EP3433882A1

EP3433882A1 - Superconductor device for operating in an external magnetic field

Info

Publication number: EP3433882A1
Application number: EP17715063.8A
Authority: EP
Inventors: Tabea Arndt; Marijn Pieter Oomen
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2016-03-24
Filing date: 2017-03-22
Publication date: 2019-01-30
Also published as: RU2697426C1; KR20180132083A; DE102016204991A1; CN108886087A; WO2017162714A1; KR102147325B1; JP6735842B2; JP2019516212A; US20190103543A1

Abstract

The invention relates to a superconductor device (1a, 1b) for operating in an external alternating magnetic field, having two superconductive contact elements (2) and a current conducting section (5) which connects the contact elements in a longitudinal direction that corresponds to the power flow direction from one contact element (2) to the other contact element (2) and which comprises a superconductive layer applied onto a substrate (8). The superconductive layer is at least partially interrupted in the longitudinal direction by means of a recess (4), in order to form individual filaments (3) which form current paths for transporting current. At least two adjacent filaments (3) are connected in a conductive manner by omitting the recess (4) in an intersection region (6) which is formed on the substrate (8) and where four current paths are conductively connected. At least one ohmic resistance barrier (7), in particular one respective ohmic resistance barrier, is provided in current paths of the adjacent filaments (3), said current paths lying opposite one another with respect to the intersection and being offset in a layer plane longitudinal direction and in a layer plane transverse direction perpendicular to the longitudinal direction.

Description

description

Superconductor device for operation in an external magnetic field

The invention relates to a superconducting device for operation in an external alternating magnetic field, comprising two superconducting contact elements and a connecting them in one of the current flow direction of a contact element to the other contact element corresponding longitudinal direction

Current-carrying section with a substrate broke up ^¬ th superconductor layer, said superconductor layer Wenig ^¬, current paths for the transport stream forming filaments is cut through by means of a recess least partially in the longitudinal direction to form individual.

The use of superconductors has also been proposed in alternating magnetic fields (alternating magnetic fields), for example in superconducting electrical machines. When using electric conductors in alternating magnetic fields alternating field losses occur, which can be divided into various components ent ^¬ speaking the physical causes. In superconductors, there are over normal conductors additional effects / components, another problem is that these alternating field losses can be for use particularly troublesome under duty characteristics ^¬ gen in the cold and prohibitive, as a multiple of the alternating field losses is then required at room temperature, which the Reduced efficiency.

In normal conductors, in magnetic field inserts usually no monolithic conductor, but a stranded conductor is used with advantage. This minimizes the adverse effects of skin effect (current displacement) and eddy current losses.

Also superconductors, which are usually made of billets or bolts, for example NbTi, Nb3Sn, MgB2 or Bi 2223, the use of superconducting filaments is known. Filaments in superconductors not only have a posi ^¬ tive increase the stability of superconductivity result, but also the alternating field losses can be reduced.

An important group of alternating field losses in Supralei ^¬ tern are the so-called hysteresis, which thereby cause ^¬ unable that in the conductor penetrating magnetic fields must change with the outer magnetic field in its direction AEN countries and thus held in magnetization processes. Since the extent of the superconductor perpendicular to the magnetic field determines the size of the hysteresis losses, formation of thin filaments is advantageous. But the filaments in Supralei ^¬ tern are usually electrically connected to one another to, for a normal-conducting forcibly at the ends via the contacts, to which the power is fed or discharged, and possibly to the other about the (resistive) matrix. The associated alternating field losses are called Kopplungsver ^¬ losses.

In such a filamentization and coupling via the contact elements and / or the matrix, the problem arises that there is a coupling between the individual filaments, in particular by the external alternating magnetic field voltages and currents in through the filaments together with connec ^¬ tions be induced between these conductor loops formed on contact elements, whereby the coupling losses arise. For normal conductor and multifilament superconductors it is therefore known to twist them against each other, so that the resulting due to the alternating magnetic field electrical ^¬ rule fields cancel in adjacent loops. This concept is also known as "twisted pair".

Such a configuration is not possible with layered superconductors, which are applied as a layer to a substrate. In order to reduce the hysteresis losses, it has been proposed in this regard that the initially in the width continuous superconductor layer in the longitudinal direction in strips, so-called To divide "striations" This is, for example, in ei ^¬ nem article by Coleman B. Cobb et al "hysteretic loss reduction in striated YBCO", Physica C 382 (2002), pp. 52 -. 56 described. There, it is assumed that the problem is that the layer superconductors, which can have widths of up to 1 cm, exhibit unacceptable hysteresis losses when operating in alternating magnetic fields perpendicular to the layer. It is investigated how these hysteresis losses at Un ^¬ the superconductor layer terteilung in thin, linear filaments ( "striations") behave. The result is generally that, although possible to reduce the hysteresis losses, since the dimension of the filaments perpendicular to the field direction thereof the However, in a real application where the filaments are shorted at least at the beginning and end by electrical contact elements (or by matrix and shunt layers), these are so-called

"Striated conductors" large between the filaments Indukti ^¬ onsschleifen, which are in turn the cause of increased alternating magnetic field ^¬ losses (coupling losses). The filaments thus correspond substantially "untwisted" partial conductors with electrical connection to the contacts.

The invention is therefore based on the object to provide a possible ^¬ ness to reduce the coupling losses at in individual filaments to be divided superconductor layers.

This object is achieved by a superconducting device according to claim 1. Advantageous embodiments emerge from the subclaims.

A superconductor device according to the invention of the type ge ^¬ called is characterized in that two adjacent ones of the filaments are conductively connected in a fabric ^¬ th on the substrate the crossing area, are conductively connected to the four current paths by omitting the recess at least, with respect to itself the crossing opposite, offset in the longitudinal direction and a direction perpendicular to the longitudinal direction transverse direction of the layer plane, at the intersection meeting current paths of the adjacent filaments at least one, in particular in each case one ohmic resistance barrier is provided. In this case, the use of a respective resistance barrier is preferred. In this way it is achieved that at least un ^¬ terhalb the critical current of a filament creates a Kreu on ^¬ cut area, the filament changing, the barrier-free flow paths-use current path. The barrier thus erzwin- gene in the crossover region, the side, so the Fila ^¬ management, changing current paths, so that in each case opposite by a Kreu ^¬ cut area separate, formed by the current paths conductor loops through a current path, equal in absolute value for a symmetrical configuration of tensioning - voltages are generated due to the generated from the perpendicular to the layer plane ste ^¬ Henden, time-varying external magnetic field component electric fields. In other words, the provision of the crossing regions and the resistance barriers results in the generation of two current paths crossing in the crossing region, along which the electric fields (and thus also the induced voltages) cancel each other out in a symmetrical configuration, ie four geometrically at least similar current paths. The effect is in this case at least in the range up to the critical current of a filament is the same, which also would result if an isolated by the at ^¬ whose current path bridge to the other filament would see pre ^¬.

In other words, it can thus be said that the present invention allows a two-dimensional realization, lying in the layer plane, of a "rotation" of current paths against one another. Accordingly, the effect also arises in the present invention, at least in part, of viewing along a current path at least for the most part, with corresponding symmetry, cancel out the electric fields. Thus, a layered superconductor according to the invention does not simply have straight-line filaments / striations which completely define the current paths, but rather countries, the current paths intersect each other in the layer plane in a defined way such that the induced electrical ^¬ rule fields along the current paths cancel each other at least partially. The resistance barriers, which are local regions of defined resistance, thus lead to the decoupling of the current paths. Although enters through such resistance barriers for some current values purely

resistive loss component in phase with the transport stream on which, however, the present invention will be which are explained here yet nä- ago, expediently less than the coupling losses in pure "striated conductors" held ^¬ th, the latter also are also shifted in phase or may be ,

It should be noted at this point that an unbalanced current distribution over the two current paths is created by the inventive design ^¬ tion, so that at least temporarily ^¬ an asymmetrical division of the partial flows of Ge ^¬ samtstromes occurs. Thus, only the reflection of ^¬ standing wheelchair access first current path will first be used until the critical current of a single filament is reached and the resistance-free current transport is exhausted here. Then, the second current path, wherein the resistance barriers must preferably ^¬ be overcome as cheap and here the current rises, ideally to as the critical current of a filament turns. The second

Current path takes over, so to speak, the "excess current", yet the second current path has the task to compensate the induced electric field, so that at least teilwei ^¬ se an advantageous reduction of the invention ^¬ field losses occurs.

The advantage of lower alternating field losses, however, is offset by two limitations which are less important in comparison with this, namely, on the one hand, a possible reduction of the

Current density based on the total cross section of the Supralei ^¬ tereinrichtung by the particular configuration used. On the other hand, as already indicated, electricity is transport with respect to the second current path on the before ^¬ Trains t two resistive barriers may comprise ^¬ with ohmic losses type a resistivity and there. However, these are advantageous - in contrast to the coupling losses due to induction - in phase with the transport stream.

It should be noted that when using at least one resistance barrier only on one side of the clear division into the different current paths is present only on one side, yet an at least partial cancellation of electric fields is achieved. Preferably, as said, however, to provide both sides of the intersection region Wider ^¬ standing barriers, as already mentioned above, so that the following description shall refer mainly to this is exemplary.

While it is conceivable in theory to construct complex nets of current paths by the use of crossing regions in the case of a multiplicity of filaments, this is ultimately unnecessary and clearly too complicated, since in the end it is sufficient to achieve the reduction of the coupling losses (alternating field losses). each having two filaments in the layer plane in accordance with the invention proposed, a "twisted pair", that is mutually rotated current paths to replicate. thus, a particularly advantageous Substituted ^¬ staltung the present invention provides that a

is provided even number of filaments, wherein the filaments in disjoint (disjoint), two Benach ^¬ disclosed filaments containing filament are divided and filaments of a filament group via at least one

Junction, in particular an odd number of crossing areas are connected. With a very high number of crossing regions over the length of the conductor, however, the even or odd number of crossing regions is negligible. Has a current-carrying section, therefore, in ^¬ way of example six filaments, to form three groups of adjacent filaments, each having at least an intersection area, and consequently two in the wenigs- form at least one junction intersecting current paths. An odd number of crossing areas means that an even number of conductor loops is formed, so that alternately the by Wechselmag- netfeld induced electric field encounters the current in opposite ^¬ translated directions, so that it in a symmetrical configuration, ideally, to a lifting of the effects comes. The resistance barriers at several intersection areas are to be arranged in such a way that there is always a current path which does not lead across any of the resistance barriers. Overall, in this embodiment, only care must be taken that always between the two filaments of a

Filament group in the crossing region, the electrical connection is made and preferably the corresponding offset resistance barriers are provided.

A particularly advantageous development of the present invention provides that the resistance values of the at least one resistance barrier are respectively selected so that an ohmic power loss is smaller in absolute value than a Redu ^¬ cation of the power loss due to coupling be ^¬ nachbarter filaments. Here, the resistance values may, for example, be in a range of less than 0.5 ηΩ, in particular less than 0.1 ^¬ sondere ηΩ. With externally produced contacts on high-temperature superconductors easy to get into the range of about 6 ηΩ, so that the said low ^¬ ren values for the individual resistance barrier appear slightly he ^¬ reichbar. This results in the end the advantage that the coupling losses (alternating field losses) not simply be in-phase ohmic resistance loss it sets ^¬ but actually takes place an overall reduction in losses. Resistance values for the individual resistance barriers can also be roughly estimated by making a comparison with a conventional striated conductor with non-intersecting filaments, for example, assuming six filaments of 0.1 m in length, a substrate width of 0.012 m , ei ^¬ ner filament separation (width of the recess) of 10 ym and a thickness of the superconducting layer on the substrate of 3 ym, it follows from the law of induction and, assuming a total current of 120 A, finally a power dissipation density of 10 ⁷ W / m ³ . After five such "induction loops" (by five adjacent pairs of filaments) exist, one can estimate a maximum of the resistive power dissipation density such that five times the above-mentioned coupling losses should not be exceeded, in which example about 0.6 ηΩ Once, as stated, resistance values in this range are easily attainable, it has been demonstrated that such a conductor construction can be advantageous over a "striated conductor" or a monolithic conductor. Specifically, it can be provided that the resistance values are calculated by a simulation and / or in a model and / or determined by evaluating test measurements, in particular thus empirically. Conveniently, be ^¬ standing programmed simulation environments can already be used to look at the behavior of superconducting device that losses and currents at different resistance values so that an optimum resistance value is found. Conveniently, the at least one Widerstandsbarrie ^¬ re by laser treatment and / or mechanical treatment of the layer and / or a localized Dotie ^¬ tion / depletion of the layer and / or by using a local coating and / or weakening the superconducting structure in Substrate be realized. There are thus many conceivable in the Supraleittechnologie basically be ^¬ knew ways to generate targeted and locally resistance barriers low resistance in filaments. Particularly preferred is a use of a laser, once it is known for example to produce the Aussparun ^¬ gen between the individual filaments as well by a laser and the barrier as well as a (less intensive) use of the laser in the resistance for the barrier provided spatial resistance range on the remaining filament can be made.

