Fault current limiter with a plurality of superconducting elements, at least one of which with an electric contact between its superconducting film and its electrically conducting substrate

[0001] The invention relates to a fault current limiter with a superconducting device comprising a string of superconducting elements, each of

- electrically conductive substrate,

- superconducting film, and - electrically insulating an intermediate layer sandwiched between the substrate and the superconducting film, the superconducting layers of the adjacent superconducting elements of this series being electrically connected, especially in series, the electrically conductive substrate of each superconducting element of this series being electrically insulated from each electrically conductive substrate of these adjacent superconducting elements in this string, whose superconducting films are electrically connected in series with the superconducting layer of said superconducting element.

[0002] Such a superconducting device is known from US 7,071,148 B1.

[0003] Superconducting interference current limiters are used to limit the current flowing through the load side of an electrical circuit in the event of a short on the load side. In the simplest case, the interference current limiter contains a superconducting device with very low loss. As long as the current through the superconducting device does not exceed the critical current, the superconducting device is practically invisible in the electrical circuit, and what determines the current in the electrical circuit are load characteristics, especially resistance.

[0004] In the event that the load resistance drops (i.e. there is a short circuit in the load), the current in the circuit increases and finally exceeds the critical current. In this case, the superconducting device cools down (i.e. becomes normally conductive), which results in high active resistance of the superconducting device. As a result, the current in the electric circuit drops accordingly and the load is protected against high electric current.

[0005] The superconducting material of the superconducting device must be cooled to a low temperature in order to obtain its superconducting state. To facilitate and reduce cooling costs, high temperature superconductor materials (HTS materials - high temperature superconductor) can be used. HTS materials have a critical temperature above 30 K and can often be cooled with liquid nitrogen (LN2).

[0006] An interference current limiter with many superconducting devices using HTS material is known from the superconducting HTS (dielectric) film

US 5,986,536. It contains several elements, each of which contains embedded on an electrically insulating substrate, in particular made of a material that allows the textured growth of the film

HTS, such as Yttrium stabilized ZrO2, with a thin intermediate layer of Ag. These superconducting elements, i.e. their HTS films, are connected in series.

[0007] Interference current limiters of this type comprising superconducting elements with textured superconducting layers deposited on a dielectric substrate are rather expensive to manufacture. Furthermore, such interference current limiters have a relatively long cooldown after cooling has occurred.

[0008] DE 2410148A discloses a switching device comprising a plurality of aluminum plates cut in a meandering manner, where the plates are covered with superconducting layers and have aluminum oxide layers between them. Superconducting layers of adjacent plates are connected in series by protruding contacts.

[0009] US 7,071,148B1 describes a combined superconducting article in which two adjacent and similarly oriented segments, each comprising a metal-based substrate, a buffer layer, and a superconducting coating, are electrically connected via a third, opposite such segment located on top of these two segments.

Object of the invention [0010] The object of the invention is to provide a surge current limiter that is cost-effective in production and that is able to provide a short recovery time after cooling.

Brief description of the invention [0011] The object is achieved, according to the invention, by means of an interference current limiter as set out in the beginning, characterized in that at least one of the superconducting elements comprises an electrical contact between its superconducting film and its electrically conductive substrate through its an insulating layer, the electrical contact being located essentially in the middle between the areas, where the superconducting element is electrically connected to the previous and next superconducting element.

[0012] According to the invention, the fault current limiter (FCL) is generally a superconducting device comprising a plurality of superconducting elements; each of these superconducting elements has a superconducting film, especially an HTS film, deposited on an electrically conductive substrate, especially a metal substrate. The superconducting film and the electrically conductive substrate are (at least to a very large extent) isolated from each other; for this purpose, there is an insulating intermediate layer embedded between the electrically conductive substrate and the superconducting film. It is noted that, for example from US 6,765,151, superconducting wires based on electrically conductive substrates with HTS material deposited on top.

[0013] A superconducting element based on an electrically conductive substrate is much more cost effective in manufacturing than a superconducting element based on a dielectric substrate, especially because of the cost of the substrate differing by an index of about 50. In addition, an electrically conductive substrate, usually a metal substrate, also offers much better thermal conductivity than a typical dielectric substrate. Consequently, after rapid cooling, which usually heats the superconducting element above the critical temperature of the superconducting film material, it can be cooled much faster so that the interference current limiter regains its normal operating capacity much faster.

