EP1644952A1

EP1644952A1 - Method and device for current limitation with an automatic current limiter

Info

Publication number: EP1644952A1
Application number: EP04738058A
Authority: EP
Inventors: Kaveh Niayesh; Friedrich Koenig
Original assignee: ABB Research Ltd Switzerland; ABB Research Ltd Sweden
Current assignee: ABB Research Ltd Switzerland; ABB Research Ltd Sweden
Priority date: 2003-07-10
Filing date: 2004-07-01
Publication date: 2006-04-12
Anticipated expiration: 2024-07-01
Also published as: PL1644952T3; CN100446152C; CN1820340A; DE502004005030D1; EP1644952B1; ATE373871T1; KR20060036448A; WO2005006373A1; US20070041138A1

Abstract

The invention relates to a method and a device (1) for combined current limitation and power breaking and to a switchgear having said device (1). In a combined current limiter/power braker (1) according to the invention, a movable electrode (3, 3') is guided automatically along a resistance element (5) for the current limiting path (31) by an overcurrent-dependent force (Fmag) for the purpose of current limitation and brought to an insulator (8) in a serial arrangement for power breaking purposes. Examples of embodiments are, inter alia, the utilization of Lorenz force for automatic current limitation; movable electrodes (3, 3') realized by means of liquid metal (3) or a movable solid conductor (3'); an electrical resistance (RX) increasing non-linearly in the direction of movement (x) for smooth power limitation characteristics and a resistance element (5) in the form of a dielectric matrix (5) with several channels (3a) for the liquid metal (3). Amongst the advantages achieved are electric arc-free, reversible current limitation and power breaking, which is also suitable for high voltages and currents, rapid reaction times, little wear and easy maintenance.

Description

DESCRIPTION

Method and device for current limiting with a self-operated current limiter

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 DE 40 12 385 AI discloses a current-controlled shutdown device is based, the operating principle 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 DE 26 52 506 a high current electrical switch with liquid metal is disclosed. On the one hand, a liquid metal mixture is used for wetting solid metal electrodes and for reducing the contact resistance. In this process, the liquid metal is removed by mechanical displacement. tion, 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 DE 199 03 939 AI discloses a self-recovering current limiting device with liquid metal. Between two solid metal electrodes, a pressure-resistant insulating housing is arranged, in which liquid metal is arranged in compressor chambers and in intermediate connecting channels connecting the compressor chambers, so that a current path is provided for nominal currents between the solid 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. As a result of avalanche-like formation of gas bubbles in the connection channels, the liquid metal evaporates into the compressor chambers, so that a current-limiting arc is ignited in the now liquid-metal-empty connection channels. After the overcurrent has subsided, the liquid metal can condense again and the current path is ready for operation again. In 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 when the liquid metal evaporates due to evaporation. 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. By recon- densation of the liquid metal is immediately ^'again after a short circuit, a conductive state, so that no off-state is present.

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 resistance element and brought into a second position in which it is in series with the resistance 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 the US Pat. No. 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 through the current limiting device on a first current path and 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 is guided in a transition 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 s Furthermore, in a third operating state, the movable electrode is in series with an insulator and thereby an insulation path 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 conductors 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 St ombegrenzungsverfahren 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 opposition Stand 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 electrode deflection required for the required electrical resistance.

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 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 FIGS. 1 a, 1 b show a self-actuated current-limiting device according to the invention with liquid metal in nominal current operation and in the current limiting case;

2, 3 show two self-operated current limiting devices according to the invention with mechanical sliding contact in rated current operation (dot-dashed line) and in current limiting case; Fig. 4 shows a current limiting switch with liquid metal trapping mechanism in nominal current operation;

Fig. 5 is a graph showing the variation of the resistance of the current limiter as a function of the position of the liquid metal column; and

6 shows a combined liquid metal current limiter and liquid metal power switch with external magnetic field drive for the liquid metal.

