WO1992006482A1

WO1992006482A1 - Process for increasing the electric strength and improving the leak resistance of insulation sections and application of this process to vacuum switches

Info

Publication number: WO1992006482A1
Application number: PCT/DE1991/000728
Authority: WO
Inventors: Wolfgang Schlenk; Karl-Heinz Gunzelmann; Jutta Sill; Ernst-Ludwig Hoene
Original assignee: Siemens Aktiengesellschaft
Priority date: 1990-09-28
Filing date: 1991-09-12
Publication date: 1992-04-16
Also published as: DE4030806A1

Abstract

According to the invention, the effective insulation section can be increased by coating with an insulating material. The coating is applied by thermal spraying, especially via a plasma spray process or a high-speed flame spraying process, the spray powder being, for example, aluminium oxide (Al2O3). In a vacuum switch reinforced by this process with mutually movable contacts in a switch casing of metal components, with an internal insulation section between the open contacts and an outer ceramic insulation section between the metal parts of the switch casing, a thermally sprayed coating (10) is applied over the outer insulation section to the metal parts (2, 3) of the switch casing (1).

Description

Process for increasing the dielectric strength and improving the leakage current behavior of insulation sections and applying this process to vacuum switches

The invention relates to a method for increasing the dielectric strength and reducing the leakage currents of insulation sections. In addition, the invention relates to the use of this method in vacuum switches with a metallic switching vessel. In this context, the invention also relates to such a vacuum switch with mutually movable contacts in a switching vessel made of metallic parts, with an inner insulation gap between the opened contacts and an outer insulation gap between the metallic parts of the switching vessel.

There is an outer insulation section between the movable and the fixed contact piece of a vacuum interrupter, so that when the contacts are open, there is a galvanic separation due to the inner insulation section. The outer insulation section is e.g. realized by a ceramic insulator ring, which is connected to the metal flanges or metal caps of the switch housing on both end faces by a metal / ceramic connection.

For cost reasons, the length of the ceramic insulator ring should be kept as short as possible. The dielectric strength of such an insulation section is indeed on the vacuum side, i.e. at a vacuum pressure <10 mbar, at approx. 40 kV / mm. Outside, i.e. t, ~ against the environment, this value drops to approx. 3 kV / mm at atmospheric pressure.

To improve the dielectric strength and reduce leakage currents in the outdoor area, a In order to provide the ceramic insulator with an insulating tube which is designed as a shrink tube, this insulating tube is wider than the length of the insulator. In addition, it is known to increase the dielectric strength by covering any peaks present on the metal-ceramic transition. Finally, in DE-OS 28 33 820 a vacuum switch is described with a vacuum vessel containing an insulating element for receiving a fixed contact and a moving contact, which is provided by a coating of a grease compound of a water-repellent material and provided on the outer surface of the insulating element is characterized by an insulating tube made of water-repellent, shrinkable material on the coating made of the fat compound.

The use of an insulating tube in particular has the disadvantage of a limited durability of the plastic in aggressive industrial atmospheres, when exposed to UV radiation outdoors and other disruptive influences. In particular, moisture can creep under the shrink tube, so that the dielectric strength and leakage current behavior deteriorate.

In contrast, the object of the invention is to improve the voltage resistance and the leakage current behavior of the ceramic in the exterior without having to use insulating sleeves with the disadvantages mentioned.

The object is achieved in that the effective insulation distance is increased by a coating of insulating material. In the case of a component with an already existing insulation gap, a layer is produced for this purpose by thermal spraying, which layer covers both the insulation gap and the adjacent metallic areas of the component. In the method according to the invention, thermal spraying is advantageously used in order to coat a ceramic insulator as an insulation section and associated metallic parts with the insulating material throughout. This can be done on the one hand with a plasma spraying process or on the other hand with a high-speed flame spraying process. A ceramic powder, for example A ^ O _j , is preferably used as the insulation material.

In particular, the method according to the invention is used in vacuum switches with a metallic switching vessel. In such a vacuum switch, a thermally sprayed layer is applied to the metallic parts of the switching vessel beyond the outer insulation gap. Both caps of the switching vessel are advantageously provided with the thermally sprayed layer on the ring area adjoining the insulation section.

Since the thermal spraying processes are easy to control, the process according to the invention can be implemented with comparatively little effort. The coating produced by thermal spraying advantageously has only a low and closed porosity to the outside. A weather-proof insulation gap is thus created on the surface of the switching device, which is resistant to high temperatures even with aggressive media.

Further advantages and details of the invention emerge from the following description of exemplary embodiments in conjunction with the patent claims, reference being made in particular to the use of vacuum switches in the single figure of the drawing. The figure shows a vacuum switch in schematic, partially sectioned representation. A vacuum switch requires an airtight switching vessel 1, for example with two metallic caps 2 and 3 and an intermediate ring 4 made of ceramic insulation material, for electrically isolated connections. The switching vessel is made vacuum-tight by respective metal / ceramic connections of parts 2 and 3 with part 4.

Two contact bolts 5 and 6 are introduced into the vacuum-tight switching vessel 1, the contact bolt 5 being rigidly connected to the upper metal cap 2 and the contact bolt 6 being designed to be movable in the longitudinal direction of the switching vessel via a bellows 7. 1 contact pieces 8 and 9 sit on the contact pins 5 and 6 within the switching vessel.

