RU71033U1 - HIGH-TEMPERATURE SUPERCONDUCTING MATERIAL - Google Patents

Abstract

The utility model relates to devices for operation as part of cryogenic helium systems. A current lead based on a high-temperature superconducting material contains a mechanical base, “cold” and “warm” current terminals, heat exchange elements, current-carrying elements from conductive and superconducting materials, while the mechanical base is made of a cryogenic temperature-resistant electrically conductive or non-conductive material, the current-carrying elements are optimized for the length of the mechanical base and consist of three parts in mechanical and electrical contact with each other - non-superconducting, superconducting and combined, while the non-superconducting and superconducting parts of the current-carrying element are soldered to the “warm” and “cold” current terminals, respectively, and the combined part is formed by parallel connection of the non-superconducting and superconducting parts, the superconducting part is made of wire based on the first-generation high-temperature superconducting material. The utility model may find application in cryogenic plants.

Description

The utility model relates to devices for operation as part of cryogenic helium systems.

Known current lead, designed to operate as part of cryogenic helium systems (Supercond. Sci. Technol. 11 (1998) 1091-1054). It consists of two separate parts, which in working condition are electrically and mechanically interconnected:

- non-superconducting (copper) part

- a superconducting part made on the basis of high-temperature superconducting (HTSC) wires of the 1st generation, made of a Bi-2223 superconductor in a silver matrix. As a mechanical basis, a steel rod is used, to which steel disks are attached. HTSC tapes are attached to the discs with bolts. The “cold” contact of the current lead is made of copper, the electrical contact between the “cold” terminal and the HTSC tapes is provided using copper wires. The superconducting part of the current lead is cooled by a stream of helium gas.

For the current lead to work, additional cooling of the non-superconducting part with liquid nitrogen is required to maintain the temperature of the upper point of the superconducting part (or the lower point of the non-superconducting part) below the temperature of the superconducting transition at full rated current.

The closest device in technical essence and the achieved effect is a current lead for operation as part of cryogenic helium systems, cooled by a stream of gaseous helium

cryogenic helium systems, cooled by a stream of helium gas without additional cooling with liquid nitrogen (www.cryomagnet.ru, catalog, 2006, p. 25). The current lead contains a mechanical base (stainless steel tube), heat exchange elements, as well as two current terminals (contacts). The heat-exchange elements in the form of copper rings are soldered to a mechanical base, the conductive part, the current-carrying elements of the current lead, is soldered into the slot of the rings. The use of rings allows one to intensify the heat transfer between the gaseous helium stream and the conductive part of the current lead, and the rings also serve as places for a local increase in heat capacity and decrease in thermal conductivity, which protects the current lead from overheating in the event that its superconducting part goes to normal. The conductive part (current-carrying elements) consists of brass strips, on which high-temperature superconducting (HTSC) tapes of the first generation are soldered based on the Bi-2223 superconductor in a silver-gold matrix, both HTSC tapes and brass strips are soldered along the entire length of the current lead.

The current lead has the following technical parameters:

- working current - 200 A;

- maximum current 300 A;

- heat gain to liquid helium at a current of 200 A (per 1 current lead) - 0.15 watts.

Known technical device current lead has the following disadvantages.

Due to the fact that the conductive part is made in the form of a parallel connection of the 1st generation HTSC tape and a brass stabilizer along the entire length of the current lead, there is excessive heat inflow to liquid helium through the brass stabilizer, in

whose use in the lower (cold) part of the current lead is not necessary, since all the current flows along the HTSC tapes.

Due to the fact that the conductive part is made in the form of a parallel connection of the 1st generation HTSC tape and a brass stabilizer along the entire length of the current lead, in operation the temperature of the HTSC tape varies from 4.2 K in the lower part of the current lead to 300 K in the upper part of the current lead. It is known that the temperature of the superconducting transition for HTSC wires of the 1st generation based on Bi-2223, which are used in the known technical device, the current lead does not exceed 110 K. Therefore, the use of HTSC tapes above the temperature of the superconducting transition is not economically profitable, since the cost of 1 m HTSC wire 1st generation is about 3,000 rubles ($ 100).

