INSULATOR ARRANGEMENT FOR A HIGH OR MEDIUM VOLTAGE SWITCHGEAR

Description

[0001] The invention relates to an insulator arrangement according to the preamble of patent claim 1.

[0002] The insulating ability of solids, such as aluminum oxide ceramics, against high-voltage stresses is generally very high, but it is limited by the finite dielectric strength of solids. This also applies to high-voltage insulators, especially ceramic insulators for medium- and high-voltage vacuum interrupters, as described, for example, in JP S48 44309 B1 and DE 699 18 156 T2. The cause is the discharge buildup within insulators, which is partly determined by the defect density in the field direction. The dielectric strength, the breakdown field strength in the solid, does not scale directly with the insulator length, but is proportional to the square root of the insulator length.The result is that, particularly for high voltages above around 100 kV, it is becoming increasingly difficult to achieve the necessary dielectric strength of, for example, vacuum interrupters for the high-voltage range, i.e. in a range of more than 72 kV. To date, this problem has been solved, particularly in vacuum interrupters in power transmission and distribution technology, by using several shorter components instead of a single, longer cylindrical insulator component. These components are connected to one another in the axial direction using a suitable, vacuum-tight and mechanically stable joining technology, such as a brazing alloy. In accordance with the law of internal dielectric strength described above, the combination of several such shorter insulators has a higher dielectric strength than a single, single-piece insulator of the same length.Overall, however, this soldering process is very cost-intensive, as a high level of technical effort is required to create the appropriate vacuum tightness for the connection.

[0003] The object of the invention is therefore to provide a ceramic insulator for a high- or medium-voltage switchgear that can be manufactured at low technical cost.

[0004] The solution to the problem consists in an insulator arrangement for a vacuum tube of a high- or medium-voltage switchgear having the features of patent claim 1 and in a vacuum tube for a high- or medium-voltage switchgear having the features of patent claim 10.

[0005] The insulator arrangement according to the invention according to claim 1 has at least one axisymmetric insulating structural element, wherein the invention is characterized in that the structural element has a conductive ring structure arranged on its inner surface and a conductive ring structure arranged on its outer surface, which are insulated from one another by the insulating structural element.

[0006] The described ring structures form equipotential surfaces in the area of ​​the structural element and also in the area of ​​the entire insulator arrangement, which overall increase the electrical strength of the insulator arrangement.

[0007] Equipotential surfaces are conductive layers on or between the structural elements that exhibit a higher electrical conductivity than the ceramic material of the structural elements. These layers are arranged perpendicular to the axis of symmetry and define equipotential surfaces for axial electric fields. This electrically divides the insulator arrangement into short axial sections, increasing the dielectric strength of the section as well as the entire insulator.

[0008] On an outer side of the structural element, a further, outer ring structure is attached, which overlaps with the ring structure inside the structural element with respect to a solder to the longitudinal axis of the structural element. In this way, however, the equipotential surfaces thus formed are not formed by conductive layers between successive structural elements, but rather as a region of greatly reduced axial electric field strength inside the insulator, with the field strength reduction in the axial direction being mediated by the shielding effect of the conductive coatings applied inside and outside. It has proven expedient for the ring structures inside and outside to be attached essentially at the same height with respect to the axis of the structural element, i.e. that at least one solder that is dropped onto the longitudinal axis of the structural element runs through both ring structures.The two ring structures are capacitively coupled to each other, creating a region of low axial field strength radially within the structural element. To expand and improve the geometric design of the equipotential surfaces, it may be advantageous to arrange the inner and outer ring structures slightly offset with respect to the solder.

[0009] In a further embodiment, it is expedient to provide at least two structural elements that are joined to one another along their end faces, with each of the at least two structural elements having at least one ring structure. Two ring structures have the advantage that the height of the insulator arrangement generally increases, thus achieving a significantly higher electrical breakdown strength. If each of these structural elements comprises another ring structure, a further increase in the breakdown field strength for the entire insulator arrangement is achieved.

