The present invention has as object an electric cable and a method for the obtainment thereof.

In particular, the present invention refers to a superconductor electric cable.

The present invention has application in the manufacturing of high-intensity magnetic field generators, for example reactors for nuclear fusion, particle accelerators or magnetic-levitation train lines.

The present invention may also have application in the transmission of high-energy electrical energy.

Electric cables are known that are made of superconductor materials, in which such materials are made of wires or strips associated with supports of various shapes and coated in order to protect the integrity of the materials themselves.

Superconductor materials are materials that have very low or zero resistivity below a certain temperature, termed critical temperature T_C. This allows a practically ideal passage of electric current, without energy dispersions, e.g. in the form of heat.

The following are among the more well-known superconductor materials used: the Niobium-Titanium (Nb-Ti) alloy and the Niobium-Tin (Nb₃Sn) intermetallic compound. These materials are termed Low Temperature Superconductors (LTS). They typically have very low critical temperatures, respectively T_C = 9 K and T_C = 18K.

These materials are available in wires which are intertwined in a known manner in order to create the cable.

The cables made in this manner operate at a very low temperature, equal to 4.2 K, and they must necessarily be cooled through the use of liquid helium.

One of the techniques used most for cooling the cable is termed Cable In Conduit Conductor (CICC). This technique dates from the 1970s and consists of intertwining the wires within a metal duct in which the liquid helium is made to flow.

Over the last few years, superconductors with high critical temperature have been developed, the so-called High Temperature Superconductors (HTS).

Materials based on compounds of ReBa₂Cu₃O_7-δ type have good characteristics, i.e. compounds based on oxygen (in variable quantity), copper, barium and where "Re" indicates yttrium or any one of the rare earth elements.

The materials have higher critical temperatures, such as T_C = 90-94 K.

Often, the latter materials are available in strips, given that it is complicated to obtain them in wire form.

In particular, the strips used are termed coated conductors since they are strips with steel core or nickel-based alloy core coated with a thin superconductor film and an external copper layer.

Also in the case of the strips, the cables are obtained by means of the CICC technique, i.e. by providing for a flow duct for the coolant liquid.

For such purpose, seats are provided on a hollow metal support in order to make the coolant flow; the strips, arranged in stacks, are housed in such seats. A metal sheath is wound in order to close the seats.

Examples of known of such electric cables can be seen in document EP 2 369 600 and document GB 2 350 474.

Disadvantageously, in order to sufficiently cool the superconductor, it is necessary to use a considerable quantity of energy to ensure the correct operation temperatures and to ensure the effectiveness of the cable.

In this context, the technical task underlying the present invention is to propose an electric cable and a method for the obtainment thereof that overcomes the abovementioned drawback of the prior art.

In particular, object of the present invention is to provide an electric cable and a method for the obtainment thereof that allow a more effective cooling of the superconductor element.

The specified technical task and object are substantially attained by an electric cable and a method for the obtainment thereof comprising the technical characteristics set forth in one or more of the enclosed claims.

Further characteristics and advantages of the present invention will be clearer from the exemplifying and hence non-limiting description of a preferred but not exclusive embodiment of an electric cable and a method for the obtainment thereof, as illustrated in the enclosed drawings in which:

• figure 1 is a perspective view partially in section of a superconductor electric cable in accordance with the present invention;
• figure 2 is a plane view in section of the cable of figure 1;
• figure 3 is a detail of the section view of figure 2 in a first embodiment; and
• figure 4 is a detail of the section view of figure 2 in a second embodiment.

With reference to the enclosed figures, reference number 1 indicates overall an electric cable, in particular a superconductor electric cable, in accordance with the present invention.

The cable 1 comprises a support body 2 and a plurality of conductor strips 3 associated with the support body 2.

The support body 2 has elongated form and is made of flexible material in a manner such that it can be wound in coils.

In particular, the support body 2 is made of a metal material.

