixed electrode 12 inside the vacuum insulating container by brazing.

[0035] The movable electrode bar 13 is disposed so as to pass through the movable end plate 18. A movable contact 15, which is capable of freely contacting and separating from the fixed contact 14, is fixed to the end of the movable electrode bar 13 by brazing, facing the fixed contact 14. That is, the movable contact 15 contacts or separates from the fixed contact 14 according to the movement of the movable electrode bar 13. A freely expandable bellows 16 is disposed in the middle of the movable electrode bar 13.

[0036] The ceramic insulator 21 is fixed to the fixed end plate 17 by brazing, and the ceramic insulator 22 is fixed to the movable end plate 18 by brazing. In the vacuum insulating vessel, the arc shield 19 is fixed to the divided ceramic insulators 21, 22 by brazing so as to be sandwiched between them. In other words, the arc shield 19 is provided between the ceramic insulators 21, 22 so as to surround the fixed contact 14 and the movable contact 15. The arc shield 19 is made of a metal such as stainless steel.

[0037] In the fifth embodiment, an electric field relaxation layer 20 is laminated and fixed to the outer peripheral surfaces of the ceramic insulators 21 and 22 . 1 , the glass layer 8, the ceramic layer 6, and the insulating layer 7 having voltage-nonlinear resistance characteristics in FIG. 4 , the glass layer 8, the interface layer 9, the ceramic layer 6, and the insulating layer 7 having voltage-nonlinear resistance characteristics in FIG. 5 , the ceramic layer 6, the interface layer 10, and the insulating layer 7 having voltage-nonlinear resistance characteristics in FIG. 6 , the ceramic layer 6, the interface layer 10, and the insulating layers 71 and 72 having voltage-nonlinear resistance characteristics in FIG. 7 , the glass layer 8, the ceramic layer 6, the interface layer 10, and the insulating layer 7 having voltage-nonlinear resistance characteristics in FIG. 8 , the glass layer 8, the ceramic layer 6, the interface layer 10, and the insulating layers 71 and 72 in FIG. 9 , the glass layer 8, the ceramic layer 6, the interface layer 10, and the insulating layers 71 and 72 in FIG. 10 , or the glass layer 8, the interface layer 9, the ceramic layer 6, the interface layer 10, and the insulating layers 71 and 72 in FIG. 11 .

[0038] Fig. 13 is a cross-sectional view showing the configuration of a modified example of the vacuum interrupter 11a according to the fifth embodiment. In the vacuum interrupter 11a of Fig. 13, the vacuum insulating container is made of an undivided ceramic insulator 23. The arc shield 19 is disposed on the inner peripheral surface of the ceramic insulator 23. In addition, an electric field relaxation layer 20 similar to that described above is laminated and fixed to the outer peripheral surface of the ceramic insulator 23.

[0039] Fig. 14 is a cross-sectional view showing the configuration of a modified example of the vacuum interrupter 11b according to the fifth embodiment. In the vacuum interrupter 11b of Fig. 14, an electric field relaxation layer 20 is laminated and fixed to the outer peripheral surface of one of the divided ceramic insulators 21, 22. In the case of Fig. 14, the electric field relaxation layer 20 is laminated and fixed to the outer peripheral surface of the ceramic insulator 22.

[0040] FIG. 15 is a plan view showing a modified example of the electric field relaxation structure used in the vacuum interrupter according to the fifth embodiment. FIG. 16 is a plan view showing a modified example of the electric field relaxation structure used in the vacuum interrupter according to the fifth embodiment. In the electric field relaxation structure of FIG. 15, electric field relaxation layers 20 are dispersedly disposed on the ceramic insulators 21, 22, and 23 shown in FIGS. 12 to 14. In the electric field relaxation structure of FIG. 15, a plurality of elongated electric field relaxation layers 20 extending in the extension direction of the fixed electrode bar 12 or the movable electrode bar 13 are intermittently disposed along the circumferential direction. In the electric field relaxation structure of FIG. 16, a plurality of elongated electric field relaxation layers 20 extending in the extension direction of the fixed electrode bar 12 or the movable electrode bar 13 are formed in a meandering wave shape, and a plurality of wave-shaped electric field relaxation layers 20 are intermittently disposed along the circumferential direction.

