JP7471929B2 - Vacuum Switchgear - Google Patents

Description

An embodiment of the present invention relates to a vacuum opening and closing device.

For example, buildings, factories, hospitals, etc. are equipped with metal-enclosed switchgear (hereinafter simply referred to as switchgear) to protect electrical circuits in power distribution systems, control power, monitor facilities, etc. Switchgear is configured by accommodating main circuit conductors, power cables, grounding devices, current transformers, vacuum circuit breakers, vacuum disconnectors, etc. in a space separated from the outside by a metal container (housing). Vacuum circuit breakers and vacuum disconnectors have vacuum switching devices (also called vacuum valves) that interrupt current by appropriately switching electrodes arranged in an insulating container to a conductive state or an insulating state. The conductive state is a state in which the contacts of a pair of electrodes are in contact (closed), and the insulating state is a state in which these contacts are separated (open). The insulating state includes a circuit interruption state and a disconnection state formed when the contacts are in contact and the electrodes are closed.

When a vacuum switchgear interrupts a load current, if the contact surface is damaged by an arc discharge, the insulation performance between the contacts may be reduced. To prevent such a reduction in the insulation performance between the contacts, a vacuum switchgear is known that is provided with an electric field mitigation member (electric field mitigation shield). Such an electric field mitigation shield is arranged, for example, so as to surround the contact of the fixed electrode and the contact of the movable electrode, respectively, and reduces the potential gradient between the contacts and the insulating container, in other words the electric field strength. As an example, the electric field mitigation shield of the contact of the fixed electrode is fixed to the side of the current-carrying shaft, and the electric field mitigation shield of the contact of the movable electrode is fixed to the sealing plate of the vacuum switchgear.

JP 2020-27782 A JP 2004-235121 A Japanese Patent Application Laid-Open No. 63-160122

When the load current is interrupted, if an arc occurs between the contacts and the electric field mitigation shield is damaged, the insulating performance of the electric field mitigation shield may decrease depending on the extent of the damage. For this reason, a shielding structure is known that provides a gap between the contacts and the electric field mitigation shield to prevent the transfer of the arc. With such a shielding structure, it is possible to suppress the transfer of the arc from the contacts to the electric field mitigation shield.

However, if arc discharge or dielectric breakdown occurs originating from the electric field mitigation shield, damage to the electric field mitigation shield may not be sufficiently suppressed. For this reason, there is a demand to suppress arc discharge and dielectric breakdown originating from the electric field mitigation shield and reduce damage to the electric field mitigation shield.

A vacuum switchgear according to an embodiment includes an insulating container, an electrode, a sealing metal fitting, and an electric field relaxation member. The insulating container is made of an insulating material and has a cylindrical shape, and has openings at both ends in the cylindrical axial direction. The electrodes are housed in the insulating container and form a pair of electrodes capable of connecting and disconnecting their contacts. The sealing metal fittings are respectively joined to the openings and close the insulating container. The electric field relaxation members form a pair and are formed of a material having a dielectric breakdown electric field strength equivalent to that of the material of the contacts, and relax the electric field strength between the insulating container and the contacts. The contacts have a first curved portion whose surface is curved with a predetermined radius of curvature. The electric field relaxation member has a second curved portion whose surface is curved with a predetermined radius of curvature. The radius of curvature of the surface of the first curved portion is smaller than the radius of curvature of the surface of the second curved portion. The surface of the second curved portion has a finer surface roughness than the surface of the first curved portion.

1 is a cross-sectional view taken along a plane including a cylindrical axis (axial core) and illustrating a schematic configuration of a vacuum switchgear according to a first embodiment. FIG. 13 is a graph showing the relationship between effective area and dielectric breakdown field strength. FIG. 2 is an enlarged schematic diagram showing the configuration of the electric field mitigation shield and the contacts in FIG. 1 . FIG. 13 is a diagram showing a schematic configuration of an electric field mitigation shield and a contact according to a second embodiment. FIG. 1 is a graph showing the relationship between surface roughness and dielectric breakdown field strength. FIG. 13 is a diagram showing a schematic configuration of an electric field mitigation shield and a contact according to a third embodiment.

The vacuum switchgear according to the embodiment will be described below with reference to Figs. 1 to 6. The vacuum switchgear (also called a vacuum valve) is provided in a vacuum disconnector of a metal-enclosed switchgear that is installed for the purpose of protecting electrical circuits in an electric power distribution system, controlling electric power, monitoring equipment, etc., and is used as a switch that cuts off a current (load current, as an example).

