JPH01122529A - Formation of vacuum breaker - Google Patents

Abstract

PURPOSE:To perform vacuum breaking excellent in the withstand voltage performance by setting shapes of an electrode and an intermediate shield so that the withstand voltage intensity across the electrode and the intermediate shield is made equal for both polarities. CONSTITUTION:An electrode 2 has the thickness D against the diameter of a certain size, and both ends on the opposite side to an intermediate shield 7 are formed in the hemispherical shape with the radius (r). Electrode bars 3 and 4 have the fixed diameter, and the intermediate shield 7 has the inner diameter with the fixed size. The gap length G of the coaxial gap g1 between the electrode 2 with such shape and the intermediate shield 7 is made constant. In a vacuum breaker having the electrode with such shape and the intermediate shield, the withstand voltage performance across the electrode and the intermediate shield is set equal for both polarities. A vacuum breaker excellent in the withstand voltage performance is thereby obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for forming a vacuum circuit breaker used in an AC circuit, and particularly relates to a method for forming a vacuum circuit breaker used in an AC circuit, and in particular, a method for forming a vacuum circuit breaker used in an AC circuit. This concerns the structure of the shield.

[Conventional technology]

FIG. 3 is a longitudinal cross-sectional view showing the structure of a current interrupting section of a conventional vacuum circuit breaker described in, for example, Japanese Patent Publication No. 61-23616. (1) is a contact, and (2) is an electrode. (3) is a fixed electrode rod that penetrates the fixed side end plate (5) and connects the above electrode (2).
is sealed on one side. A movable electrode rod (4) is connected to the movable end plate (6) via a bellows (9), and the other electrode (2) is fixed thereto. (7) is an intermediate shield, which prevents the arc generated between the contacts (1) and metal vapor from contacting or depositing on the inner surface of the insulating container (3) when the current is cut off. The intermediate shield (7) is held electrically insulated from the pair of electrodes by two insulating containers (8). (10 is a fixed shield, which is fixed to the end plates (5) and (6), respectively, and is used to relieve the electric field at the sealed portion of the insulating container (8).

[Problem that the invention seeks to solve]

Generally, the current interrupting performance of a vacuum circuit breaker is 12 to 1.
Since it increases in proportion to the fourth power, the electrode diameter also increases as the breaking capacity increases. In this case, the withstand voltage of the coaxial gap g1 formed by the electrode and the intermediate shield is reduced because the length of the gap is shortened. Therefore, in order to satisfy the withstand voltage performance of the gap g1, the inner diameter of the intermediate shield must be increased, which in turn increases the outer diameter of the insulating container, making the vacuum circuit breaker larger and more expensive. There was a problem.

By the way, as a result of research by the present inventors on the relationship between withstand voltage performance and electric field distribution of the coaxial gap g1, as the maximum electric field concentration coefficient (αmax) of the electrode approaches 1, regardless of the polarity, the coaxial gap g1 However, as shown in FIG. 2, which will be described later, it has been found that the withstand voltage characteristics of the coaxial gap g1 differ depending on the polarity of the voltage applied between the electrode and the intermediate shield.

The present invention was made to solve the above problems, and an object of the present invention is to provide a method for forming a vacuum circuit breaker that can improve the withstand voltage between the electrode and the intermediate shield.

[Means for solving problems]

The method for forming a vacuum circuit breaker of the present invention is to set the shapes of the electrodes and intermediate shield of the vacuum circuit breaker so that the withstand voltage strengths of the electrodes and intermediate shield are equal in both polarities.

[Effect]

In this invention, the withstand voltage strength of the electrode and the intermediate shield is set to be equal in both polarities, so in the case of a commonly used AC circuit, the withstand voltage strength is Maximum.

〔Example〕

First, the relationship between the withstand voltage of the gap between the electrode and the intermediate shield and the electric field concentration on the electrode surface according to the present invention is shown in the characteristic diagram of FIG. In the figure, the vertical axis represents the withstand voltage strength (kV) of the gap, and the horizontal axis represents the maximum value of the coefficient representing the degree of electric field concentration on the electrode surface, that is, the maximum electric field concentration coefficient on the electrode surface.

