KR100572363B1 - DC reactor with thermal link - Google Patents

Abstract

The present invention relates to a direct current reactor using a superconducting electromagnet of a conduction cooling method that is conduction-cooled using a cooler, particularly a GM (Gifford-McMahon) cooler, the direct current reactor comprising: a vacuum housing for thermal insulation; A GM cooler having a head exposed to an upper portion of the housing and including an upper / lower cooling portion in the housing to support the upper cooling portion by a support rod; A superconducting magnet connected to the lower cooling part of the GM cooler through a cooling rod and being electrically cooled, and supported by a support rod; It comprises a thermal link that is configured to conduct conductive cooling by connecting a double wire consisting of a metal wire and an HTS wire for supplying power to the superconducting magnet. Since the DC reactor uses a GM cooler, the conduction cooling system is compact and compact, and the manufacturing cost is low. The heat generation of the electric wire through the means for directly conducting and cooling the electric wire to the superconducting magnet through the thermal link to the cooler in vacuum. It is possible to prevent the superconducting state of the superconducting magnets from being quenched, and to prevent degradation of the PI film, which is the main insulator, while increasing the contact area through the indium plate between the copper foil and the PI film.

Superconducting Magnet, Current Limiter, DC Reactor, Thermal Link, Lamination

Description

DC reactor with thermal link {DC REACTOR WITH THERMAL LINK}             

1 is a schematic diagram of a DC reactor according to the present invention;

Figure 2a and Figure 2b is an exploded perspective view showing the stacking / assembly sequence of the thermal link used in the direct current reactor of the present invention,

3A and 3B are perspective views of the thermal links stacked and completed according to FIGS. 2A and 2B.

    <Description of Symbols for Major Parts of Drawings>

1: DC reactor housing 3a, 3b, 5a, 5b, 5c: support rod

10: GM cooler 11: head

13: Upper cooling part 15: Lower cooling part

20,120: Thermal link 21a, 21b, 121a, 121b: Pressing plate

23: metal wire 25: HTS wire

27: bushing 29: cooling rod

30: Superconducting magnet

F: PI film C1, C2: Copper foil

I: indium plate H: bonding hole

The present invention relates to a direct current reactor for a current limiter using a superconducting electromagnet of a conduction cooling method that is conduction-cooled using a cryocooler, in particular, a GM (Gifford-McMahon) cooler. It is equipped with a thermal link that can conduct and cool electric wires that provide high current to superconducting magnets under high pressure with GM cooler.

In 1911, Dutch scientist Onnes (HK, 1853–1926) found that mercury was cooled with liquid helium and the resistance disappeared at -269 ° C (4K), slightly above absolute zero (-273 ° C). This was called the 'superconducting state'. Since then, many scientists have continued their research, thinking that if you can make an electromagnet with superconducting properties, you can make an electromagnet with no power loss.

In general, the superconducting field is classified into a low temperature superconducting field of 30K or less and a high temperature superconducting field of 30K or more based on 30K. Most of the superconducting materials currently used are so-called low-temperature superconductors having a critical temperature (T _c ) of 30K or less, and Nb-Ti alloys are mainstream, and Nb ₃ Sn is partially used. These low-temperature superconductors are used for a variety of applications such as ultra-high sensitivity magnetic sensors or superconducting electromagnets for generating high magnetic fields.However, related to the electric power field, superconducting magnetic energy storage systems (SMES) convert electricity into magnetic energy and store it. ) Is the only one.

The biggest constraint that these low temperature superconductors have not been applied more widely in the power sector, except for SMES, is that they are not economical because T _c is so low that expensive liquid helium must be used as a cooling medium in the operation of the application. Possibilities to overcome the limitations of the application such as low-temperature superconducting material is from the series of T _c is found, a high-temperature superconducting material than 30K after 1986.

In 2001, as the frontier business of the Ministry of Science and Technology, the next generation of superconducting application technology development project has begun, and the research and development of superconducting wires and application devices for the application of electric power field is in progress. Applications in the power sector are expected to include superconducting cables, superconducting transformers, superconducting fault current limiters, and superconducting motors.

Double fault current limiter is a kind of circuit breaker installed to prevent damage to various power devices installed in the system due to abnormal voltage or current flowed into the power system due to lightning or short circuit. Conventional current limiters cause power outages by completely shutting off electricity, but superconducting current limiters use the characteristics of superconductivity to transform high fault currents into normal conditions, thus protecting the system without a power outage in the event of an accident. Appliance. These superconducting fault current limiters can be used for protection of transmission and distribution facilities in addition to system stabilization birds, so the demand is enormous. The developed countries have already successfully developed 15kV class small capacity superconducting fault current limiters, and are currently developing 100-300 MVA class high capacity superconducting fault current limiters.In Korea, we are currently aiming to develop 6.6kV class high temperature superconducting fault current limiters. Research is ongoing. The core technologies of the superconducting fault current limiter are large capacity superconducting coil manufacturing technology, coil protection technology, large capacity power electronic circuit technology, power system application and operation technology, and cryostat technology for superconducting current limiter.

