JPH043616B2 - - 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 A vacuum interrupter in which a vacuum vessel is formed by closing both ends of an insulating tube with metal end plates, and a decrease in the degree of vacuum can be detected by detecting the ground voltage of an intermediate shield. By forming a tapered portion on one of the sides, and forming a long gap near the inner peripheral surface of the tapered portion between the intermediate shield and the grid potential member on the side on which the tapered portion is formed, This device is designed to be able to detect a decrease in the degree of vacuum at an early stage when the degree of vacuum begins to decrease, and to be able to cut off the vacuum after the 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 shears, the degree of vacuum may 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, the vacuum interrupter is required to be able to accurately and easily test the degree of vacuum in an energized state after the vacuum interrupter is connected to the operating mechanism and the vacuum interrupter is assembled.

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. 2, 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 Figure 2, if the degree of vacuum inside the vacuum interrupter is a high vacuum of 10 ^-4 mmHg (13.33mPa) or less, the discharge starting voltage is extremely high. However, when the degree of vacuum decreases 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.

For example, as shown in FIG. 3, such a vacuum interrupter includes two identical cylindrical insulating tubes 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, . , 5b, and the inside is evacuated to a high vacuum (for example, a pressure of 10 ⁻⁵ mmHg (1.333 mPa) or less) to form a vacuum container 6.

A fixed electrode rod 7a positioned on the axis of the vacuum container 6 is hermetically introduced from one metal end plate 5a. Further, a movable electrode rod 7b is airtightly introduced from the other metal end plate 5b via a metal bellows 8 so as to be able to approach and move away from the fixed electrode rod 7a. At each inner end of these electrode rods 7a and 7b, fixed electrodes 9a and movable electrodes 9a,
9b is integrally provided.

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

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, the sizes of the vacuum gaps L ₁ , L ₂ , L ₃ , and L ₄ between the intermediate shield 10 and the shaft shield 11, bellows shield 12, metal end plates 5a, 5b, etc. are different for the fixed side and the movable side. They have the same dimensions.

Note that the intermediate shield 10 includes two capacitors.
It is connected to the 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 decreases and, for example, a discharge occurs between the intermediate shield 10 and the shaft shield 11 or the bellows shield 12, the ground voltage E ₂ of the intermediate shield 10
increases and becomes E ₁ ≒ E ₂ . Thereby, it is possible to determine whether the degree of vacuum has decreased.

D Problems to be Solved by the Invention However, in such a conventional vacuum interrupter,
Although it is certainly possible to determine that the degree of vacuum has decreased, the fixed side and the movable side are constructed symmetrically in order to equalize the electric field distribution. Also, discharge occurs simultaneously between both charging parts on the movable side. Therefore, even if a decrease in the degree of vacuum is detected in a vacuum region that can be interrupted and the operating mechanism (not shown) is activated to open the electrodes 9a and 9b,
Since the fixed side and the movable side were flash-circuited through the intermediate shield 10, it was impossible to cut off the load current or fault current.

E. Means for Solving the Problems The present inventors investigated the discharge phenomenon in vacuum interrupters and obtained the characteristics shown in FIG. 4. FIG. 4 shows the vacuum interrupter internal pressure on the horizontal axis and the discharge starting voltage on the vertical axis. In Fig. 4, solid line 14, solid line 15, and solid line 1
6 shows the characteristics when the vacuum gap sizes are P, Q, and R, respectively, where P>Q>
It is in the relationship of R.

In general, it was known that long gaps have a higher discharge starting voltage than short gaps, 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 (1.333Pa).

The present invention was made based on this knowledge, and is provided with a long 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, a metal intermediate shield surrounding at least the outer periphery of the electrode is provided in the vacuum container and insulated from both electrodes, and this intermediate shield is connected to the ground via an impedance, A long gap is formed between the intermediate shield and the system potential member on either the fixed side or the movable side, which discharges in a vacuum region that can be cut off when the degree of vacuum decreases. The vacuum region that can be interrupted is determined by the specifications (for example, rated voltage, etc.) of each vacuum interrupter.

