EP1644952B1 - Method and device for current limitation with an automatic current limiter - Google Patents

Abstract

The invention relates to a process and a device ( 1 ) for combined current limiting and circuit breaking and to a switchgear assembly with such a device ( 1 ). In a combined current limiter-circuit breaker ( 1 ) as claimed in the invention, a movable electrode ( 3, 3' ) on the one hand for current limitation is guided automatically along one resistance element ( 5 ) for the current limitation path ( 31 ) by an overcurrent-dependent electromagnetic force (F<SUB>mag</SUB>) and on the other hand for circuit breaking is moved into a series arrangement with an insulator ( 8 ). Embodiments include the following, among others: Use of the Lorenz force for automatic current limiting; movable electrode ( 3, 3' ) implemented by liquid metal ( 3 ) or movable solid-state conductor ( 3' ); an electrical resistance (R<SUB>x</SUB>) which increases nonlinearly in the direction of motion (x) for a gentle current limiting characteristic; and a resistance element ( 5 ) in the form of a dielectric matrix ( 5 ) with several channels ( 3 a) for the liquid metal ( 3 ). Advantages are among others: arc-free, reversible current limitation and current interruption, also suited for high voltages and currents, fast reaction times, low wear, and ease of maintenance.

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 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, driven against gravity in the contact gap. 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 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 connecting channels are widened conically upwards, so that the liquid level of the liquid metal varies and the rated current carrying capacity can be changed over a wide range. In addition, a meandering current path is formed by an offset arrangement of the connecting channels, so that a series of current-limiting arcs is ignited in the event of overflow-induced evaporation of the liquid metal. 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 GB 1 206 786 discloses a liquid metal based electrical high current switch. 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.

In US Pat. 4,599,671 a device for automatic current limiting according to the preamble of the independent claims is disclosed. A movable electrode is realized in the form of a slide which can be moved on rails, which can be electromagnetically deflected by short-circuit currents. In the deflected state, the carriage contacts a rail area which has a current-limiting electrical resistance for the current path. Instead of a mobile carriage, a liquid metal column which is easily movable in a channel can also serve as a movable electrode. The current limiter, in turn, has no turn-off state, but is arranged in series with a power switch to initially limit the current and then turn it off completely.

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 and power cutoff. This object is achieved according to the invention by the features of the independent claims.

In a first aspect, the invention resides in a current limiting method comprising a current limiting device comprising fixed electrodes and at least one movable electrode, wherein in a first operating state between the stationary electrodes an operating current is passed on a first current path through the current limiting device and the first current path is at least partially passed through the located in a first position movable electrode, wherein in a second operating state, the at least one movable electrode is automatically moved by an electromagnetic interaction with the overcurrent to be limited along a direction of movement in at least a second position, the movable electrode at a Transition is guided from the first position to the second position along a resistive element and in the at least one second position in series with the resistive element and thereby a current limiting second current path is formed by the current limiting device having a predetermined electrical resistance, further wherein in a third operating state, the movable electrode is in series with an insulator and thereby an insulation gap for power shutdown is formed by the device. According to the invention, therefore, a particularly simple configuration for an automatic current-limiting switch or current limiter with an integrated switch is specified. The overcurrent itself triggers the current limit. As the underlying electromagnetic interaction z. B. the Lorenz force on a current-carrying conductor in a magnetic field in question, but also a capacitive, inductive, electrostatic or otherwise electromagnetic influence of the overcurrent on the movable conductor portion or the movable electrode are conceivable. Since no insulator, but an electrical resistance is contacted by the movable electrode in current limiting case, no arc is ignited. Therefore, the current limiting method can be used even at very high voltage levels. In addition, hardly occurs wear due to erosion or corrosion of the movable electrode. The current limitation is reversible and is therefore easy to maintain and inexpensive.

In a first embodiment, the third operating state is triggered by a shutdown command, by which an external magnetic field is switched between an operation of the device as a current limiter and as a power switch.

In a further embodiment, in the third operating state, the movable electrode is moved along an opposite direction of movement into at least a third position and is in the at least one third position in series with the insulator.

In another embodiment, the movable electrode is automatically guided by the electromagnetic interaction with the overcurrent to be limited along the resistance element to an extremal second position, wherein the extremal second position is in a region where the resistance element merges into an insulator, so that the or a further isolation path for power cut is formed.

