JPS63250806A - Quenching protective device for superconducting coil - Google Patents

Abstract

PURPOSE:To prevent the damage due to a rise in temperature by a method wherein, after a transition to normal conduction has been conducted on a superconducting coil and then the coil current is increased for a short period, the current is attenuated. CONSTITUTION:In the superconducting coil 3 of the circuit consisting of a power source 1, a protective resistor 2, a superconducting coil 3, a power source switch 4, and a backward current preventing device 5, the rate of propagation of a normal conductive region is increased suddenly together with the coil current. Accordingly, when the coil current is increased for a short period after normal conductive transition has been conducted, a fairly large part of the coil 3 is forcedly transferred into normal conduction, and a large resistance is generated by the almost uniform temperature rise of the coil. At the same time, the decay time constant becomes short, and the current of the coil is attenuated. As a result, the damage due to a local temperature rise in the coil can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a quench protection device for a superconducting coil, and particularly to a quench protection device suitable for preventing a local temperature rise in a superconducting coil.

[Conventional technology]

As described in Japanese Unexamined Patent Publication No. 61-95502, the conventional device immediately cuts off the power supply to attenuate the current in the coil after the superconducting coil transitions to normal conductivity, and also thermally couples the superconducting coil to the coil. The heater generates heat to forcibly transition to normal conduction in areas other than the quench point, and the almost uniform temperature rise in most of the coil generates a large resistance, which quickly attenuates the current in the coil and This was to prevent damage due to excessive temperature rise.

[Problem that the invention seeks to solve]

The above-mentioned prior art required a heater thermally coupled to the coil to force the superconducting region of the coil to transition to normal conductivity after the superconducting coil transitioned to normal conductivity. When installing this heater in contact with the coil, it is necessary to electrically insulate it and it is difficult to make a strong thermal connection, and the inside of the coil winding must also be forced to quickly undergo a normal conduction transition. However, it is necessary to install this heater inside the coil winding, but this is actually extremely difficult due to the complexity of the coil shape and the difficulty of electrical insulation.

The purpose of the present invention is to forcibly bring the coil into a normal conduction transition without providing a heater, and to quickly attenuate the current in the coil by generating a large resistance due to an almost uniform temperature rise in the majority of the coil. An object of the present invention is to provide a quench protection device for a superconducting coil that prevents damage due to local temperature rise within the superconducting coil.

[Means for solving problems]

The above object is achieved by increasing the current in the coil for a short time and then decreasing it after the superconducting coil transitions to normal conductivity.

[Effect]

In a superconducting coil, the propagation velocity in the normal conducting region increases rapidly with the coil current. Thereby, increasing the current in the coil for a short time after the normal conduction transition forces a significant portion of the coil into the normal conduction transition, creating a large resistance due to the nearly uniform temperature rise of the coil. At the same time, the attenuation time constant of the coil current is shortened, and the current in the coil is quickly attenuated, so that damage caused by local temperature rise within the coil can be prevented.

Here, methods for increasing the current in the coil include a method using a power source, a method using a charged capacitor, and a method using mutual induction.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. 1st
In the figure, 1 is a power supply and 2 is a protection resistor.

3 is a superconducting coil, and its critical current is 990A.

4 is a power switch, and 5 is a reverse current prevention diode, which functions to allow current to flow through the protective resistor 2 only when the power switch 4 is OFF. FIG. 2 shows the temporal changes in the current in the superconducting coil 3 and the maximum temperature within the coil in this protection circuit. In FIG. 2, the horizontal axis shows time, and the vertical axis shows current and temperature. In Fig. 2, the dotted line indicates the case where the power is cut off 0.1 seconds after the occurrence of the normal conduction transition (conventional case), and the solid line indicates the case 0.1 seconds after the occurrence of the normal conduction transition.
A case is shown in which the current in the superconducting coil is increased by applying a voltage of 100 OV from the power source from 0.2 seconds to 0.2 seconds, and then the power source is shut off (in the case of the present invention).

This result shows that according to the present invention, the final maximum temperature of the superconducting coil can be suppressed to approximately 1/2 compared to the conventional case, and the protective function can be improved.

Here, a protective resistor was used as an energy absorbing device.

Next, a second embodiment of the present invention will be described with reference to FIG.

The circuit shown in FIG. 3 has a protective resistor 6. Superconducting coil 7, persistent current switch 8, etc. 8
A circuit is added, and the superconducting coil 3 and superconducting coil 7 are magnetically coupled. In Fig. 3, after the superconducting coil 7 which was operating in persistent current mode has transitioned to normal conductivity, the current in the superconducting coil 3 which has not transitioned to normal conductivity is manipulated to change the current of the superconducting coil 7 which has transitioned to normal conductivity due to mutual induction. After that, the persistent current switch 8 was turned off, and the current of the superconducting coil 7 was caused to flow through the protective resistor 6, and the current was allowed to decay. Here, for the sake of simplicity, the excitation device for the superconducting coil 7 is not shown.

〔Effect of the invention〕

According to the present invention, the resistance of the normal conducting region of the coil can be increased by manipulating the coil current after the normal conducting transition, so the current in the coil can be quickly attenuated, and the temperature rise of the superconducting coil can be suppressed and protected. System performance can be improved.

[Brief explanation of drawings]

Fig. 1 is a protection circuit diagram in the case of one superconducting coil according to an embodiment of the present invention, Fig. 2 is a characteristic diagram showing time changes in the current and maximum temperature of the superconducting coil in Fig. 1, and Fig. 3 is a diagram of the present invention. It is a protection circuit diagram when there are two superconducting coils in one embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Power supply, 2... Protective resistor, 3... Superconducting coil, 4... Switch, 5... Diode (for backflow prevention), 6 2nd-figure f', :'l( S)

Claims (1)

[Claims] 1. A superconducting device comprising at least a superconducting coil, a power source, and an energy absorption device, characterized in that, after the superconducting coil transitions to normal conductivity, a function is provided to increase the current in the coil for a short time and then attenuate it. Protective device.