DE20002591U1 - Fully transposed high-Tc composite superconductor and device for its production - Google Patents

Description

GR OO G 3077 ,j ; ,·%,··, .''·..·*.

Description

Fully transposed high-T _c composite superconductor and device for its production
5

The innovation relates to a fully transposed composite superconductor with at least an approximately rectangular cross-section, which contains several sub-conductors combined in the manner of a Roebel rod, each of which has - an at least approximately rectangular cross-section with a width B,

- at least one conductor core made of a high-T _c superconductor material in a matrix and/or sheath made of normally conductive material

as well as

- with respect to lateral bending in the plane of width B, a predetermined bending radius and a predetermined bending zone length

A corresponding compound superconductor is described in "IEEE Transactions on Applied Superconductivity*, Vol. 9, No. 2, June 1999, pages 111 to 121. The innovation also relates to a device for producing this compound superconductor.

An energy-related application of high-T _c superconductors (hereinafter abbreviated as HTS conductors), e.g. for the realization of transformer or machine windings, requires low-loss conductors with alternating current ratings up to the kilo-ampere range. However, only HTS strip conductors with a small cross-section and current-carrying capacity values of around 50 to 100 _Aeff at 77 K in the magnetic field are currently available. In addition, these strip conductors are mechanically very sensitive, and their electrical properties depend heavily on the magnitude and direction of the local magnetic field in which they are located.

GR OO G 3077 ,j : ;'V.";;' ^s

For these reasons, it is necessary to construct technically usable high-current superconductors from many individual, parallel strip conductors in the form of so-called composite conductors, e.g. in accordance with DE 27 36 157 B2, with the aim of achieving a design that is as continuous and ready for use as possible. For alternating current applications within the scope of industrial frequencies (generally up to 60 Hz), the strip conductors of such composite conductors, referred to below as partial conductors or individual conductors, must also be insulated from one another and systematically transposed or twisted in order to ensure an even current distribution in the overall cross-section and thus low alternating current losses.

Transposed composite conductors with high alternating current carrying capacity are known in principle. They can be designed as follows:

- As so-called "conductor bars", e.g. in the form of Roebel, Schränk or lattice bars, with partial conductors made of copper, e.g. for large AC machines, - as so-called "drill conductors" with partial conductors made of copper for transformers or chokes,

as so-called transposed "flat or round conductors" with partial conductors made of metallic superconductors such as NbTi in Cu (cf. the aforementioned DE 27 36 157 B2). 25

Transposing HTS conductors to increase the AC carrying capacity is also known. Specific design considerations and construction instructions in this regard refer to

- on a continuous transposition of round or practically round HTS sub-conductors in single or multiple cables (cf. e.g. so-called "Rutherford Cable" in "IEEE Transactions on Applied Superconductivity", Vol.7, No.2, June 1997, pages 958 to 961), - on achieving a continuous transposition effect in power cables by varying the pitch of stranded ribbon-shaped HTS sub-conductors from conductor layer to

GR OO G 3077

Conductor layer (so-called “pitch adjustment*; cf. WO 96/39705),

on the so-called "in-situ* transposition, i.e. the step-by-step transposition during winding manufacture directly on the winding body, e.g. a transformer winding (cf. e.g. "IEEE Transactions on Applied Superconductivity', Vol.7, No.2, June 1997, pages 298 to 301).

The literature reference from "IEEE Transactions on Applied Superconductivity" mentioned at the beginning shows the basic structure of a fully transposed composite superconductor made of HTS subconductors in the manner of a Roebel rod. The composite superconductor shown is composed of subconductors according to concepts that are realized with subconductors made of classic superconductor materials such as NbTi. However, it turns out that with such a structure only a relatively low current-carrying capacity of the entire composite conductor can be achieved.

The aim of the present innovation is therefore to design the composite superconductor with the features mentioned above in such a way that it has a comparatively higher current-carrying capacity compared to the state of the art.

