JP2599986B2 - Superconducting magnet protection method and protection device - Google Patents

Description

The present invention relates to the protection of a superconducting magnet, and more particularly to a method for protecting a superconducting magnet which is effective when the superconducting magnet breaks the superconducting state and transitions to a normal conducting state. It relates to the protection device.

[Conventional technology]

The superconducting magnet is formed by winding a superconductor that is cooled to a low temperature below the critical temperature and has zero electric resistance. When the temperature of the superconductor becomes higher than the critical temperature or a current higher than the critical current flows, the superconductor cannot maintain the superconducting state, and transitions to the normal conducting state. When the superconducting magnet shifts to the normal conducting state, resistance is generated in the superconducting magnet having zero electric resistance, and the magnetic energy of the superconducting magnet is rapidly released as Joule heat. For this reason, there is a possibility that a serious accident such as burnout or dielectric breakdown of the superconducting magnet may occur due to a rise in temperature or generation of a voltage, and various protection methods have been devised to prevent this.

FIG. 3 shows a conventional superconducting magnet protection circuit. The superconducting magnet 16 is formed by connecting three winding blocks (coils) 16a, 16b and 16c in series. As a means for protecting the superconducting magnet 16, one protective resistor 17 is provided outside in parallel with the superconducting magnet 16. The superconducting magnet 16 is excited by an excitation power supply 19 via a switch 18, but for some reason the superconducting magnet 16
If the 16 superconducting state breaks and transitions to the normal conducting state,
The excitation power supply 19 for exciting the superconducting magnet 16 is disconnected by the switch 18. This makes the superconducting magnet 16
The magnetic energy is released to a protection resistor 17 connected in parallel with the superconducting magnet 16 to protect the superconducting magnet 16. Here, there are the following restrictions on the protection resistor 17 in the protection circuit of FIG. That is, from the viewpoint of protection of the superconducting magnet 16, it is necessary to rapidly attenuate the magnet current in order to minimize the temperature rise due to heat generation in the normal conducting portion. For this purpose, a protection resistor having a large resistance value is required. However, if the resistance value is too large, the voltage across the protection resistor 17, that is, the voltage across the superconducting magnet 16 exceeds the allowable insulation voltage.
Therefore, the resistance value of the protection resistor 17 must be determined so as to be at least equal to or lower than the allowable insulation voltage.

However, the potential distribution of the superconducting magnet 16 after the power is cut off has not been taken into consideration so far, and the following problems have occurred with respect to the voltage generated in the circuit of FIG.
That is, since the highest voltage generated in the circuit of FIG. 3 is not necessarily the voltage across the protection resistor 17 but the highest voltage may be generated inside the superconducting magnet 16, the voltage across the protection resistor 17 is set below the allowable insulation voltage. Just doing is not enough.

FIG. 4 shows the respective potentials of the terminals A, B, C and D of the superconducting magnet 16 after the power is cut off in the circuit of FIG. Here, the potential of one terminal of the superconducting magnet 16 becomes the ground potential, and the potential difference between the terminals A and D becomes equal to the voltage across the protection resistor 17. FIG. 4 shows a plot of each potential distribution at a certain time after the power is cut off in each case where the superconducting state is broken and the winding block (coil) 16a or 16b or 16c breaks into the normal conducting state. A solid line shows a plot of the potential distribution when the winding block 16c undergoes normal conduction transition. Similarly, a dotted line shows a plot of the potential distribution when the winding block 16b undergoes a normal conduction transition. Similarly, the winding block 16
A dash-dot line indicates a plot of the potential distribution when c undergoes a normal conduction transition. The right side of FIG. 4 shows the voltage of the protective resistor, the voltage generated by the superconducting magnet 16 in each case, that is, the potential difference which is the difference between the maximum value and the minimum value in the potential distribution plot. First, the voltage at both ends of the protection resistor 17 is the leftmost, and then, in order from the left, the voltage generated in the superconducting magnet 16 when the winding block 16a transitions to the normal conduction, and when the winding block 16b transitions to the normal conduction. Superconducting magnet 16
And the voltage generated by the superconducting magnet 16 when the winding block 16c undergoes normal conduction transition. Therefore, it can be seen that the voltage generated by the superconducting magnet 16 becomes lowest when the winding block 16b undergoes the normal conduction transition among the three methods.