[0010] It has further been found that the structural element has an axial extension of between 10 mm and 200 mm, preferably between 20 mm and 80 mm, and particularly preferably between 20 mm and 40 mm. An axial extension in this size range represents an optimum in terms of both the electrical breakdown strength and the technical manufacturing capabilities of the structural element. Structural elements can be manufactured technically with relatively manageable effort, while also achieving high breakdown strength, particularly using the described ring structures.

[0011] It is also advantageous if the axial spacing of the ring structures, both the outer and inner ring structures, is between 5 mm and 40 mm. Within this spacing range, depending on the electrical conductivity of the ring structures, the effect of the equipotential surfaces is optimized, resulting in a technically useful balance between insulation and charge dissipation.

[0012] Furthermore, it is expedient if a further coating is provided on the structural element on its inner side and / or on its outer side, which coating has a surface resistance which is between 10 8< Ohm 10 12< Ohm, preferably between 10 8< Ohm 10 10< Ohm.

[0013] The ring structure itself can be designed in various forms. In one embodiment, the ring structure consists of a metallic structure or a conductive, self-supporting structure, in particular in the form of a ring, a strip, or a foil, which is applied to the corresponding surface of the structural element. On the other hand, it can be expedient to apply the ring structure in the form of a coating, whereby all common coating methods are suitable. In particular, so-called plasma chemical vapor deposition (PCVD) or CVD is used, but sputtering, vapor deposition, or spraying, as well as doctor blade coating and firing in the form of screen printing, can also be useful here. By applying a written layer, the conductivity or sheet resistance of the ring structure can be particularly well adjusted.

[0014] A further component of the invention is a vacuum interrupter for high and medium voltage applications, which comprises an insulating arrangement according to one of claims 1-7.

[0015] Further embodiments and further features of the invention are explained in more detail with reference to the following figures. Features with the same designation but different embodiments are provided with the same reference numerals. These are purely exemplary embodiments that do not represent a limitation of the scope of protection.

[0016] Showing: Figure 1 shows a cross-sectional view of a vacuum interrupter with an insulator arrangement, the left part of the vacuum interrupter representing the state of the art, Figure 2 shows a three-dimensional view of a structural element with a ring structure inside and outside, Figure 3 shows a cross-sectional view of the structural element from Figure 2, Figure 4also cross-sectional view of the structural element from Figure 2 with staggered arrangement of the ring structures, Figure 5 also shows cross-sectional views of the structural element from Figure 2 with an additional second ring structure on the outside, Figure 6 a structural element with ring structures and a surface coating of an outer surface, Figure 7 a structural element analogous to the representation in Figure 2 in cross-sectional view with shielding plates in the inner area Figure 8 a cross-section through an insulator arrangement with two joined structural elements and Figure 9 a graphic representation of the relationship between the breakdown field strength and the height or thickness of the insulator material of the structural element.

[0017] In Figure 1 A cross-sectional view of a typical vacuum interrupter 3 is shown, where the Figure 1viewed from left to right, on the left side corresponds to the prior art and on the right side an example of an embodiment of the invention is shown. Basically, the vacuum interrupter 3 comprises an insulating space 25 in which two switching contacts 26 are arranged along a longitudinal axis 20 through the essentially rotationally symmetrical vacuum interrupter 3. At least one of the switching contacts 26 is arranged in the vacuum interrupter 3 so that it can be moved translationally with respect to the axis 20, so that the switching contact can be opened and closed. Insulator arrangements 2 are provided in the area to the left and right of the switching contacts (in the installed position these areas are above or below with respect to the heads of the switching contacts).This insulator arrangement 2 consists, in particular in the prior art, of the connection of several structural elements 4, which are joined to one another at the end faces, wherein a corresponding joining method ensuring vacuum tightness is used.

[0018] The vacuum interrupter described here differs from the prior art in that ring structures 8 and 16, respectively, are provided on the structural elements 4 and are arranged in the inner region. Furthermore, it is expedient to also attach ring structures 16 in the outer region of the structural element 4. The ring structures 8 and 16 are arranged such that, viewed along the axis 20, they are essentially at the same height both inside and outside with respect to a longitudinal axis 20, so that at least partial overlap occurs. Furthermore, shielding plates 24 can be arranged on the structural elements 4 or on the insulator arrangement 2, which shielding plates prevent flashover between the contact 26 and the relatively conductive surfaces in the region of the ring structure 8.

