Contact resistance testing method and testing loop

Abstract

The present invention relates to the technical field of resistance testing, and in particular to a contact resistance testing method and a testing loop. The method comprises: applying a given contact pressure to enable two metal conductors to be in contact with each other; connecting a pair of wires, respectively connected to the two metal conductors, to two ends of a current source to form an input current; using the other pair of wires to introduce voltages at two ends of the metal conductors into a multimeter for measurement; and calculating a contact resistance value on the basis of a measured result, wherein the input current is a pulse current. The present invention provides a method for acquiring contact surface temperatures at different measurement points and different stages. The calculated contact resistance value is compared with an actually measured contact resistance value for verification, so as to derive a calculation formula capable of simulating contact resistance values under different contact pressures and different contact surface temperatures, thereby quickly calculating contact resistance values adapted to use environments.

Description

A method and test circuit for testing contact resistance Technical Field

[0001] This invention relates to the field of resistance testing technology, and in particular to a method and test circuit for testing contact resistance. Background Technology

[0002] Splicing fittings are mainly used to connect current between two metal conductors, such as splicing clamps and splicing conduits. In recent years, with the increase in household appliances and the increased load on factory machinery, the reliability of splicing fittings has been greatly challenged. Clamps are key components for carrying current in overhead transmission lines. Operating in high-temperature and harsh environments for extended periods, they are highly susceptible to mechanical damage and electrical contact failure. Mechanical damage mainly manifests as deformation and breakage of the clamp, while electrical contact failure is the primary failure mode of splicing clamps. In practical applications, the main manifestation of electrical contact failure is a continuously increasing contact resistance, severe overheating, and even burning of the contact surface between the clamp and the cable.

[0003] During the design, installation, and operation of splicing fittings, contact resistance is generally affected by factors such as contact type, contact pressure, material properties, and contact surface temperature. Excessive contact resistance generates a large amount of Joule heat, causing material aging and insulation layer combustion, affecting the mechanical and electrical properties of the material, and generating significant thermal stress between the contact surfaces, leading to thermal expansion of the metal and reducing the lifespan of the splicing fittings. This not only causes economic losses but may even seriously endanger personal safety.

[0004] Therefore, in order to adapt the contact resistance value to the working environment, the existing technology needs a test method for the contact resistance value between conductors under different contact pressures and contact surface temperatures to simulate the range of contact resistance variation in the subsequent use environment. Summary of the Invention

[0005] In this section, as well as in the abstract and title of this application, some simplifications or omissions may be made to avoid obscuring the purpose of this section, the abstract, and the title of this application, and such simplifications or omissions shall not be used to limit the scope of the invention.

[0006] In view of the problem that it is inconvenient to measure the contact resistance between conductors under different environmental conditions in the above or existing technologies, the present invention is proposed.

[0007] Therefore, one object of the present invention is to provide a method for testing contact resistance.

[0008] To solve the aforementioned technical problem, the present invention provides the following technical solution: a method for testing contact resistance, used to detect the contact resistance between two metal conductors, comprising,

[0009] Two metal conductors are brought into contact by applying a given contact pressure;

[0010] The input current is obtained by connecting the two ends of the current source with a pair of wires that are respectively connected to two metal conductors.

[0011] Use another pair of wires to introduce the voltage across the metal conductor into the multimeter for measurement;

[0012] Calculate the contact resistance value based on the measured results;

[0013] The input current is a pulse current.

[0014] In a preferred embodiment of the contact resistance testing method of the present invention, the application of a given contact pressure includes:

[0015] Place the two metal conductors in the working area of ​​the press.

[0016] Adjust the contact surface of the two metal conductors to match the direction of pressure application from the press.

[0017] Insulating material is added in the direction of pressure application to isolate the press from the metal conductor.

[0018] As a preferred embodiment of the contact resistance testing method of the present invention, it further includes measuring the contact resistance value under different contact pressures, which includes,

[0019] The contact pressure between the two metal conductors is increased sequentially according to the set gradient value;

[0020] Each time the pressure is increased, a transient current value of different magnitude is used as the pulse current input;

[0021] The average value of the contact resistance measured by different transient currents is used as the contact resistance for the corresponding contact pressure.

[0022] As a preferred embodiment of the contact resistance testing method of the present invention, it further includes:

[0023] Record the curve of the measured contact resistance as a function of contact pressure;

[0024] The range of contact pressures at which the contact resistance tends to stabilize with changes in contact pressure is taken as the working range.

[0025] Methods for calculating contact resistance values ​​within the operating range of contact pressure include:

[0026] Calculate the contact resistance of a single contact spot formed under a given contact pressure.

[0027] The combination of all contact spots formed between two metal conductors is taken as the contact surface;

[0028] The total contact resistance of the contact surface is calculated as the contact resistance between the two metal conductors.

[0029] In a preferred embodiment of the contact resistance testing method described in this invention, the contact spot between the two metal conductors is considered as a circle, and the formula for calculating the contact resistance of a single contact spot between the two metal conductors is as follows:

[0030] The first term is the cold-state shrinkage resistance R of the two metallic conductors at 0°C. s The calculation formula, the second term is the film resistance R formed on the contact surface of the two metal conductors. f The calculation formula is as follows: ρ1 and ρ2 are the resistivity of two metal conductors in contact, r represents the equivalent radius of the contact spot of the two metal conductors, and θ is the resistivity of the contamination film on the contact surface of the two metal conductors.

[0031] As a preferred embodiment of the contact resistance testing method of the present invention, both metal conductors are cylindrical in shape, and the two metal conductors are in contact in the form of line contact between the side surface and the bottom surface of the cylinder, or surface contact between the bottom surfaces of the cylinders.

[0032] The formula for calculating the radius r1 of the contact surface between two cylindrical metal conductors is:

[0033] In the formula, P represents the contact pressure, and E * denoted by , r represents the equivalent elastic modulus, and r represents the equivalent contact radius of a single contact spot;

[0034] Among them, the equivalent elastic modulus E * The formula for calculating the equivalent contact radius r of a single contact spot is as follows:

[0035] In the formula, E1 and E2 represent the elastic moduli of the two contacting metal conductors, μ1 and μ2 represent the Poisson's ratios of the two contacting bodies, and R1 and R2 represent the radii of the two contacting cylindrical metal conductors.

[0036] In a preferred embodiment of the contact resistance testing method described in this invention, when two cylindrical metal conductors are in line contact, the two metal conductors are considered as having a series of equivalent contact spots as the contact surface. The formula for calculating the total contact resistance between the two metal conductors is as follows:

[0037] In the formula, R c R represents the total contact resistance. s For the shrinkage resistance of a single contact, b represents the length of the contact surface, and r represents the radius of a single contact;

[0038] The hot shrinkage resistance R of a single contact sθ The calculation formula is:

[0039] In the formula: R s0 It is the cold-state shrinkage resistance at 0℃, where T is the temperature of the contact surface and α is the temperature coefficient of resistance.

[0040] In a preferred embodiment of the contact resistance testing method of the present invention, the method for obtaining the contact surface temperature includes,

[0041] Two metal conductors are brought into contact under a given contact pressure by a splicing clamp;

[0042] A pulse current is input across the two ends of two metallic conductors, and the temperature at the measuring point is obtained.

[0043] The measuring points include at least the middle of the connector clamp and the connection points between the connector clamp and the two metal conductors.

[0044] Based on the same inventive concept, the present invention also provides a test circuit for contact resistance, which is used to implement a method for testing contact resistance, comprising two sets of cables to be tested, a current source for providing input current, and a multimeter for measuring the voltage across the two ends of the cables to be tested.

[0045] The two sets of cables under test are connected to the current source and the multimeter through wires to form a circuit. After the two sets of cables under test come into contact, a contact resistance is generated. The multimeter is connected in parallel with the two sets of cables under test.

[0046] As a preferred embodiment of the test circuit for contact resistance described in this invention, the test cable is provided in at least three groups and connected sequentially through its ends, with adjacent groups of test cables connected in contact through a set of splice clamps.

[0047] The current source is a high-current generator connected to both ends of the sequentially connected test cables. Each set of splice clamps maintains contact between the two sets of test cables according to a given contact pressure.

[0048] The beneficial effects of the present invention are as follows: The present invention provides a method for obtaining the contact surface temperature at different stages and different measuring points, and compares and verifies the calculated contact resistance value with the actual tested contact resistance value, thereby deriving a calculation formula for the contact resistance value that can simulate different contact pressures and different contact surface temperatures under different operating environments, so as to quickly calculate the contact resistance value that is suitable for the operating environment. Attached Figure Description

[0049] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0050] Figure 1 is a schematic diagram of the contact resistance test principle in Embodiment 1 of the present invention.

[0051] Figure 2 is a schematic diagram of the test circuit in Embodiment 1 of the present invention.

[0052] Figure 3 is a schematic diagram of the change of contact resistance with contact pressure in Embodiment 1 of the present invention.

[0053] Figure 4 shows the contact resistance as a function of coarseness in Embodiment 2 of the present invention. A diagram illustrating the change in degree.

[0054] Figure 5 is a schematic diagram comparing the experimental and calculated values ​​of the contact resistance in Embodiment 2 of the present invention.

[0055] Figure 6 is a schematic diagram of the electrical measurement points for contact resistance in Embodiment 3 of the present invention.

[0056] Figure 7 is a schematic diagram of the contact resistance test principle in Embodiment 3 of the present invention.

[0057] Figure 8 is a schematic diagram of the test circuit in Embodiment 3 of the present invention.

[0058] Figure 9 is a schematic diagram of the temperature measurement point of the contact resistance in Embodiment 3 of the present invention. Detailed Implementation

[0059] To make the objectives, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0060] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0061] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0062] Example 1

[0063] Referring to Figures 1-3, the first embodiment of the present invention provides a method for testing contact resistance, which is used to detect the contact resistance between two metal conductors. First, the two metal conductors are brought into contact by applying a given contact pressure. Then, a pair of wires connected to the two metal conductors are used to connect the two ends of a current source as the input current. Another pair of wires is used to introduce the voltage across the two ends of the metal conductors into a multimeter for measurement. The input current is a pulse current. The contact resistance value is then calculated based on the measured results.

[0064] A pair of wires connects the two ends of a current source as the input current, and another pair of wires introduces the voltage across the two metal conductors to be measured into a multimeter for measurement. The measurement principle diagram is shown in Figure 1, where R1, R2, R7, and R8 are the resistances of the wires, R3 and R6 are the contact resistances, R4 and R5 are the lead resistances of the two metal conductors to be measured, and Ux is the voltage value across the test point. Typically, the input resistance of the voltmeter is much greater than the measuring resistance, and the resistance of the wires is also relatively small. Therefore, in the measuring wires, I2 can be approximated as I; that is, the relationship between the voltage value across the test point and the contact resistance can be expressed by the following formula: Ux = I(R3 + R4 + R5 + R6 + R...) x )

[0065] For minute contact resistances, a small current cannot guarantee the accuracy of the measurement results. However, if a large current is continuously applied, it will inevitably generate a large amount of Joule heat, which will have a certain impact on the measurement results. Moreover, this impact will become more and more obvious as the measurement time increases. By using pulsed current instead of continuous current to measure contact resistance, when the current application time is relatively short, even if a large current pulse is applied, the temperature generated will have little impact on the resistance of the contact area. Therefore, the method of using a larger pulsed current to measure contact resistance can improve the accuracy of the measurement and prevent the material in the contact area from softening.

[0066] Furthermore, applying the given contact pressure includes placing the two metal conductors in the working area of ​​the press, adjusting the contact surfaces of the two metal conductors to match the pressure application direction of the press, and adding insulating material in the pressure application direction to isolate the press from the metal conductors. In this embodiment, the two metal conductors are made of aluminum alloy. One set is an aluminum alloy round bar with dimensions of 40mm in length and 20mm in diameter, and the other set is an aluminum alloy disc with dimensions of 20mm in length and 80mm in diameter. To avoid the influence of roughness on the test results when investigating the effect of pressure on contact resistance, this section uses the same sample method to ensure that the roughness of the aluminum alloy sample is constant. A PC-5 press is used to apply pressure to the sample. The PC-5 press is a manual hydraulic press with advantages such as stable pressure application and high precision. The press dial can simultaneously display the applied pressure in tons and megapascals, with a range of 0–45 MPa. This test uses pressure to control the magnitude of the pressure. Some parameters of the PC-5 press are shown in the table below:

[0067] Table 1 Parameters of PC-5 Press

[0068] Preferably, the method for measuring contact resistance under different contact pressures includes: sequentially increasing the contact pressure between the two metal conductors according to a set gradient value; after each increase in pressure, using transient current values ​​of different magnitudes as pulse current inputs; and using the average value of the contact resistance measured by different transient currents as the contact resistance at the corresponding contact pressure. As shown in Figure 2, the two metal conductor samples to be tested are wiped clean of dust and debris and placed on a press. Insulating material is added between the sample and the press. Then, four wires are led out from the sample and connected to a pair of excitation lines and a pair of measurement lines of a micro-ohmmeter, respectively, for applying current to the micro-ohmmeter and measuring the contact resistance. In this embodiment, a Micro-Centurion II model micro-ohmmeter is used. In actual operation, the current flows in from the thick red wire and out from the thick black wire. The two thin wires serve as the measuring wires of the micro-ohmmeter. Before each test, check whether the sample is placed flat and ensure that the sample is absolutely insulated from the press. Then, tighten the oil drain valve of the press clockwise and start applying pressure. When the pressure reaches the specified value, press the start button of the micro-ohmmeter, select the transient test current for measurement and record the result. After a single test is completed, turn off the micro-ohmmeter and repeat the above process to continue testing.

[0069] Furthermore, the curves showing the change in contact resistance with contact pressure were recorded, and the range of contact pressures where the contact resistance tended to stabilize with changing contact pressure was taken as the working range. The method for calculating the contact resistance value within the working range of contact pressure includes calculating the contact resistance value of a single contact spot formed under a given contact pressure, taking the combination of all contact spots formed between the two metal conductors as the contact surface, and calculating the total contact resistance value of the contact surface as the contact resistance value between the two metal conductors. Before the test, the resistance of the aluminum alloy round bar and disk were first measured using a micro-ohmmeter, which yielded values ​​of 1.34 μΩ and 2.35 μΩ, respectively. During the test, pressures ranging from 1 to 30 MPa were applied in gradients of 1 MPa. After each pressure application, the contact resistance between the aluminum alloy samples was recorded using transient currents of 10 A, 20 A, 50 A, 100 A, and 200 A from the micro-ohmmeter. The average value of these five sets was taken as the final test result. During the test, movement between the lead wire and the aluminum alloy sample should be avoided as much as possible to prevent errors in the measurement results due to different contact positions between the lead wire and the sample. The measurement results are plotted as shown in Figure 3 after the test.

[0070] As shown in Figure 3, the contact resistance of the aluminum alloy samples decreases continuously with increasing pressure. The rate of decrease is faster at lower pressures, but slows down as the pressure increases, eventually stabilizing. This is because when the pressure is low, the contact between the aluminum alloy rod and the disk is insufficient. Applying pressure at this point causes a rapid increase in the contact area, leading to a rapid decrease in the contact resistance. As the pressure increases further, the contact area between the aluminum alloy samples increases. When the pressure reaches 15 MPa, the contact between the aluminum alloy samples is sufficient, and further pressure increases the effective contact area, causing the contact spot area to stabilize. Therefore, the final contact resistance of the aluminum alloy samples stabilizes at around 15 μΩ. The sum of the resistance values ​​of the aluminum alloy rod and disk measured separately before the test was 3.69 μΩ, still far less than the minimum measured contact resistance. This indicates that during the contact process between the aluminum alloy rod and disk, the contact resistance is the main source of the total resistance, while the conductor's own resistance accounts for only a small proportion of the total resistance.

[0071] This embodiment provides a test method for obtaining stable contact pressure, ensuring that the samples can make sufficient contact, finding a suitable contact pressure range for calculation, and facilitating subsequent test calculations.

[0072] Example 2

[0073] Referring to Figures 4-5, this is the second embodiment of the present invention. Unlike the previous embodiment, this embodiment treats the contact spot between the two metal conductors as a circle, and the formula for calculating the contact resistance of a single contact spot between the two metal conductors is:

[0074] The first term is the cold-state shrinkage resistance R of the two metallic conductors at 0°C. s The calculation formula, the second term is the film resistance R formed on the contact surface of the two metal conductors. f The calculation formula is as follows: ρ1 and ρ2 are the resistivity of two metal conductors in contact, r represents the equivalent radius of the contact spot of the two metal conductors, and θ is the resistivity of the contamination film on the contact surface of the two metal conductors.

[0075] Specifically, both metal conductors are cylindrical in shape, and the two metal conductors are in contact as either a line contact between the side surface and the bottom surface of the cylinder, or a surface contact between the bottom surfaces of the cylinders.

[0076] The formula for calculating the radius r1 of the contact surface between two cylindrical metal conductors is:

[0077] In the formula, P represents the contact pressure, and E * denoted by , r represents the equivalent elastic modulus, and r represents the equivalent contact radius of a single contact spot;

[0078] Among them, the equivalent elastic modulus E * The formula for calculating the equivalent contact radius r of a single contact spot is as follows:

[0079] In the formula, E1 and E2 represent the elastic moduli of the two contacting metal conductors, μ1 and μ2 represent the Poisson's ratios of the two contacting bodies, and R1 and R2 represent the radii of the two contacting cylindrical metal conductors. In this embodiment, the same sample as in Example 1 was used, ensuring the pressure applied by the press was 15 MPa, and the transient current supplied by the micro-ohmmeter was set to 100 A. The processed data and the resulting curve are shown in Figure 4. As can be seen from Figure 4, with the coarse... With increasing pressure, the contact resistance of the aluminum alloy samples showed an increasing trend, and the difference between the maximum and minimum contact resistance values ​​was 14.5 μΩ. This is because, at a constant pressure, as the coarseness increases... As the peak height increases, the contact area of ​​the protrusion decreases, which increases the resistance of the current contraction within the contact surface.

[0080] Furthermore, when two cylindrical metal conductors are in line contact, the two conductors are considered as having a contact surface consisting of multiple consecutive equivalent contact spots. The formula for calculating the total contact resistance between the two conductors is as follows:

[0081] In the formula, R c R represents the total contact resistance. s For the shrinkage resistance of a single contact, b represents the length of the contact surface, and r represents the radius of a single contact;

[0082] The hot shrinkage resistance R of a single contact sθ The calculation formula is:

[0083] In the formula: R s0 It is the cold-state shrinkage resistance at 0℃, where T is the temperature of the contact surface and α is the temperature coefficient of resistance.

[0084] In this embodiment, the elastic modulus is taken as E1 = E2 = 6.9e. 10 Poisson's ratio μ1=μ2=0.33, R1=0.02, R2=∞. Substituting these values ​​into the formula, the contact resistance between aluminum alloy samples under different pressures was calculated. The calculated values ​​and experimental test values ​​were then plotted as a curve as shown in Figure 5.

[0085] As shown in Figure 5, the contact resistance value calculated by this method has a good fit with the contact resistance value measured by the test, and the fitting effect of the curve is better as the load increases. This is because the influence of film resistance on contact resistance is ignored in the calculation. When the load is less than 1, the experimental result will be greater than the calculated value due to the influence of film resistance. As the load increases, the micro-protrusions on the metal surface begin to break through the oxide film to form electrical contact between metals. At this time, increasing the load will make the error between the calculated value and the experimental value of contact resistance smaller and smaller. Therefore, the calculation formula of this test method has been verified and has good reference value. It can be used as a calculation of contact resistance value in simulated actual use environment.

[0086] The rest of the structure is the same as in Example 1.

[0087] In this embodiment, by conducting tests, the calculated contact resistance value is compared and verified with the actual tested contact resistance value, thereby deriving a calculation formula for the contact resistance value that can simulate different contact pressures and different contact surface temperatures under different operating environments.

[0088] Example 3

[0089] Referring to Figures 6-9, this is the third embodiment of the present invention. Unlike the previous embodiment, this embodiment provides a test circuit for contact resistance, which is used to implement a method for testing contact resistance. It includes two sets of cables to be tested, a current source that provides input current, and a multimeter for measuring the voltage across the two ends of the cables to be tested. The two sets of cables to be tested form a circuit with the current source and the multimeter through wires. Contact resistance is generated when the two sets of cables to be tested come into contact. The multimeter is connected in parallel with the two sets of cables to be tested.

[0090] In this embodiment, a micro-ohmmeter is also used to measure the contact resistance. Since the measured contact resistance value is very low, the influence of the inherent resistance of the wire on the contact resistance must be considered. In the experimental design, the method of subtracting the wire resistance from the total resistance is used to obtain the accurate value of the contact resistance. The method of measuring twice, forward and reverse, is used to eliminate the influence of thermoelectric potential. Furthermore, the potential measurement point for measuring the clamp resistance is specified to be located on the wire at a distance from the end of the clamp. The electrical measurement point for the contact resistance is shown in Figure 6. The principle of measuring the contact resistance using a Micro-Centurion II micro-ohmmeter is shown in Figure 7.

[0091] The contact resistance to be tested is determined according to the following formula:

[0092] In the formula: R f The resistance between the two ends of the clamp was measured, and the unit is Ω, R. L The measured resistance value of the dominant conductor, in Ω; L L -R L The length of the corresponding dominant line, in mm; R C The measured resistance value of the branch wire, in Ω; L C -R C The length of the corresponding branch conductor is in mm; the distance from the L-potential measuring point to the end of the offline clamp is 25 mm.

[0093] Preferably, at least three groups of cables under test are arranged and connected sequentially at their ends, with adjacent groups of cables under test connected in contact by a set of splice clamps; the current source is a high-current generator connected to both ends of the sequentially connected cables under test, and each set of splice clamps maintains contact between the two groups of cables under test at a given contact pressure. To avoid a single clamp affecting the test results and to simulate the operating conditions as realistically as possible, this embodiment uses six identical splice tubes, each 95cm long and 150mm in diameter. 2 Three cables and 70mm diameter wires, each 85cm long. 2 Four cables are used to build the test circuit. When building the circuit, ensure that the cables between the clamps are long enough to prevent the temperatures between the clamps from affecting each other. In summary, the schematic diagram of the test circuit is shown in Figure 8.

[0094] To accurately describe the temperature distribution at various locations within the splice, the arrangement of temperature measuring points is crucial. In this embodiment, three temperature measuring points were arranged on the surface of the splice, the main cable, and the secondary cable to investigate the temperature distribution and temperature rise trend of the splice. A schematic diagram of the temperature measuring points is shown in Figure 9. Point 1 is the temperature measuring point between the clamp and the end of the main conductor; point 2 is the temperature measuring point in the middle of the clamp; and point 3 is the temperature measuring point between the clamp and the end of the secondary conductor. The temperatures in the middle of the splice, at the end of the main conductor, and at the end of the secondary conductor of the splice clamp were recorded before and after each test. The highest value of each measured temperature can be used to calculate the hot-state shrinkage resistance.

[0095] The rest of the structure is the same as in Example 2.

[0096] Testing Procedure: Before testing, select 6 clean, crack-free splice pipes and use cable cutters and a measuring tape to prepare 150mm sections with a length of 95cm. 2 Three cables and 70mm diameter wires, each 85cm long. 2 Four cables are secured with splice clamps. The insulation layer of the cables to be in contact with the splice conduit is stripped using rotary wire strippers. To ensure accurate test results, the stripped portion of each insulation layer should not exceed 30mm. The splice conduit, main conductor, and auxiliary conductor are pre-secured in a bench vise. A digital torque wrench is then used to apply pre-tightening force to the bolts, ensuring that the pre-tightening force on both bolts of the splice conduit is as equal as possible. The high-current generator is connected to the circuit using a series connection method. Once the entire experimental circuit is set, the high-current generator is started and the relevant parameters are set in preparation for testing.

[0097] The test process includes three stages: power-on heating of the clamp circuit, temperature stabilization, and power-off cooling. In the power-on heating stage, a high-current generator is used to generate industrial frequency AC power to heat the clamp, and the current is less than the rated current that the conductor can withstand. When the temperature of the clamp fluctuates by no more than 2°C within 15 minutes, the circuit temperature is considered to have reached a stable state. At this time, an infrared thermal imager is used to measure and record the temperature measurement points of the splice tube and the conductor. Then, the high-current generator is turned off and the current is reduced to zero, allowing the circuit to enter the cooling stage. Once the circuit has cooled to room temperature, it is ready to conduct the next experiment. Each experiment is conducted three times.

[0098] This embodiment provides a method for obtaining the contact surface temperature at different stages and different measuring points, so that the calculated contact resistance value is more suitable for the usage environment.

[0099] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for testing contact resistance, characterized in that: A device for detecting the contact resistance between two metallic conductors, comprising, Two metal conductors are brought into contact by applying a given contact pressure; The input current is obtained by connecting the two ends of the current source with a pair of wires that are respectively connected to two metal conductors. Use another pair of wires to introduce the voltage across the metal conductor into the multimeter for measurement; Calculate the contact resistance value based on the measured results; The input current is a pulse current.

2. The method for testing contact resistance as described in claim 1, characterized in that: The application of a given contact pressure includes, Place the two metal conductors in the working area of ​​the press. Adjust the contact surface of the two metal conductors to match the direction of pressure application from the press. Insulating material is added in the direction of pressure application to isolate the press from the metal conductor.

3. The method for testing contact resistance as described in claim 1 or 2, characterized in that: It also includes contact resistance values ​​measured under different contact pressures, which include, The contact pressure between the two metal conductors is increased sequentially according to the set gradient value; Each time the pressure is increased, a transient current value of different magnitude is used as the pulse current input; The average value of the contact resistance measured by different transient currents is used as the contact resistance for the corresponding contact pressure.

4. The method for testing contact resistance as described in claim 3, characterized in that: It also includes, Record the curve of the measured contact resistance as a function of contact pressure; The range of contact pressures at which the contact resistance tends to stabilize with changes in contact pressure is taken as the working range. Methods for calculating contact resistance values ​​within the operating range of contact pressure include: Calculate the contact resistance of a single contact spot formed under a given contact pressure. The combination of all contact spots formed between two metal conductors is taken as the contact surface; The total contact resistance of the contact surface is calculated as the contact resistance between the two metal conductors.

5. The method for testing contact resistance as described in claim 4, characterized in that: Treating the contact spot between two metal conductors as a circle, the formula for calculating the contact resistance of a single contact spot between the two metal conductors is: The first term is the cold-state shrinkage resistance R of the two metallic conductors at 0°C. s The calculation formula, the second term is the film resistance R formed on the contact surface of the two metal conductors. f The calculation formula is as follows: ρ1 and ρ2 are the resistivity of two metal conductors in contact, r represents the equivalent radius of the contact spot of the two metal conductors, and θ is the resistivity of the contamination film on the contact surface of the two metal conductors.

6. The method for testing contact resistance as described in claim 5, characterized in that: Both metal conductors are cylindrical in shape, and the two metal conductors are in contact by a line contact between the side surface and the bottom surface of the cylinder, or a surface contact between the bottom surfaces of the cylinders. The formula for calculating the radius r1 of the contact surface between two cylindrical metal conductors is: In the formula, P represents the contact pressure, and E * denoted by , r represents the equivalent elastic modulus, and r represents the equivalent contact radius of a single contact spot; Among them, the equivalent elastic modulus E * The formula for calculating the equivalent contact radius r of a single contact spot is as follows: In the formula, E1 and E2 represent the elastic moduli of the two contacting metal conductors, μ1 and μ2 represent the Poisson's ratios of the two contacting bodies, and R1 and R2 represent the radii of the two contacting cylindrical metal conductors.

7. The method for testing contact resistance as described in claim 6, characterized in that: When two cylindrical metal conductors are in line contact, the two conductors are considered as having a contact surface consisting of multiple consecutive equivalent contact spots. The formula for calculating the total contact resistance between the two conductors is: In the formula, R c R represents the total contact resistance. s For the shrinkage resistance of a single contact, b represents the length of the contact surface, and r represents the radius of a single contact; The hot shrinkage resistance R of a single contact sθ The calculation formula is: In the formula: R s0 It is the cold-state shrinkage resistance at 0℃, where T is the temperature of the contact surface and α is the temperature coefficient of resistance.

8. The method for testing contact resistance as described in any one of claims 4-7, characterized in that: Methods for obtaining the temperature of the contact surface include, Two metal conductors are brought into contact under a given contact pressure by a splicing clamp; A pulse current is input across the two ends of two metallic conductors, and the temperature at the measuring point is obtained. The measuring points include at least the middle of the connector clamp and the connection points between the connector clamp and the two metal conductors.

9. A contact resistance test circuit for implementing the contact resistance test method as described in claims 1-8, characterized in that: It includes two sets of cables under test, a current source to provide input current, and a multimeter for measuring the voltage across the two ends of the cables under test; The two sets of cables under test are connected to the current source and the multimeter through wires to form a circuit. After the two sets of cables under test come into contact, a contact resistance is generated. The multimeter is connected in parallel with the two sets of cables under test.

10. The contact resistance test circuit as described in claim 9, characterized in that: The cables to be tested are provided in at least three groups and connected sequentially at their ends. Adjacent groups of cables to be tested are connected and contacted by a set of splice clamps. The current source is a high-current generator connected to both ends of the sequentially connected test cables. Each set of splice clamps maintains contact between the two sets of test cables according to a given contact pressure.

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