Therefore, as shown in FIG.
If the superconducting state is broken at a or 16c and the state transits to the normal conducting state, it is highly possible that the highest voltage is generated inside the superconducting magnet 16, and the highest voltage generated in the circuit of FIG. May be higher than voltage. That is, when a portion having resistance occurs at both ends of the coil, and the inductance l of this portion and the resistance γ of this portion satisfy the relationship of the following equation, The highest generated voltage is the voltage RI across the protection resistor (R is the protection resistor 17
Resistance). But the central winding block
If the superconducting state is broken by only 16b and the state changes to the normal conducting state, the possibility that the highest voltage is generated inside the superconducting magnet 16 is reduced, and in most cases, the highest generated voltage in the circuit of FIG. The maximum voltage generated in the circuit of FIG. 3 is lower than at least when the superconducting state is broken and the normal winding state is established in the winding block 16a or 16c at the end. Therefore, the winding block 16
If a or 16c undergoes normal conduction transition, the resistance value of
Must be smaller than when 16b undergoes a normal conduction transition.

[Problems to be solved by the invention]

In the conventional method of protecting a superconducting magnet, there is a problem in that when the coil at the end of a coil (winding block) connected in series undergoes normal conduction, the voltage across the superconducting magnet exceeds the allowable insulation voltage. Was.

It is an object of the present invention to reduce the possibility that a maximum voltage is generated inside a superconducting magnet so that the maximum generated voltage does not exceed an allowable insulation voltage and is equal to a voltage across a protection resistor. An object of the present invention is to provide a method of protecting a magnet and a device for protecting the same.

[Means for solving the problem]

In order to achieve the above object, a method for protecting a superconducting magnet according to the present invention includes the steps of: protecting a superconducting magnet formed by connecting a plurality of coils in series with at least one protection resistor; In the superconducting magnet protection method of connecting the superconducting magnet and detecting the normal conduction transition of the superconducting magnet with a quench detector, the controller operates according to the signal from the quench detector and closes the superconducting magnet and the protective resistor, It is configured to cause a normal conduction transition of the coil located at the center, and to limit the generated voltage of the coil to an allowable insulation voltage or less.

And, when winding the coil with one wire, the configuration where the part of the coil where the magnetic field is high is located in the center and connected in series or when winding the coil with one wire, at the time of normal conduction transition The coil part where the temperature of the wire rises is located in the center and connected in series.When winding the coil with one wire, the coil part where the magnetic field is low is connected to both ends of the excitation power supply Alternatively, when the coil is wound by one wire, a portion of the coil where the temperature of the wire does not increase during normal conduction transition may be connected to both ends of the excitation power supply.

In the superconducting magnet protection device, at least one protection resistor for protecting the superconducting magnet formed by connecting a plurality of coils in series, a protection resistor is connected in parallel with the superconducting magnet, and the normal conduction transition of the superconducting magnet is performed. In the superconducting magnet protection device, which consists of a quench detector that detects the current and a switch that closes the superconducting magnet and the protection resistor when the controller operates in response to a signal from the quench detector, a coil that causes normal conduction transition is connected in series. Is arranged almost at the center.

[Action]

According to the method for protecting a superconducting magnet of the present invention, by causing normal conduction transition at the center of a plurality of serially connected coils, the generated voltage of the coils becomes equal to or lower than the allowable insulation voltage. By placing the part of the coil where the magnetic field is high at the center or connecting the part of the coil where the magnetic field is low to both ends of the excitation power source, the highest potential generated during normal conduction transition is low, and the normal conduction transition is low. For example, by placing the coil part where the temperature of the wire becomes high in the center, or connecting the coil part where the temperature of the wire does not become high at the time of normal conduction transition to both ends of the excitation power source, for example, the winding part of the outer layer becomes the inner layer. The critical temperature becomes higher than that of the winding part, and the influence of thermal intrusion from the external protective resistance side is reduced.

