Non-destructive device and method for preventing heating at lap joint of overhead line

Abstract

The invention discloses a non-destructive device and method for preventing heating at the lap joint of an overhead line. The device comprises a four-wire detection wire clamp, a Kelvin double-arm bridge, a bridge balance detection circuit, a digital potentiometer, a microcontroller, a power supply, a power supply management module and a peripheral expansion module, the four-wire detection wire clamp is used for loading power supply voltage to the lap joint of the detected overhead line; the Kelvin double-arm bridge is used for detecting the resistance value at the lap joint of the detected overhead line; the bridge balance detection circuit is connected in the Kelvin double-arm bridge and is used for detecting whether the Kelvin double-arm bridge is balanced or not; the digital potentiometer is used for adjusting the resistance of the digital potentiometer to enable the Kelvin double-arm bridge to achieve bridge balance; on the basis of the Kelvin double-arm bridge, the characteristics of measurement accuracy, portability and the like are considered, the device is suitable for high-altitude operation of the power transmission line, and a wire clamp fitting at a lap joint does not need to be disassembled in the detection process, so that unnecessary damage to equipment is avoided, and meanwhile, high efficiency and safety in the detection process are ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of overhead lines, and more specifically, relates to a non-destructive device and method for preventing heating at a splice of overhead lines. Background Art

[0002] The heating problem at the joints of overhead transmission lines not only aggravates the ineffective loss of electric energy and limits the carrying capacity of the lines, but also, in extreme cases, may cause serious deformation or even melting of the wire clamps at the joints, posing a major threat to the safe and stable operation of the transmission lines.

[0003] At present, the research on the heating problem of overhead transmission line splices is mainly concentrated in the following three aspects: 1. Research on the causes of heating of the tension clamp drain plate and the changes in heating temperature. This type of research has many theoretical results, but it is difficult to guide on-site maintenance work because it is difficult to prevent the heating of the tension clamp drain plate. 2. Research on new tension clamps, that is, to upgrade and transform the existing tension clamps so that they are not easy to heat up after installation, but the existing transmission line tension clamps that have been put into operation are huge in size and difficult to replace in batches with new tension clamps. Even if they are replaced with new tension clamps, there is still a certain probability of heating. 3. Research on optimizing the live processing operation method after heating. This type of research cannot prevent heating and can only passively wait for heating before handling. Therefore, it is urgent to study how to prevent the tension clamp drain plate from heating up after it is put into operation.

[0004] In addition to theoretical research, there are also some practical methods to "observe" the status of the tension clamp drain plate at the construction site. The commonly used method is to dismantle the wire clamp hardware at the connection and manually "visually inspect" the installation quality of the contact surface. However, this method is not only highly dependent on subjective judgment and lacks objective and unified quantitative standards, but also often causes unnecessary secondary damage to the wire clamp hardware in actual operation.

[0005] The existing technologies for detecting overheating of overhead transmission lines are:

[0006] Patent CN109186776A proposes a method, device and equipment for detecting heating of wire clamps of transmission lines. It includes: applying a rated current to the transmission line, the rated current being the current required when the transmission line is fully loaded; determining the rated temperature reached by the transmission line under the condition of inputting the rated current; detecting the actual temperature reached by the transmission line under the condition of inputting the rated current; and determining the heating point of the wire clamp by comparing the rated temperature with the actual temperature. However, this method cannot be implemented on site. The rated current of high-voltage lines is usually several hundred amperes. There is no equipment on site that can provide such a large current. Even if there is equipment with such a large power, its size and weight are also very large. The wire clamps of overhead lines are all at high altitudes. Such high power is difficult to transport to high altitudes, which is not conducive to on-site detection. It is only a laboratory method.

[0007] Patent CN113295961A proposes an edge computing method for heating warning and dynamic capacity expansion of overhead transmission line line clamps. It includes 1. Heating information collection of transmission line line clamps based on ultra-high frequency sensing; 2. Heating edge computing of line clamps based on hierarchical Bayesian processing; 3. Multi-dimensional sensor information collection and heating calculation of overhead transmission lines; 4. Dynamic capacity expansion edge computing based on echo state network model. However, this method is too complicated and uses many sensors, which is not conducive to on-site detection, and its accuracy needs to be verified.

