JPH0433092B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Field of Industrial Application The present invention relates to a vacuum interrupter, and particularly to a vacuum interrupter suitable for detecting a decrease in the degree of vacuum.

B. Summary of the Invention In a vacuum interrupter in which a vacuum vessel is formed by closing both ends of an insulating tube with metal end plates, and a drop in vacuum degree can be detected by detecting the ground voltage of an intermediate shield, the vacuum interrupter suddenly breaks when the vacuum degree drops. By installing a vacuum gap that discharges only on either the fixed side or the movable side before reaching the disabled area and detecting a decrease in the degree of vacuum, it is possible to disconnect it even after a decrease in the degree of vacuum is detected. .

C. Prior Art Vacuum interrupters inherently have a longer life both electrically and mechanically than other switching devices, and require almost no maintenance or inspection. However, in addition to a decrease in the degree of vacuum due to an increase in the number of shear breaks, the degree of vacuum may also decrease due to vacuum leakage from bellows, airtight joints, etc., although this is very rare. A vacuum interrupter (current interrupter) has a reduced degree of vacuum, resulting in a decrease in interrupter performance as a vacuum interrupter, and eventually becomes unable to interrupt the interrupter. Therefore, it is required to regularly or constantly check the degree of vacuum. Moreover, it is desired that the vacuum interrupter can accurately and easily test the degree of vacuum in the energized state after being assembled with an operating mechanism to form a vacuum interrupter.

On the other hand, the degree of vacuum of the vacuum interrupter and the discharge starting voltage of the vacuum gap have a relationship similar to Patsien's law, as shown in FIG. In FIG. 3, the horizontal axis shows the internal pressure of the vacuum interrupter, and the vertical axis shows the discharge starting voltage. In the figure, the solid line (partially broken line) 1 shows the characteristics when the vacuum gap is 10 mm. As can be seen from FIG. 3, if the degree of vacuum in the vacuum interrupter is a high vacuum of 10 ^-4 mmHg (13.33 mPa) or less, the discharge starting voltage is extremely high. but,
When the degree of vacuum deteriorates to around 10 ^-1 mmHg (13.33Pa), it will discharge at 500V.

Conventionally, it is known that by utilizing such a law, the ground voltage of the intermediate shield of a vacuum interrupter can be detected in order to constantly monitor the degree of vacuum during energization.

Such a vacuum interrupter, for example, as shown in FIG. 4, has two identical cylindrical insulating cylinders 2, 2 made of glass or ceramics, each having a thin annular sealing fitting made of Kovar or the like fixed to both ends of each. 3, 3, . A vacuum container 6 is formed by closing the container 5b and evacuating the inside to a high vacuum (for example, a pressure of 10 ⁻⁵ mmHg (1.333 mPa) or less).

A fixed electrode rod 7a located on the axis of the vacuum container 6 is introduced airtightly from a metal end plate 5a on the fixed side. Further, in the vacuum chamber 6, a movable electrode rod 7b which can freely approach and leave the fixed electrode rod 7a is connected to a metal end plate 5 on the movable side via a metal bellows 8.
It is introduced airtight from b. Both electrode rods 7
A pair of fixed and movable electrodes 9a and 9b are integrally provided at the inner end portions of the electrodes a and 7b.

Further, inside the vacuum container 6, a metal intermediate shield 10 concentrically surrounding the electrodes 9a, 9b and part of the electrode rods 7a, 7b is supported by a sealing fitting 3 at the middle part of the insulating cylinder 4. There is. The fixed electrode rod 7a includes a metal shaft shield 11 that has a smaller diameter than the intermediate shield 10 and concentrically surrounds the fixed electrode rod 7a.
is fixed. A metal bellows shield 12, which has a smaller diameter than the intermediate shield 10 and concentrically surrounds the movable electrode rod 7b and the bellows 8, is fixed to the movable electrode rod 7b.

Here, the fixed side and the movable side of the vacuum interrupter are configured so that the electric field distribution state at the time of opening is almost symmetrical in order to improve withstand voltage characteristics in a high vacuum region. That is, intermediate shield 10 axis shield 11, bellows shield 1
2. Vacuum gap between metal end plates 5a, 5b, etc.
L ₁ , L ₂ , and L ₃ have the same size gap on the fixed side and the movable side.

Note that the intermediate shield 10 includes two capacitors.
It is connected to ground via an impedance voltage divider 13 formed by connecting C ₁ and C ₂ in series.

In the vacuum interrupter having such a configuration, the system line voltage E ₁ and the ground voltage E ₂ of the intermediate shield 10 satisfy E ₁ >E ₂ if the degree of vacuum is normal. but,
When the degree of vacuum deteriorates and discharge occurs, for example, between the intermediate shield 10, the shaft shield 11, and the bellows shield 12, the ground voltage of the intermediate shield 10 decreases.
E ₂ increases and becomes E ₁ ≒ E ₂ . Thereby, it is possible to judge whether the degree of vacuum is good or bad.

