JP2911594B2 - Vacuum valve - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Purpose of the Invention] (Industrial application field) The present invention particularly relates to a vacuum valve having both a low surge property and a large current interruption property.

(Prior art) The contacts of a vacuum valve that interrupts current in a high vacuum using arc diffusivity in a vacuum are fixed,
It is composed of two movable contacts. When the current in an inductive circuit such as a motor load is cut off by using this vacuum valve, an excessive abnormal surge voltage is generated, and there is a possibility that the load device may be destroyed.

The cause of the occurrence of the abnormal surge voltage is mainly due to the interruption phenomenon that occurs when a small current is interrupted in a vacuum (current interruption is performed without waiting for the natural zero point of the AC current waveform).

The value Vs of the abnormal surge voltage due to the disconnection phenomenon is represented by the product of the surge impedance Zo of the circuit and the current disconnection value Ic, that is, Vs = Zo · Ic. Therefore, in order to lower the abnormal surge voltage Vs, the current break value Ic must be reduced.

In response to the above requirements, a vacuum switch using contacts made of an alloy of a composite of tungsten carbide (WC) and silver (Ag) has been developed (Japanese Patent Application No. 42-68447, US Pat. No. 3,683,138).
No.), which has been put to practical use.

The contact of the Ag-WC alloy has the following features: (1) WC facilitates electron emission; (2) promotes evaporation of the contact material based on heating of the electrode surface due to the collision of field emission electrons; 3) Carbide of the contact material is decomposed by the arc, generates a charged body, and exhibits excellent low breaking current characteristics in that the arc is connected.

In addition, as another contact material exhibiting low breaking current characteristics, an alloy in which bismuth (Bi) and copper (Cu) are compounded has been manufactured, and this material has been put to practical use in vacuum valves (Japanese Patent Publication No. No. -14974, U.S. Pat.No. 2,975,256, Japanese Patent Publication No. 41-12
131, US Patent No. 3246979). Of this alloy, Bi
10% by weight (hereinafter referred to as wt%) (Japanese Patent Publication No. 35-14974)
No.) has a low vapor current characteristic because of its moderate vapor pressure characteristics, and the one with Bi of 0.5 wt% (JP-B No. 41-12131) segregates at the grain boundaries. As a result, the alloy itself is embrittled, a low welding pull-out force is realized, and the high current breaking performance is excellent.

Ag and Cu are other contact materials with low breaking current characteristics.
Ag-Cu-WC alloys having a ratio of about 7: 3 have been proposed (JP-A-58-157015). It is described that in this alloy, the ratio of Ag and Cu, which is not limited in the past, is selected, so that it exhibits stable current-breaking characteristics.

Further, Japanese Patent Application Laid-Open No. 62-77439 discloses that by setting the particle size of the arc-resistant material (for example, the particle size of WC) to 0.2 to 1 μm, it is effective to improve the low breaking current characteristics. Is suggested.

Also, Japanese Patent Application No. 1-108742 suggests that a low surge property can be obtained by homogenizing high conductive components without uneven distribution.

On the other hand, the contacts for increasing the current are the Cu-
In addition to Bi alloys, Cu-Te alloys are also known (JP-B-44-23)
No. 751), and a Cu—Cr alloy material also has excellent characteristics for high withstand voltage and high current use.

(Problems to be Solved by the Invention) A vacuum circuit breaker is required to have a large current breaking performance as a basic characteristic. However, in recent years, it has been increasingly applied to an inductive circuit such as an electric motor, and With the emergence of surge impedance loads, it has become necessary to combine excellent low surge characteristics.

In order to have a low surge property, there must be sufficient vapor release from the contacts. On the other hand, in order to enable high-current interruption, the released steam must be quickly diffused, and the conductivity must be kept low during actual use, that is, when a large current is applied. Must be somewhat large.

Heretofore, there has been no contact material that satisfies both these characteristics simultaneously.

Contact point of alloy combining WC and Ag (Japanese Patent Application No. 42684684)
No. 3,683,138), the breaking current value itself is insufficient.

An alloy composed of 10 wt% Bi and Cu (Japanese Patent Publication No. 35-1497)
No. 4, U.S. Pat. No. 2,975,256), the amount of metal supplied to the interelectrode space decreases with an increase in the number of times of opening and closing, and the degradation of low breaking current characteristics appears. Withstand voltage characteristics depend on the amount of high vapor pressure elements. Has also been pointed out.

0.5wt% Bi and Cu composite alloy (Japanese Patent Publication No. 41-121)
No. 31, U.S. Pat. No. 32,469,795), the low breaking current characteristics are insufficient.

In addition, Ag-Cu-W in which the weight ratio of Ag and Cu was approximately 7: 3
C alloy (JP-A-58-157015), the particle size of the arc resistant material is 0.2
Alloy having a thickness of about 1 μm (Japanese Patent Application Laid-Open No. Sho 62-77439) and Ag-Cu alloy having a uniform high conductivity component without uneven distribution
-In the WC alloy (Japanese Patent Application No. 1-108742), although excellent low surge property can be obtained, the conductivity of the contact material is lowered for the purpose of facilitating the release of metal vapor. In addition, sufficient high current interruption characteristics cannot be exhibited.

Conversely, Cu-Bi alloy, Cu-Te alloy,
In the case of Cu and Cu-Cr alloys, sufficient low surge cannot be expected because the metal vapor release is small and diffusion is fast.

The present invention has been made based on the above-described background, and has as its object to combine an excellent large-current interrupting performance and a low and stable low-surge characteristic, and to provide a vacuum circuit breaker that is becoming more severe. The purpose is to provide a contact material that meets the requirements.

[Configuration of the invention]

(Means for Solving the Problems) As a result of research and development for solving the above-mentioned problems, the present inventors have determined that the content of the conductive component on the contact surface in the portion to be arced is the average conductivity of the contact material. The inventors have found that reducing the amount of the components is effective in achieving the object of the present invention, and have completed the present invention.

That is, the vacuum valve according to the present invention is a vacuum valve contact comprising a first layer region forming a surface layer of the contact and a second layer region forming an interior from the first layer region, The first and second layer regions are made of Ag or /
And the high conductive component consisting of Cu and Cu is continuously integrated, and the amount (b) of the average high conductive component in the second layer region in the contact is in the range of 20 to 50% by weight based on the total amount of the contact material. The amount (a) of the average high conductivity component in the first layer region in the contact is 20 to 20 times the amount (b) of the average high conductivity component in the second layer region.
80%, with the balance comprising a contact made of an arc resistant component.

In a preferred aspect of the present invention, the thickness of the first layer region can be 150 μm or less.

In another preferred embodiment of the present invention, the arc-resistant component comprises one or more metal carbides selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo and W. can do.

In another preferred embodiment of the present invention, if necessary, 0 to 3% by weight of Fe, Co,
And at least one auxiliary component selected from Ni and Ni.

In still another preferred embodiment of the present invention, the highly conductive component comprises Ag and Cu, and the ratio of Ag in the highly conductive component may be 50% or more.

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, the present invention will be described more specifically with reference to the drawings.

1. Vacuum Valve FIG. 1 is a sectional view of a vacuum valve, and FIG. 2 is an enlarged sectional view of an electrode portion of the vacuum valve.

In FIG. 1, a shut-off chamber 1 has an insulating container 2 formed of an insulating material in a substantially cylindrical shape, and sealing fittings at both ends thereof.
A metallic cover 4a, 4b provided via 3a, 3b forms a vacuum-tight structure.

A pair of electrodes 7 and 8 attached to opposing ends of the conductive rods 5 and 6 are disposed in the shut-off chamber 1.
Is a fixed electrode, and the lower electrode 8 is a movable electrode. A bellows 9 is attached to the electrode rod 6 of the electrode 8 to enable the electrode 8 to move in the axial direction while keeping the inside of the cutoff chamber 1 vacuum-tight. A metal arc shield 10 is provided on the bellows 9 to prevent the bellows 9 from being covered with the arc vapor. Also, the electrodes 7, 8
A metallic arc shield 11 in the shut-off chamber 1 so as to cover
Is provided, thereby preventing the insulating container 2 from being covered with the arc vapor. Further, the electrode 8 is fixed to the conductive rod 6 by a brazing portion 12 as shown in an enlarged manner in FIG. Contact 13a
Is brazed to the electrode 8 by brazing. The contact 13b is attached to the electrode 7 by brazing.