[0008] The patent CN112290451A proposes a transmission line clamp heating detection and cooling system and method. By carrying a drone, the infrared thermal imager can quickly obtain the infrared thermal image of the transmission line clamp. The control module can determine whether the temperature of the transmission line clamp exceeds the preset temperature threshold according to the infrared thermal image, thereby realizing rapid detection of the heating condition of the transmission line clamp. At the same time, when the ground remote control platform receives the heating warning information, it controls the spray gun to spray the hollow sphere. When the sprayed hollow sphere hits the transmission line clamp and breaks, the conductive viscous liquid inside the hollow sphere adheres to the transmission line clamp, thereby quickly enhancing the conductivity of the transmission line clamp, reducing the resistivity, and then reducing the heating temperature of the transmission line clamp. However, this is a post-heating treatment, that is, the line is heated after commissioning, and then the method is used for cooling treatment. This patent detects the resistance and other parameters of the transmission line clamp before the line is powered on, thereby preventing the clamp from heating up after power transmission. Summary of the invention

[0009] In order to solve the deficiencies in the prior art, the present invention provides a non-destructive device and method for preventing heating at the joint of overhead lines, based on the Kelvin double-arm bridge method, and conducts in-depth research on issues such as the selection of bridge arm resistance parameters. The present invention also innovatively designs a high-precision, low-resistance digital potentiometer, which is also an innovation in the core technology of the balanced bridge. In view of the problem of resistance temperature drift, the Kelvin double-arm bridge method is improved, and finally the measuring instrument has the advantages of high measurement accuracy, stable operation, compactness and portability, and is suitable for high-altitude operations on power lines.

[0010] The present invention adopts the following technical solution.

[0011] The first aspect of the present invention provides a non-destructive device for preventing heating at the joint of overhead lines, comprising a four-wire detection clamp, a Kelvin double-arm bridge, a bridge balance detection circuit, a digital potentiometer, a microcontroller, a power supply and a power management module, and a temperature measurement module; the characteristics are:

[0012] The four-wire detection line clamp includes a first clamp, a second clamp, a first detection line and a second detection line connected to the first clamp, and a third detection line and a fourth detection line connected to the second clamp;

[0013] Clamp the first clamp and the second clamp respectively at the joint R of the overhead line to be tested. x At both ends, the first detection line of the four-wire detection clamp is connected in series through the first bridge arm resistor R1, the second bridge arm resistor R2 and the digital potentiometer R p The third detection line of the four-wire detection clamp is connected to one end of the digital potentiometer R through the third bridge arm resistor R3 and the fourth bridge arm resistor R4 in series. p The second detection line of the four-wire detection clamp is connected to the positive pole of the power supply of the Kelvin double-arm bridge; the fourth output end of the four-wire detection clamp is connected to the digital potentiometer R p The other end of the digital potentiometer R p One end of is connected to the negative electrode of the power supply of the Kelvin double-arm bridge through the fifth resistor R0; wherein R1 and R2 serve as one series bridge arm of the Kelvin double-arm bridge, and R3 and R4 serve as another series bridge arm of the Kelvin double-arm bridge;

[0014] The bridge balance detection circuit includes a signal amplification module and an AD conversion module, wherein the signal input end of the signal amplification module is respectively connected to the connection points of R1 and R2 and the connection points of R3 and R4 to obtain the bridge arm output, and the output signal of the signal amplification circuit is output to the microcontroller through the AD conversion module;

[0015] The temperature measurement module transmits the temperature value of the overhead line tower connection to the microcontroller through a temperature measurement probe arranged at the overhead line connection;

[0016] The microcontroller adjusts the resistance of the digital potentiometer according to the output of the AD conversion module to balance the Kelvin double-arm bridge, and calculates the resistance value of the overhead line to be detected R according to the resistance value of the digital potentiometer at this time. x The resistance value is measured, and the detected resistance value is corrected by the measured temperature value;

[0017] The heating state of the overhead line joint is comprehensively judged based on the calibrated resistance value of the overhead line joint, the resistance value of the overhead line joint detected in the previous time unit, and the set heating threshold.

[0018] Preferably, the first detection wire, the second detection wire, the third detection wire and the fourth detection wire are copper wires, and the copper wires are wrapped with anti-corrosion insulation.

