RU2401478C1 - Gas-filled discharger - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: gas-filled discharger contains metal body in the form of can with bead, coaxially installed on it at least two electrodes, screen and hollow isolator the greater base of which is fixed on body bead and the smaller base is connected with one of the electrodes via thin collar; the other electrode is fixed on inner body butt end. Outer screen surface contains two mating segmental surfaces of rotation bodies with their generatix following formulas below:

Z = H · sin(f)^k, where R - radial coordinates of generatix points; Z - generatix points coordinates along center line; f - the argument, determining values of R and Z functions; -π/2≤f≤π/2; D - outer screen diametre; H - the parametre, characterising screen segment height; R1 - radial screen thickness; k - exponent.

EFFECT: increase in electric strength of clearance between screen and inner wall of discharger body due to lowering electric field intensity in the segment of screen surface facing inner wall of the body.

2 cl, 7 dwg

Description

The invention relates to gas-discharge equipment and can be used in the development of high-voltage gas-discharge devices, for example, surge arresters for small-sized pulse generators of X-ray and electron beams and high-voltage pulses of nanosecond duration.

Known gas-filled spark gap (authors Avilov E.A., Voinov B.A. and Yuryev A.L., AS No. 2120153, class IPC 6 H01J 17/02, publ. 10.10.98), containing at least one electrode located on the smaller base of the conical insulator, and a disk cuff, one surface of which is connected to the end surface of the conical insulator, and the other is connected to the inner flat surface of the electrode.

The disadvantage of this spark gap is the limitation of its diameter to 50 mm, at which it is still possible to conduct high-quality brazing of the ceramic-metal assembly. This limitation is caused by the high stiffness of the disk cuff and a sharp increase in mechanical stresses in the soldered seam of the small base of the insulator with an increase in the diameter of the seam. As a result, the operating breakdown voltage of such a spark gap cannot exceed 220 kV.

Closest to the claimed is a "gas-filled spark gap" (authors Belkin N.V., Golchenko A.N., Merkulov B.P., AS No. 1804263, class IPC 6 H01T 2/02, published in Bull No. 27, 09/27/96), containing a metal case in the form of a glass with a flange, two electrodes coaxially mounted in it and a conical hollow insulator. One of the electrodes is mounted on the inner end of the housing. A second electrode and a screen are fixed on the small base of the insulator, covering the protrusions of the parts with sharp edges at the junction of the parts with the insulator. A large base insulator mounted on the flanging of the housing. The electrode was fixed on the insulator by soldering through a thin insidious cuff, which, while ensuring a reliable junction, allows to increase the diameter of the spark gap up to 150-200 mm.

The disadvantages of the prototype is the following:

- a large ratio of the case diameter to the operating voltage of the arrester compared to the analogue (for the analog, this parameter is K = 50 mm / 220 kV = 0.23 mm / kV; for the prototype K = 80 mm / 300 kV = 0.27 mm / kV, i.e. . approximately 20% more), which leads to a significant increase in the dimensions and mass of small-sized pulse generators created on the basis of such arresters;

- the screen is made in the form of a cylinder with roundings at the edges, which leads to a high value of the electric field strength at these roundings and breakdowns from the screen to the arrester case when the case diameter is reduced or the working gas is used with reduced electric strength, such as hydrogen. This gas is promising for use in small-sized arresters, since it has a short recovery time for electric strength and allows an order of magnitude increase in the frequency of repetition of operations compared with nitrogen, SF6, etc. However, the incorrect design of the screen leads to breakdowns from the screen to the arrester body, an increase in the dispersion of the operation voltage of the arrester, and a decrease in its operating life.

When creating this invention, the problem was solved of creating a compact reliable small-sized spark gap with high values of the stability of breakdown voltages and service life when filling it with working gas with a lower electrical strength, such as hydrogen, compared to nitrogen and SF6.

The technical result is to increase the electrical strength of the gap between the screen and the inner wall of the housing by reducing the electric field strength on a portion of the surface of the screen facing the inner wall of the housing.

