A testing device and a testing method for high temperature superconducting tape and its cable joint

Abstract

The present invention belongs to the technical field of high-temperature superconductor design, and specifically relates to a test device and a test method for high-temperature superconducting tapes and their cable joints, including a dewar tank, a pressure source component, an electrode component and a test bench; it can provide a test environment for testing joints with multiple tapes in parallel, different pressure areas and different pressures under a low temperature environment. The design of multiple test circuits makes the device versatile and efficient. For single-tape joint tests, multiple samples can be tested in parallel to improve test efficiency. For cable joints, multiple tapes can be tested in parallel; the design of replaceable pressure heads can ensure that the joint samples are evenly stressed in all directions, avoid edge extrusion leading to tape damage, and provide different pressure areas; a quench protection circuit is added to the test device. When the sample quenches, the current can be quickly diverted to the quench protection circuit to avoid the sample from burning due to continued high current after quenching.

Description

Technical Field

[0001] The invention belongs to the technical field of high-temperature superconductor design, and in particular relates to a testing device and a testing method for a high-temperature superconducting tape and a cable joint thereof. Background Art

[0002] High-temperature superconductors can be used to manufacture magnets with higher operating temperatures and stronger magnetic fields, and are an important option for the design of future fusion reactor magnet systems. Increasing the operating temperature can significantly reduce the operating costs of the system, and increasing the magnetic field can significantly reduce the system size and reduce the difficulty of system control. At the same time, the use of high-temperature superconductors can also make it easier to design fusion reactor magnets into detachable structures, which will greatly simplify the construction and maintenance costs of reactor magnets and internal components, and improve economic benefits.

[0003] Most practical high-temperature superconducting materials have a strip structure, such as ReBCO coated high-temperature superconducting tapes. The tapes are multi-layered structures, and the main layer structures are a stabilizing layer, a superconducting layer, and a matrix layer. The stabilizing layer is generally made of copper and silver, which plays the role of shunting current to protect the superconducting layer; the matrix layer is generally made of Hastelloy alloy, which provides sufficient mechanical strength for the tape. Therefore, the joint technology of high-temperature superconducting tapes and cables is significantly different from that of traditional low-temperature superconductors, and new designs are required in terms of overlap methods, structures, and processes.

[0004] The thermal power of the magnet directly affects the thermal stability and cooling power of the magnet. When the detachable magnet is in steady-state operation, its thermal power mainly comes from the resistance heat of the detachable joint. Therefore, the joint is one of the key components of the detachable magnet. The main types of detachable joints include crimped joints and low-temperature welded joints. The detachable crimped joint has the advantages of simple process and convenient disassembly and assembly, but the controllability of the joint resistance is poor; the detachable welded joint has the advantages of low joint resistance and strong controllability, but the process is relatively complex and difficult to disassemble and assemble.

[0005] In order to conduct in-depth research on the detachable joints of high-temperature superconducting tapes and their cables, it is necessary to clarify the effects of processing technology, contact materials, pressure, joint length and other factors on joint resistance and current-carrying characteristics. However, the existing joint tests of high-temperature superconducting tapes and their cables are still in a relatively primitive form, mainly based on simple total resistance measurements based on tape critical current test devices. Therefore, a test device that can provide multiple tapes in parallel, different pressure areas and different pressures is needed. Summary of the invention

[0006] The purpose of the present invention is to provide a joint resistance testing device for high-temperature superconducting tapes and cables thereof in view of the above-mentioned defects in the prior art, which can provide a testing environment for testing joints with multiple tapes in parallel, different pressure areas and different pressures in a low temperature environment.

[0007] The technical solution of the present invention is as follows:

[0008] A testing device for high-temperature superconducting tape and cable joints thereof, comprising a dewar tank, a pressure source component, an electrode component and a testing bench;

[0009] In the test device, the Dewar tank provides a low-temperature test environment, and the interior of the Dewar tank wall is a vacuum environment;

[0010] The pressure source component is fixed in the center of the cover plate by a rod, and from the cover plate upwards are the anti-weight spring, the lower movable spring plate, the pressure spring, the upper movable spring plate, the pressure sensor, the force screw and the force wrench;

[0011] The force wrench is used to manually apply pressure. The pressure acts on the pressure sensor and is then transmitted to the movable spring plate and the pressure spring. The anti-weight spring is used to offset the weight of the movable spring plate and the spring, reducing the deviation between the pressure measurement value and the actual value.

[0012] The pressure sensor is arranged at a higher position, and the pressure control accuracy can be adjusted by changing the stroke of the pressure spring;

[0013] The pressure source components located under the cover plate are a pressure rod and a replaceable pressure block. The upper end of the pressure rod is connected to the lower movable spring plate to transmit the pressure to the replaceable pressure block, and finally the pressure acts on the test sample;

[0014] The sample is clamped between the T-shaped pressure relief table and the pressure block. The replaceable pressure block and the pressure rod are in contact with the arc surface and connected with the side openings.

[0015] The test bench is the area for sample installation and testing. The middle part is close to the pressing block, and the two ends are connected to the current lead and the platform pull rod. There are 5 pairs of electrode installation slots and their corresponding quench protection circuits;

[0016] The quench protection circuit is composed of a copper strip with a high residual resistivity, which is connected in parallel with its corresponding test circuit;

[0017] The electrode pressing plate is used to fix the end of the test sample to achieve electrical connection between the sample and the electrode; the intermediate insulating plate is used to achieve intermediate insulation between the quench protection circuit and the test sample; the T-shaped pressure reducing platform is used to reduce the pressure applied to the intermediate insulating plate;

[0018] The test circuit composed of the electrode component and the test sample needs to be completely immersed in liquid helium or liquid nitrogen. The structure of this electrode component is that one end of the electrode connecting plate is connected to the external cable, and the other end is connected to the current lead. The current lead extends from the top of the cover to the liquid nitrogen or liquid helium environment, and the lower end is fixed on the load-bearing platform and insulated from it, and at the same time contacts with the detachable electrode block, which is the connection between the electrode block and the sample.

[0019] The test sample is a high-temperature superconducting tape or its cable joint. The sample is installed between the electrode blocks of the same circuit and fixed between the pressure block and the T-shaped pressure relief platform, where the joint is directly opposite to the pressure block. The pressure block exerts pressure on the sample, and the pressure is transmitted to the T-shaped pressure relief platform. After the pressure is reduced, it is dispersed to the middle insulating pad. The middle insulating pad is machined with grooves to accommodate the quench protection circuit and liquid nitrogen. When a quench occurs, the current mainly passes through the quench protection circuit, and the pressure is finally transmitted to the load-bearing platform. The load-bearing platform is positioned by six platform tie rods, which together with the cover plate and the pressure rod form a reaction frame;

[0020] The Dewar tank is filled with liquid nitrogen or liquid helium, which can bring the temperature to about 77K and 4.2K respectively.

[0021] The underside of the Dewar cover is filled with foam insulation to reduce heat conduction

[0022] The pressure source of the device is a manual screw force adding method. In addition, a hydraulic cylinder or a pneumatic cylinder can also be used as a pressure source, wherein the hydraulic cylinder or the pneumatic cylinder can be electrically driven or manually driven.

[0023] The width of the pressing block is greater than the width of the measured strip, and the lower edge of the force-bearing surface in the length direction is chamfered to avoid edge extrusion and damage to the sample when a large pressure is applied.

[0024] Sample installation methods include pressure connection and welding.

[0025] The electrode clamp crimps the sample and electrode block and connects to the current leads.

[0026] After the sample and electrode block are welded, they are connected to the current lead through the electrode clamp.

[0027] A method for testing high-temperature superconducting tape and cable joints thereof, wherein the joint sample is installed so that the joint is in an area that can be completely covered by a pressing block;

[0028] a. For single-belt joint samples, connect both ends of the joint sample to the electrode blocks of the same circuit on both sides of the test bench;

[0029] b. For samples with multiple strip joints, weld the two ends of the same strip to two shunts respectively, and then connect the two shunts to the electrode blocks of the same circuit on both sides of the test bench respectively, and connect multiple test circuits in parallel;

[0030] (1) Install the pressing block of the specified specifications, adjust the position of the pressing block, keep its lower end surface parallel to the plane of the strip, and press it lightly;

[0031] (2) Arrange the voltage sampling points, fix the voltage leads to the platform pull rods, and lead them out through the through holes reserved in the cover plate:

[0032] a. For single-strip joint samples, weld the voltage leads 2 cm away from both sides of the joint overlap area;

[0033] b. For multi-strip joint samples, set the voltage lead for each strip using method a and obtain the voltage of the shunts on both sides of the strip;

[0034] (3) Temperature sensors are arranged on the sample surface, the upper surface of the electrode block and the side of the pressing block respectively, and the signal line is fixed to the platform pull rod and led out through the through hole reserved in the cover plate;

[0035] (4) Place the installed sample to be tested into a dewar tank, and slowly inject liquid nitrogen or liquid helium into the dewar tank until the sample to be tested and the briquette are completely immersed;

[0036] (5) Rotate the force screw to move it downward and apply a specified pressure to the joint.

[0037] (6) Pass current through the sample at a specified power-on rate and measure the voltage at each voltage sampling point. When the voltage no longer increases linearly with the current, reduce the power-on rate and continue to apply power until the voltage no longer increases. That is, the sample has completely quenched and most of the current has been diverted to the protection circuit. Record all the above data;

[0038] (7) The critical current Ic and shunt current Is of the sample are calculated by the formula U=I*R+L*Vc, where U is the measured joint voltage drop, I is the current input current, R is the joint resistance, and L is the strip length between the two voltage sampling points. The criteria for Ic and Is are 1 uV / cm and 0.1 uV / cm, respectively;

[0039] Repeat step 6 to gradually increase the applied pressure, and repeat steps 7 and 8 until the measured Ic is 95% of the maximum measured Ic value, that is, the critical pressure of the joint sample is 95% Ic.

[0040] The beneficial effects of the present invention are:

[0041] In order to study the detachable joints of high-temperature superconducting tapes and their cables, a joint testing device is provided which can connect multiple tapes in parallel, and has different pressure areas, different pressures and other testing environments, thus solving the problem that only single-tape joints can be tested under different pressures in general testing experiments.

[0042] The design of multiple test loops makes the device versatile and efficient. For single-strip joint testing, multiple samples can be tested in parallel to improve test efficiency. For cable joints, multiple strips can be tested in parallel.

[0043] The design of replaceable pressure head can ensure that the joint sample is evenly stressed in all directions, avoid edge extrusion and damage to the strip, and can provide different pressure areas;

[0044] A quench protection circuit is added to the test device. When the sample quenches, the current can be quickly diverted to the quench protection circuit to prevent the sample from being burned due to continued high current after the quench. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is a schematic structural diagram of the high-temperature superconducting joint testing device described in the present invention.

[0046] Figure 2 This is a cross-sectional view of the structure of the high-temperature superconducting joint testing device described in the present invention.

[0047] Figure 3 This is a schematic structural diagram of the high-temperature superconducting sample testing platform described in the present invention.

[0048] Figure 4 This is a cross-sectional view of the high-temperature superconducting sample test bench structure described in the present invention.

[0049] In the figure: 10-Dewar tank; 11-cover plate; 20-load-bearing platform; 21-platform pull rod; 22-pressure rod; 23-pressure block; 24-anti-weight spring; 25-pressure spring; 26-movable spring plate; 27-force screw; 28-force wrench; 29-pressure sensor; 30-current lead; 31-electrode connecting plate.

[0050] 20-load-bearing platform; 21-platform pull rod; 22-pressure rod; 23-replaceable pressure block; 32-quench protection circuit; 33-detachable electrode block; 40-electrode pressure plate; 41-middle insulating pad; 42-T-shaped pressure relief table. DETAILED DESCRIPTION

[0051] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0052] A testing device for a high-temperature superconducting tape and a cable joint thereof of the present invention comprises the following parts: a dewar tank 10, pressure source components 20-29, electrode components 30-33 and a testing bench 40-43.

[0053] In the test device, the dewar tank 10 provides a low temperature test environment, and the dewar tank is filled with liquid nitrogen or liquid helium, which can make the temperature reach about 77 K and 4.2 K respectively. The wall of the dewar tank is a vacuum environment, and the lower side of the cover plate 11 is filled with a foam insulation layer to reduce heat conduction.

[0054] The pressure source component is fixed in the center of the cover plate 11 with a rod to provide a pressure with an error of less than 1% and a range of 0-3200kgf. From the cover plate 11 upward, there are the anti-weight spring 24, the lower movable spring plate 26, the pressure spring 25, the upper movable spring plate 26, the pressure sensor 29, the force screw 27 and the force wrench 28. In this technical solution, a force wrench is used to manually apply pressure, and the pressure acts on the pressure sensor and then transmits it to the movable spring plate and the pressure spring. The anti-weight spring 24 is used to offset the gravity of the movable spring plate 26 and the spring 25, reducing the deviation between the pressure measurement value and the actual value. The pressure sensor 29 is used to measure the applied stress and is arranged at a higher position to reduce the influence of low temperature on the measurement accuracy. By changing the stroke of the pressure spring 25, the control accuracy of the pressure can be adjusted. The pressure source used in this technical solution is a manual screw force method. In addition, a hydraulic cylinder or a pneumatic cylinder can also be used as a pressure source, and the hydraulic cylinder or the pneumatic cylinder can be electrically driven or manual.

[0055] The pressure source components located below the cover plate 11 are the pressure rod 22 and the replaceable pressure block 23. The upper end of the pressure rod 22 is connected to the lower movable spring plate 26 to transmit the pressure to the replaceable pressure block 23, and finally the pressure acts on the test sample. The sample is clamped between the T-shaped pressure relief platform 42 and the pressure block 23. The replaceable pressure block 23 and the pressure rod 22 are in contact with an arc surface and connected with a hole on the side. The advantages of this design are: 1. The pressure head and the sample are automatically adjusted during the pressure process, so that the pressure on the pressurized strip in the horizontal direction is uniform; 2. The contact surface is large, which reduces the force on the pressure head and the pressure rod; 3. It is convenient for parts processing and replacement. The width of the pressure block 23 is slightly larger than the width of the measured strip, and the lower edge of the force-bearing surface in the length direction is chamfered to avoid edge extrusion and damage to the sample when a large pressure is applied.

[0056] The test bench is the area for sample installation and testing. The middle part is close to the pressing block 23, and the two ends are connected to the current lead 30 and the platform pull rod 21. There are 5 pairs of electrode 33 installation slots and their corresponding quench protection circuits 32. The quench protection circuit 32 is composed of copper bars with high residual resistivity and is connected in parallel with its corresponding test circuit. The electrode pressing plate 40 is used to fix the end of the test sample to achieve electrical connection between the sample and the electrode; the intermediate insulating plate 41 is used to achieve intermediate insulation between the quench protection circuit 32 and the test sample; the T-shaped pressure reducing platform 42 is used to reduce the pressure applied to the intermediate insulating plate 41.

[0057] A joint test device for high-temperature superconducting tape and its cable comprises: 1. a dewar tank 10; 2. a pressure source component 20-29; 3. an electrode component 30-33; 4. a test bench 40-43. The dewar tank is used to provide a low-temperature test environment, the pressure source component provides a variety of pressure loads, the electrode component is used to pass a test current, and the test bench is used to carry a test sample.

[0058] The test sample is a high-temperature superconducting tape or its cable joint. The sample is installed between the electrode blocks 33 of the same circuit and fixed between the pressure block 23 and the T-shaped pressure relief platform 42, where the joint is opposite to the pressure block 23. There are two ways to install the sample, namely pressure connection and welding. The specific implementation is selected according to the sample type and experimental requirements. The pressure block 23 applies pressure to the sample, and the pressure is transmitted to the T-shaped pressure relief platform 42. After the pressure is reduced, it is dispersed to the middle insulating pad 41. A groove is machined on the middle insulating pad 41 to accommodate the quench protection circuit 32 and liquid nitrogen. When a quench occurs, the current mainly passes through the quench protection circuit 32 to avoid burning the sample, and the heat of the circuit is absorbed by the refrigerant. The pressure is finally transmitted to the load-bearing platform 20, which is positioned by six platform pull rods 21, and together with the cover plate 11 and the pressure rod 22, it forms a reaction frame.

[0059] The test circuit composed of the electrode component and the test sample needs to be completely immersed in liquid helium or liquid nitrogen. The structure of this electrode component is: one end of the electrode connecting plate 31 is connected to the external cable, and the other end is connected to the current lead 30. The current lead 30 extends from the top of the cover plate 11 to the liquid nitrogen or liquid helium environment. The lower end is fixed on the load-bearing platform 20 and insulated from it, and is in contact with the detachable electrode block 33. Connection between the electrode block 33 and the sample: 1. The electrode pressing plate 40 presses the sample and the electrode block 33 and connects to the current lead 30, which is characterized by rapid disassembly and assembly; 2. After the sample and the electrode block 33 are welded, they are connected to the current lead 30 through the electrode pressing plate 40, which is characterized by low terminal resistance. Advantages of multiple separate electrode components: 1. For single-strip joints, multi-channel parallel testing can be performed simultaneously to improve test efficiency. In this example, five samples can be installed and tested in parallel; 2. Multi-channel parallel use can realize parallel connection of multiple strips, that is, testing of cable joints.

[0060] A method for testing a high-temperature superconducting tape and a cable joint thereof is as follows:

[0061] (8) Install the joint sample so that the joint is in an area that can be completely covered by the pressing block 23:

[0062] c. For single-belt joint samples, connect both ends of the joint sample to the electrode blocks 33 of the same circuit on both sides of the test bench;

[0063] d. For samples with multiple strip joints, weld the two ends of the same strip to two shunts respectively, and then connect the two shunts to the electrode blocks 33 of the same circuit on both sides of the test bench respectively, and connect multiple test circuits in parallel;

[0064] (9) Install the pressing block 23 of the specified specifications, adjust the position of the pressing block 23, keep its lower end surface parallel to the plane of the strip, and press it lightly;

[0065] (10) Arrange the voltage sampling points, fix the voltage lead to the platform tie rod 21, and lead it out through the through hole reserved in the cover plate 11:

[0066] a. For single-strip joint samples, weld the voltage leads 2 cm away from both sides of the joint overlap area;

[0067] b. For multi-strip joint samples, set the voltage lead for each strip using method a and obtain the voltage of the shunts on both sides of the strip;

[0068] (11) Temperature sensors are arranged on the sample surface, the upper surface of the electrode block 33 and the side of the pressing block 23 respectively. The signal line is fixed to the platform pull rod 21 and led out through the through hole reserved in the cover plate;

[0069] (12) The installed sample to be tested is placed into the Dewar tank 10, and liquid nitrogen or liquid helium is slowly injected into the Dewar tank 10 until the sample to be tested and the pressing block 23 are completely immersed;

[0070] (13) Rotate the force screw 27 to move it downward, applying a specified pressure to the joint.

[0071] (14) Apply current to the sample at a specified power-on rate and measure the voltage at each voltage sampling point. When the voltage no longer increases linearly with the current, reduce the power-on rate and continue to apply power until the voltage no longer increases. That is, the sample has completely quenched and most of the current has been diverted to the protection circuit. Record all the above data;

[0072] (15) The critical current Ic and shunt current Is of the sample are calculated by the formula U = I*R + L*Vc, where U is the measured joint voltage drop, I is the current input current, R is the joint resistance, and L is the strip length between the two voltage sampling points. The criteria for Ic and Is are 1 uV / cm and 0.1 uV / cm, respectively;

[0073] (16) Repeat step 6 to gradually increase the applied pressure, and repeat steps 7 and 8 until the measured Ic is 95% of the maximum measured Ic value, that is, the critical pressure of the joint sample is 95% Ic.

Claims

1. A test device for high-temperature superconducting tape and its cable joint, comprising a dewar tank, a pressure source component, an electrode component and a test bench; Features: In the test device, the Dewar tank provides a low-temperature test environment, and the interior of the Dewar tank wall is a vacuum environment; The pressure source component is fixed in the center of the cover plate by a rod, and from the cover plate upwards are the anti-weight spring, the lower movable spring plate, the pressure spring, the upper movable spring plate, the pressure sensor, the force screw and the force wrench; The force wrench is used to manually apply pressure. The pressure acts on the pressure sensor and is then transmitted to the movable spring plate and the pressure spring. The anti-weight spring is used to offset the weight of the movable spring plate and the spring, reducing the deviation between the pressure measurement value and the actual value. The pressure sensor is arranged at a higher position, and the pressure control accuracy can be adjusted by changing the stroke of the pressure spring; The pressure source components located under the cover plate are a pressure rod and a replaceable pressure block. The upper end of the pressure rod is connected to the lower movable spring plate to transmit the pressure to the replaceable pressure block, and finally the pressure acts on the test sample; The sample is clamped between the T-shaped pressure relief table and the pressure block. The replaceable pressure block and the pressure rod are in contact with the arc surface and connected with the side openings. The test bench is the area for sample installation and testing. The middle part is close to the pressing block, and the two ends are connected to the current lead and the platform pull rod. There are 5 pairs of electrode installation slots and their corresponding quench protection circuits. The quench protection circuit is composed of a copper strip with a high residual resistivity, which is connected in parallel with its corresponding test circuit; The electrode pressing plate is used to fix the end of the test sample to achieve electrical connection between the sample and the electrode; the intermediate insulating plate is used to achieve intermediate insulation between the quench protection circuit and the test sample; the T-shaped pressure reducing platform is used to reduce the pressure applied to the intermediate insulating plate; The test circuit composed of the electrode component and the test sample needs to be completely immersed in liquid helium or liquid nitrogen. The structure of this electrode component is that one end of the electrode connecting plate is connected to the external cable, and the other end is connected to the current lead. The current lead extends from the top of the cover to the liquid nitrogen or liquid helium environment, and the lower end is fixed on the load-bearing platform and insulated from it, and at the same time contacts with the detachable electrode block, which is the connection between the electrode block and the sample.

2. A testing device for high temperature superconducting tape and its cable joints as claimed in claim 1, characterized in that: The test sample is a high-temperature superconducting tape or its cable joint. The sample is installed between the electrode blocks of the same circuit and fixed between the pressure block and the T-shaped pressure reducing platform, where the joint is opposite to the pressure block. The pressure block applies pressure to the sample, and the pressure is transmitted to the T-shaped pressure reducing platform. After the pressure is reduced, it is dispersed to the middle insulating pad. The middle insulating pad is machined with grooves to accommodate the quench protection circuit and liquid nitrogen. When quench occurs, the current mainly passes through the quench protection circuit, and the pressure is finally transmitted to the load-bearing platform. The load-bearing platform is positioned by six platform tie rods, which together with the cover plate and the pressure rod form a reaction frame.

3. A testing device for high temperature superconducting tape and its cable joint according to claim 1, characterized in that: The Dewar tank is filled with liquid nitrogen or liquid helium, which can bring the temperature to 77K and 4.2K respectively.

4. A testing device for high temperature superconducting tape and its cable joint according to claim 1, characterized in that: The underside of the Dewar cover is filled with foam insulation to reduce heat conduction.

5. A testing device for high temperature superconducting tape and cable joints thereof as claimed in claim 1, characterized in that: The pressure source of this device is a manual screw force method.

6. A testing device for high temperature superconducting tape and its cable joint according to claim 1, characterized in that: The width of the pressing block is greater than the width of the measured strip, and the lower edge of the force-bearing surface in the length direction is chamfered to avoid edge extrusion and damage to the sample when a large pressure is applied.

7. A testing device for high temperature superconducting tape and its cable joint according to claim 1, characterized in that: Sample installation methods include pressure connection and welding.

8. A testing device for high temperature superconducting tape and its cable joints as claimed in claim 1, characterized in that: The electrode clamp crimps the sample and electrode block and connects to the current leads.

9. A testing device for high temperature superconducting tape and cable joints thereof as claimed in claim 1, characterized in that: After the sample and electrode block are welded, they are connected to the current lead through the electrode clamp.

10. A method for testing a high temperature superconducting tape and a cable joint thereof according to any one of claims 1 to 9, characterized in that: Install the joint sample so that the joint is in an area that can be fully covered by the pressing block; a. For single-belt joint samples, connect both ends of the joint sample to the electrode blocks of the same circuit on both sides of the test bench; b. For samples with multiple strip joints, weld the two ends of the same strip to two shunts respectively, and then connect the two shunts to the electrode blocks of the same circuit on both sides of the test bench respectively, and connect multiple test circuits in parallel; (1) Install the pressing block of the specified specifications, adjust the position of the pressing block, keep its lower end surface parallel to the plane of the strip, and press it lightly; (2) Arrange the voltage sampling points, fix the voltage leads to the platform pull rods, and lead them out through the through holes reserved in the cover plate: a. For single-strip joint samples, weld the voltage leads 2 cm away from both sides of the joint overlap area; b. For multi-strip joint samples, set the voltage lead for each strip using method a and obtain the voltage of the shunts on both sides of the strip; (3) Temperature sensors are arranged on the sample surface, the upper surface of the electrode block and the side of the pressing block respectively, and the signal line is fixed to the platform pull rod and led out through the through hole reserved in the cover plate; (4) Place the installed sample to be tested into a dewar tank, and slowly inject liquid nitrogen or liquid helium into the dewar tank until the sample to be tested and the briquette are completely immersed; (5) Rotate the force screw to move it downward and apply a specified pressure to the joint. (6) Pass current through the sample at a specified power-on rate and measure the voltage at each voltage sampling point. When the voltage no longer increases linearly with the current, reduce the power-on rate and continue to apply power until the voltage no longer increases. That is, the sample has completely quenched and most of the current has been diverted to the protection circuit. Record all the above data; (7) The critical current Ic and shunt current Is of the sample are calculated by the formula U=I*R+L*Vc, where U is the measured joint voltage drop, I is the current input current, R is the joint resistance, and L is the strip length between the two voltage sampling points. The criteria for Ic and Is are 1 uV / cm and 0.1 uV / cm, respectively; Repeat step 6 to gradually increase the applied pressure, and repeat steps 7 and 8 until the measured Ic is 95% of the maximum measured Ic value, that is, the critical pressure of the joint sample is 95% Ic.

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