A Testing Method for Radial Stress of Insulation-Free High-Temperature Superconducting Coils

Abstract

The present invention discloses a method for testing the radial stress of a non-insulated high-temperature superconducting coil, belonging to the field of superconducting electrical engineering. The radial stress is an important parameter of the high-temperature superconducting coil, which is mainly the superposition of winding tension, electromagnetic load and cold shrinkage force. The radial stress is related to the self-protection characteristics of the high-temperature superconducting coil. The greater the radial stress, the smaller the inter-turn contact resistance, and the current at the hot spot is more likely to be radially shunted to avoid quench. The present invention relates to the technical field of high-temperature superconducting coils. Potential points are arranged inside the coil, and the inter-turn contact resistance is inversely calculated according to the mutual inductance matrix of each turn and the measured voltage and current signals. Referring to the mapping relationship between pressure and inter-turn contact resistance, the radial stress is inversely calculated.

Description

Technical Field

[0001] The present invention belongs to the field of superconducting electrical engineering and relates to a method for testing the radial stress of a non-insulated high-temperature superconducting coil. Background Art

[0002] ReBCO second-generation high-temperature superconducting conductors have become one of the most promising superconducting materials in the field of high-field superconducting technology due to their high irreversibility magnetic field and mechanical strength. Compared with the first-generation high-temperature superconducting materials, the greatest advantage is their higher mechanical strength and high irreversibility magnetic field, showing obvious advantages in the field of high-field magnets and having broad high-field application prospects. Especially with the continuous improvement of the technical parameters of large superconducting magnetic confinement fusion devices, high-energy physics accelerator devices (super proton colliders), superconducting high-magnetic field devices, superconducting energy storage devices, and nuclear magnetic resonance imaging equipment and their requirements for the high-magnetic field operating environment, the current stage's demand for large-scale high-field applications is becoming more and more urgent.

[0003] The ReBCO high-temperature superconducting tightly wound non-insulated (NI) eliminates the inter-turn insulation of traditional coils. After a quench, the current can automatically bypass the quenched area through the inter-turn resistance contact, greatly reducing the impact of the heat generated at the quench point on the superconducting tape, and having higher electrothermal stability and better self-protection ability, which is used in the development of extremely high-field magnets.

[0004] The self-protection characteristic of the ReBCO high-temperature superconducting non-insulated coil is closely related to the inter-turn contact resistance. The smaller the contact resistance, the better the self-protection characteristic; because the greater the radial compressive stress on the surface of the ReBCO high-temperature superconducting tape, which microscopically shows unevenness, the closer the tape contacts, and the smaller the contact resistance. Existing research has hardly carried out radial stress testing and characterization analysis under low-temperature operating conditions, so it is meaningful to invent and explore the radial stress of high-temperature superconducting coils. Summary of the Invention

[0005] Non-insulated high-temperature superconducting coils are widely favored due to their high engineering current density and self-protection characteristics. Radial stress is an important parameter of high-temperature superconducting coils, mainly the superposition of winding tension, electromagnetic load, and cold shrinkage force. Radial stress is related to the self-protection characteristic of high-temperature superconducting coils. The greater the radial stress, the smaller the inter-turn contact resistance, and the current at the hot spot will be more likely to be radially shunted to avoid a quench.

[0006] The technical solution of the present invention is specifically as follows: A method for testing the radial stress of a non-insulated high-temperature superconducting coil, comprising the following steps:

[0007] Step 1, test the relationship Fr between the surface contact resistivity R of the turns of the high-temperature superconducting tape ct and the radial stress: R ct ;

[0008] Step 2: Wind a non-insulated high-temperature superconducting coil with superconducting tape. Arrange several potential points in the non-insulated high-temperature superconducting coil by turns, and calculate the mutual inductance matrix M of the turns. ij where i and j are the indexing numbers of the turns respectively.

[0009] Step 3: Excite the non-insulated high-temperature superconducting coil, and record the excitation current and the turn voltages of several potential points in real time.

[0010] Step 4: Calculate the inter-turn contact resistance according to the excitation current of the non-insulated high-temperature superconducting coil, the turn voltages of the turn coils, and the mutual inductance matrix of the turn coils.

[0011] Step 5: Calculate the inter-turn surface contact resistivity R according to the turn geometry of the coil and the inter-turn contact resistance. ct According to the relationship Fr between the inter-turn surface contact resistivity R ct and the radial stress: R ct Invert the radial stress.

[0012] The present invention has the following beneficial effects:

[0013] The present invention can measure the internal radial stress of a superconducting coil under cryogenic operating conditions, providing verification and correction for the mechanical theoretical model of the superconducting coil; the present invention can also calculate the inter-turn resistance value inside the superconducting coil, providing necessary data support for the analysis of the quench characteristics of the non-insulated coil. Description of the Drawings

[0014] Figure 1 It is a schematic diagram of a test fixture for the mapping relationship between radial stress and inter-turn resistance;

[0015] Figure 2 It is a schematic diagram of a high-temperature superconducting coil with potential points arranged by turns;

[0016] Figure 3 It is a schematic diagram of the circuit model of a non-insulated high-temperature superconducting coil. Detailed Embodiments

[0017] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, the present invention adopts the following technical solutions. The method of the present invention will be further described below with reference to the drawings and specific embodiments.

[0018] The present invention provides a method for testing the radial stress of a non-insulated high-temperature superconducting coil, including:

[0019] Step 1: Test the inter-turn surface contact resistivity R of the high-temperature superconducting tape ct and the relationship Fr between the radial stress: R ct ;

[0020] Step 2: Wind a non-insulated high-temperature superconducting coil with the superconducting tape. A number of potential points are arranged in each turn of the non-insulated high-temperature superconducting coil, and calculate the mutual inductance matrix M of each turn ij ; where i and j are the indexing numbers of each turn respectively

[0021] Step 3: Excite the non-insulated high-temperature superconducting coil and record the excitation current and the turn voltages of a number of potential points in real time

[0022] Step 4: Calculate the inter-turn contact resistance according to the excitation current of the non-insulated high-temperature superconducting coil, the turn voltages of each turn of the coil and the mutual inductance matrix of each turn of the coil

[0023] Step 5: Calculate the inter-turn surface contact resistivity R according to the geometric structure of each turn of the coil and the inter-turn contact resistance ct ; According to the relationship Fr between the inter-turn surface contact resistivity R ct and the radial stress: R ct , invert the radial stress

[0024] Specifically, Step 1 is as follows: As Figure 1 shown, align the superconducting layers of two high-temperature superconducting tapes with the non-superconducting layers uniformly, connect signal lines on both sides. The contact area of the high-temperature superconducting tapes is S, apply pressure F, then the radial stress is F / S; pass current I on both sides respectively, measure the signal line voltage as V, then the inter-turn surface resistivity is V / I×S, and test the inter-turn surface contact resistivity R ct and the corresponding relationship Fr between the radial stress: R ct . The contact resistivity R ct and the relationship Fr between the radial pressure: R ct is the experimental test value, which is mainly related to the surface roughness of the tape. The greater the radial pressure, the closer the contact between the tapes, and the contact resistivity R ct is smaller

[0025] Specifically, Step 2 is as follows: As Figure 2 shown, a number of potential points are arranged in each turn of the high-temperature superconducting coil. The potential points are led out and the turn voltages can be measured through the signal lines. The mutual inductance matrix M of each turn ij .

[0026] Specifically, Step 3 is as follows: Place the high-temperature superconducting coil in a low-temperature environment and excite the high-temperature superconducting coil at a constant rate, and record the excitation current and the turn voltages in real time

[0027] Specifically, the calculation of Step 4 is as follows: As Figure 3Shown is a 2-turn high-temperature superconducting coil (similar for multiple turns), where I1 and I2 are the circumferential currents of the turn coils, and R ct1 and R ct2 are the contact resistances between the turns respectively, U1 and U2 are the turn voltages, and I is the excitation current.

[0028] Table 1 Inductance Matrix

[0029]

[0030] Sub 1 and Sub 2 represent two turns, and L1, L2, M 12 and M 21 represent the self-inductances of turn 1 and turn 2 and the mutual inductance matrix between turn 1 and turn 2 respectively. Among them, M 21 = M 12 .

[0031] According to the mutual inductance matrix, the following set of formulas can be obtained;

[0032] ,

[0033] ,

[0034] Among them, the circumferential currents I1 and I2 of the turns are as shown in the following set of formulas;

[0035] ,

[0036] ,

[0037] Substituting the following set of formulas into the above set of formulas, we can obtain:

[0038] ,

[0039] .

[0040] In the above formula, only the contact resistances R ct1 and R ct2 are unknowns, and the rest are known quantities. Therefore, the contact resistances can be obtained.

[0041] When there are n turns, the expression of the contact resistance is as follows:

[0042] ,

[0043] Among them, L1, L n are the self-inductances of turn 1 and turn n respectively, and M in is the mutual inductance matrix between the i-th turn and the n-th turn, R cti , R ctn , R ct1$R_{i,n,1}$ is the inter-turn contact resistance of the $i$-th turn, the $n$-th turn and the 1st turn, and $I$ is the excitation current. It can be seen that there are a total of $n$ column expressions, where $n$ inter-turn resistances are unknowns, and thus the inter-turn contact resistance matrix can be obtained. .

[0044] Step 5 is specifically calculated as follows: According to the inter-turn contact resistance in Step 4 and the coil geometric structure of this turn, such as the number of turns $N$ of this turn and the average cross-sectional area $S$ per turn n , the inter-turn surface contact resistivity is obtained .

[0045] The inversion method is specifically as follows: The relationship $F_r$ between the inter-turn surface contact resistivity $R$ ct and the radial stress: $R$ ct is plotted as a graph, with the radial stress on the abscissa and the inter-turn surface contact resistivity on the ordinate. According to the calculated inter-turn surface contact resistivity $R$ ct , the radial stress is obtained by taking the value at the fixed point on the graph.

Claims

1. A test method for the radial stress of a non-insulated high-temperature superconducting coil, characterized in that Including the following steps: Step 1, test the relationship Fr between the inter-turn surface contact resistivity R of the high-temperature superconducting tape and the radial stress: R ct ; ct ; Step 2: Wind a non-insulated high-temperature superconducting coil with superconducting tape. A number of potential points are arranged in turns within the non-insulated high-temperature superconducting coil, and the mutual inductance matrix M of the turns is calculated. ij where i and j are the indexing numbers of the turns respectively. Step 3: Excite the non-insulated high-temperature superconducting coil and record the excitation current and the turn voltages at several potential points in real time; Step 4: Calculate the inter-turn contact resistance based on the excitation current of the non-insulated high-temperature superconducting coil, the turn voltages of the turn coils, and the turn mutual inductance matrix of the turn coils; Step 5: Calculate the surface contact resistivity R between turns according to the coil turn-segment geometric structure and the inter-turn contact resistance ct ; According to the surface contact resistivity R between turns ct and the relationship Fr between the radial stress: R ct , inversely calculate the radial stress.

2. The test method for the radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that Step 1 specifically is: Place two superconducting tapes on a press. Place the non-insulated high-temperature superconducting tape at the operating temperature equivalent to that of the coil. Align the superconducting layers and non-superconducting layers of the two tapes evenly. Vertically load pressure on the press and test the inter-turn surface contact resistivity R of the tape ct Relationship Fr with the radial stress: R ct .

3. A method for testing the radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that Specifically, step 2 is as follows: The non-insulated high-temperature superconducting coil is a single pancake, the superconducting tapes are in close contact, and several potential points are arranged inside the non-insulated high-temperature superconducting coil.

4. A method for testing the radial stress of a non-insulated high-temperature superconducting coil according to claim 3, characterized in that The thickness of the potential point is less than the thickness of the tape, reducing the protrusion at the potential point caused by the thickness of the potential point.

5. A method for testing the radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that, Specifically, step 3 is as follows: Excite the non-insulated high-temperature superconducting coil at a constant rate, and the rising rate of the turn voltage gradually decreases.

6. A method for testing the radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that, Specifically, step 4 is as follows: When the non-insulated high-temperature superconducting coil has n turns, the expression of the contact resistance is as follows: Among them, L1, L n are the inductances of the first turn and the nth turn respectively, and M in is the mutual inductance between the ith turn and the nth turn. R ct1 , R cti , R ctn are the inter-turn contact resistances of the first turn, the ith turn, and the nth turn respectively. I is the excitation current of the non-insulated high-temperature superconducting coil. It can be seen that there are a total of n column expressions, where n inter-turn contact resistances are unknowns. From this, the inter-turn contact resistance matrix can be obtained.

7. A method for testing the radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that, Step 5 specifically includes: based on the inter-turn contact resistance and the split-turn geometric structure obtained in Step 4, where the geometric structure includes the number of split turns N and the average contact area S per turn, n , the inter-turn surface contact resistivity is obtained .

8. A method for testing the radial stress of a non-insulated high-temperature superconducting coil according to claim 7, characterized in that, The inversion method is specifically as follows: The relationship Fr between the inter-turn surface contact resistivity R ct and the radial stress: R ct is plotted as a graph, where the abscissa is the radial stress and the ordinate is the inter-turn surface contact resistivity. According to the calculated inter-turn surface contact resistivity R ct , the radial stress is obtained by taking values at fixed points on the graph.

9. The testing method for the radial stress of a non-insulated high-temperature superconducting coil according to claim 1, wherein The resistance value of the inter-turn contact resistance and the turn mutual inductance matrix are in the same order of magnitude.

10. A method for testing the radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that, The inter-turn contact resistance is equal to the series value of the contact resistances of adjacent surfaces, that is, the turn surface contact resistivity divided by the average contact area of the turn and then multiplied by the number of turns.

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