In another embodiment, the resistance element is selected to provide a smooth turn-off characteristic with a non-linearly increasing electrical resistance for the second current path along the direction of movement of the movable electrode; and / or the resistive element is ohmic and the electrical resistance increases continuously with the second position. In this way, a gentle current limiting characteristic for a progressive current limitation is realized.

The embodiment according to claim 6 has the advantage that the magnetic field acts directly on the current-carrying movable electrode and sets them in motion by the Lorenz force. The Lorenz force is proportional to the product of magnetic field strength and current. The magnetic field can be generated externally, in particular constant or switchable, or internally, in particular by the current to be limited. By balancing the Lorenz force and a suitable restoring force, the resulting movement can be adapted to the overcurrent to be limited and to the required for the required electrical resistance Elektrodenauslenkung.

Claim 7 specifies sizing criteria for optimal design of the dynamics of the current limiting operation.

Claim 8 and 9 indicate advantageous embodiments with a liquid metal and / or a sliding contact solid-state conductor as a movable electrode. In particular, by a series connection of liquid metal columns alternately with a dielectric and high voltages and high currents can be handled efficiently and safely.

In a further aspect, the invention relates to a device for current limiting, in particular for carrying out the method comprising fixed electrodes and at least one movable electrode, 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 at least partially through the located in a first position movable electrode, wherein electromagnetic drive means for self-energized in overcurrent moving the movable electrode along a direction of movement in at least a second position are present, electrical resistance means are provided with a predetermined electrical resistance and in a second operating state, the movable electrode is at least partially in series with the resistance means and forms together with these a second current path on which the operating current can be limited to a current to be limited in a third operating state, the movable electrode is in series with an insulator and thereby an isolation path for power shutdown by the device is present.

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 self-actuated current limiting device according to the invention with liquid metal at rated current operation and in the current limiting case;

Fig. 2, 3rd

show two self-operated current limiting devices according to the invention with mechanical sliding contact in rated current operation (dash-dotted line) and in the current limiting case;

Fig. 4.

shows a current limiting switch with liquid metal trapping mechanism 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 circuit breaker with external magnetic field drive for the liquid metal.

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

WAYS FOR CARRYING OUT THE INVENTION

1a, 1b show 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.

According to the invention, the liquid metal 3 or, in general, a movable electrode 3, 3 'is set in motion by an automatic, electromagnetic interaction with the overcurrent I ₂ to be limited. In the case of the liquid metal 3, this remains in the liquid state of matter and is selectively moved by the forced movement between the different positions x ₁ , x ₁₂ or x ₂ . The pinch effect is not used. Very fast current limiting reaction times of up to less than 1 ms can be achieved. In addition, in addition to the rated current path 30 and the current limiting path 31, an insulation path (not shown) is present.

Preferably, the second operating state is activated by the overcurrent I ₂ automatically by the current-carrying movable electrode 3, 3 'by an electromagnetic force F _{mag is} moved perpendicular to the current I ₂ through the movable electrode 3, 3' and perpendicular to a magnetic field B _ext , B _int and which has a force component parallel to the direction of movement x, 1, wherein the magnetic field B _ext, B _int as an external magnetic field B _ext and / or as an internal, from a power supply 2a, 2b; 20 generated to the current limiting device 1 magnetic field B _{int is} selected. As an alternative to Lorenzkraft can also be another automatic electromagnetic interaction with the overcurrent I ₂ , z. As a capacitive, inductive, electrostatic or other interaction, are used to limit the current. This automatically means that the movement of the movable electrode is triggered and controlled without active current measurement and without active control technology.

In a first operating state (FIG. ₁ a), an operating or rated current I _{1 flows} on a first or 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 stationary 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.

Preferably the resistance means 5 comprises a dielectric matrix 5, the wall-like webs 5a for dielectric separation of a plurality of channels 3a has for the liquid metal 3, wherein the webs 5a comprise a dielectric material in the direction of movement x increasing, and preferably non-linearly increasing resistance R _x. The webs 5a thus represent individual resistors 5a of the resistive element 5 with an increasing along the channel height and preferably non-linearly increasing electrical resistance R _x . At the height of the first position x _{1 of} the liquid metal 3, the webs 5a intermediate electrodes 2c to the electrically conductive connection of the channels 3a exhibit. The channels 3a are preferably arranged substantially parallel to each other. Thus, the current-limiting second current path 31 is formed by an alternating series connection of filled with liquid metal 3 channel regions 3a and the webs 5a, which act as progressive with their length and preferably non-linearly progressive individual resistors 5a of the resistive element 5.