The present invention relates to a superconducting technology〉 high temperature superconducting technology〉 high temperature superconducting power equipment〉 high temperature superconducting current limiter〉 to the 6kV or less, especially 1.2kV 3Ф class DC reactor which can be used in the current limiter, It's about technology.

The present invention relates to a DC reactor that can be used as a high temperature superconducting fault current limiter as described above, DC reactor with a thermal link reel according to the present invention is

First, by miniaturizing the conduction cooling system using a GM cooler to provide a compact and low-cost DC reactor,

Second, to prevent the superconducting state of the superconducting magnets from quenching due to the heating of the wires by means of conducting and cooling the electric wires that apply power to the superconducting magnets directly to the cooler in a vacuum;

Third, an object of the present invention is to provide a means for successfully performing insulation of a conduction-cooled superconducting power device operating in a voltage range above a special high voltage.

In order to achieve the above object, a direct current reactor having a thermal link according to the present invention includes a housing in a vacuum state for thermal insulation; A GM cooler having a head exposed to an upper portion of the housing and including an upper / lower cooling portion in the housing to support the upper cooling portion by a support rod; A superconducting magnet connected to the lower cooling part of the GM cooler through a cooling rod and being electrically cooled, and supported by a support rod; It comprises a thermal link that is configured to conduct conductive cooling by connecting a double wire consisting of a metal wire and an HTS wire for supplying power to the superconducting magnet.

In addition, the thermal link is preferably made of a PI film after the PI film for insulation, a copper foil for conduction cooling, and an indium plate for increasing the contact area are sequentially stacked several times in sequence between the lower and upper press plates.

Hereinafter, described in detail by the accompanying drawings of the present invention.

1 is a schematic view of a DC reactor according to the present invention, in which the head 11 of the GM cooler 10 is exposed to the upper portion of the DC reactor housing 1. The inside of the housing 1 is evacuated using a pump (not shown). This GM cooler has been developed recently, and can be cooled to 4K or less, so that it can conduct a superconducting state by directly conducting and cooling the bobbin of the electromagnet without using a refrigerant. GM cooler 10 is composed of two stages, the upper cooling unit 13 and the lower cooling unit 15 contained in the housing (1). The GM cooler 10 is supported by the housing 1 top plate at the head 11, and is supported by the vertical support rods 5a and the horizontal support rods 3a at the ends of the upper cooling units 13. The sealed support type is to make the contact area with the cooler 10 as small as possible, and synthetic resin having low thermal conductivity is used. The superconducting magnet 30 is positioned below the lower cooling part 15 of the GM cooler 10 and is also supported by the horizontal supporting rods 3b and the vertical supporting rods 5b and 5c. Superconducting magnet 30 is made of a wire wound on the bobbin. The rods 3a and 3b 5a, 5b and 5c are connected to each other. The superconducting magnet 30 is connected to the lower cooling unit 15 by a plurality of cooling rods 29 so as to be electrically cooled by the lower cooling unit 15 of the cooler 10. The cooling rod 29 or the material of the cooler 10 may be a material such as oxygen-free copper (OFC), tough pitch copper, aluminum having excellent thermal conductivity, but oxygen-free copper is most preferred. . The electric wire for applying current to the superconducting magnet 30 is wrapped in the bushing 27 in the upper part of the housing 1 for airtightness and is connected to the magnet 30. In addition, the wire is roughly divided into the housing 1 and the outside, and is divided into the metal wire 23 above the bushing 27, and the one contained in the housing 1 is divided into a high temperature superconductor (HTS) wire 25. . In particular, the wires 23 and 25 are thermal links 20 connected to the cooling rods 29 of the upper cooling unit 13 and / or the lower cooling unit 15 of the cooler 10 for conduction cooling. ) Can be connected. In this way, it is possible to prevent the superconducting state of the superconducting magnet 30 from being quenched by conduction cooling while electrically insulating the wires 23 and 25 through which high current flows.

The thermal link will be described in more detail with reference to FIG. 2A or below, which is a perspective view showing a stacking / assembly procedure of the thermal link used in the DC reactor of the present invention.

First, FIGS. 2A and 3A relate to a simple thermal link 20 that conducts and cools an electric wire for supplying power to a superconducting magnet using a cooler. Lower and upper press plates 21a and 21b, which can be engaged with the bolt B and the nut N, are prepared, which press plate is made of FRP material. FRP is used because it can maintain its original form and properties even under extreme conditions. Glass fiber (GFRP), carbon fiber (CFRP), boron fiber, aramid fiber And the like.

