Quench detection and warning system and method for a superconducting magnet based on skeleton current

Abstract

The application discloses a superconducting magnet quench detection and early warning system and method based on a skeleton current, relates to the field of superconducting magnet quench detection, and comprises the following steps: constructing an electro-thermal coupling finite element model of a superconducting magnet and a conductive skeleton; simulating different quench events based on the electro-thermal coupling finite element model; determining a quench judgment threshold and different levels of quench severity index grading thresholds according to different quench events; when the superconducting magnet quench occurs, obtaining a skeleton current signal of the current shunt of the superconducting magnet to the conductive skeleton; and based on the skeleton current signal, grading the quench of the superconducting magnet according to the quench judgment threshold and the quench severity index grading threshold to perform grading early warning and protection response. The application can nondestructively detect the quench of the superconducting magnet, realize grading evaluation and optimized protection of the quench severity, and reduce the cost of the quench monitoring system.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of superconducting magnet quench detection, and particularly relates to a superconducting magnet quench detection and early warning system and method based on skeleton current. BACKGROUND

[0002] Superconducting magnets play a core role in many high-tech fields such as medical magnetic resonance imaging, particle accelerators, controllable nuclear fusion devices and superconducting energy storage systems due to their ability to generate strong magnetic fields with almost no loss. However, the stable operation of superconducting magnets faces the inherent risk of quench. Quench refers to the sudden transition of superconductor from the superconducting state with no resistance to the normal state with resistance. If timely and effective detection and protective measures are not taken, it may lead to local overheating of the magnet and even permanent damage, causing huge economic losses and safety hazards. Therefore, developing fast and reliable quench detection and protection technology is crucial to ensure the safety and economy of superconducting magnet systems.

[0003] At present, various methods have been developed for quench detection of superconducting magnets, but each has its limitations.

[0004] (1) The existing voltage-based quench detection method faces severe challenges when applied to high-temperature superconducting coils, especially to non-insulated high-temperature superconducting coils. The inherent slow normal zone propagation speed of high-temperature superconducting materials results in weak and slow development of the voltage signal generated by quench. At the same time, voltage detection is easily disturbed by electromagnetic noise and induced voltage, forcing the detection threshold to be set too high, further delaying the identification of early quench. For non-insulated coils, the inter-turn current shunt characteristic enhances stability, but also significantly masks the voltage drop in the quench region, making it more difficult or even impossible for the traditional voltage method to detect.

[0005] (2) Existing quench detection methods are mostly limited to determining whether there is quench or not, lacking the ability to quantitatively assess the degree of quench development and potential hazards. This is not conducive to implementing a graded and optimized protection strategy, which may result in overreaction to minor disturbances (such as unnecessary complete power-off of the magnet system) or inadequate response to severe quench.

[0006] (3) Other non-voltage detection methods, such as optical fiber temperature measurement, often have problems such as invasive design, high cost, insufficient system reliability or complex implementation process. SUMMARY

[0007] The purpose of the present application is to provide a superconducting magnet quench detection and early warning system and method based on skeleton current to solve the above problems.

[0008] To achieve the above purpose, the present application provides the following solutions.

[0009] In a first aspect, this application provides a superconducting magnet quench detection and early warning system based on skeleton current, comprising: a superconducting magnet and a conductive skeleton.

[0010] An electrical contact surface is formed between the superconducting magnet and the conductive frame; when the superconducting magnet loses its quench, the current of the superconducting magnet is diverted to the conductive frame.

[0011] The conductive frame has at least two spatially separated detection connection points; the detection connection points are used to capture the current flowing through the conductive frame.

[0012] A current detection circuit is provided between the two detection connection points; the current detection circuit is used to measure the skeleton current flowing through the skeleton segment between the two detection connection points, and transmit the skeleton current signal corresponding to the skeleton current to the processing unit.

[0013] The processing unit is used to construct an electrothermal coupled finite element model of the superconducting magnet and the conductive skeleton, simulate different quench events, determine the quench judgment threshold and the quench severity index classification threshold for different levels, and perform graded early warning and protection response for quench of the superconducting magnet based on the skeleton current signal and according to the quench judgment threshold and the quench severity index classification threshold.

[0014] Secondly, this application provides a method for detecting and warning of quenching in superconducting magnets based on skeleton current, comprising the following steps.

[0015] An electrothermal coupled finite element model of a superconducting magnet and a conductive framework was constructed.

[0016] Based on the electrothermal coupling finite element model, different quench events were simulated.

[0017] Based on different quench events, determine the quench judgment threshold and the quench severity index grading threshold for different levels.

[0018] When the superconducting magnet loses quench, the current shunted from the superconducting magnet to the conductive frame is acquired.

[0019] Based on the skeleton current signal, the superconducting magnet quench is classified and protected according to the quench judgment threshold and the quench severity index grading threshold.

[0020] According to the specific embodiments provided in this application, this application has the following technical effects: By detecting the shunt current in the inherent conductive skeleton of the superconducting magnet, this application can not only timely and reliably determine the occurrence of quench, but also, by analyzing the ratio of the skeleton current to the total operating current, realize the graded judgment of the severity of quench and early warning, thereby providing more intelligent and efficient protection for the superconducting magnet.

[0021] Furthermore, this application is particularly applicable to quench detection in uninsulated and metal-insulated high-temperature superconducting magnets. As mentioned earlier, the voltage signal of such coils without complete inter-turn insulation is often suppressed by inter-turn shunt current in the early stages of quench. This application directly detects the skeleton current, which is one of the shunt paths, and can reflect the quench state more directly and sensitively. By reasonably setting the quench judgment threshold of the skeleton current, it can effectively distinguish between the small, stable, and transient inter-turn current that may exist in uninsulated or metal-insulated coils during normal operation due to conductor inhomogeneity or minor disturbances, and the large and continuously increasing skeleton shunt current caused by quench.

[0022] Finally, compared to traditional invasive designs, this application can achieve graded detection simply by detecting the skeleton current, which greatly reduces detection costs and simplifies the implementation process. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of a superconducting magnet and a conductive framework provided in an embodiment of this application.

[0025] Figure 2 This is a schematic diagram of a superconducting magnet quench detection and early warning system based on skeleton current, provided as an embodiment of this application.

[0026] Figure 3 This is a schematic flowchart of a superconducting magnet quench detection and early warning method based on skeleton current provided in an embodiment of this application.

[0027] Figure 4 This is a schematic diagram of a circuit network model structure provided in an embodiment of this application; wherein, Figure 4 (a) in the diagram is a schematic diagram of a parallel circuit of a superconducting coil and a conductor frame; Figure 4 (b) in the diagram is a schematic diagram of the circuit network model of the superconducting coil; Figure 4 (c) in the text represents a coil element. x, y ) and adjacent coil micro-element ( x+ 1 ,y The equivalent circuit diagram is shown below. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] To make the objectives, features and advantages of this application more apparent and understandable, the application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] like Figures 1-2 As shown in the figure, this application provides a superconducting magnet quench detection and early warning system based on skeleton current, including: a superconducting magnet 1 and a conductive skeleton 2.

[0031] An electrical contact surface is formed between the superconducting magnet and the conductive frame; when the superconducting magnet loses its quench, the current of the superconducting magnet is diverted to the conductive frame.

[0032] The conductive frame has at least two spatially separated detection connection points; the detection connection points are used to capture the current flowing through the conductive frame.

[0033] A current detection circuit 3 is provided between the two detection connection points; the current detection circuit is used to measure the skeleton current flowing through the skeleton segment between the two detection connection points, and transmit the skeleton current signal corresponding to the skeleton current to the processing unit 4.

[0034] The processing unit is used to construct an electrothermal coupled finite element model of the superconducting magnet and the conductive skeleton, simulate different quench events, determine the quench judgment threshold and the quench severity index classification threshold for different levels, and perform graded early warning and protection response for quench of the superconducting magnet based on the skeleton current signal and according to the quench judgment threshold and the quench severity index classification threshold.

[0035] In practical applications, the superconducting magnet is a superconducting coil, which is a single-disc or stacked disc coil wound from high-temperature superconducting tapes such as rare-earth barium copper oxide (REBCO), especially a coil without insulation or with metal insulation.

[0036] In practical applications, the conductive frame serves as the structural support component of the coil and is made of conductive materials (such as copper, aluminum, stainless steel, etc.). There is some form of electrical contact surface between this conductive frame and the superconducting coil, allowing current to be diverted to the conductive frame when the superconducting portion loses quench. Figure 2The diagram illustrates the current shunting path of the bobbin in a single-pane coil. The electrical contact surface can be achieved through strip edge contact or a specially designed surface current shunting layer.

[0037] In an exemplary embodiment, the current detection circuit specifically includes: a sampling resistor 31 and a current sensor 32; one end of the sampling resistor is connected to a detection connection point, the other end of the sampling resistor is connected to one end of the current sensor, and the other end of the current sensor is connected to another detection connection point and the processing unit.

[0038] In practical applications, this current detection circuit is connected between the two detection connection points mentioned above to accurately measure the current flowing through the skeleton segment between these two points (i.e., the skeleton current). I skeleton The core component of the current detection circuit is a current sensor, as well as auxiliary components such as a precision sampling resistor. The selection of the current sensor needs to consider its range, accuracy, response speed, and electromagnetic interference resistance.

[0039] In one exemplary embodiment, the processing unit is a microcontroller, FPGA, or dedicated quench detection logic circuit. This processing unit receives the skeleton current signal from the current detection circuit, while also knowing the total operating current of the superconducting coil. I op The processing unit is responsible for implementing a superconducting magnet quench detection and early warning method based on skeleton current.

[0040] In practical applications, at least two spatially separated detection connection points are selected on the conductive frame, including a first detection connection point and a second detection connection point. The locations of these two detection connection points should be chosen to effectively capture the current flowing through a specific part of the frame. For example... Figure 2 As shown, for a disc-shaped skeleton, one detection point can be set on the inside of the skeleton and the other on the outside of the skeleton.

[0041] like Figure 3 As shown, this application provides a method for detecting and warning of quenching in superconducting magnets based on skeleton current, which includes the following steps.

[0042] S1: Construct an electrothermal coupled finite element model of the superconducting magnet and the conductive framework.

[0043] S2: Based on the electrothermal coupling finite element model, simulate different quench events.