In the figures, like parts are given the same reference numerals. WAYS OF IMPLEMENTING 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. Column above the liquid metal 3 may for example be an inert gas, an insulating liquid (non Pictured here Ausweichvol ^'umen) or vacuum be disposed.

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 moved by the forced movement selectively between the different positions x _{1 # i2} 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 gap 32 is present. Preferably, the second operating state is automatically activated by the overcurrent I ₂ by moving the current-passing movable electrode 3, 3 'by an electromagnetic force F _mag perpendicular to the current I ₂ through the movable electrode 3, 3' and perpendicular to a magnetic field B _e χ _{t #} Bi _nt and having a force component parallel to the movement direction x, 1, wherein the magnetic field B _ext , Bi _n as an external magnetic field B _ex t and / or as an internal, from a power supply 2a , 2 B; 20 is generated to the current limiting device 1 generated magnetic field Bint. As an alternative to the Lorenz force, another automatic electromagnetic alternating Effect 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 _{x 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. Here, the liquid metal 3 is in the first position x _lf wetted at least partially the fixed electrodes 2a, 2b, 2c and bridges the channels 3a electrically conductive. 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, to 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 χ ₂ , 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 Xj. 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.

FIGS. 2 and 3 show exemplary embodiments in which the movable electrode 3, 3 'comprises a solid conductor 3 ¹ with at least one sliding contact 2 d and in the first operating state with the stationary electrodes 2 a, 2 b 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 conductor 3 'is made essentially of light metal and / or lightweight construction, for example of metal-coated cork, and / or the sliding contact 2d is wetted with liquid metal to reduce friction. 2 shows an exemplary embodiment in which the solid conductor 3 ^{1 is} rotatably connected at one end to the input electrode 2 a and is slidably movable at the other end with the sliding contact along a circular arc-shaped resistance element 5. Fig. 3 shows an embodiment in which the Festkorperleiter 3, 3 'at both ends sliding contacts 2d and wall-like resistors 5a of the resistance means 5 as a balance beam along its entire length by the electromagnetic interaction against a restoring force F _r , in particular against the heavy - force, can be raised. The path positions li, I ₁₂ , 1 _{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 extremal second position 1 ₁₂ may be in the area where the resistance means 5 in an insulator goes over, so that an insulation gap 32 is present for power cut. In a transition from the first position x _lt l _x to the second position Xι ₂ , x ₂ 1-.2, 1 _{2 /} in particular to an extreme second position x ₂ , 1 ₂ , the liquid metal 3 or the solid conductor 3 'with sliding contact 2d along the resistance element 5 out. In order to achieve a gentle current limiting or switch-off characteristic, the resistance element 5 has an electrical resistance R _x , Ri for the second current path 31 which increases non-linearly along the movement direction x, 1 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 , Ri, which increases continuously with the second position x ₁₂ , x _{2 /} I ₁₂ 1 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 is also possible for two current limiters 1 to be connected in series with antiphase-effective tripping of the electrode movement, in order to achieve a current limitation and, if appropriate, a power cutoff in each current half-cycle.

4 shows a variant of the current limiter 1, in which a collecting container 3b for receiving the liquid metal 3 and for providing an insulation gap 32 for power cut-off 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 implemented liquid metal-based. Advantageously, the first current path 30 for operating current Ii, 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 , Ri as a function of the second position x ₁₂ , I _{12 of} the movable electrode 3, 3 '. Advantageously, the resistor R _x , Ri is selected up to a extre alen second position x ₂ , I ₂ to a maximum value R _x (x ₂ ), Rι (l ₂ ) non-linear rising. Also, for a given voltage level, the maximum value R _x (x ₂ ), Rι (l ₂ ) of the electrical resistance R _x , Ri should be set to a finite value or to shut off the operating current Ii to a dielectric isolation value, in accordance with a current I ₂ to be limited become.

