EP0298981B1 - Contact system for vacuum switches with an axial magnetic field - Google Patents

Abstract

Contact elements for vacuum switches with an axial magnetic field are designed for example as pot-shaped contacts with slits in the same direction, which carry a disc-like contact body and have means for suppressing eddy currents. For this, it is known in particular to incorporate radial slits in the contact element. In accordance with the invention, the contact elements (10, 20, 30, 40, 50) have, at least on their rear part, radial zones (15, 25, 35, 45, 55) which are provided with a significantly a lower electrical conductivity than the basic material. Such radial zones can be either grooves (15 to 18) on the rear side (12) of the contact element (10), diffusion regions (25, 35) of addivites which reduce the electrical conductivity of the basic material, or even a combination of both. In the case of contact elements (40, 50) produced by powder metallurgy it is also possible to incorporate the radial regions during manufacture in the form of filled portions (45) or moulded elements (55) from a material having a lower electrical conductivity than the basic material.

Description

The invention relates to a contact arrangement for vacuum switches with an axial magnetic field, the contact pieces of which contain disc-shaped contact bodies made of contact material as the base material, the contact bodies being soldered onto the contact carrier and, in order to reduce eddy currents, having radial areas which have a lower electrical conductivity than the base material.

With the increasing spread of the vacuum switching principle in the medium-voltage range, the mastery of higher breaking currents is required. Currents above 40 kA should also be safely switched off, with the aim of maintaining or reducing the outer dimensions of the switching tube. A large number of special contact geometries have been proposed which carry the switching current in the azimuthal direction in the vicinity of the contact bodies. As a result, an axial magnetic field is generated during the switching between the contact pieces, which causes a switching arc which is uniformly diffusely distributed over the entire contact surface.

The following problem generally arises with such contact configurations with an axial magnetic field: Due to the temporal change in the current in the azimuthal current path, eddy currents are induced in closed, ring-shaped contact carrier bottoms, in disk-shaped contact bodies or in contact rings. Such eddy currents generate secondary magnetic fields which weaken the amplitude of the axial magnetic field and shift its phase position with respect to the current flowing through the switch. The phase shift of the axial magnetic field, however, has the effect that a considerable axial residual magnetic field is maintained during and after the zero crossing of the current. This magnetic field prevents the charge carriers that are still present from flowing rapidly out of the contact gap and promotes undesired re-ignition of the arc.

Various solutions for avoiding eddy currents in vacuum switches with an axial magnetic field are known. For example, DE-A-2 443 141 describes a contact arrangement in which there are four current conductors which run in the form of hooks radially and azimuthally to generate the axial magnetic field and the disk-shaped contact body is radially slotted to avoid eddy currents. Furthermore, from DE-A-3 231 593 a structure of a contact made of azimuthal current conductors is known, which are formed by multiple, same-way slitting of a pot contact onto which a contact disk provided with radial slots is soldered as a contact body. In addition, EP-A-0 055 008 shows the course of current conductors for magnetic field formation, the current in the contact disk often running in a meandering manner in the arc plane and the contact body being divided into several parts by wide slots.

Correspondingly, EP-A-0 155 584 and EP-A-0 052 371 assume the need for radial slots in the contact body in contact arrangements for vacuum switches with an axial magnetic field. Alternatively, it should also be possible to use suitable current blocking bodies made of a material with high resistance, such as stainless steel and ceramic. According to EP-A-0 052 371, such blocking bodies would have to be introduced into the contact pieces with the actual contact body made of a CuFe or CuCo alloy and the underlying contact carrier of the same geometry, which consists of a CuPb or CuBi alloy is possible with great effort.

In the specialist literature (for example "IEEE Transactions on Power Apparatus and Systems" (1980), pages 2079 to 2085) it is explained in detail under what conditions slots are required in order to avoid eddy currents in the contact disk exposed to the arc, in practice consistently of The necessity of the slots as a suitable means for eddy current suppression is assumed.

A disadvantage of the prior art is that because of the wide radial slots in the contact surface facing the arc, cathode base points preferably attach to the edges thereof, which can lead to reignitions due to thermal overheating. The same applies if the current blocking bodies for the replacement of the slots lead to macroscopic inhomogeneities on the switching side. In addition, in the prior art, the slices of the disks can only be made up to about a third of the contact disk diameter in order to maintain the stability of the contact body. Because of the lack of slits in the central area of the contact pieces, the eddy currents flowing there remain fully effective.

