Patent Grant
7151331
The invention relates to the area of primary engineering for electrical switchgear assemblies, especially current limiting and circuit breaking in high, medium or low voltage switchgear assemblies. It is based on a process and a device for current limiting or circuit breaking and a switchgear assembly with such a device as claimed in the preamble of the independent claims.
DE 26 52 506 discloses an electrical high current switch with liquid metal. On the one hand, a liquid metal mixture is used for wetting the solid metal electrodes and for reducing the contact resistance. Here the liquid metal is driven against the force of gravity by mechanical displacement, for example by movable contacts or pneumatically driven plunger pistons into the contact gap. The liquid metal can be additionally stabilized and fixed in the contact gap by the pinch effect according to which a current-carrying conductor undergoes radial striction by the current which is flowing through it. External magnetic fields and magnetic stray fluxes, for example by current feeds, can cause flow instabilities in the liquid metal and are shielded and are optionally allowed during disconnection in order to support extinguishing of the arc in the liquid metal.
The disadvantage is that gradual current limitation is not possible and arcs between the solid electrodes cause oxidation in the liquid metal. The design of the high current switch comprises seals for liquid metal, inert gas or a vacuum, and is accordingly complex.
DE 40 12 385 A1 discloses a current-controlled interrupting device with an operating principle which is based on the pinch effect with liquid metal. There is an individual, narrow, liquid metal-filled channel between the two solid metal electrodes. For an overcurrent the liquid conductor as a result of electromagnetic force is constricted by the pinch effect so that the current itself pinches and separates the liquid conductor. The displaced liquid metal is collected in a storage tank and after the overcurrent event flows back again. Contact separation takes place without an arc. But the device is only suited for relatively small currents, low voltages and slow interruption times, and therefore does not offer a lasting off state.
DE 199 03 939 A1 discloses a self-recovering current limiting means with liquid metal. There is a pressure-proof insulating housing between the two solid metal electrodes; in it there is liquid metal in the compressor spaces and in the connecting channels which lie in between and which connect the compressor spaces, so that there is a current path for nominal currents between the solid electrodes. In the connecting channels the current path is narrowed relative to the compressor spaces. The connecting channels are greatly heated during short circuit currents and evolve a gas. Avalanche-like gas bubble formation in the connecting channels vaporizes the liquid metal into the compressor spaces so that a current limiting arc is ignited in the connecting channels from which liquid metal has now been removed. After decay of the overcurrent the liquid metal can condense again and the current path is again ready for operation.
WO 00/77811 discloses a development of the self-recovering current limiting means. The connecting channels are conically widened to the top, so that the fill level of the liquid metal can be varied and the rated current carrying capacity can be changed over a wide range. Moreover, a meandering current path is formed by an offset arrangement of the connecting channels so that in overcurrent-induced vaporization of the liquid metal a series of current-limiting arcs is ignited. These pinch effect current limiters require a structure which is very stable with respect to pressure and temperature; this is structurally complex. Major wear within the current limiters occurs due to current limiting by arc and burn-off residues can contaminate the liquid metal. Recondensation of the liquid metal causes a conductive state immediately after a short circuit so that there is no off state.
This application refers to the prior art which is disclosed in utility model DE 1 802 643. It shows a call device for filling stations in which a bell switch is electrically closed by a liquid metal by a vehicle rolling over an air-filled hose and it's thus being compressed such that the escaping air moves the liquid metal column between the bell contacts. The liquid metal is moved purely passively by an external action, specifically by a vehicle which is to be detected. Since the liquid metal column which is captured in the hose acts as a vehicle detector, there is no self-contained control for specific opening and closing of the switch by means of the liquid metal.
A process, a device and an electrical switchgear assembly with such a device are disclosed for improved and simplified current switching.
In a first aspect, a process is disclosed for current limiting and/or circuit breaking with a liquid metal current switch which comprises solid electrodes and a liquid metal tank with at least one channel for a liquid metal, in the first operating state between the solid electrodes an operating current being routed on a first current path through the current switch and the first current path being routed at least partially through the liquid metal which is in the first position, in a second operating state the liquid metal being moved by a dielectric fluid drive which is controlled by a control along one direction of motion into at least one second position, the working fluid being dielectric and acting mechanically directly with a definable drive pressure on one surface of the liquid metal, and the liquid metal in at least one second position being located at least partially, especially completely in series with the dielectric or the resistance material and in this way a current-limiting and/or current-interrupting second current path being formed by the current switch, for a given voltage level the maximum electrical resistance of the dielectric being dimensioned to a finite value according to the current which is to be limited or to a dielectric insulation value for interrupting the current. The working fluid is moved into direct physical contact with the liquid metal, and in the second operating state, when the liquid metal is displaced between the solid electrodes and thus the liquid metal contact is opened, bridges a dielectrically insulating distance between the solid electrodes. The fluid drive is especially suited for an arc-free current limiter, for circuit breakers with or without arc formation, and for current-limiting circuit breakers. The process can also be used at very high voltage levels. The current switching with a fluid-driven liquid metal takes place reversibly and is therefore maintenance-friendly and economical. The fluid drive is moreover characterized by high reliability and low wear.