D Problems to be Solved by the Invention However, in such a conventional vacuum interrupter,
Although it is possible to determine that the degree of vacuum has deteriorated, since the fixed side and the movable side are constructed symmetrically in order to equalize the electric field distribution, the intermediate shield 10 and the fixed side and the movable side have almost the same degree of vacuum. Discharge occurs between both movable sides. Therefore, even if a decrease in the degree of vacuum is detected in a vacuum region that can be cut off and the operating mechanism (not shown) is activated to open the electrodes 9a and 9b, the fixed side and the movable side are separated by an intermediate shield. Since it is connected through 10,
In the end, it was not possible to cut off the load current or fault current.

The present invention has been made in view of these conventional problems, and its purpose is to be able to detect a decrease in the degree of vacuum in a vacuum area that can be cut off, and to open the vacuum immediately after that detection. To provide a vacuum interrupter in which a fixed side and a movable side can be reliably disconnected through an intermediate shield without flash shorting by operating the poles.

E Means for Solving the Problems The inventors of the present invention studied the discharge phenomenon in a vacuum interrupter and obtained the characteristics shown in FIG. 2. In FIG. 2, the horizontal axis represents the internal pressure of the vacuum interrupter, and the vertical axis represents the discharge starting voltage. In FIG. 2, solid lines 14, 15 and 16 are
These represent the characteristics of vacuum gaps A, B, and C, respectively, and the relationship is A>B>C.

It was generally known that a long gap has a higher discharge starting voltage than a short gap, but as can be seen from Figure 4, this phenomenon occurs in high vacuum or near atmospheric pressure, and is 10 ^-2 mmHg. In the region around (1.333 Pa), on the other hand, the discharge start voltage is higher in the short gap than in the long gap. The short gap had sufficient withstand voltage in the region of around 10 ^-2 mmHg (1.333 Pa).

Furthermore, the present inventors have studied the discharge phenomenon when an insulating material such as glass or ceramics is present in the vicinity of the vacuum gap. As a result, when there is an insulator near the vacuum gap, unlike the phenomenon shown in Figure 2 above, 10 ^-2 mmHg
(1.333 Pa), the discharge starting voltage was higher in the long gap than in the short gap, and it was found that the short gap was easier to discharge. this is,
This is thought to be due to the large amount of secondary electron emission from the insulator.

The present invention was made based on this knowledge, and it was decided to provide a vacuum gap that discharges only on either the fixed side or the movable side in the shearable area. That is, in the vacuum interrupter of the present invention, both ends of an insulating tube are closed with metal end plates to form a vacuum container. And in this vacuum container,
Introduce the fixed electrode rod airtightly from one metal end plate,
A movable electrode rod that can approach and separate from the fixed electrode rod is hermetically introduced from the other metal end plate via a bellows. In addition, at each inner end of these electrode rods,
A pair of fixed and movable electrode rods that can be moved toward and away from each other are provided.

Furthermore, a metal intermediate shield surrounding at least the outer periphery of the electrode is provided in the vacuum container to be insulated from the electrode. Further, this intermediate shield is connected to ground via an impedance. moreover,
A vacuum gap is formed between the intermediate shield and the grid potential member on the fixed side or the movable side, and one of the vacuum gaps is used as a vacuum gap that discharges in a vacuum region where the degree of vacuum is low and can be cut off. There is.

Here, the vacuum region that can be interrupted is determined by the specifications (for example, rated voltage, etc.) of the vacuum interrupter.

Furthermore, a metal shield is provided between the other vacuum gap and an insulator in the vicinity thereof to suppress discharge of the vacuum gap.

F Effect In a vacuum interrupter with such a configuration, when the degree of vacuum decreases during energization, electric discharge occurs in the long gap provided on either the fixed side or the movable side before reaching the unbreakable region. . At this time, no discharge occurs in the other vacuum gap (short gap), and the short gap is not induced to discharge by the discharge in the long gap. The reason why the short gap does not discharge even though there is an insulator near the short gap is because this insulator has a metal shield surrounding the short gap, which prevents the influence of secondary electron emission from the insulator. This is because it can be prevented. On the other hand, discharge in a long gap is immediately detected because the ground voltage of the intermediate shield fluctuates.

Therefore, immediately after detecting a decrease in the degree of vacuum, the operating mechanism is actuated to open the electrode, thereby making it possible to cut the shear.

G. Examples Hereinafter, the present invention will be explained in detail based on each example shown in FIG.

It should be noted that the same parts as in the prior art are indicated by the same reference numerals as in FIG. 4, and the explanation thereof will be omitted.

