JPS6327810B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a vacuum valve, and more particularly, to a vacuum valve with improved withstand voltage characteristics.

[Background technology and its problems]

The shield of a vacuum valve plays a major role in preventing the arc generated between the electrodes from directly touching the insulating container when the current is interrupted, and also in preventing metal vapor from adhering to the inner surface of the insulating container. There is.

However, since the discharge causes a creeping discharge from the shield through the insulating container, improvement of the unit voltage of the vacuum bulb is hindered.

As shown in FIG. 1, a conventional vacuum valve has a vacuum container in which end plates 2 and 3 are provided at both ends of an insulating container 1, which is made up of two insulating cylinders 1a arranged side by side in the axial direction, and the inside is evacuated. is forming. The fixed electrode 4 is provided with an electrode 4c having a contact 4b on a current-carrying shaft 4a that passes through the end plate 2 in an airtight manner. In addition, the movable electrode 5
An electrode 5c having a contactor 5b is provided on the end plate 3 via a bellows 6 and movably sealed to a current-carrying shaft 5a. A metal fixed shield 7a is placed on the fixed electrode side, a metal intermediate shield 8 is placed in the middle of the vacuum container, and a metal fixed shield 7b is placed on the movable side.
has been established. These shields 7 and 8 play a major role in preventing metal vapor generated between the electrodes 4 and 5 from adhering to the inner wall of the insulating container 1 when the current is interrupted. However, since the insulating cylinder 1a is located near the metal fixed shield 7 and intermediate shield 8, the breakdown voltage is reduced. Considering the movable side as shown in FIG. 2, when an electric field is applied to the intermediate shield 8, the fixed shield 7 on the movable side becomes a cathode and the electrons e are emitted.
collides with the insulating cylinder 1a and emits secondary electrons.
Collision energy and secondary electron emission efficiency δ(E) at this time
The relationship with is the characteristic curve δ(E) shown in FIG. In FIG. 3, the vertical axis shows the secondary electron emission efficiency δ(E), and the horizontal axis shows the electron collision energy E [eV].
Positive charges are accumulated in the insulating cylinder 1a according to this curve δ(E). The electrons emitted from the insulating cylinder 1a multiply by a secondary electron avalanche, eventually leading to dielectric breakdown. Therefore, a precursor breakdown current due to electron avalanche flows at a relatively low voltage, and as a result,
Breakdown voltage becomes low. On the other hand, in recent years, the voltage of circuits using vacuum valves has significantly increased, and there is a desire for a vacuum valve that can be used stably at high voltage.

[Purpose of the invention]

The present invention has been made in view of the above points, and an object of the present invention is to provide a vacuum valve suitable for high voltage applications.

[Summary of the invention]

According to the present invention, in order to achieve such an objective,
The intermediate shield and fixed shield are formed of ceramics, and a conductive layer or a semiconductive layer is formed on the inner surface of the shield.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in detail with reference to FIG.

Note that the same parts as in FIG. 1 are designated by the same reference numerals, and the explanation thereof will be omitted. As shown in Figure 4, the insulation tube 1
A vacuum container is formed by sealing end plates 2 and 3 to both ends of an insulating container 1 in which two A are arranged side by side in the axial direction,
The fixed electrode 4 has an electrode 4c provided with a contact 4b at the tip of a current-carrying shaft 4a that passes through the end plate 2 and is sealed. The movable electrode 5 is provided with an electrode 5c having a contact 5b at the tip of an energizing shaft 5a which is movably sealed to the end plate 3 via a bellows 6 having a cover 6a. Fixed electrode side end plate 2 and movable electrode side end plate 3 are provided with fixed shields 91 and 92 made of ceramics, respectively, and a shield made of ceramics with an alumina Al ₂ O ₃ blending ratio of 98% or more is provided in the middle of the vacuum container. An intermediate shield 10 is provided. On the inner surface of each fixed shield 91, 92 and intermediate shield 10, a conductive layer or semiconductive layer 9a, 10a having a resistivity of 1 to 100 μΩ·cm is formed by coating or vapor deposition.

