JPH0963830A - Superconducting parallel circuit and its quench monitoring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the efficiency of a quench monitor by fixing leads for voltage measurement to at least two superconductors out of three or more superconductors connected in parallel, and measuring voltages which are simultaneously generated in the two superconductors. SOLUTION: Lead wires 30 are connected, via current taps 20, with superconductors 10, 11 out of superconductors 10, 11, 12, 13 connected in parallel. The lead wires 30 are connected with voltage measuring apparatuses 40, 41. The voltages generated in the superconductors 10, 11 are monitored by comparing the voltages with a previously set regulation value. The regulation value is set by considering precision of the measuring apparatuses, noise, perturbation of an external electromagnetic field, etc. When the measured voltages of the superconductors 10, 11 are higher than or equal to the regulation values, it is judged that a circuit is quenched or in its preceding stage. When only the one out of the superconductors 10, 11 generates a voltage higher than or equal to the regulation value, it is not judged that the circuit is quenched.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique applied to a superconducting circuit in which a plurality of superconductors are connected in parallel, and monitoring quench of the superconducting circuit.

[0002]

2. Description of the Related Art In recent years, superconducting devices using superconducting wires have been applied to MRI, magnetic levitation trains and the like. As a superconductor (often in the form of a superconducting wire), a metal type and a ceramic type are known. Typical examples of metallic superconductors include NbTi-based and Nb ₃ Sn-based superconductors. When using these superconductors, they are kept at a low temperature in order to realize a superconducting state. In the case of a NbTi superconducting wire which is a typical superconductor, it is usually arranged and used in liquid helium (refrigerant).

By the way, a superconductor has a specific condition (temperature, etc.)
When, the superconducting state is realized. Therefore, for example, a superconductor such as a NbTi superconducting wire is in a normal conduction state when it is not under a specific condition. Therefore, it is in a normal conduction state at room temperature. However, these are often called NbTi superconducting wires and superconductors even at room temperature.

Generally, a superconductor has a limit value called a critical current value, and even if it is in a superconducting state, it is impossible to flow an unlimited current. When this critical current value is exceeded, the superconductor loses its superconducting state and becomes a normal conducting state.
Therefore, since there is a limit to the superconducting electric current that can be passed through one superconductor (wire), a parallel circuit is often adopted when making a superconducting circuit (magnet or the like) applied to the purpose of passing a large current value. Specifically, a plurality of circuits of superconducting wires or cables are provided in parallel. In addition, if a coil is wound using a superconducting cable in which one superconducting wire is insulated and assembled (for example, a stranded wire), a parallel circuit is formed.

The critical current value of a superconductor refers to the limit value of the current at which the superconductor becomes in the normal conduction state when it exceeds this value. Actually, however, even when the superconductor is operated below this critical current value. May be in a normal conduction state. This is because the normal conduction transition (which is referred to as quench) of the superconductor may be induced by fluctuations in temperature conditions, electromagnetic stirring, mechanical vibration, and the like. For example, in the case of mechanical vibration, it is considered that this causes a magnetic field fluctuation or causes frictional heat due to the vibration, resulting in quenching of the superconductor. Quenches like this often occur suddenly.

By the way, in a superconducting parallel circuit in which a plurality of superconductors are connected in parallel, when only one of the superconducting parallel circuits undergoes normal conduction transition, quenching of the other superconductors is induced, and eventually the entire system of the superconducting parallel circuit is caused. It may be quenched. The term quench is used not only when individual superconductors transition to the normal conduction state, but also when the entire superconducting parallel circuit system is in the normal conduction state.

When the whole circuit is quenched, Joule heat is generated by the current flowing through the superconductor which has been transformed into the normal conduction state. Then, not only evaporation of a large amount of refrigerant (liquid helium etc.) may occur, but also the superconductor may be burned out. Therefore, when the entire circuit is quenched, or when there is a sign of quenching, it is necessary to take measures such as immediately stopping the operation or promptly reducing the current flowing in the circuit. Then, when the quenched superconductor is cooled again and restored to the superconducting state, the operation is restarted. Although quenching tends to occur at the stage of exciting a current from the start of operation, it may occur suddenly even during operation in the permanent current mode.