The original current-carrying capacity of its individual strip-shaped sub-conductors should be optimally exploited and the risks arising from the mechanical sensitivity and electrical anisotropy of the sub-conductors should be minimized. The composite superconductor should be able to be manufactured in practically any length.

According to the innovation, this task is solved in that for each of the partial conductors the bending radius R is greater than 100 times the width B and the bending zone length H is greater than 20 times the width B and that means are provided for fixing the partial conductors to one another.

GR OO G 3077

The measures in accordance with the innovation are based on the consideration that when constructing the composite superconductor in the manner of a Roebel bar from several, in particular fully insulated, fully transposed HTS strip conductors as sub-conductors, the necessary ongoing cranking or edgewise bending and flat bending of the sub-conductors must not fall below critical bending radii values. It was recognized that, according to the innovation, with the simultaneous selection of the bending radius" and the bending zone length depending on the partial conductor width, damage to the superconducting conductor cores of the partial conductors during bending to form the Roebel rod structure, i.e. during the so-called "Verroebeling*, is avoided. With the special selection of the two aforementioned sizes, the bending radii for the bending required for Verroebeling, including around the flat sides, can be easily maintained and are in the usual order of magnitude. In this way, each partial conductor can advantageously contribute significantly to the current-carrying capacity of the entire composite superconductor. Since the bending zone length H is significantly larger than in a structure known from classic superconductors according to the aforementioned state of the art, a relatively loose connection is obtained, which requires means for fixing the partial conductors to one another and thus to the entire composite conductor. These fixing means must be selected with the view to further processing of the composite superconductor.

Composite superconductors according to the innovation are therefore advantageously characterized by a high current-carrying capacity and the possibility of large-scale production, especially with regard to long conductor lengths.

Advantageous embodiments of the composite superconductor according to the innovation emerge from the substantive claims dependent on claim 1.
35

In order to minimize the risk of current degradation of the composite superconductor after the innovation,

GR OO G 3077

For the partial conductors, a bending radius R of at least 150 times the width B and/or a bending zone length H of at least 50 times the width B is provided.

In principle, it is possible to use different sub-conductors, e.g. with and without superconductor material, and/or with different cross-sections, for the construction of composite superconductors according to the innovation. However, with regard to an even current distribution over the entire composite conductor cross-section, it is advantageous if a combination of sub-conductors with the same structure is provided.

For the composite superconductor according to the innovation, adhesives or soldering of the partial conductors to one another are possible fixing means. Preferably, bandaging or wrapping is provided in order to give the composite superconductor sufficient flexibility. In this case, the bandaging or wrapping can be designed to be transparent or absorbent in particular in view of possible later impregnation with a synthetic resin or good access to coolant.

The composite superconductor is advantageously constructed with partial conductors, each of which has a ratio of its width B to the respective conductor thickness D of between 5 and 40, preferably between 10 and 20. Corresponding partial conductors, which are manufactured commercially, are particularly suitable for Roebeling while complying with the minimum values mentioned.

With a view to reducing alternating current losses when using composite superconductors according to the innovation, they are advantageously constructed with partial conductors, at least some of which are mutually electrically insulated.

Such composite superconductors are therefore particularly suitable for use in an AC power system

GR OO G 3077

• ft **··

such as in a transformer or an electrical machine.

For a quasi-continuous production of a composite superconductor according to the innovation, a device is advantageously provided which has means for a net-like merging of the individual partial conductors from supply spools via a bending area and a guide area in a Roebeling zone in such a way that the conductor cross-sectional position remains at least largely constant, for example horizontal, and has the means for transporting the now Roebeled structure via a feed unit and a fixing area into a winding spool. In the fixing area, the conductor structure is preferably taped or wrapped. With such a device, the basic requirements for HTS Roebel conductor production can advantageously be met. In particular, the inevitability of the very long bending zones typical of HTS must be met by a functional separation and spatial sequential distribution of the steps "position control", "holding", "bending", "moving" and "combining" or "combining".

Advantageously, the supply reels of the device can be rotatably mounted on a turntable.

In the device, the partial conductors are fed into the Roebeling zone advantageously by means of a rotating slotted guide disk. In the Roebeling zone, fixed guide elements and a Roebel channel can advantageously be present.

The innovation is explained in more detail below using the drawing. Figure 1 shows schematically the structure of a fully transposed composite superconductor according to the innovation,

Figure 2 shows in a diagram the bending zone length and the remaining bending radius as a function of the

GR OO G 3077

applied bending radius in the manufacture of composite conductors according to the innovation,

Figures 3 and 4 show bending radii for the production underlying the diagram in Figure 2,

and

Figure 5 shows a device for producing this conductor.

In the figures, corresponding parts are provided with the same reference numerals.

The section of a composite superconductor generally designated 2 according to the innovation shown in Figure 1 in an oblique view is based on known embodiments of such conductors which contain several sub-conductors 3j combined in the manner of a Roebel rod (j = number of sub-conductors with 1 < j < N). Reference is made to DE-PS 277 012 as the basic publication of a Roebel arrangement. N sub-conductors 3j require more than N + 1 grid positions. In Figure 1,

F Flat bending zone

Gi,2 Straight, non-bent pieces H Edgewise bending zone

P periodic edgewise bending zone spacing V full transposition length

D Partial conductor thickness

B Partial conductor width.

The above-mentioned dimensions are linked as follows:
P = H + Gi + F + G ₂ and

V=NxP (with &ldquor;x* = multiplication symbol).

Figure 1 also shows a plan view of a section of this composite superconductor 2 as well as a section of a single subconductor (3i) from this plan view.

&bull; *

&bull;&diams;

GR OO G 3077

The partial conductors 3j are known strip-shaped single- or multi-core HTS conductors with a rectangular cross-section, whereby preferably all partial conductors are designed in the same way and each partial conductor has the same conductor width B. The partial conductors can in particular be known embodiments which generally have the following features and properties:

- Geometry and structure : They have small, flat cross-sections (typically around 1 mm ² ) with very low thickness (typically between 0.2 mm and 0.5 mm ; width up to approx. 4 mm).

Of the various existing embodiments, so-called multifilament superconductors (with several superconducting conductor cores) are preferably suitable for the application area envisaged here: The superconducting ceramic material is embedded in the form of fine filaments in a matrix consisting in particular of silver or a silver alloy. The filaments are preferably twisted (to reduce alternating current losses). The HTS multi-material compound of the type (Bi, Pb) 2Sr ₂ Ca ₂ Cu ₃ O _x (so-called "BPSCCO-2223 material ^w " ) is well suited as a superconductor material. The silver matrix can expediently be reinforced by an additional thin shell, e.g. made of a silver-magnesium alloy. A corresponding concrete HTS standard strip conductor, which forms the basis for the following considerations based on Figures 2 to 4, is known from "IEEE Transactions on Applied Superconductivity", Vol. 9, No. 2, June 1999, pages 2480 to 2485. It has an Ag matrix surrounded by an AgMg shell with 55 oppositely twisted conductor cores or filaments made of the BPSCCO-2223-HTS material embedded in it. Its external dimensions (without insulation) are 3.6 x 0.26 mm ² . It can also be surrounded by insulation, e.g. made of Lupolene with a thickness of between 0.03 and 0.05 mm.

- Mechanical sensitivity to plastic deformation: Permissible edge fibre strains during stretching, bending or

GR OO G 3077 . .·. : _

Torsion is < 0.2%, critical bending radii are typically 50 mm (flat side) or 800-1000 mm (edge bend). - Anisotropy : A pronounced dependence of the current carrying capacity on the magnetic field direction can be observed. For example, the current that can be transported at 0.3 T and 77 K drops to about a fifth if the field direction is turned from the conductor plane to the direction perpendicular to the flat conductor side.

