RU2456696C2 - Superconductive wire of "cable-conduit" type for magnetic systems winding - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: wire contains a twisted superconductive core positioned inside a hollow flexible spiral-shaped element and a metal sheath. The sheath is designed as combined with an inner part in the form of an all-metal seamless pipe of aluminium or its alloys. The outer part is made of steel or titanium. The technical effect consists in excluding the possibility of helium leakage through welded seams. During the wire manufacture there is no need either to use special equipment requiring arrangement of an extended (to match the wire length) production site or to control helium leakage through welded seams. Variable size of the aluminium sheath inner diameter and the superconductive core crimping during such sheath presswork imposition enables adjustment of the superconductive core porosity within a wider range and to compact it to a certain degree whenever required.

EFFECT: aluminium sheath enhances superconductive wire stabilisation.

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Description

The invention relates to electrical engineering, more specifically to cable products, in particular to superconducting cable products that can be used for windings of powerful superconducting magnetic systems, including for windings of magnetic systems of a thermonuclear fusion plant of the type “TOKOMAK”, for example, manufactured according to an international project ITER, as well as for windings of SPIN superconducting energy storage devices and reactive power stabilization devices in electric networks.

Various designs of superconducting wires with channels for pumping refrigerant are known. Such designs provide an increase in the effective perimeter of the heat transfer of the wire to the refrigerant, improvement of heat transfer conditions, as well as a decrease in the filling volume of the refrigerant. Conducting wires with channels for pumping refrigerant can operate in refrigerated mode and in a closed cycle [1].

Known design [2] with several channels for circulation of the refrigerant. The conductors are made in the form of coaxial copper tubes, the space between which is filled with copper-stabilized superconducting wires of Nb-Ti and Nb-Ti-Ta alloys. The disadvantage of these designs is the high consumption of refrigerant per unit density of the transported current.

This drawback is eliminated in the well-known cable-conduit type wire [3], (“cable in sheath”, English term CIC - “cable in conduit”), which is adopted as a prototype.

This wire contains a superconducting core in the form of several (usually six) strands. Each of the strands is a twist of elementary, copper-stabilized superconducting wires. The strand can be sealed, and also entwined with a thin narrow tape, preferably in increments of not less than the width of the tape, protecting the strand from loosening. The strands are twisted around a pipe with perforated holes or a hollow flexible element, which is a spiral, twisted from a metal tape (stainless steel). The core can be sealed (porosity 30-60%) and wrapped with a thin tape. This superconducting core is housed in a non-superconducting pipe made of stainless steel or titanium, which is the sheath of the wire.

Although this design of the wire is workable and provides the required electrophysical characteristics, superconducting properties and parameters of current transpotation to create a magnetic field of the desired configuration and strength, however, it has a significant drawback. This disadvantage lies in the fact that in the manufacture of a long wire of this design, specially developed modes of transverse welding of the sheath are required for connecting pipes, each of which is six meters long. In addition, special labor-intensive, responsible and expensive methods of control of each welding seam separately and of the entire welded shell as a whole are required, which determine the possible places of helium leakage. A significant drawback of this design is also the fact that during its manufacture, the installation (installation) operation of the superconducting core in the shell necessitates the use of a long production section necessary to accommodate the entire long source pipe on it, individual segments of which are connected by welding, forming transverse welds every six meters.

Attempts to make such a cable-conduit wire by longitudinal welding of a sheath superimposed on a superconducting core have been undertaken by various manufacturers repeatedly, but have not been successful. The best sample, about 300 meters long, made in Japan, contained three sections where helium was passed through the weld. Therefore, the international team leading the ITER program has selected the wire design, which is the prototype of the invention.

The purpose of the present invention is to eliminate these disadvantages of the cable-conduit type superconducting wire.

This goal is achieved due to the fact that the superconducting cable-conduit type contains a twisted or transposed superconducting core placed on a hollow elastic element in the form of a spiral or in the form of a pipe with perforated holes, and a metal sheath. The difference is that the shell is made combined (composite). The inner part of the shell is made of aluminum or an alloy based on it, and the outer part of the shell is made of steel or titanium. The wire can be made of circular cross-section or shaped in the form of a rectangle, square, etc.