In a first embodiment, the dielectric working fluid is a dielectric gas and or a dielectric liquid, and mixing of the fluid with the liquid metal is largely avoided. With a dielectric gas drive an especially high dielectric strength can be achieved. With a dielectric liquid drive an especially fast reaction time of the current switch can be implemented.
The embodiment as shown in
An exemplary embodiment has the advantage that progressive current limitation can be accomplished with a gentle current limiting or interruption characteristic which is as free of arcs as possible.
An advantageous configuration is also disclosed for a fluid operated current-limiting switch or current limiter with an integrated switch.
An especially simple configuration of a fluid pressure drive with pressurized storage tanks for a gas or generally for a working fluid is also disclosed.
An exemplary piezo-liquid metal drive has the advantage of high reliability, low wear and efficient pressure transfer from the working fluid to the liquid metal. An especially fast reaction time of the current switch is implemented due to the incompressibility of the drive fluid.
Other exemplary embodiments relate to an especially simple configuration for the piezodrive with liquid metal, the dielectric strength in the contact-opened state being favorably influenced by the choice of the drive fluid, and dimensioning criteria for an advantageous mechanical layout of the piezo-fluid drive.
In another aspect, the invention relates to a liquid metal current switch for current limiting and/or circuit breaking, especially for executing the process, comprising solid electrodes and a liquid metal tank with at least one channel for a liquid metal, in a first operating state between the solid electrodes there being a first current path for an operating current through the current switch and the first current path being routed at least partially through the liquid metal which is in the first position, the dielectric fluid drive having a working fluid and a control, and being designed to move the liquid metal along one direction of motion into at least one second position, furthermore the working fluid being dielectric and acting mechanically directly on one surface of the liquid metal with a definable drive pressure, in the liquid metal tank there being a dielectric or a resistance material and in the second operating state the liquid metal in at least one second position being at least partially in series with the dielectric or the resistance means and in this way forming a current-limiting and/or current-interrupting second current path in the current switch, for a given voltage level the maximum electrical resistance of the dielectric being dimensioned to a dielectric insulating value for interrupting the current or to a finite value according to the current which is to be limited.
Components and dimensioning criteria are disclosed for optimum design of the fluid drive and especially the piezodrive.
Advantageous geometrical arrangements of liquid metal and resistance or insulator means are disclosed. In particular high voltages and high currents can also be efficiently and safely handled by a series connection of liquid metal columns in alternation with a dielectric.
Other details, advantages and applications of the invention follow from the claims and from the specification and figures below.
a, 1b show one embodiment of the liquid metal current switch as claimed in the invention with a gas drive in a cross section and a plan view;
a–3c show one embodiment of a liquid metal current switch with piezo-fluid drive with the liquid metal contact closed (
The same parts are provided with the same reference numbers in the figures.
a, 1b show in a cross section and a plan view one embodiment of a liquid metal current switch 1, especially a liquid metal current limiter 1 or liquid metal circuit breaker 1. The current switch 1 comprises solid metal electrodes 2a, 2b for connection of a current supply 20 and a tank 4 for the liquid metal 3. The tank 4 has a bottom 6 and cover 6 of insulating material between which there are a dielectric 5, 8, 9 and at least one channel 3a for the liquid metal 3.
As claimed in the invention, the current switch 1 has a dielectric fluid drive 12 with a control 11 in which a working fluid 9 with a definable drive pressure p1, p2 acts mechanically directly on the front surface 3b of the liquid metal 3 and moves the liquid metal columns 3 from a first position x1 into a second position x12, x2. In the first position x1, the liquid metal 3 is located at least partially in the first current path 30 for an operating current I1. In the second position x12, x2 the liquid metal 3 is at least partially and preferably completely in series with the dielectric 5, 8, 9 so that a current-limiting and/or current-interrupting second current path 31, 32 is formed by the current switch 1.
