DE1908885A1 - Electrical conductor with several stranded superconductor cores - Google Patents

Description

8002-69 / Br.vB / Ro. Dr .- / ng. Ermf Sommerfeld 1908885

Dr. D / efer v. Bezold

Pateritar.wiilie - _ '"

Munich 23, Dunanislr. 6th

Institute for Plasma Physics G.m.b.H. Munich-Garching

Electrical conductor with several stranded superconductor cores .

The present invention relates to electrical conductors for " superconducting windings or switching sections, with several superconducting wires stranded together. i -

It is known to operate superconducting windings in a bath of liquid helium in order to achieve the low working temperature of, for example, 4.2 ° K and that from the outside Dissipate inflowing heat generated in the winding. It is also known to build the winding from tubular conductors which carry the coolant, e.g. liquid or gaseous helium, inside. The winding then needs to be outside the conductor only a thermal insulation, but no heliura container. Such directly cooled, hollow conductors consist of a tube made of normal conducting Metal such as copper or aluminum, in which superconductor wheels are embedded as single wires, or the superconductor as a surface layer on its inside or outside. Naturally, such a pipe has a diameter of several Millimeters, as otherwise the coolant required for cooling cannot flow through. Such dimensions now lead to Conductors for currents above 100 A or, in the case of windings, for magnetic ones Field strengths above 1000 Oe lead to significant losses Current and field changes, e.g.> in windings for alternating current, but also with windings for direct current, which are excited and de-excited within a limited time. Eddy current losses arise in the process and hysteresis losses. The losses increase with it the square of the diameter and the magnetic field strength. You can with high field strength for the dimensioning of the recooling system of the

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Windings a · decisive role _β To this. To avoid difficulty, and at the same time to also achieve the advantage of the tubular conductor construction described above, j it is proposed according to the invention to build an electrical conductor from several superconductor cores stranded together for superconducting windings or switching paths, to surround this rope with a vacuum-tight sheath and the Space between see the individual cores of the rope and between the rope and the sheath being filled with liquid or supercritical helium at a low temperature. The structure of the conductor as a rope made up of many isolated and twisted individual cores reports significant eddy current and hysteresis losses and allows extensive contact with the coolant. '

In order to make good use of the superconductor material, it is also known to fully stabilize the superconductor <'This happens'. through the connection of the superconductor with a cross-section of high-purity copper or aluminum that is several times larger. This means that the local losses remain small in the event of flux jumps in the superconductor - because the current from the superconductor can pass into a sufficiently large cross-section of the stabilizing metal / its losses through the coolant can be continuously removed. However, this method fails with Glei c'hstromwi cklungen that are exposed to strong magnetic field changes, for example, "excitation windings of large machines, alternating current windings and cryotrons, because eddy current losses arise in the stabilizing metal, the larger its cross-section embodiment of the invention, therefore, the cross-section of the cable wires of the conductor is reduced so that the eddy current losses are negligible. hysteresis losses are thus practically · avoided that the superconductor souls of veins very thin, counter 'isolated from each other and twisted are _β Contains a vein several superconducting souls, these are also twisted, but only separated from each other by normal metal . without naming- =.,. ■ -'-

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! values can absorb temperature increase. As such heat storage j

'more liquid or supercritical helium is particularly well overall \; suitable because its related to the volume of heat storage unit I ^ ability in the temperature range of ⁰ 4-5 K more than a thousand times! is larger than that of the metals copper and aluminum used so far minium. These metals are not able to absorb a significant amount of heat; they have to pass it on to the coolant immediately if they are not to assume a temperature that is harmful to superconductivity. Therefore, the construction with large amounts of stabilizing metal, which has been customary up to now, is only operationally reliable if no gas bubbles of subcritical pressure accumulate on the surface of the stabilizing metal. This | ! Condition is also decisive for the operational safety of the ladder construction according to the invention. In the case of cooling with supercritical helium, it is fulfilled from the outset. With cooling with liquid 'helium, so subcritical pressure of the coolant, they can! By design measures, eg follow a strong flow of \ flüssigen.Kühlmittels or vertical conductor arrangement.