[0044] S3: Determine the threshold for judging queuing and the threshold for classifying the severity of queuing at different levels based on different queuing events.

[0045] S4: When the superconducting magnet loses quench, acquire the skeleton current signal of the current shunted from the superconducting magnet to the conductive skeleton.

[0046] S5: Based on the skeleton current signal, perform graded early warning and protection response for superconducting magnet quench according to the quench judgment threshold and the quench severity index grading threshold.

[0047] In one exemplary embodiment, S1 specifically includes the following steps.

[0048] Taking a superconducting coil as an example, the superconducting coil is discretized into multiple turns, and each turn is discretized into multiple coil micro-elements to construct a superconducting coil micro-element grid.

[0049] The conductive skeleton is connected as an independent parallel branch to the input and output ends of the superconducting coil micro-element mesh to construct an electrothermal coupled finite element model of the superconducting coil and the conductive skeleton; the electrothermal coupled finite element model includes a circuit network model, a heat transfer model, a magnetic field model, and boundary conditions.

[0050] In practical applications, experimental testing involves conducting controlled quench experiments on prototype coils or modules similar to those used in real-world applications. For example, quench can be induced by local heating or overcurrent, while simultaneously monitoring parameters such as the frame current, total operating current, coil voltage, and local temperature. The evolution of each physical quantity during the quench development process is analyzed to determine an appropriate threshold.

[0051] Numerical simulation: A detailed electrothermal coupled finite element model is established, considering the three-dimensional structure of the superconducting coil, the material electrothermal properties of the entire system (including the EJ characteristics of high-temperature superconductivity, thermal conductivity, inter-turn contact resistance, etc.), cooling conditions, and the initial disturbance of quench failure. Here, E represents the electric field strength, and J represents the current density. By simulating different types, locations, and energies of quench events, the response characteristics of the skeleton current are analyzed to assist in the setting and optimization of the threshold. The analysis of the skeleton current response characteristics includes recording and plotting the time evolution curve of the total skeleton current and calculating the ratio of the skeleton current to the total operating current during operation and quench failure.

[0052] The electrothermal coupled finite element model discretizes the superconducting coil to establish a detailed equivalent circuit mesh model, and strongly couples it with the heat transfer model and magnetic field model. Under boundary condition constraints, it accurately simulates the electromagnetic and thermal characteristics of the superconducting magnet during the quenching process when the frame and the input / output terminals of the coil are connected in parallel.

[0053] The construction process of the electrothermal coupling finite element model is as follows.

[0054] (1) Circuit network model: Discretize the superconducting coil into N t Turns, each turn is further discretized into n eEach coil element is a micro-coil. The entire superconducting coil is represented as a grid composed of these micro-coil elements. The skeleton is connected as an independent parallel branch to the input / output terminals of the superconducting coil, such as... Figure 4 As shown in (a)-(c), the HTS coil is a high-temperature superconducting coil. The circuit network model includes a parallel circuit of the superconducting coil and the conductor skeleton, the circuit network model of the superconducting coil, and the coil micro-element ( x, y ) and adjacent coil micro-element ( x +1 ,y The equivalent circuit of ).

[0055] a) The current parameters are explained below.

[0056] In the infinitesimal element of the coil: For the first element in the coil x Turns (1) ≤ x ≤ N t ) y One coil element (1 ≤ y ≤ n e Its current includes circumferential and radial currents.

[0057] i x,y : Flowing through the coil element ( x, y Circumferential current (helical direction).

[0058] j x,y : Flowing through the coil element ( x, y ) and adjacent turn micro elements ( x +1 ,y Radial current of the contact resistance between )

[0059] The parallel branch of the frame contains a lumped resistive element. R skeleton , I skeleton This represents the skeleton current flowing through the skeleton.

[0060] b) Other parameters of the coil element are as follows.

[0061] For each coil element ( x, y Circumferential variable resistor The equivalent resistance of the superconducting layer and the metal layer connected in parallel is as follows.

[0062] .

[0063] in, It is a coil micro element The voltage drop. When the superconducting layer is in the superconducting state, its resistance is almost zero; when quenching occurs, the resistance of the superconducting layer increases sharply, and current is diverted to the metal layer. Calculated using the following EJ relationship and parallel formula.

[0064] electric field of superconducting layer as follows.

[0065] .

[0066] in, , It is a coil micro element The effective cross-sectional area of ​​the superconducting layer, =1 μV / cm, Let be the critical current density of the infinitesimal element, which is a function of the magnetic field and temperature of the infinitesimal element. For micro elements ( x, y The magnetic field strength; For coil micro elements ( x, y Local temperature at ( ); n The power-law exponent of the EJ curve is typically 28.

[0067] Metal layer resistance as follows.

[0068] .

[0069] in, It is a metal layer on the coil micro element Temperature The resistivity below, It is the length of the infinitesimal element. It is the cross-sectional area of ​​the metal layer.

[0070] Since the superconducting layer and the metal layer are actually connected in parallel, and their current paths are the same (circumferential), their equivalent resistance is... A more precise definition would be based on the total voltage-current relationship, i.e., the coil element. voltage drop It is the common voltage of the superconducting layer and the metal layer.

[0071] .

[0072] ,

[0073] in, and For coil micro elements The metal layer current and the superconducting layer current, For coil micro elements The electric field of the superconducting layer.

