JP6727470B1 - Superconducting coil protector - Google Patents

Abstract

A plurality of superconducting coils (200a, 200b) made of superconducting wires are connected in series and excited. The protection device (100) for a superconducting coil includes a superconducting coil (200a, 200b) and a parallel circuit of a first protection resistor (40a, 40b) connected in parallel with each superconducting coil (200a, 200b). In, when a quench occurs in at least one of the plurality of superconducting coils (200a, 200b), at least one end of the parallel circuit is formed to include the plurality of superconducting coils (200a, 200b). A mechanism (90) for electrically disconnecting from the path.

Description

The present invention relates to a protection device for a superconducting coil.

The superconducting coil usually has zero electric resistance, but an abnormal phenomenon (hereinafter also referred to as “quenching”) in which the superconductivity is lost inside the coil due to a sudden change in magnetic field or temperature may occur. When the quench occurs, the current before the quench occurs may be burned or the like due to the energy consumed when passing through the superconducting coil having the electric resistance.

Japanese Unexamined Patent Publication No. 9-93800 (Patent Document 1) discloses, as a superconducting coil power supply device, a plurality of superconducting coils connected in series to an excitation power source, and a DC circuit breaker that alternately disconnects the circuit during quenching in series. There is disclosed a circuit configuration in which a protection resistor that consumes energy stored in a coil is connected in parallel with a DC circuit breaker. In the configuration of Patent Document 1, when a quench occurs, all the DC circuit breakers are operated at the same time, so that each superconducting coil can be protected from burnout due to its stored energy.

JP-A-9-93800

However, in the circuit configuration of Patent Document 1, immediately after the operation in which the DC breaker opens the contacts, a large voltage may be generated at both ends of the superconducting coil due to an induced electromotive force due to a sudden change in current. As a result, in each DC breaker 70 immediately after being turned off, a comparatively large voltage may be directly applied between the opened contacts. As a result, at the moment when each DC circuit breaker is operated, an arc may occur between the contacts immediately after the DC circuit breaker is opened, and as a result, there is a concern that the protection function due to the current interruption may deteriorate.

The present invention has been made to solve such a problem, and an object of the present invention is to reduce the current cutoff effect due to arc generation at the time of current cutoff at the time of quench occurrence in a protective device for a superconducting coil. Is to enhance the protective effect of the superconducting coil.

In one aspect of the present invention, the superconducting coil protection device includes a first protection resistor. The first protection resistor is formed of a superconducting wire and is connected in parallel with each of the plurality of superconducting coils that are connected in series and excited. The protection device further includes a plurality of superconducting coils that operate when a quench occurs in at least one of the plurality of superconducting coils in a parallel circuit of each superconducting coil and the first protection resistor. A mechanism for disconnecting the formed electrical connection with the current path is provided.

According to the present invention, it is possible to suppress a decrease in the current cutoff effect due to the generation of an arc between the contacts that are electrically disconnected when a quench occurs, so that it is possible to enhance the protection effect of the superconducting coil.

FIG. 3 is a circuit diagram illustrating the configuration of the superconducting coil protection device according to the first embodiment. FIG. 3 is a circuit diagram illustrating an example of a configuration for detecting the occurrence of quench in the superconducting coil protection device according to the present embodiment. It is a circuit diagram explaining composition of a protection device of a superconducting coil concerning a comparative example. FIG. 4 is a circuit diagram in a transient state immediately after a quench occurs in the superconducting coil protection device according to the first embodiment. It is a conceptual diagram explaining the example of connection of the protective resistance with respect to a superconducting coil. FIG. 6 is a circuit diagram illustrating a configuration of a superconducting coil protection device according to a second embodiment. FIG. 7 is a circuit diagram illustrating a configuration of a superconducting coil protection device according to a third embodiment. FIG. 8 is a conceptual external view for explaining a configuration example of the cutting machine shown in FIG. 7. It is a circuit diagram explaining the structural example of the actuator of the cutting machine shown in FIG. FIG. 7 is a circuit diagram illustrating a configuration of a superconducting coil protection device according to a fourth embodiment. FIG. 11 is a circuit diagram illustrating a configuration of a superconducting coil protection device according to a modification of the fourth embodiment. FIG. 9 is a circuit diagram illustrating a configuration of a superconducting coil protection device according to a combination of a third embodiment and a modification of the fourth embodiment. It is a circuit diagram explaining the structure of the protective device of the superconducting coil which concerns on Embodiment 5. It is a circuit diagram explaining the structural example of the high voltage circuit shown by FIG.

Embodiments of the present invention will be described below in detail with reference to the drawings. In the following, the same or corresponding parts in the drawings will be denoted by the same reference numerals, and the description thereof will not be repeated in principle.

Embodiment 1.
FIG. 1 is a circuit diagram illustrating a configuration of a superconducting coil protection device according to a first embodiment.

Referring to FIG. 1, a protection device 100 according to the first embodiment is a protection device for a plurality of superconducting coils connected in series, and includes a plurality of contactors 30 and a plurality of protection resistors 40. The present embodiment will be described on the assumption that a plurality of divided superconducting coils are connected in series by dividing the superconducting coils. In the following, in order to simplify the description, the configuration of the protection device in an example in which the superconducting coil is divided into two is illustrated.

In FIG. 1, the protective resistor 40 is connected in parallel to each of the plurality of superconducting coils. Therefore, the protection resistors 40a and 40b are connected in parallel to the superconducting coils 200a and 200b, and two parallel circuits of the superconducting coil 200 and the protection resistor 40 are formed.

The contactor 30 is connected to both ends of the parallel circuit of the superconducting coil 200 and the protection resistor 40. In FIG. 1, the three contactors 30a to 30c realize a configuration in which the contactors 30 are arranged at both ends of each of the two parallel circuits including the superconducting coils 200a and 200b. Each contactor 30 has a mechanism (not shown) that switches between an electrically connected state (on state) and a disconnected state (off state) between the contacts according to a control signal from a control circuit (not shown). As a result, in each of the contactors 30a to 30c, ON (connection state) and OFF (interruption state) between the contacts are controlled.

The superconducting coils 200a and 200b are excited by operating the exciting power supply 10 with the contactors 30a to 30c turned on. Thereby, the current Ids is generated via the superconducting coils 200a and 200b and the contactors 30a to 30c in the ON state. Since the electric resistances of the superconducting coils 200a and 200b are zero, the current Isc can be a large current.

During normal operation when the electric resistance of the superconducting coil is zero, the contactors 30a to 30c are kept in the ON state, and the current Isc has a circuit configuration that flows through the contactors 30a to 30c. In the following, when the superconducting coils 200a and 200b are comprehensively shown, they are simply referred to as the superconducting coil 200. Similarly, when the other circuit elements are also comprehensively described, the subscripts a and b are omitted.

During normal operation of the superconducting coil, it is possible to stop the excitation power source 10 or disconnect the excitation power source 10 from the current path after the excitation is completed. For example, by providing the bypass paths of the exciting power source 10 formed in parallel with the superconducting wire in parallel, the current Isc can be continuously generated even if the exciting power source 10 is stopped or disconnected. Alternatively, it is possible to connect the power supply from the excitation power supply 10 during the normal operation in consideration of the loss at the connection point between the superconducting wire and the other member.

Quenching may occur in the superconducting coil due to a change in magnetic field or temperature from a normal superconducting state. When a quench occurs, the superconducting coil changes from a superconducting state with zero electrical resistance to a normal conducting state with normal conductor loss.

As described above, in the superconducting coil, since the electric resistance of the superconducting wire becomes zero, a large current can flow. Since the magnetic field is generated in proportion to the amount of current, a strong magnetic field due to a large current can be generated around the superconducting wire. By the magnetic field, a force can be applied to the magnetic body near the superconducting coil. For example, the magnetic field can be used for MRI (Magnetic Resonance Imaging) by aligning the movement of water molecules in the body.

However, the superconducting coil also receives a force due to the reaction that gives a force to the surrounding magnetic body. Since heat is always generated when an object moves, frictional heat in the superconducting coil is generated by the force, and the superconducting coil is heated. Here, heat is merely a macroscopic expression of the movement of electrons, and in a microscopic expression, the thermal movement of electrons can be explained by following a Gaussian distribution. Since it follows a Gaussian distribution, even if a weak frictional heat is generated, electrons that undergo a vigorous thermal motion will be generated in the superconducting wire. Such electrons serve as a trigger, and the temperature around the electrons rises slightly, generating electrons that undergo more intense thermal motion. That phenomenon occurs continuously, and the temperature of the superconducting coil rises to a region not in the superconducting state, so that quenching may occur. As described above, quenching is often caused by frictional heat. The frictional heat appearing in the superconducting wire as described above is so small that it is buried in thermal noise in a normal temperature environment, but the heat capacity becomes small at a low temperature of a few [K] to 100 [K], so it is easy. Can cause a quench. Or when cooling the superconducting wire. Friction heat may be generated due to the change of the shape of superconductivity due to the thermal contraction of the superconducting wire.