FIG. 3 is an enlarged sectional view of the contact material of the present invention. The contact is composed of a first layer region 15 forming a contact surface layer, and a second layer region 13 forming an interior from the first layer region. I have.

The contact for a vacuum valve according to the present invention includes a first layer region forming a contact surface layer, and a second layer region forming an interior from the first layer region.

The current interruption phenomenon is a phenomenon caused by the breakdown of the material and energy balance at the cathode point of the arc. The size of this cathode spot is at most about 100 μm,
Therefore, the breaking characteristics of the contact material depend more on the physical properties of the extreme surface than on the average physical properties of the material.

Since the breaking current value strongly depends on the thermal conductivity of the contact material, for example, Ag / Cu-WC-Co contact material has excellent current breaking characteristics, but the conductivity is low. A large current cannot be passed.

Therefore, in order to have a low surge property and to enable a large current interruption, the thermal conductivity (or electrical conductivity) of the contact surface is reduced, and the overall (average) thermal conductivity (or electrical conductivity) is reduced. Must be somewhat high.

Therefore, in the contact of the present invention, the first layer region forming the contact surface is made of a material having a relatively low thermal conductivity (or electric conductivity), and the second layer region forming the inside from the first layer region is formed. Is made of a material having a relatively higher thermal conductivity (or electrical conductivity) than the material forming the first layer region. Here, since the second layer region occupies most of the contact, the thermal conductivity (or conductivity) of the entire contact is substantially controlled by the thermal conductivity (or conductivity) of the second layer region.

The thickness of the first layer region, that is, the distance from the outermost surface of the contact portion in the depth direction is preferably 150 μm or less, and more preferably 100 μm or less. At a value exceeding the predetermined value, the temperature does not reach a temperature at which the required amount of vaporization of the conductive component is released from the contact for ensuring low surge properties. Due to the amount of the conductive component, a phenomenon of depletion of the conductive component due to evaporation occurs with the passage of the number of times of opening / closing, resulting in lowering of the low surge property and instability of the characteristic of increasing the contact resistance temperature.

The first layer region and the second layer region are made of Ag and / or
It is continuously integrated with a highly conductive component made of Cu. Here, being continuously integrated with the highly conductive component includes both a case where the interface is clearly present and a case where the interface is not present, provided that both regions are substantially integrated. Means enough.

Ag or / and Cu is used as the highly conductive component in the first layer region and the second layer region. When one of the two layers contains only Ag or only Cu and the other coexists with Ag and Cu, a stable cutting characteristic can be obtained in both cases where both Ag and Cu coexist. The highly conductive component is composed of Ag and Cu, and the Ag in the highly conductive component is Ag.
Is preferably 50% or more.

The amount (b) of the average highly conductive component in the second layer region in the contact is in the range of 20 to 50% by weight based on the total amount of the contact material.

If the amount of the highly conductive component in the contact is less than 20% by weight, the temperature rise during energization of the contact material is undesirably high. In this type of sintered contact material, the occurrence of concentrated arc discharge, which often causes current interruption, is also due to the generation of excess metal vapor from the anode due to the temperature rise of the anode. Also, the amount of the highly conductive component in the contact requires a certain amount, and as the conductive material, it is preferable to use a material with high conductivity as much as possible, and at least 20 IACS% or more There is. However, if the amount of the highly conductive component in the contact exceeds 50% by weight, the cutting characteristics are deteriorated, which is not preferable.

In the present invention, the amount (a) of the average high conductive component in the first layer region in the contact is in the range of 20 to 80% of the amount (b) of the average high conductive component in the second layer region. is there. That is,
According to this limitation, the range of the amount (a) of the highly conductive component in the first layer region corresponds to 4 to 40% by weight based on the contact material. When (a) is less than 4% by weight, the contact surface temperature becomes extremely high locally due to the disappearance of the conductive component on the contact surface due to the discharge due to the discharge, so that the cutoff characteristics deteriorate. In addition, since an arc is applied to a portion that has been locally lost due to evaporation of the conductive component in the first layer region and current interruption occurs with a large current, the interruption characteristics are simultaneously deteriorated (only the interruption value itself is high). But the variation is large). On the other hand, when the content of (a) exceeds 40% by weight, the breaking value is undesirably increased.