[0074] In numerical implementation, According to Recalculate.

[0075] Circumferential self-inductance and mutual inductance: each coil element The voltage drop also includes the induced voltage. It is caused by the change in current of all infinitesimal elements.

[0076] .

[0077] in, It is a coil micro element and coil micro elements The mutual inductance coefficient between them, when hour, For self-perception.

[0078] Radial contact resistance For connecting coil micro elements and coil Contact resistance between them.

[0079] .

[0080] in, It is the inter-turn contact resistivity. It is the thickness of the radial contact path. It is a coil micro element With coil micro element The contact area between them.

[0081] c) Kirchhoff's laws equations are as follows.

[0082] Node Current Law (KCL): At each node, the sum of the current flowing into and out of the node is zero. Nodes are located between adjacent circumferential and radial infinitesimal elements.

[0083] The typical nodes within the coil are as follows.

[0084] .

[0085] in, i x,y-1 : Flowing through the coil element ( x, y -1) circumferential current (helical direction); j x-1,y : Flowing through the coil element ( x -1 ,y ) and adjacent turn micro elements ( x, y Radial current of the contact resistance between )

[0086] For input nodes: Total operating current Entering, part of the skeleton current Entering the skeleton, some residual current The first turn of the first micro-element enters the coil.

[0087] .

[0088] For the output node: the current flows out of the last turn of the coil. Radial current boundaries of the coil's inner and outer diameters: the radial current is zero in the radial direction of the innermost and outermost turns.

[0089] Loop Voltage Law (KVL): In every independent loop, the sum of all voltage drops is zero. For a typical closed loop in a coil, for example, a loop consisting of a coil element... , , and The resulting rectangular circuit is shown below.

[0090] .

[0091] in, It is a coil micro element The total voltage drop. It is the voltage drop across the contact resistance caused by the radial current.

[0092] d) Parallel branches of the skeleton.

[0093] The conductive framework acts as a lumped resistor It is connected in parallel with the input / output terminals of the superconducting coil.

[0094] The skeleton current is as follows.

[0095] .

[0096] in, It is the total voltage across the coil, which is the voltage difference between the coil input and output terminals obtained after solving the entire circuit network model.

[0097] (2) Heat transfer model: The energy balance equation in each coil element is as follows.

[0098] .

[0099] in, and It is a coil micro element Density and specific heat capacity (a function of temperature). It is a coil micro element Thermal conductivity (a function of temperature). It is a coil micro element The Joule heat generated in the middle, It is possible to apply to the coil micro-element External thermal disturbances (e.g., heaters) on the surface. It is a coil micro element Heat transfer between the coolant and the heat transfer fluid.

[0100] Joule heat source It is generated by the current flowing through the infinitesimal element in the circuit model and its equivalent resistance.

[0101] .

[0102] in, It is a coil micro element The volume.

[0103] Cooling as follows.

[0104] .

[0105] in, It is the heat transfer coefficient. It is the surface area exposed to the coolant. This refers to the coolant temperature.

[0106] (3) Magnetic field model: The magnetic field model is solved using the TA formula, and the governing equations are as follows.

[0107] .

[0108] Where E is the electric field, T is the current vector potential, B is the magnetic flux density, and A is the magnetomotive force. μ Where is the permeability and J is the current density, derived from the circuit network model.

[0109] (4) Critical current density: Critical current density It is the ability of superconducting materials to withstand local magnetic fields and temperatures, and it is the most important bridge connecting electricity, heat, and magnetism.

[0110] For each coil element Its critical current density The calculation depends on the local temperature at this infinitesimal element. and local magnetic field (especially its vertical component) and parallel components )as follows.

[0111] .

[0112] in, In self-field and operating temperature The critical current density below, It is the critical temperature of superconducting materials. It is the initial operating temperature of the coil. It is the critical magnetic field parameter. , and These are empirical parameters obtained by fitting experimental data.

[0113] (5) Coupled solution process: Implemented by numerical simulation software COMSOL Multiphysics or other simulation software / programming code.

[0114] 1. Initialization: Set the initial circumferential current for each coil element. and radial current .

[0115] Set the initial temperature for each microelement. .

[0116] Calculate the initial magnetic field of each micro-element based on the initial current distribution. That is, based on the initial... and Calculate each infinitesimal element .

[0117] 2. Time step iteration: For each time step Includes the following steps a) - d).

[0118] a) Solving the circuit network model (electromagnetic coupling): Based on the current time step... and Update each microelement (pass ).

[0119] Solve the system of nonlinear differential-algebraic equations involving all nodes to obtain all the... , .

[0120] Calculate the total voltage across the coil. .

[0121] Calculate the skeleton current .

[0122] b) Solving the magnetic field model: The solution obtained at the current time step... and It is used as a current source and input into the magnetic field model.

[0123] Solve the magnetic field equations and update the magnetic field distribution. .

[0124] c) Solving the heat transfer model: Based on the solution obtained at the current time step. and as well as and Calculate the Joule heat in each infinitesimal element. .

[0125] Will It is used as a heat source and input into the heat transfer model.

[0126] Solve the heat transfer equation and update the temperature at each infinitesimal element. .