In the embodiment as shown in
The second means 10, 4, 123, 124 can also comprise a compression pressure vessel 124 with a captured compressible fluid 9′ for applying a resetting force to the back surface 3c of the liquid metal 3. In doing so the compressible fluid 9′ acts as a spring with the desired resetting force. Alternatively the resetting force can also be actively applied by a pressure vessel not shown analogously to 121 or 122 filled with a compressible or incompressible fluid 9′.
The dielectric working fluid 9 can be a dielectric gas 9 and/or a dielectric liquid. The working fluid 9 will essentially not be mixed with the liquid metal 3. Preferably the dielectric working fluid 9 is an insulating gas 9, especially dry air, nitrogen, sulfur hexafluoride, argon or a vacuum, and/or an insulator liquid, especially transformer oil or silicone oil. In addition, the liquid metal column 3 can be surrounded by a protective gas and a protective liquid (not shown here).
Advantageously the drive pressure p1, p2 is set according to the switching time of the current switch 1, especially according to the overcurrent I2 which is to be limited, and to the path-time characteristic x(t) of the liquid metal 3 in the second current path 31 which is necessary for this purpose. Also the drive or fluid pressure p1, p2 should be lower than the surface tension of the surface 3b of the liquid metal 3 which has been exposed to the fluid pressure p1, p2. Preferably the liquid metal 3 is set into ordered flowing motion by the fluid drive 12. Thus the liquid metal 3 in the first and the second operating state remains in the liquid aggregate state. In this way high currents can be limited or interrupted even without the pinch effect with very fast reaction times of down to less than 1 ms.
For the pressure rating it furthermore applies: When the working volume V3 is much smaller than the storage volumes V1, V2, (V3<<V1, V2), the pressures in the storage tanks 121, 122 over time will only decrease imperceptibly. The drive pressure p3 will then be equal to p3=p1=popen contact and for contact closing p3=p2=pclose contact. For the sake of simplification the drive pressure p1 can also be chosen to be equal to the atmospheric pressure. It goes without saying that in practice a small pump is necessary to maintain at least one of the drive pressures p1, p2.
For advantageous dimensioning of the liquid metal current switch 1 the following rules apply: A cross sectional area Q of the liquid metal 3 in the first current path 30 should be dimensioned according to the current carrying capacity of the current switch 1; and/or the width S and number of segments 5a, 8a for separating the channels 3a for the liquid metal 3 and the type of working fluid 9 should be dimensioned according to the dielectric strength of the current switch 1 in a second operating state; and/or a cross section Q′, especially the channel width B, and the surface composition of the channels 3a should also be dimensioned for the liquid metal 3 and the type of liquid metal 3 according to the required surface tension of the surface 3b of the liquid metal 3 which is exposed to pressure by the working fluid 9.
Furthermore, to prevent high-speed gas flows, so-called gas jets, when gas 9 flows in to the working pressure vessel 123 there can be a flow element (not shown) for making the gas flow constant and isotropically uniform in space. The flow element can be most simply a plate perpendicular to the entering gas flow by which the gas flow is diffusely deflected in different directions and only afterward reaches the liquid metal surface 3c. The following applies to the length L of the channels 3a: on the one hand, a minimum hole length L should be chosen such that the fluid 9′ in an elastic or enclosure volume 124 does not reach the upper edge of the channel 3a in any operating state, especially not in the transient states, in order to prevent escape of the fluid 9′ from the enclosure volume 124. On the other hand, the hole length L should be selected to be as short as possible in order to obtain reaction times of the current switch 1 as fast as possible when the liquid metal contact 3 opens and closes. Moreover, the entire pressure-exposed surface 3c of the liquid metal 3 should be chosen to be as large as possible in order to exert a force as large as possible on the liquid metal 3 and to further reduce the reaction time, especially the time delay between valve triggering by the control assembly 11 and opening or closing of the liquid metal contact 3.
The dielectric 5, 8, 9 can comprise a resistance means 5 with a definable electrical resistance RX. The resistance element 5 should have an ohmic portion and is preferably purely ohmic. For arc-free current limitation the resistance element 5 has an electrical resistance Rx which increases continuously along the direction of motion x up to an extreme second position x2 for the second current path 31 and the liquid metal 3 in a transition from the first position x1 to the second position x12, x2, especially to an extreme second position x2, is guided along the resistance element 5. For arc-free switching of the current i(t) from the solid electrodes 2a, 2b, 2c to the resistance element 5 a typical minimum arc ignition voltage of 10 V–20 V which is dependent on the contact material should not be exceeded. The electrical resistance Rx as a function Rx(x12) of the second position x12 and a path-time characteristic x12(t) of the liquid metal 3 along the direction of motion x should be chosen such that in each second position x12, x2 of the liquid metal 3 the product of the electrical resistance Rx and current I2 is less than the arc ignition voltage Ub between the liquid metal 3 and the solid electrodes 2a, 2b and optionally the intermediate electrodes 2c and/or that sufficient steepness of current limitation for controlling grid-induced short circuit currents i(t) is achieved.