The electrical resistance R _x , Ri as a function R _x (ι ₂ ) / ι (li2) of the second position x ₁₂ , I ₁₂ and a path-time characteristic Xi ₂ (t), li ₂ (t) of the movable electrode 3, 3 'along the direction of movement x, 1 should be chosen so that in every second position x ₁₂ , x ₂ , I12 I2 of the movable electrode 3, 3', the product of electrical resistance R _x , Ri and current I _{2 is} smaller than a Lichtbogenzündspannung U _b between the movable electrode 3, 3 ¹ and the stationary electrodes 2 a, 2 _b and optionally intermediate electrodes 2 c is 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; Bin- / B _ext magnetic field means 2a, 2b, 20; 11 for generating the magnetic field B _ext , Bi _nt , which exerts on the current flowing through the current I _lt 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 ¹ is movable between the first current path 30 for operating current Ii, the second current path 31 for current limiting and the insulation path 32 for power cutoff. The magnetic field means 2a, 2b, 20; 11, the power supply 2a, 2b; 20 to the current limiting device 1 include to generate an internal, dependent from the limiting overcurrent I ₂ magnetic field Bι _nt . In addition, the magnetic field means 2a, 2b, 20; 11 means 11 for generating an external controllable and in particular reversible magnetic field B _ex t include.

In connection with FIG. 5, the dimensioning of a liquid metal current limiter 1 will be discussed by way of example. For controlling short-circuits, a resistance R _{x of} the current limitation dependent on the current network parameters and the breakdown behavior of the contacts 2 a, 2 b that are to be disconnected is 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: R _x (t) ^"i (t) <U _b (t) (Eq) R _x (t) * i (t) + L * di / dt (t) = U _N (t) (G2) 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 _{Ne 2} << 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 Xi2 (), the coefficient of friction α and the driving force F m ^» d ² x ₁₂ / dt ² + α • dx ₁₂ / dt (t) = F - F _r , (G3) 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.

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 F = k • i ² (t) applies additionally _. (G4) with k = geometry-dependent proportionality constant. With an external magnetic field B we have F = k '* i (t) with k' = more

Proportionality. In detail, k ¹ and k depend on the geometry of the current limiter 1, in particular the

Structure and arrangement of the resistive element 5 and the

Current paths 30, 31 and the isolation path 32, from and from the arrangement of the magnetic field means 2a, 2b, 20th

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, the equations (G2) are obtained by solving - (G4) under the boundary condition (Eq) of the resistance R _x (t) and the path-time characteristic Xι ₂ (t) of the liquid metal 3 and, finally, by the elimination of the time dependence of the resistance R _x (xι ₂ ) as a function of the second position x _i2 , as shown in Fig. 5 logarithmic. Starting from the first position x _{i #} ie when the liquid metal 3 is detached from the fixed electrodes 2 a, 2 b, 2 c, R _x initially increases disproportionately with the second position x ₁₂ , then increases linearly in a phase in which the in-line inductance L stored energy must be absorbed and then goes in a region where the current i is already limited and larger R _{x are} tolerable, again in a steeper, d. h-disproportionate increase R _x (x _i2 ) via. The total resistance of the current limiter 1 is determined in the first operating state at nominal current I _λ 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_. ₂ ) 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 permissible 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 a variable specific resistance.

The threshold current I _t h, 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. 1 a, 1 b, 4 and 6, the restoring force F _r = F _g + F _cap . From this, Ih can be estimated to It _h = [(F _g + F _cap ) / k] ^1/2 . (G6)

In the simplified case, in which the capillary forces F _{cap are} negligible and the magnetic field is generated by a coil geometry, I th = t (A ^« g • d ^« p) / (μ ^« N)] ^{1 2} , (G7) where A = cross-sectional area of the liquid metal channels 3a, p = 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 else FIG. 2 or FIG. 3), 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.

Fig. Lb 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 restart time t _d, assuming that the capillary force F _cap and the electromagnetic force F _mag with limited current i are negligible advertising, estimated to be t _d = [(2 • h) / g] ^1/2, (G8 ) where h = x ₂ -Xι = height of the liquid metal channels 3a.

