ELECTRICAL SPOOL DEVICE HAVING INCREASED ELECTRICAL STABILITY

Abstract

An electrical spool device having at least one coil winding composed of a superconducting strip conductor is specified. The strip conductor includes: a strip-type substrate having two main surfaces; at least one planar superconducting layer applied on a first main surface of the substrate; and at least one outer electrical coupling layer applied on at least one of the main surfaces of the conductor composite thus formed. In this case, the coupling layer brings about an electrical coupling of adjacent turns of the coil winding, wherein the electrical coupling is dimensioned such that the time constant for electrical charging and/or discharging of the coil winding is in the range of 0.02 seconds and 2 hours.

Claims

1. An electrical spool device comprising: at least one spool winding of a superconducting strip conductor, wherein the strip conductor comprises: a strip-shaped substrate with two main surfaces; a two-dimensional superconducting layer applied to a first main surface of the two main surfaces of the strip-shaped substrate; and an external electrical coupling layer applied to at least one main surface of two the main surfaces, wherein the electrical coupling layer provides an electrical coupling of adjacent turns of the at least one spool winding, and wherein the electrical coupling is dimensioned such that a time constant for electrical charging and/or discharging of the at least one spool winding is in a range of 0.02 seconds and 2 hours.

2. The spool device of claim 1, wherein the time constant for the electrical charging and/or the discharging of the at least one spool winding is in a range of 0.1 seconds and 10 minutes.

3. The spool device of claim 1, wherein the time constant for the electrical charging and/or the discharging of the at least one spool winding is in a range of 10 minutes and 2 hours.

4. The spool device of claim 1, wherein the strip conductor further comprises: a two-dimensional, normally conducting cover layer arranged between the two-dimensional superconducting layer and the electrical coupling layer of the strip conductor.

5. The spool device of claim 4, wherein the electrical coupling layer of the strip conductor is a direct coating on the two-dimensional, normally conducting cover layer.

6. The spool device of claim 1, wherein the electrical coupling layer of the strip conductor has a layer thickness in a range of 1 μm and 100 μm.

7. The spool device of claim 1, wherein the electrical coupling layer of the strip conductor comprises a semiconductor material, an inorganic metal compound, and/or an organometallic compound, or a combination thereof.

8. The spool device of claim 1, wherein the electrical coupling layer of the strip conductor comprises a material with an electrical resistivity in a range of 10.sup.−6 Ohm.Math.m and 10.sup.5 Ohm.Math.m.

9. The spool device of claim 1, wherein the electrical coupling layer of the strip conductor comprises an electrically conductive metallic material.

10. The spool device of claim 1, wherein the electrical coupling layer of the strip conductor comprises a material with an electrical resistivity of at least 10.sup.5 Ohm.Math.m.

11. The spool device of claim 10, wherein the electrical coupling layer has a multiplicity of flaws distributed over the layer.

12. The spool device of claim 10, wherein the coupling layer comprises an organic material.

13. An electric machine comprising: a stator; a rotor; and an electrical spool device having at least one spool winding of a superconducting strip conductor, wherein the electrical spool device is positioned within the stator and/or the rotor of the electric machine, and wherein the strip conductor of the electrical spool device comprises: a strip-shaped substrate with two main surfaces; a two-dimensional superconducting layer applied to a first main surface of the two main surfaces of the strip-shaped substrate; and an external electrical coupling layer applied to at least one main surface of two the main surfaces, wherein the electrical coupling layer provides an electrical coupling of adjacent turns of the at least one spool winding, and wherein the electrical coupling is dimensioned such that a time constant for electrical charging and/or discharging of the at least one spool winding is in a range of 0.02 seconds and 2 hours.

14. A transformer or a superconducting energy store comprising: an electrical spool device having at least one spool winding of a superconducting strip conductor, wherein the strip conductor of the electrical spool device comprises: a strip-shaped substrate with two main surfaces; a two-dimensional superconducting layer applied to a first main surface of the two main surfaces of the strip-shaped substrate; and an external electrical coupling layer applied to at least one main surface of two the main surfaces, wherein the electrical coupling layer provides an electrical coupling of adjacent turns of the at least one spool winding, and wherein the electrical coupling is dimensioned such that a time constant for electrical charging and/or discharging of the at least one spool winding is in a range of 0.02 seconds and 2 hours.

15. The transformer or a superconducting energy store of claim 14, wherein the superconducting energy store is superconducting magnetic energy store (SMES).