[0041] The ceramic insulators 21, 22, and 23 and the electric field relaxation layer 20 are manufactured by the method of embodiment 1. However, in the case of a cylindrical shape such as a vacuum valve, they can be produced by cold isostatic pressing using a rubber mold. In cold isostatic pressing, the ceramic insulators 21, 22, and 23 are set in a rubber mold, and spherical granules 1 are poured into the gap between the ceramic insulators 21, 22, and 23 and the rubber mold to fill it. After filling, the inlet for introducing the spherical granules 1 is sealed, and then isostatically pressed using water pressure. This produces a molded body subjected to the same pressure as uniaxial pressing using a mold. Then, firing is performed as described in embodiment 1, and an insulating layer 7 is provided in the same manner as in embodiment 1. This allows the production of a vacuum valve having an electric field relaxation structure in which a ceramic layer 6 having voltage nonlinear resistance characteristics and an insulating layer 7 are provided on the surface of the ceramic insulator 2.

[0042] Sixth Embodiment In a sixth embodiment, performance comparisons are made between Examples 1 to 17 and Comparative Examples 1 to 3. Fig. 17 is a diagram showing experimental results of various performances in the sixth embodiment, based on Examples 1 to 17 and Comparative Examples 1 to 3.

[0043] Regarding the layer structures of Examples 1 to 17 and Comparative Examples 1 to 3, "present" in the figures indicates that the layer structure is included, while a "hyphen" indicates that the layer structure is not included. For example, Example 1 has a layer structure including a ceramic insulator 2, a ceramic layer 6 having voltage nonlinear resistance characteristics, and an insulating layer 7. For each of Examples 1 to 17 and Comparative Examples 1 to 3, the performance such as the electric field relaxation effect, the insulating performance of the insulating layer, the peel strength of the layer, and the handling of the molded body was investigated.

[0044] The electric field relaxation effect was investigated using the vacuum interrupter 11 shown in Fig. 12. With the fixed electrode 12 connected to the voltage application side and the movable electrode 13 grounded, a voltage was applied and the potential of the arc shield 19 was measured to determine the electric field relaxation effect.

[0045] The ceramic insulator 2 was made of alumina with a thickness of 10 mm. The glass layer 8 was made of glass with a thickness of 1 mm and mainly composed of silicon oxide. The ceramic layer 6 having voltage nonlinear resistance characteristics was made of the material with the composition described in the first embodiment and had a thickness of 2 mm. The main component of the insulating layer 7 was Zn. ２ SiO ４ When the insulating layer 7 is composed of two insulating layers 71 and 72, the main component of the insulating layer 71 is Zn. ２ SiO ４ The insulating layer 72 has a thickness of 100 μm and is mainly composed of Zn. ７ Sb ２ O １２The interface layer 9, where the glass layer 8 and the ceramic layer 6 having voltage nonlinear resistance characteristics coexist, is made of glass containing silicon oxide as a main component and the ceramic layer 6 having voltage nonlinear resistance characteristics made of the material having the composition described in embodiment 1, and has a thickness of 10 μm. The interface layer 10, where the insulating layer 7 and the ceramic layer 6 having voltage nonlinear resistance characteristics coexist, is made of glass containing silicon oxide as a main component and the ceramic layer 6 having voltage nonlinear resistance characteristics made of the material having the composition described in embodiment 1, and has a thickness of 10 μm. ２ SiO ４ and coexist, and the thickness is 10 μm.

[0046] The peel strength is shown separately for the peel strength between the ceramic insulator 2 and the ceramic layer 6 having voltage-nonlinear resistance characteristics, and for the peel strength between the ceramic layer 6 having voltage-nonlinear resistance characteristics and the insulating layer 7. Furthermore, for the ceramic layer 6 having voltage-nonlinear resistance characteristics, the porosity of the molded body before firing was also investigated, and the relationship with handling of the molded body was examined.

[0047] Regarding the electric field relaxation effect, if it has an effect, it is represented by ◯, and if it has no effect, it is represented by ×. Regarding the insulating performance of the insulating layer, excellent represents excellent, good represents good and represents above the allowable level, and poor represents poor and represents below the allowable level. Regarding peel strength, excellent represents outstanding, excellent represents excellent, and good represents good. All represent levels that exceed the allowable value and are usable, with excellent being the best in order. Note that poor represents poor. Regarding handling of the molded body, excellent represents excellent, and good represents good and represents above the allowable level.

[0048] 17, Examples 1 to 17 all include at least a ceramic insulator 2, a ceramic layer 6 having voltage-nonlinear resistance characteristics, and an insulating layer 7, and all have an electric field relaxation effect. On the other hand, Comparative Examples 1, 2, and 3, which lack any one of the ceramic insulator 2, the ceramic layer 6 having voltage-nonlinear resistance characteristics, and the insulating layer 7, did not have an electric field relaxation effect. Note that in Comparative Example 1, since the ceramic insulator 2 was not included, a ceramic layer 6 having voltage-nonlinear resistance characteristics could not be produced.

[0049] Comparing Examples 1 to 17, the inclusion of glass layer 8 improved the peel strength between ceramic insulator 2 and ceramic layer 6 having voltage-nonlinear resistance characteristics from good to excellent. Furthermore, the inclusion of interface layer 9, in which glass layer 8 and ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, improved the peel strength between ceramic insulator 2 and ceramic layer 6 having voltage-nonlinear resistance characteristics from excellent to excellent, further increasing the strength. Furthermore, the inclusion of interface layer 10, in which insulating layer 7 and ceramic layer 6 having voltage-nonlinear resistance characteristics coexist, improved the peel strength between ceramic layer 6 having voltage-nonlinear resistance characteristics and insulating layer 7 to excellent or better. Furthermore, the inclusion of insulating layers 71 and 72 improved the peel strength to excellent, and the insulating performance of insulating layers 71 and 72 also improved from good to excellent.

[0050] Examples 2, 10, 11, 12, and 13 have the same layer structure, but the porosities before firing are different: 60%, 20%, 80%, 19%, and 81%, respectively. No differences were observed in performance or handling of the molded bodies between Examples 2, 10, and 11. On the other hand, in Example 12, which had a porosity of 19% before firing, the peel strength between the ceramic insulator 2 and the ceramic layer 6 having voltage nonlinear resistance characteristics was poor. In Example 13, which had a porosity of 81% before firing, the handling of the molded body was poor.

[0051] In Examples 8, 14, 15, 16, and 17, which have layer structures different from those of Examples 2, 10, 11, 12, and 13, the porosities before firing were 60%, 20%, 80%, 19%, and 81%, respectively. No differences were observed in performance or handling of the compacts in Examples 8, 14, and 15. On the other hand, in Example 16, which had a porosity of 19% before firing, the peel strength between the ceramic insulator 2 and the ceramic layer 6 having voltage nonlinear resistance characteristics was significantly reduced. Furthermore, in Example 17, which had a porosity of 81% before firing, the handling of the compact was significantly reduced. Therefore, it was found that a porosity before firing of 20% or more and 80% or less is desirable.

[0052] The configurations shown in the above embodiments are examples of the contents of the present disclosure, and may be combined with other known technologies, or embodiments may be combined with each other, and some of the configurations may be omitted or modified within the scope of the gist of the present disclosure.

[0053] 1 Spherical granules, 2, 21, 22, 23 Ceramic insulator, 3 Die, 4 Upper punch, 5 Lower punch, 6 Ceramic layer, 7, 71, 72 Insulating layer, 8 Glass layer, 9, 10 Interface layer, 11, 11a, 11b Vacuum valve, 12 Fixed electrode rod, 13 Movable electrode rod, 14 Fixed contact, 15 Movable contact, 16 Bellows, 17 Fixed end plate, 18 Movable end plate, 19 Arc shield, 20 Electric field relaxation layer.

Claims

1. An electric field relaxation structure comprising: a ceramic insulator; a ceramic layer containing zinc oxide and having voltage nonlinear resistance characteristics, laminated on the ceramic insulator; and an insulating layer laminated on the ceramic layer.

2. The electric field relaxation structure according to claim 1, wherein a glass layer is provided between the ceramic insulator and the ceramic layer.

3. The electric field relaxation structure according to claim 2, wherein an interface layer in which glass and ceramic having voltage nonlinear resistance characteristics coexist is provided between the glass layer and the ceramic layer.

4. An electric field relaxation structure according to any one of claims 1 to 3, characterized in that an interface layer is provided between the ceramic layer and the insulating layer, in which a ceramic containing zinc oxide and having voltage nonlinear resistance characteristics and an insulator contained in the insulating layer coexist.

5. The insulating layer is composed of at least two layers, and one of the two layers contains Zn. ２ SiO ４ or Zn ７ Sb ２ O １２ The electric field relaxation structure according to claim 4 , comprising:

6. A vacuum interrupter comprising: an insulating container made of the ceramic insulator; end plates fixed to both ends of the insulating container; a first electrode housed within the insulating container from one of the end plates; a second electrode housed within the insulating container from the other end plate and moving toward and away from the first electrode; and an arc shield provided in the middle of the insulating container, wherein a layer structure excluding the ceramic insulator in the electric field relaxation structure defined in any one of claims 1 to 5 is laminated on the outer circumferential surface of the insulating container.

7. A method for manufacturing an electric field relaxation structure, comprising the steps of: placing spherical granules of a material having voltage-nonlinear resistance characteristics on a ceramic insulator and applying pressure to create a molded layer of the material having voltage-nonlinear resistance characteristics; firing the ceramic insulator and the molded layer to create the ceramic insulator and a ceramic layer having voltage-nonlinear resistance characteristics; and providing an insulating layer on the ceramic layer having voltage-nonlinear resistance characteristics.

8. A method for manufacturing an electric field relaxation structure, comprising the steps of: placing spherical granules of a material having voltage-nonlinear resistance characteristics on a ceramic insulator and applying pressure to create a molded layer of the material having voltage-nonlinear resistance characteristics; applying a precursor material for an insulating layer to the surface of the molded layer; and firing the ceramic insulator, the molded layer, and the precursor material for the insulating layer to create a layered structure of the ceramic insulator, a ceramic layer having voltage-nonlinear resistance characteristics, and the insulating layer.

9. The method for manufacturing an electric field relaxation structure according to claim 7 or 8, wherein the ceramic layer having voltage nonlinear resistance characteristics has a porosity of 20% or more and 80% or less before firing.

10. A method for manufacturing a vacuum valve as claimed in claim 6, comprising the steps of: placing spherical granules of a material having voltage-nonlinear resistance characteristics on the ceramic insulator serving as the insulating container and applying pressure to create a molded layer of the material having voltage-nonlinear resistance characteristics; firing the ceramic insulator and the molded layer to create the ceramic insulator and a ceramic layer having voltage-nonlinear resistance characteristics; and providing an insulating layer on the ceramic layer having voltage-nonlinear resistance characteristics, thereby providing an electric field relaxation structure.

11. A method for manufacturing a vacuum valve as claimed in claim 6, comprising the steps of: placing spherical granules of a material having voltage nonlinear resistance characteristics on the ceramic insulator serving as the insulating container and applying pressure to create a molded layer of the material having voltage nonlinear resistance characteristics; applying a precursor material for the insulating layer to the surface of the molded layer; and firing the ceramic insulator, the molded layer and the precursor material for the insulating layer to create a layer structure of the ceramic insulator, the ceramic layer having voltage nonlinear resistance characteristics and the insulating layer, thereby providing an electric field relaxation structure.

12. The method for manufacturing a vacuum valve according to claim 10 or 11, wherein the ceramic layer having voltage nonlinear resistance characteristics has a porosity of 20% or more and 80% or less before firing.

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