In the known technical device, the flow of gaseous helium cools only the outer surface of the mechanical base, made in the form of a tube of stainless steel, and there is no cooling of the inner surface of the mechanical base by the flow of gaseous helium, which causes excessive heat inflow to liquid helium.

In the known technical device, the critical current of the 1st generation HTSC tapes based on the Bi-2223 connection is significantly reduced in an external magnetic field (Fig. 1), which degrades the technical characteristics of the current lead, since in most cases the current leads are used to supply current to superconducting magnets and exposed to an external magnetic field. Figure 1 shows the dependence of the critical current on the external magnetic field.

Where SS is a second generation superconductor (coated conductor), Bi-2223 is a first generation superconductor made by the "powder in a pipe" method.

The objective of the utility model is to develop a current lead with low heat gain, resistant to external magnetic fields based on high-temperature superconducting wires of the 1st and 2nd generation.

The problem is solved by the claimed current lead based on a high-temperature superconducting material containing a mechanical base, “cold” and “warm” current terminals, heat exchange elements, current-carrying elements of conductive and superconducting materials, in which the mechanical base is made of an electrically conductive or non-conductive material resistant to cryogenic temperatures , current-carrying elements are optimized along the length of the mechanical base and consist of three located in the mechanical and electrical con the act of the parts — non-superconducting, superconducting and combined, the non-superconducting and superconducting parts of the current-carrying element are soldered to the “warm” and “cold” current terminals, respectively, and the combined part is formed by parallel connection of the non-superconducting and superconducting parts, the superconducting part is made of wire based first-generation high-temperature superconducting material made by the method of "powder in a pipe" in a matrix of silver or its alloys, or second second generation, made using "thin film technology".

The mechanical basis of the inventive current lead for the cryomagnetic system is made of polymer materials with a low coefficient of thermal conductivity, for example, fiberglass, textolite, carbon fiber, or metal or metal-containing materials, for example, steel, non-ferrous metals and their alloys.

In the case of a mechanical base in the form of a hollow body, it has perforation along its length for additional cooling of the inner surface of the base.

Heat-exchange elements are made of conductive or non-conductive materials and represent a transverse fins of a mechanical base with a variable pitch with a decrease in it to the "warm" terminal.

The terminals of the current lead are made of a material with high electrical conductivity, while the “cold” terminal can be made conical in the form of a bayonet clamp to provide a detachable connection with the counterpart in the cryostat.

In the inventive current lead for the HTSC cryomagnetic system, the tapes are spirally wound onto a mechanical base, which allows to increase the length of the tapes, thereby reducing the thermal conductivity of the solid, and therefore reduce the heat gain to liquid helium.

Figure 2 presents the image of the inventive current lead based on high-temperature superconducting material. The current lead consists of a “cold” terminal (1), a warm terminal (3), which are interconnected by a mechanical base (2). In addition, the “cold” and “warm” terminals are interconnected by a conductive part consisting of a superconducting part (4), a combined part (5), and a non-superconducting part (6). Heat exchange elements (7) are attached to the mechanical base and the conductive part (by soldering, gluing or threaded connection and other types of connection).

The mechanical base can be made of both electrically conductive and non-conductive material, resistant to cryogenic temperatures, with a low coefficient of thermal conductivity. The mechanical base can be made in the form of a hollow body (a set of hollow bodies) - for example, a tube, as shown in figure 3 and

5, in this case, it has a perforation along its length for additional cooling of the inner surface of the base, and in the form of a monolithic body (or a set of bodies), as shown in figure 4, where the mechanical base is a set of four steel cylinders, or with a combination of hollow and monolithic bodies.

The non-superconducting part can be made of steel and its alloys or of non-ferrous metals and their alloys, in the form of a single hollow or monolithic body, or a set of bodies. For example, four brass or copper conductors of rectangular cross-section (Fig. 3), one conductor of rectangular cross-section (Fig. 4), the set of hollow and monolithic conductors in Fig. 5, where to a brass tube that simultaneously acts as a mechanical base in the non-superconducting and combined parts current lead, additionally soldered 2 copper conductors of rectangular cross section.