First Embodiment
Fig. 1 is a diagram showing a schematic configuration of a vacuum switchgear 1 according to a first embodiment, and is a cross-sectional view taken along a plane including a cylinder axis (axial core C) described later. In the following description, the direction indicated by the arrow UP in Fig. 1 is defined as up, and the opposite direction is defined as down. These directions need only match the directions when the vacuum switchgear is mounted, but may be different.

As shown in FIG. 1, the vacuum opening and closing device 1 includes an insulating container 2, a sealing metal fitting 3, an electrode 4, and an electric field relaxation member 5.

The insulating container 2 is made of an insulating material and has openings 21 (first opening 21a and second opening 21b) at both ends in the direction of the cylindrical axis (axis core C). As the insulating material, ceramics such as alumina (Al ₂ O ₃ ), glass, etc. can be used, but are not limited to these. The openings 21 are closed by a sealing metal fitting 3. Specifically, the first opening 21a is closed by a first sealing metal fitting 3a, and the second opening 21b is closed by a second sealing metal fitting 3b. The sealing metal fitting 3 can be made of a metal material such as aluminum or stainless steel (SUS). However, the material is not limited to these. The sealing metal fitting 3 is, for example, substantially disk-shaped, and its peripheral portion is joined to the end of the insulating container 2 in the direction of the axis core C, and is arranged coaxially with the axis core C.

The electric field mitigation shields 5a and 5b can be made of metal materials such as aluminum and stainless steel (SUS). However, the materials are not limited to these. The electric field mitigation shields 5a and 5b are brazed to the sealing metal fittings 3 (the first sealing metal fitting 3a and the second sealing metal fitting 3b) with, for example, silver, gold, copper, etc., and protrude from the sealing metal fittings 3 into the interior 22 of the insulating container 2. In the example shown in FIG. 1, the protruding ends of the electric field mitigation shields 5a and 5b are curved and folded back so as to reduce in diameter all around.

The electrode 4 has a current-carrying shaft 6 and a contact 7. The electrode 4 is composed of a pair of fixed electrodes 4a and movable electrodes 4b. The fixed electrode 4a has a first current-carrying shaft 6a and a first contact 7a, which will be described later, and does not fluctuate (displace) in position relative to the insulating container 2. The movable electrode 4b has a second current-carrying shaft 6b and a second contact 7b, which will be described later, and displaces (moves up and down in this embodiment) so as to be able to approach and separate from the fixed electrode 4a.

The current-carrying shaft 6 can be made of a conductive material such as copper (oxygen-free copper), aluminum, or chromium. However, the material is not limited to these. The current-carrying shaft 6 is composed of a first current-carrying shaft 6a and a second current-carrying shaft 6b that are arranged in a pair coaxially with the axial core C of the insulating container 2.

The first current-carrying shaft 6a extends from the contact 7 (specifically, the first contact 7a described below) toward the first sealing metal fitting 3a and protrudes from the hole 31a of the first sealing metal fitting 3a to the outside of the insulating container 2. The hole 31a penetrates the center of the first sealing metal fitting 3a. The first current-carrying shaft 6a is joined to the first sealing metal fitting 3a at the hole 31a, and its position in the first sealing metal fitting 3a, and ultimately in the vacuum opening and closing device 1, is fixed.

The second current-carrying shaft 6b extends from the contact 7 (specifically, the second contact 7b described later) toward the second sealing metal fitting 3b and protrudes from the hole 31b of the second sealing metal fitting 3b to the outside of the insulating container 2. The hole 31b penetrates the center of the second sealing metal fitting 3b. The second current-carrying shaft 6b advances and retreats in the direction of the axis C together with the second contact 7b described later. Therefore, between the second current-carrying shaft 6b and the hole 31b, a gap S is formed that allows the second current-carrying shaft 6b to be displaced (advance and retreat in the direction of the axis C) in the hole 31b. In other words, the shaft diameter of the second current-carrying shaft 6b is smaller than the hole diameter of the hole 31b. The second current-carrying shaft 6b is fitted with a bellows 8 that supports the second current-carrying shaft 6b so that it can advance and retreat in the direction of the axis C.

