JP3667954B2 - Quench protection circuit for superconducting magnet - Google Patents

Quench protection circuit for superconducting magnet Download PDF

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JP3667954B2
JP3667954B2 JP26368097A JP26368097A JP3667954B2 JP 3667954 B2 JP3667954 B2 JP 3667954B2 JP 26368097 A JP26368097 A JP 26368097A JP 26368097 A JP26368097 A JP 26368097A JP 3667954 B2 JP3667954 B2 JP 3667954B2
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superconducting
superconducting magnet
section
coil
protection circuit
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JPH11102807A (en
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修 尾崎
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Kobe Steel Ltd
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Kobe Steel Ltd
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Description

【０００１】
【発明の属する技術分野】
本発明は、超電導マグネットのクエンチ保護回路に関し、詳細には種々の物性測定装置、核磁気共鳴（ＮＭＲ）分析装置、ＮＭＲ断層映像装置などに用いられている超電導マグネットにおいて、その超電導マグネットがクエンチを発生した場合に、そのクエンチによって超電導コイルが破損するのを防ぐ、超電導マグネットのクエンチ保護回路に関するものである。
【０００２】
【従来の技術】
超電導マグネットは、一般に、NbTi合金（以下単にNbTiと言う）、 Nb3Sn化合物（以下単に Nb3Snと言う）などの超電導線を巻いた空心マグネットであって、超電導状態を維持するために冷却容器（クライオスタット）に入れて使用される。また超電導マグネットは、高い磁場を大きな空間に確保でき、その臨界磁場（超電導性を保持できる最高磁場) は、通常、NbTi線で11Ｔ（テスラ) 、 Nb3Sn線で23Ｔである。
【０００３】
ところで、上記超電導マグネットにおいては、機械的な擾乱等（電磁力による超電導線間の動き等の物理的な要因）によって超電導状態が破れる現象（クエンチ）を生じることが知られている。このようなクエンチが発生すると、電気抵抗を持った常電導部分が超電導マグネットのコイル内に生じることになる。例えば、図５に示すような回路構成の超電導マグネットにおいてクエンチが発生した場合、超電導マグネット11のインダクタンスがクエンチを発生した部分の超電導コイル12部分の電気抵抗値に比べて非常に大きいと、超電導マグネット11に流れている電流の減衰が遅くなる。その結果、超電導コイル12の常電導部分がジュール発熱によって熱暴走し焼損するおそれが生じることになる。なお、図５において、符号13は超電導コイル12に並列に接続した保護抵抗、14は電源をそれぞれ示す。
【０００４】
そこで、上記の問題を避けるために、従来は図６に示すように超電導マグネット11の超電導コイル12を複数のセクションａ〜ｃに分割し、その各々のセクションａ、ｂ、ｃに保護抵抗13を並列に接続した回路構成を採用している。この回路構成とすることによって、超電導コイル12のクエンチが発生した部分の電流は、クエンチした部分の電気抵抗値と、そのクエンチした部分を含んでいるセクションａ（又はｂ又はｃ）が持つインダクタンスの比に応じて減衰するが、超電導マグネット11全体のインダクタンスに比べて各セクションａ、ｂ、ｃのそれぞれが持つインダクタンスは小さいので、超電導コイル12のクエンチした部分の電流値の減衰は図５の回路構成の時よりも早くなり、クエンチした部分の焼損を防ぐことができる。クエンチしたセクションａ以外のセクションｂ、ｃでは、セクションａに蓄えられていた電磁エネルギーが電磁誘導によって転送され、セクションｂ、ｃの電流値が上昇する。また、クエンチ中の磁場変動による交流損失によってセクションｂ、ｃの超電導状態の部分が温度上昇を起こし、臨界電流値が減少する。その結果、セクションｂ、ｃで誘導によって増加した電流値が、交流損失による温度上昇で減少した臨界電流値を超えると、セクションｂ、ｃでもクエンチが発生し、セクションｂ、ｃにおいても電流値はセクションａと同等の早さで減衰することになる。
【０００５】
【発明が解決しようとする課題】
しかしながら、従来より用いられている２種類以上の異なる線種（例えばNbTi線と Nb3Sn線など）を組合せた超電導マグネットの場合には、上述した図６に示すようなセクション化を採用しても、線種間に温度マージンの差があるため、温度マージンの大きいセクションではクエンチの発生が他の温度マージンの小さいセクションよりも遅くなることになり、温度マージンの小さいセクション内にクエンチが発生した場合、温度マージンの大きいセクションに過度の誘導電流が流れることになる。その結果、温度マージンの大きいセクションに大きな電磁力がかかり機械的に破損することになる。なお、ここで言う温度マージンとは使用中の極低温温度から臨界温度までの温度差を意味する。
【０００６】
そこで、本発明は、上記従来技術の問題点を改善するためになしたものであって、その目的は、２種類以上の異なる線種を組合わせた超電導マグネットを対象として、超電導マグネットにクエンチが発生しても、そのクエンチによって超電導コイルが機械的に破損したり、焼損することのない、超電導マグネットのクエンチ保護回路を提供するものである。
【０００７】
【課題を解決するための手段】
上記の目的を達成するために、本発明に係る超電導マグネットのクエンチ保護回路は、複数の線種の超電導コイルからなる超電導マグネットを複数のセクションに分割し、セクション毎の超電導コイルに保護抵抗を並列に接続してなる超電導マグネットのクエンチ保護回路において、線種が異なり且つ線種間に温度マージンの差を有する超電導コイルの１部ずつが、線種の異なる超電導コイルのセクション内に含まれるように接続され、更に、並列に接続されている保護抵抗にダイオードを直列に接続してなるものである。
【０００８】
本発明では、複数の線種の超電導コイルからなる超電導マグネットにおいて、温度マージンが高い線種と低い線種が同一のセクション内に接続されているので、そのセクション内では、温度マージンの高い線種の部分がクエンチを起こさなくても、温度マージンの低い線種の部分が早期にクエンチを起こすので、そのセクション内に電気抵抗が生じ、これにより、そのセクションに過度の電流が誘起されなくなり、そのセクション内の温度マージンの高い線種の超電導コイルが電磁力によって機械的に破損するのを防ぐことができる。
【０００９】
上記本発明に係る超電導マグネットのクエンチ保護回路においては、並列に接続されている保護抵抗にダイオードを直列に接続している。このようにダイオードを接続すると、次のような更なる作用効果が期待される。すなわち、超電導マグネットを励磁するとき、超電導マグネットの両端及び分割した各セクションの両端に、励磁速度に応じて電位差が生じる。それ故、保護抵抗を単に並列に接続している場合は、保護抵抗にも励磁中は電流が流れており、保護抵抗でジュール発熱が起きる。その結果、超電導マグネットの冷却に用いている液体ヘリウム等の寒剤の蒸発が増加することになる。これに対して、保護抵抗とダイオードを直列に接続した場合、励磁中に超電導マグネットの両端及び分割した各セクションの両端に電位差が生じても、その電位差がダイオードのオン電圧以下であるならば保護抵抗に電流は流れないので、寒剤の蒸発が増加することを防ぐことができる。
【００１０】
【発明の実施の形態】
図１は、本発明に係る超電導マグネットのクエンチ保護回路の説明図である。この図示の回路において、超電導マグネット１は、液体ヘリウム中で10Ｔ以上の磁場を発生させるために、超電導コイル２の内層側に20Ｔを越す臨界磁場を有する Nb3Sn線を巻線した Nb3Snコイル部３を、その外層側に臨界磁場の低いNbTi線を巻線したNbTiコイル部４を配置して構成した。そして更に、 Nb3Snコイル部３は１つのセクションａのみで、またNbTiコイル部４は４つのセクションｂ〜ｅに分割して構成すると共に、 Nb3Snコイル部３のセクションａとNbTiコイル部４のセクションｂのそれぞれに、セクションａにはNbTiコイル部４のNbTi線コイルの１部分５を、セクションｂには Nb3Snコイル部３の Nb3Sn線コイルの１部分６を含むように接続し、更にセクションａ〜ｅの各セクションの超電導コイルに保護抵抗７を並列に接続した回路構成となっている。なお、図において、符号８は電源をそれぞれ示す。
【００１１】
次に、上記回路構成からなる超電導マグネット１を用い、定格の磁場まで励磁すると共に、外層側のセクションｅの部分を強制クエンチヒータ（図示せず）によってクエンチさせ、その時の各セクションａ〜ｅの電流値を測定した。また、比較のため、図２に示す従来方式によってセクションａ〜ｅに分割して接続した回路を備える超電導マグネット11の各セクションａ〜ｅの電流値を、同様にして測定した。本発明に係る超電導マグネットのクエンチ保護回路の場合の測定結果を図３に、従来方式によってセクション分割して接続した回路の場合の測定結果を図４にそれぞれ示す。
【００１２】
本発明に係る超電導マグネットのクエンチ保護回路の場合には、図３より明らかなように、セクションｅを強制的にクエンチさせても、他のセクションａ〜ｄの電流値のピークは、初期電流値（時間０の時の電流値）よりも高くなるが、その値は低く、特に Nb3Sn線コイルとNbTi線コイルとを含むように構成したセクションａとセクションｂでもそれ程高くならないことが分かる。従って、このようにセクションａ、ｂに過度の電流が誘起されなかったことから、温度マージンの高い Nb3Sn線コイルを含むセクションａ、ｂにおいて、温度マージンの高い Nb3Sn線コイルが電磁力によって機械的に破損するのを防ぐことができた。
【００１３】
これに対して、従来方式によってセクション分割して接続した回路の場合には、図４より明らかなように、セクションｅを強制的にクエンチさせた場合、温度マージンの低いNbTi線コイルからなるセクションｂ〜ｃにおいてはその電流値のピークは、初期電流値（時間０の時の電流値）よりも高くなるものの、その値は低い。しかし、温度マージンの高い Nb3Sn線コイルからなるセクションａでは２倍以上の電流値が誘起されていることが分かる。従って、この場合には、Nb3Sn 線コイルからなるセクションａに働く電磁応力は、定常時の約２倍になったため、この過大な電磁応力によってセクションａ内のNb3Sn 線コイルが塑性変形を起こし、機械的に損傷を受けていた。
【００１４】
【発明の効果】
以上説明した通り、本発明に係る超電導マグネットのクエンチ保護回路によれば、超電導マグネットがクエンチを発生しても、特定のセクションに過度の電流が誘起されないことから、そのクエンチによって超電導コイルが機械的に破損したり、焼損するのを防ぐことができる。
【図面の簡単な説明】
【図１】本発明に係る超電導マグネットのクエンチ保護回路の説明図である。
【図２】従来方式によってセクション分割して接続した回路の説明図である。
【図３】本発明に係る超電導マグネットのクエンチ保護回路の場合のクエンチ時の電流変化を示すグラフ図である。
【図４】従来方式によってセクション分割して接続した回路の場合のクエンチ時の電流変化を示すグラフ図である。
【図５】従来のセクション分割しない場合の超電導マグネットの回路の説明図である。
【図６】従来のセクション分割した場合の超電導マグネットの回路の説明図である。
【符号の説明】
１：超電導マグネット ２：超電導コイル ３： Nb3Snコイル部
４：NbTiコイル部 ５：NbTiコイル部のNbTi線コイルの１部分
６： Nb3Snコイル部の Nb3Sn線コイルの１部分 ７：保護抵抗
８：電源
ａ〜ｅ：超電導コイルを分割して接続したセクション[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a quench protection circuit for a superconducting magnet, and more specifically, in a superconducting magnet used in various physical property measuring devices, nuclear magnetic resonance (NMR) analyzers, NMR tomography devices, etc., the superconducting magnet quenches. The present invention relates to a quench protection circuit for a superconducting magnet that prevents the superconducting coil from being damaged by the quenching when it occurs.
[0002]
[Prior art]
Superconducting magnets are generally air-core magnets wrapped with superconducting wires such as NbTi alloys (hereinafter simply referred to as NbTi), Nb 3 Sn compounds (hereinafter simply referred to as Nb 3 Sn), and cooled to maintain the superconducting state. Used in a container (cryostat). A superconducting magnet can secure a high magnetic field in a large space, and its critical magnetic field (the highest magnetic field that can maintain superconductivity) is typically 11 T (Tesla) for NbTi wire and 23 T for Nb 3 Sn wire.
[0003]
By the way, in the superconducting magnet, it is known that the superconducting state is broken (quenching) due to mechanical disturbances (physical factors such as movement between superconducting wires due to electromagnetic force). When such a quench occurs, a normal conducting portion having electrical resistance is generated in the coil of the superconducting magnet. For example, when a quench occurs in a superconducting magnet having a circuit configuration as shown in FIG. 5, if the inductance of the superconducting magnet 11 is very large compared to the electrical resistance value of the superconducting coil 12 part where the quenching occurs, the superconducting magnet Attenuation of the current flowing through 11 is delayed. As a result, the normal conducting portion of the superconducting coil 12 may run out of heat due to Joule heat generation and burn out. In FIG. 5, reference numeral 13 denotes a protective resistor connected in parallel to the superconducting coil 12, and 14 denotes a power source.
[0004]
Therefore, in order to avoid the above problem, conventionally, as shown in FIG. 6, the superconducting coil 12 of the superconducting magnet 11 is divided into a plurality of sections a to c, and a protective resistor 13 is provided in each of the sections a, b and c. A circuit configuration connected in parallel is adopted. With this circuit configuration, the current of the portion where the quenching of the superconducting coil 12 occurs is the electric resistance value of the quenched portion and the inductance of the section a (or b or c) containing the quenched portion. Attenuation depends on the ratio, but since the inductance of each section a, b, c is smaller than the inductance of the entire superconducting magnet 11, the attenuation of the current value of the quenched portion of the superconducting coil 12 is the circuit of FIG. It becomes faster than the time of construction, and burning of the quenched part can be prevented. In the sections b and c other than the quenched section a, the electromagnetic energy stored in the section a is transferred by electromagnetic induction, and the current values of the sections b and c increase. In addition, due to the AC loss due to the magnetic field fluctuation during quenching, the temperature of the superconducting portions of the sections b and c increases, and the critical current value decreases. As a result, when the current value increased by induction in the sections b and c exceeds the critical current value decreased due to the temperature rise due to the AC loss, the quench occurs in the sections b and c, and the current value also in the sections b and c It will decay at the same rate as section a.
[0005]
[Problems to be solved by the invention]
However, in the case of a superconducting magnet combining two or more different types of wires used conventionally (for example, NbTi wire and Nb 3 Sn wire), the sectioning shown in FIG. 6 described above is adopted. However, because there is a difference in temperature margin between line types, quenching occurs in a section with a large temperature margin, which is slower than other sections with a small temperature margin. In this case, an excessive induced current flows in a section having a large temperature margin. As a result, a large electromagnetic force is applied to a section having a large temperature margin, resulting in mechanical damage. Here, the temperature margin means a temperature difference from a cryogenic temperature in use to a critical temperature.
[0006]
Accordingly, the present invention has been made to improve the above-mentioned problems of the prior art, and its purpose is to quench a superconducting magnet for a superconducting magnet in which two or more different wire types are combined. The present invention provides a quench protection circuit for a superconducting magnet that does not mechanically break or burn out the superconducting coil even if it occurs.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the superconducting magnet quench protection circuit according to the present invention divides a superconducting magnet composed of superconducting coils of a plurality of wire types into a plurality of sections, and a protective resistance is arranged in parallel with the superconducting coils for each section. in quench protection circuit of the superconducting magnet formed by connecting to, one part of the superconducting coil that having a difference in temperature margin between and line types Unlike the line type, included in the section of the line type different superconducting coil In addition, a diode is connected in series to protective resistors connected in parallel .
