EP4016576B1 - Electrical switching device for medium and / or high voltage applications - Google Patents

Description

The invention relates to an electrical switching device, in particular for medium and/or high voltage applications, comprising at least two contactable conductor elements which can be separated by a movement device and a housing defining a switching chamber made of one or more insulators, wherein parts of the switching chamber can be made of metal, usually in the vicinity of the contact gap, and two caps, preferably made of metal, which axially close off the housing,

The document WO02097839 discloses a switching device according to the preamble of claim 1.

In medium and/or high voltage applications, generally speaking, voltages greater than 1 kV, more complex switching devices are required due to the high voltages that can withstand the occurring electric fields, are as resistant as possible to degradation effects and also prevent arcing outside the actual switching chamber.

A classic example of this is vacuum circuit breakers (VCB), which are core components in energy transmission and distribution, particularly in their switching systems. They cover a large part of medium-voltage switching applications, i.e. switching applications in the range from 1 kV to 52 kV, for example, as well as a relevant part in low-voltage systems. Their use in high-voltage transmission systems, for example at voltages greater than 52 kV, is also increasing. While a VCB is closed most of the time, thus providing contact between the conductor elements, its main task is to interrupt currents in alternating current systems under nominal conditions, in particular for switching nominal currents on and off, or preferably for interrupting currents under fault conditions, in particular to prevent short circuits. to interrupt and protect the system. Other applications include pure switching of load currents using contacting conductor elements, which is mostly used in low and medium voltage systems.

The vacuum interrupter (VI, also vacuum switching tube) is the core element of a VCB. A vacuum switching tube usually has a pair of contacts that are formed by corresponding conductor elements, at least one of which can be moved by means of a movement device in order to be able to bring about the open and closed states of the switching device. Usually, one conductor element is moved axially with respect to the other fixed conductor element. The contacts can be made of current-conducting bolts, in particular made of metal, which provide both current and heat conduction as well as the mechanical means to hold and/or move the contacts.

A VI further comprises a vacuum-tight housing and the mentioned movement device and can also comprise a metal bellows which is connected on one side to the housing and on the other side to the moving conductor element, in particular the moving bolt. The housing is essentially formed by an insulating component, i.e. an insulator, for example a ceramic tube, which is connected to the conductor elements via connecting elements, whereby metal caps or the like are used, for example, which close off the insulating component in the axial direction to form the switching chamber. There is a permanent high vacuum within the switching chamber of less than 10^-4 hPa or 10^-4 mbar. The vacuum is necessary to ensure the "make-break operations" and to guarantee the insulation properties of the switching device in the open state.

When the switching device is in an open state, it is necessary to isolate the nominal voltage of the system, but also to isolate high amplitude surge voltages, for example can be triggered by a lightning strike into the system. When the switching device changes from the closed to the open state, thus separating the contacts of the conductor elements, rated currents or short-circuit currents must be interrupted, which lead to the appearance of temporary voltage peaks across the VI that are significantly higher than the rated AC voltages of the system.

High voltages in vacuum systems typically generate free electrons through field emission processes if the electric field strength is sufficiently high. The acceleration of the electrons in the high electric fields increases the kinetic energy of these electrons, for example up to energies exceeding several tens or even hundreds of KeV. The interaction of these high-energy electrons with the housing structures leads to the production of high-energy X-rays that can leave the vacuum interrupter. While under normal conditions the fault current within the vacuum interrupter is minimal and does not generate any significant X-rays, circumstances may arise, for example when transient high-amplitude voltage spikes occur, in which the resulting X-rays generate free electrons on and/or near the outer surface of the insulator. These electrons can be accelerated by the electric fields on and near the insulator surface, disrupt the electric field distribution in sensitive areas and lead to gas breakdown, resulting in a failure in the operation of the vacuum interrupter.

Even in cases where no detectable X-rays exist, for example in low and medium voltage applications, the high electric fields in critical areas of the vacuum interrupter, for example at the connection of the insulator and the metal caps by soldering (brazing), can lead to the ejection of electrons, resulting in a significant amount of field emission. These electrons can also locally disturb the electric field and lead to further Field amplification and/or charge multiplication by electron avalanches, which in turn can result in loss of insulation strength and/or voltage resistance of the vacuum interrupter.

