JPH0652645B2 - Vacuum valve - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a vacuum valve having improved withstand voltage performance inside a valve body.

[Technical background of the invention]

As shown in FIG. 1, the conventional vacuum valve has a structure in which two insulating cylinders 1a are arranged side by side in the axial direction, and end plates 2 and 3 are provided at both ends of the insulating container 1 to form a vacuum container having a vacuum inside. is doing. The fixed electrode 4 is provided with an energizing shaft 4a that hermetically penetrates the end plate 2 and an electrode 4c having a contactor 4b. The movable electrode 5 is provided with an electrode 5c having a contactor 5b on an energizing shaft 5a movably sealed on the end plate 3 via a bellows 6.

However, flange shields 7 and 7a are provided on the fixed and movable electrode sides, respectively, and an arc shield 9 is provided in the middle of the vacuum container via a support metal fitting 8.

Each of the shields 7, 7a and 9 plays a great role in preventing the metal vapor generated between the electrodes 4 and 5 from being attached to the inner wall of the insulating container 1 when the current is cut off. However, since there is the insulating cylinder 1a near the flange shield and the arc shield, the breakdown voltage is lowered.

This is because when considering the movable side as shown in FIG.
When an electric field is applied to the arc shield 9, the movable side flange shield 7a serves as a cathode and the emitted electrons e collide with the insulating cylinder 1a to emit secondary electrons. The relationship between the collision energy and the secondary electron emission efficiency δ (E) at this time is the characteristic curve δ (E) shown in FIG. In Figure 3, the vertical axis is 2
Secondary electron emission efficiency δ (E), horizontal axis is electron collision energy E
[EV] is shown. Insulation tube 1a follows this curve δ (E)
A positive charge is stored in. The electrons emitted from the insulating cylinder 1a multiply by a secondary electron avalanche and finally lead to dielectric breakdown. Therefore, the breakdown current due to the electron avalanche flows at a relatively low voltage, and as a result, the breakdown voltage becomes low. On the other hand, in recent years, the voltage of a circuit using a vacuum valve has been remarkably increased, and a vacuum valve that can be stably used at a high voltage has been desired.

However, as a method for eliminating the above-mentioned drawbacks, it has been considered to cover the surfaces of the arc shield 9 and the flange shields 7 and 7a with an insulating member such as alumina and epoxy resin. This can suppress the emission of field emission electrons from either shield serving as the cathode, and thus can suppress the primary electrons that enter the insulating cylinder. Therefore, it is possible to limit the progress of secondary electron avalanche on the surface of the insulating cylinder, and it can be expected that the withstand voltage performance is improved.

[Problems of background technology]

 However, there are the following drawbacks with such a device.

That is, in the vacuum valve, the components in the vacuum container must have as high thermal conductivity as possible because of the rapid temperature rise of the electrode surface due to the arc generated when the current is cut off and the temperature rise due to the heat run test. However, since the insulating material such as alumina or epoxy resin has a low thermal conductivity, the heat dissipation characteristic is remarkably deteriorated.

Further, since alumina or epoxy resin has a low dielectric strength of the insulating material itself, the withstand voltage performance is not improved as expected.

Furthermore, this type of vacuum valve requires several 1
It is necessary to perform vacuum heating to 00 ° C. Therefore, the melting point of the parts in the vacuum valve must be higher than the heating temperature. On the other hand, since the epoxy resin has a low melting point, it is necessary to lower the heating temperature in order to use the epoxy resin in a vacuum container, and the degassing process cannot be sufficiently performed.

In addition, since the melting point is high when coated with alumina etc., degassing can be sufficiently performed, but due to the difference in thermal expansion from the metal shield, the thermal expansion stress due to the arc at the time of heat treatment or interruption Cause damage and cracks.

When a slight crack is generated as well as damage, electrons are emitted through the crack, so that the effect of suppressing electron emission is lost and the withstand voltage is lowered.