The HTS high-current composite conductor 2 shown is characterized by the following main features:

1. The composite conductor is composed of several, preferably fully insulated HTS strip conductors as sub-conductors 3j. The required number N of sub-conductors with a nominal current Ihtsü for a desired nominal current IvLn of the composite superconductor is not simply the quotient IvLn / Ihtsü. It is usually much larger and can only be determined specifically with the help of the material-specific, non-linear I (B) curves and for a specific application, since I _H Tsn is defined for a stretched strip conductor in its own field, whereas IvLn is defined for the local field values at the location of the application. Even with a stretched composite conductor without an external magnetic field, the field increased by the adjacent sub-conductors at the location of each sub-conductor causes a reduction in its current-carrying capacity.

2. The partial conductors 3j are systematically and continuously transposed within the overall cross-section of the composite conductor (Roebel rod principle: continuous cranking by alternating vertical bends and flat bends).

3. When transposing, the conductor elements may only undergo pure transverse displacements, but - in contrast to stranding - no rotation, torsion or tilting. This would cause the conductor elements to deviate from the most favourable field direction and the current carrying capacity would drop significantly (anisotropy).

GR OO G 3077 _s ; : ,**&diams;**%

, .. « ti ··■·■»

4. For the partial conductor bends mentioned, different critical bending radii are decisive in both transverse directions, which must be determined for each conductor within the framework of the values specified in the new version. If these values are not met, the current-carrying capacity of the HTS strip conductors concerned degrades. The critical radii are each approximately 100 times larger than for copper strips with the same cross-section. In the diagram in Figure 2, a critical area of the bending radius R (less than 800 mm) of the known HTS standard tape conductor used as a partial conductor with an undesirable overstretching of its superconducting conductor filaments and consequently a current degradation is indicated by cross-hatching. - In addition, as indicated in Figure 3, the known HTS conductor tape springs up by a factor of about 2 after bending; i.e., one must differentiate between the applied bending radius R (on the tool) and the remaining, larger bending radius r (in the composite superconductor). Typical values for the real bending behavior of the commercial HTS standard tape conductor are recorded in the diagram in Figure 2.

5. As can also be seen from the diagram in Figure 2 based on the values R, r, k (for a lateral, approximately S-shaped bend) and H defined in Figures 3 and 4, in the specific HTS standard strip conductor used as a basis, the HTS-typical high values for the permissible bending radii R and r are correlated with relatively elongated transition or bending zones H (= bending zone length with respect to a lateral bend in the plane of the partial conductor width B) of the N partial conductors. This can possibly lead to large bending zone distances P and large full transposition lengths V = N × P in the composite superconductor, which must be taken into account in other parameters of the composite conductor, such as the number N.

6. The elongated bending zones of the partial conductors mentioned above under 5. initially have a loose connection in the overall conductor and considerable problems with the

GR OO G 3077 &Lgr;&Igr;."·&diams;**&diams;.'****

Compliance with cross-sectional tolerances. Both of these cause difficulties in winding production. This must be counteracted by suitable fixing, preferably in the form of an external bandage or braiding on or around the structure of the individual conductor elements. An external bandage is suitable in this sense if it is applied tightly enough to ensure tight tolerances, but at the same time loose enough to allow uniform internal compensation movements of the conductor elements when the composite superconductor is bent globally, e.g. during winding production. Absorbent fabric tape is preferably used for the external bandage, since in most applications the subsequent winding is impregnated with resin in order to strengthen the winding against operating and disruptive forces.

7. In the case of the internal compensation movements mentioned above, a high level of smoothness and sliding ability of the insulation surfaces of the partial conductors against each other also plays a major role - a requirement that must be taken into account by selecting an appropriate insulating material. The addition of lubricants is less advantageous because they impair the insulating properties and are detrimental to any resin impregnation of the finished winding that may be used.
25

The production of the composite superconductor according to the innovation can advantageously be carried out with a device which is shown schematically in side view in Figure 1. This device, generally designated 10, comprises in particular the following parts, namely

a large turntable 11, which can be rotated about an axis A, with supply reels 12 and 13 for partial conductors 3-j, a double bending tool 14, a rotating slotted guide disc 15, guide elements 18 fixed in a Roebel zone 17 and a Roebel channel 19, a step feed unit 20, a taping area 21, a free-running section 22 and a winder 23.

