CONDUCTIVE LAYER AS EDDY CURRENT DAMPER

Field of the invention

The invention relates to a superconducting support system with high cooling efficiency and reduced vibrations. The invention in particular relates to superconducting bearings for flywheel energy storage. The invention also relates to a magnetic levitation transportation system using superconductors. Furthermore, the invention relates to a device for producing and winding-up of yarns in ring spinning and ring twisting machines, wherein the yarn is made rotate by a twisting element and wound up onto a bobbin due to an arising velocity difference to the spindle and the bobbin.

State of the art

A superconducting support system, such as a superconducting magnetic bearing, generally comprises a magnetic field generating element, such as a permanent magnetic element, and a superconducting element. When the superconductor is cooled down below the critical temperature the magnetic field generated by the permanent magnetic element is frozen in the superconductor by flux pinning. The interaction between the generated magnetic field and the frozen magnetic field leads to an intrinsically stable floating state of the superconducting or permanent magnetic element. As a consequence of this interaction, one element is contactlessly supported by another element. Depending on the load on the support, i.e. the displacement from the rest position, both attractive and repulsive forces appear.

A fundamental challenge when constructing superconducting support systems is the provision of a sufficiently efficient cooling of the superconducting elements to temperatures below the critical temperature, e.g. to 77 K for high temperature superconductors. Using an extremely good thermal insulation generally suffices to keep the cooling costs down. Some embodiments place the superconducting element in an insulating vacuum of typically less than 10 ^"4 mbar inside a superconductor cryostat.

Superconducting support systems usually comprise a static part and a fast moving or fast rotating part, as the levitation allows for a nearly frictionless movement of the moving part, which may comprise the magnetic field generating element or the superconducting element. Examples are flywheel energy storages, maglev trains and ring spinning and ring twisting machines. Inde- pendently of whether a rotational or a linear motion takes place, small imperfections of the support system, such as small imbalances of a rotating element or unevenness of the track of a maglev train, lead to high frequency vibrations. Also, imperfections of rotating magnetic elements lead to inhomogeneities in the generated magnetic field. Finally, even a ring spinning machine with a fixated rotor due to flux pinning as described below will suffer from high frequency vibrations of the rotor as the thread slides over the surface of the rotor.

As a result of these vibrations and/or inhomogeneities, the magnetic field generated by the magnetic field generating element has a high-frequency alternating magnetic field component at the location of the superconductor of the superconducting support system which leads to a cooling problem as described below.

The high-frequency alternating magnetic field component leads to movement of the pinned flux tubes in type-ll superconductors as the flux pinning is generally not perfect. This movement in turn leads to generation of heat through dissipation in the Shubnikov phase. In particular, unpinning of flux tubes is only partially reversible. As a consequence, vibrations of the magnetic field generating element and/or the superconducting element as well as inhomogeneities of a rotating magnetic field generating element lead to generation of heat in the superconducting element which cannot easily be removed as the efficiency of the cooling device is very low due to the low temperatures, typically between 3 and 5%.

High-frequency vibrations of the magnetic field generating element such as a rotor due to imperfect balance of the rotor therefore lead to high cooling costs for keeping the superconducting elements of the corresponding stator below the critical temperature.

The above described problem occurs for instance, in superconducting magnetic bearings, such as those for flywheel energy storage, wherein high-frequency rotation of the supported element, e.g. the flywheel, leads to high-frequency vibrations due to imperfections of the mechanical balance of the supported element as well as high-frequency components of the magnetic field due to inhomogeneities of the generated magnetic field. A further scenario is found for the magnetic levitation of high-speed trains which use superconducting magnets or superconducting elements such as Supratrans in Germany, or Maglev cobra in Brasil. Here, small imperfections in the flatness of the track lead to a high-frequency alternating magnetic field which induces heat in the superconducting elements of the support system.

Conventional ring spinning and ring twisting machines are equipped with a ring-rotor-system for twisting the thread. As a consequence of the rotation of a spindle, the rotor into which the thread is hung and that is movable on the ring is made rotate. The rotor, which can for example be formed as a simple wire loop, thereby has no intrinsic drive but is taken along by the spindle through the yarn that is hung into it. Through the high friction of the rotor on the ring, through the air resistance of the ring as well as the air resistance of the yarn balloon between the thread guiding loop and the rotor, the rotor is retained behind the speed of the spindle which leads to the thread being wound up onto the bobbin.

During the movement of the rotor on the ring, friction occurs between the ring and the rotor due to the arising centrifugal force. As it is not possible to effectively dissipate the heat because of the low mass of the rotor, this results in a velocity limitation of the rotor. If the velocity of the rotor is increased further, the rotor will heat up as much as to glow through and to break. In addition, this leads to merging of thermoplastic fiber materials and to softening of honeydew-containing cotton materials.

The productivity limitation of the ring spinning method is mostly caused by the ring-rotor-system and depends on the ring, the rotor and the yarn. A productivity increase implies a speed increase of the spindle that causes, however, a strongly increasing wear on the currently available rings and rotors when the limits are exceeded. As a consequence, the delivery speed of the thread cannot be increased any further for existing ring-rotor-systems which limits the capacity of ring spinning and ring twisting machines known in the art.

From the international patent application WO 2012/100964 by the applicant, a winding and twisting device of a ring spinning or ring twisting machine is known in which the friction between the ring and the rotor is eliminated by magnetic levitation which extends the lifespan significantly and reduces the impacting forces. A ring-shaped stator with a superconducting material and a stator cooling device is arranged coaxially to the bobbin in the same way as a ring-shaped rotor, which can be rotated in relation to the stator and which generates a magnetic field, with a loop-shaped yarn guiding element. When the superconducting material of the stator is cooled down below the transition temperature, the magnetic flux of the rotor that has entered the stator is frozen so that an autostable, passive positioning of the rotor, which has initially been held in place mechanically, can be achieved by means of magnetic levitation. Due to the contactless support of the rotating rotor, the ring of the traditional ring-rotor-system which significantly limits productivity due to the generation of heat by friction may be omitted. Instead, the entire rotor with the yarn-guiding element is now made rotate fast, wherein the rotation is essentially friction free - with the exception of a weak magnetic friction - and therefore allows for significantly higher spindle speeds. During operation, the free-floating magnet ring typically rotates at high speeds of approximately 20,000 to 50,000 rpm. The yarn guiding element installed on the magnet ring constitutes an imbalance which causes vibrations of the rotating rotor. Even if the yarn guiding element is omitted, small variations along the magnet ring may cause imbalances leading to vibrations.

As a result of these vibrations and inhomogeneities in the generated magnetic field, a high- frequency alternating magnetic field is superimposed on the magnetic field which is generated by the rotor. Interaction of this high-frequency alternating magnetic field with the superconductor of the superconducting magnetic bearing leads to a cooling problem as described above.

As cooling efficiency is a limiting economic factor of superconducting support systems, such as superconducting magnetic bearings, maglev trains, and superconducting ring spinning and ring twisting machines, there is a strong interest in reducing these costs to make the respective systems more competitive.

It is therefore an object of the present invention to provide a superconducting support system with high cooling efficiency. In particular, the present invention strives to provide a highly efficient superconducting magnetic bearing which is highly stable and exhibits low cooling costs. Furthermore, highly efficient winding and twisting devices of a ring spinning or ring twisting machine shall be provided. In addition, the present invention provides a superconducting magnetic levita- tion transportation system with reduced operational costs.

Description of the invention

The problems mentioned above are solved by a superconducting support system, comprising: at least one superconducting unit that comprises at least one superconducting element and a cryo- stat with a housing, the at least one superconducting element being provided inside the housing of the cryostat, and at least one magnetic field generating element, wherein the superconducting unit and the magnetic field generating element are arranged so that one of the superconducting unit and the magnetic field generating element is contactlessly supportable through interaction of the superconducting element and a magnetic field generated by the magnetic field generating element, wherein at least one electrically conductive layer is arranged between the at least one superconducting element and the magnetic field generating element.

According to the invention, the superconducting support system comprises at least one superconducting unit and at least one magnetic field generating element, wherein the superconducting unit comprises at least one superconducting element and the magnetic field generating element generates a magnetic field such that one of the superconducting unit and the magnetic field generating element is contactlessly supportable through interaction of the superconducting element and the magnetic field generated by the magnetic field generating system. In other words, either the magnetic field generating element is contactless supported by the superconducting unit through magnetic levitation or the superconducting unit is contactlessly supported by the magnetic field generating element through magnetic levitation. Consequently, the superconducting unit and the magnetic field generating unit can be formed and arranged in a way that one of them is supported in a contactless way due to magnetic levitation during operation. The one of the superconducting unit and the magnetic field generating unit is thus movable with respect to the other one. In particular, a nearly frictionless movement, either rotation or linear movement, of the levitating element becomes possible while the other element remains stationary.

An inherently stable, passive support of the one of the superconducting unit and the magnetic field generating unit results from the equilibrium of the restoring forces caused by changes of the position and orientation of the one of the superconducting unit and the magnetic field generating unit and the pinning forces of the flux tubes in the superconducting material of the superconducting unit.