On the other hand, as a result of various experiments, we found that if a long gap is provided near an insulating member that easily generates secondary electrons, such as glass, and the structure is configured so that the electrons flying between the long gaps hit the insulating member, the insulating member It was found that because a large number of secondary electrons are emitted from the gap, a discharge occurs at an earlier stage of the vacuum drop than simply providing a long gap, making it possible to detect the vacuum drop earlier.

Fig. 5a shows a vacuum interrupter in which a long gap is simply provided inside the insulating cylinder, and Fig. 5b shows a vacuum interrupter in which a tapered part is provided on the fixed side of the insulating cylinder, and the inner diameter becomes smaller toward the end. This shows a vacuum interrupter with a long gap inside the section.
In the case of FIG. 5a, since the metal end plate 5a, the auxiliary shield 17a, and the fixed electrode rod 7a are at the same potential, the intermediate shield 10 at an intermediate potential with these members
If you draw an equipotential line 18 between them, it will look like the figure. Considering the flight of electrons perpendicular to the equipotential lines, if electrons come out from the auxiliary shield 17a, they will collide with the insulating tube 2a, but the intermediate shield 1
It was found that the electrons emitted from 0 often fly without colliding with the insulating tube 2a.

Therefore, the probability that the primary electrons generated from the shield will hit the insulating cylinder 2a is small, and the generation of secondary electrons is also reduced, so there is a possibility that a discharge will occur between the auxiliary shield 17a and the intermediate shield 10 at the beginning of the decrease in vacuum level. There are few.

On the other hand, in the case shown in Fig. 5b, the insulating cylinder 2
A is tapered so that the inner diameter decreases toward the end, and the end of the intermediate shield 10 is inclined along the inner wall surface of the insulating cylinder 2a. Therefore, if we draw equipotential lines, they will look like the figure, and electrons flying in a direction perpendicular to the equipotential lines will collide with the inner wall surface of the insulating cylinder 2a, regardless of whether they fly out from the auxiliary shield 17a or the intermediate shield 10. I understand. Therefore, there is a high probability that primary electrons will hit the inner peripheral surface of the insulating tube 2a and generate secondary electrons, and the auxiliary shield 17a
There is a high possibility that electric discharge will occur between the intermediate shield 10 and the intermediate shield 10.

In view of the above, in the present invention, by forming a tapered part in the insulating cylinder, the inner diameter of which decreases toward the end, and providing a long gap inside the tapered part, the inner circumferential surface of the insulating cylinder is This makes it easier for electrons to hit, so that a decrease in the degree of vacuum can be detected at the beginning of the decrease in the degree of vacuum.

F Effect In a vacuum interrupter with such a configuration, when the degree of vacuum decreases during energization, the gap between the auxiliary shield provided on either the fixed side or the movable side and the intermediate shield before reaching the unbreakable region. Electric discharge occurs at the long gap. That is, in the long gap, even if electrons fly out from either the auxiliary shield or the intermediate shield, the electrons fly in a direction perpendicular to the equipotential lines and collide with the inner peripheral surface of the insulating cylinder. The insulating cylinder itself easily emits secondary electrons, and as the degree of vacuum decreases, water molecules, etc. adhere to the inner peripheral surface of the insulating cylinder, making it even more likely that secondary electrons will be generated. Many secondary electrons are emitted from the inner circumferential surface of the tube, and a discharge occurs at an early stage when the degree of vacuum begins to decrease. At this time, no discharge occurs in the other vacuum gaps (short gaps), and the short gaps are not induced to discharge by the discharge in the long gaps. On the other hand, discharge in a long gap is immediately detected because the ground voltage of the intermediate shield fluctuates. Therefore, the shear can be cut by operating the operating mechanism to open the electrodes immediately after detecting a decrease in the degree of vacuum.

G. Embodiments Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings. It should be noted that this embodiment is a partial improvement of the conventional vacuum interrupter shown in FIG. 3, so the same parts are given the same reference numerals and the explanation will be omitted, and only the different parts will be explained.