[0019] It should be noted that both the ring structures 8 and / or 16 as well as the connecting regions 27, which are generally provided as conductive solder joints, serve as the already described equipotential surfaces, which act as a zone of greatly reduced field strength in the axial direction and thus prevent breakdown of the insulator arrangement 2.

[0020] The introduction of the ring structure increases the internal dielectric strength of a hollow-cylindrical high-voltage insulator. In the case of the vacuum interrupter described, part of the ultra-high vacuum-tight envelope of the vacuum interrupter is also simultaneously increased by applying conductive structures, i.e., the ring structures 8, 16 described here, to the ceramic of the structural element at shorter intervals along the inner (vacuum-side) and outer ceramic surfaces. These ring structures 8, 16 preferably have a metallic or nearly metallic conductivity that is at least three orders of magnitude higher than the conductivity of the adjacent surface 10 of the structural element 4. In this way, the ring structures 8, 16 define equipotential surfaces 9 with respect to the electric fields, which penetrate the structural element 4, in particular a ceramic body, in the radial direction.As a result, the ceramic's interior is electrically relieved of high axial field strengths in short axial sections, thus subdividing it axially. In this way, the dielectric strength is significantly increased not only along a section between two equipotential surfaces but also along the entire structural element 4. The described arrangement of the ring structures on the structural element results in an extended region of reduced electric field strength, in which the breakdown probability is statistically minimized.

[0021] In principle, this description essentially assumes ceramic structural elements 4, which are preferably depicted in the form of a hollow cylindrical insulator structure. However, a configuration of the structural element 4 not belonging to the claimed invention, using insulators based on polymers or composite materials, e.g., glass-reinforced epoxy resin or epoxy resin filled with quartz or other ceramic powders, may also be expedient. Cross-sections deviating from the symmetrical circular shape, such as ellipses or polygons, are also possible solutions.

[0022] An advantageous effect of the invention is, among other things, that the subdivision of a conventionally long ceramic structural element 4 by applying conductive equipotential surfaces 9 in the form of the described ring structures 8, 16 in the interior and preferably exterior of the structural element 4 can either be integrated into the ceramic body during production or can be subsequently applied to this structure. As shown here for Figure 9 As will be explained in more detail, this measure results in a single structural element with a given height having a higher electrical strength than the same structural element without the described conductive ring structures 8, 16.

[0023] This significantly reduces the manufacturing costs of the entire insulator assembly, depending on the required insulation thickness, since fewer separation points or connections 27 are required. Depending on the requirements, it may be sufficient to use only two structural elements instead of assembling three to form an insulator assembly 2. This eliminates a connection 27, which accounts for a particularly high proportion of the total costs of manufacturing the insulator assembly 2. Furthermore, this eliminates a source of error in the event of a potential leak in the vacuum interrupter 3.

[0024] The ring structure, which acts equivalently to an equipotential surface 9 in an area inside the ceramic, is thus not designed as a layer to be physically introduced, as is the case, for example, with the connection 27, but as a functionally equivalent but much easier to apply zone with a significantly increased electrical conductivity with respect to the adjacent surface 10 of the structural element 4. Several areas with the ring structures can be formed along a structural element in the axial direction (along the longitudinal axis) in order to further shorten the insulator part lengths loaded with high electrical field strengths, without impairing the electrical strength at the surface of the insulator body in the axial direction.

[0025] The described ring structures can be manufactured using various methods and forms. For example, applying the ring structures 8, 16 using a metallically conductive layer, e.g., in the form of fired metallic or metal oxide layers, is expedient. Suitable metal oxides or mixtures include those also used for metallizing ceramics, e.g., using the Mo / MnO process, or those used for reactive soldering of metallic and ceramic components.

[0026] Particularly suitable, particularly with regard to the outer ring structures 18, is the application of interrupted ring structures, both ring structures 16 and ring structures 8, which, for example, have the form of interrupted bands, offset bands or rings or points adjacent to one another but not touching one another.