Alternatively or in addition, the dielectric 5, 8, 9 can comprise an insulator 8 which is designed for current interruption, especially as an arc forms. The dielectric can also comprise a working fluid 9. For a given voltage level, the maximum electrical resistance Rx(x2) of the dielectric 5, 8, 9 is dimensioned to a finite value according to the current I2 which is to be limited or to the dielectric insulation value to interrupt the current I1, I2.
In the embodiments as shown in
For an especially compact arrangement the first or rated current path 30 and the current-limiting or second current path 31 are arranged essentially perpendicular to the direction of motion x, dictated by the lengthwise extension of the channels 3a, and/or are arranged essentially parallel to one another. Advantageously moreover the insulating clearance 32 for current interruption is located above the second current path 31 and/or underneath the current path 30 and parallel to it as much as possible. In this way a compact arrangement of the liquid metal 3 and its drive mechanism 12 relative to the currents I1, I2, I, which are to be switched, especially to the rated current path 30, current limiting path 31 and optionally the current interruption path 32 is implemented.
As shown, the segments 5a in turn advantageously represent individual resistances 5a of the resistance element 5 with an electrical resistance Rx which increases along the channel depth. Thus the current-limiting second current path 31 is formed by an alternating series connection of channel areas 3a which are filled with liquid metal 3 and the segments 5a which especially preferably act as individual resistances 5a of the resistance element 5 which are progressive with their length. At the height of the first position x1 of the liquid metal 3 the segments 5a should have intermediate electrodes 2c for electrically conductive connection of the channels 3a on the rated current path 30. As shown, the insulating clearance 8 can be formed by a plurality of insulating segments 8a which in the case of interruption are in an alternating series connection with the liquid metal columns 3 which have been moved down. In particular, there is switching between the second and third operating state by a control command, the control 11 for a current limitation command making available a low operating pressure p1 for raising the liquid metal column 3 and for an interruption command a higher working pressure p2 for lowering the liquid metal column 3.
In
Other details and versions of the gas drive 12, for example in
a, 3b, 3c show in cross section one embodiment of a liquid metal current switch 1, especially of a liquid metal current limiter 1 or liquid metal circuit breaker 1, with a piezo-fluid drive 12. The current switch 1 comprises in turn solid metal electrodes 2a, 2b for connecting a current supply and a tank 4 for the liquid metal 3 in which there is at least one channel 3a for the liquid metal 3. The current switch 1 has a piezoelectric drive 12 for the liquid metal 3 in which by means of a working fluid 9 with a definable drive pressure p1, p2 mechanical action is exerted directly on the first surface 3b of the liquid metal 3 and the liquid metal column 3 is moved from a first position x1 into a second position x12, x2. In the first position x1 the liquid metal 3 is at least partially in the first current path 30 for an operating current I1. In the second position x12, x2 the liquid metal 3 is at least partially and preferably completely outside of the first current path 30 so that a current limiting and/or current-interrupting second current path 31, 32 is formed by the current switch 1.
In the embodiment as shown in
Preferably the piezodrive 12 comprises a dielectric drive fluid 9: the drive fluid 9 being incompressible, and with a pressure p1, p2 which can be stipulated by the piston 100 acting mechanically directly on the first surface 3b of the liquid metal 3; and/or a pressure p1, p2 which can be defined by the piston 100 in the drive fluid 9 being slightly less than the surface tension of the first surface 3b of the liquid metal 3 which is exposed to pressure; and/or the drive fluid 9 being located between the piston 100 and the liquid metal 3; and/or the drive fluid 9 being a dielectric liquid, especially in insulator liquid 9 such as for example transformer oil or silicone oil which is essentially not mixed with the liquid metal 3.
The liquid metal 3 can be carried over the first surface 3c by the drive fluid 9. As shown in
The liquid metal 3 can also be in contact with the insulating gas 9′ by way of a second surface 3c. As shown in
The two embodiments for opening the liquid metal contact 3 as shown in
In the embodiments as shown in
In
A quantitative example is given for the design of the piezodrive 12 according to the simplest embodiment in
VF=AF·(H+gopen) (G1)
where AF=B·W=drive cross sectional area of the liquid metal column(s) to be driven, B=width of the channel 3a (or total width of all channels 3a), W=depth of the channel 3a (or of the channels 3a), H=height of the liquid metal column(s) and gopen=minimum vertical contact distance. Moreover Q=H·W=cross sectional area for a liquid metal current path 30 which is rectangular, for example. Thus AF=Q·B/H.