2 and 3 show exemplary embodiments in which the movable electrode 3, 3 'comprises a solid-state conductor 3' with at least one sliding contact 2d and in the first operating state with the stationary electrodes 2a, 2b, in the second operating state at least on one side with the resistance element 5 and third operating state is electrically connected at least on one side with the insulator 8. Advantageously, the solid-state conductor 3 'is essentially made of light metal and / or in lightweight construction, for example made of metal-coated cork, and / or the sliding contact 2d is wetted with liquid metal to reduce friction. Fig. 2 shows an embodiment in which the solid-state conductor 3 'is rotatably connected at one end to the input electrode 2a and at the other end with the sliding contact slidably along a circular arc-shaped resistance element 5 is movable. Fig. 3 shows an embodiment in which the solid-state conductor 3, 3 'sliding contacts 2d has at both ends and between wall-like resistors 5a of the resistance means 5 as a balance beam over its entire length by the electromagnetic interaction against a restoring force F _r , in particular against gravity , can be raised. The path positions l ₁ , l ₁₂ , l _{2 of} the sliding contact ₂ d correspond to the aforementioned second positions x ₁ , x ₁₂ , x _{2 of} the liquid metal column 3. The extreme second position l ₁₂ may be in the area where the resistance means 5 in an insulator 8 passes, so that an insulation gap 32 for power cut is present.

In a transition from the first position x ₁ , l ₁ to the second position x ₁₂ , x ₂ , l ₁₂ , l ₂ , in particular to an extreme second position x ₂ , l ₂ , the liquid metal 3 or the solid conductor 3 'with sliding contact 2d guided along the resistive element 5. In order to achieve a gentle current limiting or switching-off characteristic, the resistance element 5 has an electrical resistance R _x , R ₁ for the second current path 31 which non-linearly increases along the direction of movement x, l of the movable electrode 3, 3 '. The resistance element 5 should have an ohmic component and is preferably purely ohmic with an electrical resistance R _x , R ₁ , which increases continuously with the second position x ₁₂ , x ₂ , l ₁₂ , l ₂ . 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.

It can also be connected in series with two current limiter 1 with anti-phase effective triggering of the electrode movement in order to achieve a current limit and possibly power cut in each half-wave current.

Fig. 4 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 nominal current path 30 and the current limiting path 31, there is an insulation gap 32, on which the webs 5a for current limiting pass into webs 8a for current isolation. The insulating webs 8a consist essentially 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 Thus, the liquid metal 3 between the rated current path 30, the current limiting path 31 and the insulation gap 32 for power cut movable, so that an integrated current-limiting switch 1 is realized on liquid metal base. Advantageously, the first current path 30 for operating current I ₁ , the second current path 31 for current limiting and 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-limiting switch 1, a dimensioning of the electrical resistance R _x , R ₁ as a function of the second position x ₁₂ , l _{12 of} the movable electrode 3, 3 '. Advantageously, the resistor R _x , R _{1 is selected} to be non-linearly increasing up to an extreme second position X ₂ , l ₂ to a maximum value R _x (x ₂ ), R ₁ (l ₂ ). Also intended for a given voltage level of the maximum value of R _x (x _2), R ₁ (l ₂₎ of the electrical resistance R _x, R ₁ in accordance with one to limiting current I ₂ to a finite value, or for switching off the operating current I ₁ to a dielectric insulation value are measured.

The electrical resistance R _x , R ₁ as a function R _x (x ₁₂ ), R ₁ (l ₁₂ ) of the second position x ₁₂ , l ₁₂ and a path-time characteristic x ₁₂ (t), l ₁₂ (t) of the movable Electrode 3, 3 'along the direction of movement x, l should be chosen so that in every second position x ₁₂ , x ₂ , l ₁₂ , l _{2 of} the movable electrode 3, 3', the product of electrical resistance R _x , R ₁ and Current I _{2 is} smaller than an arc ignition voltage U _b between the movable electrode 3, 3 'and the fixed electrodes 2a, 2b and optionally intermediate electrodes 2c and / or that a sufficient slope of the current limit for controlling network-related short-circuit currents i (t) is achieved.