The object of the invention is therefore to provide contact pieces for vacuum switches with an axial magnetic field, in which eddy currents and thus coupled axial residual magnetic fields are prevented in the zero current crossing without disturbing slots or other macroscopic inhomogeneities impairing the contact surface of the contact body. Such contact bodies with means for suppressing eddy currents should be able to be produced in a simple manner using the known manufacturing technologies.

The object is achieved in that the radial areas starting from the rear of the contact body extend only over part of the thickness of the contact body, i.e. do not extend to the surface of their switching sides.

According to the invention, it is therefore proposed to use such contact bodies in axial field contact systems which are largely smooth on the button, but which are nevertheless conductive cause jumps to suppress eddy currents through radial areas with a significantly lower electrical conductivity than the contact material.

The radial regions can preferably be formed by grooves on the side facing away from the switching side of the contact piece. The radial regions can also be diffusion zones of an additive that reduces the electrical conductivity of the contact material. The diffusion zones can also originate from the grooves on the side facing away from the switching side of the contact piece.

Furthermore, especially in the case of contact bodies produced by powder metallurgy, the radial regions can also be fillings or molded parts made of a material with a lower conductivity than that of the base material.

Fillings or molded parts as such are already mentioned in the prior art as so-called current blocking bodies, which are intended to replace the slots in contact bodies. It is only within the framework of the teaching according to the invention, however, that they can be introduced into the blank in the powder-metallurgical production of the molded parts for the contact body in such a way that they leave the button of the finished contact body unaffected. In particular, the switch side can then be formed entirely from the base material.

It is particularly advantageous in the invention that sufficient mechanical stability is ensured for the soldering process of the contact disk onto the contact piece carrier. The switching properties of the contact piece are not changed by the smooth contact surface of the contact body.

Further advantages of the invention result from the following description of the figures of exemplary embodiments with reference to the drawing in conjunction with the patent claims.

• Fig. 1 eine Kontaktanordnung für ein Vakuumschaltgerät mit axialem Magnetfeld in Schnittdarstellung.
• Fig. 2 bis Fig. 4 drei verschiedene Ausführungsformen der zugehörigen Kontaktkörper in perspektivischer Darstellung und
• Fig. 5 verschiedene Möglichkeiten der Querschnittsform für die Nuten auf der Unterseite der Kontaktkörper,
• Fig. 6 und 7 zwei weitere Ausführungsformen von pulvermetallurgisch hergestellten Kontaktkörpern.

Show it

• Fig. 1 shows a contact arrangement for a vacuum switching device with an axial magnetic field in a sectional view.
• FIGS. 2 to 4 show three different embodiments of the associated contact body in a perspective view and
• 5 different possibilities of the cross-sectional shape for the grooves on the underside of the contact body,
• 6 and 7 two further embodiments of powder metallurgically produced contact bodies.

In Fig. 1, a contact piece 1 of a vacuum switch comprises a pot-like contact carrier 2 with obliquely circumferential slot 3. The mating contact piece 1 'has in the corresponding contact carrier 2' a slot 3 'running in the same direction in the axial direction, so that an axial overall due to the current flow Magnetic field is generated. For the contact carrier 2 or 2 'is a contact pin 4 or 4' made of copper or the like. guided. A support body 5 or 5 'made of electrically poorly conductive material, for example chrome / nickel steel in a double-T shape, is inserted in the contact carrier 2 or 2'.

On this arrangement there is in each case a disk-shaped contact body 10 or 10 'made of a suitable contact material, for example a CuCr material with 50% Cr. In the prior art, the contact body usually consists of a disk, into which slots are made radially from the circumference up to approximately two thirds of the center. The center of the pane cannot be slotted to ensure sufficient stability.

2 shows the contact body 10 with its switching side 11 and its rear side 12. It can be seen that 15 ridges of lower electrical conductivity can be produced by radially running, wedge-shaped grooves milled in from the rear. The wedge angle can be, for example, 10 to 90 '. The wedge depth is dimensioned so that the disc 10 still has sufficient mechanical stability for the soldering process on the contact carrier 2 or 2 'and support body 5 or 5'. The contact body 10 is expediently oriented azimuthally in such a way that the radial regions of the slits 3 and 3 'defined by the grooves 15 are correspondingly assigned to the contact carriers 2 and 2' according to FIG. 1.

With such a design of a contact body with grooves 15 it can be shown that there is a limited effective depth of the electrical current due to the skin effect and thus a suppression of undesired eddy currents is ensured.