The reconnection time t can be adapted to the requirements of different applications by means of 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 quality of the channels, and the type of liquid metal 3 are to be selected accordingly. 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 _1OS3 heats the current limiter 1. The temperature rise ΔT is approximately ΔT = E o _osa / (A • 1 * p '"c'), (G9) where A = cross-sectional area of the liquid metal parts (as before), l = 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 _{Eι OSs} 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 Eι _{oss 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 of energy Eι _oss 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; Bint / B _exC for the liquid metal 3. The magnetic field Bi _nt can be generated internally by the incoming or outgoing current conductor 20 and / or preferably by an external, with respect to their magnetic field direction switchable magnetic field source B _ext . 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, the liquid metal 3 in a third operating state along the opposite direction of movement -x in at least a third position Xι ₃ , x _{3 are} moved, wherein the liquid metal 3 in the at least one third position Xι ₃ , x _{3 is} in series with an insulator 8 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 analog case for negative deflections 1 and positions lι ₃ , 1 _{3 of} a movably suspended solid state conductor 3 '. In particular, the third operating state is triggered by a switch-off _command , by means of which an external magnetic field B _{exC is switched over} between operation of the device 1 as a current limiter and as a power switch. As liquid metal 3 are suitable for. Mercury, gallium, cesium, galnSn. 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 relative to the currents to be switched, in particular to Nennstromp ad 30, current limiting path 31 and power cut-off path 32, realized. 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 intermediate electrodes

2d mechanical sliding contact with path-dependent resistor 20 Power supply, conductor

3 liquid metal

3a channels for liquid metal

3b collecting container for liquid metal

3c liquid metal feed 30 current path, first current path

31 current path for current limiting, second current path

32 power interruption path, isolation route

4 liquid metal containers

5 current limiting resistive element, resistance matrix for liquid metal 5a individual resistors

6 Container lid, housing wall, insulator

8 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 /} Bi _n t external, internal magnetic field

F _likes magnetic force

F _r i restoring force current Ii operating current

1 ₂ Limited overcurrent k Proportionality constant

1, li, 1 ₂ , 1 ₂ , 1 _3; lι ₃ sliding contact positions

L mains inductance Pi, P ₂ , P ₃ gas pressure

R _{X /} Ri Current limiter resistor t Time variable

U _b arc ignition voltage

U _N mains voltage, operating voltage V _1; V ₂ , V ₃ gas volume x, x _1; x ₂ , x _i2 , x ₃ , x ₁₃ positions of the liquid metal column

Claims

A method of current limiting (1) comprising a current limiting device (1) comprising fixed electrodes (2a, 2b) and at least one movable electrode (3, 3 '), wherein in a first operating state between the stationary electrodes (2a, 2b) an operating current (Ii) on a first current path (30) through the current limiting device (1) is guided and the first current path (30) at least partially through the in a first position (xi, li) located movable electrode (3, 3 ') out is, in a second operating state, the at least one movable electrode (3, 3 ') automatically by an electromagnetic interaction with a to be limited overflow (I ₂ ) along a direction of movement (x, 1) in at least one second position (x- _.2 , x ₂ , lι ₂ , 1 ₂ ) is moved, the movable electrode (3, 3 ') in a transition from the first position (x _l7 li) to the second position (x _i2 , x ₂ , I12, I2) along a resistance element (5) is guided and in the at least one second position (x _i2 , x ₂ / I12 / 1 ₂ ) in series with the resistance element (5) and thereby a current limiting second current path (31) by the current limiting device (1) is formed, the one predeterminable electrical resistance (R _x , R _x ), characterized in that in a third operating state, the movable electrode (3, 3 ') is in series with an insulator (8) and thereby an insulation gap (32) for power shutdown by the device (1) is formed.

2. The method according to claim 1, characterized in that the third operating state is triggered by a shutdown command by which an external magnetic field (B _ext ) between an operation of the device (1) is switched as a current limiter and as a power switch.