! In a further development of the conductor according to the invention, the superconductor cores with a small diameter are brought into good heat-conducting contact with a certain amount of metal, so that the surface of the core is increased compared to the surface of the core j. The core surface is for the most part in direct contact with the coolant. The core insulation may therefore g ; do not form a coherent coating. Isolation is on. - '; The simplest way of doing this is through a very loose covering with insulating 'threads,' for example, a glass fiber thread of at least 50 / um! Diameter wound helically around the wire, where ^f at the pitch of the helix is several times the size of the twisting thickness. The veins are processed into a rope, the successive layers of which are twisted in opposite directions. The layers can be wound on an insulating, helium-permeable core, for example on a helical spring made from a plastic thread. To make good use of space, it is advisable to enclose the round or oval rope in a rectangular envelope in such a way that free flow cross-sections are created at the four corners. Nevertheless, the rope can be supported in all four directions. The inventive conductor

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, design has the consequence that the interior of the shell is at least a quarter, but preferably more than half of the coolant is filled out. Nevertheless, you get cheap and effective ones Current densities. They are also cheaper with direct current windings I than with fully stabilized windings of the usual design.

! The vacuum-tight sheaths are expediently extruded over the finished rope. With shorter ladder lengths, the rope can also ^: be pulled into the sheath. The shell can be made of metal, plastic or glass, etc. consist. If metal is used, it should not have a particularly high conductivity at the low operating temperature. Examples of suitable extrudable metals are aluminum of low purity, aluminum ^ zinc ^ alloys or non-superconducting lead alloys. Extruded plastic casings can be made vacuum-tight by a coating of metal. For example, an additional thin coating of plastic can be pressed on, which can be provided with a firmly adhering nickel coating by electroless reduction, on which another pore-free metal coating, e.g. nickel or chromium, a few µm thick is then applied in a galvariic way.

If the rope is surrounded by a metal sheath, it is advisable to to loosely wrap the rope with insulating threads, like this that on the one hand it is isolated from the shell, but the helium can penetrate from the free flow cross-section between the cores of the rope. This has the advantage that the sleeves are outside for adjacent turns not to be isolated- need * - chen. To prevent large eddy current losses in the adjacent » the sheaths lying on the side of a winding already suffice with the natural ones; Oxide layers between the individual turns. The whole winding forms a body that conducts heat well in direct current windings only cooled on its surface and to the operating temperature must be brought. The coolant inside the Htillej then does not need to circulate and only serves, due to its high specific heat storage capacity, for river jumps and Absorb and prevent heat quantities generated by changes in the field, that local overheating occurs, which could lead to a quenching of the superconductivity

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Surrounded by conductive metal, which is kept at the low operating temperature by means of tubes through which liquid or supercritical helium flows. For the first cooling you can use such
Pipes are also initially passed without liquid nitrogen
that the inside of the conductor sheaths contaminated by a substance! becomes, which solidifies when cooling to 4.2 ° K and the conductor sheaths I could clog inside. In such an arrangement with cooling.; the winding from the outside, it is sufficient to connect the fiber claddings at one or '■ both ends of the winding to a helium reservoir bottle. When the initially gaseous Hüllenfüllüng cools down
then helium can flow in and the same pressure can always be maintained * \

If the supply lines to the winding are at room temperature, it is advisable to use high-pressure helium gas cylinders,
which is then reduced to the operating pressure inside the conductor sleeve by reducing valves. If the operating pressure subcritical, the liquid-helium within the sheath when cooled to 4.2 K ^0; sig, if it is supercritical, e.g. _e = 3 ata, then the helium remains
gaseous at high density and no gas bubbles can form; · form.