[0014] As a special feature of the invention, the innovative FCL uses a string of superconducting elements, with their superconducting layers electrically connected and with their electrically conductive substrates insulated from each other. It has been found that this innovative design is beneficial for achieving both high short-circuit resistance and a sufficiently high possible voltage drop (electric field) transverse to the direction of current flow, especially> 2V / cm. Allowing high short-circuit resistance (i.e., interference current limiter resistance in fast cooling mode) to be achieved and enabling high voltage drop to be achieved can therefore be considered as further objectives of the present invention.

[0015] When the innovative FCL is in interference mode, i.e. when the load has a short circuit and the superconducting films are cooled, the external voltage drops transversely to the interference current limiter, or more precisely across to the new resistive (normally conductive) superconducting films in the interference current limiter . However, next to it is a walking current path provided by electrically conductive substrates of superconducting elements. If the voltage is high enough, it can cause a voltage breakdown from the superconducting film through the insulating intermediate layer to the electrically conductive substrate.

[0016] If the bypass current path through the substrates were activated, the short-circuit resistance of the interference current limiter would decrease significantly and the interference current by FCL would increase, threatening the load to be protected. In addition, FCL ohmic heating in the event of a short circuit would increase, extending the time required for re-cooling FCL below the critical temperature of its superconducting films. Heat dissipation alone can also destroy the superconducting material in FCL, thereby limiting the maximum voltage drop across the direction of current flow.

[0017]

By means of the invention, electrically conductive substrates of adjacent (adjacent) superconducting elements connected in series are insulated with respect to each other. As a result, only a portion of the external voltage falls across the length of the electrically conductive substrate, mainly corresponding to its fraction of the entire length of the superconducting layers connected in FCL. Thus, by means of an innovative separation of electrically conductive substrates, the voltage drop transversely to the length of the electrically conductive substrate can be adjusted and in particular reduced to a value that safely excludes voltage breakdown through the insulating layer. According to the invention, nowhere in the superconducting device is there a difference in the potential of the total external voltage across the insulating layer, but only the fraction of the total external voltage that is not high enough to cause a breakdown; so bypassing the current path through the electrically conductive substrate remains inactive.

[0018] According to the invention, at least one of the superconducting elements comprises an electrical contact between its superconducting film and its electrically conductive substrate through an intermediate (insulating) layer, the electrical contact being located substantially in the middle between the areas where the superconducting element is electrically connected with the previous and next superconducting element. By these means, the voltage drop across the insulating intermediate layer, in general, can be reduced in half, in general. It should be noted that the electrical contact should, in the direction of current flow, only extend a short distance (compared to the length of the superconducting element) in order to avoid the formation of a bypassing current path over a significant length, which would reduce short-circuit resistance.

[0019] Thus, in the innovative FCL, when it is in short-circuit mode, high superconductor resistance can be maintained and consequently low Joule heating can be maintained. The latter reduces the regeneration time of FCL after rapid cooling and allows a higher voltage drop across the superconducting layers without the risk of damaging the superconducting material.

[0020] It has been found that preferably, according to the invention, the electrically conductive substrate of each superconducting train member is electrically insulated from each electrically conductive substrate of all superconducting members within which the superconducting films are a superconducting member.

electrically connected in series with the film of said superconducting [0021] According to the invention, the electrically conductive substrate is usually metal, especially in the form of a thin strip with a thickness in the range between 5 μm and 100 μη. This thin tape can facilitate the cooling of superconducting films because they have lower heat capacity and good thermal conductivity through the substrate, in particular enabling highly effective two-way cooling of the superconducting elements from the upper side and through to the substrate side.

[0022] The electrically connected superconducting films or adjacent superconducting elements are typically connected by connecting means, wherein the superconducting films have portions of the surface area that are not covered by the joining means ("free surface portions"). This free area may be in the range, in particular, from 10% to 98% of the total surface of the film, and usually covers the vast majority of the total surface of the film.

[0023] It should be noted that the superconducting device of the inventive interference current limiter can be supplemented with superconducting elements of a different type than those described above; however, the latter will not be referred to further.

[0024] The innovative interference current limiter can be used in an electric circuit containing a voltage source, especially in a power plant or power grid connected in series with the innovative interference current limiter. The invention is particularly suitable for high voltage sources with voltages of 1000V and more, especially 10 kV and more.

