JP2018163930A - Superconducting coil device and method for protecting the same - Google Patents

Abstract

A superconducting coil device and a method for protecting a superconducting coil are provided that are capable of suppressing breakage or damage to a superconducting coil in the event of an abnormality. A superconducting coil (12), a power supply (11) for supplying current to the superconducting coil (12), a protection resistor (17) connected in parallel to the superconducting coil (12) and having a variable resistance value, and a detection means for detecting quenching of the superconducting coil (12). 15, a cutoff means 16 for disconnecting the power supply 11 from the superconducting coil 12 after a quench is detected, and a protection resistor 17 so that the voltage acting on the superconducting coil 12 after the quench is detected is below a set value. and a control means 18 for controlling the resistance value. [Selection drawing] Fig. 1

Description

  The present invention relates to a superconducting coil device and a superconducting coil protection method.

  The superconducting coil device is mainly composed of a low temperature container for maintaining a cryogenic temperature, a superconducting coil accommodated in the low temperature container, and a power source for supplying current to the superconducting coil. If there is any abnormality in the superconducting coil, the abnormality is detected by the coil voltage, temperature, etc., the power is disconnected from the superconducting coil by the switch, and the energy stored in the superconducting coil is connected by the protective resistance connected in parallel to the superconducting coil. The protection method which collect | recovers is common (refer patent document 1).

JP 58-95803 A

After the abnormality of the superconducting coil is detected, when the power source is disconnected from the superconducting coil, the voltage V ₀ acting on the superconducting coil is the product of the current I ₀ flowing through the superconducting coil and the resistance value R of the protective resistance ( V ₀ = I ₀ R). When the resistance value R of the protective resistor is large, the current flowing through the superconducting coil can be quickly attenuated, but the voltage V ₀ becomes very large, and the superconducting coil may be broken down. When the inductance L of the superconducting coil is large, if the resistance value R of the protective resistance is small, the current decay becomes slow, and the abnormality may progress and the superconducting coil may be damaged.

  This invention is made | formed in view of the said situation, and makes it a subject to provide the protection method of the superconducting coil apparatus which can suppress destruction and damage of a superconducting coil at the time of abnormality.

  In order to solve the above problems, the present invention provides a superconducting coil, a power supply for supplying current to the superconducting coil, a protective resistor connected in parallel to the superconducting coil and having a variable resistance value, and quenching of the superconducting coil. Detecting means for detecting, means for disconnecting the power source from the superconducting coil after the quench is detected, and the voltage acting on the superconducting coil after the quench is detected is less than a set value, And a control means for controlling the resistance value of the protective resistance.

The control means may gradually increase the resistance value of the protective resistance after the quench is detected.
The control means may control a resistance value of the protective resistance so that a voltage acting on the superconducting coil is constant.
The control means may change the resistance value of the protective resistance according to the following equation (1) with respect to time t, where R _{0 is} the initial resistance value of the protective resistance and L is the inductance of the superconducting coil. Good.
R = L / (L / R ₀ −t) (1)

  In the present invention, after a protective resistance having a variable resistance value is connected in parallel to the superconducting coil, current is supplied from a power source to operate the superconducting coil, and after quenching of the superconducting coil is detected A method for protecting a superconducting coil is provided, wherein the power supply is disconnected from the superconducting coil, and a resistance value of the protection resistor is controlled so that a voltage acting on the superconducting coil is not more than a set value.

In the protection method, the resistance value of the protection resistor may be gradually increased after the quench is detected.
In the protection method, a resistance value of the protection resistor may be controlled so that a voltage acting on the superconducting coil is constant.
In the protection method, the initial value of the resistance value of the protection resistor may be R ₀ , the inductance of the superconducting coil may be L, and the resistance value of the protection resistor may be changed according to the following equation (1) with respect to time t. Good.
R = L / (L / R ₀ −t) (1)

  According to the present invention, it is possible to suppress the destruction and damage of the superconducting coil at the time of abnormality.

It is a typical circuit diagram showing an example of a superconducting coil device according to an embodiment. It is a graph which shows the time change of the electric current in an Example, a voltage, and resistance value. It is a graph which shows the time change of the electric current in the comparative example, a voltage, and resistance value.

  Hereinafter, based on a preferred embodiment, the present invention will be described with reference to the drawings.

  FIG. 1 shows an example of the superconducting coil device of the present embodiment. The superconducting coil device of this embodiment includes a power source 11, a superconducting coil 12, and a protective resistor 17. The power source 11 is a DC power source that supplies a current I to the superconducting coil 12. The superconducting coil 12 and the protective resistor 17 are connected in parallel to the power supply 11. That is, during normal operation of the superconducting coil 12, current is supplied from the power supply 11 with the superconducting coil 12 and the protective resistor 17 connected in parallel.

