JPH03105902A - superconducting coil - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a superconducting coil for magnetic levitation trains, and in particular,
This invention relates to a superconducting coil impregnated and cured with a synthetic resin having a coefficient of thermal expansion similar to that of a superconducting wire.

[Conventional technology]

The superconducting coils of the superconducting magnets installed on magnetic levitation trains may quench (destruction of superconductivity) due to frictional heat when the coil conductors move due to electromagnetic force and vibration.

For this reason, the entire coil is impregnated with epoxy resin to seal the movement of the coil conductor. When a superconducting coil impregnated with epoxy resin is cooled with liquid helium and energized, thermal contraction stress based on the difference in thermal contraction rate between the superconducting wire and the impregnated resin, and
The impregnated resin may crack due to electromagnetic stress.

When a crack occurs, a small amount of heat is generated, and this heat propagates to the superconducting wire, causing the superconducting wire to locally reach a critical temperature, causing the superconducting coil to quench. Because of this, the heat shrinkage rate of the impregnated resin is 1 to 3X, which is comparable to superconducting wire.
10-'K-'' is desirable.

The superconducting wires used in the superconducting coils installed in maglev trains are currently mainly NbTi alloy wires, which have high mechanical strength.
Nb:JSn with high critical magnetic field and critical current density
It is thought that compound-based superconducting wires such as these will become mainstream.

When a compound-based superconducting wire is used, the superconducting wire will be subjected to compressive stress in the length direction due to the difference in thermal contraction rate with the impregnated epoxy resin, resulting in compressive strain or cracks in the compound layer of the superconducting wire. There is a possibility that the excitation performance of the superconducting coil will be reduced.

For these reasons, there has been a desire for a resin suitable for coil impregnation that has a heat shrinkage rate comparable to that of superconducting wires. Japanese Patent Publication No. 62-184025 describes a bismaleimide addition-curing polyimide resin having a low coefficient of thermal expansion. This bismaleimide-based addition-curing polyimide resin has a thermal expansion coefficient lower than that of metals and is expensive, so it is applied to parts that require low thermal expansion, such as insulating thin films for semiconductors and copper-clad laminates.

[Problem to be solved by the invention]

The above conventional technology does not take into account the occurrence of thermal stress due to the difference in thermal contraction rate between the impregnated resin and the compound superconducting wire, and does not take into account the occurrence of cracks in the impregnated resin, distortion of the superconducting wire compound layer, or the occurrence of cracks. There was a problem with the occurrence.

An object of the present invention is to provide a superconducting coil in which the excitation performance of the superconducting coil does not deteriorate and quenching does not occur.

[Means to solve the problem]

In order to achieve the above purpose, we used a material with a thermal expansion coefficient (linear expansion coefficient) comparable to that of superconducting wire as an impregnated resin.
0-'K-1 addition-curing polyimide was used.

Furthermore, in order to reduce the coefficient of thermal expansion, bismaleimide-based polyimides were particularly used among addition-curing polyimides.

Since the bismaleimide polymer is a granular solid, the viscosity-lowering agent 3,3'-diallylbisphenol F (
DABF) was mixed and dissolved to a viscosity that made it easy to impregnate the coil. Furthermore, in order to cause a reaction with the bismaleimide resin, dicumyl peroxide (D
CP○) was added and heat curing was performed.

[Effect]

The superconducting coil impregnated with the above addition-curing polyimide has a small difference in thermal shrinkage between the impregnated resin and the coil conductor, so
Thermal stress when cooled with liquid helium is small. Furthermore, since the resin is cured by an addition curing method that does not generate volatile components, no voids are created and sufficient resin impregnation is achieved. Therefore, it is difficult for the impregnated resin to crack, and for the superconducting wire compound layer to be distorted or cranked due to thermal stress.

Therefore, the superconducting coil can be prevented from deteriorating excitation performance or quenching.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 1 to 7.

FIG. 1 is a perspective view of a superconducting coil of the present invention mounted on a magnetic levitation train. The superconducting coil 1 is made of Nb3Sn superconducting wire, which is wound over 1000 turns into a toasted track shape to form a coil, and the entire coil is impregnated with a bismaleimide-based addition-curing polyimide resin whose coefficient of thermal expansion is comparable to that of the superconducting wire.