Preferred Examples of the Invention [0025] In a preferred embodiment of the inventive interference current limiter, the superconducting layers of at least some adjacent superconducting elements are electrically directly connected. Direct electrical connection is easy to implement. Direct electrical connection means in particular that no indirect superconducting part is involved. Superconducting elements with directly electrically connected superconducting layers are hereinafter referred to as directly electrically connected superconducting elements.

[0026] In a preferred further development of this embodiment, the directly electrically connected adjacent superconducting elements are

oriented with their superconducting layers facing each other, and

- offset relative to each other so that adjacent superconducting elements partially overlap in the overlap area, wherein the overlap area, superconductive layers of overlapping superconducting elements are electrically connected. This arrangement is simple to make.

[0027] Another advantageous development is characterized in that the superconducting layers of directly electrically connected adjacent superconducting elements are formed of superconducting superconducting electrically connected through a layer of normally conductive metal. The connection of superconducting films in this way is both simple and highly reliable due to the relatively large contact area, involving only a minimum of transition surfaces. Typically, the connecting layer exhibits a multi-layer structure that includes transient sub-layers and a middle layer. These sub-layers are either directly on the surface of the film or on the surface of the film already covered with a very thin protective layer of metal. Their task is to ensure low resistance of the separation surface with respect to the superconducting film, as well as to ensure stable mechanical bonding.

[0028] These sub-layers are usually made of precious metals or an alloy of precious metals, in particular those containing gold and / or silver. Alternatively, the sub-layers may be copper-based or copper-based alloys such as Cu-Ag, Cu-Ag-In. In addition, each sublayer may comprise several layers, such as, for example, a "basic" layer of precious metal and a second layer of copper (deposited, for example, by electroplating). In addition, these few layers may also comprise a final layer made, for example, of Ag or Au or metal alloys. The task of the final layer is to ensure the passivation of the surface before chemical reactions in order to improve the quality of soldering and thus achieve low (for example □ 10^-7 om xs) the resistance of the interface surface in the electrical connection.

[0029] The middle layer may comprise a solder which allows providing a cost-effective combination of superconducting films, alternatively sublayers deposited on these films. Usually the solder alloy is a low melting metal, for example In, Zn, Cd, Ga, Bi, Ag or alloys based on such metals. Alternatively, the middle layer may be formed as a diffusion layer, provided by cold welding (under pressure) or thermal diffusion (in, for example, 400^aboutC for Ag sublayers).

[0030] Furthermore, an embodiment is preferred in which the superconducting layers of at least some adjacent superconducting elements are electrically connected by means of bridge elements, wherein the bridge element comprises a superconducting part and wherein the superconducting layers of adjacent superconducting elements electrically connected by a bridge element are both electrically connected with this superconducting part. The bridge element and its superconducting portion allows greater freedom in joining the superconducting layers together, especially when adjacent (adjacent) superconducting elements connected in series with the superconducting layers are separated by a considerable distance. The resistance between the combined superconducting layers can be kept low during normal operation. Superconducting elements with superconducting layers electrically connected by means of a bridge element are hereinafter referred to as superconducting elements connected by means of a bridge element.

[0031] In a preferred further development of this embodiment, the adjacent superconducting elements electrically connected by means of bridge elements are

- oriented with their superconducting films facing in the same direction,

- and arranged one after the other, with a gap between two adjacent superconducting elements, the bridge element forming an electrical connection of the superconducting layers of adjacent superconducting elements through the gap. The gap is a simple solution for mutual insulation.

[0032] Another advantageous development of the above embodiment is characterized in that the bridge element comprises a dielectric substrate and the superconducting portion is a superconducting layer covering the dielectric substrate, in that the superconducting layer of the bridge element faces the superconducting layers of adjacent superconducting elements electrically connected by means of the bridge element, and in that the bridge element overlaps, especially partially overlaps, on both adjacent superconducting elements, electrically connected by means of a bridge element. The connections are simple and highly reliable due to the large contact area, with only the minimum separation surfaces formed.

[0036] In a preferred embodiment of the inventive interference current limiter, the superconducting elements are connected in an annular shape. Such a ring-shaped connection must, in the case of circular currents, be considered a series sequence of superconducting elements. In particular, only two superconducting elements can be connected into an annular shape. Preferably, the substrates corresponding to the superconducting elements as a whole are bent to give a substantially circular ring system. Ring-shaped superconducting (short-circuit) devices are used in inductive (transformer-based) interference current limiters in which the load is connected in series on the primary side, and the ring-shaped superconducting device is connected on the secondary side of the transformer to shield the secondary side in normal mode . FCL induction arresters are particularly suitable for limiting AC currents.

[0034] In another preferred example, the superconducting elements are connected in a linear series. This example is particularly suitable for limiting DC direct currents, especially in which high external voltage is divided between superconducting line elements.

[0035] In a particularly preferred embodiment, the interference current limiter is characterized in that the string of superconducting elements comprises at least three superconducting elements. In this case, internal tension can be spread more widely. This is especially important for resistance-type FCL.

[0036] It is also within the scope of the present invention to provide a method for producing a superconducting interference current limiter device as described above, characterized in that each superconducting element is subjected to a voltage applied transversely by the electrically insulating layer such that voltage breaks are induced by the intermediate (insulating) layer wherein the voltage is carried out until all bridges with low resistance in the insulating layer have been burned. The superconducting device can be used in a fault current limiter, which is cost effective in manufacturing, and offers short recovery times and can handle high external voltages. Through the firing procedure, the insulating properties of the intermediate layer can be significantly increased for later practical applications. It should be noted that this last stage can be carried out before or after the electrical connection of the superconducting elements.

In a preferred variant of the innovative method, the voltage is applied as an alternating voltage, with a gradually increasing voltage over time, in particular where the voltage increases to its maximum value in a time interval between 0.3 s and 15 s. In this way low bridges resistances are burned sequentially, that is not simultaneously as an "explosion". This process is better controlled.

Preferably, the treatment step in which the superconducting element (corresponding to its intermediate layer) is subjected to tension is carried out before the treatment step in which an electrical contact is formed between the superconducting film and an electrically conductive substrate through the intermediate (insulating) layer of said superconducting element . Otherwise, the electrical contact may be damaged by exposure to voltage.

[0039] Further benefits can be derived from the description and the attached drawings. The features listed above and below can be used according to the invention either individually or collectively in any combination. The indicated embodiments should not be understood to be exhaustive, but rather are exemplary in the description of the invention.

Drawing [0040] The invention is shown in the drawing:

Fig. 1 schematically shows a cross-sectional view of a superconducting interference current limiter device for general information, with a direct electrical connection of superconducting films with a continuous contact layer;

Fig. 2 schematically shows a cross-sectional view of the superconducting interference current limiter device for general information, with a direct electrical connection of the superconducting films with local contact layers on the contact surfaces ;

Fig. 3a schematically shows a cross-sectional view of the superconducting interference current limiter device for general information, with a direct electrical connection of the superconducting films, with extended free areas of the superconducting films;

Fig. 3b is a schematic plan view of the superconducting device of Fig. 3a;

Fig. 4 schematically shows a cross-sectional view of the superconducting interference current limiter device for general information, with the electric connection of the superconducting layers by means of bridge elements;

Fig. 5 is a schematic top view of a superconducting current limiter device for general information, with corners 90^about between superconducting elements and bridge components;

Fig. 6 schematically shows a cross-sectional view of a ring-shaped superconducting device for an innovative interference current limiter, with four superconducting elements connected directly;

Fig. 7a schematically shows a cross-sectional view of a ring-shaped superconducting device for an innovative interference current limiter, with two superconducting elements directly connected;

Fig. 7b schematically shows a cross-sectional view of a ring-shaped superconducting device for an innovative interference current limiter, with two superconducting elements connected by means of bridge elements;

[0041] The figures describe superconducting devices for use in an interference current limiter, with Fig. 2 illustrating the invention in which the insulating layers have central electrical contacts. [0042] Fig. 1 shows the superconducting device 1, with a series of three superconducting elements 2a, 2b, 2c, shown in Fig. 1. Each superconducting element 2a, 2b, 2c comprises an electrically conductive substrate 3a, 3b, 3c, which is preferably made of a sheet metal band, an intermediate layer, i.e. an insulating (dielectric) layer 4a, 4b, 4c, and a superconductive layer 5a, 5b , 5c, preferably a superconducting HTS film, and more preferably a YBa2Cu3O7-x film. The thickness of the TH substrate is typically around 5 μm to 100 μη.

In a specific example, substrates 3a, 3b, 3c are based on CrNi stainless steel, 0.1 mm thick, 10 mm wide and 200 mm long. More generally, the length of superconducting elements (measured in the direction of current flow) can vary in size from a millimeter to several meters; in our tests, 20 to 2000 mm were used, depending on the voltage drop per unit length in the cooled elements (in the example voltage drops from 0.3 to 4 V / cm were considered) and the thickness and quality of the intermediate (insulating) layer. In a given example, the intermediate layer comprising the yttrium stabilized zirconia layer is between 1 and 5 pm thick. YBa film thickness₂Cu₃ABOUT_7-x it's around 1.2 pm. Superconducting elements subside at a critical current of 320 A at -196^aboutC.

