EP0958585A1

EP0958585A1 - Current supply device for a cooled electrical device

Info

Publication number: EP0958585A1
Application number: EP98907881A
Authority: EP
Inventors: Florian Steinmeyer; Hans-Peter KRÄMER
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1997-02-07
Filing date: 1998-02-02
Publication date: 1999-11-24
Anticipated expiration: 2018-02-02
Also published as: EP0958585B1; DE19704485A1; US6112527A; DE19704485C2; JP2001510551A; DE59808460D1; JP3898231B2; WO1998035365A1

Abstract

The current supply device (2) comprises an electrical line extending between a high-temperature level (RT) and a lower temperature level (TT), to which a cooled electrical device, specially a supraconducting device, is connected on the low temperature end. The electrical line should be configured at least partially by at least one part (6a, 7a) of a cold head (3) of a pulse tube cooler comprising a regenerator (6) and a pulse tube (7).

Description

description

Power supply device for a cooled electrical device

The invention relates to a power supply device with at least one electrical line running between a higher temperature level and a lower temperature level, which is connected at its low-temperature end to a cooled electrical device. Such a power supply device is e.g. from the journal "Cryogenics", Vol. 25, 1985, rare 94 to 110.

One of the main problems in the design of cryogenic systems is the efficient introduction of relatively large currents into superconducting or semiconducting devices, such as are provided for example for generating a magnetic field or for limiting a short-circuit current or for transforming a voltage or transmitting a current. The greatest thermal leak in an insulated cryocontainer is often caused by the at least one electrical conductor of the power supply device, which is between a higher temperature level, in particular at room temperature of about 300 K, and a lower temperature level of, for example, 77 K, the temperature of the liquid nitrogen LN ₂ , runs on which the electrical device can be located. If the electrical line of the power supply device running between these temperature levels cannot be constructed with little loss and the resulting heat loss is not effectively dissipated, only the cooling effort can be technical or question the economic sense of the entire system.

When designing known power supply devices, a distinction is made in particular between line-cooled and exhaust-cooled designs. Line-cooled power supply devices are generally only cooled by heat conduction from a cold end. If the dimensions are optimized so that the sum of Joule 's losses of the metal of the line with a specific resistance p (T) and through the heat transport determined by the temperature-dependent thermal conductivity λ (T) is minimal, then the specific loss is ie the heat input per unit current, for copper about 43 W / kA when considering a single electrical line (cf. the magazine “IEEE

Transactlons on Magnetics ", Vol. MAG-13, No. 1, 1977, Rare 690 to 693).

In the case of exhaust-gas-cooled power supply devices, the enthalpy of a vaporized coolant, for example of LN ₂ at 77 K or of liquid helium LHe of 4.2 K, is used to dissipate the heat loss introduced in countercurrent. This enables the specific loss between 300 K and 77 K to be reduced to approximately 25 W / kA, with approximately 0.56 liters of LN ₂ evaporating per hour, kiloampere and power supply line.

For a given coolant supply, the amount of heat introduced into a cryostat dictates the service life of the cryogenic system after which it is necessary to refill it, or the size of a cooling unit if no cooling liquids are used. the. What is also important for a user is how high is the required power at room temperature that must be provided for cooling. This power is used, for example, in a compressor in a cooling unit or in the production of the liquid coolant.

Depending on the specific application, a large number of embodiments for power supply devices are known (cf. the literature reference mentioned at the beginning). As a rule, copper or brass is used as the material for the electrical line running between the different temperature levels. In the case of line-cooled power supply devices, the cold end is also often connected with good heat conduction, but in an electrically insulating manner, to the cold side of a refrigerator which operates in particular according to the Gifford-McMahon principle. In exhaust gas-cooled power supply devices, at least a large part of the evaporated coolant is guided along the electrical line, which should have the largest possible surface area so that an effective heat exchange takes place.

The object of the present invention is to design a power supply device with the features mentioned at the outset in such a way that the cryotechnical outlay required for it is reduced.

This object is achieved according to the invention in that at least a portion of the electrical line is formed by at least a portion of a cold head of a pulse tube cooler having a regenerator and a pulse tube. In the power supply device according to the invention, a pulse tube cooler is therefore an integral part of the device. This takes advantage of the fact that the cold head of such a pulse tube cooler is a simple component without mechanically moving parts compared to cold heads of conventional cryocoolers, which work according to the Gifford-McMahon principle, for example, which is advantageously inexpensive to manufacture and that can be isolated from high voltages due to the lack of further electrical drives. In terms of heat technology, the power supply device according to the invention thus represents an intermediate form between a line and exhaust-cooled power supply that does not require a flowing liquid coolant and thereby causes a comparatively lower heat input compared to a line-cooled power supply. It thus combines the advantages of the two conventional types of power supply.

Advantageous refinements of the power supply device according to the invention emerge from the dependent claims.

To further explain the invention and its developments, reference is made below to the drawing. In each case, schematically, as a longitudinal section, FIG. 1 shows a first embodiment of a spring feed device according to the invention, FIG

Power supply device and its figures 3 to 7 different embodiments of known pulse tube coolers. In the figures, corresponding parts are provided with the same reference symbols.

In the embodiment of a power supply device according to the invention shown in FIG. 1, generally designated 2, parts of a cold head 3 of a pulse tube cooler are used to conduct the electrical power between a warmer side, in particular at room temperature RT, and a colder side, for example at low temperature TT of 77 K LN ₂ side. The cold head 3 projects at least with its colder part into the vacuum space V of a vacuum vessel 4 or a cryostat. Instead of the vacuum space of a vacuum vessel, the interior of a (bath) cryostat can also be provided with the cold head or cold head part. The cold head has a regenerator 6 and a pulse tube 7, which are connected to one another at their low-temperature ends via an overflow line 15. The power line forms the cladding tube 6a of the regenerator 6 and / or the cladding tube 7a of the pulse tube 7 in a coaxial or parallel construction. Either regenerator and

The pulse tube must be electrically insulated from one another and form two electrical lines which are at different potential, as is assumed in the exemplary embodiment shown. Or these parts can also be connected in parallel. In the figure, 8a and 8b also denote the power connections at the warmer temperature level RT, 9a and 9b the corresponding power connections at the lower temperature level TT, with 10 an installation opening for the cold head 3 in the vacuum or cryostat vessel 4 11 an insulating mounting flange holding the cold head 3 on its warmer side, which is used for a vacuum or gas-tight sealing device of the installation opening 10, with 13 a gas inlet and / or outlet on the regenerator, with 14 a gas inlet and / or outlet on the pulse tube, with 15 the, for example, electrically insulating overflow line between the regenerator and the pulse tube, and with 16 a connection for a thermal busbar. An external power supply unit located at room temperature RT, for example, is to be connected to the power connections 8a and 8b, while a cooled electrical device, which is generally to be kept at the low temperature TT, is connected to the power connections 9a and 9b. The electrical device can be, in particular, a cable, a current limiter, a magnetic field winding or parts of an electronic system, each with superconducting material. LHe cooling technology can generally be used for classic super conductor materials such as Nb ₃ Sn or NbTi and for metal oxide superconductor materials with a high transition temperature such as Y-Ba-Cu-0- or (Bi, Pb) -Sr-Ca Cu-0 type in general an LN ₂ cooling technology can be provided. However, the electrical device can also have normal-conducting or semiconducting parts to be cooled and need not necessarily be at exactly the temperature level TT.

The embodiment shown in FIG. 2 of a power supply device designated by 22 differs from that

Embodiment according to Figure 1 in that its cold head 23 of a pulse tube cooler is used only by means of its regenerator 26 to carry current. The regenerator contains as a current-carrying part a metallic body in the form of, for example, a tightly rolled metal net 26b packed in its cladding tube 26a. Instead of the metal mesh, a porous one can be used Sintered metal granules or a bundle of thin wires or at least one thin, rolled or folded sheet metal strip or a number of profiled sheets are used. These metallic bodies are electrically contacted at the warm and cold ends, for example by soldering, welding or pressing. A bundle of thin wires is particularly suitable for introducing alternating current, since the wire thickness can be adapted to the skin depth. In the embodiment according to FIG. 2, however, the heat conduction in the regenerator is greatly increased compared to a stack of fine wire nets, so that this embodiment is preferably only considered for comparatively large currents.

In the power supply devices according to the invention, as can be seen in FIGS. 1 and 2, electrical insulation is advantageously provided by dielectrics, e.g. Plastics and / or ceramics guaranteed. At the low-temperature end, sapphire, BeO or aluminum nitride are also preferably used, which advantageously have a high thermal conductivity. As a result, other components to be cooled, e.g. Radiation shields or electrical or magnetic devices can be thermally coupled. Electrical isolation between a compressor with possibly electrical valve train and the power supply device can e.g. by an insulating connecting tube, which can be made of plastic, fiber-reinforced plastic or ceramic, for example.

