JP3537883B2 - Permanent current switch - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent current switch for use in, for example, a nuclear magnetic resonance imaging apparatus, a superconducting magnet for levitation, guidance, and propulsion of a levitation type railway vehicle.

[0002]

2. Description of the Related Art For example, superconducting magnets used for levitation railways or nuclear magnetic resonance imaging (MRI) are known.
It is used in a permanent current mode in which a constant current flows for a long time. The permanent current mode is a state in which the electric circuit of the superconducting magnet is closed in a closed loop to confine the current.

As described above, the permanent current switch is an important component having a function of opening and closing the superconducting magnet to set or cancel the permanent current mode. In the permanent current mode, the current in the closed loop electric circuit of the superconducting magnet does not attenuate and continues to flow semi-permanently, so that the superconducting magnet can maintain a constant magnetic field.

As such a permanent current switch, a superconducting wire is forcibly made into normal conduction by the heat generated by a built-in heater,
A thermal type in which a switch is opened and closed by attenuating a current in a permanent current mode is widely used.

[0005] The basic structure of this thermal type permanent current switch is such that a superconducting wire and a heater wire are wound around a winding frame, and a plurality of integrated switch elements are impregnated with epoxy resin or the like and laminated. The superconducting wire is made of, for example, copper (C) in order to maximize the electric resistance when the switch is opened.
An ultrafine multifilamentary wire whose base material is a metal having a large specific resistance such as u) -nickel (Ni) alloy is generally used.

However, a superconducting wire using a metal having a large specific resistance of such a persistent current switch as a base material is more effective than a superconducting wire using a metal having a small specific resistance such as copper or aluminum as a base material. In addition, there is an instability that quenching (transition from a superconducting state to a normal conducting state) is likely to occur during energization.

When a large current is applied to a superconducting wire, the quench current can be increased by simply increasing the cross-sectional area of the superconducting wire, but the instability against electromagnetic disturbance increases. Tend.

[0008] Therefore, in the case of a thermal permanent current switch, such as a superconducting magnet of a levitation type railway, which needs to secure a high stability while supplying a large current, a superconducting wire having a cross section as small as possible is used. Many switch elements are connected as an electric circuit so as to form a parallel switch.

FIG. 7 shows an example of a conventional thermal permanent current switch. A superconducting wire 2 and a heater wire (not shown) are wound around a winding frame (not shown) and impregnated with an epoxy resin or the like. In this configuration, a plurality of integrated disk-shaped switch elements 3 are stacked, fastened and fixed with fixing bolts 4 and adjustment nuts 5, and the switch elements 3 are electrically connected to form a parallel circuit switch.

In such a thermal type permanent current switch 1, when the number of switch elements 3 in parallel is N and the supplied current is 1, even if M of the switch elements 3 are quenched by any disturbance, In many cases, (NM) switch elements have a margin for sharing and maintaining the current I, and M is usually 1 or 2. In this manner, M of the switch elements 3 are quenched, and the current I flowing therethrough is reduced to the remaining (N−M) of the switch elements 3.
The phenomenon in which the current I is maintained in such a manner that the current is divided into two is called commutation.

[0011]

As described above, in the thermal permanent current switch 1, a plurality of disc-shaped switch elements 3 are laminated, and fixed and fixed with the fixing bolts 4 and the adjustment nuts 5,
Since the switch element 3 is electrically connected so as to be a parallel circuit switch, the switch element 3 is not connected when external vibration is transmitted or the permanent current switch 1 itself resonates.
, The relative displacement occurs repeatedly, frictional heat is generated in proportion to the friction coefficient μ of the contact surface, the fixing force F, and the amount of slip L, and the amount of heat entering the connected switch element 3 increases rapidly.

Note that the friction coefficient μ is determined by the surface condition of the contact surface, while the slip amount L is reduced as the fixing force F increases. When the amount of heat entering the switch element 3 increases, the stability (temperature margin) of the superconducting wire rapidly decreases. Therefore, when other disturbances are superimposed, the commutation of the switch element 3 is likely to occur frequently. . If the amount of heat penetration further increases, all the switch elements 3 are commutated (switch open, permanent current decay), and as a result, the function of the superconducting magnet may be lost.