GR OO G 3077 /. : &diams;**..*%

The functions of these parts of the device are listed below in the order of horizontal material flow:
5

1. The introduction of the strip-shaped HTS partial conductors 3j into the process takes place via the individually braked supply reels 12, 13, - in the case of N partial conductors of the later composite superconductor, therefore via N supply reels. These are mounted on the large, horizontally mounted turntable 11 (in the process direction) in a pendulum and rotatable manner, in such a way that their axial position transverse to the process direction is always maintained even when the turntable rotates and when it is removed from the strip material.

2. The partial conductors 3j are fed - while the large turntable rotates - like a net (ie on an imaginary conical surface) to the actual Roebeling zone 17. In front of this zone, the guide disk 15, which rotates at the same speed and has N individual slotted guides whose transverse axis is always kept horizontal, ensures precise pre-alignment of the partial conductors for entry into the Roebeling zone.

3. Between the large turntable 11 and the slotted guide disk 15, the offsets (so-called "edge-S-bending zones") are produced in the extended, special double bending tool 14 - in contrast to conventional solutions, well before the actual Verroebeln.

4. This is done in a step-by-step process, namely one part of the conductor: with the entire process stopped at each point, the double tool 14 is moved into the area of the conductor "trap" to a part of the conductor, the crimping process is carried out, the double tool is moved out of the trap area again, the large turntable - and thus the conductor trap - is rotated by one division (360°/ N), the conductor material is pulled further in the longitudinal direction of the conductor by an S-zone length H and stopped again, the double tool is moved into the

GR OO G 3077 * &iacgr; ** **

The area of the next sub-conductor is moved, the next cropping process is initiated, and so on.

5. The positional precision control of the pre-bent conductor elements, after they have passed the slotted guide disk 15 and shortly before they are combined to form a common structure 25, is provided by a special arrangement of individual, fixed guide elements 18 with the aim of converting the even distribution on an imaginary circular path (cage cross-section) into a paternoster-like path distribution and also partially forcing a phase advance or regression of the conductor elements on the distribution path. This is necessary in order to prepare the reliable side change of the top or bottom conductor elements in the composite conductor cross-section.

6. The actual combining or combining of the pre-bent and cross-sectionally pre-aligned partial conductors 3j to form the structure 25 of the composite superconductor takes place here - in the rhythm of the step process - in the simple Roebel channel 19. (In conventional systems for conventional composite conductors, however, several partial steps of the Roebelization process are combined locally and run continuously: holding, bending, moving and combining the partial conductors take place there in a small space in a single unit, the so-called "Roebel head".) The internal dimensions of the channel cross section of this Roebel channel 19 correspond approximately to the desired external dimensions of the composite superconductor, its length approximately 1.0 to 20 times the composite conductor width. In the inlet area, all inlet edges of the channel are slightly rounded.

7. The step feed of the conductor assembly 25 from its sub-conductors is provided by the feed unit 20 (gripping - pulling and longitudinal movement of the assembly - opening - retracting without assembly) immediately after the guide channel in interaction with the preset braking force of the supply spools on the turntable at the beginning of the device.

GR OO G 3077 .* &iacgr; .·"«.