Figure 2 (A) shows the cross section of the Nb3Sn superconducting wire 2 used.
Shown below. An aluminum stabilizing material 3 is placed in the center, and fine multi wires 4 shown in FIG. 2 (CB) are distributed around it. This fine multi wire 4 is Nb5, bronze 6, Nb
, Sn compound layer 7, and copper 8.

A copper stabilizing material 9 is placed on the outer periphery where the fine multi-wires 4 are distributed, and a polyvinyl formal (PVF) insulating layer 10 is coated on the outermost periphery of the Nb3Sn superconducting wire 2. This superconducting wire has a cross-sectional dimension of 1
．． 0 mm x 2. 0 m. m, and the copper ratio is 1.0.

FIG. 3 shows a sectional view of the coil taken along the line ■-■ in FIG. 1. The space between the coil conductors 2 is sufficiently impregnated with a bismaleimide-based addition-curing polyimide resin 11 having a thermal expansion coefficient comparable to that of a superconducting wire. In the examples of the present invention, two types of bismaleimide resins having the molecular structural formulas shown below were used. Since this bismaleimide resin is in powder form, 80 parts of 3,3' diallyl bisphenol F (DABF), a viscosity reducing agent, is added to 100 parts of the bismaleimide resin to dissolve it to a low viscosity. 0.1 part of dicumyl peroxide (DCP○), which is a peroxide, was added as a catalyst.

The resin blended in this way was impregnated into a coil and cured by heating. The coefficient of thermal expansion of the cured resin is 10"sK"1 for the resin where R is V.
Theal resin is 3X106K-1.

FIG. 4 is a diagram illustrating thermal contraction between superconducting coil conductors. In the figure, the range of arrows indicates the magnitude of the thermal shrinkage rate (linear shrinkage rate) when the impregnated resin is cooled from the glass transition temperature to 4.2K. When the epoxy resin 12 is used as the impregnating resin like a conventional superconducting coil, the thermal shrinkage rate in the above temperature range is about 2%.

The thermal contraction rate of the superconducting wire 2 is approximately 0.0 in the same temperature range as above.
It is 5%. Therefore, when a superconducting coil containing epoxy resin is cooled to 4.2K, the coil conductor 2 and the impregnated resin 1
The coil conductor 2 receives a compressive stress in the length direction, and the impregnated resin 12 receives a tensile stress. Table 1 shows physical property values between the conventional coil and the coil of the present invention.

The heat shrinkage stress between the coil conductors 2 is calculated using the following formula, Table 1 (
When calculating by substituting the numerical values shown in (next page), σ5=E(α
H-αΔT However, σS: Thermal contraction stress E: Young's modulus of impregnated resin αH: Coefficient of linear expansion of impregnated resin αW: Coefficient of linear expansion of superconducting wire ΔT: Temperature difference (glass transition temperature → 4.2K) Fifth It will look like the figure. The impregnated epoxy resin 12 and the coil conductor 2 are well bonded, and the difference in heat shrinkage rate is approximately 1.5%.
Therefore, epoxy resin 12 has approximately 6 kgf/I [II1
A tensile stress of 2 is applied. A compressive stress of approximately 6 kg f/ayr is applied to the coil conductor 2 due to thermal contraction of the epoxy resin 12. Therefore, the impregnated epoxy resin 12 may crack, and the compound layer of the coil conductor 2 may be compressively strained or cracked. Occurrence of such a phenomenon causes deterioration and quenching of the excitation performance of the superconducting coil.

On the other hand, in the superconducting coil of the present invention, the impregnating resin is impregnated with a bismaleimide-based addition-curing polyimide resin having a coefficient of thermal expansion of 1 to 3 x 10''K-1, which is comparable to that of superconducting wire, so that thermal stress can be prevented from occurring. ±2.4kg f/mm2(+
The coil conductor has a small compressive stress (one is a tensile stress), and there is no phenomenon that occurs with epoxy resin-impregnated superconducting coils.

