EP1644951B1 - Method and device for limiting the current in a liquid metal current limiter - Google Patents

Abstract

A method and an apparatus are disclosed for current limiting, as is a switchgear assembly having an apparatus such as this. Liquid metal is passed along a resistance element for the current limiting path, in order to achieve current limiting without any arcs for network-dependent short-circuit currents. Exemplary embodiments relate, inter alia, to: an electrical resistance, which rises non-linearly in the movement direction of the liquid metal for a soft current limiting characteristic, a resistance element in the form of a dielectric matrix having channels for the liquid metal, and a combined current limiter circuit breaker. Advantages are, inter alia, reversible current limiting and possibly current disconnection without arcs, also suitable for high voltages and currents, fast reaction times, low wear, and maintenance-friendliness.

Description

TECHNICAL AREA

The invention relates to the field of primary technology for electrical switchgear, in particular the limitation of fault currents in high, medium or low voltage switchgear. It is based on a method and a device for current limiting and of a switchgear with such a device according to the preamble of the independent claims.

STATE OF THE ART

In the DE 199 03 939 A1 discloses a self-recovering current limiting device with liquid metal. Between two fixed metal electrodes, a pressure-resistant insulating housing is arranged, is arranged in the liquid metal in the compressor rooms and in intermediate connecting the compressor compartments connecting channels, so that a current path is given for nominal currents between the fixed electrodes. In the connecting channels of the current path is narrowed compared to the compressor chambers. The connection channels are strongly heated during short-circuit currents and secrete a gas. By avalanche-like formation of gas bubbles in the connecting channels, the liquid metal evaporates into the compressor chambers, so that a current-limiting arc is ignited in the now liquid-metal-depleted connection channels. After the overcurrent has subsided, the liquid metal can condense again and the current path is ready for operation again.

In the WO 00/77811 a development of the self-recovering current limiting device is disclosed. The connection channels are widened conically at the top, so that the liquid level of the liquid metal varies and the rated current carrying capacity can be varied over a wide range. In addition, a meander-shaped current path is formed by an offset arrangement of the connecting channels, so that a series of current-limiting arcs is ignited when the liquid metal is vapor-driven. Such pinch effect current limiters require a very stable in terms of pressure and temperature construction, which is structurally complex. Due to the current limitation by means of an arc, large wear occurs inside the current limiter and burnt-off residues can contaminate the liquid metal. As a result of the recondensation of the liquid metal, a conductive state returns immediately after a short circuit, with the result that no switch-off state is present.

In the DE 40 12 385 A1 discloses a current-controlled shutdown device whose operating principle is based on the pinch effect with liquid metal. Between two solid metal electrodes, a single, narrow, filled with liquid metal channel is arranged. In the event of overcurrent, the liquid conductor is contracted due to the electromagnetic force due to the pinch effect, so that the current itself strangulates and separates the liquid conductor. The displaced liquid metal is collected in a reservoir and flows back after the overcurrent event. The contact separation takes place without an arc. However, the device is only suitable for relatively small currents, low voltages and slow turn-off times and does not provide a permanent turn-off state.

In the DE 26 52 506 discloses a high current electrical switch with liquid metal. On the one hand, a liquid metal mixture is used for wetting solid metal electrodes and for reducing the contact resistance. In this case, the liquid metal by mechanical displacement, z. B. by moving contacts or pneumatically driven plunger, against gravity in the Contact gap driven. By pinch effect, according to which a current-carrying conductor by the current flowing through it undergoes a radial Striktion, the liquid metal can be additionally stabilized in the contact gap and held. External magnetic fields and magnetic leakage fluxes, eg. B. by the power supplies, can cause flow instabilities in the liquid metal and are shielded and optionally approved when switching off to assist in extinguishing the arc in the liquid metal. The disadvantage is that a gradual current limitation is not possible and cause arcs between the solid electrodes oxidation in the liquid metal. The design of the high-current switch includes seals for liquid metal, inert gas or vacuum and is correspondingly expensive.

In the GB 1 206 786 discloses a liquid metal based electrical high current switch according to the preamble of the independent claims. The liquid metal forms in a first position a first current path for the operating current and is guided during current switching along a resistive element and brought into a second position in which it is in series with the resistive element and reduces the current to a small fraction. The high-current switch is designed to generate high-intensity current pulses in the mega- ampere and sub-millisecond range for plasma generation.

PRESENTATION OF THE INVENTION

The object of the present invention is to specify a method, a device and an electrical switchgear with such a device for improved and simplified current limitation. This object is achieved according to the invention by the features of the independent claims.