[0044] The superconducting film 5a of the left superconducting element 2a is electrically connected to the superconducting film 5b of the superconducting element 2b, which is the next superconducting element in series connection of the superconducting elements 2a-2c of the superconducting device 1. The superconducting film 5b of the superconducting element 2a, in turn, is electrically connected to the superconducting film 5c of the superconducting element 2c, which is again the next superconducting element in series. The electrical connection is established by means of a continuous connecting layer 6 deposited on top of the central superconducting element 2b. The connecting layer typically comprises a multilayer structure, which in turn comprises transient sub-layers and a middle layer.

[0045] The sub-layers are formed on the surface of the superconducting film already coated with a very thin (0.07μm) protective layer of precious metal, such as Ag or Au. In this particular example, these sub-layers also contain a second layer of Cu, 1 μ thick, deposited by electroplating. The sub-layers are provided only in the area of ​​the surface to be connected, i.e. the rest of the surface of the superconducting elements are kept free from any sub-parts of the connecting layer.

[0046] The middle layer is provided by a solder containing one or more metals from the group Sn, Zn, In, Cd, Bi or combinations thereof. The melting point of the solder was 100 to 200^aboutC. The thickness of the middle layer in the example under consideration may vary between 2 and 30 pm. The resistance provided in this example at the interface between the connecting layers is below 5x10^-7 ohms x cm², measured at -196^aboutC, it is at the boiling point of liquid nitrogen.

[0047] The superconducting elements 2a, 2c are aligned in parallel, and the superconducting element 2b is oriented opposite to them, so that its superconducting film 5b faces the superconducting films 5a, 5c. There is a gap 7 between the superconducting elements 2a and 2c, which means that also electrically conductive substrates 3a and 3c are electrically insulated from each other. Accordingly, here these electrically conductive substrates 3a, 3b, 3c of all superconducting members 2a, 2b, 2c of the superconducting device 1 are electrically insulated with respect to each other, which is generally recommended in the invention.

[0048] The gap 7 may also be filled with an additional insulator (such as epoxy resin or Teflon, for example) to limit the spread of the solder metal of the bonding layer into the gap and thus avoid the possibility of shorting the electrically connected substrates 3a and 3c.

[0049] In addition, in order to achieve an improved degree of insulation between the substrate and the superconducting film, each superconducting element is pretreated by subjecting voltage applied transversely through the intermediate layer so that current breaks are induced by the electrically insulating layer, wherein the voltage is maintained until low resistance bridges in the insulating layer will not be burned. DC voltage, which can vary from 10 to 200V, is applied between the superconducting film and the electrically conductive substrate. The voltage varies linearly in a way in which the maximum voltage is reached within 1-5 seconds; the maximum voltage value is determined before processing as 80% of the breakdown voltage, measured in an electrically insulating layer of the same type but with a homogeneous structure, i.e. without low resistance bridges. All procedures for such pre-treatments are preferably carried out at room temperature. By cooling the superconducting elements, the maximum breakdown voltage usually increases.

[0050] The superconducting device is, during operation, cooled, for example with liquid nitrogen (LN2), preferably on both sides (bottom and top), so that each superconducting element is cooled directly from the superconducting layer and through the substrate (cooling means) are not shown).

[0051] In the next superconducting devices disclosed in Figs. 2 to 7, corresponding features and procedures may be used, unless otherwise described, in particular with respect to voltage pretreatment, cooling means and filling the insulating gap.

[0052] Fig. 2 shows a superconducting device 21 similar to the superconducting device shown in Fig. 1. Here, the superconducting layers 5a, 5b are connected by means of a connecting layer part 6a and the superconducting layers 5b, 5c are connected by a connecting layer part 6b . The parts 6a, 6b of the connecting layer are separate and therefore electrically insulated from each other and are made of normally conductive metal, especially gold or silver. The parts 6a, 6b of the connecting layer, respectively, extend only in the overlap areas 22a, 22b of the superconducting elements 2a, 2b, 2c. The surface area parts 23a, 23b, 23c, which are free of connecting means (here free of parts of the electrically conductive connecting layer), help to increase the resistance of the superconducting device 21 under interference current conditions. This is due to the fact that the cooling preferably occurs in parts of the superconducting elements that are not "bypassed" by another superconducting element or bridge element.