Accordingly, in order to improve the temperature margin of the switch element 3 with respect to commutation, the cooling performance of the interface between the switch elements 3 where mechanical heat is generated is improved, and the amount of heat entering the switch element 3 is increased. (Mechanical calorific value must be reduced). Since the amount of heat generation is related to the friction coefficient μ of the contact surface, the fixing force F, and the amount of slip L, the friction coefficient μ and the amount of slip L need to be as small as possible. Further, in order to reduce the slippage amount L as the fixing force F increases and to suppress the relative vibration between the switch elements 3, it is better to secure a predetermined frictional force P (= μF) by using a permanent current switch. Because it is effective for improving the stability of 1,
The fixing force F must be as large as possible and the friction coefficient μ must be at least 0.05 or more.

As described above, by selecting the friction coefficient μ, the fixing force F, and the slip amount L, the amount of heat generation can be significantly reduced. Therefore, an object of the present invention is to suppress the influence of mechanical frictional heat generated by such relative vibration between switch elements, and to obtain a highly stable thermal permanent current switch.

[0015]

In order to achieve the above object, the invention according to claim 1 comprises a plurality of ring-shaped plate-like switch elements for opening and closing a transition between a normal state and a superconducting state of a superconducting wire. the thermal persistent current switch configured by parallel connection, respectively disposed between the respective switching element mutually Ri Do from a material having good thermal conductivity, and the cylindrical portion, of the cylindrical portion
A first space consisting of a flange integrally formed on the outer peripheral surface;
And at both ends of the switch element group,
The cylindrical shape of the first spacer is substantially vertically divided.
A second spacer and a cylinder of the first and second spacers
Part and a fixed shaft inserted into the hole of each switch element;
An adjusting nut screwed to the end of the fixed shaft, and a head of the fixed shaft
And a disc spring disposed between the second spacers.
A permanent current switch including a switch element restraining mechanism . In order to achieve the above object, the invention according to claim 2 opens and closes the transition between the normal state and the superconducting state of the superconducting wire.
Connecting multiple ring-shaped switch elements in parallel
In the configured thermal persistent current switch,
Between the elements and on the circumferential edge side and the switch element group.
A material with good thermal conductivity that is arranged on the peripheral edge of the end
Annular plate spacer made of a material, and each of the switch elements
A fixed shaft penetrating the circumference of the
An adjusting nut screwed to an end of the shaft; and a head of the fixed shaft.
A disc spring disposed between the second spacers.
A permanent current switch including a switch element restraining mechanism .

[0016]

According to the inventions corresponding to the first and second aspects, since a member having good thermal conductivity is applied to the spacer in contact with the switch element of the permanent current switch, the cooling performance of the contact surfaces of the switch elements is greatly increased. The temperature rise of the switch element due to mechanical heat is greatly reduced, and a permanent current switch having high stability against quench such as commutation can be obtained.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings. In this embodiment, the superconducting wire is forcibly made into normal conduction by the heat generated from a built-in heater to attenuate a current in a permanent current mode. It is intended for thermal permanent current switches that open and close switches.

<First Embodiment> FIG. 1 is a sectional view of a first embodiment of a thermal permanent current switch according to the present invention. This is shown in FIG.
Superconducting wire 2 and heater wire (not shown) on winding frame (not shown)
And a plurality of disc-shaped switch elements 3 integrally impregnated with epoxy resin or the like; a plurality of spacers 6 disposed between the switch elements 3 and at upper and lower ends of the switch elements 3; It comprises a fixed shaft 4 having a head 4a and a male screw 4b on the other end, an adjusting nut 5 , and a disc spring 9.

More specifically, a spacer 6 to be described later is arranged between the switch elements 3, and the spacers 6 are arranged at the upper and lower ends to be laminated. In this case, when the fixed shaft 4 is inserted through a hole existing in the center of each switch element 3,
With the disc spring 9 inserted in the head 4a side of the fixed shaft 4 beforehand, it is inserted into a hole existing at the center of each switch element 3, and the adjusting nut 5 is screwed into the male screw 4b of the fixed shaft 4 to switch each switch. The entire element 3 is laminated and fixed. in this case,
It goes without saying that each switch element 3 is electrically connected to be a parallel circuit switch.