In the combined part of the current lead, superconducting HTSC tapes of the first or second generation are in parallel electrically connected to a non-superconducting material. Moreover, the set of non-superconducting bodies in the combined part may differ from the set of non-superconducting bodies in the non-superconducting part of the current lead to reduce heat inflow to liquid helium. Also, the set of HTSC tapes in the combined part of the current lead can differ from the set of HTSC tapes in the superconducting part of the current lead to reduce heat inflow to liquid helium. For example, in the design (Fig. 5), in the combined part, the temperature of which is higher than the temperature of the superconducting part, and, therefore, the current carrying capacity of HTSC tapes is lower, the number of HTSC tapes is four (the superconducting part consists of two HTSC tapes). In addition, in the execution (Fig. 5), the non-superconducting part is represented by a combination of a brass tube and two rectangular copper conductors, in the combined part, copper conductors

rectangular sections are not used because the temperature of the combined part is less than the temperature of the non-superconducting part, respectively, higher than the current-carrying non-superconducting material.

The superconducting part is a HTSC wire of the first or second generation, and the use of HTSC wires of the second generation is preferable for the reasons described below. The use of a superconductor of the 2nd generation (film HTSC) in current leads will improve their technical and economic characteristics. So, for example, the existing samples of film HTSCs (2nd generation) have a critical current density higher than HTSC wires made by the powder in a pipe method (first generation). It is necessary to take into account that film HTSCs have a weaker dependence of the critical current on the external magnetic field perpendicular to the largest wire size (see Fig. 1). (HTS Wire: Status and Prospects, Physica C, Vol. 386 (April 15, 2003)), which is an important parameter when creating HTSC current leads for cryomagnetic systems with a high value of the scattered magnetic field.

Figure 1: SS - the second-generation superconductor (coated conductor), Bi-2223 - the first-generation superconductor, made by the method of "powder in a pipe".

In addition, according to experts, the cost of 1 kA * m VSTP of the 1st generation conductor is an order of magnitude higher than the cost of copper wires, and in industrial production the cost of 1 kA * m of film HTSC wires will be lower than the cost of 1 kA * m for copper (Chernoplekov N. A., "High Current Superconductivity: Physics, Technology, Economics", proceedings of the 2nd international conference Fundamental Problems of Superconductivity (Zvenigorod, 2006)).

The test results showed that the heat gain associated with the current leads per one current lead is not more than 0.10 watts at 200 A.

Thus, the inventive current lead based on a high-temperature superconducting material has a low heat gain, is resistant to external magnetic field.

Claims (5)

1. A current lead for a cryomagnetic system based on a high-temperature superconducting material, containing a mechanical base, “cold” and “warm” current terminals, heat exchange elements, current-carrying elements of conductive and superconducting materials, characterized in that the mechanical base is made of an electrically conductive resistant to cryogenic temperatures or non-conductive material, current-carrying elements are optimized along the length of the mechanical base and consist of three in mechanical and electrical contact between the parts - non-superconducting, superconducting and combined, while the non-superconducting and superconducting parts of the current-carrying element are soldered to the "warm" and "cold" current terminals, respectively, and the combined part is formed by parallel connection of the non-superconducting and superconducting parts, the superconducting part is made of wire based on high-temperature first-generation superconducting material made by the method of "powder in a pipe" in a matrix of silver or its alloys, or the second Debris manufactured using "film technology". 2. The current lead for the cryomagnetic system according to claim 1, characterized in that the mechanical base is made of polymer materials with a low coefficient of thermal conductivity, for example fiberglass, textolite, carbon fiber, or metal or metal-containing materials, for example, steel, non-ferrous metals and their alloys. 3. The current lead for the cryomagnetic system according to claim 1, characterized in that the mechanical base, in the case of a hollow body, has perforation along its length for additional cooling of the inner surface of the base. 4. The current lead for the cryomagnetic system according to claim 1, characterized in that the heat exchange elements are made of conductive or non-conductive materials and represent a transverse fins of a mechanical base with a variable pitch with a decrease in it to the "warm" terminal. 5. The current lead for the cryomagnetic system according to claim 1, characterized in that the terminals are made of a material with high electrical conductivity, and the "cold" terminal is conical in the form of a bayonet clamp to provide a detachable connection with the counterpart in the cryostat.