[0053] In particular, in the superconducting device 21 of Fig. 2, the insulating layers 4a, 4b, 4c have a central electrical contact 24a, 24b, 24c to limit the voltage drop transversely to the insulating layers 4a-4c.

[0054] It should be noted that on top of the superconducting films 5a-5c, a very thin covering layer (or protective layer) of conductive metal, in particular precious metal, such as silver or gold, can be deposited. However, the thickness of the covering layer should be small enough so that no significant current bypass is formed relative to the superconducting film below. Preferably, however, no cover layer is used.

[0055] Fig. 3a and Fig. 3b show the superconducting device 31, with a series of four superconducting elements 2a-2d electrically connected in series, in cross-section (Fig. 3a) and in a top view (Fig. 3b). The superconducting elements 2a-2d have an alternating orientation with adjacent superconducting elements with their superconducting layers 5a-5d facing each other (it should be noted that the insulating layers are not shown here, for simplicity). In the top view in Fig. 3b, overlap areas 22a, 22b, 22c can be clearly seen. They constitute about 20% of the total surface of the superconducting layer, with the remaining 80% belonging to free parts 23a-23d of the surface.

[0056] Fig. 4 shows an alternative construction of the superconducting device 41, here showing a series of three superconducting elements 2a, 2b, 2c, each with superconducting layers 5a, 5b, 5c (again, for simplicity, intermediate insulating layers are not shown). The superconducting elements 2a-2c are all oriented identically to their superconducting films facing the same side (here: top side) and are separated by slits 45a, 45b.

[0057] The superconducting layers 5a-5c are pairs electrically connected in series by means of bridge elements 42a, 42b, each of which contains a dielectric (electrically insulating) substrate 43a, 43b and a superconducting layer 44a, 44b, preferably a layer of high temperature superconducting thin film (HTS) ). The bridge elements 42a, 42b overlap the superconducting elements (corresponding to the superconducting layers 5a-5c) that connect them in overlap areas 46. In this particular example, the dielectric substrates 43a, 43b are made of either yttrium stabilized zirconia ceramics or sapphire (monocrystalline Al2O3).

[0058] Fig. 5 shows a top view of the superconducting device 51 to be used in the interference current limiter. There is a series of six straight superconducting elements 2a-2f, oriented in parallel, all with their superconducting layers facing up. By means of five bridge elements 42a-42e attached on top, superconducting elements 2a-2f (their corresponding superconducting layers) are electrically connected in series. Bridge elements 42a-42e are oriented perpendicular to superconducting elements 2a2f to make the superconducting device 51 more compact. At the beginning and end of the superconducting device 51 (corresponding to the string of superconducting elements 2a-2f) there are two metal pads 52a, 52b, especially Cu pads for internal connectors that are galvanically mounted on superconducting elements 2a and 2f.

[0059] Figs. 1 to 5 show a linear sequence of superconducting elements. Figures 6 to 7b show annularly shaped superconducting elements, in particular for use in inductive (transformer-based) interference current limiters.

[0060] Fig. 6 shows the superconducting device 61 with the superconducting elements 2a, 2b, 2c, 2d arranged in an annular shape. Each has an electrically conductive 3a-3d substrate and an intermediate insulating layer 4a-4d and a superconducting film 5a-5d. Each superconducting element 2a-2d is directly electrically connected to its upstream and following adjacent superconducting element 2a-2d, creating an electrical connection only between the superconducting layers 5a-5d, but not between electrically conductive substrates 3a-3d. The electrically conductive 3a-3d ring substrates are all electrically insulated from each other. The superconducting elements 2a-2d are generally bent as a circular arc.

[0061] Fig. 7a shows a superconducting device 71 for an innovative interference current limiter similar to that shown in Fig. 6, but containing only the superconducting elements 2a, 2b with the direct electrical connection of their superconducting layers 5a, 5b. Note that intermediate insulating layers are not shown, for simplicity.

[0062] Fig. 7b shows a superconducting device 72, comprising two superconducting elements 2a, 2b, with their superconducting layers 5a, 5b electrically connected via bridge elements 42a, 42b. Again, intermediate insulating layers are not shown, for simplicity.

Alstom Technology Ltd.

Bruker HTS GmbH

Proxy:

77P31010PL00

EP 2 302 710 B1