The magnetic field generating element can comprise at least subsections with a permanent magnetic material that generate the magnetic field. Alternatively or additional, one or more electromagnets may be provided to generate the magnetic field, in particular if the magnetic field generating element remains stationary. Even superconducting electromagnets may be used. Other subsections of the magnetic field generating element and the superconducting unit can also be made of other, also nonmagnetic materials.

To enable the formation of a superconducting state in an area of the superconducting unit, the at least one superconducting element provided at least in subsections of the superconducting unit has to be cooled to temperatures below the transition temperature. According to the invention, the cooling is effected by placing the at least one superconducting element inside the housing of a cryostat. If multiple superconducting subsections of the superconducting unit are provided along with normally conducting or insulating subsections of the superconducting unit, a plurality of cryostats may be provided. The one or more cryostats are connected to or provided with one or more cooling devices which are adapted for creating low temperatures required for the formation of the superconducting state of the superconducting elements. The cooling device may be provided inside the housing of the cryostat or may be arranged externally and connected to the cryostat via suitable pipes. A number of different cryostats are known in the art and may be applied to the present invention. By way of example, the cryostat may be a bath cryostat which can be filled with liquid cryogen, such as liquid nitrogen if type-ll superconductors with transition temperatures above 77 K are used. Other cryostats such as closed-cycle cryostats for which no liquid cryogen is necessary or continuous-flow cryostats wherein the superconducting element is cooled by a liquid cryogen boiling inside the cryostat may be used in variants of the present invention. Through different combinations of multiple cooling devices which differ in taking advantage of different physical effects for the generation of cold, said cryostats can also be interconnected redundantly in order to increase the reliability of the system.

The superconducting elements can be surrounded and/or coated by an appropriate thermal insulation to minimize cooling losses. In particular, the cryostat may comprise a closed jacket inside the housing and set apart from the housing wherein the superconducting element is placed inside the jacket and the jacket is filled with liquid or gaseous cryogen. The liquid or gaseous cryogen may be circulated through the jacket by means of a cooling device connected to the jacket via pipes. The space between the jacket and the housing may be evacuated, in particular to pressures below 10 ^"4 mbar, or filled with one or more heat insulating materials. Further elements as known in the art, such as heat exchangers, compressors, pumps or the like may be provided as needed. By circulation of the liquid or gaseous cryogen as the cooling medium, a temperature of the superconducting element below the transition temperature can be maintained. Furthermore, a control unit, such as a processor, may be provided in combination with a temperature sensor to control the temperature of the cryostat, for instance by controlling the flow rate of the cryogen.

The superconducting elements can comprise or consist of a type-ll superconductor as the superconducting material.

In one embodiment, the superconducting material can be a ceramic high temperatures superconductor from the group of rare earths barium-copper oxides (SE) BaCuO, for example yttrium- barium-copper oxides (YBaCuO) or from the group of bismuth-strontium-calcium-copper oxides (BiStCaCuO). Also variants of the invention that have a superconducting material, which has an even higher transition temperature than the groups mentioned above, in the stator are possible.

Segments of normally conductive and/or insulating materials can be arranged between the superconducting subsections, i.e. the cryostat housings enclosing the respective superconducting elements. To save material, however, these intermediate segments can also be omitted com- pletely. Multiple cryostats of the superconducting unit can be connected to a single cooling device via appropriate pipes.

Due to the magnetic levitation in operation of the superconducting support system, an air gap is formed between the at least one superconducting unit and the at least one magnetic field generating element. Depending on the configuration, a ring-shaped or a linear air gap may be formed. The air gap can have a width of 0.1 millimeters to a few centimeters, depending on the application.

As described above, during operation of the device, the levitating element will generally rotate with a high frequency or linearly move with a high velocity such that any imbalance of the levitating element or unevenness of the track will lead to the above-mentioned high-frequency alternating magnetic field which generates heat inside the superconducting elements.

To avoid such heat generation, the present invention proposes at least one electrically conductive layer arranged between the at least one superconducting element and the magnetic field generating element. The electrically conductive layer may in particular be arranged such that at least some of the magnetic field lines of the magnetic field generated by the magnetic field generating element which are pinned inside the superconducting element pass through the electrically conductive layer. In other words, the electrically conductive layer is provided such that it intersects at least some of the magnetic flux tubes pinned by the superconducting element.

As a consequence, the high-frequency alternating magnetic field generated by the motion of the levitating element, i.e., the superconducting unit or the magnetic field generating element, induces eddy currents inside the electrically conductive layer, which, according to Lenz's rule, attenuate the vibration of the moving element. As a positive effect, this dampening stabilizes the movement of the levitating element such that an unstable motion which may be hazardous to nearby equipment or personnel can be avoided. In addition, the eddy currents are induced in the electrically conductive layer instead of affecting the flux pinning of the superconducting elements such that the superconducting elements may be at least partially shielded from the alternating magnetic field. The vibrational energy is ultimately dissipated inside the electrically conductive layer due to the finite resistivity of the material of the layer. As the electrically conductive layer may be provided separately from the superconducting elements, the resulting heat may easily be removed.

In particular, the electrically conductive layer may be arranged so that at least one side of the electrically conductive layer is exposed to the exterior of the cryostat. In other words, at least one side of the electrically conductive layer may be in contact with the ambient air surrounding the cryostat. As a result, heat generated through dissipation of the eddy currents induced in the electrically conductive layer can easily be transferred to the ambient air and thus carried away. The vibrational energy of the levitating element thus does not lead to an increase of the temperature of the superconducting elements which is hard to reduce, but merely to an increase of the temperature of the electrically conductive layer which can easily be reduced at room temperature, i.e. without costly or inefficient cooling mechanisms.

According to a specific embodiment, the electrically conductive layer may be provided as part of the housing of the cryostat. The electrically conductive layer may in particular, form at least part of a wall of the housing facing the magnetic field generating element. Alternatively, the entire wall of the housing may be made of one or more electrically conductive materials wherein the wall of the housing facing the magnetic field generating element acts as the electrically conductive layer.

Common cryostats for superconductors generally have a housing made of materials providing the required mechanical resistance, such as stainless steel, carbon-fiber-reinforced polymers (CFRP), or glass-fiber-reinforced polymers. This is in particular the case if the space between the jacket and the housing is evacuated to provide vacuum insulation of the superconducting element. In this case, the wall of the housing has to be provided with enough mechanical resistance to withstand the external air pressure without bending. Suitable materials for an electrically conductive layer forming part of the housing wall are for instance, Cu-Ag-micro composites and Cu-Nb-micro composites. Using these materials, the entire thickness of the housing wall facing the magnetic field generating element may be formed of micro composites. Alternatively an inner support structure of the housing wall may be formed of a high resistance material, such as stainless steel or the other materials mentioned above, while a part of the housing wall facing the magnetic field generating element may be covered or coated with the electrically conductive layer. The resulting structures of the housing provide the required mechanical resistance for a vacuum insulation of the superconducting elements.

According to an alternative embodiment, the electrically conductive layer may be provided between the cryostat and the magnetic field generating element. According to this embodiment, the electrically conductive layer is therefore provided outside the housing of the cryostat and consequently, at a significantly higher temperature than the temperature of the superconducting element. As a result, the efficiency of a cooling mechanism for cooling the electrically conductive layer is substantially higher than the efficiency of the cooling mechanism for cooling the super- conducting element. In other words, the vibrational energy of the levitating element which may be the superconducting unit or the magnetic field generating element is dissipated at room temperature instead of the low temperature of the superconducting element so that the generated heat can be easily removed. For an alternating magnetic field, the electrically conductive layer acts as a low-pass filter which filters out the high-frequency components of the alternating magnetic field while letting low-frequency components pass through.

According to a specific embodiment, the electrically conductive layer may be provided on the housing, i.e. with one side of the electrically conductive layer being in contact with the wall of the housing. In particular, the respective wall of the housing may be covered or coated with the electrically conductive layer. While a suitable material with high mechanical resistance may be used for the wall of the housing to provide stability against the ambient air pressure, the electrically conductive layer provided on the housing shields the enclosed superconducting element from the high-frequency alternating magnetic field generated by the magnetic field generating element.

According to a further embodiment, the electrically conductive layer may be provided on the magnetic field generating element, i.e. with one side of the electrically conductive layer being in contact with the magnetic field generating element. Also, two or more electrically conductive layers may be provided with one layer in contact with the housing and one layer in contact with the magnetic field generating element. As the magnetic flux tubes are pinned to the superconducting elements, arranging the electrically conductive layer on the magnetic field generating element provides the same shielding effect with respect to high-frequency components of the generated magnetic field. Arranging the electrically conductive layer on the magnetic field generating element is simple and further guarantees that no heat is directly transferred from the electrically conductive layer to the cryostat.

Alternatively or additionally, the electrically conductive layer may be provided inside the air gap, i.e. with a gap between the housing and the electrically conductive layer as well as a gap between the electrically conductive layer and the magnetic field generating element. Suitable support elements may be provided to connect the electrically conductive layer to the superconducting unit or a frame of the support system.

In a further development, a heat-insulating layer may be provided between the electrically conductive layer and the housing. In particular, the heat-insulating layer may be provided on the housing with the electrically conductive layer being provided on the heat-insulating layer. In this case, no additional support elements are needed. Providing a heat-insulating layer between the electrically conductive layer and the housing reduces the heat transfer from the electrically conductive layer to the housing and thereby to the superconducting element.

The electrically conductive layer may have a thickness between 0.05 mm and 5 mm. A layer of this thickness suffices to permit induction of eddy currents according to the skin effect. A thin electrically conductive layer allows for a reduction of the vertical or radial distance between the superconducting unit and the magnetic field generating element which simplifies the contactless support of the levitating element. Also, highly conductive materials are generally expensive such that a thin electrically conductive layer helps to reduce overall costs.

The electrically conductive layer may have an electrical conductivity at 25°C of 3x10 ⁶ S/m or more, in particular of 5x10 ⁶ S/m or more. The electrical conductivity may be determined according to DIN EN 80000-6 or I EC 60050. Alternatively, the electrically conductive layer may have an electrical conductivity at 25°C of 50% IACS (International Annealed Copper Standard) or more. The above-mentioned electrical conductivities guarantee that the bulk of the vibrational energy comprised in the high-frequency alternating magnetic field is absorbed by the electrically conductive layer through induction of eddy currents while only a small part is absorbed by the superconducting element itself.

The electrically conductive layer may comprise or consist of at least one material selected from the group consisting of Al, Au, Cu, Ag, and graphene. Among these materials, Al, Ag, and graphene provide the mechanical resistance required for a vacuum insulation. For cost efficiency, the wall of the housing of the cryostat may be formed of Al with an Au, Cu, Ag, or graphene layer formed on the Al structure. The above-mentioned materials provide a sufficiently high electrical conductivity to effectively shield the high-frequency alternating magnetic field of the moving levitating element such as a rotating rotor of the below described winding and twisting device.

The electrically conductive layer may be arranged and dimensioned, i.e. a lateral extent of the electrically conductive layer may be chosen, so that the electrically conductive layer shields at least the at least one superconducting element from a magnetic field of the magnetic field generating element. In other words, the extent of the electrically conductive layer is chosen such that those magnetic flux tubes connecting the permanent magnets of the magnetic field generating element and the superconducting elements of the superconducting unit along the shortest way pass through the electrically conductive layer. Alternatively, the extent of the electrically conductive layer may be chosen to cover at least those areas of the housing facing the magnetic field generating element and covering the superconducting elements. The above described ar- rangements guarantee that most of the high-frequency magnetic flux is absorbed by the electrically conductive layer.

The superconducting support system may further comprise a cooling device adapted to actively cool the electrically conductive layer. As the electrically conductive layer has at least one side facing the exterior of the cryostat, simple cooling devices known in the art such as a fan, a water cooler, or the like may be used as the cooling device. As the heat generated by dissipation of the induced eddy currents can be removed via the at least one side facing the exterior of the cryostat, cooling of the electrically conductive layer can be carried out at room temperature and therefore with a significantly higher efficiency than cooling of the superconducting element.

The present disclosure also provides a superconducting magnetic bearing, wherein the at least one superconducting unit is provided as part of at least one stator of the superconducting magnetic bearing, and wherein the at least one magnetic field generating element is provided as part of at least one rotor of the superconducting magnetic bearing, and further comprising a stator cooling device, the stator cooling device being adapted to cool the at least one superconducting element to a temperature below a transition temperature of the superconducting element.

The at least one stator may in particular be the at least one superconducting unit and the at least one rotor may in particular be the at least one magnetic field generating element of the above described embodiments. Furthermore, the stator cooling device may be provided as any one of the above described cryostats, wherein the housing may be optional as the entire superconducting magnetic bearing may be provided inside a housing at vacuum pressures.

The present disclosure in particular provides a superconducting bearing, in particular of a flywheel energy storage system, comprising: at least one stator that comprises at least one superconducting element and a stator cooling device, the stator cooling device being adapted to cool the at least one superconducting element to a temperature below a transition temperature of the superconducting element, and at least one rotor that generates a magnetic field, wherein the at least one stator and the at least one rotor are positioned relative to one another to facilitate levi- tation of the at least one rotor during operation, and wherein at least one electrically conductive layer is arranged between the at least one superconducting element and the at least one rotor. Any of the above described embodiments and arrangements of the at least one electrically conductive layer may be applied to the superconducting magnetic bearing according to the present embodiment. Passive magnetic bearings using flux pinning of magnetic fields in superconducting elements are commonly known in the art. For the sake of clarity, redundant descriptions of well-known elements of superconducting magnetic bearings as well as repetitions of the configurations of stator and rotor described below with respect to a winding and twisting device according to the present invention as well as the above-described electrically conductive layer are omitted in the following. The use of the superconducting elements, in particular comprising type-ll superconductors, allows for a passive magnetic bearing which provides frictionless and stable levitation of the rotor. High temperature superconductors passively stabilize a magnetic support of the rotor, for instance using permanent magnet lift bearings, by providing a restoring force due to flux pinning. Hybrid systems with permanent magnet lift bearings that provide the lifting force and superconducting elements that provide the restoring force allow for handling heavy loads, as is common in flywheel energy storage systems. The superconducting magnetic bearing in particular allows operating in vacuum which allows flywheels to reach RPMs up to 40,000. Also, the fact that superconducting magnetic bearings can be operated in vacuum as they do not require lubricants which would evaporate in a vacuum makes them ideal candidates for operation under higher requirements on cleanliness and sterility or for the handling of infectious, poisonous or even radioactive materials, for instance in hermetically sealed spaces.

According to the present disclosure, at least one rotor generating a magnetic field is supported by at least one stator that comprises at least one superconducting element and a stator cooling device. Alternatively, the at least one rotor may comprise at least one superconducting element and the stator may generate a magnetic field. The embodiments described below may be easily adapted to such a situation by exchanging the roles of rotor and stator with respect to the above described magnetic field generating element and superconducting unit. To support an essentially free rotation, the rotor or the stator may be respectively configured to generate an essentially rotationally symmetric magnetic field with respect to the axis of rotation of the rotor. By way of example, the rotor may comprise one or several permanent magnets which may be arranged in contact with each other along the circumference of the rotor. Furthermore, a, typically ring- shaped, support element may be part of the rotor on which the array of permanent magnets is arranged. Alternatively, a ring-shaped permanent magnet may be used.

Depending on the implementation of the superconducting magnetic bearing, the rotor may further be connected to or comprise a tool or a flywheel mass. The flywheel mass may in particular be formed as a cylinder or a cone, wherein the at least one stator is coaxially arranged inside the flywheel mass or along the periphery of the flywheel mass. Alternatively, a flywheel mass may be connected to a shaft according to the well-known shaft- and hub architecture, as opposed to the above described open-core flywheel architecture. In any case, the rotor may comprise one or several permanent magnets which are arranged relative to the one or more superconducting elements of the stator such as to facilitate magnetic levitation of the rotor during operation and to generate an essentially rotationally symmetric magnetic field.

The superconducting bearing, or the entire device, may be placed inside a vacuum or may be operated in ambient air. In the latter case, one of the above-described cryostats may be provided as a stator cooling device for keeping the one or more superconducting elements at a temperature below the transition temperature of the superconducting material of the superconducting elements. In this case, a housing enclosing the at least one superconducting element is provided as part of the cryostat, i.e. the stator cooling device. Between this housing of the stator cooling device and the rotor, a gap is formed due to the magnetic levitation during operation. All of the above described arrangements of the electrically conductive layer may equally be applied to the superconducting bearing. In particular, the electrically conductive layer may be provided as part of the housing of the stator cooling device, may be provided on the housing and/or on the rotor, may be provided between the stator cooling device and the rotor, and/or may be provided inside the ring-shaped gap. Also, a heat-insulating layer may be provided between the electrically conductive layer and the housing of the stator cooling device.

In the first case, the stator cooling device may be connected to the at least one superconducting element via one or more thermally conducting elements such as cables or a thermally conducting plate to maintain the at least one superconducting element at a temperature below the transition temperature. In this case, as the superconducting bearing is provided inside a vacuum, no housing around the superconducting elements is needed. The above mentioned electrically conductive layer may be arranged on the superconducting elements, in particular with a heat- insulating layer therebetween, in the ring-shaped gap between the superconducting elements and the rotor, and/or on the rotor. Furthermore, a housing around the superconducting elements may be provided as a support structure for the electrically conductive layer or the electrically conductive layer may be arranged as part of such a housing. The stator cooling device may be one of the above described cryostats or any other cryocooler known in the art.

All of the embodiments described above with respect to the electrically conductive layer may be applied to the electrically conductive layer in a superconducting bearing. In particular, the above described thicknesses, electrical conductivities and materials may be selected. Also, a cooling device adapted to actively cool the electrically conductive layer may be provided. In the embodiment wherein the superconducting bearing is arranged within a vacuum, a thermally conducting structure such as a wire or plate or a cooling circuit, for instance based on water as a cooling medium, may be used to actively cool the electrically conductive layer.