In all the aforementioned embodiments, the electromagnetic drive means 2a, 2b, 20; 11; B _int, B _ext magnetic field means 2a, 2b, 20; 11 for generating the magnetic field B _ext, B _int, which exerts on the current flowing through the current I ₁ , I ₂ movable electrode 3, 3 'a Lorenz force F _mag with a force component parallel to the movement direction x, 1, so that the movable electrode. 3 3 'is movable between the first current path 30 for operating current I ₁ , the second current path 31 for current limiting and the isolation path 32 for current cutoff. The magnetic field means 2a, 2b, 20; 11, the power supply 2a, 2b; 20 to the current limiting device 1 to generate an internal, dependent from the limiting overcurrent I ₂ magnetic field B _int . In addition, the magnetic field means 2a, 2b, 20; 11 means 11 for generating an external controllable and in particular reversible magnetic field B _ext include.

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

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 $$\mathrm{m}\mathrm{•}{\mathrm{d}}^{\mathrm{2}}{\mathrm{x}}_{\mathrm{12}}\mathrm{/}{\mathrm{dt}}^{\mathrm{2}}\mathrm{+}\mathrm{\alpha }\mathrm{•}\mathrm{d}{\mathrm{x}}_{\mathrm{12}}\mathrm{/}\mathrm{dt}\left(\mathrm{t}\right)\mathrm{=}\mathrm{F}\mathrm{-}{\mathrm{F}}_{\mathrm{r}}\mathrm{,}$$

wobei F_r=Rückstellkraft, insbesondere F_r=F_g+F_cap mit F_g=m•g gleich Gravitationskraft, wobei m=Masse des Flüssigmetalls 3 und g=Erdbeschleunigung, und F_cap gleich Kapillarkraft.In connection with FIG. 5, the dimensioning of a liquid metal current limiter 1 will be discussed by way of example. 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: $${\mathrm{R}}_{\mathrm{x}}\left(\mathrm{t}\right)\mathrm{•}\mathrm{i}\left(\mathrm{t}\right)\mathrm{<}{\mathrm{U}}_{\mathrm{b}}\left(\mathrm{t}\right)$$

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

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 $$\mathrm{m}\mathrm{•}{\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="imgf0004.png"\; state="\{\{state\}\}">d</figure-callout>}}^{\mathrm{2}}{\mathrm{x}}_{\mathrm{12}}\mathrm{/}{\mathrm{<figure-callout\; id="2"\; label="dt"\; filenames="imgf0004.png"\; state="\{\{state\}\}">dt</figure-callout>}}^{\mathrm{2}}\mathrm{+}\mathrm{\alpha }\mathrm{•}\mathrm{d}{\mathrm{x}}_{\mathrm{12}}\mathrm{/}\mathrm{dt}\left(\mathrm{t}\right)\mathrm{=}\mathrm{F}\mathrm{-}{\mathrm{F}}_{\mathrm{r}}\mathrm{.}$$

where F _r = restoring force, in particular F _r = F _g + F _cap with F _g = m • g equals gravitational force, where m = mass of the liquid metal 3 and g = gravitational acceleration, and F _cap equals capillary force.

mit k=geometrieabhängige Proportionalitätskonstante. Bei externem Magnetfeld B gilt F = k'•i(t) mit k'=weitere Proportionalitätskonstante. Im Detail hängen k und k' von der Geometrie des Strombegrenzers 1, insbesondere der Struktur und Anordnung des Widerstandselements 5 sowie der Strompfade 30, 31 und der Isolationsstrecke 32, ab und von der Anordnung der Magnetfeldmittel 2a, 2b, 20.In FIG. 5, for example, an electromagnetic Lorenz force F = F _{mag was} assumed, which is exerted on the liquid metal 3 by self-interaction of the current i (t) to be limited. Then in addition $$\mathrm{F}\mathrm{=}\mathrm{k}\mathrm{•}{\mathrm{i}}^{\mathrm{2}}\left(\mathrm{t}\right)$$

with k = geometry-dependent proportionality constant. With an external magnetic field B, F = k '• i (t) with k' = further proportionality constant. In detail, k and k 'depend on the geometry of the current limiter 1, in particular the structure and arrangement of the resistance element 5 and the current paths 30, 31 and the insulation gap 32, and on the arrangement of the magnetic field means 2a, 2b, 20.

By way of example, FIG. 5 assumed a short-circuit 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.