Therefore, when operating the superconducting circuit, it is necessary to monitor the quench. A conventional quench monitor method will be described with reference to FIG. FIG. 2 is a schematic diagram showing a part of a circuit in which four superconductors 10, 11, 12, and 13 are connected in parallel. 1 of these superconductors
A current tap 21 is attached to a book (for example, the superconductor 10) and connected to a voltage measuring device 42 via a lead wire 31. If the superconductor 10 to which the current tap 21 is attached is in the superconducting state, the voltage value between the left and right current taps 21 shown in the figure is ideally zero (however, in reality, disturbance of the external electromagnetic field, noise of the measuring instrument, etc. Therefore, some voltage is detected). When the superconductor 10 is quenched, resistance is generated, so that the voltage is detected by the voltage measuring device 42. A predetermined value (threshold value) of the detected voltage value may be set in advance, and it may be determined that the circuit has been quenched when the detected voltage value becomes equal to or higher than the specified value. Thus the quench can be monitored.

The specified value is determined from the inductance of the circuit, the value of current flowing, and the like. Specifically, for example, L
The value is set with reference to the value of (dI / dt), but noise and accuracy of the voltage measuring device are also taken into consideration. During operation of the circuit shown in FIG. 2, if a voltage higher than a specified value is generated between the attached current taps 21, the circuit is determined to be in a quench state or the previous stage, and the operation is promptly stopped. I will take it. In this way, quenching of the entire circuit is prevented, or even when the quenching of the entire circuit is reached, burnout of the superconductor is prevented, and evaporation of expensive refrigerant (liquid helium or the like) is suppressed.

[0010]

The problem will be described with reference to FIG. 2 again. For example, when a quench occurs in the superconductor 11, a resistance is generated in the superconductor 11, so most of the current flowing in the superconductor 11 is distributed to the other three superconductors, that is, the superconductors 10, 12, and 13. It will be transferred. Then, a current larger than the current that has been flowing up to then flows through the other three superconductors, so that the possibility of quenching these superconductors increases. In other words, there is a high possibility that the entire circuit will be quenched.

However, in the normal operation, the current value is set to a value that is somewhat lower than the critical current value of each superconductor, so even if one of the four superconductors is quenched, the other three superconductors are superconducting. The body does not always quench. Unless the other three are quenched, the entire circuit is not quenched, and the quenched superconductor is restored to the superconducting state again. Thus, the normal operation of the superconducting parallel circuit is maintained. Therefore 4
Immediately stopping the operation of the circuit when one of them is quenched is not always an efficient operation method.

However, in the conventional quench monitor system, a current tap is attached to one of a plurality of superconductors to measure the voltage, so that there is the following problem. Referring to FIG. 2 as an example, if a quench occurs in the superconductor 10 to which the current tap 21 is attached and the other three superconductors 11, 12, and 13 are not yet quenched at that stage, the conventional method is used. At this stage, it was judged that the circuit was quenched or the stage before that.

Therefore, in the conventional quench monitor system, it is determined that the circuit is quenched when the superconductor 10 to which the current tap 21 is attached is quenched.
It was not always possible to say that an efficient driving method could be created. That is, the entire circuit is not quenched, and even if the superconductor 10 naturally recovers to the superconducting state eventually, the operation of the circuit is stopped (or a measure to reduce the current value is taken). As a result, the operating cost is increased. As a result, the replacement of parts may be unnecessarily caused, and there is a problem that the cost of replacement parts and the cost of replacement work increase.

In order to deal with such a problem, a method of attaching the lead wires 32 to all the superconductors 10 to 13 as shown in FIG. 3 can be considered. According to this method, even when the superconductor 10 is quenched, for example, another superconductor 1
Since it is possible to measure whether or not 1 to 13 are quenched,
There is an advantage that it can be more accurately determined whether or not the entire circuit is quenched. Therefore, it is economical without taking unnecessary measures to stop the circuit operation or reduce the current value. However, this method also had the following problems.

In the system of FIG. 3, the current tap 22 is different from the conventional one.
The number of connecting points between the refrigerant region and the outside is increasing from the lead 32 through the lead 32. Therefore, external heat easily enters the refrigerant for maintaining the cryogenic temperature. If the amount of invasion of heat from the outside increases, the evaporation consumption of the refrigerant increases and the operating cost increases. In particular, the currently commonly used refrigerant is expensive liquid helium, so increasing the amount of evaporation thereof is not desirable from the viewpoint of cost as well as protection of effective resources.