In addition to the superconducting elements and the permanent magnets used for the stability of the bearing, the superconducting magnetic bearing may further comprise one or more lift bearing permanent magnets arranged on the at least one rotor and the at least one stator which provide the lifting force, in particular for rotors of a flywheel energy storage system. Furthermore, the superconducting bearing may comprise one or more permanent magnets of the rotor and a stator coil assembly for electromagnetic interaction with these permanent magnets of the rotor to provide a driving force, and to extract rotational energy in the case of a flywheel energy storage system.

A large number of variations of the arrangements of the permanent magnets and superconducting elements of a superconducting magnetic bearing are known in the art and compatible with the described enhanced superconducting bearing as long as the rotor and the stator are arranged relative to one another such that a gap is formed between the stator and the rotor due to magnetic levitation during operation of the device. The above-described electrically conductive layer being provided on the rotor, on the stator and/or inside the gap shields the superconducting elements of the stator from the high-frequency components of the magnetic field generated by the rotor due to vibrations or imperfections of the rotating rotor. Such vibrations are generally present as a result of an imperfect balance of the rotor, in particular the flywheel, as well as radial growth and bending modes. Dissipation of the vibrational energy of the rotor through dissipation of the induced eddy currents inside the electrically conductive layer helps to suppress these modes and to stabilize the rotation of the rotor. Therefore, the described arrangement of an electrically conductive layer between the superconducting elements and the rotor adds to the safety of flywheel energy storage systems where a stable operation is a prerequisite for a large number of applications, such as battery replacements in electric vehicles or small-scale energy storage systems.

The present disclosure also provides a magnetic levitation transportation system, comprising a superconducting support system according to any one of the above described embodiments, further comprising: magnetic guide means, and a movable vehicle placed over the magnetic guide means, the vehicle comprising a vehicle frame, wherein the at least one superconducting unit is attached to the vehicle frame, wherein the at least one magnetic field generating element is provided as part of the magnetic guide means, wherein the magnetic guide means and the superconducting unit are arranged relative to one another so that the vehicle levitates over the magnetic guide means during operation, and wherein the at least one electrically conductive layer is arranged between the at least one superconducting element and the magnetic guide means.

The present disclosure in particular provides a magnetic levitation transportation system, comprising: magnetic guide means, a movable vehicle placed over the magnetic guide means, the vehicle comprising a vehicle frame with one or more superconducting units attached to the vehicle frame, wherein the magnetic guide means and the superconducting units are arranged relative to one another so that the vehicle levitates over the magnetic guide means during operation, wherein the superconducting units comprise at least one superconducting element and a cryo- stat with a housing, the at least one superconducting element being provided inside the housing of the cryostat, and wherein at least one electrically conductive layer is arranged between the at least one superconducting element and the magnetic guide means.

Magnetic levitation transportation systems are commonly known in the art. For the sake of clarity, redundant descriptions of well-known elements of magnetic levitation transportation systems using superconducting elements as well as repetitions of the above-described configurations of the electrically conductive layer are omitted in the following. Standard technologies for maglev transportation systems employ electromagnetic suspension (EMS) technology or electrodynamic suspension (EDS) technology. In the present disclosure, a transportation system using EMS technology is provided with one or more superconducting units comprising at least one superconducting element to constitute a superconducting magnet. Consequently, the superconducting units may comprise superconducting electromagnets provided inside the housing of a cryostat which generate the magnetic fields required for making the movable vehicle levitate above the magnetic guide means. In particular, the magnetic guide means may comprise a steel monorail or dual rail, wherein attractive magnetic forces between the superconducting electromagnets of the vehicle and the rail(s) leads to magnetic levitation. By way of example, the vehicle frame which the one or more superconducting units are attached to may have a C-shaped structure surrounding the one or more rails of the magnetic guide means.

Alternatively, a magnetic levitation system according to the present invention may provide magnetic guide means with a sequence of permanent magnets while superconducting magnets being part of the superconducting units generate magnetic fields so that the vehicle is levitated by the repulsive and attractive forces between the magnetic fields of the magnetic guide means and the vehicle. As in the previous case, a monorail or a dual rail may be provided as magnetic guide means. Also, superconducting blocks may be used instead of superconducting magnets wherein a magnetic field generated by the magnetic guide means is frozen in the superconducting blocks such that the vehicle levitates over the track.

Independent of which technology is used, moving the vehicle over the magnetic guide means at a high velocity introduces a high-frequency magnetic field component which results from high- frequency vibrations of the magnetic guide means and/or the vehicle as well as imperfections in the evenness of the magnetic guide means. The high-frequency magnetic field component interacts with the electrically conductive layer arranged between the at least one superconducting element, e.g. the at least one superconducting coil, of the superconducting units and the magnetic material and/or the permanent magnets of the magnetic guide means.

As in the previously described systems, the electrically conductive layer thus serves as a magnetic shield absorbing the vibrational energy in terms of eddy currents induced in the electrically conductive layer. The vehicle may therefore be identified with the above described stator while the magnetic guide means may be identified with the above described rotor. Propulsion of the vehicle is further provided by arranging one or more linear motors along the magnetic guide means which interact with magnets of the vehicle in a controlled way as known in the art.

As described above, the at least one superconducting element, e.g. the superconducting coils, are provided inside the housing of one or more cryostats which are part of the superconducting units. The cryostats are configured to maintain the temperature of the superconducting elements below the critical temperature of the superconducting material of the superconducting elements. Any of the embodiments of the cryostat, such as a bath cryostat, described above, may equally applied to the cryostats of the vehicle. Likewise, a cooling device may be provided as part of the cryostat or connected to the cryostat as described above.

Furthermore, all of the arrangements of the electrically conductive layer with respect to the superconducting elements as described above may be equally applied to the electrically conductive layer of the magnetic levitation transportation system. In particular, the electrically conductive layer may be provided as part of the housing of the cryostat, provided between the cryostat and the magnetic guide means, provided on the housing facing the magnetic guide means, provided on the magnetic guide means and/or provided inside the air gap formed between the magnetic guide means and the superconducting units during operation of the transportation system, wherein in particular a heat-insulating layer may be additionally provided between the electrically conductive layer and the housing of the cryostats. Also, the electrically conductive layer of the transportation system may have the above- described thickness and/or electrical conductivity and may comprise or consist of any of the above described materials. Keeping the material costs in mind, the electrically conductive layer may in particular be provided as part of the vehicle, e.g. as part of the housing or on the housing of the cryostats. As described above, a lateral extent of the electrically conductive layer may be chosen so that the electrically conductive layer covers at least the at least one superconducting element when viewed perpendicular to the plane of movement of the vehicle. Also, a cooling device adapted to actively cool the electrically conductive layer may be provided. However, if the electrically conductive layer is provided as part of the vehicle, the airflow due to the motion of the vehicle generally suffices for cooling.

As in the previous systems and devices, providing an electrically conductive layer between the at least one superconducting element of the vehicle and the magnetic guide means both dissipates the high-frequency component of the magnetic field and dampens vibrations of the moving vehicle. As the high-frequency component of the magnetic field is dissipated inside the electrically conductive layer instead of the superconducting element, the cooling system comprising the cryostat and a cooling device may be simplified and operational costs related to cooling the superconducting units can be reduced. As a result of the dampening, flatness requirements to the magnetic guide means, i.e. the track, may be relaxed. Both, reduced cooling costs and reduced constructional requirements help to make the maglev transportation systems more competitive.

The present disclosure also provides a winding and twisting device comprising any of the superconducting support systems described above, wherein the at least one superconducting unit is provided as part of at least one stator of the winding and twisting device, and wherein the at least one magnetic field generating element is provided as part of at least one rotor of the winding and twisting device, and further comprising a rotatable spindle, wherein the rotor and the stator are arranged co-axially to the spindle so that a ring-shaped air gap is formed co-axially to the spindle between the rotor and the stator, and wherein the at least one electrically conductive layer is arranged between the at least one superconducting element and the rotor.

The present disclosure thus provides a winding and twisting device of a ring spinning or ring twisting machine, comprising: at least one stator that comprises at least one superconducting element and a cryostat with a housing, the at least one superconducting element being provided inside the housing of the cryostat, at least one rotor that generates a magnetic field, and a rotatable spindle, wherein the rotor and the stator are arranged coaxially to the spindle so that a ring- shaped air gap is formed coaxially to the spindle between the rotor and the stator, characterized in that at least one electrically conductive layer is arranged between the at least one superconducting element and the rotor.