The total resistance of the current limiter 1 is determined in the first operating state at nominal current I ₁ by the liquid metal sections 3 and can therefore be set to predetermined values by providing a suitable liquid metal cross section. The maximum resistance R _x (x ₁₂ ) of the current limiter 1 can be dimensioned by selecting the resistance material 5 and by its geometric shape in accordance with a desired voltage level and maximum allowable overcurrent I ₂ .

In particular, a resistance R _{x which} increases nonlinearly with the distance x can be realized by materials having different specific resistances. 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.

The threshold current I _th , from which the current limiting device 1 is activated, occurs when the electromagnetic drive force F _mag exceeds the restoring force F _r . In the exemplary embodiments according to FIGS. 1a, 1b, 4 and 6, the restoring force F _r = F _g + F _cap . From this, I _th can be estimated $${\mathrm{I}}_{\mathrm{th}}\mathrm{=}{\left[\left({\mathrm{F}}_{\mathrm{G}}\mathrm{+}{\mathrm{F}}_{\mathrm{cap}}\right)\mathrm{/}\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">k</figure-callout>}\right]}^{\mathrm{1}\mathrm{/}\mathrm{2}}$$

wobei A=Querschnittsfläche der Flüssigmetall-Kanäle 3a, ρ=Massendichte des Flüssigmetalls 3, d=Länge der magnetfelderzeugenden Spule in der Stromzuführung 2a, 2b, 20, µ=magnetische Permeabilität in der Spule bzw. im Flüssigmetall und N=Anzahl Windungen der Spule. Die Reaktionszeit t_u bis zur vollen Strombegrenzung, d. h. bis zum Erreichen der Endposition gemäss Fig. 1b (oder auch Fig. 2 oder Fig. 3), kann durch geeignete Dimensionierung der Magnetfeldmittel 2a, 2b, 20, 11 und der Rückstellkräfte F_g, F_cap auf vorgebbare Werte dimensioniert werden.In the simplified case, in which the capillary forces F _{cap are} negligible and the magnetic field is generated by a coil geometry applies $${\mathrm{I}}_{\mathrm{th}}\mathrm{=}{\left[\left(\mathrm{A}\mathrm{•}\mathrm{G}\mathrm{•}\mathrm{d}\mathrm{•}\mathrm{\rho }\right)\mathrm{/}\left(\mathrm{\mu }\mathrm{•}\mathrm{<figure-callout\; id="1"\; label="N"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">N</figure-callout>}\right)\right]}^{\mathrm{1}\mathrm{/}\mathrm{2}}\mathrm{.}$$

where A = cross-sectional area of the liquid metal channels 3a, ρ = mass density of the liquid metal 3, d = length of the magnetic field generating coil in the power supply 2a, 2b, 20, μ = magnetic permeability in the coil or in the liquid metal and N = number of turns of the coil , The reaction time t _u up to the full current limit, ie until reaching the end position according to FIG. 1b (or also FIG. 2 or FIG. 3), can be achieved by suitable dimensioning of the magnetic field means 2a, 2b, 20, 11 and the restoring forces F _g , F _cap be dimensioned to predeterminable values.

wobei h=x₂-x₁=Höhe der Flüssigmetall-Kanäle 3a.Fig. 1b shows the position of the liquid metal 3 in the current limiting case. Due to the current limiting effect, the electromagnetic force F _mag on the liquid metal 3 decreases and the liquid metal 3 flows under the action of the gravitational force F _g back to the starting position between the electrodes 2a, 2b, 2c. The reconnection time t _d can be estimated on the assumption that the capillary force F _cap and the electromagnetic force F _mag are negligible at a limited current i $${\mathrm{t}}_{\mathrm{d}}\mathrm{=}{\left[\left(\mathrm{2}\mathrm{•}\mathrm{H}\right)\mathrm{/}\mathrm{<figure-callout\; id="1"\; label="G"\; filenames="imgf0001.png,imgf0003.png"\; state="\{\{state\}\}">G</figure-callout>}\right]}^{\mathrm{1}\mathrm{/}\mathrm{2}}\mathrm{.}$$

where h = x ₂ -x ₁ = height of the liquid metal channels 3a.