As shown in FIG. 1, a truncated cone-shaped insulating tube 2a at the top in the figure is used, and for this reason, the metal end plate 5a and the sealing fitting 3 at the top have small outer diameters. There is. Metal end plates 5a, 5b
Auxiliary shields 17a and 17b surrounding the outer ends of the fixed electrode rod 7a and the movable electrode rod 7b are fixed to the electrode rods 17a and 17b. The structure is as described above, and the auxiliary shield 17a is located near the inner peripheral surface of the insulating cylinder 2a.
and the intermediate shield 10, there is a long gap that discharges in an area where it can be cut off when the degree of vacuum is reduced.
L ₅ is formed. The long gap _L5 is the longest gap in this vacuum interrupter.
Note that gap length is not strictly limited to straight line distance;
It means the flight distance of electrons flying in a direction perpendicular to equipotential lines between members with different potentials. In the present invention, in order to make it easier for primary electrons flying between the auxiliary shield 17a and the intermediate shield 10 to hit the insulating cylinder 2a made of glass, the equipotential line 18 drawn between the auxiliary shield 17a and the intermediate shield 10 is used as an auxiliary The shield 17a side and the intermediate shield 10 side are configured to be symmetrical. That is, in this embodiment, the upper side of the intermediate shield 10 is inclined and the tip thereof is bent so that the upper end of the intermediate shield 10 is along the inner wall of the insulating cylinder 2a.

In this vacuum interrupter, when the degree of vacuum decreases during energization, the vacuum gap _L5 discharges before reaching a vacuum region that cannot be cut off. This results in
The ground voltage of the intermediate shield 10 fluctuates, and a decrease in the degree of vacuum is detected via the impedance voltage divider 13. Immediately after this detection, that is, before the vacuum gap on the other movable side maintains the withstand voltage and this part starts discharging, the operating mechanism (not shown) is activated to move the movable electrode rod 7b from the fixed electrode rod 7a. By separating them and opening the electrodes 9a and 9b, they 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. Further, the long gap is not limited to the fixed side as in this embodiment, but may be provided on the movable side.

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.

H. Effects of the Invention As described above, according to the present invention, a discharge occurs between the intermediate shield and the grid potential member on either the fixed side or the movable side in a region where the degree of vacuum is reduced and it is possible to Moreover, since the long gap is provided along the inside of the tapered part formed at the end of the insulating cylinder, the electrons emitted from the shield are directed in a direction perpendicular to the equipotential line. As the electrons fly and collide with the inner peripheral surface of the insulating tube, more secondary electrons are generated. Therefore, discharge can be caused in this part at an earlier stage of the vacuum degree decreasing than when a long gap is provided without considering the relationship between the equipotential line and the insulating cylinder. At this time, since the other vacuum gaps have sufficient withstand voltage, they can be disconnected immediately by opening immediately after detecting a decrease in the degree of vacuum.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the vacuum interrupter according to the present invention, Fig. 2 is a graph showing Patsien's law, Fig. 3 is a sectional view of a conventional vacuum interrupter, and Fig. 4 is a case where the vacuum gap length is different. 5A and 5B are graphs showing the relationship between the internal pressure of the vacuum interrupter and the discharge starting voltage, and are explanatory diagrams of the present invention. 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, _L5 ...Long gap.

Claims (1)

[Claims] 1. A vacuum vessel is formed by closing both ends of an insulating cylinder with metal end plates, and a fixed electrode rod is airtightly introduced into the vacuum vessel from one metal end plate, and the other metal end plate is closed. A movable electrode rod is airtightly introduced via a bellows so that it can approach and separate from the fixed electrode rod, and a pair of fixed and movable electrodes that can be moved toward and away from each other are provided at each inner end of these electrode rods. In a vacuum interrupter capable of freely opening and closing a grid circuit, a vacuum interrupter is provided in which a metal intermediate shield surrounding at least the outer periphery of both electrodes is insulated from both electrodes, and this intermediate shield is connected to earth via an impedance. A tapered part is formed on either the fixed side or the movable side of the insulating cylinder, and the inner diameter becomes smaller toward the end, and the intermediate shield and the taper are formed near the inner circumferential surface of the tapered part. A vacuum interrupter characterized in that a long gap is formed between the system potential member on the side where the vacuum is lowered and discharges in a vacuum region where the degree of vacuum is reduced and can be cut off.