16. The spool device of claim 1, wherein the electrical coupling layer of the strip conductor has a layer thickness in a range of 2 μm and 20 μm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The disclosure will be described below using a number of exemplary embodiments with reference to the appended drawings, in which:

[0036] FIG. 1 depicts a schematic view of a detail through a spool device according to the prior art.

[0037] FIG. 2 depicts a schematic view of a detail of a spool device according to an exemplary embodiment.

[0038] FIG. 3 and FIG. 4 depict schematic cross-sectional representations of examples of strip conductors in such a spool device.

[0039] FIG. 5 depicts a schematic representation of an example of the dependence of the magnetic flux of such a spool device in dependence on the current.

[0040] In the figures, elements that are the same or have the same function are provided with the same reference signs.

DETAILED DESCRIPTION

[0041] FIG. 1 depicts a detail from a spool device 21 with a spool winding 23 according to the prior art. A partial region of a cross section of the spool winding 23 in an edge region of the winding is shown. The spool winding 23 here includes a multiplicity of turns w.sub.i, of which, by way of example, only the edge regions of two turns are shown in full and the edge areas of the two adjoining turns are partially shown. The individual turns w.sub.i are formed by winding a strip conductor 1, the structure of which will now be explained in more detail. The strip conductor 1 has a metallic substrate 3, on one main surface of which a two-dimensional superconducting layer 5 is formed. This superconducting layer 5 is covered by a normally conducting cover layer 7, which may likewise be formed from a metallic material, (e.g., copper and/or silver). Each of the layers shown may include a number of partial layers and additional intermediate layers may also be arranged between the individual layers, in particular, one or more buffer layers between the substrate 3 and the superconducting layer 5. In this strip conductor 1 according to the prior art, the conductor assembly thus formed is wrapped by an electrically insulating plastic tape 10. This insulator is used to electrically isolate the adjacent spool turns w.sub.i.

[0042] The problem with the conventional spool device 21 of FIG. 1 is on the one hand that the spool device is relatively susceptible to thermal damage to the thin superconducting layer 5 in the event of a sudden quench. A further disadvantage of the conventional spool device 21 is that the insulator 10 is comparatively thick. Due to its contribution to the total thickness of the strip conductor 1, the current density that may potentially be achieved in the entire spool winding 23 is also limited.

[0043] FIG. 2 depicts a schematic view of a detail through a spool device 21 according to an exemplary embodiment. The illustration is analogous to the illustration of the conventional spool device in FIG. 1. Here, too, the edge region of a spool winding 23 is shown, e.g., the underside of a flat spool. In contrast to the spool device of FIG. 1, the strip conductor 1, from which the winding is formed, is not wrapped with an insulator 10, but is provided with an enclosing electrical coupling layer 11. This coupling layer 11 may be applied as a direct coating on the conductor assembly, the aforementioned conductor assembly being formed similarly to in FIG. 1 by a metallic substrate 3, a superconducting layer 5 arranged thereon, a normally conducting cover layer 7 arranged thereon, and optionally further intermediate layers not shown here.

[0044] In the spool element 21 of FIG. 2, the entire strip conductor 1 is made significantly thinner than in the conventional spool element 21 of FIG. 1. On the one hand, the electrical coupling layer 11 is made thinner than the insulator 10 in the conventional spool winding. On the other hand, the substrate 3 and the normally conducting cover layer 7 are also chosen to be comparatively thin here. All of this favors a comparatively high current density in this spool winding 23.

[0045] A difference between the spool device of FIG. 2 and the spool device of FIG. 1 is that the electrical coupling layer 11 electrically connects the adjacent turns w.sub.i of the spool winding to one another in such a way that a transverse conductivity is made possible between the superconducting layers 5 of adjacent turns. The effective resistance for this cross connection (over the length of a spool turn) is only indicated extremely schematically in FIG. 2 as R.sub.q. In the example of FIG. 2, the layers 3 and 7 adjoining the superconducting layer 5 are also formed as metallic conductors. In contrast, the coupling layer 11 is formed in this example from a semiconducting material. Overall, this results in a moderately conductive cross connection between the superconducting layers 5 of adjacent turns. The layer thickness and the resistivity of the coupling layer 11 (and thus the resistance R.sub.q the cross connection) are set in such a way that, in combination with the total inductance of the spool winding, there is a time constant for electrical charging and discharging in a range of 0.02 seconds and 2 hours.

[0046] As an alternative to the semiconducting coupling layer 11 present in the example of FIG. 2, this coupling layer may also be formed from an insulating material with a number of flaws (e.g., gaps). In this case, an electrical connection between the conductive substrate 3 of a given turn and the metallic cover layer 7 of the adjacent turn may be made possible in the region of the flaws, for example, by spikes in the respective metallic layers that penetrate the electrically insulating coupling layer 11.