It is particularly preferred if the at least one resistance barrier is arranged directly adjacent to the respective crossing region, since then a particularly clear definition of the current paths is made possible.

It should be noted that within the scope of the present invention it is quite possible to deviate from a straight, continuous course of the filaments, but this is not necessarily necessary. In fact, the invention can be realized in a particularly simple manner by virtue of the fact that a recess or furrow is not continuously formed over the entire length of the current-carrying section by the superconductor layer which separates the filaments, but has interruptions at the intended crossing regions, so that the crossing areas entspre ^¬ accordingly arise. In addition, of course, also a corresponding lateral constriction of the intersection region the ^¬ still will be intended and contemplated. ^¬ is deviated as little as possible abge from the straight course of the individual filaments, this results in the most compact realization of the present invention.

Further advantages and details of the present invention will become apparent from the embodiments described below and with reference to the drawing. Showing:

1 is a first explanatory serving ^¬ example of a superconductor ^{device according} to the invention,

2 shows the current profile in different current paths,

Fig. 3 shows a second embodiment of a erfindungsge ^¬ MAESSEN superconducting device, and Fig. 4 a plurality of crossing areas in a filament group.

Fig. 1 shows an extremely simple, for illustration geeigne ^¬ tes embodiment of a superconducting device according to the invention la, in which two filaments 3 connecting two contact elements 2 are provided, which are separated by Ausspa ^¬ ments 4. The plane of the drawing of FIG. 1 is the layer plane of the superconductor layer. The Stromführungsab ^{¬ section} 5 is as known between the contact elements. 2

Here, however, the filaments are not separated 3 over the entire current-carrying section 5, but centrally in a Kreu ^¬-cutting section 6 and a total of a symmetrical design ^¬ from forming an electrically conductive manner. This sym- metry is broken, however, immediacy ^¬ adjacent bar through the crossing portion 6 at opposite with respect to the intersection region 6, transversely and longitudinally offset, locally provided in resistance areas resistance barriers. 7 The resistance barriers 7 have an extremely low ohmic resistance value, in this case in the range of less than 0.1 ηΩ, and were produced by laser treatment, although other possibilities for generation are also conceivable. As the superconductor material of the superconductor layer disposed on the substrate 8, YBCO is used herein.

An external alternating magnetic field runs perpendicular to the layer plane according to the arrows 9 and can thus induce an electric field indicated by the arrows 10, that is to say due to the change over time.

The provision of the resistance barriers 7 now accelerated initially the use of a first, ge ^¬ marked by solid arrows 11 the current path, which consequently changes in the crossing area 6 from the left filament 3 to the right filament 3, wherein in the present case illustrates a situation in which the transport stream from bottom to top in Fig. 1 runs. If the critical current of a filament 3 is exceeded, the second current path, which leads across the resistance barriers 7 and is identified by dashed arrows 12, is also used. The first and the second current paths thus intersect in the crossing region 6, so that overlapping current paths in the layer plane of the superconductor layer can be created by the resistance barriers 7 and the crossing region 6. The decisive advantage of this current routing is that the electric fields (arrows 10) cancel each other along the first current path and the second current path, since, as can be easily seen, in the two "loops" or conductor loops the electric field (arrow 10) is for each ^¬ weiligen current path again in the direction of the partial stream and induces once against this direction. this means that in the ideal case, the effect of the outer Wechselmagnetfel ^¬ of and thus the coupling loss will be neutralized.

