EP1039495B1 - Method for limiting current in low voltage networks, its associated arrangement and special use of this arrangement - Google Patents

Description

The invention relates to a method for limiting current in low-voltage networks, in which occur in the operating case at the operating currents occurring diffuse arc modes of an arc and in the case of short circuit, the arc is split into successive partial arcs. In addition, the invention relates to an arrangement for carrying out the method as well as to specific uses of this arrangement.

In low-voltage networks, in addition to the operating currents, short-circuit currents of up to 200 kA _{eff must be} controlled by switching devices and distributors. The switching of such currents with circuit breakers requires considerable technical effort and is associated with selective switches with a drastic reduction in the life of the switching device. When arcing occurs, the high currents can cause major damage to equipment as well as a high risk to people. Therefore, circuit breakers are required which interrupt these currents with as little effort as possible and / or significantly limit them. Also suitable for the same purpose would be components that can afford such a limit regardless of a shutdown, so as to relieve the actual switching element.

Using conventional air circuit breakers with splitter chambers, the potential for short-circuit shutdowns in low-voltage networks prospective currents by the voltage build-up of usually 300 - 400 V, which occurs when the arc enters the arc splitter chamber, can be significantly reduced. As a result, on the one hand, the switching chamber work and the associated thermal loads considerably reduced by switching devices. On the other hand, the current forces or the resulting mechanical stresses in the current distributions remain considerably below the maximum possible value.

In the low-voltage range, current-limiting components are still known which operate on the basis of carbon-filled, conductive polymers in which the conductivity for high current densities decreases by several orders of magnitude compared to the rated current range. Because of the comparatively low conductivity of the polymers, however, this principle can only be used up to nominal currents of a maximum of a few 10 A, since otherwise the forward losses become prohibitively high.

The object of the invention is therefore to propose new methods for limiting current, and to provide corresponding arrangements and to specify associated applications.

The object is achieved by the objects of the method claims. Associated arrangements are indicated by the related claims. The use claims, in contrast, include specific uses of the arrangement provided.

In the context of the invention, therefore, vacuum interrupters are used successfully for current limitation in the low and medium voltage range. Neither the technical or patent literature nor from practice so far current-limiting vacuum interrupters or corresponding arrangements of vacuum switching contacts are known.

In the invention, however, vacuum interrupters are used with such contact configurations in which a direction of the current in the arc transversal internal magnetic field occurs, the arc is divided by suitable divider plates in partial arcs. Optionally, the arc can also remain in one piece, wherein in this If the divider plates are used outside the arc wire as arc cooling plates.

The used within the scope of the invention vacuum interrupters with current-limiting property thus consists of at least two contacts with measures for generating radially directed magnetic fields, of which at least one contact in the direction of the power supply to the other contact is movable, from a vacuum-tight envelope, an insulator and a electrically largely insulated suspended, the main contacts enclosing laminated core for arc distribution.

Advantageously, a modified vacuum interrupter can be used in circuit breakers, which thereby additionally receive a current-limiting function and therefore can be used for larger rated currents than is possible with vacuum interrupters of conventional construction. The vacuum interrupters are kept closed in a known manner in the operating state and actively opened when a fault occurs by a suitable drive mechanism.

Another advantageous application is given by the ability to use the interrupters as a current-limiting fuse element. The central idea is to keep the interrupter for operating currents closed only by spring force. Upon the occurrence of a short circuit, such a high contact-removing current force is generated by the short-term high currents between the contacts that the contacts separate from each other. By a suitable mechanism, the springs can then unlatch when a preset release force is exceeded, so that the contacts completely separate from each other by the magnetic forces and the pressure force acting in the arc. As a result, the contact arrangement can build up the described current-limiting effect and the current flowing in the distribution network current in comparison to the prospective short-circuit current low current values limit. The passive switching in this case working vacuum interrupter thus has a fuse-like, current-limiting effect and can be used either as a single-working fuse or a suitable design, similar to a circuit breaker, also reset multiple times.