[0008]
In the present invention, in a superconducting magnet composed of a superconducting coil of a plurality of line types, a line type having a high temperature margin and a line type having a low temperature margin are connected in the same section. Even if the part does not quench, the part of the line type with a low temperature margin will quench early, resulting in an electrical resistance in that section, which prevents excessive current from being induced in that section. It is possible to prevent the superconducting coil having a high temperature margin in the section from being mechanically damaged by electromagnetic force.
[0009]
In the quench protection circuit for a superconducting magnet according to the present invention, a diode is connected in series to a protection resistor connected in parallel . When the diode is connected in this way, the following further effects can be expected. That is, when the superconducting magnet is excited, a potential difference is generated at both ends of the superconducting magnet and both ends of each divided section according to the excitation speed. Therefore, when the protective resistors are simply connected in parallel, current also flows through the protective resistors during excitation, and Joule heating occurs in the protective resistors. As a result, evaporation of cryogen such as liquid helium used for cooling the superconducting magnet increases. On the other hand, when a protective resistor and a diode are connected in series, even if a potential difference occurs at both ends of the superconducting magnet and both ends of each divided section during excitation, protection is provided if the potential difference is less than the diode on-voltage. Since no current flows through the resistor, it is possible to prevent the evaporation of the cryogen from increasing.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is an explanatory diagram of a quench protection circuit for a superconducting magnet according to the present invention. In the circuit of this illustration, the superconducting magnet 1 in order to generate a magnetic field above 10T in liquid helium, Nb 3 Sn that winding the Nb 3 Sn wire having a critical magnetic field of over 20T on the inner layer side of the superconducting coil 2 The coil part 3 was configured by arranging an NbTi coil part 4 wound with an NbTi wire having a low critical magnetic field on the outer layer side. Further, the Nb 3 Sn coil portion 3 is composed of only one section a, and the NbTi coil portion 4 is divided into four sections b to e, and the section a of the Nb 3 Sn coil portion 3 and the NbTi coil portion. Each of the four sections b includes a portion 5 of the NbTi wire coil of the NbTi coil portion 4 in the section a, and a portion 6 of the Nb 3 Sn wire coil of the Nb 3 Sn coil portion 3 in the section b. The circuit configuration is such that the protective resistors 7 are connected in parallel to the superconducting coils of the sections a to e. In the figure, reference numeral 8 denotes a power source.
[0011]
Next, the superconducting magnet 1 having the above circuit configuration is used to excite the rated magnetic field, and the section e on the outer layer side is quenched by a forced quench heater (not shown). The current value was measured. For comparison, the current values of the sections a to e of the superconducting magnet 11 having a circuit divided and connected to the sections a to e by the conventional method shown in FIG. FIG. 3 shows the measurement results in the case of the quench protection circuit for the superconducting magnet according to the present invention, and FIG. 4 shows the measurement results in the case of a circuit connected by dividing the section according to the conventional method.
[0012]
In the case of the quench protection circuit for a superconducting magnet according to the present invention, as apparent from FIG. 3, even if the section e is forcibly quenched, the peak of the current value in the other sections a to d is the initial current value. Although it is higher than (current value at time 0), the value is low, and it can be seen that section a and section b configured to include the Nb 3 Sn wire coil and the NbTi wire coil are not so high. Therefore, since no excessive current was induced in the sections a and b in this way, in the sections a and b including the Nb 3 Sn wire coil having a high temperature margin, the Nb 3 Sn wire coil having a high temperature margin is electromagnetic force. It was possible to prevent mechanical damage.
[0013]
On the other hand, in the case of the circuit connected by dividing the section by the conventional method, as is clear from FIG. 4, when the section e is forcibly quenched, the section b composed of the NbTi wire coil having a low temperature margin. In c, the peak of the current value is higher than the initial current value (current value at time 0), but the value is low. However, it can be seen that a current value more than twice is induced in the section a composed of the Nb 3 Sn wire coil having a high temperature margin. Therefore, in this case, the electromagnetic stress acting on the section a composed of the Nb 3 Sn wire coil is about twice that in the steady state, so that the excessive electromagnetic stress causes the Nb 3 Sn wire coil in the section a to be plastically deformed. And was mechanically damaged.
