Automatic test system and method for critical current of superconducting magnet

Abstract

The invention discloses an automatic test system and method for the critical current of a superconducting magnet, and belongs to the field of superconducting magnet test. The system comprises a superconducting magnet to be tested, a clamping tool, a cooling unit, a data acquisition module, an excitation module and a control unit. When the device is used for measuring the critical current of the superconducting magnet to be measured, the excitation module and the data acquisition module are uniformly coordinated by the control unit, so that the control unit can automatically analyze the quenching condition of the superconducting magnet to be measured, manual participation can be effectively reduced, and the detection efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the field of superconducting magnet testing, and in particular relates to an automatic testing system and method for critical current of a superconducting magnet. Background Art

[0002] As an electrical device, superconducting magnets provide corresponding magnetic fields for actual needs through multi-layer coils wound with superconducting tapes. Superconducting magnets are widely used in many fields and industries such as electricity, instruments, and medical treatment.

[0003] During the winding process of superconducting magnets, the critical current of the pancake coil of the superconducting magnet is not consistent with the theoretical value due to factors such as tension, speed and tolerance of the skeleton processing. As an important parameter in superconducting magnets, if the critical current value is not tested and the actual critical current value of the superconducting magnet does not reach the theoretical value, the superconducting magnet will be quenched due to excessive current during use, and even the magnet will burn out, which will damage the entire device.

[0004] During the detection of the critical current of a superconducting magnet, excitation is required. Due to factors such as hysteresis loss, the magnet will heat up. If the magnet is excited for a long time, the superconducting magnet will quench due to excessive heat generation. If the magnet is still excited when the superconducting magnet is quenched, the magnet will burn out. During the detection process, the superconducting magnet needs to be excited in stages. At present, the critical current test of superconducting magnets is all done manually. If the theoretical critical current value of the superconducting magnet is very large, the critical current test process of a single superconducting magnet will be extremely cumbersome. If batch testing is required, the test volume will increase dramatically. Summary of the invention

[0005] Aiming at the problem of low efficiency in current superconducting magnet critical current testing, the present invention provides an automatic testing system and method for superconducting magnet critical current.

[0006] The technical solution of the present invention is: an automatic test system for critical current of a superconducting magnet, comprising a superconducting magnet to be tested, a clamping fixture, a control unit, an excitation module, a data acquisition module and a cooling unit;

[0007] The superconducting magnet to be tested is fixedly installed by a clamping fixture, and its input lead is connected to the excitation module, and the output lead of the superconducting magnet to be tested is connected to the data acquisition module;

[0008] The control unit is connected to the excitation module and the data acquisition module respectively through a bus;

[0009] The cooling unit cools down the superconducting magnet to be tested through internal cooling liquid.

[0010] The present invention also provides an automatic testing method for critical current of a superconducting magnet, the method comprising the following steps:

[0011] Step 1: Perform an initial manual test to determine the optimal excitation rate, demagnetization rate, upper limit value of the voltage across the coil, and constant current output time of the superconducting magnet to be tested;

[0012] Step 2: Turn on the excitation output terminal of the excitation unit and set the excitation current output to 0, configure the initial value of the excitation number n to 1, the reference critical current value a, the voltage lower limit value U0, the excitation rate b, the demagnetization rate c, the voltage upper limit value U, the quench condition judgment value K and the constant current output time t, and turn on the data acquisition unit to start collecting the voltage u at both ends of the superconducting magnet coil and draw a curve graph, where the data acquisition frequency is 1Hz;

[0013] Step 3: Divide the stages of the step-by-step excitation process according to the reference critical current value a, divide the value a by 10, and obtain the quotient a1 and the remainder a2. The first a1 excitation processes are called the first stage of step-by-step excitation, corresponding to the excitation step target current value I1, starting from 0A and increasing by 10A each time. The next a2 excitation processes are called the second stage of step-by-step excitation, corresponding to the excitation step target current value I2, starting from Initially, the voltage is accumulated every 1A;

[0014] Step 4: Determine whether n is greater than a1. If n is less than or equal to a1, perform the first stage of step-by-step excitation; if n is greater than a1, directly perform the second stage of step-by-step excitation, i.e., step 7.

[0015] Step 5: Record the number of times k that the voltage value u across the superconducting magnet coil is greater than 1.5U when the current output value I of the excitation module increases during each excitation process, and determine whether k is greater than K. If k is greater than K, the superconducting magnet is determined to be unqualified, and demagnetization is performed, and the test ends; if k is less than K, proceed to step 6;

[0016] Step 6: When the current output value I of the excitation module is equal to the target current value I1 of the corresponding step, the current output value is maintained for a period of time t, and it is determined whether the voltage value u across the superconducting magnet coil is greater than U0. If u is greater than U0, it is determined that the superconducting magnet is unqualified, and demagnetization is performed, and the test ends; otherwise, the value of n is increased by 1, and the test returns to step 4;

[0017] Step 7: Perform the second stage of excitation in stages. If n is greater than N, the tested superconducting magnet is deemed qualified, and demagnetization is performed. The test ends. Otherwise, proceed to step 8.

[0018] Step 8: Record the number of times k that the voltage value u across the superconducting magnet coil is greater than 1.5U when the current output value I of the excitation module increases during each excitation process, and determine whether k is greater than K. If k is greater than K, the superconducting magnet is determined to be unqualified, and demagnetization is performed, and the test ends; if k is less than K, proceed to step 9;

[0019] Step 9: When the current output value I of the excitation module is equal to the target current value I2 of the corresponding step, the current output value is maintained for a period of time t, and then it is determined whether the voltage value u across the superconducting magnet coil is greater than U0. If u is greater than U0, the superconducting magnet is determined to be unqualified, and demagnetization is performed, and the test ends; otherwise, the value of n is increased by 1, and the test returns to step 7.

[0020] The present invention has the following beneficial effects:

[0021] (1) Based on the characteristic that the voltage across the superconducting magnet coil is a constant value during the uniform speed excitation process, the system can autonomously test, compare and analyze the characteristics of the voltage across the superconducting magnet coil during the excitation process to determine whether the superconducting magnet meets the requirements and realize automatic testing of the critical current of the superconducting magnet.

[0022] (2) In response to the need for large-scale critical current testing of superconducting magnets, only one manual test is required to determine the initial value required to be set for the system, and then the superconducting magnets can be automatically tested in batches, which can save a lot of testing time and labor costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the structural diagram of the batch automatic test system for superconducting magnet critical current;

[0024] Figure 2 The flowchart is a method for batch automatic testing of critical current of superconducting magnets. DETAILED DESCRIPTION

[0025] To facilitate understanding of the solution and effects of the embodiments of the present invention, a specific application example is given below. Those skilled in the art should understand that this example is only for facilitating understanding of the present invention, and any specific details thereof are not intended to limit the present invention in any way.

[0026] like Figure 1 As shown, the present invention provides an automatic testing system for critical current of a superconducting magnet, comprising a superconducting magnet to be tested, a clamping fixture, a cooling unit, a control unit, an excitation module and a data acquisition module;

[0027] The superconducting magnet to be tested is fixedly installed by a clamping fixture, and its input lead is connected to the excitation module, and the output lead of the superconducting magnet to be tested is connected to the data acquisition module;

[0028] The control unit is connected to the excitation module and the data acquisition module respectively through a bus;

[0029] The cooling unit cools down the superconducting magnet to be tested through internal cooling liquid.

[0030] In this embodiment, the cooling liquid used in the cooling unit is liquid nitrogen, which is contained in a foam box. The superconducting magnet to be tested is fixedly installed in the liquid nitrogen by a clamping fixture, that is, the superconducting magnet to be tested is tested in a low temperature environment of 77K.