Figur 1

eine erste Anordnung von in einer Vakuumschaltröhre befindlichen Kontakten mit zugeordneten Lichtbogenteilerplatten in seitlicher Schnittdarstellung,

Figur 2

die Draufsicht auf eine Anordnung gemäß Figur 1,

Figur 3

eine bevorzugte Anordnung mit Kontakten für Transversalmagnetfelder in seitlicher Schnittdarstellung,

Figur 4

eine Draufsicht auf die Anordnung gemäß Figur 3,

Figur 5

eine Anordnung mit Topfkontakten zur Generierung eines radialen Magnetfeldes und zugehörigen Teilerplatten,

Figur 6

eine Draufsicht auf die Anordnung gemäß Figur 5,

Figur 7

eine Schnittdarstellung zur Verdeutlichung der Funktion der Teilerplatten und

Figur 8

unterschiedliche Beispiele für vom Stand der Technik vorbekannte Elektrodengeometrien.

Further details and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the drawing in conjunction with further subclaims. Show it

FIG. 1

a first arrangement of located in a vacuum interrupter contacts with associated arc divider plates in side sectional view,

FIG. 2

the top view of an arrangement according to Figure 1,

FIG. 3

a preferred arrangement with contacts for transverse magnetic fields in a lateral sectional view,

FIG. 4

a top view of the arrangement according to Figure 3,

FIG. 5

an arrangement with pot contacts for generating a radial magnetic field and associated divider plates,

FIG. 6

a top view of the arrangement according to Figure 5,

FIG. 7

a sectional view to illustrate the function of the divider plates and

FIG. 8

different examples of previously known from the prior art electrode geometries.

1 and 2, two contact pins are shown in FIG. 1, via which currents are conducted to contact carriers 3 and 4 with associated contact supports 9. There is an extinguishing arrangement 5, as it is known in principle from air switches, which consists of individual extinguishing plates 6a to 6j, wherein a peripheral ceramic boundary 7 is present. The latter becomes clear from the plan view according to FIG.

Figures 1 and 2 thus show an arrangement which is similar to those used in conventional low-voltage circuit breakers Air switch chambers, with suitable materials for an indicated vacuum interrupter chamber VS are used. This arrangement exhibits good current-limiting behavior at high short-circuit currents. However, an arc of several 10 kA which burns stationary in the region of the divider plates 6a to 6j may, if appropriate, destroy the divider plates and the outer contact area which is loaded by the arc and therefore do not permit a sufficient service life.

For the sake of brevity, the arrangement according to Figures 1 and 2 is not for the actual operational switching of the generally occurring operating currents, i. usually currents of a few 100 A up to a few kA. Although the arcs occurring in this case arise between the contact pads of the separating pieces that are being separated, they are in intensive mode, but change into the diffuse mode with increasing contact spacing. In this case, the projections on the electrodes expand over the entire surface and can thus also burn in undesired switching chamber areas. Such arrangements are therefore to be used only as security elements.

In FIGS. 3 and 4, 11 and 12 denote two contact pins for conducting current, one of which is designed to be movable via a bellows (not shown). The actual vacuum interrupter is not shown in detail. There are contact pieces 13 and 14 are present, each having corresponding slots for generating radial or transverse magnetic fields. Between the laterally tapered contacts 13 and 14, an assembly 15 is present, which consists in detail of individual divider plates 16a to 16h and associated ceramic or metal parts. In particular, the divider plates 16a to 16k are inserted into a ceramic holder 17 at the end and, according to FIG. 4, at least one radial slot 18 is present.

With this arrangement, a desired for a current limiting splitting of the arc in successive Partial arcs are achieved in the event of a short circuit while controlling the diffuse arc mode occurring during operating currents. The arrangement consists essentially of two switching pieces 13 and 14 and the arrangement 15 with the annular arc divider plates 16a to 16h.

Basis of this embodiment is that the operation of vacuum switching contacts with radial magnetic field and rotating arc is modified in that the circulating arc is directed by the magnetic field in a splitter stack and thereby - while maintaining the rotation - is split into a series of cascaded, rapidly rotating individual arcs. By this hitherto unknown measure, both the thermal load of all affected contact parts can be kept low, and at the same time such a large amount of burning voltage are constructed that the prospective short-circuit current is limited to controllable in this geometry amplitudes.