The spacers 6 disposed between the switch elements 3 among the spacers 6 have a flange integrally formed at the center of the outer peripheral surface of the cylindrical portion as shown in FIG. A low-friction material 7 is fixed to the collar and the outer peripheral surface of the cylindrical portion, and is made of a material having good electrical conductivity, such as aluminum or an aluminum alloy. The spacers 6 provided at the upper and lower ends of the switch element 3 have a shape obtained by substantially vertically dividing the cylindrical portion of the radiation fin 8 in FIG.

By configuring the permanent current switch 1 as described above, a predetermined fixing force F is secured to the switch element 3 even at a low temperature, and the cooling performance of the contact surfaces of the switch elements 3 is greatly improved. Therefore, the temperature rise of the switch element 3 due to mechanical heat generation due to vibration or the like is greatly reduced, the margin for quench such as commutation is greatly improved, and the permanent current switch becomes stable.

The spacer 6 may be made of a material having good thermal conductivity, such as copper, a copper alloy, or aluminum nitride, in addition to aluminum and an aluminum alloy. As shown in FIG. 2, installing a radiation fin having a T-shaped cross section in the spacer 6 to increase the contact area with the refrigerant is also an effective method in terms of improving the cooling performance of the spacer itself.

Further, the friction coefficient μ of the sliding surface of the spacer 6
In order to reduce the heat generation, a low-melting-point metal such as indium-tin alloy, lead-tin alloy, indium, tin, or lead may be fixed to the sliding surface of the spacer 6 as the low friction material 7, and the absolute value of heat generation can be reduced. It is practical because it is effective.

Although the first embodiment has been described on the assumption that the switch element 3 and the spacer 6 have a separable structure, one of the switch elements 3 to be laminated has a heat conductive material such as aluminum. The spacer 6 made of a material having good properties is integrally formed with an adhesive or the like, and the heat generating portion is specified.
A method for improving the heat dissipation can also be adopted.

When the spacer 6 in contact with the switch element 3 of the permanent current switch is made of a material having good heat conductivity, such as aluminum or copper, the shape and shape of the spacer 6 depend on the magnitude and direction of the environmental magnetic field. A closed loop current circuit is formed and Joule heat may be generated.
As a method of structurally avoiding such a closed loop current circuit and suppressing the generation of Joule heat, the spacer 6 may be divided.

FIG. 6 shows the results of an experiment on the relationship between the temperature rise of the switch element 3 and the heat input time when the above-mentioned sliding friction heat of 1 W / sec is generated in the spacer 6 per one permanent current switch. This shows a case where the spacer 6 of the heat generating portion is made of aramid paper having poor heat conductivity (conventional configuration) and a case of aluminum (configuration of the present invention).

From this, the heat input to the switch element 3 of the permanent current switch 1 is significantly smaller in the case of an aluminum spacer having good heat conductivity than in the case of aramid paper having poor heat conductivity. It can be seen that the temperature margin for commutation No. 3 is greatly improved.

When a material having good thermal conductivity such as aluminum or copper is used for the spacer 6 in contact with the switch element 3 of the permanent current switch 1, the cooling property of the switch element 3 is improved, but the operation of the permanent current switch 1 is improved. The characteristics (increase in the amount of heat generated by the heater required to attenuate the permanent current mode) may be degraded. However,
Since the switch element 3 is sufficiently impregnated with an epoxy resin or the like, its operation characteristics are not greatly affected, and there is no operational problem.

However, mechanical heat (sliding friction heat) generated on the contact surfaces of the switch elements 3 increases in proportion to the friction coefficient μ of the sliding surface. Therefore, a low-melting-point metal such as indium-tin alloy, lead-tin alloy, indium, tin, or lead is adhered to the slip surface of the spacer 6 as the low friction material 7 so that the friction coefficient μ of the sliding surface is 0.05 <. μ <
Since it can be reduced to a size satisfying 0.5, it is extremely effective in reducing the absolute value of heat generation.