If the conductor according to the invention is used for alternating current
or direct current or as a frequently changing strength
magnetically controlled switching path (Kryotron), so you have to
If you expect significant losses during operation, it is not enough to keep away the% of the heat flowing in from the outside on the surface of the entire winding by means of a cooled screen. Each conductor in the interior of the envelope must then be continuously cooled. In this case
the coolant inside the shell is constantly being fed through
chilled replaced. The conductor sleeve is at suitable intervals; fresh coolant supplied, which then through the conductor sleeve ^; flows and can flow out again after a certain distance.
If the conductor sheaths are at ground potential, the cooling rack can be closed

: and dissipation, through metal pipes within the thermal insulation!

.follow. Are metallic conductor sheaths with the conductor cable in electrical ·.

; tric contact, the repeated coolant supply and discharge _; \ line via insulating pipes or metal pipes with an insulating intermediate piece. Then the conductor cover must also be j

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jdung are electrically isolated from the other windings " i The details of the invention are based on the drawing, in more detail J explained. Show it:

Fig. 1 Cross section of a conductor for direct current of high current strength j ',

Fig. 2 cross section through a wire of a conductor after .Fig. 1;

3 shows a cross section through a direct current winding made of conductors according to FIG. 1; .

FIG. 4 shows a schematic representation of a winding according to FIG. 3 including the cooling device! ".- '.' ■. -,;

5 shows a cross section through a conductor for an alternating current winding;

Fig. 6 cross section through a wire for a conductor according to

Pig. 5s'. / ^{; :}

7 shows a cross section through a cryotron conductor; ■

8 shows a connecting piece for two conductors according to FIG. 1 and FIG. 9 cross section through a conductor with multiple rope ₀

Fig. 1 shows the cross section of a conductor for direct current of, for example, 10,000 A. On a wavy folded and! Perforated plastic webs 1 are superconducting insulated wires 2. wound in opposite directions twisted in several layers. Through a '. loose wrapping 3 with insulating threads, the rope is insulated from an outer sheath 5. The casing made of an aluminum alloy is applied to the finished cable by extrusion. At the four corners of the casing, free flow cross-sections 4 remain for the coolant, which can also flow in the channels of the web 1. The refrigeration unit penetrates through the loose wrapping 3 between the individual wires. The cooling surface for the veins is therefore large. -.- ■ "■ -." ^r

! -Fig. 2 shows the cross section of a wire of the conductor according to! 1. 6 is the superconducting soul «It consists, for example, of the '. hard superconductor niobium-titanium. The soul is of a coat 7 ^; ■ Surrounded by high-purity copper, which can have such a large cross-section that full stabilization occurs. _B In order to achieve high effective current densities *, however, the cross-section can be significantly reduced without adversely affecting operational reliability. However, if the winding is dimensioned in this way, a

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: Extinction of the superconductivity, the winding current j

• be quickly degraded to prevent the whole;

magnetic energy of the winding inside the conductor in heat I.

; is implemented. To isolate the individual wires against each other ^;

ren, they get a loose winding with an insulating ]

Thread 8th;

FIG. 5 shows the cross section of a winding which is made up of conductors according to FIG. 1 and is used, for example, to excite a turbo generator, 10 is a winding made of a conductor according to FIG. 1. The windings are wound next to and on top of one another without insulation and are supported from each other. They are enclosed by a shield 12 made of copper, but not vacuum | needs to be tight and useful to reduce eddy current losses has longitudinal and transverse slots. A longitudinal slot is denoted by 16. The screen 12 is in a thermally conductive connection with a flat tube 13 * which carries liquid or supercritical helium inside. The shield and cooling pipe are at ground potential. They are held in place in a vacuum container 14 by spacers 15. . ^N

The vacuum container 14 consists of poorly conductive metal, for example stainless steel, and is at ground potential. The spacers 15 can be constructed from pressure-resistant ceramic disks in such a way that there are always only a few points of contact between the individual parts, so that the heat transfer remains low λ. . ~ ■ - · ■■■■

Flg. 4 schematically shows a winding 21 made of conductors 1 with a screen 22, inlets 23 of the coolant a dry cooler 24, as well as Sfcromzüge 25 for winding with Pressure bottles 26 for gaseous helium, and DC clamps 27. 28 is the outer vacuum container of the thermal insulation. The spacers between the vacuum container and the screen are not shown. The space between the screen and the vacuum container is useful filled with super insulation, i.e. reflective foils, so that the heat radiation is reduced.

