JPS61170007A - Protecting device for superconductive magnet - Google Patents

Abstract

PURPOSE:To use an extreamly ordinary diode on the market when an operation current is an ultra heavy current by constituting a diode circuit splitting a current into plural diodes. CONSTITUTION:A diode circuit 9A is composed of both a unit of a diode 12a in which plural of, for instance, two of compact, lightweight and same rating diodes 13 of small current capacity are connected in parallel, and another unit of diode 12b which is connected in reverse parallel with this unit of the diode 12a. When a superconductive breakdown is generated in a permanent current switch 2, a voltage IOP.RN much higher than a turn-on voltage of the diode 13 is added to the diode circuit 9A. As, according to a direction of a current, the plural diodes 13 of either the unit of diode 12a or 12b receive momentarily a voltage higher than all of the turn-on voltages, they turn on. Therefore, almost all of operation currents IOP are split into the diodes 13, a permanent current switch superconductive body 4 of a permanent current switch 2 is completely protected without any burning.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a protection device for a superconducting magnet, and particularly to a device for protecting a persistent current switch from superconductor breakdown during persistent current operation.

[Conventional technology]

Figure 3 is a circuit diagram showing the Ri conductive magnet and conventional protection device presented at the J/th Cryogenic Engineering Research Conference (10) is a refrigerant, liquid helium (
It is a cryogenic container that satisfies the requirements of 3) and has a superconducting coil (
1) Persistent current switch (k) and diode circuit (
? ) is stored. These superconducting coils (1), persistent current switches (2), and diode circuits (2) are connected in parallel with each other, and their lead wires are connected to the cryogenic container (10
) and connected to an excitation power source (7) for the superconducting coil (1). In addition.

The diode circuit (1> consists of diodes (//a) and (//b) connected in antiparallel as shown in the figure. Also, the persistent current switch (1) consists of a persistent current switch superconductor ), this permanent-current switch superconductor (41
) and thermal insulation to insulate them from the cryogenic vessel (10') filled with liquid helium (?) It consists of (4).A heater (!
1, by leading the lead wire to the outside of the cryogenic container (10) and connecting it to the heater power source (fl).

It is designed to be supplemented. Further, I8 indicates the output current of the excitation 61 [source (7)], and IC indicates the excitation current of the superconducting coil (/).

Next, the operation will be explained. When the superconducting coil (1) is excited, first, the persistent current switch superconductor (4+) is heated by the heater ti)K to cause superconductivity breakdown and enter the normal conducting state (this normal current, conducting state). The equivalent circuit of the superconducting magnet in is K as shown in Fig. 9. Note that RN is the resistance value of the persistent current switch superconductor (Hiro) in the normal conduction state.

The diode circuit (de) is a diode (/la>(//
As long as a voltage lower than the turn-on voltage in b) is applied across the diode, the output current 8 from the magnetic power source (7) whose impedance is at its maximum is increased at a constant rate over time. When the output current Is reaches the operating current IOP, the current increase is stopped, and the inductance of the electromotive conductive coil (1) is increased for a period sufficiently longer than the time constant determined from the resistance 11 [RN] of the persistent current switch superconductor (Hiro). Then, the current of the heater of the persistent current switch (-2) is cut off.As a result, the permanent It current switch superconductor +lI)
is cooled by liquid helium (,71K) and eventually reaches a superconducting state.In this superconducting state, a 1° superconducting coil (
1) Driving Kamairuko. P is flowing and the superconducting coil (1
) is a permanent tL current switch superconducting with both ends of the conductor (
Hiroshi) I'm in a state where I'm short-circuited because I'm busy. Therefore, if the output current Ia of the excitation power source is decreased here,
The superconducting coil (/l) is a constant current K that is continuously rotated by the operating current IOP.Furthermore, if this process is followed in reverse, the superconducting coil (tl is Sakata).

By the way, in the above-mentioned superconducting magnet.

Since the permanent current switch superconductor (Hiro) is thermally insulated from the refrigerant by the thermal insulator (6), it is difficult to be cooled. In addition, in order to increase the normal conductive resistance @RN, the low-resistance stabilizing copper that is normally clad in the permanent four-current switch superconductor (Si) is removed from the permanent current switch superconductor (River, etc.). Therefore, since the persistent current switch superconductor (4c) is superconductively unstable, it must be protected from electromotive conduction breakdown.Therefore, in the above-mentioned superconducting magnet, a diode circuit (TE) which is a protection device is used. is supposed to have that protective effect.

Next, the diode circuit (TE) which is a protection device will be explained. This diode circuit (Te) consists of one diode C1ta) and (l/
b), but first an individual diode (//aH//
Regarding the characteristic b), [To explain, the voltage-current characteristic of the diode at room temperature is as shown by the broken line curve in FIG. 3. The diode used in the experiment was Mitsubishi Electric FD COOO.
B (specification of fLOA when the average forward current is 1/°C). The transition to a state in which a voltage higher than the voltage across the diode is applied and the impedance of the diode becomes sufficiently small is herein referred to as turn-on. As shown in the figure, the turn-on voltage Vi, which is the forward voltage for turning on, is usually about /V. The supplementary voltage (or starter voltage) ve of the superconducting coil (/l) is often 17 or more. Therefore, if the diode circuit (de) connected as shown in Fig. 3 is used at room temperature, the diode will increase the supplemental voltage. The diode is turned on by Me, and the superconducting coil (/) cannot be excited.However, when the diode is cooled to an extremely low temperature, its current-voltage characteristics become as shown in the solid curve in Figure 3.This solid curve is These are experimental results in liquid helium (LHe). That is, the diode turn-on voltage vtJ at extremely low temperatures is sufficiently larger than the diode turn-on voltage vtl at room temperature, and reaches rvlC in this experimental result. When the direction voltage exceeds the turn-on voltage Vtu, a diode current begins to flow, and as the N current increases, the forward voltage drop becomes smaller.As is clear from these characteristics, the diode circuit ( If the turn-on voltage of the switch (L) is set high, the impedance of the diode during energization or de-energization is almost infinite.Therefore, the shunt current to the diode during energization is almost equal to the permanent current switch (L). When superconducting breakdown occurs in the voltage field, P@RN is applied to the diode circuit (9), but this voltage is usually sufficiently large compared to the diode turn-on voltage vtJ at cryogenic temperatures, so is immediately turned on.The result.

Most of the current flowing through the persistent current switch (2) will be bypassed by the diode circuit (?), and the persistent current switch (2) will be prevented from burning out and itself will be protected.

In this way, a very large current flows into the diode circuit (9). For example, a superconducting coil (/l) that is operated with a current of about too much is not unusual for I#, and can be said to be an extremely common superconducting coil today.

When the superconducting breakdown of persistent current switch-1 is complete, a current close to that of a human flows into the diode circuit (de), which is a protection device. However, tooh class diodes are quite special in the field of power electronics, and... In addition, it is significantly more expensive than a diode with a small flow capacity, and the thermal design of the diode is difficult, so the cooling fins and the like of the diode become large, resulting in a significant increase in volume and weight.

In addition, in other recent large-scale superconducting experiments, the operating current was 100
It may reach 00kVC in some cases. At present, it is nearly impossible to pass such a large current through one diode, and it is also completely impractical in terms of cost, volume, etc.

[Problem that the invention seeks to solve]

Conventional protection devices constructed as described above require a fairly large space for mounting the diode inside the cryocontainer, which increases the surface area of the cryocontainer and prevents the intrusion of radiant heat from the container surface. As a result, the amount of evaporation of liquid helium increases, resulting in the problem that the long-term continuous operation time of the superconducting coil has to be shortened. Also,
Initial cooling of superconducting magnets from room temperature is busy, but there is a problem in that the amount of liquid helium used for initial cooling increases due to an increase in the weight to be cooled due to the increase in the weight of the diode. Furthermore, in the case of ultra-high current operation of the 10,000 A class, there was a problem in that it required a great deal of effort, time, and expense to develop the diode itself, which hindered the development of the superconducting coil itself, which was originally important.

This invention was made to solve the above-mentioned problems, and it allows the diode circuit to be made smaller, lighter, and lower in price.It also reduces the consumption of liquid helium, which is the most expensive maintenance cost for superconducting magnets. The purpose is to obtain a protective device that can reduce the

[Means for solving problems]

The protection device according to the present invention consists of a plurality of small, lightweight diodes with low current capacity connected in parallel in the same current direction.
It consists of one diode and another l diode connected anti-parallel to this l diode.

[For production]

In the diode circuit according to the present invention, since the current capacity of each diode constituting the diode in units of l is small,
Since each diode can be a mass-produced commercial item, the cost can be very low. Moreover, the weight per unit current capacity is also reduced because the diode can easily be heated.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) to (g) and (lO) are exactly the same as those explained with respect to FIG. The diode circuit (nine people) was constructed using a diode circuit (unlike the diode circuit shown in Fig. 3), which had a small current capacity, was lightweight, and had the same rating (tJ) connected in the same current direction in multiple series, for example, λ pieces. unit diode (l commi) and this l unit diode (l
Another l unit diode (l
It consists of (b).

When superconductivity vZ,m occurs in the persistent current switch (c).

A voltage IOP@Pht that is sufficiently higher than the turn-on voltage of the diode (13) is applied to the diode circuit (y*)K.

Depending on the direction of the current, either one of the l unit diodes (
Multiple diodes (13) of lcomi) or (lcob)
are turned on because they all momentarily receive a voltage higher than the turn-on voltage. As a result, almost all of the operating current rop is shunted through the diode (tJ)K, and the persistent current switch superconductor (da) of the persistent current switch (k) is completely protected without burning out. Note that there may be any number of diodes (13) constituting l units of diodes (/komi) or (/kob), and therefore,
Even for the superconducting coil (1) through which an extremely large operating current flows, a commercially available working ordinary diode can be used.

Next, Figure 2 shows the functional differences depending on the type of diode. Figure 1 compares the current per product of volume and weight for various types of diode stacks made by Mitsubishi Electric. Source: “IP Mitsubishi Semiconductor Data Book”
High power semiconductors, stack edition (published by M Bundo Shintosha, Showa!
The diode stacks used in the study were FDSroocX, FDF3!0OCP, and WDF.
3/&00CJ, FD83 and 00CH, and for the sake of fairness, all models of power diode stacks are the same in terms of specifications other than those to be compared. In order to ensure a fair comparison, the following items have the same specifications.

Structure: 2-piece diode stack connection...
... Center tap method % type % Fin... Made of steel As is clear from Figure 2, the self-cooling output current per unit of the product of the weight and volume of the diode stack is the self-cooling output 1 of the diode stack. Flow compensation force is small #Window becomes larger. That is, the operating WL flow value ro of the superconducting coil (/l)
When the current capacity of the diode circuit (9A) is determined from p, we need a small diode stack with as small a self-cooling output current specification value as possible to configure this circuit (of course, this stack is made up of small diodes). Figure 2 shows that the product of volume and weight becomes smaller when many are connected in parallel.

The diodes (/J) that make up the diodes (l) or (z-b) in units of l are not the same model.

Even when the rated current capacities are different, the same effects as in the above embodiment can be achieved.

In addition, in the above embodiments, whether or not the superconducting coil (1) had superconductivity breakdown was not a particular issue. However, if the superconducting coil (1) breaks down, the superconducting coil (
1) It should be added that it also has its own protective function. In other words, the superconducting coil (1) is a diode (/
J) is a device that consumes energy equivalent to the product of the forward voltage and the operating current IOP, and the energy possessed by the superconducting coil (1) is reduced. Further, since both ends of the superconducting coil are short-circuited, even if the persistent current switch (C) is disconnected for some reason, it is possible to prevent the coil from burning out due to the occurrence of arc discharge.

〔Effect of the invention〕

As described above, according to the present invention, a diode circuit is constructed that shunts current to a plurality of diodes, so even when the operating current is extremely large, a commercially available ordinary diode can be used, and the device can be made at a low cost. It has the effect of Furthermore, since a plurality of small diodes are used in combination, the product of volume and weight of the entire diode circuit is reduced.

Therefore, the cryogenic container can be a small one with a small amount of helium evaporation, and the initial cooling weight is also reduced, so there is an effect that less liquid helium is required for initial cooling.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram according to an embodiment of the present invention, Fig. 2 is a characteristic curve diagram of a diode stack that supports the effects of this invention, Fig. 3 is a circuit diagram showing a superconducting magnet and a conventional protection device, Fig. 1 is an equivalent circuit diagram during excitation (or extinguishing) of the superconducting magnet shown in Fig. 3, and @! Figure is a voltage-current characteristic curve diagram of a conventional diode. (1) Superconducting coil, (ko)... Persistent current switch, (J) (ri)・Fist excitation 3 power supply, (DeA) 11・Diode circuit, (t2e1)...Diode in l unit, (1cob)...Diode in l unit, (tJ )...diode. In Figure 1, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] A superconducting magnet comprising a cryogenic container housing a superconducting coil, a persistent current switch, and a diode circuit connected in parallel, and an excitation power source outside the cryogenic container and connected in parallel with the superconducting coil, wherein the diode circuit is characterized by consisting of one unit of diode, which is a plurality of small, lightweight diodes with small current capacity connected in parallel in the same current direction, and another unit of diode, which is connected in antiparallel to this one unit of diode. A protection device for superconducting magnets.