[0047] According to a further possible alternative, the coupling layer may also be formed from a moderately electrically conductive metallic material which has a comparatively high layer thickness. Also in this embodiment, the resistance of the cross connection may be suitably set in order to set a time constant within the stated range of values in conjunction with the inductance of the spool winding.

[0048] FIG. 3 depicts a schematic cross-sectional view of a strip conductor 1, which may be used in a spool device and may be constructed overall in a manner similar to the strip conductor of FIG. 2. The strip conductor 1 includes a metallic substrate 3, which has two main surfaces 31a and 31b. A two-dimensional superconducting layer 5 is deposited on the first main surface 31a over a stack of buffer layers that are not shown here. This superconducting layer 5 is in turn covered by a metallic cover layer 7. This cover layer 7 may include copper, silver, or a stack of both materials. The substrate, the superconducting layer 5, and the cover layer 7 as well as the buffer layers not shown together form a conductor assembly 9. This conductor assembly 9 is enclosed here over its entire cross section by an electrical coupling layer 11. This electrical coupling layer is electrically conducting or semiconducting or electrically insulating with a multiplicity of flaws (gaps) distributed over the layer. It provides sufficient electrical coupling from turn to turn within a spool winding constructed with this strip conductor 1. The coupling layer may be formed for example as a thin semiconductor layer. The semiconducting property may be achieved either by doping a material that is not inherently conductive (e.g., diamond) and/or also by an intrinsically semiconducting material. By doping diamonds, for example, low resistivities in the range down to below 10.sup.−6 Ohm.Math.m may be achieved. Numerous other materials are also conceivable for this coupling layer 11.

[0049] Not wrapping the tape conductor with an insulator 10 makes it possible to choose the thickness d1 of the entire strip conductor to be very thin. The thickness d11 of the coupling layer 11, (e.g., applied by direct coating), may be advantageously chosen to be significantly thinner than that of a conventional insulator film. The thickness of the substrate d3 and/or the thickness of the cover layer d7, and thus also the thickness of the entire conductor assembly d9 enclosed by the coupling layer 11, may also be chosen to be very thin in order to achieve overall a high current density.

[0050] FIG. 4 depicts a schematic cross-sectional view of an alternatively designed strip conductor, as it may also be used in a spool device 21 as disclosed herein. The underlying conductor assembly 9 is constructed analogously or very similarly to the conductor assembly 9 of FIG. 3. The coupling layer 11 is also formed from a material with similar properties. As a difference from the example of FIG. 3, this coupling layer is not deposited as an enclosing layer, but only on one side of the conductor assembly. In the example of FIG. 4, the coupling layer is deposited on the first main surface 33a of the conductor assembly 9, which corresponds to the first main surface 31a of the substrate 3. This first main surface of the substrate is the surface to which the superconducting layer 5 is applied. It also corresponds to the first side 35a of the strip conductor 1. Such a coupling layer 11 on this first side of the strip conductor 1 also achieves a sufficient electrical coupling of the successive turns when a winding is produced from the strip conductor, because the metallic layers are connected by the semiconducting, conducting, or at least flawed coupling layer 11. Analogously to the example of FIG. 2, the individual layer thicknesses may also be made very thin here. Because the coupling layer 11 is only applied on one side here, the total thickness d1 of the strip conductor 1 may even be chosen to be even thinner.

[0051] FIG. 5 depicts a schematic representation of the dependence of the magnetic flux B on the current I in a spool device according to an example. In the case of this spool device, the coupling layer is formed from a semiconducting material, as a result of which a moderate electrical coupling of adjacent turns is achieved. This allows protection from damage of the superconductor in the event of high currents. This protective function is to be explained in more detail below in connection with FIG. 5. The curve 51 shows the theoretical linear profile of the magnetic flux B in dependence on the current I, which is to be expected for a conventional, winding-insulated spool. In contrast, curve 53 shows the actually observed profile of the magnetic flux B for a spool device. For low currents I, which are well below the critical current 55, the actual curve 53 essentially follows the linear theoretical curve 51, because the conductor material here is superconducting and the voltage drop across the winding is accordingly negligible. The current flowing through the spool device thus flows through the superconducting material of the spool turns (e.g., the spiral main path). When the current in the superconducting material reaches the range of the critical current 55, however, the voltage drop across the superconducting part of the winding is no longer negligible. Therefore, in the range of the critical current 55, other paths are also relevant for the current transport, because their resistances are no longer negligible in comparison with the resistance of the superconductor material, which is then increasing rapidly according to the U-I characteristic. This is in principle both for a conventional turn-insulated spool winding and for the spool winding according to the exemplary embodiment with electrical coupling of the turns. An important difference between insulation of the turns and coupling of the turns is that, in the case of a winding with an insulator between the turns, the parallel current path leads over the normally conducting parts of the strip conductor, that is to say for example the metallic substrate and/or the metallic cover layer. In the regions of the winding in which the superconduction breaks down first, this leads to a strong local heat development in the relevant normally conducting parts of the strip conductor, in other words to the formation of so-called hot spots. This in turn leads to what is known as quenching of the spool winding, e.g., a complete breakdown of the superconducting properties due to overheating of the superconductor material and resultant exceeding of the transition temperature of the superconductor. If the current in the spool cannot be reduced quickly enough by active measures, this area may even heat up to such an extent that the strip conductor is ultimately irreparably damaged, and the spool is destroyed.