3, star-shaped regions of lower electrical conductivity than those of the base material are produced in a contact body 20 with the switching side 21 and rear side 22 by local diffusion of suitable components. The components for the diffusion zones have, for example for a CuCr contact material, for example iron (Fe), cobalt (Co), nickel (Ni), titanium (Ti) or aluminum (AI), i.e. components which form a mixed crystal with copper and thus the Effectively reduce electrical conductivity, proven.

To produce the star-shaped regions 25, the diffusion zones are expediently delimited by masks. The diffusion takes place from the rear side 22 of the contact piece 20.

Leaving the contact material 10 unchanged, either of the contact pieces 10 and 20 towards the entire switching side 11 or 21 or of the contact piece 30 towards the central region 36, ensures the desired arc distribution during the switching process.

In further embodiments of the invention, it is also possible to construct a contact piece in the combination of FIGS. 2 and 3. Grooves are first introduced into the contact piece from the rear and the diffusion of the conductivity-reducing additive is effected from the base of the grooves.

5 shows that the grooves 15 according to FIG. 2 also have a semicircular profile 16 in their cross section, can have a rectangular profile 17 or a trapezoidal profile 18. Other shapes are also conceivable. The grooves 16 to 18 can advantageously be the starting point for diffusion zones 25 according to FIG. 3.

6 and 7 show contact bodies 40 and 50 which are produced by the sintering impregnation process by impregnating a chrome structure with liquid copper. The powder-metallurgical manufacturing process of such disks 40 and 50 enables radial regions, for example spoke-shaped or star-shaped, to be produced as webs from a material of lower conductivity than that of the base material, simultaneously with the production of the molded part. To produce such contact bodies, segment-like powder regions of such materials are introduced into the powder bed, which lead to the desired regions of low conductivity in the subsequent impregnation process. Different powders can be layered, for example, by means of sheets arranged in a star shape, which are removed after the filling process.

By means of a suitable filling process, such radial areas can be produced in a simple manner which - corresponding to the exemplary embodiment according to FIG. 3 described for diffusion zones - end below the buttons. Radial segments can also be introduced from the circumference up to a predetermined position to the center of the circular disk. The limits can be parallel or radial. It is advisable to select the areas as narrowly as possible, but instead to select a larger number, for example eight or more, but at least four, in a circle-symmetrical manner over the pane.

In a powder metallurgical production, radially extending powder fillings can be introduced directly into the molded body 20 with the switching side 21 and soldering side 22 according to FIG. 3, starting from the rear side 22 up to close to the switching side 21, each forming approximately bar-shaped webs 25 due to parallel boundaries and forming in the Cross the disc center. The webs 25 define star-shaped or spoke-shaped areas and leave the contact surface 21 of the contact body 20 unchanged.

6, the different powder layers 44 and 55 can be present in such a way that the powders of the material for the radial areas of low conductivity either remain undissolved or else dissolved in the finished material. In the latter case, however, the choice of material must ensure that there is no homogeneous solution in the impregnation metal. For example in the case of Cu powder compacts with embedded segments, e.g. The subsequent impregnation process from iron (Fe) powder leads to the Fe powder bodies being dissolved or dissolved, the Fe in the form of FeCr precipitating again on immediately adjacent Cr grains of the impregnation material.

In FIG. 7, areas 55 with poor electrical conductivity are introduced as narrow webs in a contact body 50. In this case, however, the areas 54 made of base material are specifically separated by sheets, for example made of iron (Fe), cobalt (Co), titanium (Ti), nickel (Ni), aluminum (Al) or alloys thereof. The sheets 55 can be inserted radially from the circumference into the powder bed for the compact, which can be achieved in a simple manner by suitably folded sheet metal strips. The height of the sheet metal strip is chosen to be lower than the total thickness d of the contact disk.

Due to the sintering and impregnation process, the inserted webs 55 result in the desired webs of lower conductivity than that of the base material. The outer region of the contact body 50 can then be turned off, so that the star-shaped structure of the webs formed by the plates 55 is created. However, a highly conductive central area 56 remains in the contact body 50.

The contact bodies 10, 20, 30, 40 or 50 described in detail above can be easily soldered onto the contact carriers 2 or 2 'and the support bodies 5 or 5' of the contact pieces 1 or 1 'according to FIG. 1. The different contact bodies are each appropriately oriented such that the radial areas of lower electrical conductivity are correspondingly assigned to the slot 3 or 3 'of the contact carrier 2 or 2'.