The lower press plate 21a is first positioned with a PI film (F) for insulation. Representative of the PI (polyimide) film is DuPont's Kapton ^R film. Next, the conductive cooling copper plate C1 is positioned. The copper plate is made of anoxic copper (OFC) having good thermal conductivity. Subsequently, an indium plate I is positioned thereon to increase the contact area, and indium may be substituted with a high thermal conductivity and a ductile metal (eg, lead or aluminum) to improve thermal contact. Indium plate (I) and the like is more specifically in order to prevent an adverse effect on heat transfer because there is a cavity or the like when the oxygen-free copper thin plate (C1) and the PI film (F) contact. The indium plate I spreads when the upper and lower pressing plates 21b and 21a are pressed by the bolts / nuts to increase the contact area between the components. The thermal breakdown voltage of the thermal compound having a thickness of about 1 mm other than indium was measured, and the value was between 4.5 kV and 7.1 kV, and the average value measured 10 times was 6 kV. When converted into an electric field, since it has a very low dielectric strength of 6 kV / mm, insulation breakdown may occur in a general thermal compound, which may cause deterioration of PI film (F), which is a main insulating material, and thus, indium is preferably used in the present invention. In addition, although the indium plate I is illustrated as being interposed only on the upper portion of the copper foil C1 in FIG. 2A, the indium plate I is most preferably located above and below the copper foil C1. In addition, in order to prevent such deterioration, it is preferable to adopt PI film F, which is a main insulator, having a thickness of 100 μm or more, so that the system can be electrically and safely insulated even at a voltage range of special high voltage of kV or more.

The number of times of repeated stacking of the PI film (F), the copper foil (C1), and the indium plate (I) is necessary to solve the heat generation of a high current flowing wire so that the superconducting state of the superconducting magnet is not quenched. Repeated enough. Then, finally, the PI film F is placed again, and the upper pressing plate 21b is positioned thereon, and then, the bolt B and the nut N are tightened.

The completed thermal link 20 is shown in FIG. 3A. One end of the copper foil (C1) protruding outside the pressing plate (21a, 21b) and the cooling rod 29 and the cooling rod 29 connected to the end of the upper cooling portion 13 and / or the lower cooling portion 15 of the GM cooler (10) It is connected via a connecting means, the other end of the copper plate (C1) is connected to the HTS wire 25 is possible to conduct cooling.

2B and 3B, the thermal link 120 shown in FIGS. 2A and 3B is stacked to connect with the HTS wires in addition to the copper thin plates used for conduction cooling. That is, the PI film (F), the copper foil (C1) for conduction cooling (C1), and the indium plate (b) on the lower pressing plate (121a) of the pressing plates (121a, 121b) that can be engaged with the bolt (B) and the nut (N). The stacking order of I) is the same as that of FIG. 2A, except that the PI film F and the copper foil C2 are further positioned on the indium plate I. At the end of the copper foil C2, a coupling hole H is formed for connection with the HTS wire 25. The laminated copper foil C2 is to ensure the superconducting state of the superconducting magnet by conducting and cooling the heat generated from the wire more effectively due to the high current.

Next, the indium plate I is positioned next to the copper foil C2, and the lamination order is repeated as necessary as in FIG. 2A, and the indium plate I is similar to the copper plate C1 in FIG. 3A. In addition to being positioned at the top of (C2), it is also preferable to be located up and down to prevent degradation of the PI film (F) more completely. Finally, the PI film F and the upper pressing plate 121b are placed, and the bolts B and the nuts N are tightened.

Although the thermal links 20 and 120 shown in FIGS. 3A and 3B are shown as two repeated stacks for simplicity, the repetition of the number of layers is determined by the thermal calculation of the system. Also in FIG. 1, in the thermal link 120 of FIG. 3B, which is connected to the cooling rod 29 connected to the upper cooling unit 13 and / or the lower cooling unit 15 of the cooler 10, the HTS wire 25 is provided. One end portion of the copper foil plate C2 protrudes from the coupling hole H side as shown in comparison with the one end of the copper foil plate C1 to be connected to the copper foil plate C1. In the thermal link 120 copper foil plate C1 of FIG. 3B, the opposite end of the end bitten by the pressing plates 121a and 121b is the end of the upper cooling part 13 and / or the lower cooling part of the cooler 10 in FIG. 1. It is connected to the cooling rod 29 connected to the portion 15.

Referring to the operation and effects of the conduction cooling DC reactor of the present invention described above are as follows.