[0052] In the embodiment with an electrical coupling layer, such quenching may be avoided by the following mechanism. This is because an additional parallel current path (with resistance Rq) is formed here via the coupling layer, which acts as a cross connection from turn to turn. Although the coupling layer under certain circumstances only causes a moderately strong electrical coupling, a significant proportion of the current may flow via this path when the critical current 55 is reached due to the much shorter path and much larger cross section of these cross connections. The overall path is made up in the manner of cascade of a series connection of the individual cross connections of the turns lying one above the other. Because the distance from turn to turn is so short and the material cross section for this current path is so large, there is no particularly strong local heating that would lead to local overheating of the winding. As a result, the spool device may be operated at a total current I which may be significantly above the critical current 55. Initial experiments were able to achieve a factor of two or more. In this operating mode, the so-called “residual current” (that is approximately the current that exceeds the critical current 55) flows through the cross-current path, while a current that corresponds approximately to the critical current 55 flows furthermore through the superconducting winding and leads to the formation of an approximately constant magnetic flux B. As a result, the observed plateau in the magnetic flux occurs for currents above the critical current 55, although the total value of the current I exceeds the critical current 55. An advantage of this coupling of the turns compared to conventional windings with insulation of the turns is that the superconducting properties do not break down even with total currents above the critical current and the spool winding is protected from quenching and thermal damage to the conductor material by the “harmless parallel current path”. So it has an increased electrical stability.

[0053] In order to achieve the protective function described, a higher time constant for charging and discharging the winding is accepted compared to the prior art, resulting from the parallel connection of the various current paths as described above. By precisely coordinating the resistances and inductances of the respective current paths, however, a charging rate that is still tolerable for the respective application may be set.

[0054] Although the disclosure has been described and illustrated more specifically in detail by the exemplary embodiments, the disclosure is not restricted by the disclosed examples and other variations may be derived therefrom by a person skilled in the art without departing from the scope of protection of the disclosure. It is therefore intended that the foregoing description be regarded as illustrative rather than limiting, and that it be understood that all equivalents and/or combinations of embodiments are intended to be included in this description.

[0055] It is to be understood that the elements and features recited in the appended claims may be combined in different ways to produce new claims that likewise fall within the scope of the present disclosure. Thus, whereas the dependent claims appended below depend from only a single independent or dependent claim, it is to be understood that these dependent claims may, alternatively, be made to depend in the alternative from any preceding or following claim, whether independent or dependent, and that such new combinations are to be understood as forming a part of the present specification.

LIST OF REFERENCE SIGNS

[0056] 1 Strip conductor [0057] 3 Substrate [0058] 5 Superconducting layer [0059] 7 Normally conducting cover layer [0060] 9 Conductor assembly [0061] 10 Insulator [0062] 11 Electrical coupling layer [0063] 21 Spool device [0064] 23 Spool winding [0065] 31a First main surface of the substrate [0066] 31b Second main surface of the substrate [0067] 33a First main surface of the conductor assembly [0068] 33b Second main surface of the conductor assembly [0069] 35a First side of the strip conductor [0070] 35b Second side of the strip conductor [0071] 51 Theoretical linear profile [0072] 53 Actual profile [0073] 55 Critical current [0074] B Magnetic flux [0075] d1 Total thickness of the strip conductor [0076] d3 Layer thickness of the substrate [0077] d5 Layer thickness of the superconducting layer [0078] d7 Layer thickness of the cover layer [0079] d9 Layer thickness of the conductor assembly [0080] d11 Thickness of the protective layer [0081] I Current [0082] R.sub.q Resistance of the cross connection [0083] w.sub.i Turns