In a first aspect, the invention resides in a method for current limiting with a current limiting device comprising fixed electrodes and a container with at least one channel for a liquid metal, wherein in a first operating state between the fixed electrodes an operating current is passed through the current limiting device on a first current path and the first current path is at least partially passed through the liquid metal located in a first position, wherein in a second operating state, the liquid metal is moved in at least one second position along a direction of movement, is guided along a resistance element during the transition from the first position to the second position, and the at least one second position is in series with a resistive element and thereby a current-limiting second current path is formed by the current-limiting device having a specifiable electrical resistance , wherein the resistive element is ohmic and increases non-linearly and continuously to the second position to achieve a smooth turn-off, wherein the electrical resistance as a function of the second position initially increases disproportionately with the second position in a logarithmic representation, then linear with the second position in one phase increases, in which the energy stored in a network inductance must be absorbed, and then in a region in which the short-circuit current is already limited and larger electrical resistances are tolerable, goes back to a steeper, ie disproportionately increasing function of the second position. In this way, a gentle current limiting characteristic for a progressive current limitation is realized. In particular, the electrical resistance as a function of the second position and the path-time characteristic of the liquid metal along the direction of movement is chosen so that in each second position of the liquid metal, the product of electrical resistance and current smaller than one Arc ignition voltage between the liquid metal and the fixed electrodes and intermediate electrodes and a sufficient slope of the current limit for controlling network-related short-circuit currents is achieved.

Such a current limiting method is suitable for limiting network-related short circuits. According to the invention, the liquid metal remains in the liquid state of aggregation and is selectively moved between the different positions by means of a forced movement. The pinch effect is not used. Very fast current limiting reaction times of up to less than 1 ms can be achieved. The method specifies sizing criteria for optimizing the dynamics of the current limiting operation. Since no liquid is wetted and contacted by the liquid metal in the current limiting case, no insulator, but a suitably dimensioned electrical resistance, no arc is ignited. Therefore, the current limiting method can be used even at very high voltage levels. There is hardly any wear due to burning or corrosion of the liquid metal. The current limitation is reversible and is therefore easy to maintain and inexpensive.

The embodiment according to claim 3 has the advantage of a compact arrangement of the liquid metal relative to the current paths to be switched.

The embodiment according to claim 4 has the advantage that by a series connection of liquid metal columns alternately with a dielectric and high voltages and high currents can be handled efficiently and safely.

Claims 5 and 7 indicate particularly simple configurations for a current-limiting switch or current limiter with integrated switch with liquid metal.

Claim 6 shows an advantageous, because automatic and at the same time self-recovering current limit.

In a further aspect, the invention relates to a device for current limiting, in particular for execution the method comprising fixed electrodes and a container having at least one channel for a liquid metal, wherein in a first operating state between the fixed electrodes, a first current path for an operating current through the current limiting device is present and the first current path leads at least partially through the liquid metal located in a first position wherein electrical resistance means are provided with a preselectable electrical resistance, positioning means for moving and spatially positioning the liquid metal along a direction of movement along the resistance means to at least a second position, and in a second operating condition the liquid metal is at least partially in series with the resistance means; forms together with these a second current path on which the operating current can be limited to a current to be limited, wherein the resistance element is ohmic and the electrical resistance and to achieve a smooth turn-off characteristic increases non-linearly and continuously with the second position, wherein in a logarithmic representation of the electrical resistance as a function of the second position initially increases disproportionately with the second position, then increases linearly with the second position in a phase in which the in Energy stored in a network inductance must be absorbed, and then in a region in which the short-circuit current is already limited and larger electrical resistances become tolerable, again changes into a disproportionately increasing function of the second position. In particular, the electrical resistance is dimensioned as a function of the second position and the positioning means have such a path-time characteristic of the liquid metal along the direction of travel that in each second position of the liquid metal the product of electrical resistance and current is less than an arc ignition voltage between the liquid metal and the solid electrodes and intermediate electrodes and a sufficient slope of the current limit for controlling network-related short-circuit currents can be achieved.

Further embodiments, advantages and applications of the invention will become apparent from the dependent claims and from the following description and the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1a, 1b

show a current limiting device according to the invention with liquid metal at nominal current operation and in current limiting case;

Fig. 2

shows a current limiting switch in the form of a series arrangement of liquid metal current limiter and switch;

Fig. 3, 4

show current limiting switches with trapping mechanisms for liquid metal at rated current operation;

Fig. 5

Figure 4 is a graph of the variation of the resistance of the current limiter as a function of the position of the liquid metal column; and

Fig. 6

shows a combined liquid metal current limiter and liquid metal gas-powered circuit breaker for the liquid metal.

In the figures, like parts are given the same reference numerals.

