A method and system for non-destructive accurate positioning of ground loop resistance defects

Abstract

The present application relates to the technical field of power system transmission line operation and maintenance detection, and particularly relates to a grounding loop resistance defect nondestructive accurate positioning method and system. The present application adopts a two-stage architecture of "coarse positioning + fine positioning", first locks the defect to a specific branch interval through an auxiliary constant current source, and then realizes accurate positioning of the defect point through a coupled voltage sensor, with a positioning accuracy of meters or even sub-meters, solving the problem that traditional methods can only determine the defect branch but cannot locate the specific connection point, and greatly improving the field maintenance efficiency. In the fine positioning stage, the present application adopts a thin film electrode coupling method, which is completely non-invasive and does not damage the cable outer sheath and grounding structure, without stripping the insulating layer or disassembling the grounding box, truly realizing nondestructive detection, without affecting the normal operation of the cable during the detection process, and having both safety and economy.

Description

Technical Field

[0001] This invention relates to the field of power system transmission line operation and maintenance testing technology, and in particular to a non-destructive and precise method and system for locating grounding circuit resistance defects. Background Technology

[0002] With the development of urban power transmission and distribution networks, 110kV and above high-voltage single-core cables are widely laid using various methods such as direct burial, cable trenches, tunnels, and conduits. The cable metal sheath grounding system is a key structure to ensure the safe operation of cables. It is susceptible to abnormal grounding circuit resistance due to construction damage, bolt corrosion, loose connections, and medium corrosion. In particular, defects such as incomplete soldering, detachment, and poor contact are prone to occur at connection points such as lead-sealed joints and crimped grounding terminals.

[0003] Currently, the industry's methods for locating defects in grounding loop resistance have the following shortcomings:

[0004] (1) Infrared thermometry is only effective in the later stages of defects, when heat is conducted to the surface of the cable or accessories, and cannot detect early internal contact defects;

[0005] (2) Ultrasonic testing technology is only effective for the state of intermittent arc discharge when the grounding wire is completely disconnected, and it is also a means of detecting defects in the later stage.

[0006] (3) Eddy current testing technology is difficult to detect small-sized defects inside metal connections, such as sand holes and internal cold welds;

[0007] (4) Power outage detection methods are limited by power supply reliability and are difficult to implement widely;

[0008] (5) Existing methods for detecting resistance in live circuits can only determine the branch or general area where the defect is located, and cannot pinpoint the defect to a specific connection point (such as the lead seal or terminal crimping). On-site repair still requires extensive investigation, resulting in low efficiency and high cost.

[0009] (6) Existing precise positioning methods often require stripping the outer sheath of the cable or dismantling the grounding box structure, which is a destructive test and affects the cable insulation integrity and operational safety.

[0010] Therefore, how to provide a non-destructive testing method that can accurately locate grounding loop resistance defects from branch to connection point without damaging the line structure or affecting the normal operation of the cable is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0011] The technical problem to be solved by this invention is: how to complete the entire process of detection, from branch identification to precise location of defect points, without damaging the cable's outer sheath and grounding structure, while the cable is in a live operating state.

[0012] To solve the above-mentioned technical problems, the first technical solution proposed by this invention is: a method for non-destructive and precise location of grounding loop resistance defects, comprising the following steps:

[0013] S1. Auxiliary constant current source coarse positioning: Inject a constant DC current into the grounding circuit under test, measure the current of each branch and the voltage of the circuit, and determine the defective branch with abnormal resistance by calculating the resistance value of each section of the circuit, and lock the defect in the interval between the lead-sealed connection points on both sides of the branch.

[0014] S2. Grounding disconnection at injection point: Select a signal injection point on one side of the defective branch and disconnect the grounding connection at the injection point to provide access conditions for the injection of alternating excitation signals;

[0015] S3, Signal Source Access and Excitation Output: Connect the alternating signal source between the metal sleeve of the injection point and the ground, and output an alternating excitation signal with a set frequency and amplitude to the grounded circuit under test;

[0016] S4. Thin film electrode installation: On the surface of the outer sheath of the cable in the defective branch, multiple thin film electrodes are sequentially attached along the cable route. Each electrode and the cable metal sheath form a coupling capacitance through the outer sheath insulation layer, serving as a non-intrusive voltage sensing unit.

[0017] S5. Coupling voltage detection and defect judgment: Measure the coupling response voltage amplitude at each thin film electrode in sequence and compare the voltage amplitude change pattern between adjacent electrodes; when the ratio of coupling voltage amplitude between the electrodes on both sides of a certain position changes abruptly, the position is determined to be a loop resistance defect point.