The rotor and the stator can be formed and arranged in a way that the rotor can be supported in a contactless way due to magnetic levitation during operation. This shall be understood as the rotor being free-floating and hence supported in a contactless way after cooling down of the superconducting element of the stator below the critical temperature. By maintaining an optimal distance between the rotor and the stator through pinning of the flux tubes of the inhomogene- ous magnetic field of the rotor permeating the stator when lowering the temperature of the superconducting element below its transition temperature, an inherently stable, passive support of the rotor is possible both without as well as with rotation of the rotor. Therefore, complex control and/or sensor units for active bearing control of the rotor can be omitted. The absence of wear is insured through the optimal distance which results in a high reliability and robustness. Thanks to the contactless support of the rotor, the rotational velocity of the thread and the spindle can be increased. In addition, the ring of the traditional ring-rotor-system as a substantially productivity- limiting (due to its creation of friction heat) component may be omitted as described below, such that the rotation velocities of the thread and the spindle can be further increased, which, in turn, leads to a drastic productivity increase in connection with a possible increase of the diameter of the bobbin.

The rotor and the stator do not necessarily have to be formed in a ring-shaped way if one or more ring-shaped yarn guiding elements for guiding the circulating thread inside the air gap are present. As a consequence, the coaxial arrangement of the rotor and the stator with respect to the spindle may also be expressed with respect to the one or more ring-shaped yarn guiding elements. In addition, the subsections mentioned below can in particular, be arranged along the circumference of a coaxial circle around the spindle axis.

The rotor can comprise at least subsections with a permanent magnetic material that generate a magnetic field. This is to be understood such that the rotor is magnetized at least in sections along its circumference or that it has permanent magnets. Other subsections of the stator and the rotor can also be made of other, also nonmagnetic materials. This is in particular true for the yarn guiding elements. To facilitate a levitation of the rotor, in particular materials that reduce the weight of the rotor can be used. Alternatively, a ring-shaped permanent magnet may be provided as part of the rotor wherein an essentially rotationally symmetric magnetic field is generated by the rotor. To enable the formation of a superconducting state in an area of the stator, the at least one superconducting element provided at least in subsections of the stator has to be cooled to temperatures below the transition temperature. If superconducting subsections of the stator alternate with normally conducting or insulating subsections of the stator, a plurality of cryostats may be provided along the circumference of the stator. The stator can have two or multiple superconducting subsections that are spaced in relation to one another in the circumferential direction of the spindle. Hence, the superconducting part does not have to extend over the whole circumference so that the cryostats may be formed significantly more compact and energy-saving.

Segments of normally conductive and/or insulating materials can be arranged between the superconducting subsections, i.e. the cryostat housings enclosing the respective superconducting elements. To save material, however, these intermediate segments can also be omitted completely. In this case, the stator only comprises the ring-shaped yarn guiding element(s) and two or multiple superconducting subsections having at least one superconducting element inside a corresponding cryostat that are arranged on these yarn guiding elements. In particular, the superconducting subsections can be arranged in regular intervals in the periphery, i.e. along a circle around the spindle axis, of the spindle.

For each superconducting subsection of the stator, the rotor can have an appropriately arranged subsection with a permanent magnetic material. In this case, one superconducting subsection or cryostat of the stator and a subsection of the rotor are located opposite to one another, which can ensure a particularly effective pinning of the magnetic flux tubes. Ideally, the respective subsections can have equal or comparable extensions in the circumferential direction. In particular, the rotor and the stator can have exactly three subsections. Multiple cryostats of the stator can be connected to a single cooling device via appropriate pipes.

According to an embodiment, the rotor and the stator can be arranged in a coplanar way with the stator enclosing the rotor, wherein the thread may be guided through the air gap from above. The terms "above" and "below" shall be understood here and in the following with regard to a ring spinning or ring twisting machine that stands on a mounting surface. The fiber material and/or the thread is usually guided from above to the bobbin that is wound up on the sleeve, in the process of which a so-called yarn balloon is formed due to the fast rotation of the thread. In the coplanar arrangement, the rotor is located within the stator in a radial direction wherein in particular a ring-shaped yarn guiding element of the rotor may be located within a ring-shaped yarn guiding element of the stator. Such an arrangement is particularly compact and enables an efficient cooling of the superconducting areas. The thread can be guided in a particularly simple way from above through the air gap between the ring-shaped yarn guiding elements and be wound up onto the bobbin below the rotor. In this process, the thread will generally slide on the surface of the yarn guiding element of the rotor so that said surface can advantageously be formed in a smooth way. In addition, the cross-section of the yarn guiding element can be designed in a way, for example by means of roundings, that tearing of the thread on the lower edge of the ring can be prevented.

According to an alternative development, the rotor and the stator can be arranged parallel to each other at an axial distance to one another with the thread being guided from outside through the air gap. The terms "inside" and "outside" shall be seen in this context in relation to the spindle axis. The rotor can be arranged in a way as to be located above or below the stator as long as the axial distance from the stator and the rotor is small enough to enable the magnetic field of the rotor to enter the superconducting area of the stator. Due to the axial distance between the rotor and the stator, an air gap is formed through which the thread is guided from the outside. In this process, the yarn guiding elements of the rotor and the stator may be located opposite to one another at least partially in the vertical direction, i.e. along the spindle axis. As in the previous development, the yarn guiding elements can also in this case be formed with rounded edge profiles in order to avoid tearing of the thread. In a further development of this type, two stators can be arranged in a way that their delimitation areas located axially opposite to one another are respectively located opposite to an axial delimitation area of the rotor. Therefore, two ring- shaped air gaps are formed, wherein the thread can be guided either through one or the other air gap. The above described further developments of the at least one electrically conductive layer may be applied accordingly in this case.

According to the invention, a ring-shaped air gap is formed coaxially to the spindle between the rotor and the stator. The position and extension of the air gap during operation of the device may be such that the thread to be wound up is wound up onto the rotating bobbin on the lower end of the yarn balloon through the air gap. For example, the air gap can have a width of 2 to 5 mm. Through the rotation of the spindle and the sleeve put onto said spindle with the bobbin, the thread is taken along in circulation in the known way. As, due to air friction of the yarn balloon, the circulation of the thread occurs more slowly than the fast rotation of the spindle, the thread is twisted and spun while being wound up.

As described above, during operation of the device, the rotor will generally rotate with a high frequency either because the thread is guided through a ring attached to the rotor or the rotor is spun up due to friction between the thread circulating within the air gap and the rotor or a yarn guiding element of the rotor. In most cases, the rotor will be rotating with several thousand rounds per minute. For such a high frequency rotation, any imbalance of the rotor will lead to the above-mentioned high-frequency alternating magnetic field which generates heat inside the superconducting elements. However, even if the rotor is fixated through flux pinning of a non- rotationally symmetric magnetic field, circulation of the thread in contact with a yarn guiding element of the rotor induces vibrations of the rotor which lead to a high-frequency alternating magnetic field.

Any of the above described developments and arrangements of the at least one electrically conductive layer may be applied to the winding and twisting device according to this embodiment. During operation of the ring spinning or ring twisting machine, the electrically conductive layer acts as a low-pass filter which filters out the high-frequency components of the alternating magnetic field while letting low-frequency components pass through. As the vibrational frequencies of the rotor of the proposed ring spinning or ring twisting machines lie in the range from several hundred Hz to more than 1 kHz, the vibrational component of the alternating magnetic field is dissipated in the electrically conductive layer instead of being dissipated in the superconducting element. This is also a direct result of the electrically conductive layer being provided closer to the alternating magnetic field then the superconducting element.

The electrically conductive layer may have a thickness between 0.05 mm and 5 mm. A layer of this thickness suffices to permit induction of eddy currents according to the skin effect. A thin electrically conductive layer allows for a reduction of the vertical or radial distance between the stator and the rotor which simplifies the contactless support of the rotor. Also, highly conductive materials are generally expensive such that a thin electrically conductive layer helps to reduce overall costs.

The electrically conductive layer may be arranged and dimensioned, i.e. a lateral extent of the electrically conductive layer may be chosen, so that the electrically conductive layer shields at least the at least one superconducting element from a magnetic field of the rotor. In other words, the extent of the electrically conductive layer in the circumferential direction and the vertical (for a coplanar configuration of rotor and stator) or radial (for a vertical stacking of rotor and stator) direction is chosen such that those magnetic flux tubes connecting the permanent magnets of the rotor and the superconducting elements of the stator along the shortest way pass through the electrically conductive layer. Alternatively, the extent of the electrically conductive layer may be chosen to cover at least those areas of the housing facing the rotor and covering the super- conducting elements. The above described arrangements guarantee that most of the high- frequency magnetic flux is absorbed by the electrically conductive layer.

The present disclosure further provides the embodiment of a winding and twisting device as described above, wherein the rotor and/or the stator have at least one ring-shaped yarn guiding element that is arranged coaxially to the spindle, wherein the yarn guiding element of the rotor and/or the yarn guiding element of the stator delimit the air gap so that a thread to be wound up can circulate in the ring-shaped air gap, and wherein the electrically conductive layer is provided as part of the yarn guiding element of the rotor and/or the yarn guiding element of the stator.

According to this embodiment, the yarn guiding elements form ring-shaped delimitation elements, wherein the circulating thread slides on the surface of one or both delimitation elements. The friction that arises in this process is extremely low so that very high speeds of the spindle can be achieved. Together with the air friction, the friction with the yarn guiding element determines the relative velocity between the circulating thread and the spindle rotation. Consequently, the surface texture of the ring-shaped yarn guiding element determines the spinning quality using the friction.