The proposed wire design has the following advantages compared to the prototype:

- the proposed wire design allows to increase the construction length of the wire, the length of which is limited only by the capabilities of the receiving container, since the manufacture of the inner aluminum pipe of the combined sheath is carried out by crimping the superconducting core on a hydraulic cable press for applying an aluminum sheath to the communication cables;

- the complete elimination of the possibility of helium leakage through the transverse welds of the shell, since there are no transverse welds, because the inner aluminum part of the combined (composite) shell is all-metal, seamless, and therefore helium does not penetrate the inner all-metal part of the shell;

- there is no need to use special expensive methods to control the leakage of helium through transverse welds;

- the proposed design of the wire does not require, in its manufacture, the creation of special equipment and does not require an extended production area equal to the length of the wire;

- the wire of the proposed design can be made on existing and mastered equipment of cable plants: twisting machines, a hydraulic cable press for applying an aluminum sheath to communication cables (sometimes for communication cables an aluminum sheath is applied to paper insulation), equipment for applying a metal sheath to the cable by means of longitudinal welding due to high-frequency heating of the welded edges;

- varying the dimensions of the inner diameter of the aluminum shell and compression of the superconducting core during pressing allows you to change the porosity of the superconducting core in a wider range and, if necessary, compact it to a much greater extent than is possible in the design of the prototype;

- the imposition of an inner sheath of high-purity aluminum (99.995%), the production of which has been successfully mastered in the country, can improve the stability of the wire and thereby increase its reliability, since the electrical conductivity of this aluminum increases by 1000 times at the operating temperature of the wire compared to electrical conductivity at room temperature ;

- These advantages significantly reduce the cost of the wire, which is very expensive.

The invention is illustrated in figure 1, 2 and figure 3.

Figure 1 shows a cross section of the proposed superconducting wire, a circular cross-section of the type "cable-conduit" containing a superconducting core placed on a hollow elastic element in the form of a spiral, and a metal combined (composite) sheath with its inner part in the form of an all-metal seamless pipe from aluminum and the outer part of the shell is made of steel.

Figure 2 presents a cross-sectional diagram of a cable-conduit type superconducting wire with a circle section containing a superconducting core placed on a hollow elastic element in the form of a thin-walled pipe with perforated holes in the pipe wall, and a metal combined (composite) sheath with its inner part in the form of an all-metal seamless pipe made of aluminum and the outer part of the shell of steel.

Figure 3 shows a rectangular cross-section of a cable-conduit type superconducting wire in a combined (composite) sheath with its inner part in the form of an all-metal seamless aluminum pipe and the outer part of the steel sheath. The superconducting core is made of nine superconducting transposed strands of rectangular cross section wound around a rectangular spiral.

Below, as examples, specific modifications of the superconducting cable-conduit type of the proposed design are presented, intended for windings of powerful superconducting magnetic systems.

Example 1

Superconducting cable-conduit wire of circular cross section. In Fig.1 shows a cross section of the proposed device, which is a superconducting wire type "cable-conduit" for the windings of magnetic systems of thermonuclear fusion plants type TOKOMAK. The wire contains: a flexible hollow stainless steel element in the form of a spiral - 1. On this flexible hollow element there is a superconducting core wound from six superconducting strands - 2. Each of these six superconducting strands 2 is a twist of elementary copper-stabilized superconducting wires. The superconducting core is wrapped with a thin metal tape 3, which protects the core from loosening and dissolving during the manufacture of the wire. Strand 2 can also be sealed and entwined with a thin narrow tape to protect it from loosening and dissolving during the manufacture of the wire. The superconducting core is enclosed in a combined metal shell. The inner part 4 of this combined (composite) shell is made of aluminum. The manufacture of an internal aluminum seamless pipe 4 of this combined (composite) sheath is carried out by crimping the superconducting core on a hydraulic cable press to apply an aluminum sheath to the communication cables. The outer part of the combined (composite) shell 5 is made of steel.