[0018] Furthermore, the auxiliary constant current source positioning method in step S1 is the 3A DC power supply test method: inject DC current between the two phase copper busbars of the cross-interconnected grounding box with a 3A constant current source, measure the DC current distribution on the three-phase metal sleeve with a high-precision DC current clamp meter, solve the resistance of each loop by establishing the Kirchhoff current and voltage equations, and determine the defective branch by comparing with the theoretical value.

[0019] Furthermore, the thin-film electrode mentioned in step S4 is a flexible conductive thin film, which is attached to the outer surface of the cable outer sheath in a wrap-around or semi-wrap-around manner. The coupling capacitance between the electrode and the metal sheath is determined by the dielectric constant, thickness and electrode area of ​​the cable outer sheath, and the coupling capacitance value is not less than 100pF.

[0020] Furthermore, the specific method for defect judgment in step S5 is as follows: For a uniformly distributed loop resistance, the coupling voltage at each electrode shows a monotonically decreasing trend along the cable direction; when there is a contact resistance defect in the loop, the voltage gradient on both sides of the defect point changes abruptly. By comparing the ratio of the coupling voltage amplitude measured by adjacent electrodes, when the ratio deviates from the normal attenuation ratio threshold, it is determined that there is a defect point between the two electrodes.

[0021] Furthermore, for cross-interconnected grounding systems, the detector continuously attaches electrodes along the cable route according to the cross-interconnected transposition method and performs detection, comparing the coupling voltage distribution pattern in each transposition segment to determine the location of defects at the lead seal or connection terminal.

[0022] Furthermore, for single-ended grounding systems, by changing the signal source injection position, alternating excitation signals are injected alternately at both ends of the cable. The magnitude and attenuation trend of the coupling voltage at each detection point before and after the signal source position change are compared. Combined with the bidirectional detection results for cross-verification, the precise location of loop resistance defects can be achieved.

[0023] Furthermore, the frequency range of the alternating excitation signal in step S3 is 133Hz, 640Hz or 1280Hz, and the power range is 0~5W; the signal frequency and amplitude are adaptively adjusted according to the cable length, outer sheath material and on-site interference conditions to ensure the signal-to-noise ratio of the coupling voltage detection.

[0024] To solve the above-mentioned technical problems, the second technical solution proposed by the present invention is: a non-destructive and precise positioning system for grounding loop resistance defects, including an auxiliary constant current source positioning module, a non-invasive precise positioning module, and a handheld control terminal module;

[0025] The auxiliary constant current source positioning module is electrically connected to the grounding circuit under test. It is used to inject a constant DC current into the grounding circuit and measure the current distribution of each branch, calculate the resistance of each section of the circuit, and determine the defective branch.

[0026] The non-invasive precision positioning module includes an alternating signal source unit, a thin film electrode group, and a coupling voltage detection unit. The alternating signal source unit is used to inject an alternating excitation signal into the grounding circuit under test. The thin film electrode group is attached to the surface of the cable outer sheath to form a coupling capacitor voltage divider. The coupling voltage detection unit is used to collect the coupling response voltage at each electrode and analyze the defect location.

[0027] The handheld control terminal module communicates wirelessly with the auxiliary constant current source positioning module and the non-invasive precision positioning module, respectively, and is used to issue detection commands, receive detection data and output positioning results.

[0028] Optionally, the auxiliary constant current source positioning module includes a 3A constant DC current source, a high-precision DC current clamp meter, and a processing unit; the output terminal of the DC current source is connected to two-phase copper busbars in the cross-interconnected grounding box, the DC current clamp meter is clamped to the outside of the three-phase grounding cable, and the processing unit establishes a set of equations and solves for the resistance value of each circuit segment based on the measured current and voltage data.

[0029] Optionally, the alternating signal source unit has a built-in DDS direct digital frequency synthesis circuit and power amplifier circuit, outputting a sinusoidal alternating signal with a frequency range of 133Hz, 640Hz or 1280Hz and a power range of 0~5W adjustable. The output terminal is equipped with overvoltage protection and impedance matching network.

[0030] Optionally, the thin-film electrode assembly consists of multiple flexible conductive thin-film electrodes, with an insulating adhesive layer on the back of the electrodes for attaching to the surface of the cable outer sheath; the number of electrodes is configured according to the length of the detection interval and the positioning accuracy requirements, with no less than one electrode per single detection interval.

[0031] Optionally, the coupling voltage detection unit includes a high input impedance preamplifier circuit, a bandpass filter circuit, and an RMS detection circuit; the input impedance of the preamplifier circuit is not less than 100MΩ, the center frequency of the bandpass filter circuit is consistent with the output frequency of the alternating signal source, and the output of the RMS detection circuit is sent to the handheld control terminal for data analysis.