The pulse tube coolers used for a power supply device according to the invention are known per se

Embodiments assumed (see, for example, "Cryocoolers 8", Plenum Press, New York, 1994, pages 345 to 410; or "Ädvances in Cryogenic Engineering", Vol. 35, Plenum Press, New York, 1990, pages 1191 to 1205; or "INFO PHYS TECH" of the VDI Technology Center, No. 6 / Febr. 1996, with the title: "Pulse tube cooler: New refrigeration machines for superconducting technology and cryoelectronics", 4 pages; or US 5, 335, 505 A). Such a pulse tube cooler has a cold head 33 according to FIG. 3 This cold head has two tubes which are connected to one another, one tube is designed as a so-called regenerator 36 and contains in its interior a body which stores the gas heat periodically, for example in the form of stacked tubes This body is used for power conduction in the embodiment of a power supply device 22 according to the invention according to Figure 2. In contrast, the other tube is a so-called pulse tube 37, which only has heat exchangers formed at its warm and cold ends, for example, by fine copper meshes 38 or 39 and is otherwise hollow, both n Not necessarily tubular parts 36 and 37 are connected at their low-temperature ends TT by means of an overflow channel 40 for a coolant. A first supply line 41 serves to supply the regenerator 36 with a generally uncooled, in particular at room temperature RT working gas, for example He gas, pulsating under high pressure via the valve train 42a at a frequency, for example between 2 Hz and 50 Hz. During a low-pressure phase of the pulse tube cooler, working gas is also discharged again via the supply line 41 by means of a valve drive 42b. The pulse tube 37 can be be connected to a second supply line via a connecting channel (not shown in the figure), which depending on the design of the pulse tube cooler leads to a further valve train (not shown in the figure) or to a buffer volume of the working gas of, for example, a few liters (see Figure 5) to 7). FIG. 3 also shows a compressor 43 which is connected to the first connecting line 41 by means of an outgoing line 41a with a (high-pressure) valve 42a for the working gas under high pressure and a return line 41b with a (low-pressure) valve 42b for the working gas is connected under low pressure.

While in the embodiment of the cold head 33 of a known pulse tube cooler shown in FIG. 3, the regenerator 36 and the pulse tube 37 are arranged spatially parallel or, if appropriate, also spatially one behind the other, the embodiment of the cold head 45 of another known pulse tube cooler shown in FIG. 4 is a concentric (coaxial) arrangement of pulse tube 47 and this surrounding regenerator 46 is provided. In this embodiment, the working gas is conveyed by means of a pump device 48 with working pistons 48a.

In all of these embodiments of known pulse tube coolers, a pressure wave generated by the working piston 48a or by the compressor 43 with valve drive is periodically admitted, which is pre-cooled in the regenerator 36 or 46 and is relaxed in the pulse tube 37 or 47 so that a useful cooling capacity arises. The relaxed, cold gas then cools the regenerator as it flows out of the pulse tube. FIGS. 5 to 7 show embodiments of corresponding phase shifters at the warm end of the pulse tube, a cold head 33 according to FIG. 3 being used as a basis. According to FIG. 5, a buffer volume 51 with throttle 52 is provided for this. In addition, as shown in FIG. 6, a second inlet can take place from the warmer regenerator side via a line 53 with a nozzle 54. According to FIG. 7, a corresponding phase shifter can also be formed with four valves 42a, 42b, 55a and 55b.

In addition, power supply devices according to the invention can also be based on two-stage and multi-stage variants of pulse tube coolers (cf., for example, magazine "Cryogenics", vol. 34, 1994, pages 259 to 262).

Of course, other embodiments of power supply devices according to the invention are also conceivable than those shown in FIGS. 1 and 2: Design features of the power supply device 2 according to FIG. 1 and the power supply device 22 according to FIG. 2 can be combined, so that the electrical current then flows both within the regenerator and via its cladding tube. All variants can also be designed coaxially and in parallel, with one, two or more power lines with different potentials being conceivable in a cold head. A plurality of power supply devices can also be operated on one compressor. If a cooling stage is not sufficient for a specific application, two-stage or multi-stage versions can also be built up by adding the warmer end of another, colder one at the cold end of the warmer stage

Stage is connected. A corresponding arrangement can can be regarded as a thermal series connection of several cold heads.