Thus, it is difficult to identify when and where the quench occurs. Therefore, when the occurrence of the quench is detected, the path of the current Isc including the superconducting coils 200a and 200b is quickly cut off before the quench is expanded, and the magnetic energy accumulated in each superconducting coil is superconducted. It is necessary to consume it outside the coil by a protective resistor or the like. Thereby, the liquid helium or liquid nitrogen in the superconducting coil body and the low temperature tank for cooling the superconducting coil can be protected.

In particular, in a high-temperature superconducting wire, the quality of the material changes at a location where the temperature rises due to quenching, so that the superconducting wire itself is destroyed. This is known as burnout, but since the burned part cannot be reused, it can be reused only in the part where quenching has not occurred. If the above-mentioned protection by current interruption cannot be performed properly, quenching may spread over the entire superconducting coil, and the entire superconducting coil may burn out.

On the other hand, the low-temperature superconducting wire is unlikely to change its material, and if cooled again, the superconducting coil is often reusable. However, there is a problem that liquid helium or liquid nitrogen stored in a cooling cryostat is lost by vaporization.

For these reasons, the protective device is required to immediately shut off a large current when a quench occurs in either of the superconducting coils 200a and 200b.

FIG. 2 is a circuit diagram illustrating a configuration example for detecting the occurrence of quench in the superconducting coil protection device according to the present embodiment.

Referring to FIG. 2, in the parallel circuit of the superconducting coil 200 and the protection resistor 40, a galvanometer 45 is connected in series with the protection resistor 40 in order to detect the occurrence of quench. Thereby, the series circuit of the galvanometer 45a and the protection resistor 40a is connected in parallel with the superconducting coil 200a, and the series circuit of the galvanometer 45b and the protection resistor 40b is connected in parallel with the superconducting coil 200b. It

When the superconducting coil 200 is in the superconducting state and its electric resistance is zero, no shunt to the protective resistor 40 occurs in the parallel circuit of the superconducting coil 200 and the protective resistor 40, and the total current flows through the superconducting coil 200. Flowing As a result, the current is not detected by the galvanometer 45 when the quench has not occurred.

On the other hand, when the electric resistance of the superconducting coil 200 is not zero due to the occurrence of quench, a shunt to the protective resistor 40 occurs in the parallel circuit of the superconducting coil 200 and the protective resistor 40. As a result, when quenching occurs, a current flows through the galvanometer 45. Therefore, when the quench occurs in the superconducting coil 200a, the galvanometer 45a detects the current, and when the quench occurs in the superconducting coil 200b, the galvanometer 45b detects the current. As a result, the occurrence of quench in the superconducting coils 200a and 200b can be detected by monitoring the detection values of the galvanometers 45a and 45b by the control circuit (not shown).

In the protection device 100 of FIG. 1, when the occurrence of quench is detected in any of the superconducting coils 200a and 200b, some or all of the contactors 30a to 30c are turned off. By turning off one of the contactors 30a and 30b, in the parallel circuit of the superconducting coil 200a and the protection resistor 40a, the electrical connection with the path of the current Isc can be cut off. In particular, when both the contactors 30a and 30b are turned off, both ends of the parallel circuit can be electrically disconnected from the path of the current Isc, so that the protection performance of the superconducting coil is improved.

Alternatively, by turning off one of the contactors 30b and 30c, it is possible to disconnect the path electrical connection of the current Isc in the parallel circuit of the superconducting coil 200b and the protection resistor 40b. In particular, when both the contactors 30b and 30c are turned off, both ends of the parallel circuit can be electrically disconnected from the path of the current Isc, so that the protection performance of the superconducting coil is improved.

Further, if all of the contactors 30a to 30c are turned off, both ends of the parallel circuit of the superconducting coil 200a and the protection resistor 40a and both ends of the parallel circuit of the superconducting coil 200b and the protection resistor 40b are in the normal operation. By separating from the path of the current Isc, the protection performance of the superconducting coil can be further improved.

In the first embodiment, the contactors 30a to 30c are, in the parallel circuit of the superconducting coil 200 and the protection resistor 40, “mechanism for disconnecting electrical connection with the path of the current Isc including the superconducting coils 200a and 200b during normal operation. Corresponding to one embodiment. The protection resistor 40 corresponds to an example of "first protection resistor". In order to simplify the description, basically, all the contactors 30a to 30c are turned off when a quench is detected in any of the superconducting coils.

Next, a comparison with the circuit configuration of Patent Document 1 will be described in order to explain the current interruption effect at the time of detecting the occurrence of a quench in the protection device according to the present embodiment. FIG. 3 is a circuit diagram illustrating a configuration of a superconducting coil protection device according to a comparative example.

Referring to FIG. 3, protective device 100# according to the comparative example is a protective device for a plurality of superconducting coils 200a, 200b, similar to FIG. 1, and includes a plurality of DC circuit breakers 70 and a plurality of protective resistors. And 60.

Protective device 100# according to the comparative example is different from protective device 100 in FIG. 1 in that direct-current circuit breakers 70a to 70c are provided instead of contactors 30a to 30c. Further, in the protection device 100#, the protection resistor 60 is connected in parallel with the DC circuit breaker 70 instead of the superconducting coil 200, as in Patent Document 1. That is, in the comparative example of FIG. 3, the protection resistors 60a to 60c are connected in parallel with the DC circuit breakers 70a to 70c.

Also in the protective device 100# according to the comparative example, when the occurrence of the quench is detected in any of the superconducting coils 200a and 200b, the DC circuit breakers 70a to 70c operate to open the contacts (OFF state). Then, the current Isc flowing through the superconducting coils 200a and 200b before the occurrence of quench flows through the protective resistors 60a to 60c. Thereby, the protective resistors 60a to 60c can consume the energy stored in the superconducting coils 200a and 200b.

On the other hand, in the protective device 100# according to the comparative example, since the change in current in the superconducting coils 200a and 200b is large at the moment when the DC circuit breakers 70 are turned off, the induced electromotive force at that time causes the superconducting coil 200a, The voltage generated at both ends of 200b may increase. As a result, in each DC breaker 70 immediately after being turned off, a comparatively large voltage is directly applied between the opened contacts. If the applied voltage at this time is higher than the dielectric breakdown voltage of the DC circuit breaker 70 in this state, an arc is generated between the contacts immediately after opening, so that a current path is formed in the space between the contacts. Moreover, there is a concern that the DC circuit breaker 70 will not be able to cut off the current.

Referring again to FIG. 1, in protective device 100 according to the first embodiment, protective resistors 40a and 40b are connected in parallel to superconducting coils 200a and 200b. With such a configuration, as described below, it is possible to reduce the voltage applied between the contacts opened when the contactor 30 is turned off, and suppress the generation of an arc.

FIG. 4 shows a circuit diagram in the transient state immediately after the occurrence of the quench in the protection device 100 according to the first embodiment.

Referring to FIG. 4, when the occurrence of quench is detected, some or all of the contactors 30a to 30c are turned off from the state where the contactors 30a to 30c are turned on. Since turning off the contactor 30 involves opening the electrical connection between the contacts by a physical mechanism, even when all the contactors 30a to 30c are turned off, the actual off timing between the contactors 30a to 30c will be the same. Makes a difference.

For this reason, immediately after the occurrence of the quench, a transient state occurs in which some of the contactors 30 are turned off (contacts are actually opened) while the other contactors 30 are turned on. FIG. 4 shows, as an example, a circuit diagram of a transient state when the contactor 30a is turned off before the contactors 30b and 30c are turned off.

In FIG. 4, the contactor 30a in the off state is equivalently shown by the resistance element 36 having the electric resistance Rb. When the voltage applied to both ends of the resistance element 36 is higher than the dielectric breakdown voltage, an arc is generated, and the contactor 30a is turned on to lose the current interruption function. The electrical resistance Rb (resistive element 36) corresponds to the electrical resistance between the contacts of the contactor 30 (hereinafter, also referred to as dielectric breakdown resistance) immediately before the dielectric breakdown occurs.

