JPS645446B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a protection device for a superconducting coil, and in particular, protects the superconducting coil from quenching (rapid transition from superconducting state to normal conducting state) caused by internal disturbance or disturbance during operation of the superconducting coil. This invention relates to a superconducting coil protection device that protects superconducting coils.

FIG. 1 is an electrical wiring diagram showing a conventional superconducting coil protection device. In FIG. 1, a superconducting coil 1 has first terminals 10 at both ends thereof.
1. The second terminal 102, the first voltage detection terminal 103 and the second voltage detection terminal 104 connected to the first and second terminals 101 and 102, and the inductance of the superconducting coil 1. A midpoint terminal 105 is provided. Power connection terminal 201, 2
02 is connected to first and second terminals 101 and 102 via a switch 3 such as a high-speed circuit breaker. The voltage comparator 4 compares the voltage between the first terminal 101 and the midpoint terminal 105 with the voltage between the second terminal 102 and the midpoint terminal 105, and outputs an output that opens the switch 3 when the difference exceeds a predetermined value. It is something that causes The protection circuit 5 is, for example, a resistor, and the first,
It is connected between the second terminals 101 and 102,
When the switch 3 is opened, a current is supplied to the superconducting coil 1, and this current is attenuated.

Next, the operation will be explained. Now, if the superconducting state of the superconducting coil 1 continues stably, no voltage will be generated between the first terminal 101 and the midpoint terminal 105 and between the second terminal 102 and the midpoint terminal 105. Furthermore, when the excitation current i from the power supply connection terminals 201 and 202 changes, a voltage called Ldi/dt is generated between the first terminal 101 and the midpoint terminal 105 and between the second terminal 102 and the midpoint terminal 105. , if the midpoint terminal 105 is exactly the midpoint of the inductance of the superconducting coil 1, the inductances L between the two terminals are equal, and exactly balanced voltages are generated. In this state, the voltage comparator 4 is configured not to operate, and is configured, for example, by a bridge connection.

Next, causes of internal disturbances within the superconducting coil 1, such as frictional heat caused by wire movement where the wire partially moves due to electromagnetic force, or flux jump, which is the sudden intrusion of magnetic flux into the superconducting coil 1. As a result, when the superconducting coil 1 partially generates heat and the superconducting state of that part is broken, it becomes normal conductive and a voltage is generated. This normal conduction transition does not occur in the entire superconducting coil 1 at once, but seeds are formed somewhere due to the above-mentioned causes, and only when it becomes irrecoverable does it spread to the entire superconducting coil 1. happens. This speed is said to propagate at several to several tens of m/s, and this phenomenon occurs between the first terminal 101 and the midpoint terminal 105 and between the second terminal 102 and the midpoint terminal 10.
The probability that two events will occur in exactly the same form at the same time is extremely low. Therefore, the first terminal 101 and the midpoint terminal 10
5 and between the midpoint terminal 105 of the second terminal 102 are compared and monitored by the voltage comparator 4, the occurrence of quench can be detected relatively early.
When the voltage comparator 4 detects the occurrence of this quench, the switch 3 is opened and the superconducting coil 1
flows through the protection circuit 5, and the resistance R of the protection circuit 5
The current is attenuated by the attenuation time constant L/R determined by the inductance L of the superconducting coil 1 and the inductance L of the superconducting coil 1, thereby protecting the superconducting coil 1.

In practice, in order to prevent malfunctions due to noise, etc., a detection level is set in the voltage comparator 4 so that the voltage comparator 4 operates after the normal conductivity region has been established to a certain extent, and a certain amount of time delay is established. It is given.

The conventional device configured as described above is extremely simple and effective for a single superconducting coil 1, but a plurality of superconducting coils 1 are installed coaxially in multiple layers, and each one receives an exciting current independently of the other. , protection becomes impossible as explained below. That is, when a plurality of superconducting coils 1 are individually excited, the external magnetic field changes when viewed from the corresponding coil. In particular, in the case of a hybrid magnet configured by coaxially installing a water-cooled normal conducting coil within a plurality of superconducting coils 1,
No matter how much consideration is given to axially symmetrical magnetic field distribution, the center terminal 10 of each superconducting coil 1
If 5 is selected incorrectly, imbalance will occur in voltage generation due to magnetic field fluctuations, and the protection circuit 5 will be activated even if there is no abnormality.

In general, superconducting magnets can produce strong magnets with minimal excitation power, but there is a limit to the magnetic field.
The maximum is 8T (Tesla) to 12T. The world's strongest magnets are around 30T, but to make up for the shortfall, a water-cooled normal conducting magnet is installed inside the superconducting magnet to create a hybrid magnet that can generate up to 10MW of excitation power. In this case, the disadvantages mentioned above arise. In addition, the excitation power source for a normally conductive magnet generally has a large capacity and has many noise elements, so that the protection circuit 5 is often activated even if there is no abnormality. Further, the size of the superconducting coil 1 is reduced by using a superconducting material that can withstand higher magnetic fields in the center, and the inner layer may be made of two or more materials than the outer layer, and this is called grading. Therefore, even if the inner layer and the outer layer are made in exactly the same coil shape, they cannot be considered independently of each other, and the operation of the protection circuit 5 becomes even more complicated.

This invention was made in order to eliminate the above-mentioned conventional drawbacks. An embodiment of the present invention will be described with reference to the drawings below.