In addition, if there are many places where the voltage taps are attached, there is of course a problem that the cost and the cost of the attachment work increase. In addition, the space to install the tap in the superconducting equipment,
Alternatively, a space required for the installation work is also required, which may limit the degree of freedom in designing superconducting equipment.

[0017]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a superconducting parallel circuit capable of efficient quench monitoring. That is, the present invention provides a superconducting parallel circuit in which at least two superconductors among three or more superconductors connected in parallel have leads for voltage measurement attached thereto. In addition, as an efficient quench monitoring method, 3 connected in parallel
A method for measuring the voltage by attaching a voltage measuring lead to at least two superconductors of at least two superconductors, and measuring the voltage generated simultaneously in at least two superconductors.

The superconducting parallel circuit of the present invention is intended for a circuit in which three or more superconductors are connected in parallel for applications such as a superconducting coil, a permanent current switch, and a superconducting fault current limiter. Also provided is a method of monitoring the occurrence of a quench in such a superconducting circuit.

A lead wire is attached to at least two of three or more superconductors connected in parallel, and the voltage generated in the superconductor to which the lead wire is attached is monitored through the lead wire. The voltage value to be measured is compared with a specified value set in advance. The specified value is appropriately set in consideration of the accuracy and noise of the measuring instrument, the disturbance of the external electromagnetic field, and the like. Then, when at least two of the superconductors whose voltage is being measured generate a voltage equal to or higher than the specified value in at least two superconductors, it is determined that the circuit has been quenched or is in the previous stage. Therefore, if only one of the superconductors whose voltage is measured generates a voltage higher than the specified value, it is not determined that the circuit has been quenched.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION As an example, a superconducting parallel circuit in which four superconductors are connected in parallel will be described. FIG. 1 is a conceptual diagram showing a parallel portion of a superconducting circuit. Here, superconductor 1
Reference numerals 0, 11, 12, and 13 denote, for example, superconducting coils, and the four coils are electrically connected in parallel at connecting portions 60 and 61. The connection method is solder connection, solid phase connection, pressure bonding, or the like.

The current is shunted to four superconductors between the connecting portions 60 and 61, respectively. Ideally, if the four superconductors are the same, the shunt current will be equally divided into quarters. However, actually, the current values flowing through the respective superconductors 10 to 13 are not equal. This is because a minute difference in connection resistance actually exists. In the case of a superconducting circuit, even a very small difference in resistance value has a great effect on shunt current.

The left and right connecting portions 6 of the superconductors 10 and 11
Current taps 20 are provided inside 0 and 61, respectively, and lead wires 30 are connected to them. The superconductor 10 and the lead wire 30 are connected by soldering or the like. This lead wire 30 is drawn out from the inside of the refrigerant (liquid helium) to the room temperature space, and the voltage measuring device 4
0, 41.

When the superconductors 10 to 13 are in the superconducting state, no voltage is generated in the superconductors 10 and 11. If, for example, the superconductor 12 is quenched in this state, a voltage is generated in the superconductor 12. Then, most of the current flowing in the superconductor 12 is generated by the other superconductors 10, 11,
It will be divided into 13. However, each superconductor 1
Since there are connection resistances of 0, 11, and 13, a minute current also flows in the superconductor 12.

As the current flowing through the superconductor 12 is shunted, the current flowing through the other superconductors becomes large. However, even if the critical current value of each superconductor is not exceeded, the superconductors 10, 11 and 13 will not be quenched.
In this case, these superconductors maintain normal operation without being quenched, and eventually the superconductor 12 returns to the superconducting state again. This is similar to redundancy in the field of aircraft and electrical equipment.

In the above case, the voltage measuring devices 40 and 41
Since a voltage higher than the specified value is not generated at, it is not determined that a quench has occurred. Therefore, it is possible to prevent unnecessary measures for stopping the circuit operation. On the other hand, if one of the other superconductors is quenched as a result of the current flowing in the superconductor 12 being shunted to the other superconductor, the current is further distributed by the second quench. In this case, since the number of remaining superconductors that have not yet been quenched is further reduced, the burden on the remaining superconductors that receive the shunting due to the second quench is accordingly increased. Therefore, if the quench of one superconductor further induces the quench of the second, there is a high possibility of inducing the quench of the third time, and eventually the quench of the entire circuit is increased.