Therefore, it is difficult to coat the shield of the vacuum valve with an insulating material such as alumina or epoxy resin, and it is difficult to put a vacuum valve suitable for high voltage with good withstand voltage performance into practical use.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and it is possible to prevent electrons emitted from the shield end portion from colliding with the insulating container due to field emission and being charged on this surface, so that a high creepage withstand voltage can be obtained. It is an object of the present invention to provide a vacuum valve having

[Outline of Invention]

The present invention has been made in order to achieve the above-mentioned object, and a pair of electrodes that can be contacted and separated is provided in a vacuum container composed of an insulating container and an end plate that closes the insulating container, and at least the pair of electrodes is provided. One is movably sealed to the end plate through a bellows, and one end side is held by the end plate in the insulating container to provide a metal cylinder portion, respectively, and an arc shield surrounding the electrode. An outer shield that covers the end portion of the arc shield with the metal cylinder portion, and that includes the metal cylinder portion installation region outside the vacuum container and covers the outer periphery of the end portion of the insulating container. The feature is that it is provided.

Example of Invention

An embodiment of the present invention will be described in detail below with reference to FIGS. 4 and 5.

The same parts as those in FIG. 1 are designated by the same reference numerals and the description thereof will be omitted. As shown in FIG. 4, two ends of an insulating container 1 in which two insulating cylinders 1a are arranged side by side in the axial direction are sealed with end metal cylindrical portions 2a and 3a sealed to end plates 2 and 3, respectively, and a vacuum is formed. The container 4 is formed, and the fixed electrode 4 is provided with an electrode 4c having a contactor 4b at the tip of a current-carrying shaft 4a that penetrates the end plate 2 and is sealed. Further, the movable electrode 5 is provided with an electrode 5e having a contact 5b at the tip of a current-carrying shaft 5a that is movably sealed to the end plate 3 via a bellows 6. External shields 10 and 10 are provided on the end metal cylindrical portion 2a on the fixed electrode side and the end metal cylindrical portion 3a on the movable electrode side, respectively.
A support metal fitting 8 is provided on the connecting portion 8 of the insulating cylinder 1a in the middle of 0 and 10.
a is provided to hold the arc shield 9 and the supporting cylinder 8
The insulating cylinder 1a is sealed and supported by b.

Since the end portion 9a of the arc shield 9 is arranged so as to be covered by the end metal cylindrical portion 2a or 3a, the electrons emitted from the end portion 9a of the arc shield by field emission are shown in FIG. Thus, it does not collide with the inner wall surface of the insulating cylinder 1a, but is directed toward the end metal cylindrical portions 2a and 3a and the end plates 2 and 3 as indicated by a ⁻ .

Therefore, as shown in FIG. 2 and FIG. 3, the electron avalanche is generated and the surface insulation is destroyed by the repetition of collision on the insulator surface → secondary electron emission → re-collision → re-secondary electron emission →. The phenomenon of doing will be suppressed.

The above is the case where the end plate 2 has a positive polarity with respect to the arc shield 9 in FIG. 5, but when it has a reverse polarity, the end plate 2 at the tip 2c of the end metal cylindrical portion 2a in FIG. Although the electric field may become large and field emission electrons may be generated from the junction 2d between the insulator and the metal, these may be generated by shielding the junction 2d by the external shield 10 as shown in FIG. The concentration of the electric field from the portion is relaxed and secondary electrons are not generated.

On the other hand, at this time, the electric field at the end portion 10a of the outer shield is slightly strengthened, but the insulation design is relatively easy because it is outside the vacuum valve, and an insulating gas such as SF _{6 having} a good insulating property is provided outside. By using it, insulation strength higher than vacuum insulation can be obtained.

Although FIG. 5 has described the portion of the end plate 2, it is clear that the end plate 3 is the same as the above with only the polarities being reversed.

With such a configuration, the insulation in the vacuum valve is substantially free of so-called creeping insulation. That is, in FIG. 5, the insulating cylinder 1a
As can be seen in the figure, the electric field strength of the portion 9b of the arc shield 9 having an electric field directed toward the electric field is much smaller than the electric field strength of the shield end portion 9a. There is no electron collision.

Therefore, since the insulation in the vacuum valve is only so-called inter-electrode insulation, a small vacuum valve having a high withstand voltage can be obtained by fully utilizing the withstand voltage characteristics of the electrode valve metal material for the vacuum valve.