However, is as has already been indicated, a unsym ^¬ metric division of the partial flows of the current paths at least at times before, as is evident from the current waveforms of FIG. 2. In this case, the curve 13 corresponds to the total current, whose maximum in magnitude ideally corresponds to substantially twice the critical current of a filament 3. The curve ^¬ ve 14 shows the course of the partial flow for the first current path (arrows 11 in Fig. 1), the curve 15 the course for the second current path (arrows 12 in Fig. 1). Until the critical current I _c in the first current path is reached, only current flows in the first current path, after which the second current path takes over the excess current; in the case of the falling total current edge, the opposite occurs accordingly. Nevertheless, the second current path fulfills the task of compensating for the induced electric field, so that at least partially the vorteilhaf ^¬ te reduction of coupling losses occurring. The current paths or filaments need not necessarily diverge as pronounced pronounced, as shown in the illustrative first embodiment of FIG. Si It only needs to be ensured that the resistance barriers 7 force the illustrated current flow.

Accordingly, FIG. 3 shows a second exemplary embodiment of a superconducting device 1b according to the invention, wherein for the sake of simplicity the reference symbols of FIG. 1 have been retained for corresponding components. In contrast to the illustration of FIG. 1, six filaments 4 are vorgese ^¬ hen here, which are divided into three groups of filaments 16 of each two neighboring filaments 3. Between

Filament groups 16, the recess 4 is continuous, while within the filament groups 16, the recess 4 is interrupted to form the crossing regions 6, wherein a possible course of the resistance barriers 7 is interpreted accordingly. Accordingly, the current flow is also ge ^¬ according to the first current path, see. here the arrow 17, and in the second current path, cf. here the arrow 18, again dashed, forced. The crossing regions 6 are each located in the middle of the current-carrying section 5, so that in each case opposite electric fields occur along the current paths at equal lengths.

In this case, the number of crossing regions 6 does not necessarily have to be limited to one, as shown schematically by the filament pair 16 of FIG. 4. There, three crossing ^regions 6 are realized, which are equidistant over the length of the

Stromführungsabschnitts 5 are distributed. Thus canceling induced electric fields resulting from geometrically identical current paths composite conductor loops thus be optimal in their effects along the filaments wech ^¬ selnden current paths.

Although the invention in detail by the preferred embodiment has been illustrated and described in detail, the invention is not limited ^¬ by the disclosed examples and other variations can be derived therefrom by the skilled artisan without departing from the scope of the invention.

Claims

claims

1. superconducting device (la, lb) for operation in an external alternating magnetic field, comprising two superconducting contact elements (2) and one in a current flow direction of a contact element (2) to the other Kontaktele ^¬ ment (2) corresponding longitudinal direction connecting current guide section (5) with a to a substrate (8) placed broke ^¬ th superconductor layer, said superconductor layer is least partially severed wenigs- in the longitudinal direction to form individual, current paths for the transport stream-forming filaments (3) by a recess (4), characterized in in that at least two adjacent ones of the filaments (3) are conductively connected in an intersection region (6) formed on the substrate (8) to which four current paths are conductively connected by omitting the recess (4), wherein in relation to the intersection, in the longitudinal direction and a longitudinal direction perpendicular to the transverse direction of the layer plane offset current paths the adjacent filaments (3) at least one, in particular in each case one, ohmic resistance barrier ^¬ (7) is provided.

2. superconductor device (la, lb) according to claim 1, characterized in that an even number of Fila- elements (3) is provided, wherein the filaments (3) in ele ^¬ ment foreign, each two adjacent filaments (3) ^¬ de filament (16) are divided and filaments (3) ei ^¬ ner filament (16) are at least one Kreuzungsbe ^¬ rich (6), particularly an odd number of cross-breeding areas (6), respectively.

3. superconductor means (la, lb) according to claim 1 or 2, characterized in that the resistance values of Wenig ^¬ least a resistance barrier (7) are each selected such that an ohmic power loss value is smaller than a reduction of the power loss due to Kopp ^¬ lung adjacent filaments (3).

4. superconductor means (la, lb) according to claim 3, characterized in that the resistance values calculated by Simula ^¬ tion and / or in a model and / or are determined by evaluation of test measurements.

5. Superconductor device (1a, 1b) according to one of the preceding claims, characterized in that the at least one resistance barrier (7) by laser treatment and / or mechanical treatment of the layer and / or a localized doping or depletion of the layer and / or Use of a local coating and / or a superconducting weakening structure in the substrate (8) is realized.

6. superconductor means (la, lb) according to any one of the preceding claims, characterized in that at least ei ^¬ ne resistance barrier (7) immediately adjacent to the depending ^¬ weiligen intersection region (6) is arranged.