WAYS FOR CARRYING OUT THE INVENTION

1a, 1b shows an embodiment of a liquid metal current limiter 1. The current limiter 1 comprises solid metal electrodes 2a, 2b and intermediate electrodes 2c for a power supply 20 and a container 4 for the liquid metal 3. The container 4 has a bottom 6 and cover 6 of insulator material, between which an electrical resistance means 5 with at least one channel 3a for the liquid metal 3 is arranged. Over the liquid metal column 3, for example, a protective gas, an insulating liquid (with not shown here alternate volume) or vacuum may be arranged.

In a first operating state (FIG. ₁ a), an operating or rated current I _{1 flows} on a rated current path 30 from the input electrode 2 a via liquid metal 3 and optionally intermediate electrodes 2 c to the output electrode 2 b. In this case, the liquid metal 3 is in the first position x ₁ , at least partially wets the solid electrodes 2 a, 2 b, 2 c and electrically bridges the channels 3 a. In a second operating state (FIG. 1 b), the liquid metal 3 is moved along the direction of movement x, given by a height extent of the channels 3 a, into a second position x ₂ , lies there in series with the electrical resistance means 5 and forms with it a second current path or current limiting path 31 for a current I ₂ to be limited. For a particularly compact arrangement, the rated current path 30 and the current-limiting second current path 31 are arranged parallel to one another and both perpendicular to the height extent of the channels 3a on a variable, by the second position x ₁₂ , x _{2 of} the liquid metal 3 predeterminable height. For an arc-free commutation of the current i (t) from the fixed electrodes 2a, 2b, 2c to the resistance element 5, a typical, dependent on the contact material, minimum Lichtbogenzündspannung of 10 V - 20 V is not exceeded.

Preferably, the resistive means 5 comprises a dielectric matrix 5 having wall-like ridges 5a for dielectric separation of a plurality of liquid metal channels 3 a, the ridges 5 a comprising a dielectric material having a non-linearly increasing resistance R _x in the direction of movement x. The webs 5a should at the height of the first position x _{1 of} the liquid metal 3 intermediate electrodes 2c for the electrically conductive connection of the channels 3a. The channels 3a are preferably arranged substantially parallel to each other. The wall-like webs 5a represent individual resistors 5a of the resistance element 5, so that the current-limiting second current path 31 is formed by an alternating series connection of the channels 3a and the individual resistors 5a.

The positioning means 3a; 20, B, 12 for moving and spatially positioning the liquid metal 3 along a movement direction x in at least one second position x ₁₂ , x ₂ include the channels 3a and a transport or drive means 20, B, 12 for the liquid metal 3, in particular also one Drive control 11 (as shown in Fig. 6). Preferably, an electromagnetic drive 20, B or a mechanical drive with a dielectric fluid 12 is provided, through which the liquid metal 3 between the nominal current path 30 and the current limiting path 31 is movable.

In a transition from the first position x ₁ to the second position x ₁₂ , x ₂ , in particular to an extreme second position x ₂ , the liquid metal 3 is guided along the resistance element 5. In order to achieve a gentle turn-off characteristic, the resistance element 5 has a non-linearly increasing electrical resistance R _x for the second current path 31 along the movement direction x of the liquid metal 3. The resistance element 5 should have an ohmic component and is preferably purely ohmic with an electrical resistance R _x which increases continuously with the second position x ₁₂ , x ₂ .

Typically, the second operating state is triggered by an overcurrent. Preferably, the current limit is automatically activated, in particular by electromagnetic force F _mag , which acts on the current flowing liquid metal 3, wherein the liquid metal 3 in an external magnetic field B or in an internal, by a power supply 2a, 2b; 20 generated magnetic field B is arranged.

2 shows the current limiter 1 according to the invention connected in series with an electrical switch 7, in particular a power switch 7. In this arrangement, a current-limiting switch 1, 7 is realized, in which the current limitation is previously achieved by the method according to the invention with liquid metal 3 and then a power cut-off conventionally done. In electromagnetic drive of the liquid metal 3 can also be two current limiter 1 with antiphase effective triggering of the liquid metal movement to be connected in series, in each current half-wave, a current limit and, where appropriate

To achieve power shutdown.

Fig. 3 shows a variant of the current limiter 1, in which a collecting container 3b for receiving the liquid metal 3 and to provide an insulation gap 32 for power cut is present. In addition, as shown, there may be a liquid metal feed 3c for filling the liquid metal 3 in the channels 3a and switching the device 1 back on. In addition, in addition to the rated current path 30 and the current limiting path 31, an insulation gap 32 may be provided, on which the webs 5a for current limiting pass into webs 8a for current isolation. The insulating webs 8a essentially consist of insulating material, are preferably arranged in the region of the collecting container 3c and together with the channels emptied by the trapped liquid metal 3 form the insulating path 32.