Although FIG. 6 shows another embodiment of the present invention, the same parts as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted. In FIG. 6, end plate cylinders 2b and 3b are respectively fixed to the end plate 2 and the end plate 3 and located inside the insulating cylinder 1a, and the arc shield 9 is placed inside the cylinders.
The front end portion 9a is arranged as shown. Further, the metal support 8 of the arc shield 9 is provided with an intermediate outer shield 11 for the purpose of relaxing the electric field strength to the outside of this portion.

With such a configuration, the field emission electrons emitted from the tip portion 9a of the arc shield 9 are directed to the end plate 2 or 3 and further to the end plate cylinder 2b or 3b and do not reach the insulating cylinder 1a. Also, it is clear that the electric field at the tip 2c or 3c of the end plate cylinder 2b or 3b is relaxed by the effective shielding action of the outer shield 10 and does not generate field emission electrons.

Further, since the external electric field in the portion of the intermediate shield 8 is effectively shielded by the intermediate external shield 11, the electric field is relaxed and good withstand voltage characteristics can be obtained.

FIG. 7 compares the dark current of the valve of the present invention shown in FIGS. 4 and 5 with that of a conventional valve. That is, when the breakdown voltage is plotted on the horizontal axis and the dark current is plotted on the vertical axis, the characteristic A of the conventional valve has a sharp rise in the dark current characteristic, which is due to the electron multiplication effect due to the creepage. On the other hand, the valve of the present invention exhibits a stable dark current characteristic B.

In a vacuum valve, when the dark current reaches a constant value IC of about several mmA, the breakdown voltage of the conventional valve is V ₁ , the breakdown voltage of the valve of the present invention is V ₂ , and the characteristic of the valve of the present invention is You can see that it is good.

〔The invention's effect〕

As described above, according to the present invention, it is possible to effectively prevent the field emission electrons emitted from the metal portion installed in the vacuum valve from colliding with the inner surface of the insulator container and multiplying it, thereby causing dielectric breakdown. A pressure-resistant compact vacuum valve can be obtained.
In addition, by using an insulating gas such as SF ₆ as the external insulation, the insulation characteristics are dramatically improved.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a conventional vacuum valve, FIG. 2 is a cross-sectional view showing main parts of an arc shield and a flange shield of the conventional vacuum valve, and FIG. 3 shows secondary electron emission characteristics. Fig. 4 is a characteristic curve diagram, Fig. 4 is a schematic vertical sectional view of the vacuum valve of the present invention, Fig. 5 is a potential distribution diagram of the arc shield end portion of the present invention and a main portion of the end plate metal cylinder, and Fig. 6 is a book. FIG. 7 is a schematic vertical sectional view of another embodiment of the invention, and FIG. 7 is a comparative curve diagram of dark current characteristics of the vacuum valve of the present invention and a conventional vacuum valve. 1 ... Insulation container, 1a ... Insulation cylinder, 2,3 ... End plate, 2a, 3
a ... end metal cylindrical portion, 4 ... fixed electrode, 5 ... movable electrode, 6
... bellows, 9a ... end of arc shield, 10 ... outer shield, 11 ... intermediate outer shield.

Continuation of front page (56) References JP-A-48-21168 (JP, A) JP-A-48-101562 (JP, A) JP-A-50-103677 (JP, A) JP-A-53-131480 (JP , A) JP-A-57-80625 (JP, A) JP-A-60-100324 (JP, A) Practical development Sho-55-66350 (JP, U)

Claims (1)

[Claims] 1. A pair of electrodes that can be contacted and separated from each other are provided in a vacuum container composed of an insulating container and an end plate closing the insulating container, and at least one of the pair of electrodes is movable to the end plate through a bellows. Along with being sealed to the inside of the insulating container, one end side is held by the end plate to provide a metal cylindrical portion, and an arc shield surrounding the electrode is further provided, and an end portion of the arc shield is provided. A vacuum valve which is covered with the metal cylindrical portion, and is provided with an external shield outside the vacuum container, the outer shield including the metal cylindrical portion installation region and covering an outer periphery of an end side of the insulating container.