For example, as shown in FIG. 1, the vacuum interplater of the present invention includes metal end plates 5a,
An auxiliary shield 17 made of a cylindrical metal fixed to the same potential as 5b and concentrically and with the same diameter as the intermediate shield 10.
a, 17b (system potential members) are provided.
A vacuum gap is provided between the intermediate shield 10 and the auxiliary shield 17a on the stationary side, which discharges electricity in an area where the vacuum level is low and can be cut off.
L ₄ is formed. Vacuum gap _L4 is the longest vacuum gap in this vacuum interrupter. Note that the gap length is determined by the flight distance of electrons flying in a direction perpendicular to equipotential lines between members of different potentials.

Further, the vacuum gap L ₄ is connected between the intermediate shield 10 and the auxiliary shield 17b on the movable side.
A shorter vacuum gap L ₅ is formed. Further, on the inner surface of the insulating cylinder 2 on the movable side, a metal shield 18 is formed in a cylindrical shape with approximately the same length as the insulating cylinder 2 and surrounds the vacuum gap _L5 to suppress generation of electrical discharge in the vacuum gap _L5 . is installed.

In this vacuum interrupter, when the degree of vacuum decreases during energization, the vacuum gap _L4 discharges before reaching a vacuum region that cannot be cut off. This results in
The ground voltage of the intermediate shield 10 fluctuates, and deterioration of the degree of vacuum is detected via the impedance voltage divider 13. Immediately after this detection, the metal shield 18 suppresses the discharge of the vacuum gap _L5 on the other movable side and maintains the withstand voltage, and before the degree of vacuum further deteriorates and the vacuum gap _L5 starts discharging, By activating the operating mechanism (not shown) to separate the movable electrode rod 7b from the fixed electrode rod 7a and opening the electrodes 9a and 9b, the shear can be cut.

In the above embodiment, the insulating tube 4 was formed by combining two insulating tubes 2, but the present invention is not limited to such an embodiment, and the intermediate shield 10
It may be constructed with a single insulating tube as long as it can detect the voltage to ground. Also, vacuum gear L ₄
The length of the insulating cylinder 2 on the fixed side corresponding to this may be made longer than the insulating cylinder 2 on the movable side. Furthermore, the insulating cylinders 2 on the fixed side and the movable side may be joined via a metal tank that also serves as an intermediate shield.

On the other hand, the elements of the impedance voltage divider 13 are not limited to capacitors, but may be resistors or a combination of capacitors and resistors. Further, in the above embodiment, the longest vacuum gap _L4 is provided on the fixed side, but it goes without saying that these gaps may be provided on the movable side.

H. Effects of the Invention As described above, according to the present invention, vacuum gaps are formed between the intermediate shield and the grid potential member on the fixed side or the movable side, and one of the vacuum gaps is connected when the degree of vacuum decreases. A vacuum gap that discharges in a vacuum area that can be cut off, and a metal shield that suppresses discharge between the other vacuum gap and an insulator in the vicinity, prevents leakage in the early stages of vacuum deterioration (high (vacuum), discharge occurs only in one of the vacuum gaps, and discharge is suppressed in the other vacuum gap, so that the other vacuum gap has sufficient withstand voltage. Therefore, if you perform the opening operation immediately after detecting a decrease in the degree of vacuum by measuring the voltage of the intermediate shield, the other vacuum gap will maintain the withstand voltage, so there will be no flashover between the fixed side and the movable side via the intermediate shield. It can be cut off with certainty.

[Brief explanation of drawings]

Fig. 1 is a longitudinal sectional front view showing one embodiment of the vacuum interrupter of the present invention, Fig. 2 is a graph showing the relationship between the internal pressure of the vacuum interrupter and the discharge starting voltage when the vacuum gap length is different, and Fig. 3 is a graph showing the relationship between the internal pressure of the vacuum interrupter and the discharge starting voltage when the vacuum gap length is different. FIG. 4 is a vertical sectional front view of a conventional vacuum interrupter. 4...Insulating tube, 5a, 5b...Metal end plate, 6...
...Vacuum container, 7a...Fixed electrode rod, 7b...Movable electrode rod, 8...Bellows, 9a...Fixed electrode, 9
b...Movable electrode, 10...Intermediate shield, 13...
... Impedance voltage divider, 17a, 17b ... Auxiliary shield, 18 ... Shield, L ₄ , L ₅ ... Vacuum gap.

Claims (1)

[Scope of Claims] 1. A fixed electrode rod having an electrode attached to the inner end is hermetically introduced from one metal end plate of a vacuum container in which both ends of an insulating tube are closed with metal plates, and a fixed electrode rod having an electrode attached to the inner end is introduced into the vacuum container from the other metal end plate. A movable electrode rod with an electrode at the end is introduced airtightly through a bellows, and a metal intermediate shield surrounding at least the outer periphery of the electrode is provided in the vacuum container near the insulator, and this intermediate shield is used to control the impedance. In a vacuum interrupter connected to the atmosphere through The vacuum gap is characterized by a vacuum gap that discharges in a vacuum region that can be cut off, and a metal shield that suppresses the discharge of the vacuum gap between the other vacuum gap and an insulator in its vicinity. Vacuum interrupter.