DE2256921A1 - PROCESS FOR PRODUCING A WINDING AND WINDING PRODUCED BY THIS PROCESS - Google Patents

Description

138/72 We

Aktiengesellschaft Brown, Boveri & Cie, Baden (Switzerland)

Process for producing a winding and winding produced according to this process

The invention relates to a method for producing an impregnated winding, in particular one from superconducting Conductor material existing winding, which is used to generate electromagnetic DC or alternating fields serves and which has at least one cooling channel for the passage of a liquid or gaseous cooling medium is provided, as well as a winding produced according to this process.

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For the previously built, superconducting high-field windings with current densities of more than 10'000-15 ¹ 000 A / cm, such as experimental solenoids, beam guiding or beam focusing magnets, mainly solid, thin wires made of transition metal alloys, such as NbZr or NbTi, were sheathed with a thin copper bar, or then thin strips coated with the intermetallic compound Nb., Sn.

However, all of these windings generating magnetic fields show instabilities in their operating behavior, referred to as degradation and training effects. she achieve the critical current and field values measured on short wire samples in a transverse magnetic field not, or only after several transitions from the superconducting to the normally conducting state.

It has been recognized that the causes are in part in coupled, thermal and magnetic instabilities and on the other hand, the possibility of wire movement during the build-up of the magnetic field. ·

The above-mentioned superconductors also have the disadvantage that they are unacceptable even at a frequency of 1 Hz

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have high alternating field losses and e.g. for the construction of beam guiding magnets for synchrotron accelerators are unsuitable.

Experimental and theoretical investigations have shown that both the instabilities, so-called plus jump instabilities, as well as the alternating field losses depend strongly on the diameter of the superconductor. This resulted on the development of inherently stable pilament conductors, consisting of a large number of very thin superconducting ones Filaments, for example consisting of NbTi, which are in a normally conductive matrix, for example consisting of Cu or Al, embedded and metallically well connected to this. Through further measures such as twisting the filaments in the conductor and transposing several twisted conductors, the Magnetic instabilities and the losses in alternating fields are further reduced.

Use is sufficient for stable and degradation-free behavior of alternating field generating windings the described filament conductor alone is not. Research and experience have shown that for the Conception of such windings further, in the following

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-A- the briefly described conditions must be observed.

a) Mechanical instabilities caused by moving the ladder must be avoided. Owns a leader within the Winding the opportunity to move under the force of the variable magnetic field move, it can heat up as much as a result of the frictional heat generated or as a result of the kinetic energy otherwise converted into heat, that the critical temperature of the superconductor, possibly with the help of thermally triggered Flux jumps, exceeded and the winding partially or completely in the normally conducting state is brought. As a result of the very low specific heat of the superconductor and the stabilizing matrix A very small movement is sufficient for this process.

An attempt was made to prevent this possibility of movement by creating uninterrupted, high conductor lines wound layer windings were produced. With this procedure, the mechanical stress state in the conductor of the already wound layers due to the easy, plastic deformability of the

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involved insulating materials and the elastic behavior of the conductor and the supporting winding carrier through each newly applied layer changed. On the -finished winding are in this way from the innermost layer to the outermost position considers progressively zones with tensile stresses, without stresses, compressive stresses present without tension and tension in the conductor. Dangerous zones with ladder movement opportunities are present where there are mechanical tensions disappeared in the ladder. Mechanical stability cannot be guaranteed with this method will.

It is known that a complete impregnation of the winding with a suitable one is more promising Impregnation agent such as an epoxy impregnation resin. If the impregnation is successful, all gaps are filled and if the binding properties are good between the Hs.rz and the insulating materials involved, the windings are mechanically tight with one another tied together.

However, the following partially contradicting conditions must be observed:

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cL) The contraction of the materials involved differs greatly when cooling from room temperature to operating temperature, ie to 4 IC. The conductor, consisting of NbTi filaments, embedded "

in Cu, at 4 IC, there is a contraction of J \ JL / 4-- ^

-5
-300 · 10, a pure impregnation resin on the other hand

one of Δ £, / <£ ■ * -600-1200 · 10 ~ ⁵ .