The superconducting coil 12 is accommodated in the cryogenic container 13. Examples of the refrigerant used for the cryogenic vessel 13 include liquid nitrogen and liquid helium. The superconductor used for the superconducting coil 12 is not particularly limited, and examples thereof include an oxide superconductor and a metal superconductor.
Examples of the oxide superconductor include Bi ₂ Sr ₂ CaCu ₂ O _{8 + δ} (Bi2212), Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _{10 + δ} (Bi2223), REBa ₂ Cu ₃ O _7-x (RE123), and the like. Examples of RE include one or more rare earth elements such as Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
Examples of the metal superconductor include NbTi and Nb ₃ Sn.

  The superconducting coil device of this embodiment has a detecting means 15 that detects quenching of the superconducting coil 12. As the detection means 15, for example, voltage input parts 14 are provided at both ends and the middle part of the superconducting coil 12, and a bridge circuit is configured together with a resistor (not shown) provided inside the detection means 15. A configuration for detecting a quench based on a voltage is given. The method of quench detection in the detection means 15 is not particularly limited. Even if the quench is detected based on changes such as an electrical change, a magnetic change, and a thermal change in the superconducting coil 12 and the refrigerant in the cryogenic vessel 13. Good.

  The superconducting coil device of the present embodiment has a blocking means 16 as means for disconnecting the power supply 11 from the superconducting coil 12. An example of the shutoff means 16 is a shutoff switch that can be repeatedly opened and closed. The interruption means 16 is disposed between the parallel circuit of the superconducting coil 12 and the protective resistor 17 and the power supply 11. In a state where the power supply 11 is disconnected from the superconducting coil 12 by the blocking means 16, the protective resistor 17 is connected to the superconducting coil 12.

  In the present embodiment, a resistor having a variable resistance value is used as the protective resistor 17. Further, a control means 18 for controlling the resistance value of the protective resistor 17 is provided. When quenching is detected by the detection means 15, the control means 18 operates the cutoff means 16 by the control signal 18 a of the cutoff means 16 and disconnects the power supply 11 from the superconducting coil 12. Further, the control means 18 changes the resistance value of the protective resistor 17 by the control signal 18 b of the protective resistance 17 when quenching is detected by the detecting means 15.

  The control means 18 controls the resistance value of the protective resistor 17 so that the voltage acting on the superconducting coil 12 becomes a set value or less. The control means 18 may include a recording device, a calculation device, and the like that store data, programs, and the like necessary for control.

  The state of the circuit after the power supply 11 is disconnected from the superconducting coil 12 can be analyzed as a transient phenomenon when the interruption means 16 is opened. During steady operation when the shut-off means 16 is closed, the resistance value of the superconducting coil 12 is negligibly small compared to the resistance value of the protective resistor 17, so that the current flows through the path including the superconducting coil 12, It can be understood that substantially no current flows in the path including the current.

  When the blocking means 16 is opened, the circuit including the superconducting coil 12 becomes a closed loop in which the protective resistor 17 is connected in series with the superconducting coil 12. When the resistance value of the wiring portion connecting the protective resistor 17 to the superconducting coil 12 is neglected, the voltage acting on the protective resistor 17 and the voltage acting on the superconducting coil 12 are determined if the direction is taken in one direction along the closed loop. The sum is zero. That is, the voltage acting on the superconducting coil 12 is opposite in sign to the voltage acting on the protective resistor 17, and the absolute value of each voltage is substantially the same.

  Immediately after the blocking operation of the blocking means 16, a large amount of current flows in the closed loop. For this reason, when the resistance value of the protective resistor 17 is large, the voltage acting on the protective resistor 17 increases and the voltage acting on the superconducting coil 12 also increases. By reducing the resistance value of the protective resistor 17, the voltage acting on the superconducting coil 12 can be suppressed. In addition, when the current flowing through the superconducting coil 12 is attenuated, the resistance value of the protective resistor 17 is increased, and the current acting on the superconducting coil 12 can be promoted without excessive voltage.

  The change in the resistance value of the protective resistor 17 may be a temporal change or a step change. For example, the control unit 18 may gradually increase the resistance value of the protective resistor 17 after the quench is detected. The temporal change of the voltage acting on the superconducting coil 12 after quenching may be changed below a set value corresponding to the performance of the superconducting coil 12 or the like. For example, the voltage acting on the superconducting coil 12 may be a constant value not more than a set value.

  According to the self-induction of the coil, a voltage is generated in the superconducting coil 12 according to the product of the time differential dI / dt of the current I and the inductance L. Therefore, when the current I decreases at a substantially constant rate with respect to the time t, the voltage acting on the superconducting coil 12 can be made substantially constant. The voltage V of the protective resistor 17 is the product of the current I and the resistance value R. In order to decrease the current I by a linear expression at time t, the resistance value R of the protective resistor 17 may be increased so as to be inversely proportional to the linear expression at time t.

  For example, the resistance value R of the protective resistor 17 may be changed according to the following formula (1) with respect to the time t.