At the moment when the quench occurs, the current and voltage change with time and can be regarded as alternating current. It is difficult for the alternating current to flow through the superconducting coils 200a and 200b having a large inductance value. In the protection device 100 according to the first embodiment, since the protection resistors 40a and 40b are connected in parallel with the superconducting coils 200a and 200b, the above-mentioned alternating current due to the energy stored in the superconducting coils 200a and 200b causes the protection resistor 40a. , 40b. Therefore, by lowering the electrical resistance (impedance) of the protective resistors 40a and 40b, it is possible to lower the voltage applied to both ends of the superconducting coil 200 in which quenching has not occurred.

Further, even when the contactor 30a is off, the path of the current i flowing through the superconducting coil 200 is secured by the protection resistors 40a and 40b, so that the sudden change of the current i can be avoided. Thereby, the voltage (L·(di/dt)) corresponding to the induced electromotive force generated in the superconducting coil 200 having the inductance value L can be suppressed. Therefore, since the voltage generated across the superconducting coil 200 is reduced, the voltage applied between the terminals of the contactor 30a which is turned off immediately after the contactor 30a is opened can be suppressed. As a result, according to the circuit configuration of the protection device 100 according to the first embodiment, it is possible to suppress the arc generation when the contactor 30 is off, as compared with the circuit configuration of the comparative example.

Generally, the contactor 30 has a lower on-resistance than the DC breaker 70. Generally, the on-resistance of the contactor 30 is on the order of 10 [μΩ], while the on-resistance of the DC breaker 70 is on the order of 1 [mΩ].

On the other hand, the contactor 30 is more likely to generate an arc than the DC breaker 70. Both the contactor 30 and the DC breaker 70 are composed of at least two conductors, and by disconnecting the contact between the conductors, an off state in which the contacts are opened is formed. In the contactor 30, unlike the DC circuit breaker 70, since the contact surface of the conductor is not placed in a vacuum or in a gas for extinguishing an arc, an arc is relatively likely to occur between the separated conductors.

In other words, in the protection device according to the first embodiment, by using the circuit configuration (FIG. 1) that suppresses the arc generation as described above, instead of the DC breaker 70 in the comparative example, the arc is relatively moved. The contactor 30, which is likely to be generated but has a low on-resistance, can be applied as a “mechanism for disconnecting electrical connection” in a parallel circuit including the superconducting coil 200 when a quench occurs.

By using the contactor 30 having a low on-resistance, it is possible to suppress the amount of heat generated by Joule heat in the contactor 30 when no quench occurs. By suppressing the amount of heat generation, it is possible to arrange the contactor 30 in the low temperature tank filled with liquid helium or liquid nitrogen in common with the superconducting coil 200 and the superconducting wire. As described above, since the heat capacity of liquid helium or liquid nitrogen becomes small at low temperatures, if an element with high on-resistance is used as the "mechanism for disconnecting electrical connection", it is necessary to arrange it outside the cryogenic tank. As a result, there is a concern that the structure of the device will be complicated and efficiency will be reduced.

Next, the electrical resistance of the protection resistors 40a and 40b will be described.
The sum of the voltages generated across the superconducting coils 200a and 200b is applied between the resistance element 36 shown in FIG. 4, that is, the contact of the contactor 30 in the off state. As described above, when the impedance due to the inductance of the superconducting coils 200a and 200b is sufficiently larger than the impedance due to the protective resistances 40a and 40b (for example, about 10 times or more) at the time of quenching, the electric resistance R1 , R2 is applied to the resistance element 36.

Therefore, if the sum of the electrical resistances R1 and R2 of the protection resistors 40a and 40b is smaller than the dielectric breakdown resistance Rb of the resistance element 36, that is, if Rb>R1+R2, the resistance element 36 and the protection element are protected in the state of FIG. Even if a current path including the resistors 40a and 40b is formed, it is possible to avoid generation of an arc due to dielectric breakdown.

The dielectric breakdown resistance Rb is difficult to accurately quantify because it is determined by the distance between contacts (electrodes), the material between electrodes and the like, but generally it is about 1 [kΩ] or more. is there. However, a lower value of (R1+R2) is preferable in order not to cause dielectric breakdown reliably. On the other hand, if R1 and R2 are too small, an excessive current will flow through the protection resistors 40a and 40b when a quench occurs. Therefore, in practice, the electrical resistances R1 and R2 of the protection resistors 40a and 40b can be determined so that (R1+R2) is lower than the dielectric breakdown resistance Rb by several tens to several hundreds [Ω].

When the protection resistors 40a and 40b are not connected in parallel with the superconducting coil 200 as in the comparative example, the equivalent frequency f of the alternating current when the quench occurs and the inductance of each of the superconducting coils 200a and 200b. When L1 and L2 are used, it is necessary to satisfy Rb>2·π·f·(L1+L2) in order to prevent dielectric breakdown. The frequency f is not constant because it changes with time, but it is usually about 1 [kHz]. Therefore, when (L1+L2) is 100 [H], 2·π·f·(L1+L2) has an impedance of about 1 [MΩ], which is sufficiently higher than the dielectric breakdown resistance Rb. For this reason, it is difficult to avoid generation of an arc due to dielectric breakdown when the contactor 30 is turned off.

Even in a system using a relatively small superconducting coil, (L1+L2) is usually 1 [H] or more, and in this case, 2·π·f·(L1+L2) is about 10 [kΩ]. Is higher than about 1 [kΩ] introduced as a general value of the dielectric breakdown resistance Rb. Therefore, even in such a small system, it is difficult to avoid generation of an arc when the contactor 30 is off.

FIG. 5 is a conceptual diagram illustrating an example of connecting a protective resistor to a superconducting coil.
With reference to FIG. 5, the protective resistor 40 connected between the nodes Nx and Ny can be easily attached by using a layout in which the distance between the nodes Nx and Ny corresponding to both ends of the superconducting coil 200 is shortened. It will be possible.

As described above, in the protection device according to the first embodiment, the protection resistor 40 is connected in parallel with each of the plurality of superconducting coils 200, and the superconducting coil 200 and the protection resistor 40 are connected in parallel when a quench occurs. In the above, by adopting a circuit configuration in which the "mechanism for disconnecting electrical connection" of the path of the current Isc at the time of normal operation is arranged, it is possible to suppress arc generation at the time of disconnecting electrical connection by the mechanism. As a result, when quenching occurs, it is possible to suppress a decrease in the current interruption effect due to arcing, and thus it is possible to enhance the protective effect of the superconducting coil 200.

Furthermore, by having a circuit configuration that suppresses arc generation, it is possible to apply the contactor 30, which is a current interruption element having low on-resistance while easily generating arc, as the "mechanism for disconnecting electrical connection". Become. As a result, the amount of heat generated by the contactor 30 during normal operation is suppressed, so that the "mechanism for disconnecting electrical connection" can be arranged in the low temperature tank in common with the superconducting coil 200 and the superconducting wire. As a result, it is possible to avoid complication of the device structure and decrease in efficiency.

Although the case where the number of superconducting coils is two is shown in the first embodiment, the number of superconducting coils is arbitrary as long as the number of superconducting coils is two or more through the first embodiment and each subsequent embodiment described below. Is. Usually, since the winding distance of the superconducting coil is fixed, even if there is a single coil on the electric circuit, it is often arranged in a divided manner. As a result, by connecting three or more superconducting coils, the magnetic field Often occurs.

Embodiment 2.
FIG. 6 is a circuit diagram illustrating the configuration of the superconducting coil protection device according to the second embodiment.

6, the superconducting coil protection device 110 according to the second embodiment is connected in parallel to the contactors 30a to 30c, respectively, as compared with the protection device 100 (FIG. 1) according to the first embodiment. Further provided are protective resistors 60a-60c, switch circuits 32a, 32b arranged in series with the respective protective resistors 40a, 40b, and a protective resistor 80 for the entire superconducting coils 200a, 200b.

In the configuration of FIG. 6, the switch circuit 32 corresponds to one example of the “first switch circuit”, and the protective resistor 60 corresponds to one example of the “second protective resistor”. Further, the series circuit including the switch circuit 32 and the protection resistor 40 corresponds to the “first series circuit” and is connected in parallel with each superconducting coil 200.

A series circuit of the protection resistors 40a and 40b and the switch circuits 32a and 32b is connected in parallel to the superconducting coils 200a and 200b. The protection resistor 80 is connected in parallel to the entire series circuit of the superconducting coils 200a and 200b and the contactors 30a to 30c. The configuration of the other parts of superconducting coil protection device 110 according to the second embodiment is similar to that of the first embodiment (FIG. 1), and therefore detailed description will not be repeated.