After the cooling process, the tension created by the winding has an additional, by the various contraction of ladder and resin-related stress geometrically superimposed. ■

In addition, temporary high temperature differences develop during cooling, which is also the case high mechanical stresses in the · system. ■

If the winding is energized, the current-carrying conductor forms as a result of the magnetic field acting forces, which differ from the existing Superimpose the stress state again.

Isn't the impregnation resin of these loads Grown, cracks develop in the resin, whereby the mechanical tension energy converted into heat enough j to the winding in the normal conducting

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To drive state and in turn degradation and training effects occur.

The resin should therefore in its contraction behavior to that of the conductor and it should be in the hardened state "at deep Temperatures have high mechanical strength. In principle, this is possible by filling of the resin with suitable fillers.

To achieve a high current density, the windings must be wound very tightly and compactly. To a To achieve complete impregnation, it has to be Resin have a very low viscosity. Unfortunately, this is greatly increased by a filler, so that complete impregnation is jeopardized. The fine channels and gaps in the winding work also as a filter, so that the filler does not get into the winding, or not in the desired amount penetrates.

b) Also the best filamerite conductors known to date are not loss-free in periodic V / echselfeld applications « These time- and field-dependent losses converted into heat increase the temperature of the winding. As a result of the

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functional connection of the critical currents, fields and temperatures, the temperature increase is not allowed be more than about 0.2 K ", since otherwise there will be an impermissibly strong reduction in the critical current density. This requires intensive cooling of the interior of the winding.

Another need to be able to dissipate the heat generated in the winding as well as possible occurs at a transition from the superconducting to the normally conducting state. This transition begins in one Points of the conductor by exceeding the critical state of the superconductor. This then has a Zone with relatively high electrical resistance, see above that as a result of the current flowing in it, warming occurs, which spreads rapidly and further parts of the superconductor can become normally conductive. This complicated thermal and electromagnetic process is complete when all of the field energy has been converted into heat. This can result in high local temperatures, which can lead to the destruction of the winding. Good heat distribution and dissipation can this process usually not, but completely prevented but grounded and delayed.

The impregnation of a winding acts as a result of the

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thermal conductivity struggled against this requirement.

An attempt was made to dissipate heat using the
Winding inserted cooling tubes through which the cooling medium flows and the associated, highly heat-conductive cooling plates. These work perfectly,
if they are present in sufficient numbers and correct
are distributed. However, they have the disadvantages that they take up a relatively large amount of changing space, that is to say
reduce the current density and that in it as a result of the
Alternating field additional eddy current losses.

Attempts have been made to circumvent these disadvantages by adding
Fabric, consisting of thin, insulated copper wires as intermediate layers, were inserted into the winding in such a way that their edge-side ends protrude and from
liquid helium were washed around. This method has the disadvantages that it makes the impregnation much more difficult
will and that as a result of the relatively thin and long
Copper wires nevertheless occur fairly, high temperature gradients.

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Another known method consists in using strips running in the axial direction between the layers to be inserted in such a way that cooling channels through which helium flows are created between the strips. The cooling effect achieved is good; the winding can be impregnated however, cannot be carried out.

c) As mentioned under b), in all metallic parts that are located in the area of the alternating field, Induced turbulent currents and additional sources of loss generated. This applies in particular to winding support structures, support structures and large ones Cooling aids, such as pipes, sheets, etc. and made of metal existing cooling channels. ·

The object of the invention is to create a method of manufacturing a winding like the one mentioned above Disadvantages eliminated.

The method according to the invention is characterized in that that when winding the. Winding at least one to that corresponding insert forming cooling channel inserts, polygamy is made of such a material that it will after completion of the winding and after

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Impregnation process or a thermal treatment the impregnation removed from the winding by means of a chemical or thermal process can be.

It is zv / square if you use inlays made of Woods metal, the melting point of which is higher than the impregnation and curing temperature and lower than the softening temperature of the impregnation agent.

It is advantageous if, in order to improve the heat dissipation, at least in the area of the cooling ducts, a Impregnating agent with good thermal conductivity is used.

The invention also relates to a winding produced by the method according to the invention superconducting conductor material, which is characterized in that it has a plurality of cooling channels and that between each two adjacent cooling channels thermally highly conductive material in the impregnation compound is embedded in order to dissipate the heat from this intermediate area into the adjacent cooling channels (18).