[0127] d) Critical current density update: Use the updated [current density] and Recalculate the value of each coil element .

[0128] 3. Repeat step 2 until the simulation time ends or the predetermined timeout determination condition is reached.

[0129] In an exemplary embodiment, based on the electrothermal coupled finite element model, different quench events are simulated, specifically including: setting different types of quench initial disturbance events in the electrothermal coupled finite element model; wherein, the different types include local heating, local current overload and critical current decay.

[0130] Determine the operating parameters during the simulation of the initial disturbance event of the quench failure; the operating parameters include the total operating current, coolant temperature, initial temperature, and material property parameters; the material property parameters include EJ curve parameters and heat transfer physical parameters.

[0131] The electrothermal coupling finite element model is solved based on the operating parameters to simulate different quench events; the different quench events are quench events of different types, locations and energies.

[0132] In practical applications, the specific analysis process of response characteristics is as follows.

[0133] (1) Model building and discretization.

[0134] Geometric model: Based on the actual geometric dimensions of the superconducting coil and the frame, a three-dimensional model is constructed, namely the electrothermal coupling finite element model.

[0135] Mesh generation: The entire computational domain (including superconducting tape, inter-turn insulation / contact area, skeleton and cooling medium) is divided into small mesh cells (i.e. micro elements).

[0136] Physical field equations: Define partial differential equations and boundary conditions for circuit network model, heat transfer model and magnetic field model on each infinitesimal element.

[0137] (2) Simulation of initial disturbance when quench is lost.

[0138] Define the initial quench disturbance: Set different types of initial quench disturbance events in the model, including local heating, local current overload, and critical current decay.

[0139] Local heating: Applying short-term or continuous external thermal power to one or several micro-elements to simulate quenching caused by external thermal disturbances.

[0140] Local current overload: By modifying the initial current or critical current of certain micro-elements, the quench caused by uneven local current distribution is simulated.

[0141] Critical current decay: Simulates the local decrease in critical current caused by strip defects or mechanical stress, which leads to quench failure.

[0142] Parameter settings: Set the operating parameters during the simulation process, such as the total operating current. I op Coolant temperature T coolant Initial temperature T op And material property parameters (such as EJ curve parameters, heat transfer physical parameters, etc.).

[0143] (3) Solve the above electrothermal coupled finite element model by coupling.

[0144] (4) Data extraction and analysis.

[0145] Skeleton current response: Throughout the simulation, the skeleton current is recorded and plotted in real time. I skeleton The time evolution curve.

[0146] Coil internal state: Record the spatial distribution and temporal evolution of temperature, current density, electric field and magnetic field of each micro-element inside the coil.

[0147] Whirlpool Detection Criteria: Based on simulation data, determine when a coil whirlpool has occurred (e.g., when the temperature of a certain micro-element exceeds a certain threshold). T c The time point and severity when the electric field reaches a threshold.

[0148] Correlation analysis: Analyze the ratio of the skeleton current to the total operating current during the occurrence and development of quench. For example, what is this ratio when a 1 cm resistance region appears inside the coil? What is this ratio when the coil temperature reaches 100 K?

[0149] In one exemplary embodiment, S3 specifically includes the following steps.

[0150] During the simulation of different quench events, the time evolution curve of the skeleton current and the simulation parameters of each coil micro-element inside the superconducting magnet are recorded and plotted in real time; the simulation parameters include the spatial distribution and time evolution of temperature, current density, electric field and magnetic field.

[0151] The quench judgment threshold and the quench severity index grading threshold for different levels are determined based on the time evolution curve of the skeleton current and the simulation parameters.

[0152] In one exemplary embodiment, S5 specifically includes the following steps.

[0153] Determine whether the skeleton current corresponding to the skeleton current signal exceeds the quench judgment threshold.

[0154] If so, it is determined that the superconducting magnet has experienced a quenching event.

[0155] The severity index of quench failure is determined based on the skeleton current corresponding to the skeleton current signal and the total operating current.

[0156] Based on the severity index and the severity index grading threshold, the quench event is divided into different severity levels, and graded early warning and protection responses are performed according to the severity level.

[0157] If not, it is determined that the superconducting magnet has not experienced a quenching event.

[0158] In an exemplary embodiment, the quench severity index SI is: ;in, I skeleton For the skeleton current; I op This represents the total operating current.

[0159] In practical applications, the operation and monitoring of superconducting coils are as follows.

[0160] Normal operating conditions: When the superconducting coil is operating normally and stably, the superconducting tape is in a state of zero resistance or extremely low resistance, and most (ideally all) of the total operating current is released. I op Flowing along the superconducting layer. At this time, the skeletal current flows through a specific section of the skeletal framework. I skeleton It is extremely small, theoretically close to zero, or a calibrable and stable background value.

[0161] Quench Occurrence and Current Shunting: When a quench occurs at a point inside the coil, that region transitions to a normal state and exhibits significant resistance. According to Kirchhoff's laws, the total operating current will redistribute, with a portion of the current bypassing the high-resistance quench region and being shunt through parallel low-resistance paths. This application utilizes this portion of the current shunt to the conductive frame.