The switch circuits 32a and 32b are turned on/off according to a control signal from a control circuit (not shown). The switch circuits 32a and 32b are turned on during normal operation when the superconducting coils 200a and 200b are not quenched. However, when the quench is not generated, the electric resistance of the superconducting coils 200a and 200b is zero, so that the entire current flows through the superconducting coils 200a and 200b. Therefore, no current flows through the switch circuits 32a and 32b. Therefore, by placing the galvanometers 45a and 45b (FIG. 2) in a series circuit including the switch circuit 32 and the protection resistor 40, it is possible to detect the occurrence of quench.

Here, consider a case where the occurrence of quench is detected in the superconducting coil 200a. According to the occurrence of the quench, as in the first embodiment, first, the contactors 30a to 30c are turned off. When the contactors 30a to 30c are off, the switch circuits 32a and 32b are maintained in the on state. Therefore, when the contactors 30a to 30c are off, the protective resistors 40a and 40b are connected in parallel to the superconducting coils 200a and 200b. As a result, as in the first embodiment, the voltage generated at both ends of superconducting coils 200a and 200b is suppressed, so that it is possible to suppress the generation of arc when the contactors 30a to 30c are off.

After the contactors 30a to 30c are turned off, the switch circuits 32a and 32b are controlled to be turned off from on. For example, the switch circuits 32a and 32b can be turned off after a lapse of a fixed time measured by a timer or the like from the start of the off operation of the contactors 30a to 30c.

After the switch circuits 32a and 32b are turned off, the stored energy of the superconducting coils 200a and 200b may be consumed by the current flowing through the series circuit of the superconducting coils 200a and 200b, the protective resistors 60a to 60c, and the protective resistor 80. it can.

As described in the first embodiment, the electrical resistances of the protection resistors 40a and 40b are required to be set low in order to suppress the arc when the contactors 30a to 30c are off. Therefore, there is a concern that the amount of current when the stored energy of the superconducting coils 200a and 200b is consumed by the protective resistors 40a and 40b becomes large.

In the protection device 100 according to the second embodiment, each of the electrical resistances of the protection resistors 60a to 60c connected in parallel with the contactors 30a to 30c is equal to each of the protection resistors 40a and 40b connected in parallel with the superconducting coils 200a and 200b. Higher than the electrical resistance of. As a result, it is possible to reduce the amount of current when the stored energy of the superconducting coils 200a and 200b is consumed after the contactors 30a to 30c are turned off. Furthermore, by providing the protection resistor 80, the current can be further reduced.

If the electric resistances of the protection resistors 40a and 40b are too low, the current flowing through the superconducting coils 200a and 200b and the switch circuits 32a and 32b becomes excessively large, so that an arc is generated when the switch circuits 32a and 32b are turned off. Is concerned. Therefore, it is preferable that the electrical resistance of each of the protective resistors 40a and 40b be within 1/10 of the electrical resistance of each of the protective resistors 60a to 60c.

It is expected that a large current will momentarily flow through the switch circuits 32a and 32b when a quench occurs, but since the current is generally applied for a short time of several [ms] or less, the current withstand capabilities are compared. It is also possible to use a relatively small element. For example, by using a power semiconductor element such as an IGBT (Insulated Gate Bipolar Transistor) or a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), a switch circuit 32a, 32b is formed by an element that does not physically open and close between conductors. Can be configured. As a result, the switch circuits 32a and 32b can be turned on/off at a higher speed than the DC breaker 70 and the contactor 30, and the on/off control is also easy.

Generally, regarding the on/off response speed, the contactor is on the order of 1 [ms], whereas the power semiconductor element is on the order of 10 [ns], and the power semiconductor element is on the order of the contactor. High-speed operation of 4 to 5 digits or more is possible. Therefore, when a quench occurs, after confirming that the contactors 30a to 30c are off, the switch circuits 32a and 32b can be quickly turned off to switch the current path due to the energy stored in the superconducting coils 200a and 200b to a high resistance path. is there.

As a result, according to the superconducting coil protection device of the second embodiment, in addition to the effect described in the first embodiment, the amount of current after the contactor 30 is turned off can be reduced. As a result, the effect of protecting the superconducting coil can be further enhanced by reducing the Joule heat generated at the quenching point.

Since the protective resistors 60a to 60c and the protective resistor 80 are energized to consume all the magnetic energy stored in the superconducting coils 200a and 200b, the generated Joule heat also increases. Therefore, it is preferable that the protection resistors 60a to 60c and the protection resistor 80 are arranged outside the low temperature tank in which the superconducting coils 200a and 200b are arranged and a cooling mechanism is provided.

It should be noted that the arrangement of the protective resistor 80 can be omitted in the circuit configuration of FIG. On the contrary, in the first embodiment and each of the subsequent embodiments, a circuit configuration in which the protection resistor 80 is not arranged is exemplified, but in each circuit configuration, the protection resistor 80 is additionally connected as in FIG. It is also possible to do so.

Embodiment 3.
In the third embodiment, a circuit configuration for protecting the superconducting coil by physically cutting the superconducting wire when a quench occurs will be described.

FIG. 7 is a circuit diagram for explaining the configuration of the superconducting coil protection device according to the third embodiment.
Referring to FIG. 7, a superconducting coil protection device 120 according to the third embodiment is different from the protection device 100 according to the first embodiment (FIG. 1) in place of contactors 30a to 30c. It is different in that cutting machines 90a to 90c for physically cutting the superconducting wire are provided at both ends of the coils 200a and 200b, and that protective resistances 42a and 42b corresponding to the superconducting coils 200a and 200b are further provided. .. The protection resistor 42 corresponds to an example of “third protection resistor”.

The cutting machines 90a and 90b are arranged corresponding to both ends of the superconducting coil 200a. Similarly, cutting machines 90c and 90d are arranged corresponding to both ends of the superconducting coil 200b. The cutting machine 90 physically cuts the superconducting wire at the location.

The protection resistor 40a is connected in parallel with the superconducting coil 200a between the node Nix inside the cutting place by the cutting machine 90a and the node Niy inside the cutting place by the cutting machine 90b. On the other hand, the protection resistor 42a is connected in parallel with the superconducting coil 200b between the node Nox outside the cutting place by the cutting machine 90a and the node Noy outside the cutting place by the cutting machine 90b. Therefore, the protection resistor 42a is connected in parallel to the series circuit including the superconducting coil 200a and the cutting machines 90a and 90b.

The connection relationship between the protection resistors 40b and 42b and the superconducting coil 200b and the cutting machines 90c and 90d is the same as the above-described connection relationship between the protection resistors 40a and 42a and the superconducting coil 200a and the cutting machines 90c and 90d. is there. Further, since the configuration of the other portions of protective device 120 for the superconducting coil according to the third embodiment is similar to that of the first embodiment (FIG. 1), detailed description will not be repeated.

FIG. 8 is a conceptual external view for explaining a configuration example of the cutting machine, and FIG. 9 is a circuit diagram for explaining a configuration example of the actuator of the cutting machine. Although FIG. 8 illustrates the cutting machines 90a and 90b, the cutting machines 90c and 90d corresponding to the superconducting coil 200b can also be configured in the same manner as the cutting machines 90a and 90b.

Referring to FIG. 8, each of cutting machines 90 a and 90 b has two blades 23 fixed by screws 92. The cutting machines 90a and 90b are connected to the shaft 15 which is rotated by the output of the motor 96 shown in FIG. The blades 23 are arranged such that the superconducting wires at both ends of the superconducting coil 200 are located between the two blades 23. The motor 96 corresponds to an example of “actuator”.

Therefore, according to the rotation of the shaft 15 by the operation of the motor 96, the two blades 23 operate with the screw 92 as an axis, and the superconducting wire is cut by the same principle as the scissors. Since the cutting machines 90a and 90b are connected to the common shaft 15, they operate simultaneously. As a result, at both ends of the parallel circuit of the superconducting coil 200a and the protection resistor 40a, the electrical connection by the superconducting wire is simultaneously cut off according to the operation of the motor 96. As a result, it is possible to suppress the generation of arcs associated with cutting.

The blade 23 of the cutting machine 90 can be prevented from obstructing the magnetic field generated by the superconducting coils 200a and 200b by being made of a non-magnetic material. Furthermore, by making the cutting machines 90a and 90b with an insulator, even if the blade 23 is in contact with the superconducting coils 200a and 200b, the cutting machine 90a and 90b can be safely maintained in this state. By making the cutting machines 90a and 90b stand by in such a state, it is possible to cut the superconducting wire in a short time with a minimum operation. Note that ceramic is an example of a non-magnetic and insulator material. The cutting machines 90a and 90b can be made of ceramic. It is relatively easy to manufacture the cutting machine 90 by molding ceramics, and the ceramics can be used in a low temperature tank containing the superconducting coils 200a and 200b. Also, the motor 96 is usually arranged outside the cryostat, and only the power is transmitted to the cutting machines 90a and 90b inside the cryostat.

In addition, in FIG. 8, the configuration of scissors is illustrated for the cutting machine 90, but when a force is applied to one place such as a puncher for stationery, the superconducting wire is cut at a plurality of places at the same time, and the like. Any structure can be applied as long as the superconducting wire can be physically cut. The cutting machine 90d is preferably arranged in the low temperature tank in common with the superconducting coil 200.

Referring to FIG. 9, motor 96 is connected in series with semiconductor switch 97 between power supply wiring 11 and ground wiring 12. An output shaft (not shown) of the motor 96 is connected to the shaft 15 shown in FIG. The semiconductor switch 97 can be composed of a MOSFET, an IGBT, or the like. ON/OFF of the semiconductor switch 97 is controlled according to a control signal Sgt from the microcomputer 98.

The microcomputer 98 detects the occurrence of the quench based on the sensor signal from the sensor that detects the quench (for example, the galvanometers 45a and 45b in FIG. 2). When detecting the occurrence of the quench, the microcomputer 98 generates the control signal Sgt to turn on the semiconductor switch 97. On the other hand, when the quench is not generated, the control signal Sgt is generated so as to keep the semiconductor switch 97 off. The microcomputer 98 corresponds to an example of the “control circuit”, and also generates the on/off control signals of the contactors 30a to 30c and the switch circuits 32a and 32b in the first and second embodiments based on the sensor signal. be able to.

With the configuration shown in FIGS. 8 and 9, when the occurrence of a quench is detected, the drive current from the power supply wiring 11 is supplied to the motor 96 according to the control signal Sgt, so that the cutting machine is operated according to the operation of the motor 96. 90a and 90b operate to cut the superconducting wire. Accordingly, both ends of the parallel circuit of the superconducting coil 200a and the protection resistor 40b are electrically disconnected from the path of the current Isc in response to the occurrence of the quench.

Here, it is desirable that the motor 96 operate at high speed according to the control signal Sgt. Since the resistance value of the superconducting wire is zero, it is not necessary to give a current capacity by the cross-sectional area, and the cross-sectional area can be in the order of several [μm ² ] to several [mm ² ]. Therefore, the superconducting wire can be cut even if a small motor having a rated power of 50 [W] or less is used. Further, the response time of the small servo motor is generally about 2 [ms], but the response time is the time required until the change of the rated rotation operation is settled, while the cutting machines 90a to 90d In order to cut the superconducting wire, it is sufficient to obtain a motor output that allows the shaft 15 to make one rotation from one half rotation to one rotation.

Considering these, for example, when a servo motor that operates at a relatively high speed is applied as the motor 96, generally, it is within about 1 [μs] from the reception of the sensor signal to the output of the control signal Sgt. It is possible to set the time from the generation of the control signal Sgt to the rotation of the motor 96 within about 1 [ms].

Further, the motor 96 can cut the superconducting wire with a small operation after the start of operation. Therefore, it is possible to further speed up the cutting of the superconducting wire from the detection of quench occurrence by adding control such as increasing the drive current at the start of operation.

On the other hand, when using a relatively large servomotor when the superconducting wire to be cut is thick and the torque required for cutting is large, or when it is necessary to cut the superconducting wire at a higher speed. However, there is a concern that the dead time until the output shaft of the motor 96 actually rotates becomes large at the time of starting from the stopped state.

Even in such a case, it is possible to speed up the cutting by controlling the motor. The cause of the dead time is a frictional force acting when operating from a stopped state. In general, considering that the static friction coefficient is larger than the dynamic friction coefficient, the torque required to change the motion from the operating state is smaller than the torque required to operate from the completely stopped state. Therefore, when the quench does not occur, the motor 96 (servo motor) is operated within a range in which the cutting machines 90a to 90d do not cut the superconducting wire (for example, reciprocating operation within a minute angle range), and the occurrence of the quench is detected. Then, by controlling the motor 96 (servo motor) to the extent that the superconducting wire is cut by the cutting machines 90a to 90d, it is possible to speed up the cutting of the superconducting wire from the detection of quench occurrence. Is.

In the protection device according to the third embodiment, the cutting machine 90 is used instead of the contactor 30, so that the superconducting coils 200a and 200b are included by the ON resistance of the contactor 30 and the like when the quench is not generated (normal operation). No extra electric resistance is applied to the current path. As a result, in addition to the effects described in the first and second embodiments, the loss (Joule heat) generated in the protection device during normal operation can be suppressed. This is an effect obtained by physically cutting the superconducting wire regardless of the opening of the contacts to realize an "electrically disconnecting mechanism" in the parallel circuit including the superconducting coils 200a and 200b.

On the other hand, the physical cutting of the superconducting wire causes irreversible damage to the device, so it is desirable that the number of cutting points is small in order to speed up the recovery. It is understood that in order to interrupt the current path including the superconducting coils 200a and 200b during the normal operation when a quench occurs, it is sufficient to cut the superconducting wire at one place of the current path. In the circuit configuration of FIG. 7, two or more cutting machines 90a to 90d are arranged corresponding to both ends of each superconducting coil 200, that is, two superconducting coils 200a and 200b. Therefore, in particular, by cutting both ends of the superconducting coil in which the quench has occurred, it is possible to separate the quenching part and the normal part.

For example, when the superconducting coil 200a is quenched, only the cutting machines 90a and 90b operate, while the cutting machines 90c and 90d are maintained in a stopped state. As a result, the superconducting coil 200b can be reused after the stored energy is consumed by the protective resistors 40b, 42a, 42b.

After the operation of the cutting machine 90, the stored energy in the superconducting coil (for example, 200a) in which the quench is generated is consumed by the protective resistance (for example, 40a) connected in parallel with the superconducting coil. On the other hand, the stored energy of the non-quenched superconducting coil (eg, 200b) is consumed by the protective resistance (eg, 42a) connected in parallel with the quenched superconducting coil (eg, 200a). ..

As a result, similarly to the protection resistor 60a in the second embodiment, the protection resistor 42a or 42b can reduce the amount of current when the stored energy of the superconducting coil is consumed. As described above, it is possible to further provide the protection resistor 80 similar to that shown in FIG. The higher the electric resistance of the protective resistance 42a or 42b, the higher the effect of reducing the amount of current, but in practice, it is preferable to determine the electric resistance in consideration of the following points.

Specifically, it is preferable that the electric resistances of the protection resistors 42a and 42b be determined depending on the allowable current amount of the wirings connected to the protection resistors 42a and 42b. As is well known, the current capacity of the wiring is proportional to the thickness of the wiring, and in general, it is about 1 [A] per 1 [mm ² ] in the steady state and 1 [mm] for the instantaneous value. ² ] is about 10 [A]. That is, the larger the cross-sectional area of the wiring, the larger the current can flow.

On the other hand, like the protection resistors 60a and 60b of the second embodiment, the protection resistors 42a and 42b are assumed to be arranged outside the low temperature tank in order not to vaporize liquid helium or liquid nitrogen in the low temperature tank. It Since the wirings at both ends of the protection resistors 42a and 42b are connected to the low temperature tank, they also affect the superconducting coil 200 during normal operation. Specifically, the thicker the wiring, the greater the external heat introduced into the inside of the low temperature tank via the wiring, which promotes vaporization of liquid helium or liquid nitrogen. Therefore, it is preferable to make the wiring thin, and for that purpose, it is necessary to increase the electric resistance of the protective resistors 42a and 42b.

For example, when a current is generated from magnetic energy in the superconducting coil when the quench occurs and ΔI [A] is reduced, the time is Δt [s], and the inductance value of the superconducting coil 200 is L [H]. The applied voltage V is represented by L·(ΔI/Δt). As an example, if Δt=1 [s], L=100 [H], and ΔI=1 [kA], then V=100 KV. At this time, if the electric resistance of the protective resistors 42a and 42b is 1 [MΩ], the current can be suppressed to 100 [kV]/1 [MΩ]=0.1 [A]. However, since a large amount of energy is consumed in the protective resistors 42a and 42b, it is preferable to dispose the cooling mechanism as in the protective resistors 60a and 60b (Embodiment 2).

On the other hand, if the electric resistances of the protection resistors 42a and 42b are increased, there is a concern that the current changes rapidly. The time constant of the current for consuming the stored energy of the superconducting coil 200 is (L/R)[s] by using the inductance value of the superconducting coil 200 and the electric resistance R of the protective resistors 42a and 42b. ] Is shown. Therefore, when the electric resistance R is large and the time constant is small, the rising speed of the electric current after the cutting of the superconducting wire by the cutting machine 90 becomes large, and energy instantaneously flows into the protective resistance 42a or 42b to generate a large amount of heat. Will occur. When these are combined, for example, the electrical resistance of the protection resistors 42a and 42b can be set to about 100 [Ω] to 100 [kΩ]. In this case, the cross-sectional area of the connection wiring with the low temperature tank can be set to about 1 to 10 [mm ² ], and the above-mentioned connection is usually used rather than the normal conduction wiring connected in series to the superconducting coil. Wiring can be made thin.

Here, the distance between the protection resistors 42a and 42b and the superconducting coils 200a and 200b, and the change in the amount of current due to the residual inductance and the residual resistance due to the connection wiring length of the protection resistors 42a and 42b and the superconducting coils 200a and 200b. Is not a big problem. Therefore, in order to prevent the Joule heat generated in the protective resistors 42a and 42b from propagating through the wiring and flowing into the superconducting coils 200a and 200b, that is, the low temperature tank, the protective resistors 42a and 42b and the superconducting resistors are suppressed. The coils 200a and 200b are preferably arranged with a distance secured, for example, about several [m].

Further, as described above, when a voltage of 100 [kV] is generated at the time of quenching, there is a concern that the superconducting coil 200 may be damaged due to easy dielectric breakdown. On the other hand, in the configuration of the third embodiment, as described above, both ends of the superconducting coil 200 in which the quench has occurred are simultaneously cut by the cutting machine 90, so that dielectric breakdown can be made less likely to occur. ..

Since the dielectric breakdown voltage is inversely proportional to the distance, when cutting only one place, the distance is short and the dielectric breakdown occurs during the cutting. On the other hand, by physically cutting both ends of the superconducting coil 200 at the same time, the dielectric breakdown distance can be increased, so that it is possible to safely cut even a portion where a large potential difference is generated. Ideally, it is desirable to cut both ends of the superconducting coil at the same time, but actually it is preferable to cut both ends with a time difference of about 1 [ms]. As described above, since the protective resistances 40a and 40b are connected in parallel to the superconducting coils 200a and 200b, the current path is secured even when only one end of the superconducting coil 200 is disconnected due to the time difference. This is because the effect of preventing arc generation can be expected if it is about 1 [ms].

Although FIG. 7 shows a configuration example in which four cutting machines 90a to 90d are arranged corresponding to both ends of each superconducting coil 200, that is, two superconducting coils 200a and 200b. In the configurations of Embodiments 1 and 2 (FIGS. 1 and 7), it is possible to replace each contactor 30 with a cutting machine 90. With such a configuration, the number of cutting machines 90 arranged is smaller than in the configuration example of FIG. 7. On the other hand, the protection resistors 42a and 42b similar to those in FIG. 7 cannot consume the stored energy of the superconducting coil 200 in which the quench has not occurred, so that the above-described effects of the protection resistors 42a and 42b can be obtained. Disappear.

Further, although FIG. 7 shows an example in which the superconducting coils 200a and 200b are formed by one long superconducting wire, the superconducting coils 200a and 200b are formed by connecting two or more superconducting wires. Even in such a case, the protection device according to the third embodiment can be applied.

Fourth Embodiment
FIG. 10 is a circuit diagram for explaining the configuration of the superconducting coil protection device according to the fourth embodiment.

Referring to FIG. 10, a protection device 130 for the superconducting coil according to the fourth embodiment is different from protection device 100 (FIG. 1) according to the first embodiment for protection resistor 40 and superconducting coil 200. In parallel, the switch circuit 17 and the DC circuit of the battery 31 as the "DC power supply" are connected in parallel. The series circuit of the switch circuit 17 and the battery 31 corresponds to one example of the “second series circuit”.

In the configuration example of FIG. 10, the DC circuit of the switch circuit 17a and the battery 31a is connected in parallel to the protection resistor 40a and the superconducting coil 200a. Similarly, the switch circuit 17b and the DC circuit of the battery 31b are connected in parallel to the protection resistor 40b and the superconducting coil 200b. The battery 31 (DC power supply) is connected to the superconducting coil 200 with the same polarity as the exciting power supply 10.

The switch circuits 17a and 17b are turned on/off according to a control signal from a control circuit (not shown), similarly to the switch circuits 32a and 32b of the second embodiment. The switch circuits 17a and 17b are turned off during normal operation when the superconducting coils 200a and 200b are not quenched. As a result, when no quench occurs, a current path similar to that of the first embodiment is formed.

When the quench occurs, an electric resistance is generated in the superconducting coil 200, which causes a voltage drop. Further, due to the change of the current i of the superconducting coil 200, a voltage indicated by L·(di/dt) corresponding to the induced electromotive force is generated at both ends of the superconducting coil 200 (inductance value L).

Immediately after the occurrence of the quench, the electric resistance generated in the superconducting coil 200 is low, and the change in the current Isc is still small, so the voltage generated across the superconducting coil 200 is relatively small. Therefore, it is preferable to turn off the contactor 30 as soon as possible after the occurrence of quench. On the other hand, actually, from the time of the occurrence of the quench, the occurrence of the quench is detected based on the signals from the sensors (the galvanometers 45a and 45b in FIG. 2), and further, the detection of the occurrence of the quench causes the contactor 30 or the cutting machine 90 to operate. There is a time delay before the current path is cut off by.

In the protection device 130 according to the fourth embodiment, when the occurrence of a quench is detected, the switch circuit 17 corresponding to the superconducting coil 200 in which the quench has occurred is turned on. For example, when the occurrence of quench in the superconducting coil 200a is detected, the switch circuit 17a is turned on. As a result, the DC voltage Vc having the opposite polarity to the induced electromotive force can be applied to both ends of the quenched superconducting coil (for example, 200a).

Before the occurrence of the quench, the current Isc is generated in the direction from the left side to the right side on the paper surface. In the configuration of FIG. 10, when the current Isc decreases due to the occurrence of the quench, the current can be supplied from the battery 31a in the direction in which the decrease from Isc is prevented. As a result, by reducing |(di/dt)| in the superconducting coil 200, the voltage generated across the superconducting coil 200 can be reduced.

Therefore, in the protection device according to the fourth embodiment, the voltage applied between the opened contacts of the contactor 30 which is turned off when the quench occurs can be reduced as compared with the first embodiment. As a result, the effect of suppressing the occurrence of arc when the current is interrupted due to the detection of the occurrence of quench is further enhanced, so that the effect of protecting the superconducting coil 200 can be further enhanced.

In the configuration of FIG. 10, the switch circuit 17 can be turned off after the contactor 30 is safely turned off. Thereby, the stored energy of superconducting coil 200 can be consumed in the same manner as in the first embodiment.

A power semiconductor element can be used for the switch circuits 17a and 17b, similarly to the switch circuits 32a and 32b (FIG. 6). However, unlike the switch circuits 32a and 32b (FIG. 6), a current for consuming the stored energy of the superconducting coil 200 does not directly flow into the switch circuits 17a and 17b, so a low on-resistance element is selected. The need is low. On the other hand, since a large voltage may be applied, it is preferable to apply a high breakdown voltage semiconductor element made of SiC (silicon carbide) or the like to the switch circuits 17a and 17b.

In FIG. 10, as a fourth embodiment, an example in which a series circuit (fourth embodiment) of a switch circuit 17 and a battery (DC power supply) 31 is combined with the circuit configuration of the first embodiment (FIG. 1) Although described, the fourth embodiment can be combined with each of the circuit configurations described in the second and third embodiments. For this combination, in the circuit in which the contactor 30 is replaced with the cutting machine 90 in the first and second embodiments, a series circuit of the switch circuit 17 and the battery (DC power supply) 31 is connected in parallel to each superconducting coil 200. Make sure that it also includes the configuration.

Modification of the fourth embodiment.
FIG. 11 is a circuit diagram illustrating a configuration of a protection device for a superconducting coil according to a modification of the fourth embodiment.

Referring to FIG. 11, protective device 140 for the superconducting coil according to the modification of the fourth embodiment has a battery (DC power supply) 31 compared to protective device 130 (FIG. 10) according to the fourth embodiment. The difference is that a capacitor 33 connected in parallel is further provided. The polarity of the battery 31 is the same as in FIG. In the configuration example of FIG. 11, a series circuit of a battery 31a and a capacitor 33a connected in parallel and a switch circuit 17a is connected in parallel to the superconducting coil 200a. Similarly, a series circuit of the battery 31b and the capacitor 33b, which are connected in parallel, and the switch circuit 17b is connected in parallel to the superconducting coil 200b. The other configuration of protection device 140 is similar to that of protection device 130 of FIG. 10, and therefore detailed description will not be repeated.

In the configuration example of FIG. 11, the capacitor 33 is charged by the battery 31 before a quench occurs. As a result, when the switch circuit 17 is turned on when a quench occurs, it is possible to supply a current in a direction that prevents the above-described decrease of the current Isc by both the charge stored in the capacitor 33 and the battery 31. This makes it possible to enhance the effect of reducing |(dIsc/dt)| and further reduce the voltage generated across the superconducting coil 200.

The current supplied from the capacitor 33 can also be controlled by the operation of the switch circuit 17. Generally, using the amount of change ΔV of the voltage V between terminals of the capacitor, the time Δtc required for the ΔV, and the capacitance value C of the capacitor, the current Ic of the capacitor is expressed by Ic=C·(ΔV/Δtc). Be done. When the switch circuit 17 is on, the Δtc in the capacitor 33 depends on the switching speed of the switch circuit 17, that is, the time required for the switch circuit 17 to transit from the off state to the on state. By configuring the switch circuit 17 using a power semiconductor element made of GaN (gallium nitride) or SiC (silicon carbide) having a wide band gap, Δtc can be shortened to, for example, about 1 [ns]. ..

By doing so, it is possible to instantaneously generate a relatively large current even when the voltage across the capacitor 33 is on the order of several tens of [V]. As a result, the instantaneous current supply from capacitor 33 can further reduce the voltage generated across superconducting coil 200 during the transient period when arcing may occur, as compared with the fourth embodiment.

As a result, in the protection device according to the fifth embodiment, as compared with the fourth embodiment, the effect of suppressing the arc generation at the time of the current interruption accompanying the detection of the quench generation is further enhanced, so that the protection effect of the superconducting coil 200 is improved. It can be further increased.

In FIG. 11, as a modified example of the fourth embodiment, a series circuit of a battery (DC power supply) 31 and a capacitor 33 connected in parallel to the circuit configuration of the first embodiment (FIG. 1) and a switch circuit 17 is provided. However, it is also possible to combine the modification of the fourth embodiment with each of the circuit configurations described in the second and third embodiments.

As an example, FIG. 12 shows a configuration example of a superconducting coil protection device 150 according to a combination of the third embodiment and the modification of the fourth embodiment. The protection device 150 is a circuit configuration in which the series circuit according to the modification of the fourth embodiment is connected in parallel to each of the superconducting coils 200a and 200b in the protection device 120 (FIG. 7) according to the second embodiment. Have.

As in the case of the fourth embodiment, the modification of the fourth embodiment can be combined with the circuit configuration in which the contactor 30 is replaced with the cutting machine 90 in the first and second embodiments. Enter it for confirmation.

Embodiment 5.
In the fifth embodiment, a circuit configuration for applying a higher voltage to superconducting coil 200 than in the fourth embodiment and its modification when a quench occurs will be described.

FIG. 13 is a circuit diagram for explaining the configuration of the superconducting coil protection device according to the fifth embodiment.

Referring to FIG. 13, protective device 160 for the superconducting coil according to the fifth embodiment includes high voltage circuit 50 as a “DC power supply” as compared with protective device 130 (FIG. 10) according to the fourth embodiment. Different in points. The polarity of the high voltage circuit 50 is the same as that of the battery 31 in FIGS. 10 and 11.

In the configuration example of FIG. 13, the series circuit of the switch circuit 17a and the high voltage circuit 50a is connected in parallel to the superconducting coil 200a, and the series circuit of the switch circuit 17b and the high voltage circuit 50b is connected to the superconducting coil 200b. Connected in parallel. That is, in FIG. 12, the series circuit of the switch circuit 17 and the high-voltage circuit 50 corresponds to an example of the “second series circuit”. The other configuration of protection device 160 is similar to that of protection device 130 of FIG. 10, and therefore detailed description will not be repeated.

The high voltage circuits 50a and 50b can be configured by, for example, a Cockcroft-Walton circuit (FIG. 14) capable of outputting a DC voltage obtained by boosting the output voltage of the AC power supplies 35a and 35b.

FIG. 14 is a circuit diagram illustrating a configuration example of the high voltage circuit 50.
Referring to FIG. 14, the high voltage circuit 50 has a plurality of diodes 54 and a plurality of capacitors 56 connected in series between an input terminal 51 and an output terminal 52. FIG. 14 shows a two-stage Cockcroft-Walton circuit as an example.

The AC power supply 35 and the capacitor 56 are connected in parallel with the first-stage diode 54 having an anode connected to the input terminal 51. In the second and subsequent stages, the capacitor 56 is connected in parallel to the two diodes connected in series. The cathode of the diode 54 at the final stage is connected to the output terminal. As a result, the DC voltage corresponding to twice the amplitude of the AC voltage of the AC power supply 35 is held in each capacitor 56, so that the output terminal 52 can output the DC voltage with the AC voltage amplitude boosted. it can.

In FIG. 13, the output terminals 52 of the high voltage circuits 50a and 50b are connected to the switch circuits 17a and 17b, and the input terminals 51 of the high voltage circuits 50a and 50b are connected to the superconducting coils 200a and 200b. The high voltage circuits 50a and 50b are disconnected from the AC power supplies 35a and 35b after the capacitors 56 are charged. After that, when a quench occurs, the output voltage Vh from the high voltage circuits 50a and 50b is the same as the DC voltage Vc from the batteries 31a and 31b in the third embodiment (FIG. 10) in response to turning on of the switch circuits 17a and 17b. Is applied to both ends of the superconducting coils 200a and 200b.

In particular, it is known that the Cockcroft-Walton circuit illustrated in FIG. 14 can generate an instantaneous high voltage with a simple circuit configuration although the stored energy is small, and the output voltage Vh is from the battery 31 (FIG. 10). It can be higher than the DC voltage Vc. Further, the output voltage Vh of the Cockcroft-Walton circuit is a high voltage immediately after the switch circuits 17a and 17b are turned on, but is rapidly attenuated thereafter.

Thereby, in the protection device according to the fifth embodiment, when the occurrence of the quench is detected, the protection device is limited to a short time immediately after the occurrence of the quench (for example, several [ms] to several tens [ms]). A voltage higher than that of the form 4 can be applied to the superconducting coil 200. Thereby, the effect of reducing the voltage across superconducting coil 200 caused by the induced electromotive force can be enhanced more than in the fourth embodiment. Further, it is possible to prevent the occurrence of burning due to the continuous application of high voltage to the superconducting coil 200.

As a result, in the protection device according to the fifth embodiment, the voltage applied between the opened contacts of the contactor 30 which is turned off at the time of occurrence of the quench can be reduced as compared with the fourth embodiment. It is possible to further enhance the effect of suppressing arc generation when the current is interrupted due to detection.

In FIG. 14, as a fifth embodiment, a series circuit of a high voltage circuit 50 (DC power supply) 31 and a capacitor 33, which are connected in parallel, and a switch circuit 17 is added to the circuit configuration of the first embodiment (FIG. 1). Although an example of combination has been described, the embodiment is applied to each of the circuit configurations described in the second and third embodiments and each of the circuit configurations in which the contactor 30 is replaced with the cutting machine 90 in the first and second embodiments. It is also possible to combine five.

Here, the "mechanism for disconnecting electrical connection" at both ends of the superconducting coil common to all the embodiments will be further described.

As described in the first to third embodiments, the “mechanism for disconnecting electrical connection” in the present embodiment includes at least the contactor 30 and the cutting machine 90. As described above, for the "mechanism for disconnecting the electrical connection", it is desirable that the electrical resistance added by the protective device to the current path before the occurrence of the quench is smaller. With respect to the cutting machine 90, a "mechanism for disconnecting electrical connection" can be realized without adding electric resistance. The contactor 30 has a mechanism that ensures electrical connection between the contacts by contact between the conductors due to electromagnetic force. Therefore, as described above, the on-resistance of the contactor is on the order of 10 [μΩ], which is lower than the on-resistance of the DC circuit breaker (generally, on the order of 1 [mΩ]).

Here, the contactor and the DC breaker are composed of at least two conductors, and by disconnecting the physical contact between the conductors, an OFF state in which the contacts are opened is formed. The above-mentioned on-resistance is determined by the contact resistance between the conductors and the parasitic resistance depending on the dimensions of the conductors. In particular, the difference in ON resistance between the contactor and the DC breaker is caused by the difference in contact resistance between the conductors.