8. The production of an external bandage takes place in the device in the bandaging area 21, - again in time with the step process, at a standstill, immediately after the feed unit. A necessary compromise between looseness and securing the contour of the conductor assembly can be achieved by a special measure. For example, the conductor stack is temporarily thickened by a tension strip (width approximately 1.7 x partial conductor width, length approximately 1.5 x bending zone distance according to Figure 1), which is placed on top of the stack, then wrapped in the bandage and then pulled out again. Bandaging is preferably done here with glass fabric tape "on a gap", i.e. with a gap between the turns of the tape. The degree of looseness of the assembly can be adjusted by selecting the strip thickness, the band spacing and the tension force during bandaging. For example, to bandage a structure 25 of the composite superconductor made of 13 HTS standard tape conductors, a slippery, 6 mm wide tension strip made of Hostaphan with a thickness of 0.35 mm and a fabric tape made of glass silk with a width of 6 mm and a thickness of 0.1 mm, each with a gap of 9 mm, can be wound.

The essential features of the described manufacturing process can be transferred to mechanical bandaging processes as part of an industrial bandaging plant.

9. The finished composite superconductor 2 is fed via the "free-running section" 22 (e.g. via corresponding rollers) to a winding device in the form of the winder 23 at the end of the device 10. The winder is set to a constant total conductor tension, equally during forward movement, reverse movement or standstill. The free-running section is always necessary to compensate for local partial conductor displacements inside the composite, caused by the inevitable transition from the stretched to the wound (curved) state of a composite conductor. It is known from the manufacturing process and winding behavior of conventional transposed conductors that such a free-running

GR OO G 3077 .· * .**».·*,

15

running distance must correspond to at least one full transposition length.

Claims (12)

1. A fully transposed composite superconductor with at least an approximately rectangular cross-section, which contains several sub-conductors combined in the manner of a Roebel rod, each of which - an at least approximately rectangular cross-section with a width B, - at least one conductor core made of a high-T _c superconductor material in a matrix and/or sheath made of normally conductive material as well as - with respect to lateral bending in the plane of width B, a predetermined bending radius R and a predetermined bending zone length H characterized in that for each of the sub-conductors ( 3 _j ) - the bending radius R is greater than 100 times the width B as well as - the bending zone length H is greater than 20 times the width B and that means are provided for fixing the partial conductors 3 _j to one another. 2. Composite superconductor according to claim 1, characterized by partial conductors ( 3 _j ) with a bending radius R of at least 150 times the width B. 3. Composite superconductor according to claim 1 or 2, characterized by partial conductors ( 3 _j ) with a bending zone length H of at least 50 times the width B. 4. Composite superconductor according to one of the preceding claims, characterized by a combination of partial conductors ( 3 _j ) with the same structure. 5. Composite superconductor according to one of the preceding claims, characterized by fixing means in the form of adhesive bonds or soldering of the partial conductors ( 3 _j ) to one another or preferably by bandaging or braiding. 6. Composite superconductor according to claim 5, characterized by a bandaging or wrapping which is permeable or absorbent for an impregnating agent or a coolant. 7. Composite superconductor according to one of the preceding claims, characterized by partial conductors ( 3 _j ) with a ratio of their width B to the respective conductor thickness D between 5 and 40, preferably between 10 and 20. 8. A composite superconductor according to one of the preceding claims, characterized in that at least some of its subconductors ( 3 _j ) are mutually electrically insulated. 9. Device for producing the composite superconductor according to one of claims 1 to 8, characterized by means for a net-like merging of the individual partial conductors ( 3 _j ) of supply spools ( 12 , 13 ) via a bending region and a guide region in a winding zone ( 17 ) such that the conductor cross-sectional position remains at least largely constant, and by means for transporting the now wound structure ( 25 ) via a feed unit ( 20 ) and a fixing region ( 21 ) into a take-up spool ( 23 ). 10. Device according to claim 9, characterized in that the supply reels ( 12 , 13 ) are rotatably attached to a turntable ( 11 ). 11. Device according to claim 9 or 10, characterized in that the feeding of the partial conductors ( 3 _j ) into the Roebeling zone ( 17 ) takes place by means of a rotating slotted guide disk ( 15 ). 12. Device according to one of claims 9 to 11, characterized by a Roebel zone ( 17 ) with fixed guide elements ( 18 ) and a Roebel channel ( 19 ).