If the thermal shrinkage rate of the impregnated resin is smaller than that of the coil conductor, tensile stress is applied to the coil conductor. Tensile stress is more likely than compressive stress to cause performance deterioration due to strain in the compound layer of the conductor, and the electromagnetic force of the coil acts in the direction of pulling the conductor. Distortion tends to occur in the compound layer.

FIG. 6 shows the relationship between the decrease in quench current Iq with respect to the critical power supply value Ic of the Nb3Sn superconducting wire and the strain of the Nb3Sn superconductor. The quench current begins to decrease at a strain of 0.4%, and is 0.5, which corresponds to the difference in thermal expansion coefficient between the addition-curing polyimide resin used in the superconducting coil of the present invention and the coil conductor ±IX10''5K-'. %
At a strain of , the reduction in quench current is about 5%. If this difference in thermal expansion coefficient is expanded to ±2X10-'K-1,
Since the equivalent strain is 1.0%, the decrease in quench current is approximately 2
It is 5%. At a strain of 1.5%, which corresponds to the difference in thermal shrinkage between the epoxy resin and the coil conductor, the quench current decreases by about 70%. Judging from the above, the range of the thermal expansion coefficient of the addition-curing polyimide resin used in the superconducting coil of the present invention is the thermal expansion coefficient of the superconducting wire of 2 x 10-'K-
1 to 3X10-'K''1 with a width of ±IX10-'K-1 is appropriate.
Bismaleimide-based addition-curing polyimide resins have adhesive strength equivalent to epoxy resins, so they can be used satisfactorily as impregnating resins.

Figure 7 compares the effects of the present invention with the conventional example. The vertical axis shows the coil current density when the conventional example is set to 1.0, and the horizontal axis shows the magnetic field when the conventional example is set to 1.0. This shows the relationship between coil current density and magnetic field. As is clear from the figure, the characteristic P of the supercurrent coil of this embodiment is much superior to the conventional characteristic Q in terms of coil current density, and is close to the characteristic R of the wire. In other words, it was found that while conventional superconducting coils quench at a coil current density of 1 per unit (PU), the superconducting coil of this example can be excited up to a coil current density of 1.2 per unit. .

〔Effect of the invention〕

According to the present invention, since the bismaleimide-based addition-curing polyimide resin is used as the impregnating resin of the superconducting coil, the thermal stress between the coil conductor and the impregnating resin is small, and the occurrence of cracks in the impregnating resin and the superconducting wire compound layer are reduced. No distortion or cracks occur. Therefore, it is possible to prevent deterioration or quenching of the excitation performance of the superconducting coil. Therefore, it is possible to provide a superconducting coil for magnetically levitated trains that has high current density and high reliability.

[Brief explanation of drawings]

Fig. 1 is a perspective view of a superconducting coil for a magnetically levitated train according to an embodiment of the present invention, Fig. 2 is a cross-sectional view of the superconducting wire used, and Fig. 3 is a cross-section of the superconducting coil along line mm in Fig. 1. Figure 4 is an explanatory diagram of thermal contraction of a superconducting coil. Figure 4 is an explanatory diagram of thermal contraction of a superconducting coil. Figure 5 is a thermal contraction stress and linear expansion coefficient difference of the conductor of the superconducting coil and the impregnated resin. 6 is an explanatory diagram showing the relationship between the reduction in quench current with respect to the critical current of a compound superconducting wire and the strain of the compound superconducting wire. FIG. 7 is an explanatory diagram showing the relationship between the superconducting coil of the present invention and the conventional one. It is a characteristic diagram which shows the relationship between the coil current density and criticality of an example. ■...Superconducting coil, 2...N b , S n
Superconducting wire, 11... addition-curing polyimide. Figure 1 Figure 3 Figure 2 Figure 4 <A) >d (γU) Figure 7

Claims (2)

[Claims] 1. In a superconducting coil in which an enamel-insulated superconducting wire composed of a stabilizing material and a superconducting wire is wound many times and impregnated with a synthetic resin, the synthetic resin has a thermal expansion coefficient of 1 to 3 x 10_L^5K_L^1. A superconducting coil characterized by being made by impregnating and curing curable polyimide. 2. 2. The superconducting coil according to claim 1, wherein the addition-cured I-type polyimide is bismaleimide-based.