[0019] Preferably, the calculation formula for selecting the resistance parameters R1, R2, R3, and R4 of the four bridge arms of the Kelvin double-arm bridge is:

[0020]

[0021] Among them, R p is the resistance value of the digital potentiometer, R x is the resistance value of the overhead line connection under test calculated when the bridge is balanced, U out is the actual output voltage of the voltage source, U A is the voltage at the connection point of the first resistor R1 and the second resistor R2, U B is the resistance at the connection point of the third resistor R3 and the fourth resistor R4, I1 is the current on R1, and I2 is the current on R2.

[0022] Preferably, the signal amplification module is specifically an operational amplifier, the non-phase input terminal of the operational amplifier is connected between the first resistor R1 and the second resistor R2 of the Kelvin double-arm bridge, the inverting input terminal of the operational amplifier is connected between the third resistor R3 and the fourth resistor R4 of the Kelvin double-arm bridge, and the output terminal of the operational amplifier is connected to the input terminal of the AD conversion module.

[0023] Preferably, the microcontroller uses a binary search method to dynamically adjust the resistance value of the digital potentiometer to balance the bridge. When the voltage difference between the positive input and the negative input of the operational amplifier after passing through the AD conversion module is less than the voltage difference threshold ψ, it indicates that the bridge is balanced.

[0024] Preferably, the digital potentiometer is composed of a plurality of resistors and a plurality of MOS tubes, and the number of connected resistors is controlled by controlling the conduction of different MOS tubes. When the nth MOS tube is controlled to be turned on and the remaining MOS tubes are turned off, n resistors are connected; all MOS tubes are controlled by independent MOS tube gate drive chips, and all gate drive chips are uniformly connected to a microcontroller for unified control.

[0025] Preferably, the MOS tube in the digital potentiometer is a low on-resistance MOS tube, the on-resistance of the MOS tube is less than or equal to 1 mΩ, and the resistance accuracy is less than or equal to 1%.

[0026] Preferably, the power supply and power management are composed of a DC / DC boost module and a low voltage dropout regulator LDO module. The bridge balance detection circuit is powered by a voltage that is boosted by the DC / DC boost module and then transformed by the low voltage dropout regulator LDO module; and the positive pole of the power supply of the Kelvin double-arm bridge is the output of the DC / DC boost module.

[0027] Preferably, the heating state of the overhead line joint is comprehensively judged according to the calibrated resistance value of the overhead line joint, the resistance value of the overhead line joint detected in the previous time unit, and the set heating threshold, specifically:

[0028] Calculate the comprehensive resistance value of the overhead line joint after fusion correction and the resistance value of the overhead line joint detected in the previous time unit:

[0029]

[0030] Among them, R x,t This is the corrected resistance value of the overhead line joint, R x,t-1 is the corrected resistance value of the overhead line joint in the previous time unit; α is the set coefficient;

[0031] When the comprehensive resistance value is greater than the set heating threshold, the heating state is considered abnormal.

[0032] The set heating threshold is: if the four-wire detection clamp is a compression type tension clamp, the heating threshold is the set standard resistance value of the conductor at the overhead line joint; if the four-wire detection clamp is a non-compression type tension clamp, the heating threshold is 1.1 times the set standard resistance value of the conductor at the overhead line joint.

[0033] The second aspect of the present invention provides a non-destructive method for preventing heating at the splice of overhead lines using the device described in the first aspect of the present invention, characterized in that it comprises:

[0034] Calculate and adjust the resistance parameters of the Kelvin double-arm bridge;

[0035] Adjust the resistance of the digital potentiometer to balance the Kelvin double-arm bridge;

[0036] Use a Kelvin double-arm bridge that achieves bridge balance to measure the resistance of the overhead line joint; and measure the temperature of the overhead line tower joint in real time to calibrate the detected resistance;

[0037] The heating state of the overhead line joint is comprehensively judged based on the calibrated resistance value of the overhead line joint, the resistance value of the overhead line joint detected in the previous time unit, and the set heating threshold.

[0038] The beneficial effect of the present invention is that, compared with the prior art, this patent proposes an innovative method, which accurately measures the key parameters such as the contact resistance at the overlap of the transmission line, and comprehensively calculates and compares it with the standard value with the previous test results, so as to predict in advance whether there is a risk of heating at the location after power transmission. This method transforms the post-control of heating into the pre-control when there is no heating, which not only greatly reduces the defect rate after commissioning, but also avoids the operational risk of heating during live operation. It also provides quantitative data for the acceptance stage of the transmission line, so that the acceptance work is freed from the reliance on the subjective judgment of the construction personnel, and improves the operation and maintenance efficiency of the overhead transmission line. Moreover, the non-destructive device for preventing heating at the overlap of the overhead line does not need to remove the wire clamp hardware at the overlap during the detection process. It only needs to clamp the fixture of the device at both ends of the drainage plate, thereby avoiding unnecessary damage to the equipment and ensuring the efficiency and safety of the detection process. In addition, due to the special design and processing of the digital potentiometer in the device, the device is small and light as a whole, with high measurement accuracy, and is suitable for high-altitude operation of power lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 It is a circuit principle diagram of a non-destructive device for preventing heating at the joint of overhead lines in the present invention;

[0040] Figure 2 It is the hardware structure of the detection device.

[0041] Figure 3 Schematic diagram of the joints of the measurement lines at the construction site;

[0042] Figure 4 Schematic diagram of the measurement of tension wire clamp and drainage plate;

[0043] Figure 5 Schematic diagram of the digital potentiometer structure. DETAILED DESCRIPTION

[0044] In order to make the purpose, technical scheme and advantages of the present invention clearer, the technical scheme of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0045] Embodiment 1 of the present invention proposes a non-destructive device for preventing heating at the joint of overhead lines, comprising a four-wire detection clamp, a Kelvin double-arm bridge, a bridge balance detection circuit, a digital potentiometer, a microcontroller, a power supply and a power management module, and a temperature measurement module; the characteristics are:

[0046] like Figure 4 As shown, the four-wire detection line clamp includes a first clamp, a second clamp, a first detection line and a second detection line connected to the first clamp, and a third detection line and a fourth detection line connected to the second clamp;

[0047] like Figure 3 As shown, the first clamp and the second clamp are respectively clamped at the overlapping point R of the overhead line to be tested. x At both ends, the first detection line of the four-wire detection clamp is connected in series through the first bridge arm resistor R1, the second bridge arm resistor R2 and the digital potentiometer R p The third detection line of the four-wire detection clamp is connected to one end of the digital potentiometer R through the third bridge arm resistor R3 and the fourth bridge arm resistor R4 in series. p The second detection line of the four-wire detection clamp is connected to the positive pole of the power supply of the Kelvin double-arm bridge; the fourth output end of the four-wire detection clamp is connected to the digital potentiometer R p The other end of the digital potentiometer R p One end of is connected to the negative electrode of the power supply of the Kelvin double-arm bridge through the fifth resistor R0; wherein, Figure 1 As shown, R1 and R2 serve as one series bridge arm of the Kelvin double-arm bridge, and R3 and R4 serve as the other series bridge arm of the Kelvin double-arm bridge;

[0048] The bridge balance detection circuit includes a signal amplification module and an AD conversion module, wherein the signal input end of the signal amplification module is respectively connected to the connection points of R1 and R2 and the connection points of R3 and R4 to obtain the bridge arm output, and the output signal of the signal amplification circuit is output to the microcontroller through the AD conversion module;

[0049] The temperature measurement module transmits the temperature value of the overhead line tower connection to the microcontroller through a temperature measurement probe arranged at the overhead line connection;

[0050] The microcontroller adjusts the resistance of the digital potentiometer according to the output of the AD conversion module to balance the Kelvin double-arm bridge, and calculates the resistance value of the overhead line to be detected R according to the resistance value of the digital potentiometer at this time. x Resistance value:

[0051]

[0052] R p is the resistance value of the digital potentiometer, R xThe resistance value of the measured overhead line joint calculated when the bridge is balanced;

[0053] Correct the detected resistance value by measuring the temperature value;

[0054] The heating state of the overhead line joint is determined based on the calibrated resistance value of the overhead line joint and the set heating threshold.

[0055] It should be noted that if Figure 2 As shown, the microprocessor uses an STM32F407 single-chip microcomputer with a main frequency of up to 170MHz to ensure the operation of the system process; the AD conversion module uses a 32-bit ADC with an internal precise voltage source to ensure sampling accuracy.

[0056] Preferably, the first detection wire, the second detection wire, the third detection wire and the fourth detection wire are copper wires, and the copper wires are wrapped with anti-corrosion insulation.

[0057] Preferably, the parameters of the four bridge arm resistors of the Kelvin double-arm bridge are selected as follows:

[0058]

[0059] Among them, U out is the actual output voltage of the voltage source, U A is the voltage at the connection point of the first bridge arm resistor R1 and the second bridge arm resistor R2, U B is the resistance at the connection point between the third bridge arm resistor R3 and the fourth bridge arm resistor R4, For r 21 and r 31 The sum of the partial pressures, For R p The voltage across the terminals, Figure 1 r 11 、r 12 、r 21 、r 22 are the internal resistances of the first detection line, the second detection line, the third detection line, and the fourth detection line respectively; r 31 、r 32 、r 41 and r 42 are the internal resistance of the wires in the Kelvin double-arm bridge, r 21 and r 31 The resistance is much smaller than R p , so the voltage divided by Much smaller than can be neglected, so we can get:

[0060]

[0061] When the bridge is balanced, U A =UB ,have:

[0062] set up

[0063] When the bridge is unbalanced, that is, R x When the resistance value of R' x =R x +ΔR, then U A , U B The voltage difference between them is:

[0064]

[0065] Where ΔR is the difference between the resistance when the bridge is unbalanced and when the bridge is balanced, R' x is the resistance value of the overhead line connection when the bridge is unbalanced, R x It is the resistance value at the joint of the overhead line under test when the bridge is balanced;

[0066] Taking the derivative of ΔU, we can get:

[0067]

[0068] when When k is a positive number, we can obtain Since ΔR is very small compared to R1, Approximately 0, k is approximately 1, that is, when R2=R1, the voltage difference reaches its maximum value.

[0069] In short, when selecting the bridge arm resistance parameters R1, R2, R3, and R4, the calculation formula is:

[0070]

[0071] Among them, R p is the resistance value of the digital potentiometer, R x is the resistance value of the overhead line connection under test calculated when the bridge is balanced, U out is the actual output voltage of the voltage source, U A is the voltage at the connection point of the first bridge arm resistor R1 and the second bridge arm resistor R2, U B is the resistance at the connection point of the third bridge arm resistor R3 and the fourth bridge arm resistor R4, I1 is the current on R1, and I2 is the current on R2.

[0072] Specifically, the parameter values ​​of the final bridge arm resistance in this embodiment are R1=R3=100Ω, R2=R4=1MΩ;

[0073] Preferably, the signal amplification module is specifically an operational amplifier, the non-phase input terminal of the operational amplifier is connected between the first resistor R1 and the second resistor R2 of the Kelvin double-arm bridge, the inverting input terminal of the operational amplifier is connected between the third resistor R3 and the fourth resistor R4 of the Kelvin double-arm bridge, and the output terminal of the operational amplifier is connected to the input terminal of the AD conversion module.

[0074] Preferably, the microcontroller uses a binary search method to dynamically adjust the resistance value of the digital potentiometer to balance the bridge. When the voltage difference between the positive input and the negative input of the operational amplifier after passing through the AD conversion module is less than the voltage difference threshold ψ, it indicates that the bridge is balanced.

[0075] Preferably, if Figure 5 As shown, the digital potentiometer is composed of a plurality of resistors and a plurality of MOS tubes. The number of connected resistors is controlled by controlling the conduction of different MOS tubes. When the nth MOS tube is controlled to be turned on and the remaining MOS tubes are turned off, n resistors are connected; all MOS tubes are controlled by independent MOS tube gate drive chips, and all gate drive chips are uniformly connected to a microcontroller for unified control.

[0076] Preferably, the MOS tube in the digital potentiometer is a low on-resistance MOS tube, the on-resistance of the MOS tube is less than or equal to 1 mΩ, and the resistance accuracy is less than or equal to 1%.

[0077] Preferably, the power supply and power management are composed of a DC / DC boost module and a low voltage dropout regulator LDO module. The bridge balance detection circuit is powered by a voltage that is boosted by the DC / DC boost module and then transformed by the low voltage dropout regulator LDO module; and the positive pole of the power supply of the Kelvin double-arm bridge is the output of the DC / DC boost module.

[0078] It should be noted that, preferably, in addition to the temperature measurement module, this embodiment also adds a threshold alarm and an instant printing module to form a peripheral expansion module. The threshold alarm module is used to automatically trigger an alarm when abnormal heating of the contact resistance is detected; the instant printing module is used to print the measurement results instantly through the built-in printer.

[0079] Preferably, the heating state of the overhead line joint is comprehensively judged according to the calibrated resistance value of the overhead line joint, the resistance value of the overhead line joint detected in the previous time unit, and the set heating threshold, specifically:

[0080] Calculate the comprehensive resistance value of the overhead line joint after fusion correction and the resistance value of the overhead line joint detected in the previous time unit:

[0081]

[0082] Among them, Rx,t This is the corrected resistance value of the overhead line joint, R x,t-1 is the resistance value of the overhead line joint after correction in the previous time unit; α is the set coefficient; in this embodiment, α is set to 0.2;

[0083] When the comprehensive resistance value is greater than the set heating threshold, the heating state is considered abnormal.

[0084] The set heating threshold is: if the four-wire detection clamp is a compression type tension clamp, the heating threshold is the set standard resistance value of the conductor at the overhead line joint; if the four-wire detection clamp is a non-compression type tension clamp, the heating threshold is 1.1 times the set standard resistance value of the conductor at the overhead line joint.

[0085] Embodiment 2 of the present invention proposes a non-destructive method for preventing heating at the splice of overhead lines using the device described in Embodiment 1 of the present invention, which is characterized by comprising:

[0086] Calculate and adjust the resistance parameters of the Kelvin double-arm bridge;

[0087] Adjust the resistance of the digital potentiometer to balance the Kelvin double-arm bridge;

[0088] Use a Kelvin double-arm bridge that achieves bridge balance to measure the resistance of the overhead line joint; and measure the temperature of the overhead line tower joint in real time to calibrate the detected resistance;

[0089] The heating status of the overhead line joint is comprehensively judged by comparing the calibrated resistance value of the overhead line joint with the set standard resistance value and the change in the last test result.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the relevant field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents, and any modifications or equivalent replacements that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A non-destructive device for preventing heating at the joint of overhead lines, comprising a four-wire detection clamp, a Kelvin double-arm bridge, a bridge balance detection circuit, a digital potentiometer, a microcontroller, a power supply and a power management module, and a temperature measurement module; characterized in that: The four-wire detection line clamp includes a first clamp, a second clamp, a first detection line and a second detection line connected to the first clamp, and a third detection line and a fourth detection line connected to the second clamp; Clamp the first clamp and the second clamp respectively at the joint R of the overhead line to be tested. x At both ends, the first detection line of the four-wire detection clamp is connected in series through the first bridge arm resistor R1, the second bridge arm resistor R2 and the digital potentiometer R p The third detection line of the four-wire detection clamp is connected to one end of the digital potentiometer R through the third bridge arm resistor R3 and the fourth bridge arm resistor R4 in series. p The second detection line of the four-wire detection clamp is connected to the positive pole of the power supply of the Kelvin double-arm bridge; the fourth output end of the four-wire detection clamp is connected to the digital potentiometer R p The other end of the digital potentiometer R p One end of is connected to the negative electrode of the power supply of the Kelvin double-arm bridge through the fifth resistor R0; wherein R1 and R2 serve as one series bridge arm of the Kelvin double-arm bridge, and R3 and R4 serve as another series bridge arm of the Kelvin double-arm bridge; The bridge balance detection circuit includes a signal amplification module and an AD conversion module, wherein the signal input end of the signal amplification module is respectively connected to the connection points of R1 and R2 and the connection points of R3 and R4 to obtain the bridge arm output, and the output signal of the signal amplification circuit is output to the microcontroller through the AD conversion module; The temperature measurement module transmits the temperature value of the overhead line tower connection to the microcontroller through a temperature measurement probe arranged at the overhead line connection; The microcontroller adjusts the resistance of the digital potentiometer according to the output of the AD conversion module to balance the Kelvin double-arm bridge, and calculates the resistance value of the overhead line to be detected R according to the resistance value of the digital potentiometer at this time. x The resistance value is measured, and the detected resistance value is corrected by the measured temperature value; The heating state of the overhead line joint is comprehensively judged based on the calibrated resistance value of the overhead line joint, the resistance value of the overhead line joint detected in the previous time unit, and the set heating threshold.

2. A non-destructive device for preventing heating at the joint of overhead lines according to claim 1, characterized in that: The first detection line, the second detection line, the third detection line and the fourth detection line are copper wires, and the copper wires are wrapped with anti-corrosion insulation sheaths.