In the present invention, the rest of the contact material excluding the conductive component is constituted by the arc-resistant component. The arc resistant component generally needs to be a substance that is stable even at a high temperature of a melting point of 2500 K or more.

The breaking current value does not become sufficiently low simply by reducing the thermal conductivity. For example, in the case of Ag / Cu-WC-Co contact material, even if the input energy due to the ion collision from the arc plasma is reduced due to the decrease in current, the melting point is high, so the WC heated to a high temperature as a solid or liquid by the arc is used. The sensible heat is released with the cooling, and the metal vapor required for maintaining the arc can be maintained to a low current value. As described above, the arc-resistant material not only keeps the thermal conductivity of the contact material low, but also plays a role in relaxing the cooling of the conductive material that is the arc maintaining material when the current decreases.
In order to keep the breaking current low, the material must be stable even at a high melting point of 2500K or higher.

As such arc-resistant materials, specifically, Ti, Zr, H
f, V, Nb, Ta, Cr, Mo and W, a metal carbide of one or more metals selected from the group consisting of TiC, ZrC,
One or more selected from the group consisting of HfC, VC, NbC, TaC, Cr ₃ C ₂ , Mo ₂ C, and WC are preferred.

If necessary, one or more components selected from Fe, Co, and Ni can be included as sintering aids as auxiliary components.
The content is preferably in the range of 0 to 3% by weight based on the total amount of the contact material. Even when the auxiliary component is zero, although the threshold value has some variation, the threshold value is generally low. On the other hand, when the content exceeds 3% by weight, the breaking characteristics rapidly decrease.

Next, an example of a method for manufacturing the contact material will be described.

Here, the highly conductive material is Ag or Ag-Cu alloy, and the arc resistant material is
WC, and Ag or / and Cu-WC whose sintering aid is Co
The case of -Co contact material is mainly shown.

Prior to production, the arc resistant components and auxiliary components are classified according to the required particle size. The classification operation is performed by using, for example, a sieving method and a sedimentation method in combination to easily obtain a powder having a predetermined particle size. First, a predetermined amount of WC, Co and / or C having a predetermined particle size, and WC
A predetermined amount of Ag having a predetermined particle size that is sufficiently larger than the particle size is prepared, mixed, and then pressed and molded to obtain a powder compact.

Then, the powder compact was subjected to a hydrogen atmosphere having a dew point of −50 ° C. or less or a degree of vacuum of 1.3 × 10 ⁻¹ Pa or less at a predetermined temperature,
For example, it is temporarily sintered at 1150 ° C. × 1 hour to obtain a temporarily sintered body.

Next, a predetermined amount of Ag or / and Cu is infiltrated into the residual pores of this temporary sintered body at 1150 ° C. × 1 hour, and Ag and / or Cu—Co
-Obtain WC alloy. The infiltration is performed mainly in a vacuum, but is also possible in hydrogen.

The same applies to Ag- and / or Cu-WC containing no Co. Carbon is preliminarily mixed with WC or Ag and / or Cu, or both, to obtain a temporarily sintered body.

The control of the ratio Ag / (Ag + Cu) of the conductive component in the alloy when both Ag and Cu were present was performed as follows. For example, an ingot having a predetermined ratio of Ag / (Ag + Cu) was subjected to vacuum melting at a temperature of 1200 ° C. and a degree of vacuum of 1.3 × 10 ⁻² Pa, cut, and used as a material for infiltration. Another method of controlling the ratio of conductive components Ag / (Ag + Cu) is to mix a predetermined amount of WC in advance before making a temporary sintered body, and then infiltrate the remaining Ag or Ag + Cu. This also makes it possible to obtain a contact alloy having a desired composition.

A contact having a uniform composition produced in this manner is, for example, 60 contacts.
By placing the film at a temperature of 0 ° C. for a predetermined time, the amount of the conductive component only on the surface can be reduced.

There are two types of conductive components contained in the contact material, those introduced during powder compounding and those introduced during infiltration. The former is distributed in the form of islands in the contact material, and its size is
In this case, the size of the Ag or / and Cu powder at the time of compounding is about 44 μm in this case, while the latter is present between WC skeletons having a particle size of 5 μm or less. Both are mixed on the processed surface of the contact, but if heating is performed at a temperature equal to or higher than the melting point of the conductive component, the conductive component will re-melt. The conductive component disappears from the wide part (into the inside of the skeleton and exudes from the brazed part correspondingly), and as a result, the amount of the conductive component on the contact surface (first layer region) can be reduced.