In Equation (1), the initial resistance value of the protective resistor 17 is R ₀ , and the inductance of the superconducting coil 12 is L. The increase of the resistance value R of the protective resistor 17 may be stopped when the current I is sufficiently attenuated. When the maximum resistance value of the protective resistor 17 is R _max , as shown in the following equation (2), the resistance value R can be changed in the same manner as in equation (1) only during R <R _max. Good.

  When the resistance value of the protective resistor 17 is changed with time, the origin of the time t may be when the quenching of the superconducting coil 12 is detected or when the power source 11 is disconnected from the superconducting coil 12. Although there may be a time lag in the operation and control of the blocking means 16 or the protective resistor 17, it is preferable to perform protection in a short time according to the durability of the superconducting coil 12.

  As mentioned above, although this invention has been demonstrated based on suitable embodiment, this invention is not limited to the above-mentioned embodiment, A various change is possible in the range which does not deviate from the summary of this invention.

  The superconducting coil device may include means for displaying the state of the superconducting coil, means for reporting the occurrence of a quench by an alarm or communication, and the like.

  Hereinafter, the present invention will be specifically described with reference to examples. In addition, this invention is not limited only to this Example.

(Example)
In this embodiment, when the inductance L of the superconducting coil is 10H (Henry) and the current value I ₀ flowing through the superconducting coil at the time of quenching is 100A, the maximum voltage V ₀ acting on the superconducting coil is 100V. The following example was assumed.

After detecting the abnormality of the superconducting coil with the coil voltage and disconnecting the superconducting coil and the power source, the resistance value R of the protective resistance is expressed in the range in which the initial value R ₀ is 1Ω and the maximum value R _max is 100Ω, as shown in Equation (1) It was changed as follows. Changes in the voltage V and current I of the superconducting coil with respect to time t are shown in FIG. In the graph, the voltage V is negative. The maximum voltage acting on the superconducting coil is 100V, and the current is completely attenuated in about 10 seconds.

(Comparative example)
In this comparative example, the resistance value R of the protective resistance was made constant at 1Ω, similar to the initial resistance value _R0 in the example. Conditions other than the resistance value R were the same as in the example. FIG. 3 shows changes in the voltage V and current I of the superconducting coil with respect to time t together with the resistance value R of the protective resistor. When the maximum voltage acting on the superconducting coil is 100 V, the current decays with a time constant of 10 seconds. A time constant τ of an RL circuit composed of a resistance value R and an inductance L is represented by τ = L / R. The current decays exponentially and does not decay completely after 30 seconds.

DESCRIPTION OF SYMBOLS 11 ... Power supply, 12 ... Superconducting coil, 13 ... Cryogenic container, 14 ... Voltage input part, 15 ... Detection means, 16 ... Shut-off means, 17 ... Protection resistance, 18 ... Control means, 18a ... Control signal of cutoff means, 18b ... Control signal for protection resistance.

Claims (8)

A superconducting coil;
A power supply for supplying current to the superconducting coil;
A protective resistor connected in parallel to the superconducting coil and having a variable resistance value;
Detecting means for detecting quenching of the superconducting coil;
Means for disconnecting the power source from the superconducting coil after the quench is detected;
A superconducting coil device comprising: control means for controlling a resistance value of the protective resistance so that a voltage acting on the superconducting coil is equal to or lower than a set value after the quench is detected.   2. The superconducting coil device according to claim 1, wherein the control unit gradually increases a resistance value of the protective resistance after the quench is detected. 3.   The superconducting coil device according to claim 1, wherein the control unit controls a resistance value of the protective resistance so that a voltage applied to the superconducting coil is constant. The control means changes the resistance value of the protective resistance according to the following equation (1) with respect to time t, where R _{0 is} the initial resistance value of the protective resistance and L is the inductance of the superconducting coil. The superconducting coil device according to any one of claims 1 to 3, wherein
R = L / (L / R ₀ −t) (1) In a state where a protective resistance having a variable resistance value is connected in parallel to the superconducting coil, current is supplied from a power source to operate the superconducting coil.
After the quench of the superconducting coil is detected, the power supply is disconnected from the superconducting coil, and the resistance value of the protective resistor is controlled so that the voltage acting on the superconducting coil is equal to or lower than a set value. To protect the superconducting coil.   The method for protecting a superconducting coil according to claim 5, wherein after the quench is detected, the resistance value of the protection resistor is gradually increased.   The method of protecting a superconducting coil according to claim 5 or 6, wherein a resistance value of the protective resistor is controlled so that a voltage acting on the superconducting coil is constant. The initial value of the resistance value of the protective resistor is R ₀ , the inductance of the superconducting coil is L, and the resistance value of the protective resistor is changed according to the following equation (1) with respect to time t. The method for protecting a superconducting coil according to any one of 5 to 7.
R = L / (L / R ₀ −t) (1)

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