[0014]
【The invention's effect】
As described above, according to the quench protection circuit for a superconducting magnet according to the present invention, even if the superconducting magnet generates a quench, no excessive current is induced in a specific section. Can be prevented from being damaged or burned out.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a quench protection circuit for a superconducting magnet according to the present invention.
FIG. 2 is an explanatory diagram of a circuit which is divided into sections and connected by a conventional method.
FIG. 3 is a graph showing a current change during quenching in the case of a quench protection circuit for a superconducting magnet according to the present invention.
FIG. 4 is a graph showing a current change at the time of quenching in the case of a circuit connected by dividing a section by a conventional method.
FIG. 5 is an explanatory diagram of a circuit of a conventional superconducting magnet without section division.
FIG. 6 is an explanatory diagram of a circuit of a superconducting magnet when a conventional section is divided.
[Explanation of symbols]
1: superconducting magnet 2: superconducting coil 3: Nb 3 Sn coil unit 4: NbTi coil unit 5: 1 parts of the NbTi wire coil of NbTi coil section 6: Nb 3 Sn coil portion of the Nb 3 1 part of Sn coils 7: Protective resistor 8: Power source a to e: Section in which superconducting coils are divided and connected

Claims (2)

複数の線種の超電導コイルからなる超電導マグネットを複数のセクションに分割し、セクション毎の超電導コイルに保護抵抗を並列に接続してなる超電導マグネットのクエンチ保護回路において、線種が異なり且つ線種間に温度マージンの差を有する超電導コイルの１部ずつが、線種の異なる超電導コイルのセクション内に含まれるように接続され、更に、並列に接続されている保護抵抗にダイオードを直列に接続してなることを特徴とする超電導マグネットのクエンチ保護回路。Dividing the superconducting magnet comprising a plurality of line types of the superconducting coil into a plurality of sections, the quench protection circuit of the superconducting magnet formed by connecting a protective resistor in parallel to the superconducting coil in each section, and varies linetype Senshu one part of the superconducting coil that having a difference in temperature margin between are connected to be included within the section of the line type different superconducting coil, further, a diode in series with the protection resistor connected in parallel A superconducting magnet quench protection circuit characterized by being connected . 複数の線種の超電導コイルからなる超電導マグネットを複数のセクションに分割し、セクション毎の超電導コイルに保護抵抗を並列に接続してなる超電導マグネットのクエンチ保護回路において、線種が異なり且つ線種間に温度マージンの差を有する超電導コイルの１部ずつが、線種の異なる超電導コイルのセクション内に含まれるように接続されてなるとともに、複数の線種がＮｂＴｉ合金とＮｂ ３ Ｓｎ化合物であることを特徴とする超電導マグネットのクエンチ保護回路。 In a superconducting magnet quench protection circuit in which a superconducting magnet consisting of a superconducting coil of multiple wire types is divided into a plurality of sections and a protective resistance is connected in parallel to the superconducting coil of each section, the wire types are different and between wire types Each of the superconducting coils having a difference in temperature margin is connected so as to be included in the sections of the superconducting coils having different wire types, and the plurality of wire types are NbTi alloy and Nb 3 Sn compound. quench protection circuit of the superconducting magnet according to claim.
JP26368097A 1997-09-29 1997-09-29 Quench protection circuit for superconducting magnet Expired - Lifetime JP3667954B2 (en)

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DE19930404C2 (en) * 1999-07-02 2001-05-10 Bruker Ag Faellanden Actively shielded superconducting magnet arrangement with improved field interference compensation
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DE102009029379B4 (en) * 2009-09-11 2012-12-27 Bruker Biospin Gmbh Superconducting magnet coil system with quench protection to avoid local current peaks
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