[0027] Also possible are layers that can be formed by sputtering, vapor deposition, spraying, or CVD or PCVD processes as metallic, metal oxide layers or even as metal borides, carbides, or metal nitrides. It is also possible to apply organically bonded, conductive lacquers, which are freed from the organic phase by thermal treatment. Graphitic or graphite-containing layers, e.g., using the Aquadag process, are also suitable for representing the corresponding ring structures. This also applies to graphite structures created by appropriate abrasion of a carbon / graphite source. The described process is an exemplary excerpt of possible representations of the described ring structures 8 and 16.

[0028] The corresponding ring structures 8, 16 on the structural elements 4, in their arrangement in the insulator arrangement 2, can be provided with the so-called shielding systems or shielding plates 24, as is shown, for example, in the Figure 7 but also in the Figure 1 This results in an additional function, which can, for example, consist in these shielding plates 27 providing shielding of the ceramic surface against deposition of metal vapor resulting from the switching arc.

[0029] The ring structures 8, 16 do not necessarily have to be continuous, i.e., uninterrupted, but can also be implemented as flat structures consisting of closely spaced conductive structures applied in a grid pattern, e.g., dots or lines. Such layers are particularly advantageous for producing using screen printing methods such as doctor blades.

[0030] In Figure 2a three-dimensional representation of a structural element 4 is given, which is essentially rotationally symmetrical, in this case in cylindrical form, and which has a ring structure 8 on an inner surface 6, which in Figure 2 is shown in dashed lines and an outer ring structure 16 is arranged on an outer side. As shown in Figure 3 , which is a cross-sectional view of the Figure 2 As can be seen from FIG. 1, the ring structures 16 and 8 extend at the same height with respect to an axial extension of the structural element 4. This means that a plumb line 18 dropped onto the axis 20 passes through both the inner ring structure 8 and the outer ring structure 16, at least in an overlapping area.

[0031] In the Figures 4 and 5Ring structures 8 and 16 are shown, where there is not a 100% overlap in the axial direction, whereby these ring structures 8 and 16 are slightly shifted axially to each other, but there is still an overlap area. Figure 5 Two ring structures 16 are applied to the outside of the structural element 4, wherein both ring structures 16 preferably have an overlap region in the axial direction with the ring structure 8 in the inner region 6 of the structural element 4. This means that a solder 18 can be placed on the axis 20 such that it runs through both ring structures 8, 16.

[0032] In Figure 6 a structural element 4 is shown, which has an analogous embodiment to the structural element 4 in Figure 3which, however, has an additional surface coating 22 on its outer surface, which preferably has a sheet resistance of typically 100 megohms per square, which is a poor conductor or, to put it another way, not an insulator. In this way, an ohmic as well as non-linear current-voltage characteristic acts on this surface 22. This serves to control the electric field on the surface and to reduce the charging of the surface with electrical charges. In this way, particularly voltage-resistant structural elements 4 can be produced. Alternatively, the conductive coating with a high sheet resistance between 10 8 < ohms and 10 12 < ohms can also be applied to the inside or to both sides of the ceramic. The resistance layer can be applied either underneath the ring structures 8, 16 or, in another embodiment, extend over the ring structures 8, 16.

[0033] In the Figures 2 to 7 Insulator arrangements 2 are shown, each consisting of only one structural element 4. In this exemplary embodiment, these insulator arrangements 2 are designed with ring structures 8, 16 only in the central region for the sake of clarity. However, the ring structures 8, 16 have a typical distance in the axial direction, which is between 10 mm and 40 mm. A typical structural element 4, as shown in the Figures 2-7 can therefore have several ring structures 8 and 16 on the inside and outside, which lead to the advantageous internal electrical effects already described. In this respect, the Figures 2-7 are purely exemplary in nature and serve in particular to illustrate the arrangement of the ring structures 8 and 16 in general. Figure 8 An insulator arrangement 2 is shown, which is composed of two structural elements 4. The structural elements 4 in Figure 8are joined to one another at the end face by connection 27. Connection 27 also consists of a metallically conductive layer and also represents an equipotential surface 9.

[0034] By applying the ring structures 8 and 16, additional equipotential surfaces 9 are introduced into the insulator structure 2, which have the positive electrical properties already described. Figure 9, it can be seen that a root-shaped curve exists between the breakdown field strength 28, which is plotted on the Y-axis, and the height or thickness of the ceramic insulating body, which is plotted on the X-axis and is provided with the reference number 29, which is shown by the curve 30. This means that with a height of, for example, 5 length units of a structural element 4, a dielectric strength, in this example of 60 kV, is achieved. With 10 length units of the same material and the same thickness, a dielectric strength of only approximately 90 kV is generated. This means that either the structural element 4 has to be made very long in order to achieve a high dielectric strength, or several structural elements 4 have to be joined together, each of which has the corresponding equipotential surfaces 9. The equipotential surfaces 9 are in this caseInsulator arrangements 2 for vacuum interrupters are represented by the solder joints. The additional ring structures 8 and 16 described here, on the one hand, shorten the distances between the equipotential surfaces 9, so that, for example, with a distance of 5 length units between the ring structures, a dielectric strength of 60 kV can be achieved. On the other hand, a virtual equipotential surface 9' is introduced in the ceramic region between the ring structures 8, 16, which, without a solder joint, causes a virtual shortening of the ceramic. With 2x5 length units along the same structural element, a dielectric strength of 120 kV can already be achieved, whereas a conventional structural element according to the prior art would only achieve a dielectric strength of 90 kV according to the same example.This means that the total length of the insulator arrangement 2 can be significantly reduced, which on the one hand represents a significant reduction in the manufacturing process effort, which in turn is reflected in a significant cost reduction with a smaller installation space for the vacuum interrupter 3.

Claims

1. Insulator arrangement (2) for a high-voltage or medium-voltage switchgear assembly having at least one axially symmetrical insulating ceramic structure element (4), characterized in that the structure element (4) has a conductive annular structure (8) arranged on the inner surface (6) thereof and a conductive annular structure (16) arranged on the outer surface (14) thereof, said annular structures being insulated from one another by the insulating structure element, wherein the outer and the inner annular structure (16) are mounted with respect to one another in such a way that they have an overlap with respect to a perpendicular (18) on the longitudinal axis (20) of the structure element (4), and the two annular structures are capacitively coupled to one another.

2. Insulator arrangement according to Claim 1, characterized in that the annular structure (8) has an electrical conductivity that is at least eight powers of ten higher than the conductivity of the adjoining surface of the structure element.

3. Insulator arrangement according to Claim 1 or 2, characterized in that the annular structure (8) has an axial extent (10) that is at least half the thickness and at most four times the thickness of the structure element (4) in the radial direction.

4. Insulator arrangement according to Claim 1, characterized in that at least two structure elements (4, 4') are provided, which are joined to one another along their end faces, wherein each of the at least two structure elements (4, 4') has at least one annular structure (8, 16).

5. Insulator arrangement according to one of Claims 1 to 4, characterized in that the structure element (4, 4') has an axial extent between 10 mm and 200 mm, preferably between 20 mm and 80 mm, particularly preferably between 20 mm and 40 mm.

6. Insulator arrangement according to one of the preceding claims, characterized in that the distance between the annular structures (8, 16) in the axial direction is between 5 mm and 40 mm.

7. Insulator arrangement according to one of the preceding claims, characterized in that a further coating of the structure element is provided on the inner side thereof and / or on the outer side thereof, said coating having a sheet resistance between 108 ohms and 1012 ohms, preferably between 108 ohms and 1010 ohms.

8. Insulator arrangement according to one of the preceding claims, characterized in that the annular structure (8, 16) is in the form of a metallic structure, in particular is designed in the form of a ring or in the form of a strip.

9. Insulator arrangement according to one of Claims 1 to 5, characterized in that the annular structure (8, 16) is attached in the form of a conductive coating.

10. Vacuum interrupter for high-voltage or medium-voltage applications, comprising an insulator arrangement according to one of Claims 1 to 7.