The invention was described above using a CuCr base material with 30 to 60% chromium as the contact material. Contacts can also be produced according to the invention with other contact material systems, for example based on CuW or CuMo.

Claims (14)

1. A contact arrangement for vacuum switches with an axial magnetic field, the contact pieces (1, 1') of which contain disc-shaped contact bodies (10, 10', 20, 20', 30, 30', 40, 40', 50, 50') of contact material as base material, wherein the contact bodies 110,10', 20, 20', 30, 30', 40, 40', 50, 50') are soldered to contact carriers (2, 2') and have, for the reduction of eddy currents, radially extending areas (15, 25, 35, 45, 55), which have a lower electric conductivity than the base material, characterised in that the radial areas (15, 25, 35, 45,55) extend emanating from the rear side of the contact bodies (10, 10', 20, 20', 30, 30', 40, 40', 50, 50') along only one part of the thickness (d) of the contact bodies (10,10', 20, 20', 30, 30', 40, 40', 50, 50'), i.e. not up to the surface of their switching sides (11, 21, 31, 41, 51).

2. A contact arrangement according to claim 1, characterised in that the radial areas (15, 25, 35, 45, 55) are narrow compared to the circular segments of base material lying therebetween and that at least four radial areas (15, 25, 35, 45, 55) are distributed in the contact body (10, 20, 30, 40, 50) in circular symmetry.

3. A contact arrangement according to claim 1, characterised in that the individual areas either have parallel boundaries and form in the contact body (10, 20, 30, 50) beam-shaped webs (15, 25, 35, 55) or in that the individual regions have radial boundaries and form in the contact body (40) wedges (45) with a base area like a circular sector.

4. A contact arrangement according to claim 1, characterised in that the radial areas (35, 45, 55) extend so far, emanating from the periphery of the contact body (30, 40, 50), that a central area (36, 46, 56) is maintained with continuously high electric conductivity.

5. A contact arrangement according to claim 1, characterised in that the radial areas are formed by grooves (15) on the side facing away from the switching face (11) of the contact body (10), which have in their cross-section a triangular (15), quadrilateral (17, 18) or semi-circular profile (16).

6. A contact arrangement according to claim 1, characterised in that the radial areas (25, 35) are diffusion zones of additives in the base material of the contact bodies, which, because of mixed crystal formation reduce the electric conductivity of the base material, wherein the additives are diffused-in from the side (22) opposite the switching side (21) of the contact body (20) and the diffusion depth is at least 50% of the thickness (d) of the contact body (20), but less than its total thickness.

7. A contact arrangement according to claims 5 and 6, characterised in that the radial areas are formed by grooves (15) on the side opposite the switching side of the contact body (10) as well as by the diffusion zones (25) emanating from these, which, emanating from the base of the groove (15), reach at least 50% of the remaining thickness of the contact body, but less than its total thickness.

8. A contact arrangement according to claim 1, characterised in that the contact body (40, 50) is a moulded part produced by powder metallurgy and has, emanating from its rear side, radial areas (45, 55) of a material with clearly lower electric conductivity than that of the base material.

9. A contact arrangement according to claim 8, characterised in that the radial areas (45) are filled-out with a powder of material of low electric conductivity, for example with metallic materials or insulating material.

10. A contact arrangement according to claim 8, characterised in that moulded parts (55), for example, steel, of a material of clearly lower electric conductivity than that of the base material, are introduced into the contact body (50).

11. A contact arrangement according to one of the preceding claims, characterised in that the contact bodies (10, 20, 30) consist of a CuCr base material with a mass content of chromium of between 30% and 60%, preferably 50%.

12. A contact arrangement according to claim 6 or claim 7, characterised in that the additive reducing the electric conductivity of the base material by diffusion is one of the following elements: iron (Fe), nickel (Ni), cobalt (Co), aluminium (Al), titanium (Ti), zirconium (Zr), antimony (Sb), tin (Sn), silicon (Si) or a combination of these elements.

13. A contact arrangement according to claim 9, characterised in that the metallic materials for filling-out the radial areas (45) in the contact body (40), produced by powder metallurgy, are selected from iron (Fe), cobalt (Co), nickel (Ni), silicon (Si), titanium (Ti), zirconium (Zr) or combinations or alloys of these elements.

14. A contact arrangement according to claim 9, characterised in that the insulating materials for filling-out the radial areas (45) in the contact body (40), produced by powder metallurgy, are ceramic materials such as Si0₂, Zr0₂, A1₂0₃ or carbides, such as SiC or TiC.

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