FIG. 4 shows a further variant in which the isolation gap 32 is realized without catching container 3b. Here, the drive mechanism for the liquid metal 3 is realized by a rotary drive 11 'for the current limiter 1. In the second operating state, the device 1 is rotated at a predeterminable rotational speed such that due to the equilibrium between frictional and capillary forces on the one hand and the centrifugal force on the other hand, the liquid metal 3 assumes a second position x ₁₂ in the region of the resistance element 5 and forms a current limiting path 31. By increasing the rotational speed and thus the centrifugal force, the liquid metal 3 is urged into the region of the isolation webs 8a and forms together with these the insulation gap 32. Since the liquid metal is conductive, the requirements for the dielectric strength of the isolation webs 8a are increased here, which z. B. by wider isolation bridges 8a and / or a suitable choice of material is achieved.

In both variants, therefore, the liquid metal 3 is movable between the nominal current path 30, the current limiting path 31 and the insulation gap 32 for the current cutoff, so that an integrated current-limiting switch 1 based on liquid metal is realized. Advantageously, the first current path 30 for operating current I ₁ , the second current path 31 for current limiting and in particular the isolation path 32 are arranged substantially perpendicular to the direction of movement x and / or substantially parallel to each other. This results in a particularly simple configuration for an integrated current limiter - circuit breaker 1, which works exclusively with liquid metal 3.

Fig. 5 shows for the current limiter 1 or current limiting switch 1, a dimensioning of the electrical resistance R _x as a function of the second position x _{12 of} the liquid metal 3. Advantageously, the resistance R _{x is} up to an extreme second position x ₂ to a maximum value R _x (x ₂ ) non-linear rising selected. Also, for a given voltage level, the maximum value R _x (x ₂ ) of the resistor R _x should be rated to a finite value or to shut off the operating current I ₁ to a dielectric isolation value, in accordance with a current I ₂ to be limited.

The electrical resistance R _x as a function R _x (x ₁₂ ) of the second position x ₁₂ and a path-time characteristic x ₁₂ (t) of the liquid metal 3 along the direction of movement x should be selected so that in every second position x ₁₂ , x _{2 of} the liquid metal 3 is the product of electrical resistance R _x and current I _{2 is} smaller than an arc ignition voltage U _b between the liquid metal 3 and the fixed electrodes 2a, 2b and intermediate electrodes 2c and / or that a sufficient slope of the current limit for controlling network-related short-circuit currents i ( t) is achieved.

$${\mathrm{R}}_{\mathrm{x}}\left(\mathrm{t}\right)\mathrm{•}\mathrm{i}\left(\mathrm{t}\right)\mathrm{+}\mathrm{L}\mathrm{•}\mathrm{di}\mathrm{/}\mathrm{dt}\left(\mathrm{t}\right)\mathrm{=}{\mathrm{U}}_{\mathrm{N}}\left(\mathrm{t}\right)$$

wobei t=Zeitvariable, L=Netzinduktivität im Kurzschlussfall, U_N=Betriebs- oder Netzspannung, d/dt gleich erste und d²/dt² gleich zweite Zeitableitung. In Gleichung (G2) wurde angenommen, dass der Widerstand im Netz R_Netz << L ist und die Netzspannung U_N bei Kurzschluss aufrechterhalten wird. Ferner gilt die Bewegungsgleichung (G3) für das Flüssigmetall 3 mit der Masse m, der Position oder Auslenkung x₁₂(t), dem Reibungskoeffizienten α und der antreibenden Kraft F $$\mathrm{m}\mathrm{•}{\mathrm{d}}^{\mathrm{2}}{\mathrm{x}}_{\mathrm{12}}\mathrm{/}{\mathrm{dt}}^{\mathrm{2}}\mathrm{+}\mathrm{\alpha }\mathrm{•}{\mathrm{dx}}_{\mathrm{12}}\mathrm{/}\mathrm{dt}\left(\mathrm{t}\right)\mathrm{=}\mathrm{F}\mathrm{-}{\mathrm{F}}_{\mathrm{r}}\mathrm{,}$$

wobei F_r=Rückstellkraft, insbesondere gleich Gravitationskraft F_r=m•g mit g=Erdbeschleunigung. In Fig. 5 wurde beispielhaft eine elektromagnetische Kraft F=F_mag angenommen, die durch Selbstwechselwirkung des durchfliessenden Stroms i(t) auf das Flüssigmetall 3 ausgeübt wird. Dann gilt zusätzlich $$\mathrm{F}\mathrm{=}\mathrm{k}\mathrm{\circ }{\mathrm{i}}^{\mathrm{2}}\left(\mathrm{t}\right)$$