The DC reactor of the conduction cooling method used in the special high pressure range can cool the high temperature superconducting DC reactor to 120K or less by conduction cooling using the GM cooler 10 without using a refrigerant. Since the metal wire 23, which is the current induction part of the present invention, is in contact with the room temperature on the upper surface of the bushing 27, the high temperature superconducting current induction line is cooled to 80K. Therefore, the temperature between the high temperature superconducting current inlet wire and the high temperature superconducting DC reactor will be distributed between 80K and 120K.

When the DC reactor according to the present invention is used in an apparatus such as a high temperature superconducting fault current limiter, an analysis of the contact pressures of both ends of the apparatus is required. The design for applying the DC reactor according to the present invention to the current limiter is a matter for the 1.2kV DC reactor type high temperature superconducting current limiter using a magnetic core reactor, and when the voltage rises, it can be designed by repeating the following analysis. In the steady state, less than 2% of the line voltage between the grid is applied across the magnetic core reactor, and the high-temperature superconducting DC reactor is connected in parallel to the magnetic core reactor. However, if a fault occurs in the system, the load will be grounded or short-circuited and the system will lose its impedance. During this time, the system's voltage will be across the DC reactor. In other words, a high voltage is applied across the DC reactor for about 100 ms from the time of failure of the system to the breaker trip. When a high voltage is applied to the DC reactor, both voltages across the DC reactor are applied across the current-carrying part, so this part must be insulated against the voltage across the DC reactor.

When the load disappears from the system, the voltage across the DC reactor is as shown in the following equation (1).

Here, V _{m, LL} represents the maximum value of the line voltage.

When the DC reactor of the present invention is applied to Equation (1), the voltage across the DC reactor is determined according to the line voltage by the voltage conversion ratio of the magnetic core reactor.

In the DC reactor thermal link 120 illustrated in FIG. 3B, an electric field is concentrated at the corners of the copper plates C1 and C2, and an electric field per 1 kV is calculated at 12.3 kV / mm in the 1.2 kV DC reactor. Therefore, in the case of an equal electric field, the electric field per 1 kV is 8 kV / mm, so the electric field concentration at the edge of the copper plate is 1.54 times the equal electric field. To prevent this problem, the edges of the copper foils C1 and C2 were rounded to alleviate electric field concentration. Therefore, the electric field of the thermal link was 12.3 kV / mm per 1 kV, and the thickness of the PI film (F). Is 125kV / mm, the expected breakdown voltage was 13kV. However, in actual experiments, the breakdown voltage was 16.4kV, which shows that the breakdown voltage of the thermal link insulation increased more than the simulation. The edge machining of such a copper foil is useful in the thermal link 20 of FIG. 3A as well.

As described above, the DC reactor with a thermal link according to the present invention is

First, because GM cooler is used, the conduction cooling system can be miniaturized, compact and low manufacturing cost.

Second, it is possible to prevent the superconducting state of the superconducting magnets from being quenched by heat generation of the wires through means of conducting and cooling the electric wires that apply power to the superconducting magnets through the thermal link to the cooler in a vacuum.

Third, while increasing the contact area between the oxygen-free copper thin plate and between the copper thin plate and the PI film, it is possible to prevent degradation of the PI film, the main insulating material,

Fourth, the electric field concentration part of the thermal link can be applied as an electric field 1.54 times larger than the equal electric field structure of the DC reactor, it can be used as a production technology of ultra-high pressure high temperature superconducting power equipment to be commercialized in the future.

Claims (5)

A vacuum housing 1 for thermal insulation; The head 11 is exposed to the upper part of the housing 1, and the upper and lower cooling parts 13 and 15 are included in the housing 1, and the upper cooling part 13 is supported by the supporting rods 3a and 5a. GM cooler 10 is to be supported; A superconducting magnet 30 connected to the lower cooling unit 15 and the cooling rod 29 of the GM cooler 10 to be electrically cooled, and supported by the supporting rods 3b and 5b and 5c; DC reactor with a thermal link consisting of a thermal link is configured to electrically cool by connecting a double wire consisting of a metal wire and HTS wire to supply power to the superconducting magnet 30 and GM cooler (10). The method of claim 1, wherein the thermal link (20) Between the lower and upper press plates 21a and 21b, the PI film F for insulation and the copper foil plate C1 for conduction cooling are repeatedly stacked several times in sequence, and finally the PI film F is covered. DC reactor with thermal link. The method of claim 2, wherein the thermal link 120 And a copper foil (C2) connected to the PI film (F) and the HTS wire (25) next to the conductive cooling copper foil (C1). The method of claim 2 or 3, wherein the thermal link (20) (120) An indium plate (I) is interposed between the PI film (F) and the conductive cooling copper plate (C1) and (C2) to prevent degradation of the PI film while increasing the contact area. One DC reactor. The method of claim 2 or 3, The one end edge of the said copper foil (C1) (C2) is rounded, and the direct current reactor provided with the thermal link characterized in that it is designed to reduce electric field concentration.

Images