Method for forming contacts of vacuum switching device in two stages

Abstract

The invention relates to a method for forming contacts (1, 2) of a vacuum switchgear (100), comprising the following steps: S1) generating an arc between the surfaces of the contacts (1, 2) by means of a DC power supply for a first duration; S2) extinguishing the arc by reducing the current intensity of the DC power supply; and S3) subsequently applying an AC voltage to the contacts (1, 2) for a second duration. The invention also relates to a vacuum switchgear (100) configured to implement the method.

Description

[0001] Technical field of the invention

[0002] The invention relates to a method for forming a contact of a vacuum switching device, in particular a vacuum switching tube, and also relates to a vacuum switching device, which is configured to implement the method.

[0003] Fig.11 An example of a conventional vacuum switching tube is shown, which has a contact device, which consists of a fixed contact 1 and a contact 2 that can move in the axial direction, wherein these contacts are equipped with contact pins 3 or 4. The contacts 1, 2 are usually designed as contact disks with flat contact surfaces. This contact device is enclosed in a vacuum-tight housing, which consists of an intermediate piece 5, ceramic insulators 6 and 7 adjacent to the intermediate piece, two end flanges 8 and 9, and a bellows 10. In addition, shielding parts 11 and 12, which are fixed to the intermediate piece 5, and shielding parts 13 and 14, which are also components of the end flanges 8 and 9, are connected to the housing.

[0004] In order to meet the dielectric requirements of the vacuum switching tube, the contact discs 1, 2 are shaped or processed. For this purpose, in a typical manner, the surfaces of the contact discs 1, 2 are subjected to an alternating voltage only, mainly in different strokes. In this process, unevenness of the contact discs 1, 2 (e.g. micro-points and micro-particles) is eliminated and the surfaces of the contact discs 1, 2 are homogenized. An electric field is formed between the micro-points on the surfaces of the contact discs 1, 2, which, when the applied alternating voltage is sufficiently large, leads to arcs or flashovers and thus homogenizes the contact disc material mainly in the z direction, i.e. perpendicularly to the surfaces of the contact discs 1, 2. This process leads to an increase in the dielectric strength of the vacuum switching tube.

[0005] However, especially just before flashover, harmful X-ray radiation (X-Ray), especially X-ray bremsstrahlung, is emitted due to the changed acceleration direction of the electrons in the electric field.

[0006] Fig.12 The surface of the contact disks 1, 2 is shown after forming with a pure AC voltage according to the prior art. The changes in the surface are shown here only in partial areas.

[0007] Furthermore, the process state of the forming can deteriorate again due to the currentless and current-carrying switches (or switching on and off), and microparticles and micropoints can form again on the surface of the contact pads 1 , 2 . SUMMARY OF THE INVENTION

[0009] There is a need for a method for shaping contacts of vacuum switching devices, by which the surface of the contacts can be shaped consistently and more accurately and by which the X-ray radiation can be reduced. This need is met by the following technical solution.

[0010] According to a first aspect of the invention, a method for forming contacts of a vacuum switchgear comprises the following steps: S1) generating an arc between the surfaces of the contacts by means of a DC power source for a first duration, the DC power source preferably being adjusted to form a specific current intensity; S2) extinguishing the arc by reducing the current intensity of the DC power source or by adjusting the travel between the contacts to zero; and S3) subsequently applying an AC voltage to the contacts for a second duration. If the travel between the contacts is adjusted to zero in step S2), then in step S3), before applying the AC voltage, this travel is subsequently adjusted to a value greater than zero.

[0011] The forming is carried out in at least two stages, first with direct current and then with alternating voltage. Before the typical contact forming process which is carried out with alternating voltage, the contacts are preformed with direct current. In this novel preforming process, the vacuum switching device can be installed in a circuit, for example with a welding transformer, and a direct current with a low current intensity (for example several hundred amperes) can be applied. This current can flow for a defined duration of, for example, a few seconds.

[0012] It is of course possible to carry out additional shaping measures, such as AC voltage shaping, etc., before step S1 ), after step S3 ) or in between.

[0013] By applying a direct current, possibly in both polarities, an optimal effect can be achieved by uniform loading of the contacts. Due to heating of the contacts and the resulting potential release of metal vapor, the process can be repeated several times (including pauses). The relatively small stroke compared to the prior art also has a positive effect on the propagation of metal vapor outside the contact gap.