mit k=geometrieabhängige Proportionalitätskonstante. Bei externem Magnetfeld B gilt F = k' ∘ i(t) mit k'=weitere Proportionalitätskonstante. Bei mechanischem Antrieb gilt F=mechanisch erzeugte Druckkraft auf Flüssigmetall 3, die z. B. durch Steuerung oder Regelung in Abhängigkeit eines abzuschaltenden Stroms i(t) oder eines Überstroms i(t) gewählt werden kann.To control short circuits, a current-limiting parameter R _{x of} the current limiting parameters and the breakdown behavior of the contacts 2 a, 2 b that are to be disconnected are necessary. The greater the slope of the short-circuit current i (t), the lower R _x must be selected. In the worst case, the maximum short-circuit current amplitude and the maximum short-circuit current inductance are assumed. Then: $${\mathrm{R}}_{\mathrm{x}}\left(\mathrm{t}\right)\mathrm{•}\mathrm{i}\left(\mathrm{t}\right)\mathrm{<}{\mathrm{U}}_{\mathrm{b}}\left(\mathrm{t}\right)$$

$${\mathrm{R}}_{\mathrm{x}}\left(\mathrm{t}\right)\mathrm{•}\mathrm{i}\left(\mathrm{t}\right)\mathrm{+}\mathrm{L}\mathrm{•}\mathrm{di}\mathrm{/}\mathrm{dt}\left(\mathrm{t}\right)\mathrm{=}{\mathrm{U}}_{\mathrm{N}}\left(\mathrm{t}\right)$$

where t = time variable, L = line inductance in case of short circuit, U _N = operating or mains voltage, d / dt equals first and d ² / dt ² equals second time derivative. In equation (G2) it was assumed that the resistance in the network R _network << L and the mains voltage U _{N is maintained} in the event of a short circuit. Furthermore, the equation of motion (G3) applies to the liquid metal 3 with the mass m, the position or deflection x ₁₂ (t), the friction coefficient α and the driving force F $$\mathrm{m}\mathrm{•}{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0003.png"\; state="\{\{state\}\}">d</figure-callout>}}^{\mathrm{2}}{\mathrm{x}}_{\mathrm{12}}\mathrm{/}{\mathrm{<figure-callout\; id="2"\; label="dt"\; filenames="imgf0003.png"\; state="\{\{state\}\}">dt</figure-callout>}}^{\mathrm{2}}\mathrm{+}\mathrm{\alpha }\mathrm{•}{\mathrm{<figure-callout\; id="12"\; label="dx"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">dx</figure-callout>}}_{\mathrm{12}}\mathrm{/}\mathrm{dt}\left(\mathrm{t}\right)\mathrm{=}\mathrm{F}\mathrm{-}{\mathrm{F}}_{\mathrm{r}}\mathrm{.}$$

where F _r = restoring force, in particular equal to gravitational force F _r = m • g with g = gravitational acceleration. In FIG. 5, an electromagnetic force F = F _mag , which is exerted on the liquid metal 3 by self-interaction of the flowing current i (t), was assumed by way of example. Then in addition $$\mathrm{F}\mathrm{=}\mathrm{k}\mathrm{\circ }{\mathrm{i}}^{\mathrm{2}}\left(\mathrm{t}\right)$$

with k = geometry-dependent proportionality constant. With an external magnetic field B, F = k '∘ i (t) with k' = further proportionality constant. For mechanical drive applies F = mechanically generated compressive force on liquid metal 3, the z. B. can be selected by control or regulation in dependence of a current i (t) or an overcurrent i (t) to be disconnected.

In FIG. 5, it has been assumed by way of example: a short-circuit-induced current gradient di / dt = 15 kA / ms, U _N = 1 kV, I ₁ = 1 kA, maximum short-circuit current I ₂ = 50 kA and plausible parameter values for k, m and α. Then, by solving the equations (G2) - (G4) under the boundary condition (G1), the resistance R _x (t) and the path-time characteristic x ₁₂ (t) of the liquid metal 3 and finally by eliminating the time dependence of the resistance R _x (x ₁₂ ) as a function of the second position x ₁₂ , as shown in Fig. 5 logarithmic. Starting from the first position x ₁ , ie when detaching the liquid metal 3 from the fixed electrodes 2a, 2b, 2c, R _x initially increases disproportionately with the second position x ₁₂ , then increases linearly in a phase in which the in the network inductance L stored energy must be absorbed and then goes in a region where the current i is already limited and larger R _x tolerable, again in a steeper, ie disproportionate increase R _x (x ₁₂ ) over.