The specified technical result is achieved in that, in comparison with the known gas-filled spark gap, containing a metal body in the form of a bead with a flare, at least two electrodes are coaxially mounted in it, at least two electrodes, a screen and a conical hollow insulator, the large base of which is fixed to the flanging of the case, and the small one is connected to one of the electrodes through a thin cuff, the other electrode is fixed to the inner end of the housing, the new one is that the outer surface of the screen contains two sections m surface of bodies of revolution, whose generatrix is described by the formulas:

where R is the radial coordinates of the points of the generator;

Z - coordinates of the points of the generator along the axis of rotation;

f is an argument defining the values of the functions R and Z; -π / 2≤f≤π / 2;

D is the outer diameter of the screen;

H is a parameter characterizing the height of the screen;

R1 is the radial thickness of the screen;

k is an exponent.

The implementation of the screen with the surface described by formulas (1) and (2) allows, for given values of D, H and R1, determined by the design of the ceramic-metal assembly, and the optimal choice of parameter k, to reduce the electric field strength on the screen surface to the utmost. For k = 1, formulas (1) and (2) describe a classical rotation ellipsoid. Changing the parameter k up or down relative to the value k = 1 allows you to increase the radius of curvature in areas of increased field strength in different parts of the screen surface, which leads to a decrease in tension to a safer level.

The execution of the screen from two paired sections allows you to compensate for the difference in distortions in the configuration of the electric field caused by the location of the electrode on one end of the screen and the insulator on the other. It also helps to reduce the field strength on the screen surface.

Reducing the electric field on the surface of the screen in comparison with the prototype makes it possible to reduce the diameter of the spark gap, use a working gas with lower electrical strength (for example, hydrogen) compared with nitrogen and SF6 gas, and increase the stability and resource of the spark gap.

Figure 1 shows the construction of the arrester prototype, where:

1 - housing;

2 - electrode mounted on an insulator;

3 - electrode mounted on the housing;

4 - screen;

5 - conical insulator;

6 - thin cuff.

Figure 2 shows the surface of equal potential in the arrester prototype.

Figure 3 shows a graph of the dependence of the electric field on the surface of the screen and the electrode of the arrester of the prototype on the distance along the generatrix.

Figure 4 shows the design of the inventive spark gap.

Figure 5 shows the contours of the screen and electrode of the inventive spark gap; the screen contour is calculated by the formulas (1) and (2).

Figure 6 shows the surface of equal potential in the inventive spark gap.

7 shows a graph of the dependence of the electric field on the surface of the screen and the electrode of the inventive spark gap on the distance along the generatrix.

The gas-filled spark gap shown in Fig. 1 comprises a metal housing 1 in the form of a flare cup, two electrodes 2 and 3 coaxially mounted in it, a shield 4 and a conical hollow insulator 5. The large base of the insulator 4 is fixed to the flare of the housing 1, and a small one is connected to the electrode 2 through a thin insidious cuff 6. The electrode 3 is mounted on the inner end of the housing.

When high voltage is applied to the prototype arrester, an electric field appears in it. One of the characteristics of the field is the distribution of lines of equal potential over the volume of the spark gap (see figure 2). The thickening of lines of equal potential on radius surfaces near points A and B means the presence of increased field strength on them compared to the cylindrical portion of the screen. Figure 3 shows a graph of the dependence of the field strength on the surface of the screen and electrode on the distance along the generatrix. The graph clearly shows that the field strength in the radius sections increases to 55 kV / mm, and in the interelectrode gap to 75 kV / mm. Such field strengths are achievable only when nitrogen, SF6 gas, and mixtures thereof are used as the working gas. Hydrogen-filled arresters work well at lower field strengths in the gap (not more than 50 kV / mm), therefore, filling the prototype arrester with hydrogen will lead to breakdowns from the electrode to the housing, and, as a result, reduce the stability and resource of the arrester.

In the inventive spark gap due to the smooth change in the curvature of both parts of the screen surface, it was possible to reduce the field strength by almost 2 times compared with the prototype. Figure 4 shows the design of the inventive spark gap. It, like the prototype, contains a metal case 1 in the form of a bead with a flare, two electrodes 2 and 3 coaxially mounted in it, a shield 4 and a conical hollow insulator 5. The large base of the insulator 5 is fixed to the flare of the housing 1, and the small one is connected to the electrode 2 through a thin insidious cuff 6. The electrode 3 is mounted on the inner end of the housing.