The switching pieces 13 and 14 have in their plan similarities with the spiral contacts used in the vacuum switching technology. In this case, the magnetic force acting on the intense arc created between the separating contact pads has components that drive the arc toward a revolving race 19. In this arc migration, an extension of the arc is achieved by chamfering the contact pieces 13 and 14. During this movement process, the arc will go into the diffuse mode and thereby extend over the entire contact piece surface, if a dependent of the contact piece diameter D limiting current of I _G ≈ 15-25 kA is not exceeded. On the other hand, with instantaneous currents exceeding this limit value, the arc is maintained in contracted mode, and its voltage requirement during wandering as a result of the extension increases to a few 100 V and thus the current limitation becomes effective. Near the race 19 the voltage requirement of a long arc, at least for the recurrent unstable arc configurations will be greater than the sum of the voltage requirement of partial arcs that burn between two individual divider plates 16a to 16h or between the raceway 19 and one of the divider plates 16a to 16h. For such arc configurations, the commutation of the long arc into the area of the divider plates and its division occurs within a few μs. In this process, the burning voltage and the associated current limit is only slightly reduced. Only when the instantaneous current falls below the limit value I _G before zero current, does the arc withdraw from the splitter plate region and change to the diffuse mode. It spreads over the contact surface and the arc voltage decreases with decreasing current.

The running direction of the contracted arcs between each two of the divider plates 16a to 16h is determined by the local magnetic field, which depends on the current flow in the contact pieces or races and the divider plates. The directions of individual partial arcs can therefore be different for the individual arcs, as shown in FIG. 7 for a section of the divider plates and races.

Since the current-limiting effect should start as quickly as possible during a shutdown and is directly related to the arc voltage build-up, the arc must migrate rapidly from the contact pads in the direction of the divider plates. In addition, the commutation must be done quickly in the field of divider plates, so that reignitions in the back of the bow and thus arc voltage dips are avoided.

These demands on the arc behavior can be met by the structural design of the contact pieces and divider plates. The main body of the contact pieces should be made of oxygen-free copper (Cu) or the material of the contact pads such as As chrome-copper (CrCu) or tungsten-copper (Wcu) exist. From the literature, numerous investigations are known, according to which these materials are suitable for their running and Neuzündverhaltens for vacuum switch contacts. The switching pieces are preferably formed as spiral contacts and have 3-6, preferably 4 slots, which may be designed according to Appendix 4 or one of the in the application 19624920.1 v. 21. 06. 1996 have described forms. The bevel of the contact pieces should be characterized by an angle of inclination ψ with respect to the contact surface of ψ = 15-45 °, preferably ψ = 30 °, since the angular behavior of the arc is only slightly affected by reignitions. The running range of the arc in the outer region of the spiral vanes can, as shown by way of example in Appendix 2, also formed by an additionally applied raceway of a erosion resistant contact material such as chromium-copper (CrCu), tungsten-copper (WCu) or tungsten carbide-copper (WCCu) become. Other possible contact geometries with radial magnetic fields, such as, for example, the so-called pot contact (English: contrate contact) or the so-called "windmill wing contact" are also suitable with appropriate modification.

Both oxygen-free copper (Cu) and chromium-copper (CrCu), which guarantee a perfect onset and run of the arc due to their commutation behavior, as well as stainless steels, can be used as material for the divider plates. By using magnetic stainless steels, by increasing the magnetic field component that drives the arc into the divider plates, the division of the arc can be facilitated. To avoid eddy current losses at rated and operating currents, the divider plates should be provided with at least one slot in the radial direction. The width b of the divider plates should be about b ≈ 0.1 - 0.3 * D, where D is the outer diameter of the contacts. The width a of the races is usefully not greater than that of the divider plates; but it must be wider than the largest possible base diameter. It is therefore chosen to be a ≈ 0.5 - 1.0 * b.

In a modification of the arrangement according to Figures 3 and 4 are known from the vacuum switching pot contacts used. In these pot contacts the radial magnetic field is generated by appropriate slotting in the carrier part of the pot. Side must also be made here a bevel, so that corresponding divider plates can be inserted.

In FIGS. 5 and 6, 21 and 22 represent two contact pins for current guidance, one of which is designed to be movable via a bellows (not shown). The actual vacuum interrupter VS is again indicated only. There are pot contact pieces 23 and 24 available, as they are already known from the prior art. Such slotted pot contacts can, if two symmetrically opposed pot contact pieces 23 and 24 have mutually inclined slots produce a transversely with respect to the current direction in the arc magnetic field, so that such contact pieces are also referred to as radial field contacts. On the actual pot contacts 23 and 24 are applied to the actual contact rings 29 of contact material. The rings 29 have according to the arrangement of Figure 3 has a specific shape. Specifically, it is achieved by the inner in the closed state of the switch contacting part of bevels with a predetermined angle ψ that there is a greater clearance in the outer region. In this free space engage from the outside according to Figure 2 divider plates 26a to 26h, which are externally supported by a ceramic part 27.

