DE102020204312B3 - Method for the two-stage formation of contacts of a vacuum switching device and vacuum switching device, configured to carry out the method - Google Patents

Abstract

The present invention relates to a method for forming contacts (1, 2) of a vacuum switching device (100), comprising the following steps: S1) generating an arc between the surfaces of the contacts (1, 2) by means of a direct current source for a first period of time ; S2) extinguishing the arc by reducing the amperage of the direct current source; and S3) subsequent application of an alternating voltage to the contacts (1, 2) for a second period of time. The present invention also relates to a vacuum switching device (100) which is configured to carry out the method.

Description

Technical field of the present invention

The present invention relates to a method for forming contacts of a vacuum switching device, in particular a vacuum interrupter. The present invention also relates to a vacuum switching device which is configured to carry out the method.

From the DE 197 14 655 A1 a method is known for conditioning the contacts of a vacuum interrupter by means of an application of a direct current, the stroke between the switching contacts being variable.

the DE 885 266 B discloses a method for forming electronic contacts using an alternating current or a direct current which changes polarity.

11 shows an example of a conventional vacuum interrupter having a contact arrangement consisting of a fixed contact 1 and an axially movable contact 2 consists, these contacts with contact pins 3 respectively. 4th are provided. The contacts 1 , 2 are usually designed as contact disks each with a flat contact surface. This contact arrangement is enclosed in a vacuum-tight housing which consists of a central part 5 , for example made of a metallic material, adjoining ceramic insulators 6th and 7th , two end flanges 8th and 9 and a bellows 10 consists. Shields are also connected to the housing 11 and 12th attached to the middle part 5 are attached, as well as umbrellas 13th and 14th that are also parts of end flanges 8th and 9 are.

To achieve the dielectric requirements of vacuum interrupters, the contact disks 1 , 2 formed or conditioned. The surfaces of the contact disks, among other things, are traditionally used for this purpose 1 , 2 only applied with an alternating voltage for different strokes. During this process, bumps will appear on the contact washers 1 , 2 (such as microtips or microparticles) and the surfaces of the contact discs 1 , 2 homogenized. Between the microtips on the surfaces of the contact discs 1 , 2 An electric field builds up which, if the applied alternating voltage is large enough, leads to an arc or flashover and thus the contact disk material primarily in the z-direction, ie orthogonal to the surfaces of the contact disks 1 , 2 , homogenized. This process leads to an increase in the dielectric strength of the vacuum interrupter.

In particular shortly before the rollover, however, the changing direction of acceleration of the electrons in the electric field results in the emission of harmful X-rays (X-ray), in particular X-ray brake radiation.

12th shows a surface of contact disks 1 , 2 after pure alternating voltage formation according to the state of the art. There is only a change in the surface in some areas.

In addition, through currentless and current-carrying switching, the formed conditioning state can be worsened again, and microparticles and microtips can again appear on the surfaces of the contact discs 1 , 2 form.

Summary of the invention

There is a need for a method for forming contacts of a vacuum switching device by means of which the surfaces of the contacts can be formed sustainably and more precisely and by means of which the x-ray radiation can be reduced. This need can be met by the subject matter of independent claim 1. The present invention is further developed in accordance with the dependent claims.

According to a first aspect of the invention, a method for forming contacts of a vacuum switching device has the following steps: S1) generating an arc between the surfaces of the contacts by means of a direct current source, which preferably sets a certain current intensity, for a first period of time; S2) extinguishing the arc by reducing the current intensity of the direct current source or by setting a stroke between the contacts to zero; and S3) subsequent application of an alternating voltage to the contacts for a second period of time. If the stroke between the contacts was set to zero in step S2), this stroke is then set again to a value greater than zero in step S3) before the alternating voltage is applied.

The formation takes place in at least two stages, ie first with a direct current and then with an alternating voltage. Before the classic formation process of the contacts with the alternating voltage, the contacts are preformed with the direct current. In this novel process of preforming, the vacuum switching device can be installed in a circuit with, for example, a welding transformer, and the direct current can be applied with a current that tends to be rather low (for example a few 100 amperes). This current can be defined for a Duration of for example several seconds flow.

It is of course possible to carry out additional formation measures before step S1), after step S3) or in between, such as alternating voltage formation or the like.

By applying the direct current, if necessary in both polarities, an optimal effect can be achieved through the even loading of the contacts. The process can be repeated a few times (including breaks) due to the problem of heating up the contacts and the resulting potential metal vapor release. Likewise, a relatively small stroke compared with the prior art can have a positive effect on the metal vapor spread outside the contact gap.

The steps S1) and S2) of preforming before the classic step S3) of contact forming with the alternating voltage remove a considerable part of the unevenness on the surfaces of the contacts, microparticles are bound and the entire material structure can advantageously be changed.

Step S1) can basically achieve dielectric stabilization against mechanical influences such as, for example, currentless switching.

In addition, advantages can be achieved for the subsequent, classic final contact formation with the alternating voltage. Firstly, higher limit values for the dielectric strength can be achieved, secondly, fewer flashovers occur until the final value of the dielectric strength is reached (i.e. a reduction in the process time is achieved), and thirdly, the radiation exposure through the pretreated surfaces of the contacts is reduced.

In comparison with the conventional formation, the formation according to the invention can also be carried out with smaller strokes, and it therefore leads to a low vaporization of the rear space or of the ceramics in the vacuum switching device. The low vapor deposition has positive effects on the dielectric behavior of the vacuum switching device.

The DC forming is carried out with manageable effort and little use of the safety equipment, among other things. The process of direct current forming can be integrated into a device for alternating voltage contact forming with little effort.

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

In one embodiment, steps S1) and S2) are repeated between 1 and 60 times, preferably between 1 and 30 times, more preferably between 1 and 12 times, before step S3) is carried out. It is possible to reverse the polarity or the direction of current flow.

In one embodiment, the alternating voltage is applied in a frequency band between 1 Hz and 1 kHz with a current intensity in a range between 10 and 800 A, preferably between 80 and 200 A.

In one embodiment, the first and / or the second current flow duration is in a range between 1 and 100 s, preferably between 10 and 50 s.

In one embodiment, step S3) is repeated between 3 and 15 times, preferably between 5 and 12 times, in succession.

The parameters mentioned above have led to good results, which are described in more detail in the description of the figures.

In one embodiment, the contacts are moved towards one another in a step S10) before step S1) such that they touch one another. After step S10), step S1) is carried out, during which the contacts are separated from one another by one stroke, so that an arc is drawn between the contacts. Steps S2) and S3) are then carried out. Steps S10), S1) and S2) are preferably repeated at least once in succession before step S3) is carried out. It is possible to reverse the polarity.

This exemplary embodiment can be referred to as “contact ignition”. The contacts are pulled to a small stroke of, for example, a few millimeters under current load, whereby the arc is drawn between the contacts. The arc usually does not spread over the entire surface; rather, there are several small partial arcs which, due to their own movement (and other complex processes), sweep over the entire or partially entire surface. At least one arc occurs at the last two points of contact between the surfaces of the contacts. The arc roots move from there over the entire area of the surfaces of the contacts. To When the first period of time has elapsed, the current is switched off and the contact stroke is moved back to the zero position (at which the contacts touch each other). The process can be repeated as often as required and in both polarities. The product of the first time period with the number of cycles is referred to as the action time and can be in the range between 1 s and 100 s. In this exemplary embodiment, it should be mentioned that it can be advantageous to selectively set the ignition points on the surfaces of the contacts for different contact geometries.

By implementing an additional control, for example using electromagnetic fields, the base point propagation can be controlled in a targeted manner. As a result, an optimized utilization of the surfaces of the contacts can be achieved during direct current formation, i.e. the area utilization coefficient can be increased. The use of the controller can also shorten the process time depending on the current.

In another exemplary embodiment, the contacts are separated by one stroke in a step S11) before step S1). After step S11), step S1) is carried out, during which the contacts are further separated from one another by one stroke, an arc being drawn between the contacts. Steps S2) and S3) are then carried out. Preferably, steps S11), S1) and S2) are at least one. It is possible to reverse the polarity.

This exemplary embodiment can be referred to as “contactless ignition”. Compared to the previous exemplary embodiment of “contact ignition”, a defined small contact stroke of a few millimeters is initially set for contactless ignition. An arc is then ignited, for example by means of an HF transformer. The arc or arcs arise at the points with the smallest distance from one another and, as with contact ignition, spread from there partially or over the entire area of the surfaces of the contacts. In this exemplary embodiment, it should be mentioned that it can be advantageous to selectively set the ignition points on the surfaces of the contacts for different contact geometries.

In a further embodiment, the contacts are built into the vacuum switching device during forming. This has economic advantages, since the vacuum in the vacuum switching device is used as the process medium at the same time. The DC forming is carried out with manageable effort and very little use of the safety equipment, among other things. The process of direct current forming can be integrated into a device for alternating voltage forming with little effort.