[0031] In the device of this embodiment, the excitation module adopts a KEPCO current source for excitation, the data acquisition module adopts a NI-PXI sampler, and both the excitation module and the data acquisition module are connected to the control unit via a GPIB serial port.

[0032] The superconducting magnet to be tested is wound from a complete superconducting tape, and the input lead and output lead of the superconducting magnet to be tested are welded to the two ends of the superconducting tape in a four-wire system. The input lead and output lead of the superconducting magnet to be tested are ordinary copper wires.

[0033] like Figure 2 As shown, the present invention proposes a batch automatic testing method for superconducting magnet critical current, the method comprising the following steps:

[0034] Step 1: Perform an initial manual test to determine the optimal excitation rate, demagnetization rate, upper limit value of the voltage across the coil, and constant current output time of the superconducting magnet to be tested;

[0035] Step 2: Turn on the excitation output terminal of the excitation unit and set the excitation current output to 0A, configure the initial value of the excitation times n to 1, the reference critical current value a(A), the voltage lower limit value U0(A), the excitation rate b(A / s), the demagnetization rate c(A / s), the voltage upper limit value U(V), the quench condition judgment value K and the constant current output time t(min), and turn on the data acquisition unit to start collecting the voltage u(V) at both ends of the superconducting magnet coil and draw a curve graph, where the data acquisition frequency is 1Hz;

[0036] Step 3: Divide the stages of the step-by-step excitation process according to the reference critical current value a, divide the value a by 10, and obtain the quotient a1 and the remainder a2. The first a1 excitation processes are called the first stage of step-by-step excitation, corresponding to the excitation step target current value I1, starting from 0 (A), and increasing by every 10 (A). The next a2 excitation processes are called the second stage of step-by-step excitation, corresponding to the excitation step target current value I2, starting from Initially, the value is accumulated by 1(A) at a time.

[0037] Step 4: Determine whether n is greater than a1. If n is less than or equal to a1, perform the first stage of step-by-step excitation; if n is greater than a1, directly perform the second stage of step-by-step excitation, i.e., step 7.

[0038] Step 5: Record the number of times k when the voltage value u across the superconducting magnet coil is greater than 1.5U when the current output value I of the excitation module increases during each excitation process, and determine whether k is greater than K. If k is greater than K, the superconducting magnet is determined to be unqualified, and demagnetization is performed, and the test ends. If k is less than K, proceed to step 6;

[0039] Step 6: When the current output value I of the excitation module is equal to the target current value I1 of the corresponding step, the current output value is maintained for t (min) time, and then it is determined whether the voltage value u across the superconducting magnet coil is greater than U0. If u is greater than U0, it is determined that the superconducting magnet is unqualified, and demagnetization is performed, and the test ends; otherwise, the value of n is increased by 1, and the test returns to step 4;

[0040] Step 7: Perform the second stage of excitation in stages. If n is greater than N, the tested superconducting magnet is deemed qualified, and demagnetization is performed. The test ends. Otherwise, proceed to step 8.

[0041] Step 8: Record the number of times k when the voltage value u across the superconducting magnet coil is greater than 1.5U when the current output value I of the excitation module increases during each excitation process, and determine whether k is greater than K. If k is greater than K, the superconducting magnet is determined to be unqualified, and demagnetization is performed, and the test ends. If k is less than K, proceed to step 9;

[0042] Step 9: When the current output value I of the excitation module is equal to the target current value I2 of the corresponding step, the current output value is maintained for t (min) time, and then it is determined whether the voltage value u across the superconducting magnet coil is greater than U0. If u is greater than U0, it is determined that the measured superconducting magnet is unqualified, and demagnetization is performed, and the test ends; otherwise, the value of n is increased by 1, and the test returns to step 7;

[0043] The reference critical current value a(A) in step 2 is specifically: the theoretical critical current value of the superconducting magnet designed and calculated according to the requirements.