Such, with the distance x non-linearly increasing resistance R _x can be realized for example by materials having different resistivities. A non-linearly increasing total resistance R _x can also be realized by a suitable geometric guidance of the current path in a resistance element with homogeneous resistivity. The non-linear graduation of the resistance R _x can also be achieved by a combination of both measures, namely by a suitable geometrical current conduction in a resistance element with variable resistivity.

Fig. 6 shows a combined liquid metal current limiter 1 and liquid metal power switch 1 with gas drive 12 for the liquid metal 3. With a displacement of the liquid metal 3 in the positive direction of movement + x, the current i is guided on the current limiting path 31 and limited as discussed above. Alternatively, the liquid metal can 3 in a third operating state along the opposite direction of movement in at least a third position -x x _13, are moved x _3, wherein the liquid metal 3 in the at least one third position x _13, x ₃ is in series with an insulator 8 and thereby an insulation gap 32 for power shutdown is formed by the device 1. As shown, the insulation section 8 may be formed by a plurality of insulation webs 8a, which are in the case of disconnection in alternating series connection with the downwardly displaced liquid metal columns 3. In particular, the third operating state is triggered by a switch-off command, wherein the liquid metal 3 is moved by an electromagnetic drive with a switchable external magnetic field B or by a mechanical drive with a dielectric fluid 12. In Fig. 6 a gas drive 12 is exemplified, in which a first gas pressure vessel 121 with gas volume V ₁ and pressure p ₁ and a second gas pressure vessel 122 with gas volume V ₂ and pressure p ₂ via a controllable gas pressure valve 13 with the Working pressure vessel 123 with working volume V ₃ and working pressure p ₃ communicate. It can also be a combined valve, z. B. a three-way valve, instead of two separate valves 13 may be provided. By choosing appropriate pressures, z. B. p ₁ <p ₂ , and activation of the valves 13 can be selectively switched back and forth between the first, second and third operating state. For example, for the current limitation 31, gas from 121 having pressure p _{1 flows} into the working volume V ₃ and the liquid-metal columns 3 rise to x ₁₂ or x ₂ . For nominal current operation 30, gas from 122 is temporarily flowed in and the liquid metal mirror is lowered to x = 0. For power cut-off 32, the container 122 is opened with pressure p ₂ and the liquid metal _{3 is} lowered to the third position x ₁₃ or extreme third position x ₃ . The trapped gas in the containment volume 124 causes a restoring spring force. Further details and variants of the gas drive 12, z. B. three pressure vessel with three different pressures each for one of the three operating conditions and in particular connection of the volume 124 to a pressure vessel, are possible and are hereby expressly mitumfasst. Alternatively or in addition to Pressure vessels 121, 122, the liquid metal drive can also be performed magnetically with external or internal magnetic field B or mechanically with piston. Alternatively or in addition to gas, another dielectric working fluid, for. As oil used. As liquid metal 3 are suitable for. As mercury, gallium, cesium, GaInSn o. Ä ..

Advantageously, the isolation path 32 for power cutoff is arranged above the second current path 31 and / or below the first current path 30. As a result, a compact arrangement of the liquid metal 3 and its drive mechanism 12 relative to the currents to be switched, in particular to the nominal current path 30, current limiting path 31 and, if necessary, power-off path 32, is realized. Also, the current limiter 1 in Fig. 6 as a current-limiting switch 1, as described, be designed.

Applications of the device 1 relate to, inter alia, the use as a current limiter, current-limiting switch and / or circuit breaker 1 in power supply networks, as a self-recovering fuse or as a motor starter. The invention also includes an electrical switchgear, in particular a high or medium voltage switchgear, characterized by a device 1 as described above.

LIST OF REFERENCE NUMBERS

1

Liquid metal current limiter

2a, 2b

Solid metal electrodes, metal plates

2c

between electrodes

20

Power supply, conductor

3

liquid metal

3a

Channels for liquid metal

3b

Capture container for liquid metal

3c

Feed for liquid metal

30

Current path for operating current, first current path

31

Current path for current limiting, second current path

32

Power interruption path, isolation route

4

Liquid metal container

5

Resistive element for current limiting, resistance matrix for liquid metal

5a

individual resistors

6

Isolator, container lid, housing wall

7

Switch, circuit breaker

8th

Isolator for power interruption

8a

Single insulators

9

flexible membrane

10

Valve for liquid metal supply

11

Drive control, magnetic field control

11 '

rotational motion

12

Gas drive for liquid metal

121-124

Gas Cylinders

13

Gas pressure valves

α

coefficient of friction

B

magnetic field

F _likes

magnetic force

F _r

Restoring force

i

electricity

I ₁

operating current

I ₂

limited overcurrent

k

proportionality

L

line inductance

P ₁ , P ₂ , P ₃

gas pressure

_Rx

Resistor of the current limiter

t

time variable

U _b

arc striking voltage

U _N

Mains voltage, operating voltage

V _i , V ₂ , V ₃

gas volume

x, x ₁ , x ₂ , x ₁₂ , x ₃ , x ₁₃

Position of the liquid metal column

Claims (13)