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To improve heat dissipation, it is advisable to if arranged between the cooling channels, thermal good conductive material from one through thin, with one electrical insulation provided thermally highly conductive wires, for example Cu or Al wires, formed Fabric or braid.

Around the winding secure against high loads form, it is advantageous if between the layers wound from electrically insulated superconductor Reinforcing fibers are inserted between layers of such a type and material properties that these together with the impregnating agent, form an eddy current-free, mechanically high-strength system, the contraction of which at operating temperature corresponds to that of the superconductor. It is useful if the intermediate layers are made of fabrics, preferably glass fiber fabrics or braids exist. In order to improve heat dissipation, it is advantageous if the intermediate layers are thermally good conductive material such as metal for example Cu or Al or graphite powder are coated. It is advantageous to if the metal coating has one effect to avoid eddy current losses in alternating magnetic fields, has relatively high electrical resistance by

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"for example in narrow, parallel or meander-shaped, is applied strips separated from one another by narrow spaces.

The invention is explained below with reference to the drawing, for example. Show it;

Fig.l a method for producing an inventive Winding;

2 shows a section through an exemplary embodiment of a winding according to the invention,

3 shows a section along the line III ~ III in FIG. 2,

Fig. 4 to 6 different sections through an example Embodiment of a winding according to the invention;

7 shows a section along the line VI-VII in FIG by an embodiment of a superconducting quadrupole winding according to the invention, for example;

FIG. 8 is an end view of that shown in FIG Winding;

FIG. 9 is a plan view of the one shown in FIGS. 7 and 8 Winding; and

FIG. 10 shows a section through a further exemplary embodiment a winding according to the invention arranged in a closed cooling circuit.

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In Figure 1 is a prepared for the impregnation, superconducting winding inclined in a mold.

In this example, the mold "consists of two inner ones divisible mold halves 1 and 2, in which the edge disks 3 and 4 and the support sleeves 5 and 6 are inserted. To At the end of the winding process, the bandage 7, which consists of a fabric tape, is attached and the mold with the two outer mold halves 8 and 9 closed. Ensure a vacuum-tight seal the seals 10. ·.

Pure very dense windings with thin superconductors 11 The impregnation takes place with a diameter of approx with a low-viscosity impregnating agent, most advantageously in the closed mold described. After several hours of evacuation at an elevated temperature the impregnating agent is let in through the inlet pipe, by means of the annular groove 14 over the circumference distributed over the winding and pressed through the winding using increased pressure until it is free of gas bubbles flows out through the outlet pipe · 15. By closing of the outlet pipe, the impregnating agent can be a

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be subjected to high static pressure, as a result of which it penetrates into the finest pores of the winding.

To facilitate or enable complete impregnation of the winding, a low-viscosity, unfilled impregnation agent of such a type is advantageously used that the impregnation agent and material of the intermediate layers 12 have a contraction behavior that is adapted to that of the superconductor 11. This can be achieved, for example, with a system of a selected epoxy resin filled with 60-70 VoI <fo layered glass silk fabric. With this system, a high mechanical strength is achieved at the same time, which corresponds to that of a high-alloy steel, so that it acts as a mechanical reinforcement of the winding body.

The edge disks 3 and 4 are provided with radially arranged slots 16 through which the inserts 17 to are guided to the inner edge of the mold, and which, together with the annular groove 14, passage openings for the impregnating resin form. The material of these prefabricated edge discs also consists of a system of dense pressed fabric, e.g. glass silk fabric, and an ex-

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hardened impregnating resin such as an epoxy resin of Contraction behavior is adapted to that of the superconductor.

The support sleeves 5 and 6 consist of the same material system as the edge disks 3 and 4. They are used for Compliance with the exact, cylindrical inner geometry of the winding and as mechanical reinforcement,

The bandage arranged on the outer circumference of the winding consists of the same glass fiber fabric as the intermediate layers 12 and is also used for mechanical reinforcement of the winding body.