Similar challenges exist on the inner surfaces of the vacuum interrupter, while an additional problem must be solved. When the current is interrupted (both nominal current and short-circuit current), parts of the contact material are vaporized and distributed within the switching chamber as hot metal vapor. This metal vapor can settle on the insulator surface and builds up a conductive metal layer over time. This metal layer, even if it is only weakly conductive, can also disrupt the electric field outside and inside the vacuum interrupter and thus deteriorate the voltage resistance of the vacuum interrupter over time. In this context, it has been proposed to provide a shielding element, which can also be made of metal, in the contact area of the conductor elements to catch free metal particles from the conductor elements, but this also has an influence on the field distribution within the switching chamber, but also on the insulator.

For the reasons mentioned above, the housing of the switching chamber, and in particular the insulator, which is usually made of ceramic, must be able to withstand high voltages across its surface, even in the presence of X-rays and free electrons or, in some cases, even when the insulator is contaminated by dust particles that are electrostatically deposited on the outer surface of the insulator. Since the insulator contributes significantly to the cost of a vacuum interrupter (or other switching device) and also negatively influences the cost of other structural elements of the vacuum interrupter (or other switching device), it is necessary to optimize the housing in order to achieve maximum dielectric strength with minimum component size.

This problem has so far been solved by choosing the inner and outer geometry of the vacuum interrupter such that the expected electric field strengths do not exceed empirically derived limits for a specific geometry of the vacuum interrupter. Since these limits cannot be predicted precisely, especially for triple point areas and/or sharp metal edges, the design of vacuum interrupters not only depends on electric field calculations during the development process, but also requires a large amount of empirical optimization. This also applies to the build-up of metallic layers from the inner surfaces of the insulator, which, as already mentioned, are usually avoided today by using shield structures (shield elements) within the switching chamber. Nevertheless, the deposits of the metal vapor and their influence on the dielectric strength of the vacuum interrupter VI cannot be predicted quantitatively in a sufficiently accurate manner.

It should also be noted that the design processes mentioned all lead to a reduction in the insulation properties of the outer structure of the vacuum interrupter to well below the dielectric strength of air or other gases surrounding the vacuum interrupter, so that housing and/or insulator sizes - in terms of length and/or diameter - are required that are not optimal in terms of cost and installation space. The addition of shielding elements with respect to the metal vapors leads to distortions of the electric fields on the insulator that occur during operation, which can lead to strong fields at certain points and thus to an overload of the insulator caused by charges building up there. However, as already explained, other causes also lead to such local high fields on the insulator of the housing of the vacuum interrupter, whereby the problems described here also apply to other switching devices, such as gas switches, in addition to the vacuum interrupter mentioned as an example.

As a rule, the known VIs are often constructed largely symmetrically to an -imaginary- center plane of the tube in order to minimize the number of different components and the complexity of the structure. However, the real environment of the tube generally distorts the electric field strongly, so that areas of the tube are strongly electric - in the sense of a high average electric field strength.

There is therefore a need to master the different requirements for dielectric strength, such as high lightning impulse voltages with highly transient switching edges - for example 1.2 µm rise time and an exponentially falling trailing edge with a time constant of 50 us, nominal voltages of 50 Hz or 60 Hz fundamental frequency with harmonic components up to the kHz range, as well as so-called nominal power frequency withstand voltage 50/60 Hz at up to twice the nominal voltage amplitude, for up to one minute load duration, through the design of the switching device.

It is therefore the object of the present invention to provide a switching device with a housing comprising a - preferably cylindrical - insulator and axial end caps, which has an increased dielectric strength with minimal size and manufacturing costs of the switching device, in particular a switching device which has an improved dielectric strength particularly in the areas of the housing which are subject to high electrical loads - as explained above. This object is achieved by the subject matter of the present invention, as disclosed in the description, the figures and the claims.

Accordingly, the subject matter of the present invention is an electrical switching device according to claim 1.