The exemplary embodiments described above can be used for all contact materials and their production technologies, for all voltage levels (high, medium and low voltage) and for all contact geometries.

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

Figure list

• 1 zeigt ein Flussdiagramm eines Verfahrens zum Formieren von Kontakten einer Vakuumschaltvorrichtung gemäß einem ersten Ausführungsbeispiel;
• 2 zeigt ein Flussdiagramm eines Verfahrens zum Formieren von Kontakten einer Vakuumschaltvorrichtung gemäß einem zweiten Ausführungsbeispiel;
• 3 zeigt ein Flussdiagramm eines Verfahrens zum Formieren von Kontakten einer Vakuumschaltvorrichtung gemäß einem dritten Ausführungsbeispiel;
• 4 zeigt eine Oberfläche von Kontakten vor dem Formieren;
• 5 zeigt eine Mikroskopieaufnahme eines Schliffes quer zur Oberfläche des Kontakts der 4;
• 6 zeigt eine Mikroskopieaufnahme eines Schliffes quer zur Oberfläche eines nur mit Gleichstrom formierten Kontakts;
• 7 zeigt eine Oberfläche des mit Gleichstrom formierten Kontakts ohne anschließender Kontaktformierung mit Wechselspannung;
• 8 zeigt die Oberfläche des mit Gleichstrom formierten Kontakts der 7 mit anschließender Kontaktformierung mit Wechselspannung;
• 9 zeigt eine Draufsicht auf einen Kontakt, der eine Teilbelastung von einigen kA für einige ms erfahren hat;
• 10 zeigt ein Schliffbild des Kontakts der 9, der die Teilbelastung von einigen kA für einige ms erfahren hat;
• 11 zeigt ein Beispiel einer herkömmlichen Vakuumschaltvorrichtung in Gestalt einer Vakuumschaltröhre;
• 12 zeigt eine Oberfläche von Kontakten nach reiner Wechselspannungsformierung gemäß dem Stand der Technik.

The aspects defined above and further aspects of the present invention emerge from the exemplary embodiments described below. The invention is described in more detail below with reference to the exemplary embodiments, to which the invention is not limited, however, so that it can be carried out.

• 1 shows a flow chart of a method for forming contacts of a vacuum switching device according to a first embodiment;
• 2 shows a flow diagram of a method for forming contacts of a vacuum switching device according to a second embodiment;
• 3 shows a flow chart of a method for forming contacts of a vacuum switching device according to a third embodiment;
• 4th shows a surface of contacts before forming;
• 5 shows a microscopic picture of a section transverse to the surface of the contact of FIG 4th ;
• 6th shows a microscopic image of a section across the surface of a contact formed only with direct current;
• 7th shows a surface of the contact formed with direct current without subsequent contact formation with alternating voltage;
• 8th shows the surface of the contact formed with direct current in FIG 7th with subsequent contact formation with alternating voltage;
• 9 shows a plan view of a contact that has experienced a partial load of a few kA for a few ms;
• 10 shows a micrograph of the contact of the 9 who has experienced the partial load of a few kA for a few ms;
• 11 Fig. 10 shows an example of a conventional vacuum interrupter in the form of a vacuum interrupter;
• 12th shows a surface of contacts after pure alternating voltage formation according to the prior art.

Figure description

The drawings are shown schematically. It should be noted that similar or identical elements are provided with the same reference symbols in different figures.

1 Figure 3 shows a flow diagram of a method for forming contacts 1 , 2 a vacuum switching device 100 according to a first embodiment. The contacts 1 , 2 are preferably designed as contact washers that have a flat contact surface.

In a step S1) an arc is generated between the surfaces of the contacts by means of a direct current source, which preferably sets a certain current strength, and a direct current flows through the contacts 1 , 2 for a first period of time. The first period of time can be 1 s to 100 s. Step S1) can basically achieve dielectric stabilization against mechanical influences such as, for example, currentless switching. In a step S2), the arc is extinguished after the first period of time has elapsed by reducing the current intensity of the direct current source or switching it off completely. Alternatively, there can be a hub between the contacts 1 , 2 can be set to zero (zero stroke). In a step S3), an alternating voltage is subsequently applied to the contacts for a second period of time 1 , 2 created. If the stroke between the contacts was set to zero in step S2), this stroke is then set again to a value greater than zero in step S3) before the alternating voltage is applied.

