RU2374718C1 - Vacuum switching unit - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: vacuum switching unit contains insulating casing, arc-suppressing electrodes and screen system at least from five screens, part of which are isolated and two of near-flange are under electrode potential. Central and isolated screens are implemented in the form of solid of revolution, generatrix of which allows echelon form, additionally each of ends of screen of minor diametre is enveloped by end of major diametre of adjoining screen, and annular channels between adjoining screens in areas of reciprocal overlapping and annular slots between casing and screen fulfil conditions: L≥M; 4≤P/S≤15; where L - length of annular channel; M - width of annular channel; P - depth of annular slot; S - width of slot at the middle of slot depth.

EFFECT: increasing of electric strength of inner insulation of chamber and its keeping up to total output of electrical resource.

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Description

The invention relates to the field of high-voltage switching equipment, and more specifically to vacuum controlled arresters and vacuum interrupter chambers (chambers) for a rated voltage of more than 35 kV, for example, for 60 kV chambers used in 110 kV circuit breakers with two cameras connected in series at each pole .

Known industry produced in Russia camera type KDV-35. ("Electrical Engineering", No. 9, 2001, p.22.) [1]. The dielectric strength of the internal insulation of this chamber is ensured by a screen system of five screens, of which three are insulated, and two flange-mounted are electrically connected to the arcing electrodes. The central of the insulated shields, covering the electrodes, and two other insulated shields are mounted on the ceramic insulating casing and together with the flange shields protect the insulating casing from metallization by the products of electrode erosion that occurs under the influence of a vacuum arc during current switching. The applied screen system provides the required electric strength of the internal insulation of 95 kV when tested with a one-minute voltage of industrial frequency and 190 kV when exposed to a standard lightning impulse voltage. Screens provide preservation of electric strength at the required level, not lower than 80% of the initial one. At the same time, there is a tendency to decrease the electric strength of the internal insulation of the chambers as the electrical resource is developed. The nature of this phenomenon, as shown by a survey of the chambers after running out of resources, is the insufficient protection of the insulating casing from metallization. To the maximum extent, metallization is observed in areas of the insulating casing not covered by screens.

The closest technical solution to the proposed technical essence and the achieved effect is a camera with a screen system of five screens, of which three are isolated, and two flange are under the potential of the electrodes. The central insulated screen, covering the arcing electrodes, is made in the form of two truncated cones, connected to each other by ends of large diameters. Each of the ends of the smaller diameter of the Central screen is covered by another insulated screen, also having the shape of a hollow truncated cone. In turn, each of the ends of the smaller diameter of the insulated screens is covered by a flange screen. Thus, a more dense protection of the insulating housing from metallization is achieved. The geometry of the screens is selected so that the voltage is evenly distributed over the housing (US Patent No. 3792214, class 200-144V, publ. 12.02.1974) [2].

However, this screen system also contains significant disadvantages that impede its use in high voltage cameras. The main disadvantage is the penetration of the products of electrode erosion through the screen system, despite the mutual overlap of the screens, to the insulating casing, and its metallization as the electrical resource of the chamber is developed. Penetration of erosion products behind the screens to the housing is due to insufficient mutual overlap of the screens and the straightness of the gaps between them. The second disadvantage is the excessive concentration of the electric field at the junction of the conical screens with the insulating casing due to the large width of the annular slots between the casing and these screens due to their taper. Excessive concentration of the electric field at the junction of the conical screen with the insulating casing creates the conditions for initiating breakdown along the surface of the insulating casing, which prevents the achievement of higher values of the internal insulation of the chamber.

The purpose of the invention is to increase the dielectric strength of the inner insulation of the chamber and preserve it until the electrical resource is completely depleted by eliminating the through span between adjacent screens of the products of electrode erosion towards the surface of the insulating body and the direction of these products mainly on the surface of the screens, as well as by reducing the electric voltage fields at the junction of the screens with the insulating casing, optimization of the width and depth of the annular gap between the screen and the casing.

This goal is achieved by the fact that in a vacuum switching device containing an insulating casing, arcing electrodes and a screen system of at least five screens, some of which are insulated, and two flange are under the potential of the electrodes, while the central and insulated screens are made in in the form of bodies of revolution, and each of the ends of the screen, of smaller diameter, is covered by the end of the larger diameter of the adjacent screen. What is new is that the central and isolated screens are made in the form of bodies of revolution, the generators of which are stepped in shape, while the annular channels between adjacent screens in the areas of their mutual overlap and the annular slots between the body and the screens must satisfy the conditions

L≥M

4≤P / S≤15,

where L is the length of the annular channel;

M is the width of the annular channel;

P is the depth of the annular gap;

S is the width of the slit in the middle of the depth of the slit.