In contrast to known winding and twisting devices, the yarn guiding elements according to the present disclosure do not form a loop or a similar device that circulates with the thread, but only delimitation elements that are arranged coaxially to the spindle axis and that define the extent of the air gap. Due to the friction of the thread that is sliding on the yarn guiding elements of the rotor, the rotor will generally be slowly made rotate during the operation of the device. As no significant masses have to be accelerated during the startup of the device, the ring spinning or ring twisting machine can be started significantly faster because the thread can be made rotate practically instantly due to the low friction with the yarn guiding element of the rotor.

The yarn guiding elements may be formed in a way as to facilitate a guiding of the thread to be wound up that is horizontal, i.e. oriented in the circulation direction, and optionally a guiding of the thread that is vertical, i.e. oriented along the spindle axis. This takes place for example due to the yarn guiding element forming deflecting elements for the thread through their arrangement on the rotor and/or stator. To avoid tearing of the thread during operation, the yarn guiding elements can be formed with an appropriately smooth surface and in particular with a rounded shape. During the spinning process, the thread slides in the circulation direction on the smooth surface of the yarn guiding element(s) that prevent(s) the thread from being entangled in the rotor and/or stator which may in particular not be formed rotationally symmetric. The yarn guid- ing elements are therefore used to keep the thread away from potential surface irregularities and edges of the winding and twisting device.

According to the present disclosure, the electrically conductive layer may be provided as part of the yarn guiding element of the rotor and/or the stator. In particular, the electrically conductive layer may be coated on a surface of the yarn guiding element. If this surface is in contact with the circulating thread, a material with sufficient wear resistance, such as Al, Ag, or graphene, may be used for the electrically conductive layer. In the disclosed configuration, the electrically conductive layer serves both as a magnetic shield for the high-frequency alternating magnetic field and as a guiding element for the circulating thread.

The technical problems mentioned above are also solved by a ring spinning or ring twisting method, in which fiber material is twisted and subsequently a thread is wound up, wherein a winding and twisting device as described above is provided, wherein the rotor is held coaxially at a distance to the stator by a rotor holding device, wherein the temperature of the at least one superconducting element of the stator is reduced below the transition temperature of the superconducting element, wherein the rotor is released by the rotor holding device, and wherein the spindle is rotated with a frequency of at least 20,000 rpm.

Through initial holding of the rotor at a distance to the stator which is structurally predetermined or selectable, startup of the device is substantially facilitated in the proposed solution.

The above-described ring spinning or ring twisting devices allow driving the spindle with a significantly increased rotation frequency as no yarn guiding ring rotating around the spindle axis is provided anymore. As a consequence, no additional masses have to be accelerated and no unnecessary heat is generated by the circulation of the yarn guiding ring. As a result, rotation frequencies of 20,000 rounds per minute or more become possible for the described winding and twisting device. For such a high rotation frequency, the above described vibration of the rotor is effectively dampened via induction of eddy currents in the electrically conductive layer, wherein unnecessary heat generation in the superconducting element is effectively prevented. As a result, even higher rotation frequencies become possible, thereby further increasing the production capacity of the ring spinning or ring twisting machines. As the generated heat can be removed at room temperature, the cooling mechanism for the superconducting elements can be simplified and made more cost-efficient. In summary, the present disclosure provides a winding and twisting device of a ring spinning or ring twisting machine which allows for a very high production capacity with reduced cooling costs.

Further features and exemplary embodiments as well as advantages of the present invention will be explained in greater detail by means of the drawings in the following. It is clear that the embodiments do not exhaust the field of the present invention. It is further clear that some or all of the features described in the following can also be combined with one another in a different way.

Figures 1 A-D show alternative arrangements of the electrically conductive layer with respect to the superconducting unit and the magnetic field generating element of a superconducting support system according to the present invention.

Figure 2 shows a schematic representation of a cross-sectional view of a flywheel energy storage system according to the present invention.

Figure 3 shows a schematic representation of a magnetic levitation transportation system known in the art.

Figure 4 shows a cross-section of the transportation system of Figure 3 along the line A - A.

Figure 5 shows a schematic representation of the magnetic levitation system of a transportation system according to the present invention.

Figure 6 shows a schematic representation of a winding and twisting device for ring spinning machines according to one embodiment of the invention, in which the stator and the rotor are arranged in parallel and at an axial distance to one another.

Figure 7 shows a schematic representation of a winding and twisting device for ring spinning machines according to another embodiment of the invention, in which the stator and the rotor are arranged in a coplanar way and in which the stator encloses the rotor.

In the Figures described in the following, identical reference signs denominate the same elements. For the sake of clarity, identical elements will only be described when they appear for the first time. However, it is clear that the variants and embodiments of an element described with reference to one of the Figures can also be applied to the respective elements in the remaining Figures. Figures 1 A-D show schematic representations of a plurality of alternative arrangements of the electrically conductive layer with respect to the superconducting unit and the magnetic field generating element of a superconducting support system according to the present invention. The specific, non-limiting example shown in Figures 1 A-D demonstrate the arrangement of the electrically conductive layer for the case of a winding and twisting device, wherein the superconducting unit is provided as part of the stator and the magnetic field generating element is provided as part of the rotor. The relative positions of the electrically conductive layer, the superconducting element and the permanent magnets may, however, equally be applied to the flywheel energy storage system shown in Figure 2 and to the magnetic levitation transportation system shown in Figures 3 to 5.

Figures 1 A-D show close ups of those parts of the stator 1 and the rotor 2 of the embodiments shown in Figures 6 and 7 which are relevant for the magnetic levitation. For clarity, the representation is reduced to the permanent magnet 21 of the rotor 2 and the cryostat 25 together with the stator cooling device 9 of the stator 1. In the particular, non-limiting embodiment, the interior 23 of the cryostat 25 is connected to the stator cooling device 9 via supply line 9a and return line 9b for the circulation of the cryogen. Other embodiments of the cooling device 9, for instance such which extract heat from the cryostat or the superconducting element by thermally conducting elements such as wires or plates, can be used.

In the exemplary embodiments shown in Figures 1 A-D, the superconducting element 19 is kept at a temperature below the transition temperature by circulating a liquid cryogen through the interior space 23 of the cryostat 25. As a consequence, a bath cryostat is used in the depicted embodiments. Aside from the interior space 23, the cryostat has a housing 22 which surrounds the superconducting element 19 which may be connected by thermally insulating support elements to the housing 22.

According to a first variant, the electrically conductive layer 28a may be formed as part of the housing 22, wherein the electrically conductive layer is provided between the superconducting element 19 and the rotor 2, more specifically between the superconducting element 19 and the at least one permanent magnet 21 of the rotor 2. In the depicted example, the electrically conductive layer 28a extends over the entire thickness of the housing wall 22 which is possible if a highly conductive material with sufficiently high mechanical resistance is used. This is in particular relevant if the cryostat comprises an inner jacket (not shown) surrounding the superconducting element and filled with liquid cryogen, wherein the space between the housing 22 and the jacket is evacuated for better heat insulation. In this case, the mechanical resistance of the elec- trically conductive layer 28a must be high enough to withstand the ambient air pressure without bending of the wall element. Alternative to an electrically conductive layer locally replacing the wall of the housing 22, only an upper layer or upper part of the housing wall facing the permanent magnet 21 may be built as an electrically conductive layer.

An alternative variant is shown in Figure 1 B where the electrically conductive layer 28b is provided on the housing 22 of the cryostat 25 between the rotor 2 and the housing 22. The non- limiting variant shows the electrically conductive layer 28b provided on and in contact with a thermally insulating layer 29 which in turn is provided on, i.e. in contact with the wall 22 of the housing of the cryostat 25. Provision of a heat insulating layer 29 between the housing 22 and the electrically conductive layer 28b suppresses unwanted heat conduction from the heat generated by the eddy currents to the cryostat 25.

Such unwanted heat conduction is even better suppressed with the variant shown in Figure 1 C wherein the electrically conductive layer 28c is provided inside the air gap 14 and only connected via thin, ideally heat insulating support elements to the stator 1. In this variant, both sides of the electrically conductive layer 28c are exposed to the ambient air such that efficient cooling of the electrically conductive layer is provided through the air flow during operation of the device.

Finally, the electrically conductive layer 28d may also be provided on the rotor 2, for instance in contact with the permanent magnet 21 , as shown in Figure 1 D. Although not shown, a heat insulating layer may also be provided between the electrically conductive layer 28d and the rotor 2. A number of variations are possible, for instance by connecting the electrically conductive layer 28c of Figure 1 C to the rotor 2 instead of the stator 1. Also, multiple electrically conductive layers may be provided between the superconducting element 19 and the permanent magnet 21 of the rotor 2 by combining arrangements taken from Figures 1 A-D.