〔Example〕

 One embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, a superconducting magnet 21 formed by connecting a plurality of coils 1 and 2 in series is protected by at least one protection resistor 17, and the protection resistor 17 is protected by a superconducting magnet.
The quench detector (not shown) detects the normal conduction transition of the superconducting magnet 21 in parallel with the superconducting magnet 21, and a controller (not shown) operates according to a signal from the quench detector to connect the superconducting magnet 21 to the superconducting magnet 21. In the superconducting magnet protection method in which the protection provision 17 is closed via the switch 18, a normal conduction transition is caused in the inner layer of the coil located substantially in the center of the series so that the generated voltage of the coil is limited to the allowable insulation voltage or less. Configuration.

When the coil is wound with a single wire, the portion of the coil where the magnetic field is high is located in the inner layer of the central coils 1 and 2) and the coil is wound with a single wire. When the coil is wound with a single wire, the magnetic field becomes low when the coil is wound with a single wire. A configuration in which the part is connected to both ends of the excitation power supply 19 via the outer layer terminals 4 and 6, or a part of the coil where the temperature of the wire does not rise during normal conduction transition when the coil is wound with one wire Excitation power supply 1 via terminals 4 and 6
It may be configured to connect to both ends of 9.

In the protection device for the superconducting magnet 21, at least one protection resistor 17 for protecting a superconducting magnet formed by connecting a plurality of coils 1 in series, and at least one protection resistor 17 for protecting the superconducting magnet, are connected to the supercurrent magnet 21. And a quench detector (not shown) for detecting the normal conduction transition of the superconducting magnet 21 and a controller (not shown) operated in response to a signal from the quench detector to In a superconducting magnet protection device comprising a protection resistor 17 and a switch 18 for closing, a coil causing a normal conduction transition is arranged substantially at the center of the series.

The present invention achieves the initial object by making the part where the superconducting state breaks and transitions to the normal conducting state be in the center of the superconducting magnet instead of the end of the winding. , An inner layer terminal 3 is provided on a solenoid-wound winding block (coil) 1 shown in FIG.
And the terminal 4 on the outer layer side. Similarly, the winding block 2 has the terminal 6 on the outer layer side of the terminal 5 on the inner layer side. In the arrangement as shown in FIG. 1, when each winding block generates a magnetic field in the same direction, the magnetic field is higher in the inner layer winding part than in the outer layer winding part of each winding block, The transition from the superconducting state to the normal conducting state occurs in the winding part of the inner layer. Therefore, the terminal 3 on the inner layer side and the terminal 5 on the inner layer side are connected, and the terminals 4 and 6 on the outer layer side are connected.
By connecting the two winding blocks 1 and 2 in series such that each of them is connected to an external protection resistor 17, the super electric magnet 21 as a whole is composed of the outer layer of the winding block 1 and the inner layer of the winding block 1. This means that the connection is made in the order of the unit, the inner layer of the winding block 2 and the outer layer of the winding block 2. As a result, the part where the superconducting state is broken and moves to the normal conducting state (the inner layer part of the winding block) can be made not the end part of the winding but the center part in the superconducting magnet, and the terminal 3 on the inner layer side The maximum generated voltage in the circuit as shown in FIG. 3 is lower than in the case where each of the reference numerals 5 is connected to an external protection resistor. Here, the two winding blocks 1 and 2 are wound in opposite directions, and since the magnetic field is lower in the winding portion of the outer layer than in the winding portion of the inner layer, the critical temperature is higher than the winding portion of the inner layer. Therefore, there is an advantage that the influence of thermal intrusion from the external protection resistor side can be reduced.

Next, another embodiment of the present invention will be described with reference to FIG. As shown in FIG. 2, there are three solenoid-wound winding blocks (coils) 7, 8 and 9, and when these are connected in series and used, the solenoid-wound winding block 7 has an inner layer. There is a terminal 10 on the side and a terminal 11 on the outer layer,
Similarly, the winding block 8 has terminals 12 on the inner layer side and terminals 13 on the outer layer side. Similarly, the winding block 9 has terminals 14 on the inner layer side and terminals 15 on the outer layer side. Here, in the arrangement of the respective winding blocks as shown in FIG. 2, of the three winding blocks, the magnetic field of the center winding block 8 becomes the highest, and the respective winding blocks become The magnetic field is higher in the inner layer winding portion than in the outer layer winding portion. In this case, the transition from the superconducting state to the normal conducting state occurs in the winding portion of the inner layer of the central winding block 8. Therefore, the outer-layer terminals 11 and 15 of the outer-layer winding blocks 7 and 9 are respectively connected to external protection resistors, and the inner-layer terminal 10 of the outer-side winding block 7 and the terminal 12 of the center-winding block 8 are connected. Or 13 and the three winding blocks 7, 8 and 9 are connected in series such that the terminal 14 on the interior side of the outer winding block 9 and the remaining terminals of the center winding block 8 are connected. By connecting, the part where the superconducting state breaks and transitions to the normal conducting state can be made not the end part of the winding in the superconducting magnet but the center part, and the inner layer terminals are protected externally respectively. The maximum generated voltage in the circuit as shown in FIG. 3 is lower than that in the case of connecting to a resistor. Here, it is assumed that the winding blocks 7, 8, and 9 are wound in such a direction that a desired magnetic field is generated.

〔The invention's effect〕

According to the method and apparatus for protecting a superconducting magnet of the present invention, by causing normal conduction transition in the center coil of the serially connected coils, the maximum generated voltage at the time of normal conduction transition can be reduced. The resistance value of the protection resistor can be set as large as possible, and the effect of protecting the superconducting magnet is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing another embodiment of the present invention, FIG. 3 is a circuit diagram showing a conventional technique, and FIG. 3 is a graph showing the potential at the time of normal conduction transition of each coil. 1,2… Coil, 17… Protective resistor, 18… Switch, 19… Excitation power supply, 21… Superconducting magnet.

Claims (6)

(57) [Claims] A superconducting magnet comprising a plurality of coils connected in series is protected by at least one protection resistor, and the protection resistor is connected in parallel with the superconducting magnet and quenches the normal conduction transition of the superconducting magnet. In the method of protecting a superconducting magnet, which is detected by a detector and a controller operates in response to a signal from the quench detector to close the superconducting magnet and the protection resistor, the coil located substantially at the center of the series A method for protecting a super-electric magnet, comprising: causing the normal conduction rotation to occur; and restricting a voltage generated by the coil to an allowable insulation voltage or less. 2. The method for protecting a superconducting magnet according to claim 1, wherein, when the coil is wound by one wire, a portion of the coil where a magnetic field is high is located at a center and connected in series. . 3. When the coil is wound by one wire, the portion of the coil where the temperature of the wire becomes high at the time of normal conduction transition is located at the center and connected in series. The method for protecting the superconducting magnet described. 4. The method for protecting a superconducting magnet according to claim 1, wherein, when the coil is wound by one wire, a portion of the coil where a magnetic field is reduced is connected to both ends of an excitation power supply. 5. The coil according to claim 1, wherein, when the coil is wound by one wire, portions of the coil at which the temperature of the wire does not increase at the time of normal conduction transition are connected to both ends of an excitation power supply. Superconducting magnet protection method. 6. At least one protection resistor for protecting a superconducting magnet formed by connecting a plurality of coils in series, connecting the protection resistor in parallel with the superconducting magnet, and detecting a normal conduction transition of the superconducting magnet. A quench detector, and a controller that operates in response to a signal from the quench detector and that operates a controller to close the superconducting magnet and the protection resistor. A protection device for a superconducting magnet, wherein a coil is disposed substantially at the center of a series.