Another technique for reducing the amount of the highly conductive component of the first layer region by a predetermined amount from that of the second layer region is to provide at least one surface of a contact having a uniform composition produced as described above.
Voltage conditioning that discharges 1KV many times or
By applying current conditioning that interrupts at least 1 KA many times, the number and energy of each are adjusted to control the thickness (depth) of the first layer region.

Further, another technique for reducing the high conductivity component of the first layer region by a predetermined amount from that of the second layer region is to separately produce alloys having a predetermined amount of composition and obtain them by overlapping them. .

(Example) Next, an evaluation method and an evaluation condition for obtaining the example data of the present invention will be described.

(1) Current cut-off characteristics When an assembling type vacuum valve with each contact mounted and evacuated to 10 ^-3 Pa or less is manufactured, when this device is opened at an opening speed of 0.8 m / sec and a small delay current is cut off The breaking current was measured. The breaking current was 20 A (effective value) and 50 Hz. The opening phase was random, and the breaking current when the circuit was cut off 500 times was measured for three contacts. The average and maximum values are shown in Tables 1-2.

(2) Large current breaking characteristics The breaking test was performed by JEC Standard No. 5 test, and the breaking characteristics of the contact material were evaluated by this.

(3) Amount of Highly Conductive Component The X-ray intensity of 100% of the conductive component was set to 100 by an X-ray microanalyzer, and the X-ray intensity of each contact surface was measured.

Examples 1 to 3 and Comparative Examples 1 to 2 Ratio of the amount (a) of the highly conductive component in the first layer region in the contact and the amount (b) of the highly conductive component in the second layer region In the sample in which the value of (b) was constant at approximately 20%, when the amount (b) of the highly conductive component in the second layer region was too small, not only the break value was high (poor), but also the variation width was large. Further, the breaking characteristics are not sufficient (Comparative Example-1). On the other hand, this numerical value (b)
Is 75%, the breaking characteristics are similarly inferior (Comparative Example-
2). Therefore, the amount (b) of the highly conductive component in the second layer region
Is preferably in the range of 20 to 50% by weight.

Examples 4 to 6, Comparative Example-3 In Examples 1 to 3 and Comparative Examples 1 and 2 described above, I mentioned about a value of almost 20%, but this value is 40-80%
(Examples 4 to 6) show good breaking characteristics and breaking characteristics. If it is 150%, the threshold value is undesirably high.

As in Examples 1 to 6, the amount (a) of the highly conductive component in the first layer region varies from 1 to 52.5 wt%. As can be seen from Table 1, when the amount (a) of the highly conductive component in the first layer region is smaller than that (b) in the second layer region and within a predetermined range, the cutting characteristics are excellent. You can see that That is, when (a) is within the predetermined value, the threshold value is small. In addition, at 4 wt% or more (Example-1), the breaking characteristics of the contacts also show acceptable values.

On the other hand, when (a) was 1 wt% or less (Comparative Example-1), the breaking characteristics were deteriorated (failed), but this was caused by the disappearance of the conductive components on the contact surface due to the evaporation due to the discharge. This is because the temperature becomes extremely high locally. In addition, in this contact, the cutting characteristics are also deteriorated at the same time (the cutting value itself is high and the variation is large). This is because the conductive component in the first layer region has an arc at a portion where the conductive component has locally disappeared due to evaporation. This is because current interruption occurred with a large current.

Examples 7 to 9, Comparative Examples 4 to 5 In Examples 1 to 6 and Comparative Examples 1 to 3 described above, the thickness of the first layer region was 50 to 65 μm, but this thickness was 150 μm.
In the case of (Example-7), improved breaking characteristics can be obtained. However, when the thickness is 400 μm (Comparative Example-4), the contact portion is divided into a first layer region and a second layer region. The conductive component in the first layer region is smaller than that in the second layer region, and the effect of improving the cutting characteristics cannot be obtained. In that sense, Comparative Example-5 in which the first layer region does not exist does not show the effect of improving the cutting characteristics.