The support body 2 has, at its interior, a cavity 4 which is extended in accordance with the support body 2 itself and which defines a flow duct 5 for a coolant liquid.

A plurality of guides 6 are fixed to the support body 2 in order to define respective seats 7 for housing the strips 3.

The guides 6 comprise a plurality of walls 8 which are extended away from the support body 2. Each pair of adjacent walls 8 defines a seat 7.

The seats 7 are extended in accordance with the extension of the support body 2 and the entire cable 1. The seats 7, and correspondingly the walls 8, have a substantially rectilinear extension, considering a rectilinear section of cable 1.

Alternatively, the seats 7, and correspondingly the walls 8, have a substantially helical extension. This has particular application in the conduction of alternating current.

Each seat 7 has a base face 9, against which the strips 3 abut, and two lateral faces 10 which are extended starting from the base face 9.

The base face 9 has a cross section oriented orthogonal to a radial direction.

The lateral faces 10 are the two opposite faces of the walls 8.

Preferably, when the guides 6 have rectilinear extension, the lateral faces 10 of each seat 7 are substantially parallel to each other.

Preferably, when the guides 6 have helical extension, the lateral faces 10 of each seat 7 are facing each other and at a constant and uniform distance from each other.

In other words, the seats 7 have substantially square or rectangular form in section.

The strips 3 are superimposed on each other in stacks. The stacks are then placed in the seats 7.

All the strips 3 have the same width. In addition, all the stacks have the same number of strips 3.

The strips 3 are of coated conductor type. In other words, each strip 3 comprises a metal core, e.g. made of steel or nickel-based alloys.

The cores are coated with a thin superconductor film. Finally, the strips 3 have an external coating made of copper that covers everything.

Preferably, the superconductor material used is of High Temperature Superconductor type. Still more preferably, the material used is of ReBCO type.

In accordance with the present invention, the cable 1 has at least one flow channel 11 in each seat 7 in order to make coolant fluid flow, also within the seats 7 themselves.

In more detail, at least one groove 12 is obtained within each seat 7 in a manner such that the coolant fluid flows herein in direct contact with the strips 3. In particular, two grooves 12 are obtained in each seat 7, preferably on the base face 9. Such grooves 12 are situated side-by-side each other and at a uniform distance from each other.

Alternatively, the grooves 12 can also be obtained on the lateral faces 10.

Each groove 12 follows the extension of the base face 9, and thus follows the extension of the seats 7 themselves.

Each groove 12 has a section transverse to the extension direction of the seat 7 with substantially semicircular form. Advantageously, this shape of the grooves 12 ensures an effective transit of the coolant fluid.

In addition, the edges 12a of the grooves 12 at the base faces 9 of the seats 7 are rounded. Advantageously, this shape of the edges 12a of the grooves 12 prevents the strips 7, pressed in the seats 7 (as will be seen hereinbelow), from being damaged by the edges 12a of the grooves 12.

Preferably in association with that stated above, the width of the strips 3 is smaller than the width of the seats 7. The width of the seats 7 is calculated as the distance between the lateral faces of the seats 7 themselves.

In such a manner, air spaces 13 come to be determined between the stacked strips 3 and each lateral face 10 of every seat 7. The coolant fluid that flows into the flow channels 11 also enters into the air spaces 13, directly reaching all the strips 3 and considerably increasing the cooling thereof.

The cable 1 further comprises a coating 14 placed around the guides 6 in order to close the seats 7. Advantageously, a band 15 is wound directly above the guides 6 and results interposed between the guides 6 and the coating 14.

Preferably, the coating 14 is metallic and is drawn coaxial to the support body 2, as will be better seen hereinbelow. For example the coating is made of steel or aluminum.

Preferably, also the band 15 is metallic.

In accordance with a further aspect of the invention, the cable 1 further comprises compression means active on the strips 7 in order to compress them inside the respective seats 7.