The bellows 8 is configured in a bellows shape expandable and contractible in the direction of the axis C, and together with the sealing metal fittings 3 (first sealing metal fitting 3a, second sealing metal fitting 3b), keeps the interior 22 of the insulating container 2 airtight. The pressure in the interior 22 of the insulating container 2 is preferably 1×10 ⁻² Pa or less. One end 8a of the bellows 8 is joined to the second sealing metal fitting 3b. The other end 8b of the bellows 8 is joined to the second current-carrying shaft 6b. The other end 8b of the bellows 8 may be joined to the second current-carrying shaft 6b via, for example, a cover member (bellows cover) that covers the other end 8b. The bellows cover suppresses adhesion of molten metal scattered by the arc to the bellows 8 and hermetically seals the gap S.

A cylindrical arc shield 9 is arranged around the fixed electrode 4a and the movable electrode 4b, surrounding these electrodes 4a, 4b, and ultimately the contacts 7a, 7b. When an arc occurs between the first contact 7a and the second contact 7b in the open-contact state, the arc shield 9 prevents the metal melted by the arc from scattering, and prevents the molten metal from adhering to the inner circumferential surface 23, which would otherwise deteriorate the insulating performance of the insulating container 2. The arc shield 9 can be made of, for example, stainless steel (SUS) or copper, but is not limited to these. The arc shield 9 has a protrusion 92 that protrudes from the outer circumferential surface 91 toward the insulating container 2. The protrusion 92 is continuous, for example, around the entire circumference of the outer circumferential surface 91, and is joined to the inner circumferential surface 23 of the insulating container 2.

The fixed electrode 4a and the movable electrode 4b each have a contact 7, which is brought into contact with and separated from each other. The contact 7 is composed of a pair of a first contact 7a and a second contact 7b. The first contact 7a corresponds to the end of the fixed electrode 4a that comes into contact with and separates from the movable electrode 4b. The second contact 7b corresponds to the end of the movable electrode 4b that comes into contact with and separates from the fixed electrode 4a.

The first contact 7a and the second contact 7b are arranged opposite each other and come into contact with and separate from each other as the movable electrode 4b is displaced relative to the fixed electrode 4a. The contact and separation of the contacts 7a and 7b causes a transition between a conductive state and an insulating state between the fixed electrode 4a and the movable electrode 4b. The conductive state is a state in which the contacts 7a and 7b are in contact (closed), and the insulating state is a state in which the contacts 7a and 7b are separated (open). The insulating state includes a disconnected state of the circuit formed when the contacts 7a and 7b come into contact and close the gap between the electrodes 4a and 4b.

The first contact 7a and the second contact 7b are formed of a conductive alloy, for example, copper chromium (CuCr). The composition of the copper chromium is not particularly limited, but as an example, it is assumed that the composition is about 75% to 65% copper (Cu) and about 25% to 35% chromium (Cr), preferably about 75% copper (Cu) and about 25% chromium (Cr). However, the material of the first contact 7a and the second contact 7b is not limited to this, and it is also possible to use an alloy such as AgW or CuCrTe.

The electric field mitigation member (hereinafter referred to as electric field mitigation shield) 5 is disposed near the contact 7 and mitigates the potential gradient, in other words the electric field strength, between the contact 7 and the insulating container 2. The electric field mitigation shield 5 is configured to include a pair of a first electric field mitigation shield 5a and a second electric field mitigation shield 5b. These electric field mitigation shields 5a, 5b are disposed one by one corresponding to each of the pair of electrodes 4a, 4b. The first electric field mitigation shield 5a is disposed near the first contact 7a. The second electric field mitigation shield 5b is disposed near the second contact 7b.

In the contact direction (axis C direction) of the contacts 7a and 7b, one electric field reduction shield 5 is disposed farther from the other contact 7 than the corresponding contact 7. That is, the first electric field reduction shield 5a is disposed farther from the second contact 7b than the first contact 7a. The second electric field reduction shield 5b is disposed farther from the first contact 7a than the second contact 7b. In other words, the first contact 7a is disposed closer to the second contact 7b than the first electric field reduction shield 5a, and the second contact 7b is disposed closer to the first contact 7a than the second electric field reduction shield 5b. As a result, in the contact direction (axis C direction) of the contacts 7a and 7b, the opposing distance between the contacts 7a and 7b is narrower than the opposing distance between the electric field reduction shields 5a and 5b. The first contact 7a protrudes in the contact direction with the second contact 7b than the first electric field reduction shield 5a. The second contact 7b protrudes further in the direction of contact with the first contact 7a than the second electric field reduction shield 5b. Therefore, when the contacts 7a and 7b are brought into contact with each other, the electric field reduction shields 5a and 5b do not interfere with each other, and there is no hindrance to the contact and separation of the contacts 7a and 7b.