In step S1) the direct current can be applied with a current strength in a range between 10 and 800 A, preferably between 80 and 200 A. The steps S1) and S2) can be repeated between 1 and 60 times, preferably between 1 and 30 times, more preferably between 1 and 12 times, as indicated by a dashed arrow in the upper area of the 1 is shown. It is possible to reverse the polarity.

In step S3) the alternating voltage can be applied in a frequency band between 1 Hz and 1 kHz with a current intensity in a range between 10 and 800 A, preferably between 80 and 200 A. The second period of time can be in a range between 1 and 100 s, preferably between 10 and 50 s. Step S3) can be repeated between 3 and 15 times, preferably between 5 and 12 times, in succession, as indicated by a dashed arrow in the lower area of the 1 is shown.

2 Figure 3 shows a flow diagram of a method for forming contacts 1 , 2 a vacuum switching device 100 according to a second embodiment. Steps S1), S2) and S3) are similar to the first embodiment.

In a step S10) before step S1) the contacts 1 , 2 moved towards each other so that they touch. After step S10), step S1) is carried out, whereby the contacts 1 , 2 meanwhile be separated from each other by a stroke, so that one or more arcs between the contacts 1 , 2 to be pulled. Steps S2) and S3) are then carried out. The hub basically defines a distance between the contacts 1 , 2 . The zero stroke is defined as the stroke at which the contacts 1 , 2 are in mechanical contact with each other.

Steps S10), S1) and S2) can be repeated at least once in succession before step S3) is carried out, as indicated by a dashed arrow in the upper area of FIG 2 is shown. It is possible to reverse the polarity. Step S3) can also be repeated as in the first exemplary embodiment, as indicated by a dashed arrow in the lower area of FIG 2 is shown.

3 Figure 3 shows a flow diagram of a method for forming contacts 1 , 2 a vacuum switching device 100 according to a third embodiment. Steps S1), S2) and S3) are similar to the first embodiment.

In a step S11) the contacts 1 , 2 before step S1) separated by a stroke that is greater than the zero stroke. After step S11), step S1) is carried out, whereby the contacts 1 , 2 meanwhile are separated by one stroke, with an arc between the contacts 1 , 2 is pulled. The stroke set in step S1) is greater than the stroke in step S11). Steps S2) and S3) are then carried out.

Steps S11), S1) and S2) can be repeated at least once in succession before step S3) is carried out, as indicated by a dashed arrow in the upper area of FIG 3 is shown. It is possible to reverse the polarity. Step S3) can also be repeated as in the first exemplary embodiment, like this by a dashed arrow in the lower area of the 3 is shown.

The vacuum switching device 100 can be configured to carry out the method according to one of the preceding claims. The contacts 1 , 2 are therefore in the vacuum switching device during the forming process 100 built-in. Preferably the vacuum switching device is 100 a vacuum interrupter. The vacuum switching device 100 can use the characteristics of the vacuum interrupter 11 have, but is not limited to.

In the third exemplary embodiment, it can be advantageous for different contact geometries to have the spatial ignition points on the surfaces of the contacts 1 , 2 selectively set.

4th shows a surface of the contacts 1 , 2 before forming. The surface serves as a reference in comparison with the formed surfaces in the drawings below.

5 shows a micrograph of a section across the surface of the contact 1 , 2 the 4th . The contact 1 , 2 consists of CuCr50. The reference number 20th denotes a copper matrix, and the reference number 21 denotes embedded chromium in the copper matrix 20th . The surface is not melted over and the grain structure made of CuCr50 is cut off relatively smoothly.

6th shows a microscopic image of a section perpendicular to the surface of the contacts formed only with direct current 1 , 2 the 5 . In area A, the CuCr50 is in contact with the copper matrix 20th and the embedded chrome 21 shown. In area B there is a remelted copper-chromium layer 22nd of the contact material shown with a thickness of about 6 µm. In area C, an embedding material for the polished section is shown. Area B shows a clear smoothing or homogenization of the surface of the contacts 1 , 2 . The overmelted area of contact material also occurs at the edges and slots of the contacts 1 , 2 (ie in the entire field-related area). The copper-chromium layer remelted by the current forming 22nd is characterized by a significantly finer structure distribution compared to the copper matrix 20th and the chrome embedded there 21 .

7th shows a surface of the contact formed with direct current 1 , 2 without subsequent contact formation with alternating voltage. The surface has a streamformed area 23 and a non-streamformed area 24 . It is clearly shown that the current-formed area 23 the majority of the surface of the contact formed with direct current 1 , 2 matters. It has been found that the surface of that contact 1 , 2 which was the anode (last) when the direct current was formed, has a different visual appearance than that contact 1 , 2 which was the cathode (last) during direct current formation. The anode looks more matt and has a visual appearance that is similar to a vapor-coated surface. In contrast, the cathode has an optical appearance with visible, typical topological melt structures that are caused by individual arc base points that act on the surface.