Figure 1 shows the proposed camera, axial section; figure 2 - zone of annular channels between adjacent screens and annular slots between the screens and the housing. The chamber contains two terminals 1 and 2, on the inner ends of which electrodes 3 and 4 are fixed. Terminal 1 is rigidly fixed to the flange 5, terminal 2 is vacuum-tightly connected to the flange 6 through a bellows 7. The insulating housing 8 is formed by at least two (the left half of FIG. 1) or, for example, four (right half) ceramic rings sealed tightly between each other. Three isolated screens 9, 10, 11 are rigidly fixed on these rings; two flange shields 12 and 13 are mounted on flanges 5 and 6 and are electrically connected to electrodes 3 and 4. Each of the ends of the smaller diameter of the screens 9-11 is covered by the end of the larger diameter of the adjacent screen. The areas of mutual overlap of adjacent screens form annular channels whose length L is not less than their width M (L≥M), Fig.2. The ends of the screens end with fillets. Between the shields 9-11 and the walls of the insulating casing 8 at the points of attachment of the shields to the casing, as well as between the shields 12, 13 and the casing, narrow and deep annular slots 14-21 are formed (Fig. 1) with a ratio of depth P to width S within 4 ≤P / S≤15 (figure 2). Since the width of the gap, as a rule, varies with depth, its value S is determined in the middle of the depth of the gap, as shown in figure 2.

The camera operates as follows. When the current is turned off by the camera, the electrodes 3 and 4 open, an electric arc arises between them, during the combustion of which ions and metal vapors are formed. The vapor pressure between the electrodes when a current of tens of kiloamperes is cut off can reach many hundreds of millimeters of mercury (many pascals). The steam heats up to thousands of degrees, so there is a process of its energetic exit from the interelectrode gap into the chamber volume and its interaction with the screen system, flanges and surfaces of other parts. When vapor flows interact with surrounding surfaces, they condense. After repeated collisions with surfaces surrounding the interelectrode gap, non-condensed vapor goes beyond the screens. To avoid condensation of vapors on the housing in the proposed screen system, annular channels are used that direct steam flows to portions Q of the outer surface of the insulated screens (in FIG. 2, one of them is indicated by a dotted line). In areas Q, the condensation coefficient is close to 100%, since the temperature of the vapor after 2-3 preliminary “contacts” with the surfaces of other electrodes decreases from thousands in the arc discharge to hundreds of degrees by the time it passes through the annular channels. In addition, Q sections are not affected by arc discharge factors. Thus, provided that the entire molecular flux flowing from the given annular channel into the Q region is reached, one can expect almost complete elimination of metallization of the chamber body. This possibility is realized if the ratio L / M≥1. In this case, the trajectories of the peripheral flow molecules do not go beyond the straight line Z indicated by the dashed line, Fig. 2. When L / M <1, the straight line Z passes by the screen and ends on the case, which will indicate metallization of the case, leading to an unacceptable decrease in the internal insulation of the camera.

It was shown ("Electrical Engineering", No. 03/01, p.10) [3] that when the screen attachment points to the camera’s insulating body exceed, for example, places 22-25, Fig. 2, the electric field strength exceeds 2.7 kV / mm, or field strengths on the screens in places at the exit from the annular slots, for example, places 26, 27, more than 9 kV / mm, there is a significant probability of initiation of overlap. Overlapping occurs on the inner surface of the insulating casing between adjacent screens. This overlap can cause a breakdown of the entire camera. It also leads to metallization of the housing and an irreversible decrease in the internal insulation of the chamber. Of course, it is possible to exclude the possibility of overlapping only by limiting the electric field strength to the values indicated above. By modeling the camera at 60 kV, it was found that with a uniform division of the voltage between the screens and with a relative depth of the gap, i.e. with a ratio of its depth P to width S more than 4 and less than 15, i.e. under the condition of 4≤P / S≤15 limitation of tension by the specified values is performed. On the contrary, at a relative P / S depth of less than 4, breakdown is initiated from points 22-25, FIG. 2. At P / S> 15, breakdowns are initiated from points 26, 27.

Information sources

1. The journal "Electrical Engineering", No. 9, p. 22, publ. 2001 year

2. US patent No. 3792214, class 200-144, publ. 02/12/1974 (prototype).

3. The journal "Electrical Engineering", No. 3, p. 10, publ. 2001 year

Claims (1)

A vacuum switching device containing an insulating casing, arcing electrodes and a screen system of at least five screens, some of which are insulated, and two flange screens are under the potential of the electrodes, while the central and isolated screens are made in the form of bodies of revolution, and each of the ends of the screens is smaller the diameter is covered by the end face of the larger diameter of the adjacent screen, characterized in that the central and isolated screens are made in the form of bodies of revolution, the generators of which have a stepped shape, while the front channels between adjacent screens in the areas of their mutual overlap and the annular slots between the body and the screens must satisfy the conditions:
L≥M;
4≤P / S≤15,
where L is the length of the annular channel;
M is the width of the annular channel;
P is the depth of the annular gap;
S is the width of the gap in the middle of the depth of the gap.

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