[0044] The voltage lower limit value U0 (V) in step 2 is specifically: the superconducting coil is affected by the material. After a constant current value is passed through the coil, a weak voltage signal will be generated at both ends of the coil. This value is related to the material length and material intrinsic coefficient used in the superconducting coil. The materials used in the same batch of superconducting magnets are consistent and can be determined during the design stage of the superconducting magnet.

[0045] The voltage upper limit value U(V) in step 2 is specifically: According to the formula:

[0046] ;

[0047] ;

[0048] Among them, φ is the magnetic flux, B is the magnetic induction intensity, K is the coefficient and is an equal constant, I is the excitation current, S is the area surrounded by the coil, E is the induced electromotive force, t is the time, and the excitation rate b (A / s) is a constant value. It can be concluded that the voltage across the coil during the excitation process is a constant value. Because it is a batch measurement, the upper limit value of the voltage across the same coil is consistent, which can be obtained through the manual test in step 1.

[0049] The process of using this implementation type device to test a batch (30 pieces in total) of superconducting magnet coils, such as Figure 2 As shown:

[0050] According to the design requirements, the reference critical current value of this batch of superconducting magnet coils is 60A, the lower voltage limit is 2.5mV, and after the initial manual test in step 1, the optimal excitation rate is 0.1A / s, the demagnetization rate is 0.2A / s, the upper voltage limit is 4V, and the constant current output time is 3min. Among them, the initial manual test in step 1 only tested one superconducting magnet coil.

[0051] The preliminary preparations for the test of the remaining superconducting magnets are the same as the initial manual test process, that is, the superconducting magnets to be tested are fixedly installed on the fixture, and after the output leads are connected to the input leads, the superconducting magnets are placed in liquid nitrogen. After completing the preliminary preparations, the excitation process is divided into 6 stages, and the excitation current increases by 10A each stage. According to the formula , , where φ is the magnetic flux, B is the magnetic induction intensity, K is the coefficient and is an equal constant, I is the excitation current, S is the area surrounded by the coil, E is the induced electromotive force, t is the time, and the excitation rate b is a constant value. It can be seen that during the uniform excitation process, the voltage across the superconducting magnet coil is theoretically a constant value. Taking into account the deviation of the acquisition system and the external signal interference, it is set that if the voltage across the superconducting magnet coil measured during the excitation process u>6V, it is determined that the superconducting magnet coil is quenched at this time, and the superconducting magnet is determined to be unqualified, and demagnetization treatment is performed.

[0052] When the nth excitation current reaches , keep the excitation current output value at This lasts for 3 minutes. If u>2.5mV after 3 minutes, it is determined that the superconducting magnet has not recovered to the superconducting state after excitation. Therefore, the superconducting magnet is also determined to be unqualified and is demagnetized.

[0053] During the test, if the critical current can reach 60A and no quenching occurs during the excitation process, the superconducting magnet is judged to meet the requirements and is demagnetized.

Claims

1. An automatic testing system for critical current of a superconducting magnet, characterized in that: It includes a superconducting magnet to be tested, a clamping fixture, a control unit, an excitation module, a data acquisition module and a cooling unit; The superconducting magnet to be tested is fixedly installed by a clamping fixture, and its input lead is connected to the excitation module, and the output lead of the superconducting magnet to be tested is connected to the data acquisition module; The control unit is connected to the excitation module and the data acquisition module respectively through a bus; The cooling unit cools down the superconducting magnet to be tested through internal cooling liquid.

2. The automatic testing system for superconducting magnet critical current according to claim 1, characterized in that: The superconducting magnet to be tested is wound from a superconducting tape, and the input lead and the output lead are welded and fixed on both ends of the superconducting tape of the superconducting magnet in a four-wire system.

3. The automatic testing system for superconducting magnet critical current according to claim 1, characterized in that: The input lead and the output lead of the superconducting magnet to be tested are common copper wires.

4. An automatic testing method for critical current of a superconducting magnet, using the system according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: Step 1: Perform an initial manual test to determine the optimal excitation rate, demagnetization rate, upper limit value of the voltage across the coil, and constant current output time of the superconducting magnet to be tested; Step 2: Turn on the excitation output terminal of the excitation unit and set the excitation current output to 0, configure the initial value of the excitation number n to 1, the reference critical current value a, the voltage lower limit value U0, the excitation rate b, the demagnetization rate c, the voltage upper limit value U, the quench condition judgment value K and the constant current output time t, and turn on the data acquisition unit to start collecting the voltage u at both ends of the superconducting magnet coil and draw a curve graph, where the data acquisition frequency is 1Hz; Step 3: Divide the stages of the step-by-step excitation process according to the reference critical current value a, divide the value a by 10, and obtain the quotient a1 and the remainder a2. The first a1 excitation processes are called the first stage of step-by-step excitation, corresponding to the excitation step target current value I1, starting from 0A and increasing by 10A each time. The next a2 excitation processes are called the second stage of step-by-step excitation, corresponding to the excitation step target current value I2, starting from Initially, the voltage is accumulated by 1A. Step 4: Determine whether n is greater than a1. If n is less than or equal to a1, perform the first stage of step-by-step excitation; if n is greater than a1, directly perform the second stage of step-by-step excitation, i.e., step 7. Step 5: Record the number of times k that the voltage value u across the superconducting magnet coil is greater than 1.5U when the current output value I of the excitation module increases during each excitation process, and determine whether k is greater than K. If k is greater than K, the superconducting magnet is determined to be unqualified, and demagnetization is performed, and the test ends; if k is less than K, proceed to step 6; Step 6: When the current output value I of the excitation module is equal to the target current value I1 of the corresponding step, the current output value is maintained for a period of time t, and then it is determined whether the voltage value u across the superconducting magnet coil is greater than U0. If u is greater than U0, it is determined that the measured superconducting magnet is unqualified, and demagnetization is performed, and the test ends; Otherwise, n is increased by 1 and returns to step 4; Step 7: Perform the second stage of excitation in stages. If n is greater than N, the tested superconducting magnet is deemed qualified, and demagnetization is performed. The test ends. Otherwise, proceed to step 8. Step 8: Record the number of times k that the voltage value u across the superconducting magnet coil is greater than 1.5U when the current output value I of the excitation module increases during each excitation process, and determine whether k is greater than K. If k is greater than K, the superconducting magnet is determined to be unqualified, and demagnetization is performed, and the test ends; if k is less than K, proceed to step 9; Step 9: When the current output value I of the excitation module is equal to the target current value I2 of the corresponding step, the current output value is maintained for a period of time t, and it is determined whether the voltage value u across the superconducting magnet coil is greater than U0. If u is greater than U0, it is determined that the measured superconducting magnet is unqualified, and demagnetization is performed, and the test ends; Otherwise, increase the value of n by 1 and return to step 7.

5. The automatic testing method of superconducting magnet critical current according to claim 4, characterized in that: The reference critical current value a in step 2 is specifically: a theoretical critical current value of a superconducting magnet designed and calculated according to requirements.

6. The automatic testing method of superconducting magnet critical current according to claim 4, characterized in that: The voltage lower limit value U0 in step 2 is specifically: the superconducting coil is affected by the material. After a constant current value is passed through the coil, a weak voltage signal will be generated at both ends of the coil. This value is related to the material length and material intrinsic coefficient used in the superconducting coil. The materials used in the same batch of superconducting magnets are consistent and can be determined during the design stage of the superconducting magnet.

7. The automatic testing method of superconducting magnet critical current according to claim 4, characterized in that: The voltage upper limit value U in step 2 is specifically: According to the formula: ， ， Among them, φ is the magnetic flux, B is the magnetic induction intensity, K is the coefficient and is an equal constant, I is the excitation current, S is the area surrounded by the coil, E is the induced electromotive force, t is the time, and the excitation rate b is a constant value. It can be concluded that the voltage at both ends of the coil during the excitation process is a constant value, and the upper limit value of the voltage at both ends of the same coil is consistent, which is obtained through the manual test in step 1.

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