Generally arise on the outside of the winding always any cavities, in the example mentioned in the annular grooves 14 and in the slots 16, which would fill with pure impregnating agent. To avoid cracks, it is advantageous to follow directly afterwards To re-press the impregnation heavily filled impregnation agent, so that the pure impregnation agent 'from the Cavities is displaced and 'there the filling material is deposited. When using suitable filler material

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also at these points an adaptation to the contraction behavior of the superconductor.

This can be done with simple winding geometries and when using superconductors with a larger diameter Impregnation process can be simplified by the outer mold halves 8 and 9 omitted and the winding in the evacuated state in a dipping process and possibly using a higher pressure in the impregnating agent is impregnated.

The winding in Figure 1 is constructed as follows; After each finished winding with the insulated superconductor 11 In one or more layers, an intermediate layer 12 is flush with the edge disks 3 and 4 Windings inserted and the next conductor layer wound over it with a high wire tension. These liners, consisting of A highly tear-resistant fabric, such as glass silk fabric, is covered with a layer before or after being inserted or a covering, through which the thermal conductivity of the intermediate layer in the impregnated and cured Condition is increased. This can be done by applying a thermally conductive powder or fillet to the fabric, for example with a graphite powder or with a metallic powder on both sides, over the whole area or partially

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pollinated or with the help of a. Binder-coated , or by providing the fabric with thin metal layers over the whole area or in parts.

These metal layers can be produced by a metal spraying process, by vapor deposition, by a chemical process or by other suitable methods. These layers must be used to avoid eddy current losses have a relatively high electrical resistance in the alternating magnetic field. This can can be achieved by the layer e.g. in narrow, parallel or meandering, through narrow Between spaces separated strips is arranged so that there is no closed electrical Form current paths. - .->

The intermediate layers can already be placed in the Winding can be impregnated with a suitable impregnating agent, which only dries but does not harden or it is also cured.- The thermally highly conductive powder can be used as a filler in the impregnating agent and with this - together on the interlayer fabric or the methods described above can be used. ·

11 - -

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Pre-impregnated but not hardened intermediate layers have the advantage that the impregnating agent is already in place during the winding process, so that the impregnation process described above is made easier or even obsolete.

The use of the intermediate layers not only improves the thermal conductivity in the winding, but also acts as a mechanical reinforcement of the winding, thus adding reinforcement to the conductor or the winding Stainless, anti-magnetic steel inserts can be avoided in many cases. All materials involved are their contraction behavior is chosen to be adapted to that of the superconductor, so that at operating temperature this does not result in any additional mechanical stresses.

In order to achieve high current densities of 30'000-5O ¹ OOO A / cm advantageously pre-impregnated glass cloth are selected from about 50 pia thickness.

The inserts 17 are grounded to form the cooling channels in the desired dimension, number and arrangement on the finished wound conductor layers inserted so that their ends the

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touch the inner edge of the mold. In the example in the figure they are for this purpose through the radial slots 16 of the edge discs. 3 and 4 passed through.

The mentioned inserts 17 consist of a material \ velches after the finished impregnated winding has been removed from the mold by chemical means or by Melt-out can be removed.

In Figures 2 and 3, a finished impregnated winding is shown with removed inserts. The deposits can consist of a low-melting metal - such as Woods metal, whose melting point higher than the impregnation and curing temperatures and lower than the softening point of the used impregnating agent. After molding, the winding is heated until the inlays melt, so that the liquid metal flows out or with a heated gas, for example nitrogen, can be pressed out. Any thin layers of resin that may be present In front of the channel openings, before this process, there are mechanical mechanisms removed. ·. .

In this way, continuously open cooling channels 18 are created through which the cooling medium, for example

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wise liquid or gaseous helium, can flow, to cool the winding to operating temperature and the permanent or temporary generated during operation Lead away alternating field losses. As a result of the arrangement of the cooling channels, the cooling of the winding mass takes place evenly and with small occurring temperature gradients, so that there are relatively small mechanical stresses arise as a result of the large, effective heat exchange surfaces In the channels, the cooling takes place quickly and with good use of the enthalpy of the cooling medium.

As can be seen from FIGS. 2 and 3, the dimensions, number and arrangement of the cooling channels can be freely selected chosen and well adapted to the needs.