[0014] Since the preforming steps S1) and S2) are provided before the typical step S3) of contact forming by AC voltage, a large part of the unevenness of the contact surface is eliminated, the microparticles are incorporated and the entire material structure can be advantageously changed.

[0015] In principle, step S1 ) can achieve dielectric stabilization against mechanical influences, such as, for example, currentless switching.

[0016] In addition, the advantages of the subsequent typical final forming of the contacts by means of an alternating voltage can be achieved. First, higher voltage strength limit values ​​can be achieved, second, fewer flashovers occur until the final voltage strength value is reached (i.e., a reduction in process time is achieved), and third, radiation loads are reduced by the pre-treated contact surface.

[0017] Furthermore, the shaping according to the invention is carried out in a shorter stroke than conventional shaping and thus results in less evaporation of the ceramic in the back space or in the vacuum switching device. Less evaporation has a positive effect on the dielectric properties of the vacuum switching device.

[0018] The direct current forming process can be carried out with intuitively controllable effort and primarily with minimal use of safety devices. The direct current forming process can be integrated into a device for forming alternating voltage contacts without great effort.

[0019] In one embodiment, a direct current with a current strength in the range between 10 and 800 A, preferably between 80 and 200 A, is selected.

[0020] In one embodiment, before performing step S3), steps S1) and S2) are repeated 1 to 60 times, preferably 1 to 30 times, and more preferably 1 to 12 times. In this case, the polarity or the direction of current flow may be reversed.

[0021] In one embodiment, an AC voltage is applied in a frequency band between 1 Hz and 1 kHz, with a current strength in a range between 10 and 800 A, preferably between 80 and 200 A.

[0022] In one embodiment, the duration of the first and / or second current flow is in the range of 1 to 100 s, preferably 10 to 50 s.

[0023] In one embodiment, step S3) is sequentially repeated 3 to 15 times, preferably 5 to 12 times.

[0024] The previously mentioned parameters yielded good results, which are described in further detail in the figure description.

[0025] In one embodiment, before step S1), the contacts are moved towards each other in step S10) so that they touch each other. After step S10), step S1) is performed, wherein the contacts are spaced apart from each other by a stroke during this period, so that an arc is drawn between the contacts. Then steps S2) and S3) are performed. Before step S3), steps S10), S1) and S2) are preferably repeated at least once in sequence. The polarity can be reversed.

[0026] This embodiment can be referred to as "contact ignition". Here, the contacts are pulled to a small stroke of, for example, a few millimeters under current load, thereby pulling an arc between the contacts. The arc does not usually propagate over the entire surface; instead, there are a plurality of small sub-arcs, which, due to their own movement (and other complex processes), completely or partially sweep over the entire surface. At least one arc is formed at the two last contact points on the contact surface. From there, the arc base moves over the entire area of ​​the contact surface. After a first duration, the current is turned off and the contact stroke is moved back to the zero position (in which the contacts are in contact with each other). The process can be repeated at any frequency and in both polarities. The product of the first duration multiplied by the number of cycles is called the action time and can be in the range of 1 second to 100 seconds. It should be mentioned in this embodiment that for different contact geometries, it may be advantageous to selectively set the ignition point on the surface of the contact.

[0027] By implementing additional control, for example by means of an electromagnetic field, the base point propagation can be controlled in a targeted manner. This allows for optimal use of the contact surface during the direct current forming process, i.e., the area utilization can be increased. The current-dependent process time can also be shortened by using the control.

[0028] In other embodiments, before step S1), the contacts are spaced apart by one stroke in step S11). After step S11), step S1) is performed, wherein during this period the contacts are further spaced apart by one stroke, wherein an arc is drawn between the contacts. Then steps S2) and S3) are performed. Preferably, before step S3), steps S11, S1) and S2) are repeated in sequence at least once. The polarity can be reversed.

[0029] This embodiment can be referred to as "contactless ignition". Compared to the previous embodiment of "contact ignition", in contactless ignition, a defined small contact stroke of a few millimeters is first set or adjusted. Then, for example, an arc is ignited by a high-frequency transformer. The arc or arcs are formed at points with a minimum distance from each other and propagate from there partially or over the entire area of ​​the contact surface, as in contact ignition. It should be mentioned in this embodiment that for different contact geometries, it may be advantageous to selectively set the ignition point on the contact surface.

[0030] In another embodiment, the contacts are installed in a vacuum switching device during the forming process. This has economic advantages, since the vacuum in the vacuum switching device is simultaneously used as a process medium. The direct current forming process is carried out with intuitively controllable costs and mainly with a reduced use of safety devices. The direct current forming process can be integrated into the device for alternating voltage forming without much effort.

[0031] The previously described embodiments are applicable to all contact materials and their manufacturing techniques, all voltage levels (high, medium and low voltage) and all contact geometries.

[0032] According to a second aspect of the invention, a vacuum switching device is configured to carry out the method described above.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The above-defined aspects and further aspects of the invention are derived from the embodiments described below. The invention is explained in more detail below with respect to the feasibility of the invention based on embodiments, but the invention is not limited thereto.

[0035] Figure 1 A flow chart showing a method for molding contacts of a vacuum switchgear according to a first embodiment;

[0036] Figure 2 A flow chart showing a method for molding contacts of a vacuum switchgear according to a second embodiment;

[0037] Figure 3 A flow chart showing a method for molding contacts of a vacuum switchgear according to a third embodiment;

[0038] Figure 4 shows the contact surface before forming;

[0039] Figure 5 Shown is the horizontal Figure 4 Micrograph of a section of the contact surface;

[0040] Figure 6 shows a micrograph of a section transverse to the surface of a contact formed only by direct current;

[0041] Figure 7 shows the surface of a contact formed by a direct current without subsequent forming of the contact by an alternating voltage;

[0042] Figure 8 Shows Figure 7 The surface of the contact formed by the direct current and subsequently formed by the alternating voltage;

[0043] Fig. 9 A top view of a contact showing a partial load of several thousand A in a few milliseconds;

[0044] Fig.10 Shows Fig. 9 A cross-section photograph of a contact that experiences a partial load of several thousand A in a few milliseconds;

[0045] Fig.11 An example of a conventional vacuum switching device in the form of a vacuum switching tube is shown;

[0046] Fig.12 The contact surface is shown after purely alternating voltage forming according to the prior art.

[0047] Description of the drawings

[0048] It should be noted that in different figures, similar or identical elements are provided with the same reference numerals.

[0049] Figure 1 A flow chart of a method for molding contacts 1, 2 of a vacuum switching device 100 according to a first embodiment is shown. The contacts 1, 2 are preferably designed as contact disks with flat contact surfaces.

[0050] In step S1), an arc is generated between the surfaces of the contacts by a DC power supply, which is preferably adjusted to form a specific current intensity, and the DC current flows through the contacts 1 and 2 for a first duration. The first duration can be 1 second to 100 seconds. In principle, dielectric stabilization can be achieved by step S1) to prevent mechanical influences, such as current-free switching. In step S2), the arc is extinguished after the first duration has expired by reducing or completely cutting off the current intensity of the DC power supply. Alternatively, the stroke between the contacts 1 and 2 can be adjusted to zero (zero stroke). In step S3), an AC voltage is then applied to the contacts 1 and 2 for a second duration. If the stroke between the contacts is adjusted to zero in step S2), then in step S3), the stroke is then adjusted again to a value greater than zero and then an AC voltage is applied.

[0051] In step S1), a direct current with a current intensity between 10 and 800 A, preferably between 80 and 200 A, may be applied. Before step S3), steps S1) and S2) may be repeated 1 to 60 times, preferably 1 to 30 times, more preferably 1 to 12 times, such as by Figure 1 The polarity can be reversed here.

[0052] In step S3), an AC voltage may be applied in a frequency band between 1 Hz and 1 kHz, the AC voltage having a current intensity between 10 and 800 A, preferably between 80 and 200 A. The second duration may be in the range of 1 to 100 seconds, preferably between 10 and 50 seconds. Step S3) may be repeated 3 to 15 times, preferably 5 to 12 times, in sequence, such as by Figure 1 As indicated by the dotted arrow in the lower area of ​​.

[0053] Figure 2A flow chart of a method for molding contacts 1, 2 of a vacuum switchgear 100 according to a second embodiment is shown. Steps S1), S2) and S3) are similar to those in the first embodiment.

[0054] In step S10) before step S1), the contacts 1 and 2 are moved towards each other so that they are in contact with each other. After step S10), step S1) is performed, during which the contacts 1 and 2 are separated from each other by a stroke, so that one or more arcs are drawn between the contacts 1 and 2. Then steps S2) and S3 are performed. The stroke essentially defines the distance between the contacts 1 and 2. Such a stroke is defined as a zero stroke, in which the contacts 1 and 2 are in mechanical contact with each other.

[0055] Before implementing step S3), steps S10), S1) and S2) may be repeated at least once in sequence, such as by Figure 2 As indicated by the dashed arrow in the upper region of . The polarity can be reversed here. It is also possible to repeat step S3) as in the first embodiment, such as by Figure 2 As indicated by the dotted arrow in the lower area of ​​.

[0056] Figure 3 A flow chart of a method for molding contacts 1, 2 of a vacuum switchgear 100 according to a third embodiment is shown. Steps S1), S2) and S3) are similar to those in the first embodiment.

[0057] In step S11), the contacts 1 and 2 are separated by a stroke greater than zero stroke before step S1). After step S11), step S1) is performed, during which the contacts 1 and 2 are further separated by a stroke, wherein an arc is drawn between the contacts 1 and 2. The stroke formed in step S1) is adjusted to be greater than the stroke in step S11). Steps S2) and S3) are then performed.

[0058] Before step S3), steps S11), S1) and S2) may be repeated at least once in sequence, such as by Figure 3 As indicated by the dashed arrow in the upper region of . The polarity can be reversed here. It is also possible to repeat step S3) as in the first embodiment, such as by Figure 3 As indicated by the dotted arrow in the lower area of ​​.

[0059] The vacuum switch device 100 can be configured to implement the method of the present invention. Therefore, the contacts 1, 2 are installed in the vacuum switch device 100 during molding. The vacuum switch device 100 is preferably a vacuum switch tube. Here, the vacuum switch device 100 can have Fig.11 The vacuum switching device has the characteristics of a vacuum switching tube, but the vacuum switching device is not limited to the vacuum switching tube.

[0060] In a third embodiment, it may be advantageous to selectively arrange spatial ignition points on the surface of the contacts 1 , 2 for different contact geometries.

[0061] Figure 4 The surface of the contacts 1, 2 before forming is shown. This surface is used as a reference in comparison with the formed surfaces in the following figures.

[0062] Figure 5 Shown horizontally Figure 4 FIG. 1 is a cross-sectional micrograph of the surface of the contacts 1 and 2. The contacts 1 and 2 are made of CuCr50. Reference numeral 20 denotes a copper matrix and reference numeral 21 denotes chromium embedded in the copper matrix 20. The surface is not over-melted and the grain structure of CuCr50 is cut relatively smoothly.

[0063] Figure 6 Shown is the horizontal Figure 5 Slice micrograph of the surface of the contacts 1 and 2 formed only by direct current. In area A, a CuCr50 contact material is shown, which has a copper matrix 20 and embedded chromium 21. In area B, a remelted copper-chromium layer 22 of the contact material with a thickness of about 6 μm is shown. In area C, the embedded material for the sliced ​​sample is shown. Area B shows a significant leveling or homogenization of the surface of the contacts 1 and 2. Overmelted areas of the contact material are also achieved at the edges and gaps of the contacts 1 and 2 (i.e. in the complete field-related area). The copper-chromium layer 22 that has been remelted by current forming is characterized by a significantly finer microstructural distribution than the copper matrix 20 and the chromium 21 embedded therein.

[0064] Figure 7 The surface of the contact 1, 2 formed by direct current is shown without subsequent contact forming by alternating voltage. The surface has a current forming area 23 and a non-current forming area 24. It is clearly shown that the current forming area 23 constitutes the majority of the surface of the contact 1, 2 formed by direct current. It has been found that the surface of the contact 1, 2 that (finally) acts as an anode in the direct current forming has a different visual appearance than the contact 1, 2 that (finally) acts as a cathode in the direct current forming. The anode appears visually more matte and has a visual appearance similar to that of a vapor-deposited surface. In contrast, the cathode has an optical appearance with a visible typical topological molten structure, which is caused or generated by the individual arc base points acting on the surface.

[0065] Figure 8 Shows Figure 7 The surface of the contact that is shaped by direct current and then shaped by alternating voltage. Figure 7The comparison shows obvious changes on the surface of the contacts 1 and 2, which are produced by the alternating voltage forming effect in step S3). The surfaces of the contacts 1 and 2 are better flattened or homogenized. Reference numeral 25 represents a typical topological structure. The typical topological structure 25 is characterized by a substantially concentric internal structure and an external structure. Both the internal structure and the external structure have a substantially round or circular outer circumference. The topological structures 25 can overlap partially or completely.

[0066] Fig. 9 and Fig.10 A top view and a slice image are shown of the contacts 1 , 2 which are subjected to a partial load of several thousand A within a few milliseconds. A molten layer of about several tens of micrometers thick forms on the surface there.

[0067] The inventors have also found through measurements that the dose rate of X-ray radiation can be reduced by about 5 times or more by the current shaping method according to the present invention compared to conventional pure AC voltage shaping. This fact is particularly important for high-voltage vacuum switching tubes, because X-ray radiation usually increases sharply in the high-voltage range.

[0068] It should be noted that the term "having" does not exclude other elements or steps. Elements described in conjunction with different embodiments may also be combined. It should also be noted that the reference numerals should not be interpreted as reflecting the scope of the invention claimed for protection.

[0069] List of Reference Numerals

[0070] 1 contact

[0071] 2 contacts

[0072] 3 contact pins

[0073] 4 contact pins

[0074] 5 Middleware

[0075] 6 Ceramic insulator

[0076] 7 Ceramic Insulator

[0077] 8 End flange

[0078] 9 End flange

[0079] 10 Bellows

[0080] 11 Shielding

[0081] 12 Shielding

[0082] 13 Shielding

[0083] 14 Shielding

[0084] 20 Copper substrate

[0085] 21 Embedded Chrome

[0086] 22 Remelted copper-chromium layer

[0087] 23 Current forming area

[0088] 24 Non-current forming area

[0089] 25 Typical topology after current shaping

[0090] 100 Vacuum switchgear

Claims

1. A method for forming contacts (1, 2) of a vacuum switch device (100), comprising the following steps: S1) generating an arc between the surfaces of the contacts (1, 2) for a first duration by means of a DC power supply; S2) extinguishing the arc by reducing the current intensity of the DC power supply or by adjusting the stroke between the contacts (1, 2) to zero; and S3) Subsequently, an alternating voltage is applied to the contacts (1, 2) for a second duration.

2. The method according to claim 1, wherein: A direct current with a current intensity ranging between 10 and 800 A is applied.

3. The method according to claim 1, wherein: Before step S3) is performed, steps S1) and S2) are repeated 1 to 60 times, wherein the repetition is achieved by reversing the polarity.

4. The method according to claim 1, wherein: An alternating voltage with a current strength in the range between 10 and 800 A is applied in a frequency band between 1 Hz and 1 kHz.

5. The method according to claim 1, wherein: The first and / or second duration is within the range of 1 to 100 seconds.

6. The method according to claim 1, wherein: The step S3) is repeated 3 to 15 times in sequence.

7. The method according to claim 1, wherein: Before step S1), the contacts (1, 2) are moved toward each other in step S10) so that the contacts are in contact with each other; After step S10), step S1) is performed, during which the contacts (1, 2) are spaced apart from each other by a stroke, thereby drawing an arc between the contacts (1, 2); and Next, steps S2) and S3) are carried out.

8. The method according to claim 7, wherein: Before implementing step S3), steps S10), S1) and S2) are sequentially repeated at least once.

9. The method according to claim 7, wherein: Before performing step S3), steps S10), S1) and S2) are sequentially repeated at least once by reversing the polarity.

10. The method according to claim 1, wherein: Before step S1), in step S11), the contacts (1, 2) are separated by a stroke; After step S11), step S1) is performed, during which the contacts (1, 2) are further spaced apart from each other by a stroke, wherein an arc is drawn between the contacts (1, 2); and Next, steps S2) and S3) are carried out.

11. The method according to claim 10, wherein: Before executing step S3), steps S11, S1) and S2) are sequentially repeated at least once.

12. The method according to claim 10, wherein: Before executing step S3), steps S11, S1) and S2) are sequentially repeated at least once by reversing the polarity.

13. The method according to claim 1, wherein: The contacts (1, 2) are installed in the vacuum switchgear (100) during molding.

14. The method according to claim 1, wherein: Step S1 ) achieves dielectric stabilization against mechanical influences.

15. The method according to claim 1, wherein: Step S1) realizes a current-free switch.

16. A vacuum switching device (100) configured to carry out the method according to one of the preceding claims 1 to 15.

Images