The equation of motion for the fluid column 3, 9 which can be moved by the piezodrive 12 is then
F·AF/AK=[mF+(H+gopen−x)·Q·B/H·ρoil]·d2x/dt2 (G2)
F=piezoelectric force, AK=piston area, mF=mass of the liquid metal and x=position of the liquid metal column(s) 3 during dynamic switching. In equation (G2), the raising of the mass of the drive fluid 9 in the storage tank 40a is ignored since it is wide, deep and flat. Equation (G2) can be numerically integrated and the reaction time tsep of the current switch 1 can be determined as a function of the channel depth W and of the minimum vertical contact distance gopen.
In
The required piezostroke Δy is equal to
Δy=B·W/AK·(Q/W+gopen) (G3)
The construction of the current switch 1 as shown in
In general, a dielectric 5, 8, 9, 9′ should be present, the liquid metal 3 in the second position x12, x2 being in series with the dielectric 5, 8, 9, 9′ and with it forming a current-limiting and/or current-interrupting second current path 31, 32 in the current switch 1. The dielectric 5, 8, 9, 9′ should have an ohmic portion and is preferably purely ohmic.
Advantageously the dielectric comprises a resistance means 5 which for arc-free current limitation has an electrical resistance Rx which increases continuously along the direction of motion x up to an extreme second position x2 for the second current path 31. For this purpose, the segments 5a have a dielectric material with a resistance Rx which increases in the direction of motion x. The liquid metal 3 is routed in a transition from the first position x, to the second position x12, x2 along the segments 5a of the resistance element 5. Thus the current-limiting second current path 31 is formed by an alternating series connection of channel areas 3a which are filled with liquid metal 3 and the segments 5a which act as individual resistances 5a of the resistance element 5 which are progressive with their length. The criteria described in
As shown, the insulating clearance 8 can be formed by a plurality of insulating segments 8a which in the case of interruption are in an alternating series connection with the liquid metal columns 3 which have been moved down. In particular, there is switching between the second and third operating state by a control command, the control 11 for a current limitation command producing a piezomotion or piezoelectric force F up for raising the liquid metal column 3 and for an interruption command a piezoelectric force down to lower the liquid metal column 3.
For one especially compact arrangement, as in
Preferably the liquid metal 3 is set into ordered flowing motion by the piezo-fluid drive 12. Thus the liquid metal 3 in the first and the second operating state remains in the liquid aggregate state. In this way high currents can be limited or interrupted with very fast reaction times of down to less than 1 ms even without the pinch effect. The piezo-liquid metal current switch 1 can also satisfy the requirements for circuit breakers mentioned in
Applications of the device 1 relate among others to use as a current limiter, current-limiting switch and/or circuit breaker 1 in power supply grids, as a self-recovering fuse or as an engine starter. The invention also comprises an electrical switchgear assembly, especially a high or medium voltage switchgear assembly, characterized by a device 1 as described above.
It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restricted. The scope of the invention is indicated by the appended claims rather than the foregoing description and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3405520 | Jul 2003 | EP | regional |
| 3405521 | Jul 2003 | EP | regional |
The present application is a continuation application which claims the benefit of the filing date of PCT/CH2004/000418 filed Jul. 1, 2004, under 35 U.S.C. §120, the priority of EP 03405520.2 and 03405521.0 filed Jul. 10, 2003, the disclosures of which are herby incorporated by reference in their entireties.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4419650 | John | Dec 1983 | A |
| 6870111 | Wong | Mar 2005 | B1 |
| Number | Date | Country |
|---|---|---|
| 312051 | May 1919 | DE |
| 1 802 643 | Dec 1959 | DE |
| 1 224 181 | Sep 1966 | DE |
| 1 294 858 | May 1969 | DE |
| 26 52 506 | May 1978 | DE |
| 40 12 385 | Mar 1991 | DE |
| 199 03 939 | Aug 2000 | DE |
| 100 48 430 | Apr 2002 | DE |
| 296 231 | Aug 1928 | GB |
| 0077811 | Dec 2000 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20060146466 A1 | Jul 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/CH2004/000418 | Jul 2004 | US |
| Child | 11328160 | US |