Characteristic curve (c) shows the relationship between withstand voltage strength and maximum electric field concentration coefficient when the polarity of the voltage applied to the electrode is negative with respect to the shield. It shows the relationship between the withstand voltage strength dust and the maximum electric field concentration coefficient when the value is positive.

Here, when the voltage applied between a pair of electrodes is V and the length of the gap between the electrodes is d, the average electrolysis Eo on the surface of the electric field is Eo = V /d ■, and the strongest electric field E on the surface of the electrodes is max is Emax
= a max −Eo ■. αmax on the right side of this equation 0 is the maximum electric field concentration coefficient mentioned above.

From FIG. 2, it can be seen that the withstand voltage characteristics of the coaxial gap differ depending on the polarity of the voltage applied between the electrode and the intermediate shield, that is, there is a polarity effect. However, since vacuum circuit breakers are generally used in AC circuits, an AC voltage is also applied between the electrodes and the intermediate shield. Therefore, in the case of an AC circuit, the withstand voltage strength is maximum at the point where the withstand voltage strength is equal in both polarities, and at the point where the characteristic curves A and B in FIG. 2 intersect. Therefore, the shape of the electrode and intermediate shield should be designed so that the withstand voltage strength is equal in both polarities, or in other words, the value of αmax corresponding to the point where characteristic curves A and B intersect can be obtained. I understand.

The reason why there is a polarity in the withstand voltage performance of the coaxial gap as described above is thought to be as follows. When the electrode has a negative polarity and the intermediate shield has a positive polarity, the withstand voltage is determined by the electron current generated by field emission from the electrode, so the greater the electric field concentration on the electrode surface, the lower the withstand voltage strength. On the other hand, when the intermediate shield has a negative polarity and the electrode has a positive polarity, the field emission electrons from the intermediate shield do not have much effect on the withstand voltage, but rather the area of the region where the electric field concentration occurs on the electrode surface has no relation to the withstand voltage. (so-called area effect), the greater the degree of electric field concentration, the smaller this area, so the withstand voltage strength is higher.

FIG. 1 is a partial sectional view showing the shapes of the electrode and the intermediate shield when the withstand voltage is equal in both polarities according to an embodiment of the present invention, and (2) is the electrode, which has a diameter of 100mm and a thickness of is 5 mm, and both ends of the intermediate shield (7) on the opposite side have a hemispherical shape with r of 15 ynm.

(3>, (4) are electrode rods with a diameter of 30 mm, and (7) is an intermediate shield with an inner diameter of 110 mm.
and the coaxial gap g of the intermediate shield (7), the gap length G is 5 mm. A vacuum circuit breaker having such a shaped electrode and intermediate shield has improved withstand voltage performance between the electrode and the intermediate shield compared to conventional vacuum circuit breakers.

In addition, although the said Example demonstrated the case where it applied to the thing with one intermediate shield, the vacuum circuit breaker which has two or more intermediate shields may produce the same effect as the said Example.

〔Effect of the invention〕

As described above, according to the present invention, in a vacuum circuit breaker, the shapes of the electrode and the intermediate shield are set so that the voltage strength between the electrode and the intermediate shield is equal in both polarities, thereby improving the voltage resistance. This has the effect of providing an excellent vacuum circuit breaker.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing the shape of the electrode and intermediate shield of a vacuum circuit breaker according to an embodiment of the present invention, and FIG. 2 is a diagram showing the withstand voltage of the gap between the electrode and intermediate shield and the electrode surface according to the present invention. FIG. 3 is a longitudinal sectional view showing a conventional vacuum circuit breaker. In the figure, (2) is an electrode, (3) is a fixed electrode rod, and (4) is an electrode.
) is a fixed electrode rod, and (7) is an intermediate shield. In addition, in the figures, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] a vacuum container consisting of an insulating container and an end plate that closes the insulating container; a pair of electrodes that are movably sealed to the end plate, at least one of which is provided in the vacuum container, and that are movably sealed to the end plate via a bellows; In a vacuum circuit breaker used in an AC circuit, which is provided in the vacuum container and includes an intermediate shield surrounding the pair of electrodes, the withstand voltage strength between the electrode and the intermediate shield is equal in both polarities. A method for forming a vacuum circuit breaker, comprising setting the shapes of the electrode and intermediate shield.