Fig. 5 shows the cross section through a conductor, which also is suitable for alternating current. The rope consists of veins 31, .the

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are laid around a center conductor in several oppositely twisted layers. The rope is located in an extruded plastic sheath 32. The structure of the core 31 is shown in FIG. jThis contains a large number of superconducting souls 41 which are embedded in a metal 42. The wire is twisted around its own axis so that the individual cores run helically around the wire axis. The insulation against the neighboring wires is \ by a helically wound around the core thread Insulating j j ensured 43rd The height of rise of the helix is several times the size of the thread thickness. " ^: j.

^: Fig. 7 shows the cross section through a conductor which can be used for a \ Kryotrony machine or switch. The rope] here consists of two layers of wires 51 which are twisted in opposite directions on a helical spring 52 made from a plastic thread. Around the rope there is a loose wrapping 53 * each in a sheath 54 as insulation. If metal is used for this, it should have a relatively poor conductivity. The veins of this rope are constructed similarly as in Fig. 6, but the embedding metal must not have a significantly larger cross-section than the sum of the cross-sections of the. superconducting souls. The souls consist of a soft superconductor, for example niobium, or of a hard superconductor, such as lead-bismuth eutectic with a critical field strength of about 13.8 kG, i.e. below the Elsenätti-; • supply. The embedding metal should have a specific resistance that is as high as possible. For this you choose ζ .B-. Alloys of nickel with copper, iron or chromium. The wires are made by providing a block of the embedding metal with holes into which the superconductor rods are fitted: and possibly soldered in. The whole thing is then worked down by hammering, orphaning or pulling to such a small cross-section * that the individual souls are only a few fm thick. When using soft superconductors, it is particularly important to achieve the smallest possible thickness for the 'souls, because this increases the critical current density _3c and, as a result of the path length effect, the specific resistance ο. To reduce the blocking losses of a cryotron, it is important to use the product j _c . ο to make it as large as possible. Because with decreasing thickness of the superconducting core, the critical field i "

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strength increases, there is also a lower limit for the thickness. Here, too, the twisting of the wire about its longitudinal axis is useful. -

'Fig. 8 shows the longitudinal section through a connecting piece: between a conductor according to FIG. 1 and a conductor according to FIG. 7. The conductor according to FIG. 1 is denoted by 61 and the conductor according to FIG. the sheath of both conductors is removed a distance of several centimeters / likewise the insulation between the cores. Then the wires 63 of the conductor 61 and the wires 64 of the conductor 62 are plugged into one another, surrounded with a copper sleeve 65, squeezed together and soldered. At this point the wires are not separated from each other <| isolated and increased eddy current losses to be feared. Therefore, such connections are placed within a winding in an area of low magnetic field strength. The sheaths of the two conductors 61 and 62 are connected to one another in a vacuum-tight manner by a sheath 66. FIG A tube extension piece 67 is soldered vacuum-tight to a ceramic tube 69 via a resilient metal intermediate piece 68, this again in the same way with a tube 70 Isolation switched on, which is important in cases where there is contact between the conductor and the conductor sheath. "

Fig. 9 shows a conductor with multiple rope, which is used for alternating \ selstrom or as a cryotron is suitable. The individual wires 71 are constructed as in Fig. 6, for example. They form six single layers Ropes 72, which are wound on coil springs 7> made of plastic. Together they lie on a coil spring 74 made of plastic. ' j They are enclosed in a vacuum-tight manner by a sleeve 75. Here: is the larger part of the interior of the shell for the coolant » flow freely.