The effect of the cooling channels can thereby be improved, that two adjacent channels in a layer are connected by cooling aids 19, which are a good thermal conductor. To avoid high eddy current losses exist these cooling aids are preferably made of a mesh or fabric made of thin, thermally highly conductive metal wires such as made of copper or aluminum. So that no closed current loops can arise, these are Metal wires isolated individually.

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In FIGS. 4 ″ to 6, sections through a ″ are for example Embodiment of a winding according to the invention shown. . ■

The winding is made with a superconductor, for example from. rectangular cross-section and provided with a electrical insulation 21 wound in layers. After each completely wound layer, one is described above Intermediate layer 12 inserted and the next conductor layer wrapped. -

I cooling layers are inserted at the required intervals, alternately consisting of the cooling aids 19 and the cooling channels 18 forming inserts, In.diesen Figures 4 to 6 these deposits have already been removed thought. In Figure 5, such a cooling layer is in plan view drawn. For generating small heat transfer resistances the cooling aids are arranged so that their lateral borders touch the inserts. Depending on Necessity and demand can be set with or without additional intermediate layers 12.

If there is a heat source in one point of the winding, for example as a result of the alternating field losses or as a result

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of a conductor section that has become normally conductive, the heat generated is due to the increased thermal conductivity the intermediate layers and cooling aids more evenly distributed and faster to the cooled ones Surfaces of the cooling channels out. By suitable dimensioning and arrangement of the thermally conductive and cooling elements, the resulting temperature increases can be kept within the desired limits *

In FIGS. 7 to 9, a possible application of the inventive method for producing cooling channels shown in a superconducting quadrupole winding 22. For the sake of clarity, only a single cooling channel is drawn in diagonally hatched from a cooling layer. The illustration shows that the insert 17, for the purpose of later formation of a continuously open cooling channel, even more complicated winding shapes can be adapted without difficulty.

Up to now, superconducting windings have mainly been cooled in a bath of liquid helium at atmospheric pressure. It was advantageous to arrange the cooling channels in a vertical position in order to achieve the thermosyphon effect to take advantage of. The cooling duct thicknesses are likely to be a hatred

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of approx. 0.4mm not to go below the circulation of liquid helium by trapped vapor bubbles not to prevent.

For larger superconducting windings, forced cooling by means of a closed cooling circuit offers various advantages. In principle, thereby the cooling medium is cooled in a refrigerating machine under pressure to the operating temperature, is pressed through the coil at a desired pressure and heated at about 1 K in ■ - returned to the heat exchanger of the cooling machine.

Essentially, the following advantages were achieved:

~ The build-up of the cryostat is made easier because it is necessary for the winding only a single high vacuum space and no intermediate passages is needed.

- The cooling can largely by means of the cooling channel geometry and arrangement as well as by means of pressure and flow rate adapted to the circumstances and requirements'.

- When using supercritical helium, an unfavorable Two-phase flow is avoided and an even, Predictable cooling can be achieved.

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- Operating conditions and operating costs for continuous operation are improved.

The use of windings provided with the erfindungsgeraäss produced cooling channels offers the advantage that their passages can be selected to be very small and thus the heat exchange surface large, and that their shape and distribution are largely freely determinable, so that an intensely effective cooling is achieved.

An example of the arrangement and structure of a winding is cooled in a closed circuit can be seen from Figure IO. The cooling medium comes in with the desired temperature, pressure and energy data through the inlet line 23 into the inlet manifold, where it is distributed into the cooling channels 18, through which it flows this is combined again in the output collector 25 and passed through the outlet line 26 back into the refrigeration system. As a result of being connected in parallel Because of the large number of channels, cooling channels can take the entire pressure drop of the cooling medium, despite the small ones Passage openings are kept within small limits and the enthalpy of the cooling medium is effectively used will.

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Due to the suitable shape and arrangement of the cooling channels, as well as the input distributor and output collector can use the Cooling channels in any combination in terms of flow can be connected in parallel or in series.

To avoid eddy current losses in alternating fields the input manifolds 24 and output collectors; 25 with advantage of one, strong with tissue or boring Synthetic resin filled with fibers and produced in a suitable process with the wrapping body vacuum tightly and pressure-tightly connected.

Claims (17)

PATENT CLAIMS 1. Process for the production of an impregnated winding, in particular a winding made of superconducting conductor material, which is used to generate electromagnetic Direct or alternating fields are used and with at least one cooling channel for conduction a liquid or gaseous cooling medium is provided, characterized in that when winding the winding inserts at least one insert corresponding to the cooling duct to be formed, which consists of a such material exists that it will be after the completion of the winding and after the completion of the impregnation process or a thermal treatment of the impregnation by means of a chemical or thermal Process can be removed again from the winding. 2. The method according to claim 1, characterized in that inserts made of Woods metal are used, its Melting point higher than the impregnation and curing temperature and lower than the softening temperature of the Impregnation agent lies. 3. The method according to claim 1 or 2, characterized in that 409816/0681 OWGINAL INSPECTfD that one between the with the electrically isolated Superconductor wound layers of reinforcing fibers • existing intermediate layers of this type and material properties specifies that this, together with the impregnation agent, is an eddy current-free, mechanical Form a high-strength system whose contraction at 'operating temperature corresponds to that of the superconductor. ■ '· - "■ 4. The method according to claim 3, characterized in that that one uses interlayers made of fabrics, in particular glass fiber fabrics or braids. 5. The method according to claim 4 »characterized in that that one coated with thermally good conductive metal Interlayers used. 6. The method according to claim 5, characterized in that intermediate layers are used in which the metal coating to avoid eddy current losses in alternating magnetic fields a relatively high has electrical resistance, for example in narrow, parallel or meander-shaped, is applied by narrow spaces separated strips. . 4098 16/0681. 7. The method according to one or more of the preceding claims, characterized in that one at least in the area of the cooling channels a material interspersed with thermally highly conductive material Impregnation agent used 8. The method according to one or more of the preceding Claims, characterized in that there is at least one between each two adjacent cooling channels thermally highly conductive insert arranged in such a way that it extends into the wall area of the two cooling channels or extends into the same. 9 · Method according to claim 3 or 4 »characterized in that one consists of reinforcing fibers existing intermediate layers before being inserted into the winding with the impregnating agent, preferably with an epoxy impregnation resin impregnated but not hardened and then with powder or foils made of thermally highly conductive material. ι ' 10. The method according to claim 3 or 4, characterized in that that the intermediate layers made of reinforcing fibers before they are inserted into the 409816/0681 . Winding with an impregnating agent interspersed with powder made of thermally highly conductive material, preferably an epoxy impregnation resin. ■ 11. winding of superconducting conductor material prepared according to claim 1, characterized in that it _y up a Hehrzahl of cooling channels (18). and that "between every two adjacent Eühlkanäleii (18) thermally highly conductive material (19) is embedded in the 'impregnation compound in order to dissipate the heat" from this intermediate area into the adjacent cooling channels (18), 12. Ϋ / icklung according to claim 11, characterized in that that the thermally highly conductive material arranged between the cooling channels (18) comes from a through thin wires with good electrical insulation, for example Cu or Al-wires formed fabric or braid (19) is made. . 13. Winding according to claim 11 or 12, characterized in that . that between the layers of reinforcing fibers wound from electrically insulated superconductor existing intermediate layers (12) of this type and 409816/0681 = Material properties are inserted so that, together with the impregnation agent, they form an eddy current-free, mechanically high-strength system form whose contraction at the operating temperature of those of the superconductor. · 14. Winding according to claim 13, characterized in that the intermediate layers (12) made of fabrics, preferably Fiberglass fabrics or braids are made. 15 winding according to claim 14, characterized in that that the intermediate layers (12) with thermally highly conductive material such as metal, for example Cu or Al or graphite powder are coated. 16. Winding according to claim 15, characterized in that the metal coating to avoid Eddy current losses in alternating magnetic fields have a relatively high electrical resistance, by dividing them, for example, into narrow, parallel or meander-shaped, narrow spaces from one another separate strips is applied. 17. Winding according to one or more of claims 11 409816/0681 to 16, characterized in that the impregnation compound at least in the area of the cooling channels (18) with a powder made of thermally highly conductive Material, "for example graphite or metal powder is interspersed. · Public company Brown, Boveri & Cie. 9-8 16/068 1 S3 Blank page