[0162] Measurement and quench determination of skeleton current: The current sampling circuit monitors the skeleton current in real time. I skeleton .when I skeletonExceeding a preset queuing threshold I quench When this threshold is reached, it can be determined that a superconducting coil has experienced a quench. For coils without insulation or with metallic insulation, this threshold can be set based on their normal inter-turn current sharing level to distinguish between normal, stable current sharing and developing, irreversible quench events.

[0163] In practical applications, the severity of queuing is assessed as follows.

[0164] By quantifying the relationship between the skeleton current and the total operating current, a dynamic assessment of the severity of quench failure can be achieved.

[0165] Calculation of quench severity index: The processing unit calculates the skeleton current. I skeleton Percentage of total operating current I op The proportion or percentage is defined as the Severity Index (SI): .

[0166] Queue severity index grading threshold setting: Based on the magnet's design parameters, operational experience, and a detailed electrothermal coupling finite element model, thresholds for multiple quench severity indices are pre-set, classifying quenches into different severity levels. For example, they can be classified as follows.

[0167] Level 0 (Normal / Stable Operation): SI< SI Level0 (For example, <0.5%).

[0168] Level 1 (Initial / Minor Overshoot): SI Level0 ≤SI< SI Level1 (For example, 0.5%≤SI<2%).

[0169] Level 2 (Medium / Developing and Falling Behind): SI Level1 ≤SI< SI Level2 (For example, 2%≤SI<10%).

[0170] Level 3 (Severe / Irreversible Loss): SI≥ SI SI Level2 (For example, ≥10%).

[0171] (Note: The percentage values ​​above are for illustrative purposes only and should be determined for specific magnets in actual applications.)

[0172] Step 5: Tiered early warning and protection response.

[0173] Based on the determined severity level of the quench, the processing unit triggers pre-set corresponding warning signals and protection actions. Table 1 illustrates the correspondence between the skeleton current ratio and the quench level, as well as the protection actions that may be triggered at each level, as shown in Table 1 as an exemplary classification scheme.

[0174] Table 1. Lookup Table for Criticality Levels and Protection Responses (Example)

[0175]

[0176] Currently, various methods have been developed for quench detection in superconducting magnets, but each has its limitations:

[0177] Voltage threshold method: This method monitors the voltage across a specific section of the superconducting coil, and determines quench failure when the voltage exceeds a preset threshold. This is currently the most widely used quench failure detection method.

[0178] Its main limitations are: (1) Insensitive to quench detection of high-temperature superconducting materials: High-temperature superconducting materials (such as REBCO) usually have high heat capacity and large superconducting transition temperature margin, resulting in very slow propagation speed in the normal region, usually on the order of centimeters per second, far lower than the order of meters per second of low-temperature superconducting materials. This means that in a high-temperature superconducting coil, a significant local hot spot may have already formed and caused damage to the conductor, while the resulting resistance voltage is still very weak, far from reaching the detection threshold of the traditional voltage method.

[0179] (2) Noise interference and high detection threshold: Voltage signals are highly susceptible to interference from electromagnetic noise, power supply ripple, and induced voltage generated during rapid excitation or demagnetization of magnets. To avoid misjudgment, the voltage detection threshold often needs to be set high, which further delays the effective identification of early quenching, especially for slowly developing quenching processes.

[0180] (3) Limitations of fixed threshold: Traditional fixed voltage thresholds are difficult to adapt to changing operating conditions and are also difficult to distinguish between different degrees and speeds of quench events.

[0181] Fiber optic thermometry: This method directly measures temperature changes by embedding fiber optic sensors (such as fiber Bragg gratings) in superconducting tapes or coil windings to determine quench failure.

[0182] Its main limitations are: (1) Invasiveness and manufacturing complexity: The implantation of optical fibers increases the complexity and cost of manufacturing superconducting coils and may have an adverse effect on the mechanical and electromagnetic properties of superconducting tapes. Optical fibers themselves are relatively fragile and are easily damaged or generate significant signal noise in complex electromagnetic and mechanical environments, leading to detection failure.

[0183] (2) Adaptability to the low propagation speed of high-temperature superconducting materials: Discrete fiber optic sensors are incompatible with the slow and localized propagation characteristics in the normal region of high-temperature superconducting coils, which may cause them to miss early hot spots located between sensors. Continuous distributed fiber optic sensing technologies (such as those based on Rayleigh scattering) require powerful real-time data processing capabilities, which are costly. In addition, the sensitivity of most fiber optic temperature measurement technologies decreases significantly in the low-temperature region (especially below 15-20 K) due to the reduction in the thermal expansion coefficient of the material.

[0184] Acoustic detection method: This method is based on the acoustic emission signals that may be generated during the quench process (such as material microcracks, mechanical disturbances caused by thermal expansion, or refrigerant boiling).

[0185] Its main limitations are: (1) Signal complexity and processing difficulty: The acoustic signal source is complex and the signal-to-noise ratio is low. Precise signal acquisition and complex post-processing algorithms are required to effectively extract the quench feature signal. Whether the acoustic signal generated by the early quench event with low energy in high-temperature superconducting magnet is significant enough and can be reliably identified still needs further research.

[0186] (2) Reliability and specificity issues: In high-temperature superconducting magnets, mechanical disturbances are not the main cause of quench failure, and many non-quench-related mechanical events may also generate acoustic signals, making it difficult to accurately judge quench failure by passive acoustic monitoring alone, especially in the early stages of temperature change of 1 K or less.