[Action of the invention]

Conductive layer 1 deposited on the inner surface of intermediate shield 10
0a and the metal layer 9a deposited on the inner surface of the fixed shields 91, 92, the metal layer 9a, 10
Since a is covered with ceramics, the conductive layer 9
The radiation current from a and 10a is suppressed. This suppresses secondary electron avalanche on the inner surface of the insulating container 1a, increasing the breakdown voltage.

The relationship between this precursor breakdown current and the applied voltage is shown in FIG. In the figure, the vertical axis shows the precursor breakdown current, and the horizontal axis shows the applied voltage. Curve I _a is the case where the insulating member is not coated, and curve I _b is the case where the inner surface of the ceramic is electrically conductive coated. Dielectric breakdown occurs when this precursor breakdown current reaches a predetermined limit _Ic . Since this precursor breakdown current is suppressed, the dielectric breakdown voltage is improved. In this way, the electric field strength of the conductive layers 9a and 10a on the inner surface of the ceramic can be increased.

Further, the arc generated between the electrodes 4a and 4c touches the conductive layer 10a of the intermediate shield 10, and the conductive layer 1
The temperature of 0a increases. The ceramic of the intermediate shield 10 has a blending ratio of alumina (Al ₂ O ₃ ) of 98% or more, so it has excellent heat resistance. Even if the temperature of the conductive layer 10a increases due to the arc, it will not melt. The thickness of the shield made of ceramics is selected depending on the insulation class. The material for the inner surface of the ceramics does not necessarily have to be a conductive layer, and may be a semiconductive material in order to lower the electric field at the sealed portion of the insulating container 1a.

With such a configuration, the volume of the vacuum container can be reduced, resulting in significant cost reductions.

In addition, an intermediate shield 10 and a fixed shield 9
Since the gap length of 1 and 92 can be shortened, it is possible to prevent the metal vapor generated between the electrodes 4 and 5 from adhering to the inner surface of the insulating cylinder when the current is interrupted. The steam is insulated container 1a
It is possible to prevent a drop in pressure resistance due to adhesion to the inner surface of the surface.

[Overall effect]

As detailed above, according to the present invention, the intermediate shield and the fixed shield are formed of ceramics,
Since a conductive layer or a semiconductive layer is formed by vapor deposition or coating on the inner surface of this ceramic, it is possible to improve the creepage withstand voltage between both shields, reduce the overall size, and significantly reduce costs.
We can provide vacuum valves suitable for high voltage and large capacity.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view showing a conventional vacuum valve;
Fig. 2 is a cross-sectional view showing the main parts of the intermediate shield and fixed shield of a conventional vacuum valve, Fig. 3 is a characteristic diagram showing secondary electron emission characteristics, and Fig. 4 shows the vacuum valve of the present invention. The vertical cross-sectional view and FIG. 5 are characteristic diagrams showing the relationship between applied voltage and precursor breakdown current. 1a... Insulating cylinder, 1... Insulating container, 2, 3...
End plate, 4... Fixed electrode, 5... Movable electrode, 6...
Bellows, 9a, 10a...conductive layer or semiconductive layer, 10...shield, 91, 92...fixed shield.

Claims (1)

[Claims] 1 A pair of electrodes that can be moved into and out of contact with each other is arranged in a vacuum container consisting of an insulating container and an end plate that closes the insulating container, and at least one of the pair of electrodes is movably sealed to the end plate via a bellows. and a fixed shield supported by the end plate, and an intermediate shield surrounding the electrode, wherein the intermediate shield and the fixed shield are made of alumina (Al ₂ O ₃ ) with a blending ratio of 98% or more. A vacuum valve characterized in that it is made of ceramics and has a conductive or semiconductive layer having a resistivity of 1 to 100 μΩ·cm on the inner surfaces of the intermediate shield and the fixed shield.