The proposed wire differs from the wire manufactured for the fusion installation developed by the international project ITER in that its shell is made of a combination (composite) with its inner part made of aluminum and the outer part made of steel, while the wire made for ITER contains only steel sheath.

Varying the dimensions of the inner diameter of the shell 4 of aluminum and compression of the superconducting core during pressing allows you to change the porosity of the superconducting core in a wider range, and if necessary, compact it to a much greater extent than is possible in the design of the prototype.

The imposition of inner cladding 4 of high purity aluminum (99.995%), the production of which has been successfully mastered in the country, can improve the stabilization of the superconducting cable-conduit type (cable-in-sheath, English term CIC - “cable in conduit”). At the same time, its reliability is increased, since the electrical conductivity of this aluminum increases at a working temperature of this wire by 1000 times in comparison with its electrical conductivity at room temperature.

The proposed wire has the following advantages compared to the prototype:

Complete elimination of the possibility of helium leakage through transverse welds, since the inner part 4 of the combined (composite) shell is made of aluminum, is seamless and therefore helium does not penetrate the inner part of the shell made of aluminum. In the manufacture of a long wire containing only a steel sheath, specially designed transverse welding modes of the sheath are required for connecting pipes, each of which is six meters long. At the same time, to eliminate helium leakage through transverse welds, each welding seam and the entire shell must be subjected to expensive special control performed by highly qualified specialists. The proposed wire eliminates the need for special expensive methods for monitoring helium leakage through transverse welds.

The proposed wire, in its manufacture, does not necessitate the creation of special equipment, as well as an extended, equal to the length of the wire production site for placing on it the entire steel pipe into which the superconducting core is drawn. In addition, special control and measuring equipment is not required to measure the pulling force of the superconducting core in a steel pipe, which is necessary to exclude the possibility of a break in the core or pipe.

The proposed wire can be made on existing and mastered equipment of cable plants: twisting machines, a hydraulic cable press for applying an aluminum sheath to communication cables (sometimes on a core with paper insulation), equipment for applying a steel sheath to a cable by longitudinal welding due to high-frequency heating of the welded edges.

The proposed wire design allows to increase the construction length of this wire, the length of which is limited only by the capabilities of the receiving containers. In the manufacture of the prototype wire, a production section is required, the length of which is not less than the length of the welded pipe, for example 1000 m, since the core is pulled into a steel sheath located horizontally, elongated over the entire length of the welded pipe.

These advantages can significantly reduce the cost of the wire, which is very expensive.

Example 2

Superconducting cable-conduit wire of circular cross section. Figure 2 shows a cross-sectional diagram of the proposed superconducting wire type "cable-conduit", having the shape of a circle. This wire contains a central flexible hollow element, which is a thin-walled metal pipe 6, with perforated holes 7. These holes 7 serve as channels for supplying liquid helium directly to superconducting strands 8 for better cooling with liquid helium of each of the six strands wound around the hollow elastic element 6 Each of the six strands 8 is a twist of elementary, copper-stabilized superconducting wires. The strand 8 can be sealed and entwined with a thin narrow tape 9, preferably in increments of not less than the width of the tape, protecting the strand from loosening and dissolving during the manufacturing process. The core can be sealed (porosity 30-60%) and also wrapped with a thin tape 10. The superconducting core is enclosed in a combined (composite) shell. The inner part of this shell 11 is made of aluminum in the form of a seamless tube. The outer part of the combined shell 12 is made of titanium.

For the longitudinal welding of the outer shell 12 of a titanium strip, a CO ₂ laser with a focal length of 0.2 mm can be used, which allows a high concentration of the energy beam to be produced over a very limited area of the welded pipe edges. This allows you to keep unchanged such characteristics of titanium as its high corrosion resistance and good deformability in the cold state. The advantages of the proposed wire compared to the prototype are the same as in the previous example.

The wire works as follows. The use of a wire with a large cross-section of the conductive core and a correspondingly high current strength allows you to create large windings in powerful magnets. The cooling of the winding is carried out using forced circulation of helium inside the combined shell. The wire mainly works in superconducting magnetic systems, which are a solenoid located in a cryogenic shell. The superconducting current in the wire can be caused by the passage of current through the wire from an external current source or can be induced by an external magnetic field. The wire is wound in the form of a winding of the desired configuration and used as windings of a superconducting electromagnet or windings of another cryoelectric device.