1. Method for current limiting (1), in particular in electrical power supply networks, having a current limiting apparatus (1) which has solid electrodes (2a, 2b) and a container (4) with at least one channel (3a) for a liquid metal (3), in which an operating current (I₁) is carried on a first current path (30) through the current limiting apparatus (1) between the solid electrodes (2a, 2b) and the first current path (30) is at least partially passed through the liquid metal (3), which is located in a first position (x₁), in a first operating state, in which the liquid metal (3) is moved along a movement direction (x) to at least one second position (x₁₂, x₂) in a second operating state, and is passed along a resistance element (5) during the transition from the first position (x₁) to the second position (x₁₂, x₂), and is connected in series with the resistance element (5) in the at least one second position (x₁₂, x₂) and in consequence a current-limiting second current path (31) is formed through the current limiting apparatus (1) and has a predeterminable electrical resistance (R_x), characterized in that

   a) the resistance element (5) is purely resistive, and the electrical resistance (R_x) rises non-linearly and continuously with the second position (x₁₂, x₂) in order to achieve a soft disconnection characteristic, wherein

   b) in logarithmic representation the electrical resistance (R_x) first of all increases more than proportionally with the second position (x₁₂) as a function (R_x(x₁₂)) of the second position (x₁₂) and then rises linearly with the second position (x₁₂) in a phase in which the energy which is stored in a network inductance must be absorbed, and then, in a region in which the short-circuit current (i(t)) is already limited and greater electrical resistances (R_x) are tolerable, changes once again to a more than proportionally rising function (R_x(x₁₂)) of the second position (x₁₂).
2. Method according to Claim 1 characterized in that the electrical resistance (R_x) is chosen as a function (R_x(x₁₂)) of the second position (x₁₂), and the distance/time characteristic (x₁₂(t)) of the liquid metal (3) along the movement direction (x) is chosen such that

   a) in every second position (x₁₂, x₂) of the liquid metal (3), the product of the electrical resistance (R_x) and of the current (I₂) is less than an arc striking voltage (U_b) between the liquid metal (3) and the solid electrodes (2a, 2b) and intermediate electrodes (2c), and

   b) an adequate current limiting gradient is achieved to cope with network-dependent short-circuit currents (i(t)).
3. Method according to one of the preceding claims,
   characterized in that

   a) the movement direction (x) of the liquid metal (3) is predetermined by a height extent of the at least one channel (3a), and/or

   b) the current-limiting second current path (31) runs essentially at right angles to a height extent of the at least one channel (3a) and at a variable height which can be predetermined by the second position (x₁₂, x₂) of the liquid metal (3).
4. Method according to one of the preceding claims,
   characterized in that

   a) a plurality of channels (3a) are arranged essentially parallel to one another and are separated from one another by wall-like webs (5a),

   b) in which the webs (5a) form individual resistances (5a) of the resistance element (5), and the current-limiting second current path (31) is formed by alternating series connection of the channels (3a) and of the individual resistances (5a), and

   c) in particular, in that the webs (5a) have intermediate electrodes (2c) for the operating current (I₁) to pass through at the same height as the solid electrodes (2a, 2b).
5. Method according to one of the preceding claims,
   characterized in that

   a) the electrical resistance (R_x) rises to a maximum value (R_x(x₂)) at an extreme second position (x₂), and/or

   b) for a given voltage level, a maximum value (R_x(x₂)) of the electrical resistance (R_x) is designed to have a finite value on the basis of a current (I₂) to be limited, or is designed to have a dielectric isolation value for disconnection of the operating current (I₁).
6. Method according to one of the preceding claims,
   characterized in that

   a) the second operating state is initiated by an overcurrent (I₂) and/or

   b) the current limiting is activated autonomously, in particular by electromagnetic force (F_mag) which acts on the liquid metal (3) through which current is flowing, with the liquid metal (3) being arranged in an external magnetic field (B) or in an internal magnetic field (B) which is produced by a current supply (2a, 2b; 20).
7. Method according to one of the preceding claims, characterized in that, in a third operating state,