The electric field mitigation shield 5 (first electric field mitigation shield 5a and second electric field mitigation shield 5b) is formed of a material having the same breakdown electric field strength as the material of the contacts 7 (first contacts 7a and second contacts 7b). The breakdown electric field strength (Eb) is determined by the effective area (Seff). Figure 2 shows the relationship between the effective area and the breakdown electric field strength. The effective area is the area of the target system, for example, the total surface area of all target components, that has an electric field strength of 90% or more of the maximum electric field strength. The breakdown electric field strength is calculated as the effective area raised to the power k multiplied by α (Eb = α x Seff^k). k and α are coefficients determined by the material, and the value of k is approximately -0.2 to -0.3.

The relationship between the effective area and the breakdown field strength varies depending on the material (constituent material) of the target system, but generally, as shown in FIG. 2, the larger the effective area, the lower the breakdown field strength. Therefore, in order to increase the breakdown field strength, it is preferable to make the effective area smaller. As described above, the contact 7 is made of a material such as copper chromium that has excellent properties in both insulation performance and current interruption performance. In contrast, the electric field mitigation shield 5 is made of a material that has a breakdown field strength equivalent to that of copper chromium, such as stainless steel (SUS). Note that the material of the electric field mitigation shield 5 is not limited to this, and for example, when an alloy such as AgW or CuCrTe is used as the contact material, any material that has a breakdown field strength equivalent to these may be used as the shield material.

Here, for example, in the case of a vacuum disconnector, although it is necessary to interrupt the load current, it is not required to interrupt the problem current to the extent that a vacuum circuit breaker would need to interrupt it, so the surface area of the contacts 7 may be smaller than that of a vacuum circuit breaker. Therefore, in order to reduce the size and cost of the vacuum switchgear 1 according to this embodiment, it is possible to reduce the size of the contacts 7. However, the smaller the contacts 7, the higher the electric field strength acting on the contacts 7, which is likely to lead to a decrease in voltage resistance performance. For this reason, in this embodiment, an electric field mitigation shield 5 is arranged near the contacts 7 so as to cover the periphery of the first current-carrying shaft 6a and the second current-carrying shaft 6b, respectively, to mitigate the electric field strength near the contacts 7 and achieve high voltage resistance.

On the other hand, when the electric field strength near the contact 7 is alleviated by placing the electric field mitigation shield 5, the electric field strength near the electric field mitigation shield 5 may become equal to or greater than the alleviated electric field strength. In this case, there is a risk that insulation breakdown will occur starting from the electric field mitigation shield 5 when the voltage is increased, or that an arc discharge will occur when the load current is interrupted. If the electric field mitigation shield 5 is damaged as a result of these, the damaged portion will become a weak point in the insulation, and the insulating performance of the vacuum disconnector may be reduced.

In this embodiment, the electric field mitigation shield 5 and the contacts 7 are appropriately shaped, and the electric field balance between them is controlled to suppress the occurrence of dielectric breakdown and arc discharge in the electric field mitigation shield 5. Next, the shapes of the electric field mitigation shield 5 and the contacts 7 will be described.

FIG. 3 shows an enlarged schematic view of the electric field mitigation shield 5 and the contacts 7 in FIG.
3, the contacts 7 (first contact 7a and second contact 7b) are circular, flat plate-like members that are substantially concentric with the axis C. A first surface 71 of the contacts 7 is a surface that comes into contact with the opposing contact 7 (the second contact 7b in the case of the first contact 7a, and the first contact 7a in the case of the second contact 7b). A second surface 72 of the contact 7 is a fixed surface to the current-carrying shaft 6 and the electric field mitigation shield 5. The contacts 7 are fixed to the current-carrying shaft 6 and the electric field mitigation shield 5 by brazing the second surface 72 to them with silver, gold, copper, or the like, for example.

The contact 7 has a flat portion 73 and a curved portion (hereinafter referred to as the first curved portion) 74. The flat portion 73 is a flat portion that comes into contact with and separates from the opposing contact 7. The first curved portion 74 is a peripheral portion of the contact 7, and is continuous with the entire periphery of the flat portion 73. The surface 75 of the first curved portion 74 is a continuous surface that is free of uneven portions, such as protrusions, depressions, or grooves.

