EP0172411B1 - Vacuum contactor with contact pieces of cucr and process for the production of such contact pieces - Google Patents

Description

The invention relates to a vacuum contactor for the low-voltage and high-voltage range with contact pieces, the buttons of which face each other. In addition, the invention also relates to the method for producing a contact piece for such a vacuum contactor.

Materials made of copper and chrome are known from the prior art. If they are used as contact materials, such as in US-A 4048117 and GB-A 2123852, they are used throughout for vacuum circuit breakers. In such circuit breakers, for example medium-voltage circuit breakers, it is important to switch equally high voltages in the kV range and high currents in the kA range. Since the switching frequency for circuit breakers is comparatively low, the service life of the contact pieces used is designed for switching numbers of a few 10 ⁴ .

GB-A 2066298 also discloses a method for producing contact pieces for vacuum switching devices in which, among other things, a CuCr material is made by powder metallurgy by the fact that two melts are atomized from the liquid state due to the miscibility of the mixture in this system and the powder mixture is further processed by sintering into the contact piece.

In addition to the circuit breakers, the vacuum contactors also belong to the vacuum switchgear class. These are characterized by their long service life, with switching numbers> 10 ⁶ at nominal current usually being sought.

Due to the long life required, particularly high demands are made on the material for contact pieces of vacuum contactors, especially with regard to the erosion behavior. On the one hand, breaking currents of up to about 5 kA must be mastered safely during the entire service life; on the other hand, favorable welding behavior, i.e. a low welding force is required, so that the opening of the contact pieces is guaranteed even after switching on high operating currents. The maximum frequency of the stripping current values should be significantly below 5 A.

It is known to use a composite material based on tungsten and copper as the contact material for vacuum contactors. In it, the tungsten (W) is used as a high-melting and therefore particularly fire-resistant component, while the copper (Cu) as an electrically and thermally highly conductive material prevents the button from overheating. The effect of cooling the scaffolding due to the lower-boiling material against overheating can also be used. Such WCu materials are preferably produced by sintering a framework from the high-melting component and then impregnating this framework with the low-melting component. To reduce the welding force and the tear-off current, further metallic components, for example tellurium or antimony, are usually added.

Tungsten and copper based materials are successfully used for vacuum contactors in the high voltage range with switching currents up to approx. 3 kA. Due to increased technical requirements with regard to switching currents and switching numbers, especially in the area of low voltage technology up to 1 kV, improvements in the contact material are necessary that WCu materials only meet to a limited extent. The reason for this lies in the special burn-up mechanism of this system: In the event of an arc load, copper and tungsten are melted and vaporized at the same time in the cathode base points due to the extremely high temperatures, but copper is preferably evaporated out of the framework in the edge areas of the base points with their lower temperature load. After numerous nominal current circuits have expired or after a series of high current circuits, local copper depletion in the structure and thus the formation of tungsten-rich spots in the button can occur. A typical structure of a tungsten-copper contact surface subject to frequent switching therefore contains torn and scaly areas.

For dielectric and thermal reasons, the above surface structures naturally limit the switching properties and thus the service life of the contact material. Up to now _, the contact material has been optimized for the specially required properties by choosing suitable concentration ratios and specific powder particle sizes. However, there is a need in particular in the area of low voltage to look for other contact materials with improved erosion behavior.

The object of the invention is therefore to provide a vacuum contactor which has the same good switching properties as contactors with contact pieces made of tungsten copper (WCu) in the initial state, but which also has a longer life span with a constant resistance due to a more favorable erosion behavior of the contact pieces has high switch-on and switch-off capacity.

The object is achieved in that the contact pieces consist of a melting material made of copper and chromium, which consists of a copper matrix with evenly distributed fine-particle dendritic chromium deposits and which is composed of 75 to 40% by mass of copper and 25 to 60% by mass of chromium.

To produce a contact piece for such a vacuum contactor, a copper-chromium melting material is produced by arc melting, in which finely divided dendritic chromium precipitates are evenly distributed in a copper matrix and that for contact piece is further processed. In this case, the melting material is preferably formed, so that a directional structure is created.

It was found that copper-chromium melting alloys produced with excellent results according to the process according to German patent application P 3303170.3, which corresponds to EP-A-0115292 as the prior art to be considered according to Art. 54 (3) and (4) EPC Are suitable as a contact material in the switching tubes of vacuum contactors in the low-voltage and high-voltage range.

The invention was preceded by an analysis of the metallurgical and in particular the thermodynamic conditions: the material sought should be a composite material in order to take advantage of the favorable properties of this contact material class. It was recognized that the described unfavorable combustion structure of tungsten copper is primarily due to the strongly differing vapor pressures of the two metals used to date. The invention was then based on the finding that a metal combination had to be sought, the components of which, despite different other properties, have similar vapor pressures where possible. Such a combination is especially given by a material based on copper and chrome.

As already mentioned at the beginning, a material based on copper and chromium is known per se as a contact material. So far, however, this has advantageously been used for contact pieces in the case of vacuum medium-voltage circuit breakers which are highly loaded in terms of current and voltage. For this area of application, the cheap, flat burn-up pattern and the resulting good dielectric strength are used. Since this does not require a high number of switching operations, the burnout rate of copper-chromium, which is considerable when switching large short-circuit currents, can be easily tolerated.

In particular, copper-chrome materials have so far been considered unsuitable for vacuum contactors by experts due to the noticeable burn-up rate observed in the vacuum circuit breaker. For example, such a differentiation of the field of application of the known contact materials from the monograph by A. Keil et alii “Electrical contacts and their materials”, (Springer Verlag 1984), chap. 4.3 “Switchgear”, especially Table 4.7, p. 359, and Th. E. Brown jr. "Vacuum Interruption", (M. Dekker Inc. 1984), p. 600.

The invention has now surprisingly recognized that a melting material based on copper-chromium can also be used for vacuum contactors. This overcomes the prejudice prevailing among experts!

Contrary to expectations, the erosion resistance of this material could be proven especially under contactor conditions, with which such a material easily meets the required number of operations of> 10 ⁶ at nominal current while maintaining the switch-on and switch-off capacity for high operating currents. For example, measurements with a nominal current of 600 A and approximately 10 ⁶ switching operations resulted in a height loss of <1 mm per contact. When the rated current was doubled, a burnout of <1 mm per contact piece was also found with a switching number of 3x10 ⁵ .

An explanation of the above unexpectedly favorable combustion behavior should be sought in the structure of the material with its finely divided dendritic chrome deposits, whereby the arc formation that is different from that of the circuit breakers in vacuum contactors must also be taken into account. The similar evaporation behavior of copper and chromium forms an essential basis for maintaining the switching capacity due to the largely identical vapor pressure curves of both components.

Tests have confirmed that a CuCr melting material with a composition in mass proportions of about 25 to 60% chromium is suitable for vacuum contactors. It was found that such a melting material already has sufficient properties after the melting metallurgical production by arc melting. So that a line-shaped alignment of the chrome dendrites runs perpendicular to the button of the contact pieces, the melt material is preferably reshaped, so that there is a directional structure perpendicular to the button. Forming is preferably carried out by full forward extrusion with a degree of deformation> 60%.

It has been shown that the requirements for the material, such as, in particular, low welding force and low tearing currents, can generally be met by the base material copper-chromium. In special cases, the required properties can also be improved by adding tellurium, antimony, bismuth and / or tin. Various methods are possible for introducing such additives into the previously manufactured contact pieces, for example melting, diffusing or storing in depressions.

The vacuum contactor according to the invention can also have an unpaired contact arrangement with a contact piece made of pure CuCr melting material and the opposite contact piece made of CuCr melting material with additives, without losing the advantageous properties in switching operation.

Further advantages and details of the invention result from the following description of exemplary embodiments, in which reference is made in part to the figures of the drawing.

1 to 4 show different possibilities for introducing specific additives into contact pieces.

example 1

From a powder mixture of the composition in mass fractions of 60% copper (Cu) and 40% chromium (Cr) is to be used to produce a melting block using the arc melting process: for example, the blank should have dimensions of 80 mm in diameter and 400 mm in length. For this purpose, the powder mixture of the appropriate composition is pressed isostatically at a pressure of 3000 bar and then sintered in a vacuum at temperatures just below or in the case of the formation of a liquid phase about 50 ° C. above the copper melting point. The sintered blank is used as a melting electrode in an arc melting furnace and remelted under helium as a protective gas. In order to achieve the required high energy density, the arc current must be at least 1000 A for the given dimensions. The melted electrode material solidifies in a water-cooled copper mold.

Instead of the composition in mass fractions of 60% copper and 40% chromium, other compositions in the range between 25 and 60% chromium can also be selected.

A semi-finished product for contact pieces is then produced from the melting block thus produced by arc melting by full forward extrusion. Forming degrees of more than 60% are used, e.g. of 78%. In this case, after turning off the melting block, a bar diameter of 35 mm results from a blank diameter of 75 mm as a semi-finished product. This semifinished product has a directional structure, in which the chrome dendrites present in the material are now present in a row-like orientation with a preferred direction. If, after a possible turning off of the surfaces with impurities, disks of, for example, 5 mm thickness are cut off from this rod as contact pieces, there is inevitably a button perpendicular to the present directional structure.

Example 2

After metallurgical production as in Example 1, the melting block with a diameter of 80 mm is cut into 5 mm slices. Three contact pieces with a diameter of 35 mm can then be punched out of these disks.

The contact pieces manufactured according to example 1 or 2 can be installed in the switching tubes of vacuum contactors. However, previously, as described with reference to Examples 3 to 5 in connection with the figures, special additional components can also be introduced into the contact pieces.

Example 3

Contact pieces of the composition are to be produced in proportions by mass of 58.5% copper (Cu), 38.5% chromium (Cr) and 3% tellurium (Te): For this purpose, contact pieces made of copper are first made according to the example by arc melting and subsequent shaping and chrome, for which a composition in mass fractions of 60% copper and 40% chromium is selected. Tellurium should be alloyed into the contact disks after forming and cutting.

The latter is illustrated in detail with reference to FIG. 5: A CuCr disk 1 is introduced into a correspondingly designed graphite crucible 2 with a graphite paper 3 interposed. Tellurium powder 4 is applied in excess to the surface of the CuCr disk 1. The crucible 2 is then heated to 1150 ° C. and held under protective gas for about 1 hour. The result is a contact piece 5 of the required composition, the tellurium offered being alloyed in quantitatively.

The tellurium content can be from 0.1 to 10%, depending on the requirements for welding force and tear-off current.

In the same way as described for tellurium (Te), antimony (Sb), bismuth (Bi) or tin (Sn) or combinations of these metals can also be introduced into the contact pieces.

Example 4

Contact pieces of the composition in mass fractions of 48.5% copper (Cu), 48.5% chromium (Cr) and 3% antimony (Sb) are to be produced. First, contact pieces of the composition in mass fractions of 50% copper and 50% chromium are produced again by arc melting and subsequent forming. After the disks have been removed, the antimony is introduced by diffusion: For this purpose, a recess is worked into the contact piece, into which the antimony is inserted.

The latter is illustrated in detail with reference to FIG. 2: A copper-chromium contact piece 20 is formed with a recess 21 approximately as a cup. It is on an A'203 plate 22. Antimony powder 23 is brought into the recess of the contact piece 20. After heating to about 1000 ° C. under protective gas and holding for about 2 hours, a diffusion zone 24 with the above-mentioned concentration forms in the copper-chromium disk. The depth formation and antimony concentration of the diffusion zone 24 can be controlled via the temperature holding time and the antimony supply.

An alternative possibility is illustrated with the aid of FIG. 3: Here there is a copper-chrome disk 30 in an A1 ₂ 0 ₃ crucible 31, which is covered with a plate 32 made of carbon. Antimony powder 33 is present in excess between the base plate of the A ' ₂ 0 ₃ crucible 31 and the copper-chromium disk 30. After heating to about 1000 ° C., a diffusion zone 34 is formed starting from below after about 2 hours. The depth of the diffusion zone is specified in accordance with the anticipated burnup.

In the same way, instead of antimony (Sb), tin (Sn) or combinations of antimony, tellurium and / or tin can also be introduced into the contact pieces.

Example 5

Contact pieces with locally introduced additives are to be produced: for this purpose, disk-shaped contact pieces of the composition are first produced again in mass fractions of, for example, 50% copper and 50% chromium by the process described in Example 1 or 2. At a suitable point, depressions are worked into the surface of these contact disks, for example as a central hole, in the form of several holes or as an annular groove. Metals or alloys with a melting point below the melting point of the copper-chromium eutectic are then introduced into the depressions as granules or a suitable form. The metals tellurium, antimony or the alloys antimontelluride, bismuth telluride and tin telluride have proven to be advantageous. The additional components are melted in the recesses.

The latter is illustrated with reference to FIG. 4: A CuCr disk 40 with a central bore 41 is located in a graphite crucible 42 with a lid 43. The additional components are introduced into the bore 41 as a seal 45. After melting, it forms a thin layer 46 on the top surface of the contact piece 40, which serves as a button.

For use in vacuum contactors, there is now in particular the possibility of building unpaired arrangements. It has been shown that a contact arrangement for vertical installation in a switching tube can advantageously be designed in such a way that one contact piece made of copper and chromium consists of one of the compositions specified according to Example 1 or 2, while the associated opposite contact piece consists of copper and chromium with specific ones Additions exist. The latter contact piece can be designed according to Examples 3 to 5.

In the switching tube, in particular the contact piece above can consist of pure melting material with or without deformation.

Claims (14)

1. Vacuum contactor for the low-voltage and high-voltage field with contact pieces, the switching areas of which lie opposite each other, characterised in that the contact pieces are made of a fused material of copper and chromium, which is consisting in a copper matrix with an even distribution of small dendritic chromium deposits in the copper matrix, and which is composed of 75 to 40% mass portions of copper and 25 to 60% mass portions of chromium.

2. Vacuum contactor according to claim 1, characterised in that the fused material has a directional structure whereby the switching surface of the contact pieces is arranged perpendicular to the directional structure.

3. Vacuum contactor according to claim 1 or 2, characterised in that in the contact piece additions of at least one of the metals tellurium (Te), antimony (Sb), bismuth (Bi) and/or tin (Sn) as well as alloys thereof are present for lowering the welding strength.

4. Vacuum contactor according to claim 3, characterised in that the mass portion of the additions lies between 0.1 and 10%.

5. Vacuum contactor according to claim 3 and 4, characterised in that the additions are present starting from the switching surface of the contact piece only to a determined penetration depth of the contact piece.

6. Vacuum contactor according to claim 3 and 4, characterised in that the additions are present only locally in predetermined locations on the switching surface of the contact piece.

7. Vacuum contactor according to one of the preceding claims, characterised in that one contact piece consists of pure CuCr-fused material and the contact piece lying opposite consists of CuCr-fused material with additions.

8. Method for manufacturing a contact piece for a vacuum contactor according to claim 1 or one of claims 3 to 7, characterised in that are melting a fused material is produced which consists of a copper matrix with an even distribution of dendritic chromium deposits in fine particles and in that the fused material is further processed to a contact piece.

9. Method according to claim 8 for manufacturing a contact piece for a vacuum contactor according to claim 2, characterised in that the fused material undergoes after are melting a forming process whereby a directional structure is created with which the dendritic chromium deposits are stretched into a preferred direction.

10. Method according to claim 9, characterised in that the fused material is formed by forward extrusion.

11. Method according to claim 10, characterised in that the percentage reductions is > 60%.

12. Method according to claim 8 for manufacturing a contact piece for a vacuum contactor according to one of claims 3 to 7, characterised in that the contact piece is produced after working out from the fused material by alloying the additions in the liquid copper phase of the contact piece.

13. Method according to claim 8 for manufacturing a contact piece for a vacuum switch according to one of claims 3 to 7, characterised in that the contact piece after working out from the fused material is produced by diffusion of the additions in the solid copper phase of the contact piece.

14. Method according to claim 8 for manufacturing a contact piece for a vacuum contactor according to one of claims 3 to 7, characterised in that recesses are worked into the switch surface of the contact piece into which the additions are brought in and melted in them.

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