FIG. 2 is an electrical wiring diagram showing an embodiment of the superconducting coil protection device according to the present invention, and FIG. 3 is a partially enlarged view of FIG. 2. In the figure, parts that are the same as or equivalent to those in FIG. In FIG. 2 and FIG. 3, the superconducting coil 1 is composed of a first superconducting coil 1a, a second superconducting coil 1b, and a third superconducting coil 1c, each of which has a graded layered structure, with terminals at both ends of each. The first terminals 101a, 101b, 101c, the second terminals 102a, 102b, 102c, and the first terminals connected to the first terminals 101a, 101b, 101c.
Voltage detection terminals 103a, 103b, 103
c, and second terminals 102a, 102b, 10
The second voltage detection terminal 104 connected to 2c
a, 104b, 104c, and the midpoint terminal 105a,
105b and 105c. Power supply connection terminals 201a, 201b, 201c, 202a, 2
02b, 202c are switches 3 such as high speed circuit breakers
The first terminals 101a, 1 via a, 3b, 3c
01b, 101c and second terminals 102a, 102
b, 102c. Voltage comparison device 4
are the first, second, and third superconducting coils 1a, 1b,
1c, each of the first terminals 101a, 101
b, 101c and midpoint terminals 105a, 105b, 1
05c and the second terminal 102a, 102
b, 102c and midpoint terminals 105a, 105b, 1
Compare the voltage between 05c for each coil,
When the difference in at least one coil exceeds a predetermined value, an output is generated that opens the switches 3a, 3b, and 3c. Protection circuit 5a, 5
b, 5c are resistors, for example, and the first terminal 101
a, 101b, 101c and the second terminal 102a,
102b and 102c, and when the switches 3a, 3b, and 3c are opened, the first, second, and third
A current is supplied to the superconducting coils 1a, 1b, and 1c, and this current is attenuated. A water-cooled normal conductive coil 6 is installed at the center inside the superconducting coil 1, and has a hybrid configuration together with the superconducting coil 1.

Next, the operation will be explained. Now, the current flowing through the first superconducting coil 1a is i ₁ , and the current flowing through the first terminal 101 is
The inductance between a and the midpoint terminal 105a is L ₁ ,
Let L 2 be the inductance between the second terminal 102a and the midpoint terminal 105a, i ₆ be the current flowing through the normally conducting coil ₆ , and let M ₁ and M ₂ be the mutual inductances caused by the current i ₆ to the inductances L ₁ and L ₂ . , the voltages V ₁ and V ₂ between the terminals of the inductances L ₁ and L ₂ are respectively expressed by the following equations. However, it is assumed that the superconducting state is maintained.

V ₁ = L ₁ di ₁ / dt + M ₁ di ₆ / dt V ₂ = L ₂ di ₁ / dt + M ₂ di ₆ / dt As shown in Fig. 2, the first superconducting coil 1a is configured vertically and completely symmetrically. Then, L ₁ =
L ₂ , M ₁ =M ₂ holds true, and no matter what fluctuations occur in i ₁ and i ₂ , V ₁ =V ₂ always holds true, and voltage balance is maintained. This holds true for any combination of the first, second, and third superconducting coils 1a, 1b, and 1c and the normal conducting coil 6. Therefore, in the normal operation mode in which the superconducting state is maintained, the first, second, and third superconducting coils 1a, 1
Even if the excitation currents b, 1c and the normal conducting coil 6 are changed independently, the voltage balance will not be disrupted as long as there is no normal conducting transition, and quench detection will be performed perfectly.

In addition, instead of quenching, the normal conduction coil 6
If it is assumed that an abnormality occurs, for example, an interlayer short circuit occurs somewhere, an asymmetry will generally occur in the upper and lower magnetic flux distributions of the normally conducting coil 6 in FIG. 2. At this time, since M ₁ ≠ M ₂ , V ₁ ≠ V ₂ , and the voltage comparator 4 produces an output and switches 3a, 3b, 3c.
is opened, and the protection circuits 5a, 5b, 5c are
The safety of the device is maintained by passing current through the second and third superconducting coils 1a, 1b, and 1c to attenuate it. Further, in this case, a switch (not shown) of the power supply circuit may be opened for the normal conduction coil 6 as well.

As described above, according to the present invention, for each superconducting coil of a plurality of superconducting coils installed in layers,
Bring out the voltage detection terminals from both ends and the middle point,
I have configured this to compare with each other, so
Not only is the quench detected completely, but it also has the effect of providing safety protection even when combined with other coils.

[Brief explanation of the drawing]

FIG. 1 is an electrical wiring diagram showing a conventional superconducting coil protection device, FIG. 2 is an electrical wiring diagram showing an embodiment of the superconducting coil protection device according to the present invention, and FIG.
The figure is a partially enlarged view of FIG. 2. In the figure, 1a, 1b, 1c are the first, second,
Third superconducting coil, 101a, 101b, 10
1c is the first terminal, 102a, 102b, 102
c is the second terminal, 103a, 103b, 103c
are first voltage detection terminals, 104a, 104b,
104c is a second voltage detection terminal, 105a, 1
05b, 105c are middle point terminals, 201a, 201
b, 201c, 202a, 202b, 202c are power supply connection terminals, 3a, 3b, 3c are switches, 4
is a voltage comparator, 5a, 5b, 5c are protection circuits,
6 is a normal conducting coil. In each figure, the same parts or corresponding parts are denoted by the same reference numerals or a suffix attached to the same reference numerals.

Claims (1)

[Claims] 1 A plurality of superconducting coils formed in multiple layers coaxially, a normal conducting coil arranged at the center of the plurality of superconducting coils, and a voltage at both ends and a midpoint of each of the plurality of superconducting coils, a voltage comparison device that compares each superconducting coil and is activated when a differential voltage exceeds a predetermined value; and a protection circuit that receives current from the plurality of superconducting coils and attenuates the current when the voltage comparison device is activated. A superconducting coil protection device characterized by comprising: