Test method for strain clamp

Abstract

The invention discloses a test method for a strain clamp, and the method comprises the steps: carrying out the crimping and drainage plate assembly of the strain clamp, and fastening a bolt on a drainage plate to a preset initial torque value through a digital display torque wrench; measuring the contact resistance of a drainage plate of the strain clamp; arranging a T-shaped thermocouple at a monitoring point position of the strain clamp; sequentially applying currents with different percent calculated current-carrying capacities to the strain clamp through a large current generator, and recording transient temperature rise data corresponding to each monitoring point position; and measuring the contact resistance and transient temperature rise data under different bolt torques under the current of each percentage calculation current-carrying capacity. According to the invention, the actual working state of the strain clamp under different drainage plate assembly conditions can be simulated, the bolt torque of the strain clamp is taken as an independent variable, the contact resistance between the drainage plates under different torques is measured, and the overall temperature distribution of the clamp is measured through the temperature measurement probe, so that the test accuracy is improved. Therefore, real-time measurement of three kinds of data of bolt torque, contact resistance and wire clamp temperature rise is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of strain clamp, in particular to a test method for strain clamp. BACKGROUND

[0002] High-voltage overhead line is the backbone of each power system, and its state is related to the safe and reliable operation of the entire power system. In overhead lines, strain clamp, as an important component fitting, not only bears the tension of the conductor, but also bears the load current of the line. Its mechanical and electrical properties are constantly tested by external environment and high-strength electromagnetic field, and its operating state is related to the safe and reliable operation of overhead lines. However, due to the problem of non-standard torque of the fastening bolt at the drain plate of the strain clamp during construction, the strain clamp overheats seriously, and the strain clamp deformation and even melting accidents occur easily during the peak period of electricity consumption, which endangers the safe operation of the power system. When the drain plate fastening bolt is loose, the gap between the drain plates increases, resulting in an increase in the contact resistance between the plates, thereby causing heating. Therefore, the experimental study on the temperature rise of the drain plate of the overhead line strain clamp considering the torque of the bolt is an important way to analyze the heating accident of the clamp, and the prerequisite for this study is to simulate the actual working state of the drain plate of the strain clamp.

[0003] To realize the simulation experiment of the actual state of the drain plate of the strain clamp, the existing scheme is mainly divided into simulation calculation and field measurement.

[0004] Simulation calculation refers to measuring the main data of the operating clamp, including the bolt pre-tightening force of the drain plate, environmental temperature and load flow parameters, first constructing a simulation model of the strain clamp through simulation software, then inputting the initial parameters, and calculating the transient temperature on the surface of the strain clamp by the simulation software. This method is low in cost, and the transient temperature of the strain clamp in the simulation process can be obtained.

[0005] The field measurement method mainly uses an infrared temperature sensor for measurement. The infrared temperature sensor is a non-contact temperature measuring device based on the blackbody radiation law, which realizes temperature measurement by receiving the infrared radiation energy emitted by the object. Its technical principle mainly includes full-radiation temperature measurement method, brightness temperature measurement method and colorimetric temperature measurement method, which is suitable for temperature monitoring in special environments such as high temperature, strong corrosion or long distance.

[0006] The above-mentioned several research methods can obtain the transient temperature of the drain plate of the strain clamp, but there are also some problems. The simulation calculation method can calculate by inputting the average value of long-term operation, although it is convenient to operate, but since this method uses the steady-state data (such as the annual average load flow of the line) in the long-term operation process, it is difficult to reflect the size of the contact resistance between the drain plates in the actual situation, resulting in an error of more than 20% between the results and the actual situation.

[0007] The direct measurement method uses an infrared thermal imaging sensor to measure the temperature of the in-service line, and the measurement result is real-time, but the infrared temperature measurement is easily disturbed by some environmental factors, such as environmental temperature, dust in the air, and the like, and there is a large error in the infrared temperature measurement on the polished metal surface. In addition, the in-service line cannot be measured, and the temperature change trend of the strain clamp under the action of different state quantities cannot be observed, which is not conducive to the observation of the transient temperature rise of the strain clamp under the coupling of multiple state quantities. SUMMARY

[0008] Therefore, it is necessary to propose a test method for a strain clamp in view of the above problems.

[0009] A test method for a strain clamp, the strain clamp comprising a clamp body, a drainage plate, a compression tube, and an anchor rod; the clamp body is connected with the compression tube through the drainage plate, and the compression tube is fixedly connected with a conductor; the drainage plate is connected with the clamp body through a bolt; the anchor rod is arranged in the clamp body; a T-type thermocouple is arranged on the surface of the clamp body, the surface of the drainage plate, the surface of the compression tube, and the surface of the conductor. The method comprises the following steps: The clamp body, the compression tube, the anchor rod, and the conductor are cleaned, and the clamp body and the compression tube are assembled, and the bolt on the drainage plate is fastened to a preset initial torque value through a digital torque wrench. The contact resistance of the drainage plate of the strain clamp is measured through a four-wire direct current resistance tester. A T-type thermocouple is arranged at a monitoring point of the strain clamp, and the monitoring point at least comprises the surface of the clamp body, the surface of the drainage plate, the surface of the compression tube, and the surface of the conductor. Different percentage calculation current carrying capacities are sequentially applied to the strain clamp through a large current generator. I amp The transient temperature rise data corresponding to each monitoring point is recorded. The torque value of the bolt on the drainage plate is adjusted step by step under each percentage calculation current carrying capacity. I amp The contact resistance and the transient temperature rise data under different torque values of the bolt are measured.

[0010] Preferably, before the clamp body, the compression tube, the anchor rod, and the conductor are cleaned, and the clamp body and the compression tube are assembled, and the bolt on the drainage plate is fastened to a preset initial torque value through a digital torque wrench.

[0011] Preferably, the measurement of the contact resistance of the current-draining plate of the tension clamp using a four-wire DC resistance tester specifically includes: using two current leads marked I+ and I-, connecting a current source to both ends of the conductor under test, injecting the current from the current source into the conductor under test through the current leads, and drawing current from the conductor under test to obtain the current value of the current-draining plate; using two voltage leads marked V+ and V-, connecting a voltmeter to both ends of the conductor under test to measure the voltage drop across the conductor under test; and determining the contact resistance of the current-draining plate based on the current value and voltage drop.

[0012] Preferably, the current-carrying capacity is calculated by sequentially applying different percentages of current to the tension clamp via a high-current generator. I amp The current was measured, and the transient temperature rise data corresponding to each monitoring point was recorded, specifically including: loading 25% I amp The alternating current was applied, and the transient temperature change curve of the tension clamp surface was recorded using a T-type thermocouple from 0 to 2 hours after energization. The current was then cut off, and the clamp was allowed to cool for 3 hours to return to room temperature. Repeat the application of 50%, 75%, 100%, and 125% solutions respectively. I amp Using an alternating current, a T-type thermocouple was used to record the transient temperature change curve of the tension clamp surface from 0 to 2 hours after energization. The current was then cut off, and the clamp was allowed to cool for 3 hours to ensure that the clamp as a whole returned to room temperature.

[0013] Preferably, the method further includes the step of: calculating the current carrying capacity based on the different percentages. I amp Based on transient temperature rise data measured under different bolt torques, a multi-parameter coupled temperature prediction model is constructed. The input parameters of the temperature prediction model include at least the real-time current value flowing through the tension clamp, the real-time torque value of the bolts on the drain plate, the ambient temperature, and the ambient wind speed. The temperature prediction model is used to calculate the predicted temperature value of the surface of the drainage plate.

[0014] Preferably, the method further includes: The predicted temperature value of the surface of the drainage plate is calculated using the temperature prediction model. The measured temperature value of the surface of the diversion plate and the real-time load current flowing through the tension clamp are monitored and obtained in real time. The measured temperature value is compared with the predicted temperature value under the same operating conditions; If the measured temperature value is consistently higher than the predicted temperature value and exceeds a preset threshold, then the bolt torque on the drainage plate is determined to be lower than the design requirement.

[0015] Preferably, the contact surface of the drainage plate is plastically deformed by pre-pressing to form a closely-fitted surface.

[0016] Preferably, the drainage plate comprises a first drainage plate and a second drainage plate, the first drainage plate is arranged at the end of the wire clamp body, and the second drainage plate is arranged at the front end of the compression tube; the first drainage plate and the second drainage plate are fixed by bolts after being compressed.

[0017] Preferably, the curvature of the compression tube is ≤2%, and the side margin satisfies the formula: Wherein, D represents the outer diameter of the compression tube.

[0018] The embodiment of the present application has the following beneficial effects: The present application can simulate the actual working state of the strain clamp under different drainage plate assembly conditions, take the bolt torque of the strain clamp as the independent variable, measure the contact resistance between the drainage plates under different torques, and measure the overall temperature distribution of the strain clamp through the temperature measuring probe, so as to realize real-time measurement of the bolt torque-contact resistance-strain clamp temperature rise three kinds of data. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiment or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0020] Wherein: Figure 1 A structural schematic diagram of a strain clamp is provided for the embodiment of the present application; Figure 2 A flowchart of a test method for the strain clamp is also provided for the embodiment of the present application.

[0021] Figure 3 A curve of the overall resistance of the strain clamp changing with the changing bolt torque in the test method for the strain clamp is also provided for the embodiment of the present application; Figure 4 A temperature diagram of each monitoring point under different torques when the current is 200A in the test method for the strain clamp is also provided for the embodiment of the present application; Figure 5 A temperature diagram of each monitoring point under different torques when the current is 400A in the test method for the strain clamp is also provided for the embodiment of the present application; Figure 6The application also provides a temperature diagram of each monitoring point under different torques when a current of 600 A is loaded in a test method for the strain clamp.

[0022] In the figure, 1 is a clamp body, 2 is a drainage plate, 3 is a compression pipe, 4 is an anchor rod, 5 is a bolt, 21 is a first drainage plate, and 22 is a second drainage plate. DETAILED DESCRIPTION

[0023] The technical solutions in the embodiments of the application will be apparently and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the application.

[0024] The application provides a strain clamp, as shown in the figure, comprising a clamp body 1, a drainage plate 2, a compression pipe 3, and an anchor rod 4. Figure 1 The clamp body 1 is connected with the compression pipe 3 through the drainage plate 2, and the compression pipe 3 is fixedly connected with a wire. The drainage plate 2 is connected with the clamp body 1 through a bolt 5. The anchor rod 4 is arranged in the clamp body 1. A T-type thermocouple is arranged on the surface of the clamp body 1, the surface of the drainage plate 2, the surface of the compression pipe 3, and the surface of the wire. The application arranges the anchor rod 4 in the clamp body 1, significantly improves the overall tensile strength and mechanical stability, and avoids deformation or slippage caused by tension; the compression pipe 3 is fixedly connected with the wire, ensuring a reliable current conduction path and mechanical anchoring, reducing contact resistance fluctuation; the drainage plate 2 is connected with the clamp body 1 through the bolt 5, facilitating accurate adjustment of the torque value to optimize the contact resistance and support torque gradient adjustment in experiments; the T-type thermocouple is arranged on the key surfaces including the clamp body 1, the drainage plate 2, the compression pipe 3, and the wire, realizing real-time temperature accurate monitoring of multiple points, facilitating locking of the heat source point and quantifying temperature rise change; such integrated design not only provides a high-precision basis for the bolt torque and temperature rise relationship experiment, but also can early warn the bolt 5 loosening risk in power operation and maintenance, effectively prevent the fuse accident, and improve the power grid safety and maintenance efficiency.

[0025] In some embodiments, the contact surface of the drainage plate 2 is subjected to pre-pressing treatment to make the metal plastically deform and form a closely fitted surface.

[0026]

[0027] ​Pre-compression treatment eliminates micro-gaps and oxide layers between contact surfaces, allowing metals to adhere directly and reducing the impedance of the current conduction path. This ensures that the initial value of the contact resistance of the current guide plate 2 is low and stable, facilitating accurate measurement in subsequent torque adjustment experiments.

[0028] The pre-compression process creates a dense structure through plastic deformation of the metal, enhancing its resistance to creep and corrosion. The tightly fitting surfaces can withstand long-term vibration and thermal cycling, such as changes in current load, reducing contact degradation caused by bolt torque relaxation and extending the service life of the clamp.

[0029] A tightly fitted surface promotes uniform heat conduction and avoids the formation of localized hot spots. In the experimental method, the pre-compressed drain plate 2 is subjected to a high current, such as 100%. I amp At the same time, the surface temperature rise data is more stable, reducing the risk of melting.

[0030] Preloading bolt 5 provides consistent initial contact conditions for subsequent adjustments using a digital torque wrench. This establishes a reliable benchmark for bolt torque gradient experiments (e.g., gradual torque adjustment), facilitating accurate output of the critical torque table and providing effective guidance for maintenance decisions.

[0031] For example, during the initial assembly stage, the contact surface of the drain plate 2 is pre-pressed, such as by applying 50 MPa pressure using a hydraulic press, to plastically deform the metal surface and form a smooth, mating surface with Ra ≤ 1.6 μm. Subsequently, measurements were taken using a four-wire DC resistance meter, and the results showed that the contact resistance after pre-pressing stabilized below 5 μΩ, whereas it could have exceeded 10 μΩ without pre-pressing. When 80% of the pressure was applied... I amp When the current is applied, combined with the T-type thermocouple and the surface point of the designated drain plate 2, the temperature rise is only 15°C, which may exceed 25°C without treatment, proving that the pre-pressure treatment effectively suppresses Joule heat accumulation.

[0032] After pre-compression, the bolt torque of the drain plate 2 was gradually reduced, from 100% of the standard torque to 70%. Because pre-compression creates a tight fit, the increase in contact resistance is small even with reduced torque; for example, when the torque is reduced to 80%, the resistance only increases by 10%. In contrast, the resistance of the uncompressed sample surges by 30% when the torque is reduced to 85%, accompanied by hot spots on the surface of the drain plate 2, with T-type thermocouples showing temperatures >100°C. This experimental result directly provides a basis for outputting a critical torque table. For example, this critical torque table can clearly define 100%... I amp The safe torque under current is 85%, which can be used to formulate specific operation and maintenance standards, such as requiring a key check on bolt torque before the high-temperature season.

[0033] In some embodiments, the drain plate 2 includes a first drain plate 21 and a second drain plate 22. The first drain plate 21 is provided at the end of the clamp body 1, and the second drain plate 22 is provided at the front end of the crimping tube 3. The first drain plate 21 and the second drain plate 22 are crimped together and then fixed by bolts 5.

[0034] After the bolt 5 is crimped, a rigid-flexible transition zone is formed between the first drain plate 21 and the second drain plate 22. The vibration energy of the conductor is absorbed by the crimping tube 3, which reduces the fretting wear of the bolt connection surface and avoids the warping of the contact surface caused by stress concentration in the traditional integral drain plate 2.

[0035] Furthermore, T-type thermocouples are arranged on the surface of the first drain plate 21 and the surface of the second drain plate 22. If the temperature rise of the second drain plate 22 is significantly higher than that of the first drain plate 21, it indicates that the pressure pipe 3 has poor contact. If the temperature rise of the double plate joint surface is the highest, it verifies that the bolt torque is insufficient, resulting in increased contact resistance.

[0036] In some embodiments, the curvature of the press-fit pipe 3 is ≤2%, and the distance between the edges satisfies the formula: This configuration ensures uniform current distribution and prevents localized overheating due to deformation.

[0037] in, This indicates the outer diameter of the pressure fitting 3.

[0038] Qualified side margins It can ensure that the contact resistance between the crimping tube 3 and the wire is balanced throughout the entire circumference, eliminating local hot spots caused by uneven crimping.

[0039] This invention also provides a test method for tension clamps, which can simulate the actual working state of tension clamps under different assembly conditions of the drain plates 2. Using the bolt torque of the tension clamp as the independent variable, the contact resistance between the drain plates 2 under different torques is measured, and the overall temperature distribution of the tension clamp is measured by a temperature probe, thereby realizing real-time measurement of three data: bolt torque, contact resistance, and clamp temperature rise.

[0040] like Figure 2 As shown, this method is implemented through the following steps: Step 1: Crim the tension clamp and assemble the drain plate 2, and tighten the bolts 5 on the drain plate 2 to the preset initial torque value using a digital torque wrench; Specifically, before crimping, the crimping pipe 3, anchor rod 4 and conductor need to be cleaned to prevent the stains and oxide film on the tension clamp and conductor surface from affecting the crimping quality.

[0041] First, use a cleaning agent such as gasoline or alcohol to remove the oxide film from the aluminum tube section of the clamp body 1 and the anchor rod 4; second, use a cleaning agent to clean the crimping tube 3 and the inner wall of the clamp body 1, and remove the burrs, rough edges and uneven parts of the clamp body 1 and the wire.

[0042] The pipe insertion procedure for anchor bolt 4 is as follows: Step 101: Measure the dimensions of the crimping tube 3 and push the wire clamp body 1 into the preset binding position. Then, tighten and secure the wire, and use a wire stripper or handsaw to cut each layer of aluminum wire at the cutting mark.

[0043] Step 102: After cleaning the wire with a cleaning agent (such as gasoline or alcohol), apply electrical grease to the wire for lubrication and rotate it in the direction of rotation to push it into the clamp body 1.

[0044] Step 103: Attach the crimping tool to the clamp body 1 and apply pressure sequentially to the end face of the clamp body 1. The crimping operation shall be performed in accordance with the industry standard DL / T5285-2018. The crimping sequence shall be "applying pressure sequentially from the anchor bolt 4 pull ring side across the non-pressurized area towards the pipe opening", that is, starting from the anchor bolt 4 side, crimping sequentially towards the pipe opening.

[0045] Step 104: Push the crimped anchor rod 4 into the crimping tube 3 opening to prepare for the crimping operation of the clamp body 1.

[0046] Step 105: Cross the non-pressed area of ​​the clamp, align the end face of the crimping tool with the surface of the tension clamp, and crimp towards the anchor rod 4 ring side. Apply pressure sequentially to the end face of the clamp body 1 to complete the crimping.

[0047] After crimping, visually inspect the clamp body 1 and the wire: the wire should not have loose strands, deformation or surface damage, and the clamp should not have cracks or irregular deformation.

[0048] To test the crimping effect, the stripping length, end distance, anchor bolt 4, aluminum tube and bending degree need to be tested. The testing standard refers to DL / T5285-2018.

[0049] Specifically, after crimping, there should be no obvious bending at the crimped joint between all wires and the clamp body 1; if the bending exceeds 2%, it should be corrected; if it cannot be corrected, it must be cut off and re-crimped. The edge distance dimension after crimping... Calculate using the following formula: .

[0050] The assembly steps for the drainage plate 2 are as follows: S1011, Pre-treatment of the diversion plate 2 before assembly First, use sandpaper to polish and remove the oxide film and stains on the surface of the diversion plate 2 until the contact surface of the diversion plate 2 is polished until it is bright and clean.

[0051] When the surface is bright and clean, the resistance is measured using the four-wire method. Theoretically, the contact resistance level should be in the range of 50-800 microohms.

[0052] Subsequently, the drain plate 2 is secured using appropriate tools such as a bench vise to prevent displacement during the crimping process.

[0053] Finally, before the formal pressing, a pre-pressing process is performed to initially adjust the plastic deformation of the metal material, making the pressing surface tighter.

[0054] S1012, Assembly of the drainage plate 2 First, set the torque value using a digital torque wrench, referring to standard DL / T5285-2018.

[0055] Before operation, the head of the digital torque wrench must be tightly connected to bolt 5 to ensure a secure connection and prevent slippage or displacement during tightening.

[0056] The assembly process begins with rotating the digital torque wrench. During tightening, the digital torque wrench displays the current torque value in real time, allowing the operator to monitor torque changes on the screen.

[0057] After the torque reaches the preset value, check whether the torque of bolt 5 has reached the preset value.

[0058] Step 2: Measure the contact resistance of the current-draining plate 2 of the tension clamp using a four-wire DC resistance tester; Specifically, the DC Resistance Tester used in this invention is an instrument for precision resistance measurement, and its low resistance range typically has a built-in four-wire measurement function.

[0059] Before operation, locate the two current leads marked with I+ and I-, and the two voltage leads marked with V+ and V-. Before use, the DC resistance tester must be zeroed.

[0060] The four-wire method is a high-precision resistance measurement method. Its core idea is to use four independent wires to transmit current and measure voltage separately, ensuring complete isolation between the voltage measurement terminal and the current path, thus eliminating the influence of contact resistance and wire resistance on the measurement results. Using a DC resistance meter, the contact resistance of the clamp can be accurately and quickly determined.

[0061] The principle of the four-wire method is as follows: Compared to the two-wire method, the four-wire method adds two voltage leads marked V+ and V-, with a line resistance of R.S1 and R S2 A voltmeter is connected across the resistor via a voltage lead. The voltage drop V across the voltage lead... s for: ; where I s This refers to the current flowing through the voltage lead; Since the voltmeter has extremely high internal resistance, the current flowing through it can be ignored, therefore the value of Vs can be disregarded, that is: .

[0062] Therefore, the actual voltage drop measured by the meter is equal to the actual voltage drop across the resistor, calculated by the following formula: Among them, V x This represents the true voltage drop across the resistor being measured. At this point, the resistance value of the resistor to be measured is calculated using Ohm's law: ;R x V is the resistance value of the conductor being measured (unit: ohms, Ω); m I is the voltage drop (unit: volt, V) measured through the voltage lead; I is the known constant current (unit: ampere, A) applied by the constant current source through the current lead (force end).

[0063] Using two current leads marked I+ and I-, connect the current source to both ends of the conductor under test. The current source is responsible for injecting current into the conductor under test through the current leads and drawing current out of the conductor to measure the current value of current-lead plate 2. For the most accurate overall resistance, it should be connected to the outermost side of the conductor under test.

[0064] Using two voltage leads marked V+ and V-, connect a voltmeter to both ends of the conductor under test to measure the voltage drop across the conductor, so as to obtain the voltage drop across the current-carrying plate 2.

[0065] To ensure measurement accuracy, the connection point must be located inside the connection point of the two current leads, completely isolating it from the current path to avoid the influence of the wire resistance in the current path on the measurement results.

[0066] The contact resistance of the drain plate 2 is determined based on the current value and voltage drop of the drain plate 2.

[0067] Start the DC resistance tester and select the appropriate measurement range and test current based on the approximate range of the resistance to be measured.

[0068] Once the measurement begins, the instrument will automatically calculate and display the resistance value of the conductor being measured.

[0069] To avoid random errors, the above steps need to be repeated three times. Record the measurement results, discard any outliers, and if the measurement results deviate significantly from the expected values, it may be necessary to check the accuracy of the testing equipment and connecting wires.

[0070] Step 3: Arrange T-type thermocouples at the monitoring points of the tension clamp. The monitoring points include at least the surface of the clamp body 1, the surface of the drain plate 2, the surface of the crimping tube 3, and the surface of the conductor. Specifically, to ensure that the sensing surface of the T-type thermocouple is in complete contact with each measured surface, all installation locations must be cleaned with acetone or alcohol before installation to thoroughly remove oil, impurities, and other contaminants that affect thermal conductivity.

[0071] During installation, an adhesive that matches the coefficient of thermal expansion of the substrate must be selected. When bonding, ensure that the measuring end of the T-type thermocouple is completely in contact with the substrate and apply constant pressure.

[0072] For curved surface installation scenarios, special fixtures must be used to ensure a contact area of ​​≥85%, the curing temperature must be controlled within the range of 120℃ to 150℃, and the curing time must be no less than 2 hours.

[0073] By measuring the temperature on the surface of the clamp body 1, the area through which the anchor rod 4 is installed is monitored. If the temperature rise is abnormal, such as >80℃, it directly indicates mechanical stress concentration or overload risk.

[0074] The condition of the bolt connection surface is monitored by measuring the temperature of the surface of the drain plate 2. When a sudden temperature rise is detected (e.g., ΔT > 15℃ when the torque drops to 80% of the rated value), the increase in contact resistance caused by the loosening of bolt 5 can be quantified. This step is part of the torque gradient experiment.

[0075] Temperature measurement of the surface of crimped connector 3, combined with the requirement of ≤2% curvature, indicates an abnormal temperature, suggesting a wire crimping defect. The uniformity of current distribution was verified by measuring the temperature on the surface of the conductor and comparing the temperature rise at a distance of 10 cm from the pressure tube 3.

[0076] Step 4: Apply different percentages of current carrying capacity to the tension clamp sequentially using a high current generator to calculate the current carrying capacity. I amp The current was measured, and the transient temperature rise data corresponding to each monitoring point was recorded. Specifically, the current carrying capacity of overhead lines I amp This refers to the maximum current value that a conductor can transmit while ensuring its safe operation.

[0077] Loading 25% I ampThe alternating current was applied, and a T-type thermocouple was used to record the transient temperature change curve of the tension clamp surface from 0 to 2 hours after energization. The current was then cut off, and the clamp was allowed to cool for 3 hours until it returned to room temperature.

[0078] Repeat the above steps by setting the current to 50%, 75%, 100%, and 125% of the calculated current carrying capacity, while recording the transient temperature change curve of the tension clamp surface measured by the T-type thermocouple.

[0079] Step 5: Calculate the current carrying capacity for each percentage. I amp Under the given current, the torque value of the bolt 5 on the drain plate 2 is gradually adjusted, and the contact resistance and transient temperature rise data under different bolt torques are measured.

[0080] Specifically, while maintaining the carrying capacity I amp Without changing the torque of bolt 5, the changes in contact resistance and surface transient temperature of the diversion plate 2 are measured.

[0081] Adjust the torque of bolt 5 to the standard value using a digital torque wrench, referencing DL / T5285-2018, and then measure the contact resistance.

[0082] Use a high-current generator to load 50%. I amp The alternating current was applied, and a T-type thermocouple was used to record the transient temperature change curve of the tension clamp surface from 0 to 2 hours after energization. The current was then cut off, and the clamp was allowed to cool for 3 hours until it returned to room temperature.

[0083] Maintaining load capacity I amp If the torque value of bolt 5 remains unchanged, reduce the torque value of bolt 5 by 10% of the standard value each time and repeat the contact resistance measurement.

[0084] Furthermore, the method further includes the following step: calculating the current carrying capacity based on the different percentages. I amp Based on transient temperature rise data measured under different bolt torques, a multi-parameter coupled temperature prediction model is constructed. The input parameters of the temperature prediction model include at least the real-time current value flowing through the tension clamp, the real-time torque value of the bolt 5 on the diversion plate 2, the ambient temperature, and the ambient wind speed. The temperature prediction model is used to calculate the predicted temperature value of the surface of the drainage plate 2.

[0085] Specifically, the current carrying capacity is calculated based on the different percentages obtained in steps 4 and 5. I amp(For example, 25%, 50%, 75%, 100%, and 125%) I amp A multi-parameter coupled temperature prediction model was constructed using transient temperature rise data measured under different bolt torques (e.g., gradually adjusted from the standard torque value to 70% of the standard value).

[0086] The temperature prediction model uses a multiple regression analysis method. The input parameters include at least the real-time current value (unit: A) flowing through the tension clamp, the real-time torque value (unit: N·m) of the bolt 5 on the diversion plate 2, the ambient temperature (unit: °C), and the ambient wind speed (unit: m / s).

[0087] Specifically, according to Determine the contact resistance R of the drain plate d Where T is the real-time torque value on the diversion plate 2, d is the nominal diameter of the bolt 5, and K is the torque coefficient.

[0088] according to Determine the heat generation power Q generated by the contact resistance of the drain plate 2. J Where I is the real-time current value flowing through the tension clamp, and R... d The contact resistance of the guide plate; according to Determine the Reynolds number R e Where v is wind speed and u is ambient temperature T. E air viscosity at that time, according to Determine the ambient temperature T E air viscosity u at that time; according to Determine the Nusselt coefficients Nu; where R e Here, C and n are empirical values, representing the Reynolds number. according to Determine the thermal conductivity of air l a ; according to Determine the ambient thermal resistance R E , where l a Where is the thermal conductivity of air, and Nu is the Nusselt coefficient; Ultimately, according to Determine the temperature T1 of the drainage plate 2; where T1 is the temperature of the drainage plate 2; Q J The heat generated by the contact resistance of the drain plate 2; T E R represents ambient temperature. E For environmental thermal resistance.

[0089] The model building process includes data preprocessing, parameter fitting, and validation: First, the experimental data are normalized to eliminate the influence of dimensions; second, the nonlinear relationship between the input parameters and the surface temperature of the drainage plate 2 is fitted by the least squares method to generate a prediction function; finally, the cross-validation method is used to evaluate the model accuracy to ensure that the prediction error is less than ±5%.

[0090] The temperature prediction model is used to calculate the predicted temperature value of the surface of the diversion plate 2, providing a theoretical basis for subsequent engineering applications.

[0091] Furthermore, the method also includes: The predicted temperature value of the surface of the drainage plate 2 is calculated using the temperature prediction model. Real-time monitoring and acquisition of the measured temperature value on the surface of the diversion plate 2 and the real-time load current flowing through the tension clamp; The measured temperature value is compared with the predicted temperature value under the same operating conditions; If the measured temperature value is consistently higher than the predicted temperature value and exceeds the preset threshold, then the bolt torque on the drainage plate 2 is determined to be lower than the design requirement.

[0092] This invention provides a quantitative analysis tool for power equipment condition assessment, which can guide operation and maintenance personnel to formulate scientific bolt tightening and maintenance strategies, and at the same time provide theoretical support for the optimization of subsequent test programs, thus helping to improve the long-term operational reliability of power equipment connection parts.

[0093] Example The first step is to use sandpaper to make the contact surface of the drainage plate 2 shiny and clean.

[0094] The second step is to use a digital torque wrench to adjust the torque of bolt 5 to the standard 80 Nm, and then use a DC resistance tester to measure the overall resistance of the tension clamp.

[0095] The third step is to connect the tension clamp with the crimped wire to the high current generator, turn on the high current generator, apply an AC current of 200A, and record the temperature change curve from 0 to 2 hours.

[0096] Fourth step: cut off the current and wait for it to cool down for 3 hours.

[0097] Fifth, set the current to 400A and 600A, and repeat the above steps.

[0098] Step 6: Set the bolt torque values ​​to 80 Nm, 60 Nm, 40 Nm and 20 Nm, and repeat the above steps.

[0099] Step 7: Turn off the high current generator and record the temperature monitoring data.

[0100] Experimental Results and Analysis Figure 3 The figure shows the overall resistance of the tension clamp as a function of the bolt torque. As can be seen from the figure, the overall resistance of the tension clamp increases as the bolt torque of the drain plate 2 decreases. The main reason is that the decrease in bolt torque causes an increase in contact resistance, which in turn leads to an increase in the overall resistance of the clamp. Moreover, when the torque is below 30 Nm, the resistance value increases rapidly.

[0101] Figures 4-6 These are the temperatures at various monitoring points of the tension clamp after thermal stability is achieved under different torques when loaded with 600A, 400A, and 200A.

[0102] Figure 4 The results show that when the current is 200A and the bolt torque is 20Nm, the highest temperature occurs at the current-draining plate 2, which is 21.5℃, higher than the temperature of the conductor, which is 20.9℃, with a temperature difference of 0.6℃; when the bolt torque is 80Nm, the highest temperature occurs at the conductor, which is 19.5℃, higher than the temperature of the current-draining plate 2, which is 18.8℃, with a temperature difference of 0.7℃.

[0103] Figure 5 The results show that when the current is 400A and the bolt torque is 20Nm, the highest temperature occurs at the current-draining plate 2, which is 31.9℃, higher than the temperature of the conductor, which is 30.5℃, with a temperature difference of 1.4℃; when the bolt torque is 80Nm, the highest temperature occurs at the conductor, which is 28.6℃, higher than the temperature of the current-draining plate 2, which is 25.3℃, with a temperature difference of 3.3℃.

[0104] Figure 6 The results show that when the current is 600A and the bolt torque is 20Nm, the highest temperature occurs at the current-draining plate 2, which is 50.3℃, higher than the temperature of the conductor, which is 48.4℃, with a temperature difference of 1.9℃; when the bolt torque is 80Nm, the highest temperature occurs at the conductor, which is 42.5℃, higher than the temperature of the current-draining plate 2, which is 37℃, with a temperature difference of 5.5℃.

[0105] Experiments show that when the torque is greater than or equal to 40 Nm, the temperature of the current-draining plate 2 of the tension clamp is lower than the conductor temperature, mainly because the surface area of ​​the current-draining plate 2 (approximately 156 cm²) is smaller. 2 It is much larger than the surface area of ​​a conductor of equal length (approximately 37 cm²). 2 This makes the heat dissipation conditions of the drain plate 2 better than those of the wire, so under normal circumstances, the temperature of the drain plate 2 is lower than that of the wire.

[0106] However, when the torque value is 20 Nm, the temperature of the current-draining plate 2 of the tension clamp will be higher than the temperature of the conductor. This is mainly because when the torque is reduced to below 30 Nm, the contact resistance value will increase rapidly, and the heat generation will also increase rapidly, ultimately causing the temperature of the current-draining plate 2 to be higher than the temperature of the conductor.

