JPH069130B2 - Vacuum valve - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a vacuum valve.

[Technical background of the invention and its problems]

As shown in FIG. 4, a conventional vacuum valve is a vacuum container whose inside is evacuated by providing end plates 2 and 3 at both ends of an insulating container 1 in which two insulating cylinders 1a are arranged side by side in the axial direction. Is forming. The fixed electrode 4 is provided with an electrode 4c having a contactor 4b on a current-carrying shaft 4a penetrating the end plate 2 in an airtight manner. Further, 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. Then, the flange shield 7 is attached to the fixed electrode side.
An arc shield 8 is provided in the middle of the vacuum container, and a flange shield 7 is provided on the movable side.

Such shields 7 and 8 are electrodes 4 and 5 when the current is cut off or cut off.
It plays a great role in preventing the metal vapor generated between them from adhering to the inner wall of the insulating container 1. However, since there is the insulating cylinder 1a near the flange shield 7 and the arc shield 8, the breakdown voltage is lowered. Considering the movable side as shown in FIG. 5, when an electric field is applied to the arc shield 8, the electron e emitted by the movable side flange shield 7 acting as a cathode collides with the insulating cylinder 1a to generate 2 Emits the next electron. 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 FIG. 6, the vertical axis represents the secondary electron emission efficiency δ (E), and the horizontal axis represents the electron collision energy E [eV]. According to this curve δ (E), positive charges are accumulated in the insulating cylinder 1a. The electrons emitted from the insulating cylinder 1a multiply by a secondary electron avalanche, and eventually lead to dielectric breakdown. Therefore, the precursor 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 circuits using vacuum valves has increased remarkably, and the emergence of vacuum valves that can be stably used at high voltages is desired.

[Object of the Invention]

An object of the present invention is to provide a vacuum valve having a high creeping pressure resistance.

[Outline of Invention]

The present invention arranges a pair of electrodes that can be contacted and separated from each other in a vacuum container consisting of an end plate that closes both ends of an insulating cylinder, and at least one of the pair of electrodes is movable to one of the end plates through a bellows. In a vacuum valve equipped with a flange shield attached to the end plate and an arc shield surrounding the electrode, the end of the insulating cylinder is tapered to form a squeezed portion, There is provided a vacuum valve characterized in that an external arc shield is fixedly provided on the outer periphery of the end plate on the outer side of the squeezed portion.

Example of Invention

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the present invention. In FIG. 1, the same reference numerals are given to the same functions in FIG. 4 and detailed description thereof will be omitted.

In FIG. 1, one end of an insulating cylinder 1a is tapered to provide a squeezed portion, and end plates 2 and 3 are fixed to the end faces thereof to form a vacuum container 1. Then, the fixed electrode 4 penetrates the end plate 2 in an airtight manner by the energizing shaft 4a, and the energizing shaft 5a attached to the movable electrode 3 penetrates the end plate 3 in an airtight manner via the bellows 6 and is fixed thereto. An external shield 9 is attached to the outside of the squeezed side of the insulating cylinder 1a in order to reduce the electric field at the end portions of the end plates 2 and 3.

The potential distribution by the outer shield 9 is shown by a broken line in FIG. 2 as an equipotential surface for every 20%. Looking at the crossing angle between the equipotential surface and the surface of the insulating cylinder 1a, it is found that they are inclined and not orthogonal, but this is the point of the present invention and will be described below.

Assuming that a negative impulse voltage enters the end plate 2 in FIG. 2, the flange shield 8 serves as a side for emitting electrons, and electrons are emitted by field emission from point A on the flange shield 8, for example. .

At this time, the electrons emitted from the point A rush into the arc shield 7 without reaching the surface of the insulator as shown by the solid line in FIG. Therefore, no secondary electron avalanche occurs on the surface of the insulator. In addition, since the electric field weakens outside the point A [direction of the point A '], the field emission itself does not occur. Therefore, it is understood that this structure is strong against a negative impulse.

On the other hand, when a positive impulse penetrates, the point B becomes the field emission point, but the electron emitted from this point is C on the surface of the insulator.
Clash at points. The important thing here is that the direction of the lines of electric force is C
The point is that it is facing the inside of the insulator.

According to experiments, the inventors have found that electron avalanche does not occur in the range of normal electric field intensity on α10 ° insulator surface when the angle α satisfies the following equation without the direction of the electric field on the insulator surface and the insulator value. Found.

In other words, the angle at which the equipotential surface intersects the surface of the insulator should not be larger than 80 °.

Of course, no matter what kind of electrode structure is adopted, a portion where the insulator and the equipotential surface are orthogonal to each other is always generated. In the case of FIG. 2, since the equipotential surface PP 'is orthogonal to the insulator surface at the point S, the point A'on the arc shield 8 and the flange shield 7 are shown.
The electrons emitted from the upper B'point may cause an electron avalanche on the surface of the insulator.

However, at point A ', the electric field is shielded by the arc shield 8 and is sufficiently low so that no field emission electrons are generated. On the other hand, although the electron emission occurs because the electric field is strong at the point B ', the potential at the equipotential surface PP' is sufficiently close to the arc shield 8, so that the electrons at the point S are sufficiently accelerated.

Therefore, the collision energy of electrons on the surface of the insulator is sufficiently higher than E _{2 in} FIG. 6, so the secondary electron emission table becomes 1 or less, and electron avalanche does not occur.

In this way, the vacuum valve of this structure is a high withstand pressure vacuum valve having sufficient creeping strength, which is more obvious than the characteristics shown in FIG.

That is, as compared with the conventional valve shown by Ia in FIG. 3, the characteristic of the valve of the present invention is Ib and the precursor current is sufficiently small.

In general, a vacuum creepage breakdown occurs in which a precursor current is generated in a certain electric field Ic, so that it is understood that the breakdown voltage of the valve of the present invention is higher than the conventional Va and becomes a high breakdown voltage of Vb.

〔The invention's effect〕

According to the present invention, a vacuum valve having a large creeping pressure resistance can be obtained by tapering the end portion of the insulating cylinder and providing the squeezed portion and providing the external arc seal on the outer side thereof.

[Brief description of drawings]

FIG. 1 is a sectional view of a vacuum valve according to an embodiment of the present invention, and FIG.
FIG. 4 is a partially enlarged view of a vacuum valve for explaining the electronic avalanche suppressing action, FIG. 3 is a characteristic diagram comparing the characteristics of the vacuum valve of the embodiment and the conventional example, FIG. 4 is a sectional view of the conventional vacuum valve, and FIG.
FIG. 6 is an explanatory diagram showing an electronic avalanche phenomenon on the surface of an insulator, and FIG. 6 is a characteristic diagram showing characteristics of the electronic avalanche phenomenon. 1 ... Insulation container 2, 3 ... End plate 9 ... External arc shield

Claims (1)

[Claims] 1. A pair of electrodes which can be brought into contact with and separated from each other is arranged in a vacuum container consisting of an insulating cylinder and end plates closing both ends of the insulating cylinder.
At least one of the pair of electrodes is movably sealed to one of the end plates via a bellows, and a vacuum valve provided with a flange shield attached to the end plate and an arc shield surrounding the electrodes is provided. A vacuum valve, characterized in that an end portion of the insulating cylinder is tapered to form a squeezed portion, and an external arc shield is provided outside the squeezed portion by being fixed to an outer circumference of the end plate.