3. The method according to any one of the preceding claims, characterized in that in the third operating state a) the movable electrode (3, 3 ') along an opposite direction of movement (-x, -1) in at least one third position (xι _3rd / x ₃ li3 1 ₃ ) is moved and b) the movable electrode (3, 3 ') in the at least one third position (xι ₃ , x ₃ , I13, 1 ₃ ) in series with the insulator (8).

4. The method according to any one of the preceding claims, characterized in that a) the movable electrode (3, 3 ') automatically by the electromagnetic interaction with the overcurrent (I ₂ ) to be limited along the resistive element (5) to an extreme second position (x ₂ , 1 ₂ ) is guided and b) the extremal second position (x ₂ , 1 ₂ ) in a region where the resistance element (5) merges into the insulator (8), so that the insulation gap (32) for Power cut is formed.

5. The method according to any one of the preceding claims, characterized in that a) the resistance element (5) to achieve a gentle turn-off with a along the direction of movement (x, 1) of the movable electrode (3, 3 ') non-linearly increasing electrical resistance ( R _x , Ri) is selected for the second current path (31) and / or b) the resistance element (5) is ohmic and the electrical resistance (R _x , Ri) is continuous with the second position (x _i2 , x _{2 /} I _{12 /} 1 ₂ ) increases.

6. The method according to any one of the preceding claims, characterized in that a) the second operating state by the overcurrent (I ₂ ) is automatically activated by the current through flossene movable electrode (3, 3 ') by an electromagnetic force (F _mag ) is moved perpendicular to the current (I ₂ ) by the movable electrode (3, 3') and perpendicular to a magnetic field (B _ex , B _int ) and having a force component parallel to the direction of movement (x, 1), wherein b) the magnetic field (B _ex , Bι _nt ) as an external magnetic field (B _ext ) and / or as an internal, from a power supply (2a, 2b; 20) to the current limiting device (1) generated magnetic field (B _int ) is selected.

7. The method according to any one of the preceding claims, characterized in that the electrical resistance (R _x , Ri) as a function (R _x (xι ₂ ), Rι (lι ₂ )) of the _second position (x _i2 , 1 ₁₂ ) and a path-time characteristic (x ₁₂ (t), l _i2 (t)) of the movable electrode (3, 3 ¹ ) along the direction of movement (x, 1) are chosen such that a) in every second position (xι ₂ , x ₂ , li _{2 #} I ₂ ) of the movable electrode (3, 3 ¹ ) the product of electrical resistance (R _x , RjJ and current (I ₂ ) smaller than an arc ignition voltage (U _b ) between the movable electrode (3, 3 ¹ ) and the fixed electrodes (2a, 2b) and optionally intermediate electrodes (2c) and / or b) a sufficient slope of the current limit for controlling network-related short-circuit currents (i (t)) is achieved.

8. The method according to any one of the preceding claims, characterized in that a) the movable electrode (3, 3 ') comprises a liquid metal (3) which is arranged in at least one channel (3a) of the current limiting device (1) and along a Hδhenerstreckung the channel (3a) between see the first current path (30) for the operating current (Ii), the second current path (31) for Strombe- and b) in particular that a plurality of channels (3a) are separated from one another by wall-like webs (5a, 8a) which in the region of the first current path (30) have intermediate electrodes (2c) for passing through the Operating current (Ij), in the region of the second current path (31) have individual resistors (5a) of the resistive element (5) and in the region of the insulation gap (32) in webs (8a) for current isolation.

9. The method according to any one of the preceding claims, characterized in that a) the movable electrode (3, 3 ¹ ) comprises a Festkorperleiter (3 ') having at least one sliding contact (2d) and in the first operating state with the fixed electrodes (2a, 2b), in the second operating state at least on one side with the resistance element (5) and in the third operating state at least on one side with the insulator (8) is electrically connected and b) in particular that the solid conductor (3 ¹ ) consists essentially of light metal and / or in Lightweight construction is made and / or the sliding contact (2d) is wetted with liquid metal to reduce friction.