The reconnection time t _d can be adapted to the requirements of different applications by a suitable design of the current limiter 1. In particular, the channel height h and the capillary forces F _cap influencing variables such as channel cross-sectional area A, channel geometry and surface condition of the channels, as well as the type of liquid metal 3 are to be selected accordingly.

wobei A=Querschnittsfläche der Flüssigmetallteile (wie zuvor), 1=Gesamtlänge des Strombegrenzers 1 oder des Widerstandselements 5, p'=mittlere Massendichte des Strombegrenzers 1 und c'=mittlere Wärmekapazität des Strombegrenzers 1. Die Verlustenergie E_loss ist im vorliegenden Fall der resistiven Strombegrenzung viel kleiner als bei Strombegrenzung durch Lichtbogen. Ein wesentlicher Vorteil des verteilten oder matrixartigen Widerstandselements 5 besteht auch darin, dass die Verlustleistung E_loss weitgehend homogen verteilt über das Volumen des Strombegrenzers 1 auftritt und dementsprechend die gesamte thermische Masse oder Wärmekapazität zur Absorption der Verlustenergie E_loss ausgeschöpft werden kann.In the thermal design of the current limiter 1 is to be noted that because of the short reaction times and Wiederanschaltzeiten the resistive element 5 can not be effectively cooled. The dissipated energy E _loss heats the current limiter 1. The temperature rise ΔT is approximately $$\mathrm{.DELTA.T}\mathrm{=}{\mathrm{e}}_{\mathrm{loess}}\mathrm{/}\left(\mathrm{A}\mathrm{•}\mathrm{l}\mathrm{•}\mathrm{\rho \text{'}}\mathrm{•}\mathrm{c\; \text{'}}\right)\mathrm{.}$$

where A = cross-sectional area of the liquid metal parts (as before), 1 = total length of the current limiter 1 or the resistance element 5, p '= average mass density of the current limiter 1 and c' = average heat capacity of the current limiter 1. The loss energy E _loss is in the present Case of resistive current limiting much smaller than current limiting by electric arc. A significant advantage of the distributed or matrix-like resistance element 5 is also that the power loss E _{loss occurs} largely homogeneously distributed over the volume of the current limiter 1 and accordingly the entire thermal mass or heat capacity for absorbing the loss energy E _loss can be exploited.

Fig. 6 shows a combined liquid metal current limiter 1 and liquid metal circuit breaker 1 with electromagnetic drive means 2a, 2b, 20; 11; B _int, B _ext 3 for the liquid metal, the magnetic field B _int can internally by the increased or efferent current conductor 20 and / or preferably selectable by an external magnetic field with respect to their direction of magnetic field source B _ext generated. In 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, in a third operating state, the liquid metal 3 can be moved along the opposite direction of movement -x to at least one third position x ₁₃ , x ₃ , wherein the liquid metal _{3 is} in series with an insulator 8 in the at least one third position x ₁₃ , x ₃ and thereby an isolation path 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. Fig. 3 shows in dashed lines the analogous case for negative deflections 1 and positions l ₁₃ , l _{3 of} a movably suspended solid conductor 3 '. In particular, the third operating state is triggered by a switch-off command, by means of which an external magnetic field B _ext between an operation of the device 1 as a current limiter and as a power switch is switched over. As liquid metal 3 are suitable for. As mercury, gallium, cesium, GaInSn.

Advantageously, the at least one 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 is realized relative to the currents to be switched, in particular to the rated current path 30, current limiting path 31 and current cutoff path 32. Also, the current limiter 1 in Fig. 6 as a current-limiting switch 1, as described above, be designed.

Applications of the device 1 relate u.a. the use as 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, fixed electrodes

2c

between electrodes

2d

mechanical sliding contact with path-dependent resistance

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

Container lid, housing wall, insulator

8th

Isolator for power interruption

8a

Single insulators

9

flexible membrane

10

Valve for liquid metal supply

11

magnetic field control

124

Back pressure vessel, trapped gas volume

α

coefficient of friction

B _ext , B _int

external, internal magnetic field

F _likes

magnetic force

F _r

Restoring force

i

electricity

I ₁

operating current

I ₂

limited overcurrent

k

proportionality

1, l ₁ , l ₂ , l ₁₂ , l ₃ , l ₁₃

Wiper positions

L

line inductance

P ₁ , P ₂ , P ₃

gas pressure

R _x , R ₁

Resistor of the current limiter

t

time variable

U _b

arc striking voltage

U _N

Mains voltage, operating voltage

V ₁ , V ₂ , V ₃

gas volume

x, x ₁ , x ₂ , x ₁₂ , x ₃ , x ₁₃

Positions of the liquid metal column

Claims (16)