Therefore, if the voltage measuring devices 40 and 41 simultaneously detect a voltage higher than the specified value, it means that the quenching of the entire circuit is very likely to occur. Therefore, in the present invention, it is determined at this point that a circuit quench has occurred or that there is a sign thereof. Although the judgment may be recognized by an operator by observing the voltage measuring devices 40 and 41, a logic circuit for judging a state in which both the voltage measuring devices 40 and 41 simultaneously detect a voltage equal to or higher than a specified value is provided. If this is done, automatic detection is possible.

In the above description, the case where the quench occurs in the superconductor 12 is considered, but the voltage measuring device 40 (or 4) is used.
Quenching may occur in the superconductor 10 (or 11) connected to 1). In this case, unless the quench of the superconductor 10 induces the quench of the superconductors 11 to 13, the quench of the superconductor 11 is not detected by the voltage measuring device 41. Therefore, the voltage measuring devices 40 and 41 do not detect the quench at the same time, and do not judge the quench of the entire circuit. In this state, the superconductors 11 to 13 do not quench and maintain the superconducting state.
Will eventually be restored to the superconducting state and normal operation will be maintained, and it is not necessary to take measures to stop the operation of the circuit.

If the quench of the superconductor 10 is
As described above, when the quench of any one of 13 is induced, the quench of the entire circuit is likely to occur, but in this case, the quench of the superconductor 11 will eventually be detected, so the voltage measurement The vessels 40 and 41 will eventually detect the quench of the superconductors 10 and 11 at the same time. At this stage, the quench of the entire circuit may be judged.

Superconductors 10 to 10 connected in parallel in this way
If any two voltages out of 13 are measured, the quench of the circuit can be efficiently detected. Of course, more than two superconductors for voltage measurement may be used, but the number of current taps attached increases and external heat easily enters the refrigerant, so the number of superconductors for voltage measurement is not so large. It is better not to have many. However, depending on the circuit, even if quenching occurs simultaneously in two superconductors connected in parallel, the whole circuit may recover without quenching. This is the case, for example, of a circuit in which a sufficiently low current is passed with respect to the critical current value. Alternatively, the number of superconductors connected in parallel is considerably large, and even if a part of them is quenched, the number of remaining superconductors is large and there is a large margin. In these cases, the voltage may be measured from three or more superconductors connected in parallel. However, even in this case, it is not necessary to attach current taps and lead wires to all of the superconductors connected in parallel and measure the voltage.

As described above, the quench monitoring method for a superconducting parallel circuit according to the present invention is an efficient and economical monitoring method and can prevent unnecessary circuit operation stop measures. Also, since it is not necessary to install many current taps, the installation work cost can be saved. Further, there is no need for an extra space for installing the current taps in the device or an extra working space. In addition, since the number of leads connected to the superconductor is small, it is possible to suppress the evaporation of the refrigerant due to the intrusion of external heat, which is economical.

[0031]

As described in detail above, the superconducting parallel circuit of the present invention enables efficient quench monitoring, and the quench monitoring method enables efficient operation and is economical.

[Brief description of drawings]

FIG. 1 is a conceptual diagram showing a quench monitoring method of the present invention.

FIG. 2 is a conceptual diagram showing a conventional quench monitoring method.

FIG. 3 is a conceptual diagram showing a conventional quench monitoring method.

[Explanation of symbols]

 10, 11, 12, 13 Superconductor 20, 21, 22 Current tap 30, 31, 32 Lead wire 40, 41, 42 Voltage measuring device 43, 44, 45, 46 Voltage measuring device 50, 51 Superconductor 60, 61 Connection Department

Claims (2)

[Claims] 1. A superconducting parallel circuit in which leads for voltage measurement are attached to at least two superconductors among three or more superconductors connected in parallel. 2. A voltage measured by attaching a voltage measuring lead to at least two superconductors of three or more superconductors connected in parallel, and measuring the voltage simultaneously in at least two superconductors. A quench monitoring method for a superconducting parallel circuit for measuring the temperature.