"Permittivity" is the ability of a material to be polarized by electric fields. Permittivity is a material property of electrically insulating polar or non-polar compounds that only becomes apparent when these compounds are exposed to an electric field.

The matrix material can be selected from the group comprising elastomers, thermosets, thermoplastics and/or glass. The various coating processes for producing the coating can be selected accordingly.

The matrix material is preferably applied as a paint, particularly in the form of a wet paint or powder paint. Other application methods such as spraying, immersion baths, casting, etc. are conceivable, but they are not the main focus of current research into the technology.

The great advantage of applying the coating as a powder coating and/or wet coating is that the refractively controlling coating produced is free of pores. Such a pore-free coating can also be achieved by casting, but the homogeneity of the coating usually suffers, especially at the edges.

When applied as a wet paint, this usually contains solvents which are not present in the matrix material or are only present in small quantities after the paint has dried.

According to an advantageous embodiment, the matrix is made of a polymeric matrix material, for example a polymeric resin, which is in the form of a polymeric binder.

A "polymer matrix" refers to a polymer or a polymeric binder. The polymeric matrix comprises in particular a resin or a resin mixture, such as epoxy resin, silicone elastomer, siloxane resin, silicone resin, polyvinyl alcohol, polyester imide and similar thermosetting, thermoplastic plastics, as well as any combinations, copolymers, blends and mixtures of the above-mentioned resins and/or plastics. The polymeric matrix can be present as a coating with a permittivity of ε _r >/= 2, filled or unfilled. The matrix preferably contains fillers with a high permittivity to air, in particular refractive dielectric insulating fillers, such as ceramic fillers, which are polar and/or easily polarizable in an electric field.

Preferably, the materials for the filler(s) are selected from Class 1 ceramic materials that meet high stability requirements and whose permittivities have a low dependence on temperature and field strength. These include, for example, compounds such as selected titanates, which have reproducibly low temperature coefficients and low dielectric losses. Their permittivity is largely independent of field strength, which has advantages for the application in question here.

• ε_r >/= 2 bis ε_r </= 200, vorzugsweise von
• ε_r >/= 10 bis ε_r </= 100.

The ceramic materials considered for the filler(s) according to the invention have relative permittivities ε _r in the range of

• ε _r >/= 2 to ε _r </= 200, preferably from
• ε _r >/= 10 to ε _r </= 100.

Fillers made of a material that is commercially available in the field of capacitor ceramics and is therefore relatively cheap and available in sufficient quantities are preferred. In particular, materials that have an almost linear temperature profile of the capacitor capacitance are considered. For example, these are in the form of one or more ceramics, in particular ceramics with metal nitride, metal carbide, metal boride and/or metal oxides such as titanium dioxide, aluminum oxide, selected compounds of ceramics comprising titanate are also suitable because of their field strength-independent permittivity. In addition to mixed oxides such as titanate and/or mixtures of various metal oxides, oxides of metal alloys in any combination with all of the aforementioned materials are also particularly suitable for fillers that exhibit largely field strength-independent permittivity.

For example, a mixture of finely ground paraelectrics such as titanium dioxide with admixtures of magnesium (Mg), zinc (Zn), zirconium (Zr), niobium (Nb), tantalum (Ta), cobalt (Co) and/or strontium (Sr) is suitable as a material for such a filler. The following compounds are mentioned here as examples: MgNb ₂ O ₆ , ZnNb ₂ O ₆ , MgTa ₂ O ₆ , ZnTa ₂ O ₆ , such as (ZnMg)TiO ₃ , (ZrSn)TiO ₄ and/or Ba ₂ Ti ₉ O ₂₀ , as well as any combinations and mixtures of the compounds mentioned.

When applied in the form of powder coating, common additives such as hardeners, accelerators and/or additives may be included in the amounts traditionally recognized as advantageous. Both thermosets and thermoplastics can be applied in the form of a powder coating.

A hardener is present when additive polymerization takes place. An accelerator, initiator and/or catalyst is used in all cases where resin is cured.

The matrix material is usually applied before, during, but preferably after the manufacture of the housing. For example, the refractive-controlling layer, which is produced by coating with the matrix material, is applied by spraying, doctoring, dipping, brushing and/or other methods that enable the production of a thin, homogeneous - in particular allowing for a coating that is as homogeneous and pore-free as possible.

The application method is preferably carried out automatically.

The refractively controlling coating is preferably a filled coating made of one or more matrix materials, which can be organic, for example in the form of a polymer, or inorganic, for example as glass, in which the filler is introduced.

The amount of filler in the refractively controlling coating can vary within wide limits. For example, a filler concentration of 1 vol.% - i.e. the almost unfilled matrix material with a relatively low refraction, which is caused almost exclusively by the dielectric barrier formed by the matrix material - can be present in the coating up to a filling of 70 vol.%. The preferred range of filler quantity is between 20 and 60 vol.%, in particular from 30 vol.% to 40 vol.% filling in the matrix material.

The filler particles of the refractive-controlling coating do not have a preferred shape; they can be embedded in the matrix in any shape and size. For example, the filler particles are irregular after appropriate grinding.

Filled paints, whose particles are as close as possible to a spherical shape, are more suitable for processing than other shapes because the specific surface area is the smallest and thus the smallest possible processing viscosity is achieved with the same degree of filling.

The size of the fillers can vary. There can be different filler fractions in the filler. The housing can be provided with differently filled coatings in different areas.

Thicker coatings and/or certain material combinations result in a stronger refraction of the field lines than others. The level of permittivity and the thickness of the applied refractive-controlling coating determine how much the electric field is evened out.

In the context of the present invention, thicknesses of the refractive-controlling coating of 10 µm to 5 mm, preferably in the range between 100 pm and 3 mm, particularly preferably in the range between 500 pm and 2 mm, have proven to be expedient.

In the present case, the permittivity of the coating according to an embodiment of the invention - filled or unfilled - is used so that the electric field on the surface of the housing of the switching chamber is pushed away by the increased permittivity compared to the uncoated surface and local field increases are thus reduced. This is explained again and shown schematically in Figure 2.

Without the refractive-controlling layer, the surface of the housing would usually be covered by an insulating gas such as nitrogen, air or sulphur hexafluoride. All of these gases have a comparatively low permittivity. Air, for example, has a permittivity of ε _r = 1.00059. A coating made of a plastic such as a resin, on the other hand, has a permittivity of at least twice the value ε _r = 2 - for example silicone resin - up to around ε _r = 9 - for example polyvinyl alcohol. This refers to the hardened resins.

The refractively controlled coating proposed here breaks the emerging field lines according to the refractive field control - refraction - because the penetration of the field into the higher permittivity material is made more difficult by the displacement of the field from the material with a higher permittivity into the material with a lower permittivity material. because the electric field is pushed away from the edge or triple point.

The triple point is the area of the housing in which a metal electrode, a solid insulator and a gaseous insulator - in this case the surrounding gas - come together.

According to an advantageous embodiment, the refractively controlling coating is at least partially applied to at least one of the contacting sides of the housing. This is particularly because the refractively controlling coating is also a dielectric barrier which, when applied to the metal electrodes, ensures that electrons have a much harder time getting out of the metal. Or, in other words, the electrical arcing between the electrodes is shifted towards higher voltages by the dielectric barrier. The refractive field shift then also shifts it towards even higher voltages.

Preferably, the refractive-controlling coating is provided on both metallic caps of the housing, which axially close off the preferably cylindrical insulator body to form the switching chamber, in whole or in part in addition to the application on the insulator body.

The refractive-controlling coating covers the housing completely or partially or in selected areas. The refractive-controlling coating is applied directly to the housing surface or, for example, to a lower layer, such as a resistive layer after the EP 3146551 B1 .

A lower layer on which the refractive-controlling coating is applied can comprise a further refractive-controlling layer as well as another, in particular a resistive layer after the EP 3146551 B1 , but preferably also, as an alternative, a resistive-capacitive layer.

Preferably, the lower layer is a thinner layer than the upper one, so that the layer thicknesses increase from the inside to the outside on the housing outer surface.

In the case of a coating on a resistive lower layer, it is particularly provided that the matrix materials of the respective coatings are compatible with one another. It is preferred, for example, that the matrix materials are at least inert to one another, but advantageously they can be mixed with one another and/or into one another as desired. It is very preferred that the matrix materials of different layers - for example the matrix material of a refractively controlling coating according to an embodiment of the present invention and the matrix material of a resistive coating according to the EP 3146551 B1 - have the same or similar chemical composition.

The coatings can also be combined in the form of layer stacks, with a resistive coating according to the EP 3146551 B1 preferably on the insulating areas of the housing of the switching device, such as on a ceramic cylinder, whereas the refractively controlling coating is provided in particular on the caps of the housing, i.e. the contacting areas. However, both coatings can extend over one another as desired and in particular also over all areas of the housing on the outside.

All layers of the overall coating of the housing cover the respective parts of the housing completely or partially, but on the outside.

Particularly suitable examples include embodiments in which the refractive-controlling coating is not applied over the entire surface of the housing, but only partially covers the housing. It is particularly preferred if the refractively controlling coating is applied to the caps, in particular to the metal caps and/or to the edges that form the caps with the insulator body.

Here, it is again particularly preferred that the refractively controlling coating extends beyond the edge, forming a border, for example also onto the surface of the insulator body.

It is irrelevant whether the insulator body itself is coated, for example with a resistive coating, or not.

• dass die untere - resistive Schicht komplett das ganze Gehäuse bedeckt und die obere refraktiv-steuernde Schicht die untere Schicht nur teilweise abdeckt;
• dass die untere Schicht die Gehäuse-Außenoberfläche nur teilweise bedeckt, insbesondere dass die untere Schicht in Form einer resistiv-kapazitiven Schicht aufgebracht ist und die obere refraktiv-steuernde Schicht die untere Schicht und die gesamte Gehäuse-Außenoberfläche ganz oder teilweise bedeckt;
• dass die untere Schicht teilweise von der oberen Schicht unbedeckt bleibt;
• dass resistiv-kapazitive Bereiche der unteren Schicht mit der refraktiv-steuernden oberen Schicht abgedeckt sind;
• dass zwei oder mehr Schichten einer Art verschiedene Gehäusebereiche bedecken und sich dabei eine oder keine Überlappung ergibt;
• etc...

All possible combinations of layers of coatings on the housing, in particular of coatings of the resistive coating in question according to the EP 3146551 B1 on the one hand and a refractive-controlling coating according to an embodiment of the present invention on the other hand, e.g.

• that the lower resistive layer completely covers the entire housing and the upper refractive-controlling layer only partially covers the lower layer;
• that the lower layer only partially covers the housing outer surface, in particular that the lower layer is applied in the form of a resistive-capacitive layer and the upper refractive-controlling layer completely or partially covers the lower layer and the entire housing outer surface;
• that the lower layer remains partially uncovered by the upper layer;
• that resistive-capacitive areas of the lower layer are covered with the refractive-controlling upper layer;
• that two or more layers of one species cover different shell areas with little or no overlap;
• etc...

According to the EP 3146551 B1 the resistive layer is applied over the entire surface of the housing outer surface, according to the present invention it can, in contrast, also only partially cover the outside of the housing, in particular it can also be applied in the form of a resistive-capacitive layer with a non-galvanically - i.e. not via a contact - electrically conductively connected area.

In principle, it is advantageous if the lower layer is thinner than the upper layer.

In principle, it is advantageous if the refractive-controlling layer is located on the resistive layer.

• Figur 1 zeigt eine Schaltvorrichtung nach einer Ausführungsform der vorliegenden Erfindung als Vakuumröhre und
• Figur 2 zeigt schematisch die Wirkung einer refraktiv steuernden Beschichtung auf einer Gehäuse-Oberfläche eines Gehäuses einer Schaltvorrichtung nach einer beispielhaften Ausführungsform der Erfindung.

A switching device according to the present invention is shown in Figure 1 shown.

• Figure 1 shows a switching device according to an embodiment of the present invention as a vacuum tube and
• Figure 2 shows schematically the effect of a refractively controlling coating on a housing surface of a housing of a switching device according to an exemplary embodiment of the invention.

Figure 1 shows in the form of a schematic diagram an embodiment of a switching device 1 according to the invention, here a vacuum interrupter. A housing 3, which is composed of two tubular ceramic parts, i.e. insulator bodies 2, is closed off by metal caps 4, which form areas with electrical contacts, and defines a switching chamber 5, into which two conductor elements 6, designed for example as bolts, with contacts 7 are guided.

The Fig. 1 The lower of the conductor elements 6 is designed to be movable according to the arrow 8 and the indicated movement device 9 and can be moved in the direction of extension 10 of the conductor elements 6, which also forms the axis of symmetry of the switching device 1, in order to bring the contacts 7 into contact or to space them apart, whereby in the present case an open, i.e. spaced-apart, state of the switching device 1 is shown. Due to the mobility of the lower conductor element 6, it is coupled to the metal cap 4 via a metal bellows 11; the metal caps 4 are therefore conductively connected to the conductor elements 6 on both sides.

There is a vacuum within the switching chamber 5, in this case with a pressure of < 10 ^-4 hPa.

However, the invention also relates to gas switches in which the gas is present inside the switch. The gas switches included here are those in which gas serves as a switching medium and, after successful shutdown, as an insulating medium. SF6 is usually used for this nowadays. Since SF6 is to be replaced as a strong greenhouse gas, switches with CO2, fluoronitrile or other alternative gases are also conceivable in the future.

In order to prevent metal vapors that are generated when the switching device 1 is opened, for example, from coming into contact with the inner surface of the insulator 2, here ceramic, a metal shielding element 12 (vapor shield) is provided in the contact area in the switching chamber 5. However, this shielding element 12 also causes a distortion of the electric field, so that in an area behind the shielding elements there would be a lower electric field during operation than in the "unshielded" areas, where charges can accumulate, for example, and thus cause further field distortions that could jeopardize the functionality of the switching device 1.

In order to counteract this, it is provided in the embodiment outlined here that a refractive-controlling coating 13 according to an embodiment of the invention is located on the outer surface of the housing 3, i.e. both on the insulator body 3 and on areas of the electrical contacts - i.e. the caps 4.

The refractively controlling coating 13 of the embodiment shown here, which is applied over the entire surface, comprises a polymer matrix which is filled with a highly permittive filler made of a ceramic material ε _r in the range of greater than or equal to 2 to 200, preferably from 10 to 100. The filler is contained in the matrix at 30 vol%. It is a mixture of titanium dioxide and aluminum oxide particles.

The refractive-controlling coating 13 is relatively inexpensive in terms of material price and relatively easy to spray on - even automatically. Its presence can be relatively easily detected using a scanning electron microscope and elemental analysis.

The Figure 2 shows schematically the effect of a refractive-controlling coating on a housing outer surface such as the one in Figure 1 shown housing 3.

Figure 2 shows schematically the course of the field and equipotential lines 15, 14 at each triple point, right half with a refractive-controlling coating 13 and left half for comparison without such a coating, according to the state of the art. As can be seen, the field lines 15 on the left run unbroken from the metal cap 4 into the surrounding gas, e.g. air. This can result in lightning discharges 16. On the right, where the coating 13 lies between the metal cap 4 and the ambient air, the field lines 15 are broken at the transition from the coating with high permittivity to the surrounding air with low permittivity - see area 17 - this breaks both the equipotential lines 14 and the field lines 15 are pulled far apart so that no arcs occur.

The refractively controlling coating 13, as proposed for the first time for this application, can reduce the length of the housing 3 of a switching device 1 and thus the overall length of the electrical switching device 1. This saves material costs. For example, a housing 3 could be produced for a specific voltage level. This exact housing 3 could then be coated with the refractively controlling coating 13 according to an embodiment of the present invention, and thus be usable for the next higher voltage level. In terms of process technology, this results in a design that can be used for two voltage levels, with the same two housings 3 being usable for two switching devices 1 at different voltage levels!

The two housings differ only in the additional refractive-controlling coating 13.

The special advantage of the application of a refractive-controlling coating presented here for the first time is that, since hardly any current flows through this coating, it is very resistant to aging and lasts longer and more reliably.

The invention proposes for the first time to apply a coating with high permittivity or at least high permittivity relative to the ambient air ε _r = 1 made of a plastic ε _r >/= 2, in particular ε _r >/= 3, in particular a filled plastic, to the housing surface of a vacuum interrupter in whole or in part, so that in critical areas, in particular at triple points, the field lines are broken and arcs are spread out as far as possible, thus preventing lightning.

The present invention is not limited to vacuum tubes, but relates to other switches, for example gas-insulated ones - for example those with SF6 and/or clean air - as switching gas. In gas switches with clean air, this is usually only used as an insulating medium and is not located in the interrupter unit, where the arc is created and the switching action is carried out.

List of reference symbols

1

switching device

2

insulator

3

Housing

4

cap

5

switching chamber

6

conductor element

7

contact

8

Arrow

9

exercise facility

10

direction of extension

11

metal bellows

12

screen element

13

refractive-controlling coating

14

equipotential lines

15

field lines

16

flash

17

area in which field lines are refractively refracted

Claims (16)

1. Electrical switching device (1) having at least two contactable conductor elements (6) that are able to be spaced apart by a movement apparatus (9), and having a housing (3) that defines a switching chamber (5) and that at least partially surrounds the conductor elements (6), wherein the housing (3) has an insulator body (2) and regions of an electrical contact (4) and wherein the housing (3) externally at least partially has a refraction-controlling coating (13) that comprises a dielectrically insulating matrix consisting of a material having a permittivity ε_r >/= 2, characterized in that the matrix of the refraction-controlling coating is present in a manner containing fillers, wherein the material of the filler particles of the at least one filler fraction is a ceramic having a permittivity in the range of 2_r >/= 3 and S_r </= 200.
2. Switching device according to Claim 1, wherein the refraction-controlling coating is present at least in a region of an electrical contact (4).
3. Switching device according to Claim 1 or 2, wherein the material of the filler particles of the at least one filler fraction comprises a ceramic containing at least a metal oxide, a metal mixed oxide and/or a titanate.
4. Switching device according to one of the preceding claims, wherein the matrix contains a total amount of filler particles in the range from 1% by volume to 70% by volume.
5. Switching device according to one of the preceding claims, wherein the resin is selected from the group of elastomers, thermosetting plastics, thermoplastics and/or glass.
6. Switching device according to one of the preceding claims, wherein the matrix is a polymeric resin and/or a polymeric resin mixture.
7. Switching device according to one of the preceding claims, wherein the polymeric resin or the polymeric resin mixture comprises at least one compound selected from the group of the following compounds: epoxy resin, silicone elastomer, siloxane resin, silicone resin, polyvinyl alcohol, polyesterimide, and any mixtures and/or combinations of the above compounds.
8. Switching device according to one of the preceding claims, wherein the refraction-controlling coating is provided in combination with at least one further coating on the outer surface of the housing (13).
9. Switching device according to Claim 8, wherein the further coating is a resistive coating.
10. Switching device according to one of the preceding claims, wherein the resistive coating completely or partially covers the housing outer surface.
11. Switching device according to one of the preceding claims, wherein the refraction-controlling coating (13) is provided at least partially above the resistive coating.
12. Switching device according to one of the preceding claims, wherein the refraction-controlling coating is present with a layer thickness of less than/equal to 5 mm.
13. Switching device according to one of the preceding claims, wherein the refraction-controlling coating is present with a layer thickness of less than/equal to 2 mm.
14. Switching device according to one of the preceding claims, wherein the refraction-controlling coating is able to be applied as a wet varnish.
15. Switching device according to one of the preceding claims, wherein the refraction-controlling coating is able to be applied as a powdered varnish.
16. Switching device according to one of the preceding claims, wherein the switching device is a vacuum switch or a gas switch.

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