The electric field mitigation shield 5 (first electric field mitigation shield 5a and second electric field mitigation shield 5b) is a flat annular shape with a diameter larger than its thickness, and is approximately concentric with the axis C. The thickness of the electric field mitigation shield 5 is the maximum length in the direction of the axis C (the vertical direction in FIG. 3). The diameter of the electric field mitigation shield 5 is the maximum length in the direction perpendicular to the direction of the axis C (the horizontal direction in FIG. 3). The outer peripheral surface 51 of the electric field mitigation shield 5 faces the inner peripheral surface 23 of the insulating container 2. The inner peripheral surface 52 of the electric field mitigation shield 5 is a fixed surface relative to the current-carrying shaft 6. The electric field mitigation shield 5 is fixed to the current-carrying shaft 6, for example, by brazing the inner peripheral surface 52 to the outer peripheral surface of the current-carrying shaft 6 with silver, gold, copper, etc.

The electric field reduction shield 5 has a base 53 and a curved portion (hereinafter referred to as the second curved portion) 54. The base 53 is a cylindrical portion supported by the current-carrying shaft 6, and both ends of the tube (the upper and lower ends in FIG. 3) are flat surfaces. The second curved portion 54 is the peripheral portion of the electric field reduction shield 5, and is continuous with the entire periphery of the base 53. The surface 55 of the second curved portion 54 is a continuous surface without uneven portions, such as protrusions, depressions, or grooves. The surface 55 corresponds to the outer peripheral surface 51 of the electric field reduction shield 5.

At the contact 7, the surface 75 of the first curved portion 74 is a curved surface that is curved with a predetermined radius of curvature. At the electric field mitigation shield 5, the surface 55 of the second curved portion 54 is a curved surface that is curved with a predetermined radius of curvature. The radius of curvature of the surface 75 of the first curved portion 74 is smaller than the radius of curvature of the surface 55 of the second curved portion 54.

In this embodiment, the electric field mitigation shield 5 and the contact 7 are each formed from materials with similar breakdown electric field strengths. In a system (hereinafter referred to as the target system) formed by the electric field mitigation shield 5 and the contact 7 on the fixed electrode 4a side and the movable electrode 4b side, the radius of curvature of the surface 75 of the first curved portion 74 is made smaller than the radius of curvature of the surface 55 of the second curved portion 54, so that the electric field strength acting on the electric field mitigation shield 5 is reduced to be lower than the electric field strength acting on the contact 7.

Therefore, in such a target system, the effective area of the second curved portion 54 can be made smaller than the effective area of the first curved portion 74. In other words, the effective area of such a target system can be concentrated in the first curved portion 74 of the contact 7. This makes it possible to increase the dielectric breakdown field strength of the electric field mitigation shield 5 in the target system relative to the contact 7. Therefore, even if an arc discharge occurs when the current is interrupted, the occurrence point can be confined between the contacts 7a and 7b, and the arc discharge between the electric field mitigation shields 5a and 5b can be suppressed. As a result, damage to the electric field mitigation shield 5 can be reduced and dielectric breakdown of the electric field mitigation shield 5 can be suppressed. In turn, it becomes possible to suppress the deterioration of the insulation performance of the vacuum switchgear 1.

The degree of reduction in the radius of curvature of the surface 75 of the first curved portion 74 relative to the radius of curvature of the surface 55 of the second curved portion 54 is not particularly limited. For example, the radius of curvature of the surface 75 may be made smaller than that of the surface 55 so that the maximum electric field strength acting on the second curved portion 54 of the electric field mitigation shield 5 is smaller than the maximum electric field strength acting on the first curved portion 74 of the contact 7 when the contacts 7a and 7b are separated (opened) and the load current is interrupted. Specifically, the maximum electric field strength acting on the second curved portion 54 of the electric field mitigation shield 5 may be about 90% or less of the maximum electric field strength acting on the first curved portion 74 of the contact 7. As an example, when the radius of curvature of the surface 75 of the first curved portion 74 is about 5 mm, the radius of curvature of the surface 55 of the second curved portion 54 may be about 20 mm.

The electric field mitigation shield 5 according to this embodiment has a base 53 and a second curved portion 54, but the base 53 may be omitted. In this case, the electric field mitigation shield is configured to have an annular curved portion having a through hole at the center that is concentric with the axis C as the portion corresponding to the second curved portion 54.

As described above, in this embodiment, the radius of curvature of the surface 75 is smaller than that of the surface 55 in the first curved portion 74 and the second curved portion 54. In addition, the curved portions 74, 54 may be formed as follows to suppress arc discharge between the electric field mitigation shields 5a, 5b. Such embodiments will be described below as the second and third embodiments. The basic configuration of the vacuum opening and closing device in these embodiments is the same as that of the vacuum opening and closing device 1 according to the first embodiment (FIG. 1). Therefore, the basic configuration of the vacuum opening and closing device will be omitted below, and the electric field mitigation shield and contacts, which are the characteristics of the second and third embodiments, will be described in detail. In this case, the same reference numerals will be used for components that are the same or similar to those in the first embodiment.

Second Embodiment
FIG. 4 shows a schematic view of the electric field mitigation shield 5 and the contacts 7 according to the second embodiment. For example, the size of the electric field mitigation shield 5 depends on the size of the space inside 22 of the insulating container 2. If the vacuum switchgear 1 is miniaturized and sufficient space cannot be secured inside 22 of the insulating container 2, the size of the electric field mitigation shield 5 is limited accordingly. In this case, the electric field balance between the electric field mitigation shield 5 and the contacts 7 can be controlled by making the surface roughness appropriate. For example, in the Fowler-Nordheim theory, the insulation performance in a vacuum is also determined by the surface roughness of the target system, for example, the target member. According to this theory, assuming a microscopic protrusion with a high degree of electric field inequality, the electric field is locally emphasized, making the field electron emission prominent, and this field electron emission is said to trigger the dielectric breakdown. FIG. 5 shows the relationship between the surface roughness and the dielectric breakdown field strength. As shown in FIG. 5, the finer the surface roughness (for example, the smaller the scale of the surface roughness), the higher the dielectric breakdown field strength. Therefore, in order to increase the dielectric breakdown field strength, it is preferable to make the surface roughness finer.

For this reason, in the electric field mitigation shield 5 according to this embodiment, the surface 55a of the second curved portion 54 has a finer surface roughness than the surface 75a of the first curved portion 74. In other words, the surface 55a is smoother than the surface 75a, and the surface 75a is rougher than the surface 55a. The method for making the surface roughness of the surface 75a finer than the surface 55a, that is, the method for making the surface 55a smoother than the surface 75a, is not particularly limited. For example, the second curved portion 54 of the electric field mitigation shield 5 may be subjected to a surface treatment such as electrolytic polishing or chemical polishing, so that the surface roughness of the surface 55a may be made finer than the surface roughness of the surface 75a. In this case, it does not matter whether the first curved portion 74 of the contact 7 is subjected to a surface treatment such as electrolytic polishing or chemical polishing. In other words, the second curved portion 54 of the electric field mitigation shield 5 may have a relatively finer surface roughness than the surface 75a of the first curved portion 74. If surface treatment is not applied to surface 75a, its surface roughness is the same as the surface roughness of surface 75 of first curved portion 74 in the first embodiment.

By making the surface roughness of surface 75a finer than that of surface 55a in this way, the dielectric breakdown field strength of the electric field mitigation shield 5 can be increased with respect to the contact 7 in the target system on the fixed electrode 4a side and the target system on the movable electrode 4b side. Therefore, arc discharge between the electric field mitigation shields 5a and 5b can be suppressed, and dielectric breakdown therebetween can be suppressed.

The surface roughness can be measured using, for example, arithmetic mean roughness (Ra), maximum height (Ry), or ten-point mean roughness (Rz). The surface roughness can be determined using any of the above-mentioned measures on randomly selected portions of the surfaces 75a, 55a of the first curved portion 74 and the second curved portion 54.

Third Embodiment
FIG. 6 shows a schematic configuration of an electric field mitigation shield 5 and a contact 7 according to the third embodiment.
6 , in the electric field mitigation shield 5 according to this embodiment, the surface 55 of the second curved portion 54 is coated with a high-voltage material having the same insulating properties and current-blocking properties as the material of the first curved portion 74, or more specifically, the contact 7. That is, a predetermined coating 56 is formed on the surface 55.