Further, providing the heat radiation fins 8 on the spacer 6 to increase the contact area of the refrigerant is also an effective means for improving the cooling performance of the spacer 6 itself. What has been described so far is a method of improving the cooling performance of the heat generating portion in order to secure a temperature margin of the switch element 3. To further improve the stability, the amount of heat input to the switch element 3 is reduced (mechanical heat generation). Needs to be reduced). The heat value is related to the friction coefficient μ of the contact surface, the fixing force F, and the slip amount L. Therefore, the friction coefficient μ is reduced to a value satisfying 0.05 <μ <0.5, and the fixing force is reduced. By increasing F and suppressing the amount of slip L, it is possible to significantly reduce the amount.

Therefore, the permanent current switch 1 is provided with a switch element restraining mechanism composed of the disc spring 9, the fixed shaft 4, the adjustment nut 5, and the like, so that the switch element 3 is controlled to suppress the influence of heat generation due to vibration. A predetermined fixing force F can be applied.

The above-described switch element restraining mechanism not only suppresses the influence of heat generation due to vibration, but also absorbs the difference in heat shrinkage of the constituent members generated when the permanent current switch is cooled, so that the switch element can be fixed to the switch element even at a low temperature. This is a function that can secure the force F.

When a material having good thermal conductivity is used for the spacer 6 in contact with the switch element 3 of the permanent current switch, a closed-loop current circuit (eddy current) corresponding to the shape depends on the magnitude and direction of the magnetic field. Induced, producing Joule heat. As a result, the amount of heat that enters the inside of the switch element increases, and the stability of the permanent current switch may deteriorate. In such a case, a good heat conductor (good conductor metal)
It is also possible to employ a method of structurally avoiding the formation of a closed loop current circuit according to the shape by dividing the spacers into a divided configuration.

On the other hand, the cooling performance of the switch element 3 is improved.
The operating characteristics of the persistent current switch (increase in the amount of heat generated by the heater when attenuating the persistent current mode) may be degraded, but the switch element 3 is sufficiently impregnated with epoxy resin or the like. However, its operation characteristics are not greatly affected and do not cause operational problems.

According to the first embodiment described above, by applying a member having good thermal conductivity to the spacer in contact with the switch element 3, the cooling of the contact surfaces between the switch elements is greatly improved, and The temperature rise of the switch element 3 due to excessive heat generation is greatly reduced, and as a result, the margin for quench such as commutation is greatly improved, and a stable permanent current switch can be realized.

<Second Embodiment> FIG. 3 is a sectional view showing a second embodiment of the permanent current switch according to the present invention. The difference from the first embodiment is that an annular plate is used as the spacer 6. It is fastened with a fixed shaft 4 and an adjusting nut 5. In this case, the same effect as in the first embodiment can be obtained.

<Third Embodiment> FIG. 4 is a sectional view showing a permanent current switch according to a third embodiment of the present invention. The difference from the first embodiment is that a male screw 4b is provided on the entire outer peripheral surface of the fixed shaft 4. Are formed, and a plurality of spacer fixing nuts 10 are screwed into the male screw 4b, and the adjustment nuts 5 are screwed into both ends of the fixed shaft 4.

<Fourth Embodiment> FIG. 5 is a sectional view of a permanent current switch according to a fourth embodiment of the present invention. A plurality of switch elements 3 are stacked, and end plates 12 and 13 are provided at both ends thereof.
The fixed shaft 4 is also arranged at the center of the switch element 3, and the adjusting nut 5 is screwed into the male screw 4 b formed at one end via a disc spring 9. A fixed sleeve 11 that is tapered is provided between the fixed shaft 4 and the fixed shaft 4 at the center. In this embodiment, effects similar to those of the above-described embodiment can be obtained.

<Modifications> In the examples described so far, the present invention has been described mainly on the basis of the configuration of a permanent current switch for a levitation type railway. However, the superconductivity used for nuclear magnetic resonance imaging (MRI) and the like has been described. The present invention can be widely applied to a permanent current switch that requires a permanent current mode switching operation such as a magnet.

[0040]

According to the present invention, it is possible to provide a permanent current switch of a high stability type, in which the influence of mechanical frictional heat generated by relative vibration between switch elements is suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a permanent current switch housed in a superconducting magnet device according to the present invention.