[0107] This experiment shows that insufficient bolt torque is the key factor leading to overheating of tension clamps. It can be reasonably inferred that in actual operation, if corrosion and other deterioration effects are added to the contact surface, the risk of overheating of tension clamps will increase significantly.

[0108] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0109] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A test method for tension clamps, characterized in that, The tension clamp includes a clamp body, a drain plate, a crimping tube, and an anchor rod; the clamp body is connected to the crimping tube via the drain plate, and the wire is crimped and fixed inside the crimping tube; the drain plate is connected to the clamp body via bolts; the anchor rod passes through the clamp body; T-type thermocouples are arranged on the surface of the clamp body, the surface of the drain plate, the surface of the crimping tube, and the surface of the wire. The method is as follows: The tension clamp is crimped and the drain plate is assembled. The bolts on the drain plate are tightened to the preset initial torque value using a digital torque wrench. The contact resistance of the current-draining plate of the tension clamp was measured using a four-wire DC resistance tester. T-type thermocouples are arranged at the monitoring points of the tension clamp, and the monitoring points include at least the surface of the clamp body, the surface of the drain plate, the surface of the crimping tube, and the surface of the conductor. The current carrying capacity is calculated by sequentially applying different percentages of current to the tension clamp using a high-current generator. I amp The current was measured, and the transient temperature rise data corresponding to each monitoring point was recorded. Calculate the carrying capacity for each percentage. I amp Under the given current, the torque value of the bolts on the drain plate was gradually adjusted, and the contact resistance and transient temperature rise data under different bolt torques were measured.

2. The test method for tension clamps according to claim 1, characterized in that, Before crimping the tension clamp and assembling the diversion plate, and tightening the bolts on the diversion plate to a preset initial torque value using a digital torque wrench, the method further includes cleaning the clamp body, crimping tube, anchor rod, and conductor.

3. The test method for tension clamps according to claim 1 or 2, characterized in that, The method of measuring the contact resistance of the current-draining plate of the tension clamp using a four-wire DC resistance tester specifically includes: using two current leads marked I+ and I-, connecting a current source to both ends of the conductor under test, injecting current from the current source into the conductor under test through the current leads, and drawing current from the conductor under test to obtain the current value of the current-draining plate; using two voltage leads marked V+ and V-, connecting a voltmeter to both ends of the conductor under test to measure the voltage drop across the conductor under test; and determining the contact resistance of the current-draining plate based on the current value and voltage drop.

4. The test method for tension clamps according to claim 3, characterized in that, The current carrying capacity is calculated by sequentially applying different percentages of current to the tension clamp using a high-current generator. I amp The current is recorded, and the transient temperature rise data corresponding to each monitoring point is recorded, specifically including: Loading 25% I amp The alternating current was applied, and the transient temperature change curve of the tension clamp surface was recorded using a T-type thermocouple from 0 to 2 hours after energization. The current was then cut off, and the clamp was allowed to cool for 3 hours to return to room temperature. Repeat the application of 50%, 75%, 100%, and 125% solutions respectively. I amp Using an alternating current, a T-type thermocouple was used to record the transient temperature change curve of the tension clamp surface from 0 to 2 hours after energization. The current was then cut off, and the clamp was allowed to cool for 3 hours to ensure that the clamp as a whole returned to room temperature.

5. The test method for tension clamps according to claim 4, characterized in that, The method further includes the following step: calculating the carrying capacity based on the different percentages. I amp Based on transient temperature rise data measured under different bolt torques, a multi-parameter coupled temperature prediction model is constructed. The input parameters of the temperature prediction model include at least the real-time current value flowing through the tension clamp, the real-time torque value of the bolts on the drain plate, the ambient temperature, and the ambient wind speed. The temperature prediction model is used to calculate the predicted temperature value of the surface of the drainage plate.

6. The test method for tension clamps according to claim 5, characterized in that, The method further includes: The predicted temperature value of the surface of the drainage plate is calculated using the temperature prediction model. The measured temperature value of the surface of the diversion plate and the real-time load current flowing through the tension clamp are monitored and obtained in real time. The measured temperature value is compared with the predicted temperature value under the same operating conditions; If the measured temperature value is consistently higher than the predicted temperature value and exceeds a preset threshold, then the bolt torque on the drainage plate is determined to be lower than the design requirement.

7. The test method for tension clamps according to claim 6, characterized in that, The contact surface of the drainage plate is plastically deformed by pre-compression treatment to form a tightly fitting surface.

8. The test method for tension clamps according to claim 7, characterized in that, The drain plate includes a first drain plate and a second drain plate. The first drain plate is provided at the end of the clamp body, and the second drain plate is provided at the front end of the crimping tube. The first drain plate and the second drain plate are crimped together and then fixed by bolts.

9. The test method for tension clamps according to claim 8, characterized in that, The curvature of the press-fit pipe is ≤2%, and the distance between the edges satisfies the formula: ,in, This indicates the outer diameter of the press-fit pipe.

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