The coating 56 may be made of the following materials depending on the material of the contact 7 including the first curved portion 74. For example, if the material of the contact 7 is copper chromium (CuCr) with 75% copper (Cu) and 25% chromium (Cr), the material of the coating 56 may be copper chromium with approximately 75% to 65% copper (Cu) and 25% to 35% chromium (Cr), or a high-pressure resistant material of the same level. The method of forming the coating 56 is not particularly limited. For example, the coating 56 may be formed on the surface 55 by ion plating, physical vapor deposition (PVD), chemical vapor deposition (CVD), or the like.

By forming the high-voltage coating 56 on the surface 55 in this way, even if an arc discharge occurs between the electric field mitigation shields 5a, 5b in the target system on the fixed electrode 4a side and the target system on the movable electrode 4b side, the damage to these can be reduced and insulation breakdown can be suppressed. For example, if the electric field mitigation shield 5 becomes larger in size than the contact 7, replacing the entire electric field mitigation shield 5 with another high-voltage material will increase costs and is not preferable. Even in such a case, in this embodiment, the second curved portion 54 can be made to have a high voltage resistance by forming a coating 56 with excellent insulating properties and current blocking properties on the surface 55 of the second curved portion 54 without changing the material of the electric field mitigation shield 5. Therefore, the insulating properties and current blocking properties of the electric field mitigation shield 5 can be improved relatively inexpensively.

It is preferable that the thickness of the coating 56 be set in consideration of some wear when the current is interrupted. For example, the number of interruptions that will occur originating from the electric field mitigation shield 5 can be estimated in advance based on the switching life of the vacuum switchgear 1 and the relative relationship between the effective area of the contacts 7 and the effective area of the electric field mitigation shield 5, and the thickness of the coating 56 can be set according to the number of interruptions, making it possible to form the coating 56 at a lower cost.

In addition, in the electric field mitigation shield 5 according to this embodiment, the coating 56 is formed on the surface 55 of the second curved portion 54 as well as on the surface of the base portion 53. That is, the coating 56 is formed over the entire area of the electric field mitigation shield 5 that is exposed to the outside. However, the coating 56 does not have to be formed over the entire area, and it is sufficient that the coating 56 is formed over at least the entire surface 55 of the second curved portion 54.

Although several embodiments of the present invention have been described above, the above-mentioned embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the gist of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims.

1...vacuum switchgear, 2...insulating container, 3...sealing metal fitting, 4...electrode, 5, 5a, 5b...electric field relaxation member (electric field relaxation shield), 6...current-carrying shaft, 7, 7a, 7b...contacts, 8...bellows, 9...arc shield, 21...opening, 53...base, 54...second curved portion, 55, 55a...surface of second curved portion, 56...coating, 73...flat portion, 74...first curved portion, 75, 75a...surface of first curved portion, C...shaft core, S...gap.

Claims (5)

an insulating container made of an insulating material and having a cylindrical shape and an opening at each end in a cylindrical axial direction;
A pair of electrodes housed in the insulating container and capable of connecting and disconnecting contacts with each other;
a sealing metal fitting joined to each of the openings and closing the insulating container;
a pair of electric field relaxation members formed of a material having a dielectric breakdown electric field strength equivalent to that of a material of the contacts, and relaxing the electric field strength between the insulating container and the contacts;
The tangent point has a first curved portion having a surface curved with a predetermined radius of curvature;
the electric field relaxation member has a second curved portion whose surface is curved at a predetermined radius of curvature,
a radius of curvature of the surface of the first curved portion is smaller than a radius of curvature of the surface of the second curved portion;
A vacuum switchgear , wherein a surface of the second curved portion has a finer surface roughness than a surface of the first curved portion . The pair of electric field relaxation members are arranged corresponding to each of the pair of electrodes,
The vacuum switchgear according to claim 1 , wherein one of the electric field relaxation members is disposed farther away from the other of the contacts than a corresponding one of the contacts is disposed in a direction in which the pair of contacts move together. The vacuum switchgear according to claim 2 , wherein the surface of the second curved portion is a continuous surface without any protrusions or depressions. The vacuum switchgear according to claim 3 , wherein the electric field relaxation member is flattened in such a way that a maximum length in a direction perpendicular to the cylindrical axis direction is greater than a maximum length in the cylindrical axis direction. 5. The vacuum switchgear according to claim 1, wherein when the pair of contacts are separated to interrupt the load current, a maximum electric field strength acting on the second curved portion is 90% or less of a maximum electric field strength acting on the first curved portion.

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