The inventive spark gap operates as follows. When the arrester is included in the discharge circuit of a pulsed high-voltage generator, a pulse voltage is applied to its electrodes. When it reaches the triggering voltage of the arrester, the interelectrode gap breaks through, and a capacitive energy storage device is quickly connected to an X-ray, electron tube, or other high-current load. This process occurs as necessary in the mode of single switching on or in the frequency mode.

Figure 5 shows the contours of the screen and electrode of the inventive spark gap obtained by calculation by the formulas (1) and (2). The screen of the claimed arrester consists of the following sections:

- AB - the outer surface of the screen;

- B-V - zone of attachment of the electrode to the screen;

- VG - the working surface of the electrode;

- AD - the radius of the final portion of the screen.

The outer surface of the screen AB consists of two sections, AO and OB, each of which is calculated according to formulas (1) and (2) for its values of the parameters D, H, R1 and k.

For the inventive spark gap, calculations of electric fields were also carried out. The distribution of lines of equal potential over the volume of the spark gap is shown in Fig.6. The density of lines of equal potential near the screen is almost the same in the AB section of the screen, which indicates the absence of field strength jumps on its surface. Figure 7 shows a graph of the dependence of the field strength on the surface of the screen and electrode on the distance along the generatrix. From the graph it follows that the field strength on the surface of the screen (plot AB) does not exceed 33-35 kV / mm, which is almost half that of the prototype. In this case, the field strength in the interelectrode gap is 47 kV / mm. This level of field strength allows the use of hydrogen as a working gas.

In a specific embodiment, a gas-filled spark gap of 500 kV was manufactured. Its screen has a diameter of 62 mm and consists of two paired sections with the following parameters:

- the section closest to the electrode is D = 62 mm, H = 17 mm, R1 = 12.5 mm, k = 1.1, 0≤f≤π / 2;

- the section closest to the insulator - D = 62 mm, H = 15 mm, R1 = 5 mm, k = 1, -π / 2≤f≤0.

The diameter of the arrester housing is 120 mm, the length is 181 mm.

The arrester was filled with hydrogen at a pressure of 3.8 MPa (38 atm) and passed life tests as part of an accelerator at 500 kV; when the energy storage capacity of the capacitive storage is about 8 J and the amplitude of the current through the spark gap is 3-3.5 kA, the rms relative spread of its operating voltages did not exceed 1.5%. Throughout the test cycle (10 ⁶ operations of the arrester), there was not a single breakdown on the housing, which proves the effectiveness of the use of the arrester with the claimed design.

The magnitude of the interelectrode gap of the spark gap is 12 mm. With a case diameter of 120 mm, the ratio of the case diameter to the operating voltage is K = 120 mm / 500 kV = 0.24 mm / kV, while in the prototype this parameter is 0.27.

Thus, the inventive spark gap is more compact compared to the prototype and can reliably work when filled with hydrogen, which has lower dielectric strength than nitrogen and SF6 gas.

Claims (2)

1. A gas-filled arrester containing a metal housing in the form of a bead with a flange, coaxially mounted in it at least two electrodes, a screen and a conical hollow insulator, the large base of which is fixed to the flanging of the housing, and the small is connected to one of the electrodes through a thin cuff , characterized in that the outer surface of the screen contains two conjugated to each other surface area of the bodies of revolution, the generatrix of which is described by the formulas:

,
Z = H sin (f) ^k ,
where R is the radial coordinates of the points of the generator;
Z - coordinates of the points of the generator along the axis of rotation;
f is an argument defining the values of the functions R and Z; -π / 2≤f≤π / 2;
D is the outer diameter of the screen;
H is a parameter characterizing the height of the screen;
R1 is the radial thickness of the screen;
k is an exponent. 2. The gas-filled spark gap according to claim 1, characterized in that the inner diameter of the housing D1, the outer diameter of the shield D, the radial thickness of the shield R1, parameter H and the interelectrode gap S are related to each other as follows:
for the section closest to the electrode, D1: D: R1: H: S = 10: 5.3: 1.1: 1.5: 1 at k = 1.1 and 0≤f≤π / 2;
for the section closest to the insulator, D1: D: R1: H: S = 10: 5.3: 0.4: 1.3: 1 at k = 1.0 and -π / 2≤f≤0.

Images