   a) the liquid metal (3) is moved along an opposite movement direction (-x) to at least one third position (x₁₃, x₃), and

   b) the liquid metal (3) is connected in series with an isolator (8) when in the at least one third position (x₁₃, x₃), thus forming an isolation path (32) for power disconnection by the apparatus (1), and

   c) in particular in that the third operating state is initiated by a disconnection command and the liquid metal (3) is moved by an electromagnetic drive with a switchable external magnetic field (B), or by a mechanical drive with a dielectric fluid (12), in particular by a gas drive (12).
8. Apparatus for current limiting (1), in particular for carrying out the method according to one of the preceding claims, having solid electrodes (2a, 2b) and a container (4) with at least one channel (3a) for a liquid metal (3), in which a first current path (30) for an operating current (I₁) is provided through the current limiting apparatus (1) between the solid electrodes (2a, 2b) in a first operating state, and the first current path (30) passes at least partially through the liquid metal (3) which is located in a first position (x₁), in which electrical resistance means (5) with a predeterminable electrical resistance (R_x) are provided, positioning means (3a; 20, B, 12, 11) are provided for movement and for spatial positioning of the liquid metal (3) along a movement direction (x) along the resistance means (5) to at least one second position (x₁₂, x₂), and the liquid metal (3) is connected at least partially in series with the resistance means (5) in a second operating state, and forms a second current path (31) together with it, on which the operating current (I₁) can be limited to a current (I₂) to be limited, characterized in that

   a) the resistance element (5) is purely resistive, and the electrical resistance (R_x) rises non-linearly and continuously with the second position (x₁₂, x₂) in order to achieve a soft disconnection characteristic, wherein

   b) in logarithmic representation the electrical resistance (R_x) first of all increases more than proportionally with the second position (x₁₂) as a function (R_x(x₁₂)) of the second position (x₁₂) and then rises linearly with the second position (x₁₂) in a phase in which the energy which is stored in a network inductance must be absorbed, and then, in a region in which the short-circuit current (i(t)) is already limited and greater electrical resistances (R_x) are tolerable, changes once again to a more than proportionally rising function (R_x(x₁₂)) of the second position (x₁₂).
9. Apparatus according to Claim 8, characterized in that the electrical resistance (R_x) is designed to be a function (R_x(x₁₂)) of the second position (x₁₂) and the positioning means (3a; 20, B, 12, 11) have a distance/time characteristic (x₁₂(t)) of the liquid metal (3) along the movement direction (x) such that

   a) in every second position (x₁₂, x₂) of the liquid metal (3), the product of the electrical resistance (R_x) and of the current (I₂) is less than an arc striking voltage (U_b) between the liquid metal (3) and the solid electrodes (2a, 2b) and intermediate electrodes (2c), and

   b) an adequate current limiting gradient is achieved to cope with network-dependent short-circuit currents (i(t)).
10. Apparatus according to one of Claims 8-9,
    characterized in that

    a) the resistance means (5) have a dielectric matrix (5) which has wall-like webs (5a) for dielectric isolation of the channels (3a) for the liquid metal (3), and the webs (5a) have a dielectric material with a resistance (R_x) which increases non-linearly in the movement direction (x), and the webs (5a) have intermediate electrodes (2c) for electrically conductive connection of the channels (3a) at the height of the first position (x₁) of the liquid metal (3), and/or

    b) a catchment container (3b) is provided for holding the liquid metal (3) and for provision of an isolation path (32) for current disconnection, and/or

    c) a supply (3c) for liquid metal (3) is provided in order to fill the channels (3a) with the liquid metal (3) and in order to reconnect the apparatus (1).
11. Apparatus according to one of Claims 8-10, characterized in that the positioning means (3a; 20, B, 12, 11) comprise the channels (3a) and a drive means (20, B, 12, 11) for the liquid metal (3), in particular an electromagnetic drive (20, B, 12, 11) or a mechanical drive with a dielectric fluid (12, 11), by means of which the liquid metal (3) can be moved between the first current path (30) for the operating current (I₁) and the second current path (31) for current limiting, and in particular an isolation path (32) for current disconnection.
12. The apparatus according to one of Claims 8-11,
    characterized in that

    a) the first current path (30) for the operating current (I₁), the second current path (31) for current limiting and, in particular, an isolation path (32) for current disconnection are arranged essentially at right angles to the movement direction (x) and/or essentially parallel to one another, and/or

    b) at least one isolation path (32) for current disconnection is arranged above the second current path (31) and/or below the first current path (30).
13. Electrical switchgear assembly, in particular high-voltage or medium-voltage switchgear assembly, characterized by an apparatus (1) according to one of Claims 8-12.

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