It may further be pointed out that the lateral extent of the electrically conductive layers 28 a-d may vary. However, the electrically conductive layer may generally be dimensioned to intersect those magnetic flux tubes connecting the permanent magnet 21 and the superconducting element 19 along a straight line. In the variants shown in Figures 1 A-D, the lateral extent of the electrically conductive layer seen from above along the rotation axis is always large enough to entirely cover the superconducting element 19. This guarantees that the bulk of the high- frequency alternating magnetic field is dissipated by the electrically conductive layer.

Figure 2 shows a schematic representation of a cross-sectional view of a superconducting bearing for a flywheel energy storage system according to the present invention. The non-limiting exemplary embodiment shows an open-core flywheel architecture wherein an open-core flywheel 100 is arranged concentric about a center line 155. The flywheel comprises a rotor 102 and a stator 101 wherein the rotor 102 comprises a cylindrical massive body 140, such as a fiber-composite rim. Furthermore, a lift bearing permanent magnet 130, a stability permanent magnet and a motor/generator permanent magnet array 131 are provided as part of the rotor 102.

The stator 101 comprises a lift bearing permanent magnet 132, a superconducting element 1 19, a stator coil assembly 154, and the mechanical supports 151 , 152, and 153. Mechanical support 151 supports stator lift bearing permanent magnet 132. Mechanical support 153 supports superconducting element 1 19. Mechanical support 152 supports stator coil assembly 154. The mechanical supports 151 to 153 are fixedly attached to a vacuum chamber 145 which surrounds the flywheel assembly.

The flywheel rotor 102 is magnetically levitated by the magnetic bearing components, including the lift bearing (comprising rotor permanent magnet 130 and stator permanent magnet 132), and the stability bearing (comprising rotor permanent magnet 121 and stator superconducting element 1 19). Rotational acceleration of rotor 102 about the centerline 155 is achieved by the electromagnetic interaction between the rotor permanent magnet 131 and the stator coil 154. Mechanical support 153 may further thermally insulate the superconducting element 1 19 from the vacuum chamber 145. Evacuating the vacuum chamber 145 not only suppresses air friction of the rotating flywheel but also makes further thermal insulation of the superconducting element 1 19 unnecessary.

Additionally, a thermally conducting structure (not shown) may be positioned between the superconducting element and the thermally insulating structure 153 which connects the superconducting element 1 19 to a cold source, such as, for example, a cryocooler. Such a cryocooler may comprise a cold head which is connected to cables that may be flexible, and that preferably act as thermal conductors at cryogenic temperatures. The cables preferably comprise copper, copper alloys, aluminum, aluminum alloys, or combinations thereof. The cables may connect to a preferably flat, thermally conducting plate by means of a conducting lug. The superconducting element 1 19 may rest on top of the thermally conducting plate so that heat can be extracted from the superconducting element via the plate. Alternatively, the superconducting element 1 19 may be provided inside a cryostat with a closed housing, wherein the superconducting element may be placed inside a cryogenic bath. In the exemplary development depicted in Figure 2, no surrounding housing of the superconducting element 1 19 is provided. Instead, the electrically conductive layer 128 is provided directly on a thermally insulating layer 129 which is in turn provided on the superconducting element 1 19. Again, the lateral extent of the electrically conductive layer 128 is chosen to effectively shield the superconducting element 1 19 from the high-frequency alternating magnetic field generated by the stability permanent magnet 121 of the rotor 102.

It is understood that the variants of the arrangement of the electrically conductive layer shown in Figures 1 A-D can be equally applied to the electrically conductive layer 128 of the superconducting bearing of the flywheel energy storage system of Figure 2, wherein, if necessary, a housing of a cryostat may be added.

The electrically conductive layer 128 provided between the superconducting element 1 19 and the permanent magnet 121 of the rotor 102 absorbs the high-frequency alternating magnetic field generated through vibrations of the flywheel 140 which result from an imperfect balance of the flywheel. As a result, rotation of the flywheel is stabilized without generating heat inside the superconducting element. Consequently, safety and cost efficiency of the flywheel energy storage system can be improved.

Figure 3 shows a schematic representation of a magnetic levitation transportation system known in the art. The Figure shows a magnetic levitation transportation system 200 with a movable vehicle 270 levitating over magnetic guide means 265. The vehicle 270 comprises a vehicle frame 275 to which superconducting units 280a and 280b are attached. Through magnetic interaction of the superconducting elements of the superconducting units with corresponding rails 260a and 260b of the magnetic guide means 265, the vehicle 270 magnetically levitates, e.g. as a result of flux tube pinning. To this end, the superconducting elements may in particular, be superconducting magnets.

Figure 4 shows a cross-section of the transportation system of Figure 3 along the line A - A. A sequence of permanent magnets or electromagnets are shown as part of the rails 260a and 260b. These magnets may be provided as part of a linear motor or in addition to a linear motor which is used for the propulsion of the vehicle 270 via electromagnetic interaction with arrays of superconducting electromagnets or superconducting blocks provided in the superconducting units 280a and 280b. The magnetic levitation transportation system shown in Figures 3 and 4 uses flux pinning wherein the vehicle is levitated by the repulsive and attractive forces between the magnetic fields of the magnetic guide means frozen in the superconducting blocks and the superconducting units of the vehicle. Although not shown in Figures 3 and 4, a monorail may be used instead of dual rails. Also, the maglev transportation system may use EMS technology with superconducting electromagnets.

Figure 5 shows a schematic representation of the magnetic levitation system of a transportation system according to the present invention. The Figure shows a close up of a superconducting unit of the maglev vehicle of Figures 3 and 4 in interaction with a rail of the magnetic guide means.

In detail, Figure 5 shows a magnetic levitation transportation system 200 with a rail 260 of a magnetic guide means 265 as a cross-sectional view. The rail 260 comprises a plurality of permanent magnets 221 as well as external ferromagnetic elements 236 and internal ferromagnetic elements 237 which are magnetized by the permanent magnets 221. The non-limiting example shown in Figure 5 uses a Halbach configuration wherein the orientation 238 of the permanent magnets 221 is indicated. The Halbach configuration is particularly effective in enhancing the magnetic flux on the side of the rail 260 facing the superconducting elements 219 of the vehicle.

The vehicle 270 comprises a vehicle frame 275 and a cryostat 225 which is arranged at a lower part of the frame so as to be opposed to the rail 260. In addition, the vehicle frame 275 holds a cooling system 209 of the cryostat 225 which is adapted to cool a working medium circulating through the cryostat 225, i.e. a cryogenic liquid, to temperatures below the transition temperature of the superconducting material of the superconducting elements 219.

The cryostat 225 comprises a housing 222, a jacket 233 and two superconducting elements 219 which are enclosed by the housing. The jacket 233 defines an internal space separated from the wall 222 of the housing of the cryostat which surrounds the superconducting elements 219 and is filled with the working medium, i.e. liquid cryogen 223. The cryostat 225 further comprises a thermal insulation 234 provided between the housing 222 and the jacket 233. The thermal insulation may be filled with a thermally insulating material or may be evacuated. The cryostat 225 is mechanically fixed to the vehicle frame 275. The jacket 233 is supplied with the working medium, which may be liquid nitrogen for high temperature superconductors, by using the cooling device 209 wherein the working medium is circulated through pipes 209a to the internal space 223 of the cryostat 225. The two superconducting elements 219 may in particular be superconducting electromagnets. Alternatively the two superconducting elements 219 may be bulk elements made of a superconducting material. The form and the dimensions of the superconducting elements 219 may be optimized to induce an optimal magnetic force supporting the levitation of the vehicle above the rail. Small variations in the field strength of the permanent magnets 221 of the magnetic guide means 265 along the track, vibrations of the track and/or the vehicle while the vehicle is moving along the track at high velocity, and/or small variations in the evenness of the track lead to the above described high-frequency alternating magnetic field experienced by the superconducting units of the vehicle when moving along the track. To absorb these high-frequency components of the magnetic field without generating heat in the superconducting elements 219, an electrically conductive layer 228 is provided in the embodiment of Figure 5 according to the present invention between the rail 260 and the cryostat 225. In particular, the electrically conductive layer 228 is provided under the cryostat 225, i.e. in contact with the housing 222. Providing the electrically conductive layer 228 underneath the cryostat 225, i.e. as part of the vehicle 270, instead of providing the layer on the track of the magnetic guide means 265, significantly reduces the required amount of highly conductive, and often expensive material.

Induction of eddy currents in the electrically conductive layer 228 dissipates the high-frequency alternating magnetic field without increasing the temperature of the superconducting elements 219. In addition, vibrations of the vehicle and/or the track are dampened through the dissipation of the eddy currents such that high velocity travel of a maglev vehicle, e.g. a maglev train, becomes safer and more competitive in terms of costs.

As with the flywheel energy storage system, the plurality of different arrangements of the electrically conductive layer shown in Figures 1 A-D can be applied to the cryostat 225 of the magnetic levitation transportation system 200 of Figures 3 to 5. Here, the permanent magnets 221 of the magnetic guide means 265 assume the role of the permanent magnet 21 of the rotor 2 in Figures 1 A-D. Also, the cooling device 209 may be integrated into the cryostat 225 instead of being provided separately.