[0187] Furthermore, the widely used voltage threshold method faces unique challenges when applied to uninsulated high-temperature superconducting coils:

[0188] Non-insulated or metal-insulated coil technology achieves a degree of "self-protection" by allowing current to be shunted between turns or through co-wound metal materials during local quench, thus improving tolerance to local defects. This is considered a major technological approach for large-scale engineering magnets. However, this advantageous current shunting characteristic poses a significant challenge to traditional voltage detection methods. When current bypasses the quench region, the voltage drop across that region decreases significantly or develops extremely slowly, making voltage-connector-based detection methods more reactive or even ineffective.

[0189] A search revealed several related patents, with similar patents listed below.

[0190] Chinese Patent Application No. CN202411567736.7, Patent Title: Superconducting Coil Queue Detection Method Using Leakage Current. The patent description states: This invention provides a superconducting coil quench detection method using leakage current, comprising the following steps: Step 1: Determining a first detection connection point on the main superconducting tape adjacent to a first current connection point, the first detection connection point and the first current connection point being equipotential points; Step 2: Determining a second detection connection point on the sampling superconducting tape, the second detection connection point and the second current connection point being equipotential points; Step 3: Connecting a leakage current sampling circuit to the first detection connection point and the second detection connection point. If the leakage current sampling circuit detects leakage current, it is determined that a quench exists in the main superconducting tape. This invention uses a leakage current sampling circuit detection method to solve the problem of difficulty in sampling the quench voltage of superconducting magnets.

[0191] Note: The main differences between this patent and this application are as follows.

[0192] (1) Different application objects: This application monitors the current in the conductive skeleton (such as the inter-disc copper disk or support skeleton) of the superconducting magnet, which is an inherent part of the magnet system. When quench occurs, the current flows from the superconducting winding to this skeleton. CN202411567736.7 monitors the leakage current in an additional "sampling superconducting tape section" set next to the main superconducting tape, which requires the addition of a new component outside the superconducting magnet system, and its application object is the superconducting tape itself, rather than the structural skeleton of the coil.

[0193] (2) The core detection parameters and objectives are different: This application not only detects whether there is shunt current in the skeleton, but more importantly, it judges the severity of quenching by the proportion of skeleton current in the total operating current, so as to realize graded early warning and protection. The objective of CN202411567736.7 is to replace voltage sampling to judge the occurrence of quenching. It detects the absolute value or presence of leakage current, and does not involve the quenching severity classification based on the current proportion.

[0194] (3) The technical innovations are different: One of the core innovations of this application is to use the proportion of skeleton current to classify the quench risk level, thereby realizing a more refined magnet protection strategy. The main innovation of CN202411567736.7 is to propose a quench detection method that detects leakage current by parallel sampling of the strip to overcome the difficulty of voltage sampling.

[0195] In summary, this application achieves the following effects.

[0196] (1) Significantly improved detection sensitivity and reliability for high-temperature superconductors and uninsulated coils: This application effectively overcomes the inherent slow propagation speed in the normal region of high-temperature superconducting materials and the suppression of voltage signals in uninsulated coils by directly measuring the physical phenomenon that inevitably occurs after quench—the current shunted to the skeleton. As a direct representation of quench, the skeleton current may have a better signal strength and timing than the far-end voltage signal, thus enabling earlier and more reliable quench detection and buying valuable time for taking protective measures.

[0197] (2) Non-invasive detection: This method uses the existing conductive frame of the superconducting coil as the sensing object. The current sensor is usually placed outside the frame or in an easily accessible location, without the need to implant any additional sensing elements (such as optical fibers) inside the superconducting winding. This not only simplifies the manufacturing and assembly process of the magnet and reduces costs, but more importantly, it avoids any adverse effects on the integrity of the superconducting winding and the original electromagnetic properties of the magnet.

[0198] (3) Achieving graded assessment and optimized protection for quench severity: By quantifying the ratio of skeleton current to total operating current, the development degree and potential hazards of quench can be dynamically assessed. Based on this graded information, differentiated and optimal protection strategies can be initiated. For example, for initial, minor quenches, only an alarm may need to be issued or operating parameters may need to be appropriately reduced; while for rapidly developing severe quenches, emergency de-energization should be initiated immediately. This refined management approach avoids unnecessary magnet shutdowns, energy waste, and thermal shock and mechanical stress caused by frequent and rapid de-energization that may result from traditional "one-size-fits-all" protection, thereby improving the overall operating efficiency and service life of the magnet.

[0199] (4) Reduced cost of quench monitoring system: Compared with complex distributed fiber optic sensing systems or acoustic detection systems that require precise signal processing, the current sampling circuit (mainly including current sensor and signal processing unit) used in this application is simpler and more economical in principle and implementation. At the same time, the current detection technology is relatively mature and has achieved a fairly high sensitivity. Therefore, this application has certain practical value for monitoring systems of superconducting magnets for engineering use.