10. Device for current limiting (1), in particular for carrying out the method according to one of the preceding claims, comprising fixed electrodes (2a, 2b) and at least one movable electrode (3, 3 ¹ ), wherein in a first operating state between the fixed Electrodes (2a, 2b) a first current path (30) for an operating current (Ii) by the current limiting device (1) is present and the first current path (30) at least partially by the in a first position (x _{1 #} l) located movable electrode (3, 3 '), wherein electromagnetic drive means (2a, 2b, 20, 11, B _int , B _ex ) are used for Ström (I ₂ ) self-actuated moving the movable electrode (3, 3 ¹ ) along a direction of movement (x, 1) in at least one second position (x _i2 , x ₂ , lι ₂ , 1 ₂ ) are present, electrical resistance means (5) with a predeterminable electrical resistance (R _x ) are present and in a second operating state, the movable electrode (3, 3 ') at least partially in series with the resistance means (5) and forms together with these a second current path (31) on which the operating current (I _α ) can be limited to a current (I ₂ ) to be limited, characterized in that in a third operating state the movable electrode (3, 3 ¹ ) is connected in series with an insulator (8) and thereby an insulation gap (32 ) is present for power cut-off by the device (1).

11. The device (1) according to claim 10, characterized in that the electromagnetic drive means (2a, 2b, 20; 11; B _int , B _ext ) magnetic field means (2a, 2b, 20; 11) for generating a magnetic field (B _ext , Bi _nt ), which exerts a Lorentz force (F _mag ) with a force component parallel to the direction of movement (x, 1) on the movable electrode (3, 3 ') flowing through the current (Ii, I ₂ ), so that the movable electrode (3, 3 ') is movable between the first current path (30) for operating current (Iχ), the second current path (31) for current limiting and the isolation path (32) for current cutoff.

12. The device (1) according to any one of claims 10-11, characterized in that a) the magnetic field means (2a, 2b, 20; 11) comprise a power supply (2a, 2b, 20) to the current limiting device (1) to a generate internal magnetic field (Bi _nt ) dependent on the limiting overcurrent (I ₂ ) and / or b) the magnetic field means (2a, 2b, 20, 11) comprise means (11) for generating an external controllable magnetic field (B _ex ).

13. The device (1) according to any one of claims 10-12, characterized in that a) the magnetic field (B _ex t _/ Bi _nt ) in accordance with a to be limited overcurrent (I ₂ ) and a travel-time characteristic required for this purpose ( x (t), 1 (t)) of the movable electrode (3, 3 ') in the second current path (31) is designed and / or b) the resistance means (5) for arc current limiting a along the direction of movement (x, 1 ) to an extreme second position (x ₂ , 1 ₂ ) of non-linearly increasing electrical resistance (R _x , R _x ) for the second current path (31).

14. The device (1) according to any one of claims 10-13, characterized ^{4 '} "characterized in that a) the movable electrode (3, 3 ¹ ) comprises a liquid metal (3) by the magnetic field means (2a, 2b, 20 11) is moved in the liquid state of aggregation and / or b) the movable electrode (3, 3 ¹ ) comprises a solid conductor (3 ') with at least one sliding contact (2d), the solid conductor (3 ¹ ) being driven by the magnetic field means (2a, 2b, 20, 11) against a restoring force (F _r ), in particular against gravity, is raised on one or both sides.

15. The device (1) according to any one of claims 10-14, characterized in that a) the first current path (30 for operating current (I _α ), the second current path (31) for current limiting and the insulation gap (32) for power shutdown in are arranged substantially perpendicular to the direction of movement (x, 1) and / or substantially parallel to each other and / or b) 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).

16. Electrical switchgear, in particular high or medium voltage switchgear, characterized by a device (1) according to any one of claims 10-15.