3. A non-destructive device for preventing heating at the joint of overhead lines according to claim 1, characterized in that: The calculation formula for selecting the resistance parameters R1, R2, R3, and R4 of the four bridge arms of the Kelvin double-arm bridge is: Among them, R p is the resistance value of the digital potentiometer, R x is the resistance value of the overhead line connection under test calculated when the bridge is balanced, U out is the actual output voltage of the voltage source, U A is the voltage at the connection point of the first resistor R1 and the second resistor R2, U B is the resistance at the connection point of the third resistor R3 and the fourth resistor R4, I1 is the current on R1, and I2 is the current on R2.

4. The non-destructive device for preventing heating at the joint of overhead lines according to claim 1 is characterized in that: The signal amplification module is specifically an operational amplifier, a non-phase input terminal of the operational amplifier is connected between the first resistor R1 and the second resistor R2 of the Kelvin double-arm bridge, an inverting input terminal of the operational amplifier is connected between the third resistor R3 and the fourth resistor R4 of the Kelvin double-arm bridge, and an output terminal of the operational amplifier is connected to the input terminal of the AD conversion module.

5. A non-destructive device for preventing heating at the joint of overhead lines according to claim 4, characterized in that: The microcontroller uses a binary search method to dynamically adjust the resistance value of the digital potentiometer to balance the bridge. When the voltage difference between the positive input terminal and the negative input terminal of the operational amplifier is less than the voltage difference threshold ψ after passing through the AD conversion module, it indicates that the bridge is balanced.

6. A non-destructive device for preventing heating at the joint of overhead lines according to claim 5, characterized in that: The digital potentiometer is composed of a plurality of resistors and a plurality of MOS tubes. The number of connected resistors is controlled by controlling the conduction of different MOS tubes. When the nth MOS tube is controlled to be turned on and the remaining MOS tubes are turned off, n resistors are connected. All MOS tubes are controlled by independent MOS tube gate drive chips, and all gate drive chips are uniformly connected to a microcontroller for unified control.

7. A non-destructive device for preventing heating at the joint of overhead lines according to claim 6, characterized in that: The MOS tube in the digital potentiometer is a low on-resistance MOS tube, the on-resistance of which is less than or equal to 1 mΩ, and the resistance accuracy is less than or equal to 1%.

8. The non-destructive device for preventing heating at the joint of overhead lines according to claim 1, characterized in that: The power supply and power management consist of a DC / DC boost module and a low-dropout regulator LDO module. The bridge balance detection circuit is powered by a voltage that is boosted by the DC / DC boost module and then transformed by the low-dropout regulator LDO module; and the positive pole of the power supply of the Kelvin double-arm bridge is the output of the DC / DC boost module.

9. A non-destructive method for preventing heating at the joint of overhead lines according to claim 1, characterized in that: The heating state of the overhead line joint is comprehensively judged according to the calibrated overhead line joint resistance value, the overhead line joint resistance value detected in the previous time unit, and the set heating threshold value, specifically: Calculate the comprehensive resistance value of the overhead line joint after fusion correction and the resistance value of the overhead line joint detected in the previous time unit: Among them, R x,t This is the corrected resistance value of the overhead line joint, R x,t-1 is the corrected resistance value of the overhead line joint in the previous time unit; α is the set coefficient; When the comprehensive resistance value is greater than the set heating threshold, the heating state is considered abnormal; The set heating threshold is: if the four-wire detection clamp is a compression type tension clamp, the heating threshold is the set standard resistance value of the conductor at the overhead line joint; if the four-wire detection clamp is a non-compression type tension clamp, the heating threshold is 1.1 times the set standard resistance value of the conductor at the overhead line joint.

10. A non-destructive method for preventing heating at the joint of overhead lines using the device according to any one of claims 1 to 9, characterized in that: include: Calculate and adjust the resistance parameters of the Kelvin double-arm bridge; Adjust the resistance of the digital potentiometer to balance the Kelvin double-arm bridge; Use a balanced Kelvin double-arm bridge to measure the resistance at the joint of the overhead line; And measure the temperature value of the overhead line tower connection in real time to correct the detected resistance value; The heating state of the overhead line joint is comprehensively judged based on the calibrated resistance value of the overhead line joint, the resistance value of the overhead line joint detected in the previous time unit, and the set heating threshold.

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