[0200] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0201] This document uses specific examples to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A superconducting magnet quench detection and early warning system based on skeleton current, characterized in that, include: Superconducting magnets and conductive frameworks; An electrical contact surface is formed between the superconducting magnet and the conductive frame; When the superconducting magnet loses its quench, the current in the superconducting magnet is diverted to the conductive frame; The conductive frame is provided with at least two spatially separated detection connection points; the detection connection points are used to capture the current flowing through the conductive frame; A current detection circuit is provided between the two detection connection points; the current detection circuit is used to measure the skeleton current flowing through the skeleton segment between the two detection connection points, and transmit the skeleton current signal corresponding to the skeleton current to the processing unit. The processing unit is used to perform graded early warning and protection response for superconducting magnet quench based on the skeleton current signal, according to the quench judgment threshold and the quench severity index grading threshold; the quench judgment threshold and the quench severity index grading threshold are obtained by simulating different quench events based on the electrothermal coupling finite element model constructed by the superconducting magnet and the conductive skeleton.

2. The superconducting magnet quench detection and early warning system based on skeleton current according to claim 1, characterized in that, The current detection circuit specifically includes: a sampling resistor and a current sensor; One end of the sampling resistor is connected to a detection connection point, the other end of the sampling resistor is connected to one end of the current sensor, and the other end of the current sensor is connected to another detection connection point and the processing unit.

3. The superconducting magnet quench detection and early warning system based on skeleton current according to claim 1, characterized in that, The processing unit is a microcontroller, FPGA, or dedicated quench detection logic circuit.

4. The superconducting magnet quench detection and early warning system based on skeleton current according to claim 1, characterized in that, The superconducting magnet is a superconducting coil.

5. A method for detecting and warning of quenching in superconducting magnets based on skeleton current, characterized in that, The superconducting magnet quench detection and early warning method based on skeleton current is applied to the superconducting magnet quench detection and early warning system based on skeleton current according to any one of claims 1-4, wherein the superconducting magnet quench detection and early warning method based on skeleton current includes: Construct an electrothermal coupled finite element model of a superconducting magnet and a conductive framework; Based on the electrothermal coupling finite element model, different quench events were simulated. Based on different loss-of-go events, determine the loss-of-go judgment threshold and the grading threshold for different levels of loss-of-go severity indicators; When the superconducting magnet loses quench, the current shunted from the superconducting magnet to the conductive frame is acquired; Based on the skeleton current signal, the superconducting magnet quench is classified and protected according to the quench judgment threshold and the quench severity index grading threshold.

6. The method for superconducting magnet quench detection and early warning based on skeleton current according to claim 5, characterized in that, The electrothermal coupling finite element model for constructing the superconducting magnet and the conductive framework specifically includes: The superconducting magnet is a superconducting coil; The superconducting coil is discretized into multiple turns, and each turn is discretized into multiple coil micro-elements to construct a superconducting coil micro-element grid; The conductive skeleton is connected as an independent parallel branch to the input and output ends of the superconducting coil micro-element mesh to construct an electrothermal coupled finite element model of the superconducting coil and the conductive skeleton; the electrothermal coupled finite element model includes a circuit network model, a heat transfer model, a magnetic field model, and boundary conditions.

7. The method for superconducting magnet quench detection and early warning based on skeleton current according to claim 5, characterized in that, Based on the aforementioned electrothermal coupling finite element model, different quench events are simulated, specifically including: Different types of quench initial disturbance events are set in the electrothermal coupling finite element model; among them, the different types include local heating, local current overload and critical current decay; Determine the operating parameters during the simulation of the initial disturbance event of quench failure; the operating parameters include total operating current, coolant temperature, initial temperature, and material property parameters; the material property parameters include EJ curve parameters and heat transfer physics parameters; The electrothermal coupling finite element model is solved based on the operating parameters to simulate different quench events; the different quench events are quench events of different types, locations and energies.

8. The method for superconducting magnet quench detection and early warning based on skeleton current according to claim 5, characterized in that, Based on different loss-of-way events, the loss-of-way judgment threshold and the grading thresholds for different levels of loss-of-way severity indicators are determined, specifically including: During the simulation of different quench events, the time evolution curve of the skeleton current and the simulation parameters of each coil micro-element inside the superconducting magnet are recorded and plotted in real time; the simulation parameters include the spatial distribution and time evolution of temperature, current density, electric field and magnetic field. The quench judgment threshold and the quench severity index grading threshold for different levels are determined based on the time evolution curve of the skeleton current and the simulation parameters.

9. The method for superconducting magnet quench detection and early warning based on skeleton current according to claim 5, characterized in that, Based on the aforementioned skeleton current signal, a graded early warning and protection response for superconducting magnet quench is implemented according to the quench judgment threshold and the quench severity index grading threshold. Specifically, this includes: Determine whether the skeleton current corresponding to the skeleton current signal exceeds the quench judgment threshold. If so, it is determined that the superconducting magnet has experienced a quenching event; The severity index of quench failure is determined based on the skeleton current corresponding to the skeleton current signal and the total operating current. Based on the queuing severity index and the queuing severity index grading threshold, the queuing event is divided into different severity levels, and graded early warning and protection response are performed according to the severity level. If not, it is determined that the superconducting magnet has not experienced a quenching event.

10. The method for superconducting magnet quench detection and early warning based on skeleton current according to claim 9, characterized in that, The severity index SI for loss of quench is: ； in, I skeleton For the skeleton current; I op This represents the total operating current.

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