The contact resistance of the contactor is lower than that of the DC circuit breaker because the contactor makes contact between the conductors by electromagnetic force, whereas the DC circuit breaker mechanically makes contact between the conductors. is there. Generally, the contact resistance between conductors changes depending on the contact force pressing between the conductors when the conductors have the same cross-sectional area, Young's modulus, material, and temperature. Specifically, it is known that the contact resistance Rtc[Ω] is proportional to 1/√(Ftc) with respect to the contact force Ftc[N], and the contact resistance decreases as the contact force increases. Become.

In the contactor, it is possible to bring the conductors into contact with each other by the pressing force of the electromagnetic force, which is easier to secure a larger force than the mechanical force. For example, by increasing the exciting current, the pressing force for easily contacting the conductors can be increased.

Normally, each of the contactor and the DC circuit breaker has a normally-off structure in which a biasing force for separating the conductors is applied by a spring or the like. Then, in the contactor, when the contactor is turned on, the contact between the conductors is secured by applying the pressing force larger than the biasing force in the direction opposite to the biasing force.

On the other hand, in the DC circuit breaker, the urging force is cut by a mechanical mechanism so that the conductors come into contact with each other. For example, by operating a claw that presses a spring that can wash the applied force, the conductors can be brought into contact with each other and the contacts can be electrically connected. Due to such a difference in configuration, in the DC circuit breaker, it is difficult to increase the contact force between the conductors as compared with the contactor, and as a result, the contact resistance between the conductors tends to increase. In this way, by using the contactor that secures the electrical connection between the contacts by the contact between the conductors due to the electromagnetic force, it is possible to reduce the on-resistance of the mechanism that reversibly disconnects the electrical connection at both ends of the superconducting coil. Can be configured with.

The contactor can be turned off by releasing the electromagnetic force and not generating the pressing force. With such a configuration, the off state due to the urging force is maintained at the time of non-energization such as a power failure in which an electromagnetic force cannot be generated, so that the current can be safely cut off. Alternatively, in the contactor, it is possible to apply the electromagnetic force in the opposite direction to that in the on state, that is, the electromagnetic force in the same direction as the urging force when the contactor is off. For example, by switching one of the exciting currents in the opposite direction at the time of turning on and at the time of turning off, the switching of the direction of the electromagnetic force as described above can be realized. With such a configuration, it is possible to surely form the contactor off state even if the mechanical biasing force of the spring or the like is reduced in the contactor arranged in the low temperature tank.

The power semiconductor element can be turned on and off at high speed on the order of several tens [ns], but the on-resistance is 100 [mΩ], so a contactor is used as the “mechanism for disconnecting electrical connection”. Is preferred. It should be noted that the contactor takes about 1 [ms] to open the contacts by disconnecting the contacts between the conductors, but the contactor must be turned off at a speed that does not cause any problem in interrupting the current when a quench occurs. You can

Further, in the present embodiment, a switching element having a current interruption function and a low on-resistance can be used as a mechanism for reversibly disconnecting electrical connection instead of the contactor 30. For example, it is possible to use a switching element made of a superconducting semiconductor element as a "mechanism for disconnecting electrical connection".

Regarding the plurality of embodiments described above, including the combinations not referred to in the specification, the configurations described in the respective embodiments may be appropriately combined within the range where inconsistency or contradiction does not occur. The points that are planned from the beginning of the application should also be confirmed.

The embodiments disclosed this time are to be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description but by the scope of the claims, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

10 excitation power supply, 11 power supply wiring, 12 ground wiring, 15 shaft, 17a, 17b, 32a, 32b switch circuit, 23 blades, 30a to 30c contactor, 31a, 31b battery (DC power supply), 33a, 33b capacitor, 35a, 35b AC power supply, 36 resistance element, 40a, 40b, 42a, 42b, 60a-60c, 80 Protection resistance, 45a, 45b Galvanometer, 50, 50a, 50b High voltage circuit (DC power supply), 51 input terminal (high voltage circuit), 52 output terminal (high voltage circuit), 54 diode (high voltage circuit), 56 capacitor (high voltage circuit), 70a, 70c DC circuit breaker, 90a to 90d cutting machine, 92 screw, 96 motor, 97 semiconductor switch, 98 microcomputer, 100 , 110, 120, 130, 140, 150, 160 protection device, 200a, 200b superconducting coil, Isc current (superconducting coil), Nx, Ny node, Rb dielectric breakdown resistance, Vc, Vh DC voltage.

Claims (9)

A protection device for a plurality of superconducting coils that are composed of superconducting wires and that are connected in series and excited.
A first protection resistor connected in parallel with each of the plurality of superconducting coils;
In a parallel circuit of each of the superconducting coils and the first protection resistor, the superconducting coils are formed to include the plurality of superconducting coils when the quench occurs in at least one of the plurality of superconducting coils. The mechanism to disconnect the electrical connection with the current path,
A second protective resistor connected in parallel with the mechanism for disconnecting each of the electrical connections;
In each of the parallel circuits, a first switch circuit connected in series with the first protection resistor is provided,
In each of the parallel circuits, a first series circuit including the first protection resistor and the first switch circuit is connected in parallel with each of the superconducting coils,
The protection device for a superconducting coil, wherein the first switch circuit is controlled from on to off after the operation of the mechanism for disconnecting the electrical connection when the quench occurs. A protection device for a plurality of superconducting coils that are composed of superconducting wires and that are connected in series and excited.
A first protection resistor connected in parallel with each of the plurality of superconducting coils;
In a parallel circuit of each of the superconducting coils and the first protection resistor, the superconducting coils are formed to include the plurality of superconducting coils when the quench occurs in at least one of the plurality of superconducting coils. It has a mechanism to disconnect the electrical connection with the current path,
The mechanism for disconnecting the electrical connection is
A protection device for a superconducting coil, which has a disconnecting mechanism for physically and irreversibly disconnecting an electrical connection by the superconducting wire itself at each of both ends of each parallel circuit according to the operation of an actuator. A protection device for a plurality of superconducting coils that are composed of superconducting wires and that are connected in series and excited.
A first protection resistor connected in parallel with each of the plurality of superconducting coils;
In a parallel circuit of each of the superconducting coils and the first protection resistor, the superconducting coils are formed to include the plurality of superconducting coils when the quench occurs in at least one of the plurality of superconducting coils. It has a mechanism to disconnect the electrical connection with the current path,
The mechanism for disconnecting the electrical connection is
A cutting mechanism that physically cuts the superconducting wire at each of both ends of each parallel circuit with the operation of an actuator;
The protection device is
Further comprising a third protection resistor provided corresponding to each of the superconducting coils,
The first protection resistor is connected in parallel to the superconducting coil at a node inside the cutting point of the superconducting wire by the cutting mechanism,
The third protective resistance, the cutting points are connected in parallel to the superconducting coils on the outside of the nodes than the superconducting coil protective device. 4. The two cutting mechanisms provided at both ends of the same parallel circuit are controlled so as to operate at the same time to cut a portion of the superconducting wire including a portion where quench is generated. Superconducting coil protector. The mechanism for disconnecting the electrical connection is
A cutting mechanism that physically cuts the superconducting wire at each of both ends of each parallel circuit according to the operation of an actuator, or
The contacts are electrically connected by contact between the conductors by the electromagnetic force, while the contacts are opened by removing the electromagnetic force or generating an electromagnetic force in a direction opposite to the direction of contact between the conductors. The superconducting coil protector according to claim 1, further comprising a contactor. Further comprising a DC power supply and a second switch circuit arranged in each of the parallel circuits,
A second series circuit including the DC power source and the second switch circuit is connected in parallel to the superconducting coil,
The DC power supply is connected with the same polarity as exciting the plurality of superconducting coils,
The superconducting coil protection device according to claim 1, wherein the second switch circuit is controlled from OFF to ON when the quench occurs. 7. The superconducting coil protection device according to claim 6, further comprising a capacitor connected in parallel with the DC power supply in each of the second series circuits. The DC power supply includes a high voltage circuit connected to an AC power supply,
The superconducting coil protection device according to claim 6, wherein the high-voltage circuit outputs a voltage obtained by boosting an output voltage of the AC power supply. In each of the parallel circuits, a galvanometer connected in series with the first protection resistor,
Further comprising a controller that operates a mechanism that disconnects the electrical connection in response to detecting the occurrence of the quench based on the output of the galvanometer,
In each said parallel circuit, the series circuit containing the said 1st protection resistance and the said galvanometer is connected to each said superconducting coil in parallel, The superconductivity of any one of Claims 1-8. Coil protector.

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