In the case of the pot contacts 23 and 24 shown in FIGS. 5 and 6, each individual contact piece consists in particular of a contact body 30 in which straight slots 31 are made at a predetermined pitch.

FIG. 7 illustrates how the division of the arc can take place in particular between the individual divider plates 6a to 6j from FIG. 1 or 16a to 16h from FIG. 3 or 26a to 26h from FIG. Thus, the desired effect of limiting the current in vacuum is achieved.

FIG. 8 shows possible geometries of the actual contact plate based on four examples I to IV, as are also known from the prior art. In this case, essentially in Example I, the so-called spiral contacts in which spiral-shaped slots 101 to 104 are present in a contact plate 100 and in the middle a circular recess 105 in the contact plate 100 is present. Such a contact geometry ensures a radial circulation of the arc.

For simplified production 205 three tangential straight slots 201 to 203 are introduced in Example II in a contact plate 200 with circular recess 205. This results in essentially the same effect.

In Examples III and IV are in the contact plates 300 and 400 with concentric grooves 305 and 405 also straight slits 301 to 304 and 401 to 404 available, which are bent at right angles in Example III and provided in Example IV with circular recess 205 are. Such slots can also be relatively easily introduced into existing contact plates.

While the arrangement according to FIGS. 3/4 and 5/6 is provided essentially for the operational switching of high currents with current limitation, the arrangement according to FIG. 1 and FIG. 2 is present essentially only as current limiting or monitoring element, with which no Reversible work is possible.

For use as current-limiting fuse elements in the arrangements according to the figures described, the contact pieces in the interrupter for the operating currents can be closed by spring force, wherein upon contact of a short circuit, a contact-removing current force is generated, which separate the contacts from each other. It is also possible for such a case, upon the occurrence of a short circuit by the current force to release a Verklinkungsmechanismus and separate the contact pieces by spring force, pneumatically or hydraulically.

In particular in the arrangements of Figure 3/4 and Figure 5/6 rotationally symmetric radial field contacts are present in which the rotating arc is split by the magnetic field and by the arc divider plate while maintaining the rotation in a series of series-connected, rapidly rotating single arc. In a certain modification, the arc may also remain in one piece, in which case the divider plates merely serve as arc cooling plates. According to Figure 1/2, it is possible to realize when using a vacuum interrupter with transverse magnetic field and a non-rotationally symmetrical contact arrangement a straight-line arc, wherein the arc is split by the magnetic field and by at least one arc divider plate while maintaining the movement in a series of series-connected individual arcs. In a specific modification, in such a non-rotationally symmetrical contact arrangement, the rectilinear arc can also remain in one piece, in which case the divider plates outside the arc path again serve as arc cooling plates.

Claims (23)

1. Method for current limiting in low-voltage networks in which during operation, with the operating currents which occur in such cases, diffuse arc modes of an electric arc occur and in which in the case of a short circuit the arc is split up into consecutive sub arcs, characterised by the use of vacuum switching tubes.
2. Method in accordance with claim 1, characterised in that at least one vacuum switching tube with at least one radial field contact is used, for which the switching contacts create a magnetic field running perpendicular to the direction of current in the arc and a circulating current is caused, with the circulating current being divided up by the magnetic field and by at least one electric arc divider plate while retaining the rotation into a series of consecutively switched, rapidly circulating individual arcs (FIG 3/4, FIG. 5/6).
3. Method in accordance with claim 1, characterised in that a radial field contact on the one hand and a chamfered plate contact on the other hand are used.
4. Method in accordance with claim 2, characterised in that at least one vacuum switching tube with at least one radial field contact is used, for which the switching contacts create a magnetic field running perpendicular to the direction of current in the arc and a circulating arc is caused, with the arc remaining in one piece and the divider plates outside the arc path being used as arc cooling plates (FIG 3/4, FIG. 5/6).
5. Method according to claim 1, characterised in that at least one vacuum switching tube with transversal magnetic field is used and that an arc running in a non-rotation-symmetrical contact arrangement is used, with the arc being split up by the magnetic field and by at least arc divider plate while retaining the movement into a series of consecutively switched individual arcs (FIG 1/2).
6. Method according to claim 1, characterised in that at least one vacuum switching tube with transversal magnetic field is used and that an arc running in a straight line in a non-rotation-symmetrical contact arrangement is used, with the arch remaining in one piece and the divider plates being used outside the arc path as arc cooling plates (FIG 1/2).
7. Method in accordance with claim 1, characterised in that suitable, especially oxygen-free vacuum tube materials are used for the contact arrangement and the arc divider plate.
8. Arrangement for current limiting in low-voltage networks using the method in accordance with claim 1 or one of the claims 2 to 7, characterised by at least one vacuum switching tube (VS) with contact pieces (13, 14; 23, 24) and by circular arc divider plates (16a - 16k, 26a - 26k) which are arranged at least partly between the contact pieces (13, 14; 23, 24).
9. Arrangement in accordance with claim 8, characterised in that the contact pieces (13, 14) in their basic shape have the form of spiral contacts (100).
10. Arrangement in accordance with claim 8, characterised in that the spiral contacts (100) feature between three and six, preferably four slits (101 -104).
11. Arrangement in accordance with claim 8, characterised in that the contact pieces (13, 14; 23, 24) are chamfered in the zones which follow on outwards from the actual contacting area.
12. Arrangement in accordance with claim 11, characterised in that the chamfering of the contact pieces (13, 14; 23, 24) has an angle of inclination (Ψ) against the contact surface of 15° > Ψ <- 45°, preferably Ψ = 30°.
13. Arrangement in accordance with claim 8, characterised in that at least the contact surface of the contact pieces (13, 14; 23, 24) consists of a fire-resistant contact material, preferably chrome copper (CrCu), tungsten copper (Wcu) or tungsten carbide copper (WCCu).
14. Arrangement in accordance with claim 8, characterised in that the divider plates (16a to 16k, 26a to 26k) consist of oxygen-free copper (Cu) or chrome copper (CrCu).
15. Arrangement in accordance with claim 8, characterised in that the divider plates (16a to 16k, 26a to 26k) consist of stainless steel, especially magnetic stainless steel.
16. Arrangement in accordance with claim 14 or claim 15, characterised in that the divider plates (16a to 16k, 26a to 26k) feature at least one slit (17, 27) in a radial direction.
17. Arrangement in accordance with claim 14 or claim 15, characterised in that the width (b) of the divider plates (16a - 16k, 26a - 26k) has a dimensioning of 0.1 D ≥ b ≤ 0.3 D, with D being the external diameter of the contacts (13, 14; 23, 24)
18. Arrangement in accordance with claim 8, characterised in that runner rings (19, 29) are formed through the contact surface contact pieces (13, 14; 23, 24) which have a width (a) smaller than the width (b) of the divider plates (16a - 16k, 26a - 26k).
19. Arrangement in accordance with claim 18, characterised in that the width (a) of the runner rings ( ) corresponds to the dimensioning 0.5 b ≤ a ≤ 1.0 b.
20. Arrangement in accordance with claim 18, characterised in that the runner rings (9, 19, 29) is made of a different material from the contact bodies ((3, 4; 13, 14; 23, 24).
21. Arrangement in accordance with claim 17, characterised in that the contact pieces (3, 4; 13, 14, 23, 24) are made of oxygen-free copper (CU) or copper chrome (CuCr).
22. Use of an arrangement in accordance with claim 8 or one of the claims 9 to 20 as current-limiting fusing element, with the contact pieces (3, 4, 13, 14; 23, 24) in the vacuum tubes (VS) being closed by spring pressure for operating currents and on occurrence of a short circuit a current force which lifts the contacts is created and the contact pieces (13, 14; 23, 24) are thereby separated from each other.
23. Use of an arrangement in accordance with claim 8 or one of the claims 8 to 21 as a current-limiting fuse element, with the contact pieces (3, 4, 13, 14; 23, 24) in the switching tubes (VS) being closed by spring pressure for operating currents and on occurrence of a short circuit an engagement mechanism being initiated by spring pressure and the contact pieces (13, 14 ;23, 24) being separated from one another by spring pressure, pneumatically or hydraulically.

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