When the auxiliary component in the contact is 3 wt% (Example-8), the breaking characteristic is slightly inferior to the case where the auxiliary component is zero (Example-9), but the value is 1.6 A or less, which is within the preferable range. It is. Higher amounts of auxiliary components rapidly reduce the cutting performance. In particular, when the auxiliary component is zero (Example-9),
Although the threshold value has some variation, the threshold value is generally low. When the amount of Co is, for example, 7%, a remarkable decrease in cutting characteristics is observed.

Examples 10 to 14 The highly conductive components in the first layer region and the second layer region are not limited to Ag shown in Examples 1 to 9 and Comparative Examples 1 to 5, and one of them has coexistence of Ag and Cu ( Examples-10, 11) and both
Even when Ag and Cu coexist (Example-12), stable cutting characteristics are exhibited.

Further, the types of auxiliary components are not only Co but also Fe and Ni (Examples).
13-14) shows stable cutting characteristics.

Examples 15 to 22 The arc-resistant components were as described in Examples 1 to 14 and Comparative Examples 1 to 5 described above.
Used a WC with a particle size of 6 μm or less. However, the ratio of the highly conductive component in the first layer region and the second layer region was Is within a predetermined value, TiC, ZrC, HfC, VC, NbC,
TaC, stable chopping characteristic and cutoff characteristics in _{Cr 3 C 2, Mo 2 C} ( Example 15-22) is obtained.

[Effects of the Invention] As described above, according to the present invention, the amount (a) of the conductive component in the first layer region of the contact material is set within a predetermined value range from that (b) in the second layer region. By reducing the number, it is possible to obtain a vacuum valve having contacts that are excellent in breaking characteristics as compared with contacts having a uniform composition in (a) and (b) and that can cut off a large current.

[Brief description of the drawings]

FIG. 1 is a sectional view of a vacuum valve to which a contact material for a vacuum valve according to the present invention is applied, and FIG. 2 is an enlarged sectional view of an electrode portion of the vacuum valve shown in FIG. FIG. 3 is an enlarged sectional view of a contact material. 1 ... shut-off chamber, 2 ... insulating container, 3a, 3b ... sealing metal fittings, 4a, 4b ... lid, 5, 6 ... conductive rod, 7, 8 ... electrode, 9
... bellows, 10, 11 ... arc shield, 12, 14 ... brazing parts, 13a, 13b ... contacts in the second layer area, 15 ... parts of the first layer area where the amount of conductive components on the contact surface is small. .

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-170822 (JP, A) JP-A-58-157015 (JP, A) JP-A-62-184727 (JP, A) JP-A-62-184727 15716 (JP, A) JP-A-59-42734 (JP, A) JP-A-60-56321 (JP, A) JP-A-62-77439 (JP, A) JP-A-3-98222 (JP, A) JP-A-2-28033 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01H 33/66 H01H 33/64

Claims (5)

(57) [Claims] 1. A vacuum valve contact comprising: a first layer region forming a surface layer of a contact; and a second layer region forming an interior from the first layer region, wherein a first layer in the contact is provided. The layer region and the second layer region are continuously integrated with a high conductive component made of Ag and / or Cu, and the average amount of the high conductive component in the second layer region in the contact (b) is the total amount of the contact material. The amount (a) of the average high conductivity component in the first layer region in the contact is the amount (b) of the average high conductivity component in the second layer region. 20. The vacuum valve according to claim 19, wherein the contact is in the range of 20 to 80%, and the balance is constituted by an arc-resistant component. 2. The vacuum valve according to claim 1, wherein said first layer region has a thickness of 150 μm or less. 3. The arc resistant component is Ti, Zr, Hf, V, Nb, T
The vacuum valve according to claim 1, wherein the vacuum valve is a metal carbide of at least one metal selected from the group consisting of a, Cr, Mo, and W. 4. 4. The method according to claim 1, further comprising 0 to 3% by weight of at least one auxiliary component selected from Fe, Co and Ni with respect to the total amount of the contact material of the contact. The vacuum valve according to claim 1. 5. The highly conductive component comprises Ag and Cu, and the ratio of Ag in the highly conductive component is 50% or more.
The vacuum valve according to any one of the preceding claims.