1. Method for current limiting having a current limiting apparatus (1) which has stationary electrodes (2a, 2b) and at least one moving electrode (3, 3'), with an operating current (I₁) being carried on a first current path (30) through the current limiting apparatus (1) between the stationary electrodes (2a, 2b) in a first operating state, and with the first current path (30) being passed at least partially through the moving electrode (3, 3') which is located in a first position (x₁, l₁), with the at least one moving electrode (3, 3') being automatically moved along a movement direction (x, 1) to at least one second position (x₁₂, x₂, l₁₂, l₂) by an electromagnetic interaction with an overcurrent (I₂) to be limited, in a second operating state, with the moving electrode (3, 3') being guided along a resistance element (5) during a transition from the first position (x₁, l₁) to the second position (x₁₂, x₂, l₁₂, l₂), and being connected in series with the resistance element (5) in the at least one second position (x₁₂, X₂, l₁₂, l₂), thus forming a current-limiting second current path (31) through the current limiting apparatus (1), which second current path (31) has a predeterminable electrical resistance (R_x, R₁), characterized in that the moving electrode (3, 3') is connected in series with an isolator (8) in a third operating state, thus forming an isolation path (32) for power disconnection by the apparatus (1).
2. Method according to Claim 1, characterized in that the third operating state is initiated by a disconnection command, by means of which an external magnetic field (B_ext) is switched over between operation of the apparatus (1) as a current limiter and as a circuit breaker.
3. Method according to one of the preceding claims, characterized in that, in the third operating state,

   a) the moving electrode (3, 3') is moved along an opposite movement direction (-x, -1) to at least one third position (x₁₃, x₃, l₁₃, l₃) and

   b) the moving electrode (3, 3') is connected in series with the isolator (8) in the at least one third position (x₁₃, x₃, l₁₃, l₃) .
4. Method according to one of the preceding claims, characterized in that

   a) the moving electrode (3, 3') is automatically guided along the resistance element (5) to an extreme second position (x₂, l₂) by the electromagnetic interaction with the overcurrent (I₂) to be limited, and

   b) the extreme second position (x₂, l₂) is located in an area where the resistance element (5) merges into the isolator (8), so that the isolation path (32) is formed for current disconnection.
5. Method according to one of the preceding claims, characterized in that

   a) the resistance element (5) is chosen, in order to achieve a smooth disconnection characteristic, with an electrical resistance (R_x, R₁) of the second current path (31) which rises non-linearly along the movement direction (x, 1) of the moving electrode (3, 3') and/or

   b) the resistance element (5) is ohmic, and the electrical resistance (R_x, R₁) rises continuously with the second position (x₁₂, x₂, l₁₂, l₂) .
6. Method according to one of the preceding claims, characterized in that

   a) the second operating state is activated automatically by the overcurrent (I₂) in that the moving electrode (3, 3') through which the current flows is moved by an electromagnetic force (F_mag) which is at right angles to the current (I₂) through the moving electrode (3, 3') and at right angles to a magnetic field (B_ext, B_int) and has a force component parallel to the movement direction (x, l), with

   b) the magnetic field (B_ext, B_int) being chosen as an external magnetic field (B_ext) and/or as an internal magnetic field (B_int) which is produced by a current supply (2a, 2b; 20) to the current limiting apparatus (1).
7. Method according to one of the preceding claims, characterized in that the electrical resistance (R_x, R₁) is chosen as a function (R_x(x₁₂), R₁(l₁₂)) of the second position (x₁₂, l₁₂) as well as a movement-time characteristic (x₁₂(t), l₁₂(t)) of the moving electrode (3, 3') along the movement direction (x, 1) is chosen such that

   a) in every second position (x₁₂, x₂, l₁₂, l₂) of the moving electrode (3, 3'), the product of the electrical resistance (R_x, R₁) and the current (I₂) is less than the arc striking voltage (U_b) between the moving electrode (3, 3') and the stationary electrodes (2a, 2b) and, if appropriate, intermediate electrodes (2c), and/or

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

   a) the moving electrode (3, 3') is composed of a liquid metal (3) which is arranged in at least one channel (3a) in the current limiting apparatus (1), and can be moved along a height extent of the channel (3a) between the first current path (30) for the operating current (I₁), the second current path (31) for current limiting and the isolation path (32) for current disconnection, and

   b) in particular, in that a plurality of channels (3a) are separated from one another by wall-like webs (5a, 8a), which have intermediate electrodes (2c) for the operating current (I₁) to pass through in the area of the first current path (30), have individual resistors (5a) of the resistance element (5) in the area of the second current path (31), and merge into webs (8a) for current isolation in the area of the isolation path (32).
9. Method according to one of the preceding claims, characterized in that

   a) the moving electrode (3, 3') comprises a solid-state conductor (3') with at least one sliding contact (2d), is electrically connected to the stationary electrodes (2a, 2b) in the first operating state, is electrically connected on at least one side to the resistance element (5) in the second operating state, and is electrically connected on at least one side to the isolator (8) in the third operating state, and

   b) in particular, in that the solid-state conductor (3') is manufactured essentially from light alloy and/or with a lightweight structure, and/or the sliding contact (2d) is wetted with liquid metal in order to reduce the friction.
10. Apparatus for current limiting (1), in particular for carrying out the method according to one of the preceding claims, comprising stationary electrodes (2a, 2b) and at least one moving electrode (3, 3'), with an operating current (I₁) being carried on a first current path (30) through the current limiting apparatus (1) between the stationary electrodes (2a, 2b) in a first operating state, and with the first current path (30) being passed at least partially through the moving electrode (3, 3') which is located in a first position (x₁, l₁), with electromagnetic drive means (2a, 2b, 20; 11; B_int, B_ext) being provided for automatic movement of the moving electrode (3, 3') along a movement direction (x, 1) to at least one second position (x₁₂, x₂, l₁₂, l₂) in the event of an overcurrent (I₂), with an electrical resistance means (5) with a predeterminable electrical resistance (R_x) being provided and, in a second operating state, with the moving electrode (3, 3') being connected at least partially in series with the resistance means (5) and together with said means forming a second current path (31) on which the operating current (I₁) can be limited to a current (I₂) to be limited, characterized in that the moving electrode (3, 3') is connected in series with an isolator (8) in a third operating state, thus forming an isolation path (32) for power disconnection by the apparatus (1).
11. Apparatus (1) according to Claim 10, characterized in that the electromagnetic drive means (2a, 2b, 20; 11; B_int, B_ext) comprise magnetic field means (2a, 2b, 20; 11) for producing a magnetic field (B_ext, B_int), which exerts a Lorenz force (F_mag) with a force component parallel to the movement direction (x, 1) on the moving electrode (3, 3') through which the current (I₁, I₂) flows, such that the moving electrode (3, 3') can be moved between the first current path (30) for the operating current (I₁), the second current path (31) for current limiting and the isolation path (32) for current disconnection.
12. Apparatus (1) according to one of Claims 10-11, characterized in that

    a) the magnetic field means (2a, 2b, 20; 11) have a current supply (2a, 2b; 20) for the current limiting apparatus (1) in order to produce an internal magnetic field (B_int) which is dependent on the overcurrent (I₂) to be limited, and/or

    b) the magnetic field means (2a, 2b, 20; 11) have means (11) for producing an external controllable magnetic field (B_ext).
13. Apparatus (1) according to one of Claims 10-12, characterized in that

    a) the magnetic field (B_ext, B_int) is designed on the basis of an overcurrent (I₂) to be limited and of a movement-time characteristic (x(t), 1(t)), which is required for this purpose, of the moving electrode (3, 3') in the second current path (31) and/or

    b) the resistance means (5) have an electrical resistance (R_x, R₁) for arc-free current limiting, which increases non-linearly along the movement direction (x, 1) to an extreme second position (x₂, l₂), for the second current path (31).
14. Apparatus (1) according to one of Claims 10-13, characterized in that

    a) the moving electrode (3, 3') is composed of a liquid metal (3) which is moved by the magnetic field means (2a, 2b, 20; 11) in the liquid aggregate state, and/or

    b) the moving electrode (3, 3') has a solid-state conductor (3') with at least one sliding contact (2d), with the solid-state conductor (3') being raised on one side or both sides by the magnetic field means (2a, 2b, 20; 11) against a resetting force (F_r), in particular against the force of gravity.
15. Apparatus (1) according to one of Claims 10-14, characterized in that

    a) the first current path (30) for the operating current (I₁) , the second current path (31) for current limiting and the isolation path (32) for current disconnection are arranged essentially at right angles to the movement direction (x, 1) and/or essentially parallel to one another, and/or

    b) the 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).
16. Electrical switchgear, in particular a high-voltage or medium-voltage switchgear assembly, characterized by an apparatus (1) according to one of Claims 10-15.

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