8th shows the surface of the contact formed with direct current in FIG 7th with subsequent contact formation with alternating voltage. Compared to the 7th there are clear changes on the surface of the contact 1 , 2 caused by the alternating voltage formation in step S3). The surface of the contacts 1 , 2 is even better smoothed or homogenized. The reference number 25th denotes typical topological structures. The typical topological structures 25th are each characterized by an inner and an outer structure which are essentially concentric. Both the inner and outer structures have a substantially round or circular perimeter. The topological structures 25th can partially or completely overlap.

9 and 10 show a plan view or a micrograph of a contact 1 , 2 that has experienced a partial load of a few kA for a few ms. There a layer of enamel about a few 10 µm thick has formed on the surface.

The inventors have also found out through measurements that the method of current shaping according to the invention results in a reduction in the X-ray dose rate compared to conventional pure alternating voltage shaping by approximately the factor 5 or higher can be achieved. This fact is of essential importance especially for high-voltage vacuum interrupters, since the X-ray radiation usually increases sharply in the high-voltage range.

It should be noted that the term “having” does not exclude other elements or steps. Elements that are described in connection with various embodiments can also be combined. It should also be noted that any reference signs in the claims should not be construed as reflecting the scope of the claims.

List of reference symbols

1

Contact

2

Contact

3rd

Contact stud

4th

Contact stud

5

Middle part

6th

Ceramic insulator

7th

Ceramic insulator

8th

End flange

9

End flange

10

Bellows

11

umbrella

12th

umbrella

13th

umbrella

14th

umbrella

20th

Copper matrix

21

embedded chrome

22nd

remelted copper-chromium layer

23

streamformed area

24

non-current-formed area

25th

typical topological structure after current forming

100

Vacuum switching device

Claims (13)

Method for forming contacts (1, 2) of a vacuum switching device (100), comprising the following steps: S1) generating an arc between the surfaces of the contacts (1, 2) by means of a direct current source for a first period of time; S2) extinguishing the arc by reducing the current intensity of the direct current source or by setting a stroke between the contacts (1, 2) to zero; and S3) subsequent application of an alternating voltage to the contacts (1, 2) for a second period of time. Method according to the preceding claim, wherein the direct current is applied with a current strength in a range between 10 and 800 A, preferably between 80 and 200 A. The method according to any one of the preceding claims, wherein steps S1) and S2) are repeated between 1 and 60 times, preferably between 1 and 30 times, more preferably between 1 and 12 times before the execution of step S3), the repeating preferably with a reversal of polarity happens. Method according to one of the preceding claims, wherein the alternating voltage is applied in a frequency band between 1 Hz and 1 kHz with a current intensity in a range between 10 and 800 A, preferably between 80 and 200 A. Method according to one of the preceding claims, wherein the first and / or the second time period is in a range between 1 and 100 s, preferably between 10 and 50 s. Method according to one of the preceding claims, wherein step S3) is repeated between 3 and 15 times, preferably between 5 and 12 times, in succession. Method according to one of the preceding claims, wherein the contacts (1, 2) are moved towards one another in a step S10) before step S1) in such a way that they touch one another; after step S10), step S1) is carried out, during which the contacts (1, 2) are separated from one another by one stroke, so that an arc is drawn between the contacts (1, 2); and steps S2) and S3) are then carried out. Method according to the preceding claim, wherein steps S10), S1) and S2) are repeated at least once in succession, preferably with a reversal of polarity, before step S3) is carried out. Method according to one of the preceding claims, wherein the contacts (1, 2) are separated by one stroke in a step S11) before step S1); after step S11), step S1) is carried out, during which the contacts (1, 2) are further separated from one another by one stroke, an arc being drawn between the contacts (1, 2); and steps S2) and S3) are then carried out. Method according to the preceding claim, wherein steps S11), S1) and S2) are repeated at least once in succession, preferably with a reversal of polarity, before step S3) is carried out. Method according to one of the preceding claims, wherein the contacts (1, 2) are built into the vacuum switching device (100) during the forming. Method according to one of the preceding claims, wherein step S1) achieves dielectric stabilization against mechanical influences such as, for example, currentless switching. Vacuum switching device (100) which is configured to carry out the method according to one of the preceding claims.

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