The details of the preceding figures can also be used in other Way to be combined with each other. One can also use machi-; nen with hard superconductors and cryotron these two conductors in

; a common shell or the hard superconductor in the inner j Ren cavity of a cryotron according to Fig. 7 or 9 accommodate. !

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Claims (1)

Claims i 1.) Electrical conductor for superconducting windings or Sehalt- L ! stretch, with several superconductor cores j | (2, 31, 51, 63, 64, 71), d a d u r c h g e k e η η draw - 1 j η e t that the rope from a vacuum-tight sheath (5, 54) to -r ! and the space between the individual wires of the rope ■ and between the rope and the sheath with liquid or supercritical ιHelium is filled as a low temperature coolant. : ; 2 ..) Electrical conductor according to claim 1, dad ure h. ge ■ = indicates that each core of the rope consists of a <sr or _; several superconducting souls (6, 41) and a metal (7 * 42) which is in good thermal contact with each soul. . ι3 ·) Electrical conductor according to claim 1 or 2.,. because it is marked dureh that, each wire is wrapped so loosely with insulating threads (43) that the coolant has direct contact with the greater part of the metal surface. ; 4.) Electrical conductor according to one of claims 1 - 3, da— ^; characterized in that the coolant is at least occupies a quarter of the interior of the shell. j j 5.) Electrical conductor according to one of claims 1 - 4, da - "j characterized in that the round or oval rope is surrounded by a sheath (5, 3k) with a rectangular cross-section, so that at the four corners between the rope and shell result in free flow cross-sections (4). j 6.) Electrical conductor according to one of claims 1 - 5, as j by characterized in that the shell, from one ! Metal of low conductivity, e.g. made of impure aluminum or ι consists of an aluminum alloy. '- "- ■'" ■ / ■■ : 7.) Electrical conductor according to claim 6, since ge - -; indicates that the rope with insulating threads ■ '; (53) is loosely wound so that the rope is isolated on the one hand by the sheath (54), but the coolant can easily penetrate from the free ■ flow cross-section between the veins of the rope (Fig. 7). S. 009835/1057 8.) Electrical conductor according to claims 6 and f, da -. ; characterized by that the complete 'conductors gene without isolation between the sheaths of the individual WinduE- \ larger windings or winding portion wound. 9 ') Electrical conductor according to claim 8, characterized in that ge jk e η η. that the windings or winding parts are located within a thermal insulation in a screen (12, 22) made of metal with good thermal conductivity, which is kept at the low operating temperature by means of tubes through which liquid or supercritical helium flows. 10.) Electrical conductor according to one of claims 1-5, characterized characterized in that the sheath (5, 54) made of an extruded plastic with a vacuum tight There is a metal coating. / ; 11.) Electrical conductor according to one of claims 1 - 10, characterized in that supercritical! Helium is maintained within the sheath of the conductor by connecting the ends of the conductor (21) to pressure bottles (26) filled with helium gas (Fig. K), '12.) Electrical conductor according to one of the preceding claims, as characterized in that the liquid. or supercritical helium the conductor casing at a plurality of locations of [length of conductor is supplied and removed again and a coolant-ι flow is maintained within the envelope. • 13.) Electrical conductor according to one of claims 1-6 and iO - 12, d a 'd u r c h g e k e η η ζ e i c h η e t that the The rope is not electrically insulated from the sheath, it is surrounded by insulation and the supply and discharge of helium take place via insulating sections. Ik .) Connection of two conductor pieces according to one of the preceding claims, characterized in that the individual wires of the cables to be connected are freed from the sheath and its insulation over a distance of several centimeters, pushed into one another, squeezed together and soldered (Fig. 8) . 009835/1057 Blank page J ? \ Il? fO