In particular, the compression means comprise a plurality of spacers 16, each placed in a respective seat 7 of strips 3. The spacers 16 compact the stacks of strips 3 in each seat 7. More precisely, the spacers 16 compact the stacks of strips 3 in each seat 7 in cooperation with the coating 14.

Indeed, the spacers 16 are placed below the coating 14, and below the band 15, and are pressed by the coating 14. For such purpose, the spacers 16 are applied in a manner so as to project slightly from the seats 7, in a manner so to be thrust inside the seats 7 during the application of the coating 16.

Advantageously, the use of the spacers 16 that press against the strips 3 allows strongly pressing the strips 3 in the seats 7, preventing them from moving. This prevents, during use, the presence of strong magnetic fields from generating induced forces on the strips 7 themselves, which would move the strips and generate friction. The elimination of such friction induced by the magnetic fields allows preventing local overheating, which can interrupt the operation of the superconductor materials used in the strips 7, and allows preventing local wear that can mechanically compromise the strips 7.

Each spacer 16 can be a single strip-like body 17 (figure 3), preferably metallic, having a width substantially equal to the width of the seats 7. Alternatively, each spacer 16 can comprise a plurality of metal wires 18 (figure 4) having substantially circular section and fit next to each other in the seats 7 above the strips 3.

The invention further attains a method for obtaining the above-described cable 1.

The method begins with the arranging of the support body 2.

This is achieved by means of hot extrusion, preferably of metal material.

In particular, the support body 2 production process provides for a cooling step downstream of the extrusion in order to ensure the size characteristics.

Together with the support body 2, the walls 8 are also extruded in the same process, such walls 8 defining the seats 7 of the guides 6.

If the guides 6 have a helical extension, following extrusion, the support body 2 and the guides 6 are subjected to twisting with constant pitch.

At this point, the strips 3 are placed in the seats 7. For such purpose, the strips 3 are unwound at constant tension from suitable coils and are superimposed on each other in order to form the abovementioned stacks. The stacks of strips 3 are then inserted in the seats 7, preferably at the same time as the stacking step. The insertion occurs by means of insertion heads (not illustrated) that push the stacks into the seats 7.

If the extension of the seats 7 is helical, the insertion heads are rotated by means of a rotating cage synchronized with the pitch of the guides 6 in a manner so as to follow the progression of the seats 7 themselves.

Subsequently, the metal band 15 is wound around the guides 6.

Finally, the coating 14 is applied by means of a drawing process. In such a manner, the seats 7 are hermetically closed. In detail, the application of the coating 14 occurs by wrapping the guides 6 with a metal tube that is then drawn in order to make it reach the correct diameter and perfectly adhere to the guides 6.

The tube is wound by arranging a metal sheet and wrapping it around the guides 6. The sheet is longitudinally welded in order to obtain the tube by means of TIG or laser process.

In accordance with the main aspect of the invention, the method comprises the step of arranging the flow channel 11 (or channels) for the coolant fluid in each seat 7.

Such step is achieved by arranging at least one of the grooves 12 in the seat 7. In detail, the grooves 12 are obtained directly during the step of extruding the support body 2 and the guides 6.

Clearly, given that the grooves 12 are obtained during the extrusion of the support body 2 and the guides 6, they are made along the extension of the guides 6 and the seats 7 themselves.

In accordance with the secondary aspect of the invention, the method further comprises the step of inserting the plurality of spacers 16 in the seats 7. Both when the spacers 16 are strip-like bodies 17, and when they are groups of adjacent wires, the introduction of the spacers 16 is achieved in an entirely analogous manner to the insertion of the strips 3.

Such step is attained before the step in which the guides 6 are wrapped by the band 15 and before the application of the coating 14. In such a manner, the latter steps contribute to achieving the necessary compression of the strips 3 in the seats 7.

The invention attains the proposed object.

Indeed, the presence of flow channels for the coolant fluid in the seats allows, as said, a direct and more effective cooling of the superconductor strips, with a reduction of the energy necessary for maintaining the superconductor material under the critical temperature.