The movable

Contact bolts are moved with the contact piece 9, so that there is an insulation gap within the vacuum when the contact pieces 8 and 9 are opened, which is able to interrupt a current. To the outside, the contact bolts 5 and 6 are insulated from one another via the ceramic ring 4, so that there is an outer insulation gap here.

Vacuum switches of this type are state of the art in a wide variety of designs. The switching capacity is determined not only by the contact stroke within the switching vessel 1 and the structure and material of the contact pieces 8 and 9 itself, but also by the dielectric strength of the outer insulation gap defined by the ceramic ring 4. For cost reasons, the height of the ceramic ring 4 should be kept as low as possible. The dielectric strength is therefore proportional to the height of the ceramic ring. It is shown in a known vacuum switch that the dielectric strength, for example on the vacuum side, is approximately 40 kV / mm, while in the outside at atmospheric pressure it is approximately 3 kV / mm. The latter discrepancy can be significantly reduced if the switching vessel 1 is provided with a ceramic coating on the outside. In addition, the leakage current behavior is significantly improved.

In the figure, the ceramic coating is indicated in section by the structure 10. Of course, it makes sense to provide only the rigid parts that are not to be contacted, ie not the movable contact pin 6, with the coating. Optionally, should only certain Be¬ rich of the metallic parts 2 and 3 to be coated, which may be realized by a ^'mask technique.

All thermal spraying processes can be used as coating technology for comparatively thick, firmly adhering layers that can be produced in the shortest possible time. These are, for example, plasma spraying, which can be used in particular in the low pressure range from 20 to 100 mbar.

The high-speed flame spraying process may also be considered. If the process is carried out in a suitable manner, layers of a predetermined thickness with a low, in particular closed out porosity and good connection to the substrate are formed. When using other coating methods that do not achieve closed porosity, the layer of a given thickness can be sealed in a simple manner, for example by glass, epoxy resin or curable adhesive, either only on the surface or in the impregnation process as a whole. This is important because only in this way is it effectively suppressed crawling under the layer by water or water absorption in the layer, which would otherwise conflict with the desired result with open porosity. Example;

In experiments, a flowable powder made of aluminum oxide (A1 ₂ 0 ₃ ) was sprayed onto the switching vessel 1 using a plasma torch in the low pressure range at about 60 mbar or in air. The ceramic ring 4 and the cylindrical region of the metallic caps 2 and 3 were provided with a closed layer which adheres well throughout. The result is an increased dielectric strength of the ceramic insulator 4 in the outer space due to the longer creepage distance and in particular also by covering any metal tips that may be present at the metal-ceramic transitions.

It has been shown that with aluminum oxide a weather-proof insulation gap can be created which is resistant up to high temperatures. In particular, especially for the use of the vacuum switch, the switching vessels can also be subjected to the usual heating processes at 250 to 400'C after thermal coating in order to achieve a good final vacuum. The vacuum switches that have been upgraded in this way have improved dielectric strength, which otherwise could only be achieved by using a considerably longer ceramic as an insulation section or by using a profile ceramic.

The described method can also be used in other applications in which the voltage resistance and the leakage current behavior of insulation sections are to be improved. This problem is also relevant, in particular in the case of X-ray tubes and / or image intensifiers. In this respect, the invention can also be used independently of vacuum switches.

Claims

1. A method for increasing the dielectric strength and reducing the leakage currents of insulation sections, that is, that the effective insulation section of a component is increased by a coating of insulating material.

2. The method according to claim 1, which also means that an insulation section already present in a component and adjacent metallic areas of the component are coated with insulating material by thermal spraying.

3. The method according to claims 1 and 2, that the insulation material is applied to the component by means of plasma spraying in the low pressure range from 20 to 100 mbar or at atmospheric pressure.

4. The method according to claims 1 and 2, that the insulation material is applied to the component by means of high-speed flame spraying at atmospheric pressure.

5. The method according to claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that as an insulating material ceramic powder, e.g. A ^ O ,, is used.

6. The method according to claim 2 to 4, so that the coating is sealed in an additional procedural step, for example by surface covering or by impregnation.

1 7. The method according to claim 6, characterized in that glass or epoxy resin is used for the sealing.

8. The method according to claim 1 or one of claims 2 to 7, suitable for use with vacuum switches.

9. Vacuum switch with mutually movable contacts in a switching vessel made of metallic parts, with an inner insulation gap between the opened contacts and an outer insulation gap between the metallic parts of the switching container, characterized in that a thermally sprayed layer (10) over the outer insulation gap (4 ) is also applied to the metallic parts (2, 5 3) of the switching vessel (1).

10. Vacuum switch according to claim 9, wherein the switching vessel consists of two pot-like caps as metallic parts, each with a bottom area and a cylindrical area and an intermediate ceramic ring as an outer insulation section, characterized in that the thermally sprayed layer (10) cylindrical part of the caps (2, 3) largely covers. 5

11. Vacuum switch according to claim 6, so that the thermally sprayed layer (10) has a closed porosity.

0

5