FIG. 2 is a cross-sectional view showing an example of a spacer on which the radiation fins of FIG. 1 are installed.

FIG. 3 is a sectional view showing a second embodiment of the permanent current switch according to the present invention.

FIG. 4 is a sectional view showing a third embodiment of the permanent current switch according to the present invention.

FIG. 5 is a sectional view showing a fourth embodiment of the permanent current switch according to the present invention.

FIG. 6 shows a relationship between a temperature rise of a switch element and a heat input time when sliding friction heat of 1 W per second is generated in a spacer per one permanent current switch according to the present invention; FIG. 4 is a characteristic diagram showing a case of aramid paper and a case of aluminum having good thermal conductivity.

FIG. 7 is a perspective view showing an example of a permanent current switch housed in a conventional superconducting magnet device for a floating railway.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Permanent current switch, 2 ... Superconducting wire, 3 ... Switch element, 4 ... Fixing bolt, 5 ... Adjustment nut, 6 ... Spacer,
7: low friction material, 8: radiation fin, 9: coned disc spring, 10: spacer fixing nut, 11: fixing sleeve.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tomohisa Yamashita 1 Toshiba-cho, Fuchu-shi, Tokyo Inside the Toshiba Fuchu factory (56) References JP-A-56-87385 (JP, A) JP-A-5-85 226708 (JP, A) JP-A-58-6106 (JP, A) JP-A-48-43289 (JP, A) JP-A-53-82736 (JP, U) JP-A-59-176171 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 39/20 ZAA H01F 6/00 ZAA

Claims (8)

(57) [Claims] 1. A thermal permanent current switch in which a plurality of ring-shaped switch elements for opening and closing a transition between a normal conducting state and a superconducting state of a superconducting wire are connected in parallel. respectively disposed, Ri Do from a material having good thermal conductivity, and the cylindrical portion, the outer peripheral surface of the cylindrical portion one
A first spacer consisting of a collar formed on the body;
The first switch is disposed at each end of the switch element group, and
The second part of the shape in which the cylindrical part of the pacer is divided almost vertically
And the cylindrical portions of the first and second spacers and the switches.
A fixed shaft inserted into the hole of the element, and screwed to the end of the fixed shaft
Adjusting nut, the head of the fixed shaft and the second space.
Switch element restraining machine consisting of a disc spring disposed between
And a permanent current switch comprising: 2. The superconducting wire between a normal conducting state and a superconducting state.
Multiple ring-shaped switch elements that open and close the transfer
In a thermal type permanent current switch configured by connecting in a row, between the switch elements, the circumference side and the switch are connected.
要素 し に 群 に 群 群 群 群
An annular plate spacer made of a material having good performance, and penetrating the peripheral edge of each switch element and the spacer.
A fixed shaft, and an adjustment nut screwed into an end of the fixed shaft;
Disposed between the head of the fixed shaft and the second spacer
And a switch element restraining mechanism comprising a disc spring . 3. Each of the switches in the spacer is required.
Low friction material is attached to the surface that comes in contact with the element
The permanent current switch according to claim 1 . 4. The spacer is made of aluminum or aluminum.
Any of aluminum alloy, copper, copper alloy and aluminum nitride
4. The method according to claim 1, wherein
A permanent current switch according to any of the above . 5. The switch element in the spacer
Contact surface or with the switch element at low friction material
The friction coefficient μ of the contact surface satisfies 0.05 <μ <0.5
The method according to any one of claims 1 to 4, wherein
On-board permanent current switch. 6. The low friction material is an indium-tin alloy,
Made of lead-tin alloy, indium, tin or lead
4. The permanent current switch according to claim 3, wherein: 7. The method according to claim 1, wherein the spacer is provided on a surface exposed to the refrigerant.
The heat radiation fin is installed, The claim 1 characterized by the above-mentioned.
Item 4. The permanent current switch according to any one of Items 3 . 8. A spacer according to a shape of the spacer.
To avoid forming loop electric circuits.
The permanent current switch according to any one of claims 1 to 3, characterized in that: