Method for testing radial stress of uninsulated high-temperature superconducting coil

Abstract

The invention discloses a method for testing the radial stress of an uninsulated high-temperature superconducting coil, and belongs to the field of superconducting electricians, and the radial stress is an important parameter of the high-temperature superconducting coil and is mainly the superposition of winding tension, electromagnetic load and cold shrinkage force. The radial stress is related to the self-protection characteristic of the high-temperature superconducting coil. The larger the radial stress is, the smaller the turn-to-turn contact resistance is, and the current at the hot spot is easier to shunt in the radial direction to avoid quenching. The invention relates to the technical field of high-temperature superconducting coils, potential points are arranged in the coil, turn-to-turn contact resistance is inverted according to a turn-to-turn mutual inductance matrix and test voltage and current signals, and radial stress is inverted by referring to the mapping relation between pressure and the turn-to-turn contact resistance.

Description

Technical Field

[0001] The invention belongs to the field of superconducting engineering and relates to a method for testing 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 advantages such as high irreversible magnetic field and mechanical strength. Compared with the first-generation high-temperature superconducting materials, their biggest advantages are higher mechanical strength and high irreversible magnetic field. They have obvious advantages in the field of high-field magnets and have broad prospects for high-field applications. In particular, with the continuous improvement of technical parameters of large-scale 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 demand for strong magnetic field operating environments, large-scale high-field applications are becoming more and more urgent at this stage.

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

[0004] The self-protection characteristics of ReBCO high-temperature superconducting uninsulated coils are closely related to the inter-turn contact resistance. The smaller the contact resistance, the better the self-protection characteristics. Since the surface of the ReBCO high-temperature superconducting tape is microscopically uneven, the greater the radial compressive stress, the tighter the tape contact, and the smaller the contact resistance. Existing research has hardly conducted radial stress testing and characterization analysis under low-temperature operating conditions, so it is very meaningful to invent and explore the radial stress of high-temperature superconducting coils. Summary of the invention

[0005] Uninsulated 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, which is mainly the superposition of winding tension, electromagnetic load and cold shrinkage force. Radial stress is related to the self-protection characteristics 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 easier to radially shunt to avoid quenching.

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

[0007] Step 1: Test the inter-turn contact resistivity R of the high-temperature superconducting tape ct Relationship with radial stress Fr: R ct ;

[0008] Step 2: Use superconducting tape to wind an uninsulated high-temperature superconducting coil. Arrange several potential points in the uninsulated high-temperature superconducting coil in turns, and calculate the turn-to-turn mutual inductance matrix M. ij ; Where i and j are the index numbers of the sub-turns respectively;

[0009] Step 3, exciting the non-insulated high temperature superconducting coil, and recording the excitation current and the sub-turn voltages at several potential points in real time;

[0010] Step 4, calculating the inter-turn contact resistance according to the excitation current of the non-insulated high-temperature superconducting coil, the sub-turn voltage of the sub-turn coil and the sub-turn mutual inductance matrix of the sub-turn coil;

[0011] Step 5: Calculate the inter-turn contact resistivity R according to the coil turn geometry and inter-turn contact resistance. ct ; According to the inter-turn contact resistivity R ct Relationship with radial stress Fr: 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 low-temperature operating conditions, and provide verification and correction for the theoretical mechanical model of the superconducting coil; the present invention can also calculate the internal turn-to-turn resistance value of the superconducting coil, and provide necessary data support for the quench characteristic analysis of an uninsulated coil. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0015] Figure 2 Schematic diagram of a high-temperature superconducting coil arranged in turns at potential points;

[0016] Figure 3 Schematic diagram of the circuit model of a non-insulated high-temperature superconducting coil. DETAILED DESCRIPTION

[0017] In order to make the purpose, technical scheme and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in each embodiment 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-mentioned purpose, the present invention adopts the following technical scheme. The method of the present invention is further described below in conjunction with the attached specific embodiments.

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

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

[0020] Step 2: Use superconducting tape to wind an uninsulated high-temperature superconducting coil. Arrange several potential points in the uninsulated high-temperature superconducting coil in turns, and calculate the turn-to-turn mutual inductance matrix M. ij ; Where i and j are the index numbers of the sub-turns respectively;

[0021] Step 3, exciting the non-insulated high temperature superconducting coil, and recording the excitation current and the sub-turn voltages at several potential points in real time;

[0022] Step 4, calculating the inter-turn contact resistance according to the excitation current of the non-insulated high-temperature superconducting coil, the sub-turn voltage of the sub-turn coil and the sub-turn mutual inductance matrix of the sub-turn coil;

[0023] Step 5: Calculate the inter-turn contact resistivity R according to the coil turn geometry and inter-turn contact resistance. ct ; According to the inter-turn contact resistivity R ct Relationship with radial stress Fr: R ct Invert the radial stress.

[0024] Step 1 is as follows: Figure 1 As shown, the superconducting layers of two high-temperature superconducting tapes are evenly aligned with the non-superconducting layers, and the signal lines are connected on both sides. The contact area of ​​the high-temperature superconducting tape is S, and the loading pressure is F, then the radial stress is F / S; the current I is passed through both sides, and the signal line voltage is measured to be V, then the inter-turn surface resistivity is V / I S, test strip interturn contact resistivity R ct Corresponding relationship between radial stress Fr: R ct . Contact resistivity R ct Relationship with radial pressure Fr: R ct It is an experimental test value, which is mainly related to the surface roughness of the strip. The greater the radial pressure, the tighter the contact between the strips, and the contact resistivity R ct The smaller.

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

[0026] Step 3 is specifically as follows: placing the high-temperature superconducting coil in a low-temperature environment, exciting the high-temperature superconducting coil at a constant rate, and recording the excitation current and the turn-by-turn voltage in real time.

[0027] Step 4 is calculated as follows: Figure 3The figure shows a 2-turn high-temperature superconducting coil (similar to multi-turn coils), where I 1 and I 2 is the circular current of the sub-turn coil, R ct1 and R ct2 They are the turn-to-turn contact resistance, U 1 and U 2 is the turn-to-turn voltage, and I is the field current.

[0028] Table 1 Inductance matrix

[0029] Sub 1, Sub 2 represent two sub-turns, and L 1 , L 2 、M 12 、M 21 Respectively represent the inductance of turn 1 and turn 2 and the turn-to-turn mutual inductance matrix of turn 1 and turn 2, where M 21 = M 12 .

[0030] According to the mutual inductance matrix, the following formulas can be obtained:

[0031] ,

[0032] ,

[0033] Among them, the sub-turn ring current I 1 and I 2 As shown in the following set of formulas;

[0034] ,

[0035] ,

[0036] Substituting the following formula into the above formula yields:

[0037] ,

[0038] .

[0039] In the above formula, only the contact resistance R ct1 and R ct2 is an unknown quantity, and the rest are known quantities. Therefore, the contact resistance can be calculated.

[0040] When N turns are divided, the contact resistance expression is as follows:

[0041] ,

[0042] Among them, L 1 , L nare the inductance of turn 1, turn n and M in is the mutual inductance matrix between the ith sub-turn and the nth sub-turn, R cti , R ctn , R ct1 is the inter-turn contact resistance of the ith sub-turn, the nth sub-turn and the 1st sub-turn, I is the excitation current, and thus, there are n columns of expressions, among which n inter-turn resistances are unknown quantities, and thus the inter-turn contact resistance matrix can be obtained. .

[0043] Step 5 is specifically calculated as follows: Based on the inter-turn contact resistance of step 4 and the coil geometry of the sub-turn, such as the number of turns N of the sub-turn, the average cross-sectional area per turn S n , the inter-turn contact resistivity is obtained .

[0044] The specific inversion method is: the inter-turn contact resistivity R ct Relationship with radial stress Fr: R ct The horizontal axis is the radial stress, and the vertical axis is the inter-turn contact resistivity. According to the calculated inter-turn contact resistivity R ct , take values ​​at fixed points in the figure to calculate the radial stress.

Claims

1. A method for testing radial stress of a non-insulated high-temperature superconducting coil, characterized in that: The following steps are involved: Step 1: Test the inter-turn contact resistivity R of the high-temperature superconducting tape ct Relationship with radial stress Fr: R ct ; Step 2: Use superconducting tape to wind an uninsulated high-temperature superconducting coil. Arrange several potential points in the uninsulated high-temperature superconducting coil in turns, and calculate the turn-to-turn mutual inductance matrix M. ij ; Where i and j are the index numbers of the sub-turns respectively; Step 3, exciting the non-insulated high temperature superconducting coil, and recording the excitation current and the sub-turn voltages at several potential points in real time; Step 4, calculating the inter-turn contact resistance according to the excitation current of the non-insulated high-temperature superconducting coil, the sub-turn voltage of the sub-turn coil and the sub-turn mutual inductance matrix of the sub-turn coil; Step 5: Calculate the inter-turn contact resistivity R according to the coil turn geometry and inter-turn contact resistance. ct ; According to the inter-turn contact resistivity R ct Relationship with radial stress Fr: R ct Invert the radial stress.

2. A method for testing radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that: Step 1 is as follows: two superconducting tapes are placed on a press, the non-insulated high-temperature superconducting tape is placed at a temperature equivalent to the operating temperature of the coil, the superconducting layers and non-superconducting layers of the two tapes are evenly aligned, the press is vertically loaded with pressure, and the inter-turn contact resistivity R of the tape is tested. ct Relationship with radial stress Fr: R ct .

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

4. A method for testing radial stress of a non-insulated high-temperature superconducting coil according to claim 3, characterized in that: The potential point thickness is smaller than the strip thickness, and reducing the potential point thickness results in a bulge at the potential point.

5. The method for testing radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that: Step 3 is specifically as follows: the non-insulated high temperature superconducting coil is excited at a constant rate, and the rate of increase of the turn voltage gradually decreases.

6. The method for testing radial stress of a non-insulated high-temperature superconducting coil according to claim 1, characterized in that: Step 4 is as follows: When the non-insulated high-temperature superconducting coil has N turns, the contact resistance expression is as follows: ， Among them, L1, L n are the inductance of the 1st sub-turn, the nth sub-turn and M in is the mutual inductance between the ith and nth sub-turns, R ct1 , R cti , R ctn is the inter-turn contact resistance of the 1st sub-turn, the i-th sub-turn and the n-th sub-turn, I is the excitation current of the uninsulated high-temperature superconducting coil, from which we can know that there are n columns of expressions, among which n inter-turn contact resistances are unknown quantities, thus the inter-turn contact resistance matrix can be obtained .

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

8. A method for testing radial stress of a non-insulated high-temperature superconducting coil according to claim 7, characterized in that: The specific inversion method is: the inter-turn contact resistivity R ct Relationship with radial stress Fr: R ct The horizontal axis is the radial stress, and the vertical axis is the inter-turn contact resistivity. According to the calculated inter-turn contact resistivity R ct , take values ​​at fixed points in the figure to calculate the radial stress.

9. A method for testing radial stress of a non-insulated high temperature superconducting coil according to claim 1, characterized in that: The resistance of the inter-turn contact resistance is of the same order of magnitude as the turn-to-turn mutual inductance matrix.

10. A method for testing 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 resistance of adjacent surfaces, that is, the contact resistivity of the sub-turn surface divided by the average contact area of ​​the sub-turn multiplied by the number of turns.

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