With the inventive integration of at least one cold head of a pulse tube cooler into a power supply device, a number of significant advantages are achieved compared to known embodiments:

1. The heat losses are significantly reduced compared to a line-cooled power supply device. The power supply device 2 according to FIG. 1 uses the electrical conductivity of the cladding tubes 6a and 7a of the regenerator 6 and pulse tube 7, which are comparatively massive anyway in order to withstand a working pressure of typically 20 bar helium gas. For example, a stainless steel tube of 1 mm wall thickness, 20 mm diameter and

200 mm in length optimally transmit a current of 32 A, the losses compared to a power supply device which is only indirectly cooled with a pulse tube cooler being reduced to one third when loaded with the nominal current. In the de-energized state there is no additional heat leak at all. For large currents, larger wall thicknesses or materials with higher specific conductivity, such as brass or bronze or copper, are advantageously used. A further reduction in losses results from the countercurrent cooling effect in the regenerator 6 and pulse tube 7, which is achieved by the cold working gas. In order to increase this effect, further improvements can be made, for example, in tubes with a variable cross-section or additional heat exchangers at different heights in the pulse tube. Measures to enlarge the surface, including can be provided for example by special ribs or by roughening or sintering the inner surfaces with a porous metal. In the case of the power supply device 22 according to FIG. 2, the savings are particularly great, since an optimized regenerator 26 has a large surface area anyway, so that the cooling by the cold working gas is particularly thermodynamically effective. 2. Since the cold head is not a separate component in the power supply device, there are corresponding cost savings. The integrated cooled power supply device also works cryotechnically good-naturedly, since it does not need to introduce a warm end piece into a cryostat system, which has to be coupled to a cold reservoir only with considerable design effort. 3. By jointly designing the power supply device and the pulse tube cooler, the cooling capacity of the pulse tube cooler can be optimally adapted to the losses of the power supply device. This makes it possible to save losses that often occur due to the necessary over-dimensioning of the cooler.

4. If the cooling capacity at the cold end is selected to be sufficiently large, for example 77 K, further cryostat losses, for example due to heat radiation, can be compensated for without further cooling unit or replenishment of cryogenic liquids. 5. Due to the simple structure, an economical adaptation to the power requirements of a given cryosystem is also possible through a modular design in which several power supply devices are connected to a common compressor with a valve train. 6. Conventional power supply devices that are optimized for a ^" certain rated current can be at the warm end dew or even freeze when the joule to be dissipated in an undercurrent is reduced. There is a risk for high-voltage power supplies that the flashover resistance is reduced. In the integrated cooled power supply device according to the invention, this effect can be counteracted in a simple manner by a corresponding reduction in the cooling capacity. For this purpose, for example, the operating frequency of the valve train or of the piston, which generates a periodic helium pressure wave, is reduced.

Claims

claims

1. Power supply device with at least one electrical line running between a higher temperature level and a lower temperature level, which is connected at its low-temperature end to a cooled electrical device, characterized in that at least a part of the electrical line consists of at least one part ( 6a, 7a, 26b) of a cold head (3, 23) of a pulse tube cooler having a regenerator (6, 26) and a pulse tube (7, 27).

2. Power supply device according to claim 1, d a - d u r c h g e k e n e z e i c h n e t that a cladding tube (6a) of the regenerator (6) and / or a cladding tube (7a) of the pulse tube (7) is provided as a line section.

3. Power supply device according to claim 1 or 2, d a - d u r c h g e k e n n z e i c h n e t that a metallic body (26b) is provided inside a cladding tube (26a) of the regenerator (26) as a line section.

4. Power supply device according to claim 3, that the metallic body (26b) is a metal net or a sintered body or a wire bundle or at least one sheet metal strip.

5. Power supply device according to one of claims 1 to 4, characterized in that with the regenerator (6) and the pulse tube (7) two different, mutually insulated line sections are formed.

6. Power supply device according to one of claims 1 to 4, d a d u r c h g e k e n n z e i c h n e t that with the regenerator (6) and the pulse tube (7) two electrically parallel line sections are formed.

7. Power supply device according to one of claims 1 to 6, g e k e n n z e i c h n e t by a spatially parallel arrangement of regenerator (6) and pulse tube (7).

8. Power supply device according to one of claims 1 to 6, g e k e n n z e i c h n e t by a spatially concentric arrangement of the regenerator and pulse tube.

9. Power supply device according to one of claims 1 to

8, d a d u r c h g e k e n n z e i c h n e t that the cold head is multi-stage.

10. Power supply device according to one of claims 1 to

9, so that the cold head (3, 23), at least with its colder part, projects into the vacuum space (V) of a vacuum vessel (4) or into the interior of a cryostat.

11. Power supply device according to one of claims 1 to

10, thanks to an electrical connection to a superconducting device.