The embodiment that is displayed schematically in the side view in Figure 6 is a section of a ring spinning machine 17 that comprises a winding and twisting device 18 according to the present invention. The stator 1 , that comprises at least one superconducting element 19 and a cryostat 25 with a housing 22, is arranged coaxially to the spindle and/or spindle axis 7 and is cooled down below the transition temperature of the superconducting element 19 by the cooling device 9. In the illustrated, non-limiting embodiment, the superconducting element 19 is located inside the housing 22 of the cryostat 25 with an insulating material 23 surrounding the superconducting element. Alternatively, a cryogen such as liquid nitrogen may surround the superconducting element 19 and cool the superconducting element down to a temperature below the transition temperature. The stator 1 , which is disposed below the rotor 2 in this exemplary development, is held by a stator holding device 10 that is only indicated schematically. However, as magnetic levitation is also possible in a suspended position, also embodiments in which the stator is disposed above the rotor as well as embodiments in which a stator is disposed below the rotor and a further stator is disposed above the rotor are comprised.

The rotor 2 and the stator 1 are arranged in parallel and at an axial distance to one another so that they are not in contact with each other and that the magnetic field created by one or more permanent magnets 21 of the rotor can permeate the superconducting elements 19 of the stator 1 . In particular, the rotor 2 and the stator 1 are formed in a way that a ring-shaped air gap 14, which is disposed coaxially to the spindle 7 and in which the thread 8 to be wound up can circulate, can be formed between the rotor 2 and the stator 1. As shown in Figure 6, the thread 8 is guided for this purpose from outside around the rotor 2 and through the air gap 14 to the bobbin 6. The stator 1 and the rotor 2 thereby comprise in particular no elements that could hamper the circulation of the thread 8 in the air gap.

In the exemplary embodiment shown here, the rotor 2 has a ring-shaped yarn guiding element 3 that is disposed coaxially to the spindle 7 and on whose surface the thread 8 slides and/or rolls off during its circulation around the spindle axis. For this purpose, the yarn guiding element 3 is disposed on the outside of the rotor 2 in a radial direction and equipped with a smooth, rounded surface in such a way that the thread 8 will not tear during guiding over the surface. In addition, also the stator 1 can have a yarn guiding element (not shown) which is also formed in a ring- shaped way and which is disposed coaxially to the spindle 7. In particular, the thread 8 can be guided in the air gap 14 between yarn guiding elements of the rotor and the stator. It is clear that, depending on the arrangement and formation, both the rotor 2 as well as the stator 1 can comprise other or differently formed yarn guiding elements as long as said elements are formed in a ring-shaped way and coaxially around the spindle axis and guarantee reliable guiding of the thread from outside through the air gap 14 to the bobbin 6. The yarn guiding elements enable the free circulation of the thread 8 and hence need not be formed as a loop that circulates around the spindle axis with the thread. As a consequence, the rotor 2 may be supported in a contactless way during operation of the device. As no significant masses have to be accelerated, the device can be started without delay.

For startup and shutdown of the winding and twisting device 18, the rotor 2 is held coaxially at a distance to the stator 1 by a rotor holding device 12, the temperature of the superconducting element 19 of the stator 1 is reduced below the critical temperature of the superconducting ele- ment 19, and the rotor 2 is subsequently released by the rotor holding device 12. For this purpose, the schematically displayed mechanical connection 24 can be retracted during operation.

The yarn 8 runs through the yarn guide 4, continues through the balloon narrowing ring 5 as well as from the outside over the yarn guiding element 3 of the rotor 2 in order to be wound up onto the bobbin 6 as, due to the friction of the circulating yarn 8 on the surface of the yarn guiding element 3 and through the air friction of the yarn balloon that is formed, a relative velocity of the spindle 7 that is held by the spindle holding device 15 and that is made rotate by the spindle rotating device 16 emerges in relation to the circulation velocity of the thread 8. The relative velocity can be influenced by the surface texture of the, in particular coated, yarn guiding element 3, by means of which the spinning quality of the produced yarn can be adjusted accordingly.

For winding up the yarn 8 onto the bobbin 6, the stator holding device 10 is displaced in a variant of the invention by means of the stator displacement device 1 1 along the spindle axis, in the process of which the yarn guiding 4 and optionally the balloon narrowing ring 5 can be moved along through an optional rigid connection 20 (indicated schematically) while, however, the spindle 7 does not change its position in relation to the ring spinning machine 17. In another variant of the invention, the position of the winding and twisting device 18 in relation to the ring spinning machine 17 remains fixed while the spindle 7 with the bobbin 6 is displaced along the spindle axis by means of the spindle displacement device 26.

According to the invention, an electrically conductive layer 28 is arranged between the superconducting elements 19 and the rotor 2. As shown in the exemplary embodiment depicted in Figure 6, the extent of the electrically conductive layer 28 is at least that it covers the superconducting elements 19. In other words, the electrically conductive layer 28 is sized such that it effectively shields the superconducting elements 19 from the high-frequency components of the magnetic field generated by the rotating and/or vibrating permanent magnets 21 of the rotor 2. As a consequence, the electrically conductive layer 28 has at least the same lateral extent as the superconducting elements 19 in the plane perpendicular to the rotation axis. As a result of the provision of an electrically conductive layer 28 between the permanent magnets 21 of the rotor 2 and the superconducting elements 19 of the stator 1 , the high-frequency alternating magnetic fields generated by vibrations of the rotor 2 due to imperfect balance of the rotor or friction of the circulating thread induces eddy currents in the layer 28 which are subsequently dissipated into heat.

As at least one side of the electrically conductive layer 28 is exposed to the ambient air of the ring spinning machine 17, a simple cooling device 27, such as a fan, suffices to remove the gen- erated heat from the electrically conductive layer 28. Even without a dedicated cooling device 27, air movement due to rotation of the rotor 2 and/or the spindle 7 may be sufficient to carry away the heat generated by the induced eddy currents.

Figure 7 shows an alternative embodiment of the winding and twisting device 18 of a ring spinning machine 17 in a schematic side view. As already in the previous embodiment, the stator 1 , which has at least one superconducting element 19, is arranged coaxially to the spindle and/or spindle axis 7 and is cooled down below the transition temperature of the superconducting material of the superconducting element 19 by the stator cooling device 9. The rotor 2 and the stator 1 are arranged coaxially with the stator enclosing the rotor so that they are not in contact but form an air gap 14 between them. The magnetic field created by the permanent magnets 21 of the rotor 2 can enter the superconducting material 19 of the stator 1. As the stator 1 is held by the stator holding device 10 and as the thread 8 circulates through the ring-shaped air gap 14, the rotor 2 must be arranged within the stator 1.

In the embodiment shown in Figure 7, the rotor 2 has a ring-shaped yarn guiding element 3 that is arranged coaxially to the spindle 7 and through which the thread 8 is led from above through the air gap 14 to the bobbin 6. Also in this case, the yarn guiding element 3 is disposed radially on the outer circumference of the rotor 2 and formed with a smooth, rounded surface so that the thread 8 can be guided with a high velocity over the surface of the yarn guiding element 3 without tearing. In addition, the stator 1 has a ring-shaped yarn guiding element 13 that is disposed radially on its inner circumference and is coated with the electrically conductive layer 28. Combined, the yarn guiding element 13 and the electrically conductive layer 28 delimit the formed ring-shaped air gap 14 together with the yarn guiding element 3. Other arrangements of the electrically conductive layer 28 are possible, for instance by providing a flat layer between the yarn guiding element 13 and the cryostat 25. As in the first embodiment, the cryostat 25 may have a housing 22 surrounding the superconducting element 19, wherein an insulating material 23 or a cooling material 23, such as a cryogen, may be provided inside the housing 22 and surrounding the superconducting element 19.

A separate cooling device 9 is provided and adapted to maintain the temperature of the interior of the cryostat 25, in particular of the superconducting element 19, below the transition temperature of the superconducting material. As shown in Figures 6 and 7, the cooling device 9 may be provided as an external cooling device, such as a cryocooler circulating liquid cryogen via pipes through the interior of the cryostat 25 or may be provided as part of the cryostat. Any of the above-described cryostats and known cooling devices may be used. Different from the embodiment in Figure 6, the exemplary embodiment depicted in Figure 7 has a vertical air gap 14 such that the electrically conductive layer 28 shielding the superconducting element 19 from the high-frequency alternating magnetic field generated by the permanent magnets 21 of the rotor 2 has to be at least partially arranged in a vertical direction.

The above-described superconducting systems applied to ring spinning or ring twisting machines, flywheel energy storage systems and magnetic levitation transportation systems simplify the cooling system of the superconducting elements as heat generation inside the superconducting elements due to vibration of the rotating or linearly moving parts is avoided by placing an electrically conductive layer between the superconducting elements and the corresponding permanent magnets. As a consequence, the cooling systems may be built more cost efficiently. In addition, induction of the eddy currents in the electrically conductive layer dissipates unwanted vibrations such that operation of the described systems becomes safer.