Example 3

Superconducting cable-conduit type wire of flat (rectangular cross-section). Figure 3 shows a cross section of the proposed superconducting wire type "cable-conduit" having a flat shape. The wire contains: a flexible hollow stainless steel element in the form of a rectangular spiral 13; nine superconducting strands 14. Each of the strands 14 (if it is a multi-strand non-monolithic structure) can be entwined with a thin metal tape 15. The superconducting core of nine strands 14 is a transposed structure, the main advantage of which is a high structural current density. It is achieved due to the uniform distribution of current between the strands and a high fill factor of the core and each core, as well as due to the low level of losses. In superconducting windings that generate time-varying magnetic fields, transposed wires are most often used, made by single-strand twisting followed by molding to a rectangular profile. All superconducting elementary wires in the strands of such wires have the same inductance and the current between them is distributed evenly, so the critical current of the transposed strands is usually equal to the sum of the critical currents of the individual superconducting wires.

The superconducting core may be wrapped with a thin tape 16. This core is housed in a combination sheath. The inner part of the shell 17 is usually made of aluminum, however, if there is a need to increase its strength, the inner part of the combined shell can be made of an alloy based on aluminum, which has higher strength properties than aluminum. The outer part of the combined (composite) shell 18 is made of steel. Although the process of high-frequency welding of the outer steel shell is inevitably accompanied by the formation of the outer and inner burrs and the inner burr (19) cuts into the inner aluminum shell 17, but, as a rule, it has dimensions (0.02-0.3 mm) and does not interfere with normal operation wires without causing helium leakage. The outer burr is removed by incisors.

The advantages of the proposed wire compared to the prototype, in addition to those already noted, are the same as in the first example:

- the complete elimination of the possibility of leakage of helium through welds, since the inner part of the combined (composite) shell is made of aluminum, is seamless and therefore helium does not penetrate the inner part of the shell made of aluminum;

- there is no need to use special expensive methods to control the leakage of helium through welds of the outer part of the shell made of steel or titanium;

- the proposed design of the wire does not require, in its manufacture, the creation of special equipment that requires a lengthy, equal to the length of the wire production site;

- the wire of the proposed design can be made on existing and mastered equipment of cable plants: twisting machines, a hydraulic cable press for applying an aluminum sheath to communication cables, equipment for applying a metal sheath to a cable by longitudinal welding due to high-frequency heating of the welded edges;

- the imposition of an inner sheath of high purity aluminum (99.995%), the production of which has been successfully mastered in the country, can improve the stability of the wire and thereby increase its reliability, since the electrical conductivity of this aluminum increases by 1000 times at the wire’s operating temperature compared to room temperature;

- the proposed wire design allows to increase the construction length of the wire, the length of which is limited only by the capabilities of the receiving containers;

- a wire with a rectangular cross-section allows to increase the density of the winding of a superconducting magnet in comparison with the density of the magnet winding by a wire with a circle cross-section;

- These advantages significantly reduce the cost of the wire, which is very expensive.

Information sources

1. W.C. Hamilton. Manufacture of a 16000 AMP superconducting conductor for the Tocomak Toroidal field coil. Large Coil program. “Proc 9 Symp. Eng. Prohl. Fusion Researh // IEEE Pub. No. 81 CH 1716-2, p. 324-327.

2. G.G. Svalov, D.I. White. Superconducting and cryoresistive winding wires. M .: Energy, 1974, pp. 108-109.

3. Advertising booklet VNIIKP "Superconducting wires in a metal sheath."

Claims (1)

A superconducting cable-conduit wire for windings of magnetic systems, including windings of thermonuclear fusion plants of the TOKOMAK type, containing a twisted superconducting core placed on a hollow elastic element and a metal sheath, characterized in that the sheath is made combined with the inner part in the form all-metal seamless pipe made of aluminum or its alloys, and the outer part is made of steel or titanium.

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