[0032] Optionally, the handheld control terminal module is a portable industrial terminal with a built-in dedicated detection software unit. It communicates with each detection module via Bluetooth and supports coarse positioning branch determination, fine positioning data acquisition, automatic defect location interpretation, detection data storage, and standardized detection report export.

[0033] The beneficial effects of this invention are:

[0034] 1. Adopting a two-level architecture of "coarse positioning + fine positioning", the defect is first locked to the specific branch section by an auxiliary constant current source, and then the defect point is accurately located by a coupled voltage sensor. The positioning accuracy can reach the meter level or even the sub-meter level, which solves the problem that the traditional method can only determine the defective branch and cannot locate the specific connection point, thus greatly improving the efficiency of on-site maintenance.

[0035] 2. The precision positioning stage adopts a thin-film electrode coupling method, which is completely non-invasive and does not damage the cable outer sheath and grounding structure. There is no need to strip the insulation layer or disassemble the grounding box, which truly realizes non-destructive testing. The test does not affect the normal operation of the cable, and it combines safety and economy.

[0036] 3. The method is highly versatile and applicable to both cross-connected grounding systems and single-ended grounding systems. Cross-connected systems can be continuously tested along the transposed segments, while single-ended grounding systems can be verified through bidirectional injection cross-verification. Both methods can accurately locate typical defects such as lead sealing points and terminal crimping points.

[0037] 4. The detection signal adopts alternating excitation + bandpass filtering, which can effectively avoid power frequency and its harmonic interference, resulting in a high signal-to-noise ratio and stable and reliable detection results. The signal frequency and amplitude can be adaptively adjusted according to the site conditions to adapt to cable lines with different voltage levels and different laying methods.

[0038] 5. The system has a high degree of integration. Coarse positioning and fine positioning share the same handheld control terminal, and data is managed in a unified manner with integrated processes. This avoids the cumbersome operation of switching between multiple devices and reduces the intensity of on-site operations and safety risks. Attached Figure Description

[0039] Figure 1 This is an overall flowchart of the non-destructive and precise location method for grounding loop resistance defects proposed in this invention.

[0040] Figure 2 This is a schematic diagram illustrating the principle of coarse positioning using an auxiliary constant current source in this invention.

[0041] Figure 3 This is a schematic diagram of the non-invasive precise positioning principle based on a coupled voltage sensor in this invention (cross-interconnection system).

[0042] Figure 4 This is a schematic diagram of the non-invasive precise positioning principle based on a coupled voltage sensor in this invention (single-end grounding system). Detailed Implementation

[0043] The following description, in conjunction with the accompanying drawings and specific embodiments, further illustrates the non-destructive and precise location method and system for grounding loop resistance defects according to the present invention.

[0044] like Figure 1 As shown, the non-destructive and precise location method for grounding loop resistance defects proposed in this invention adopts a two-stage location strategy of "auxiliary constant current source coarse location + coupling voltage sensor fine location". The overall process includes five core steps: auxiliary constant current source coarse location, injection point grounding disconnection, signal source access and excitation output, thin film electrode installation, coupling voltage detection and defect judgment. The following describes each step in detail with reference to specific implementation methods.

[0045] Step 1: Coarse positioning using an auxiliary constant current source

[0046] refer to Figure 2Taking a three-section cross-interconnected grounding loop as an example, the auxiliary constant current source coarse positioning adopts the 3A DC power supply test method. Inside the cross-interconnected grounding box, a 3A constant DC current source is connected between the copper busbars of phases AB, AC, and BC, respectively. The output current of the current source and the loop voltage are read. At the same time, a high-precision DC current probe is used to measure the DC current on the metal sleeves of phases A, B, and C. Through three measurements with different injection combinations, a system of six linear equations is established to solve for the resistance values ​​of each section of the cross-interconnected loop (i.e., RA1, RB1, RC1, RA2, RB2, RC2).

[0047] The calculated resistance values ​​for each segment are compared with theoretical or historical values. Segments exceeding the threshold are identified as defective branches with abnormal resistance. This allows the defect to be pinpointed to the lead-sealed connection points on either side of the defective branch, such as the lead-sealed section of the tailpipe, the lead-sealed section of the copper shell of the intermediate joint, or the crimped connection of the grounding terminal. The purpose of this step is to narrow down the detection range, reducing the subsequent precise location interval from the entire cable segment to the area between two lead-sealed points of the known defective branch, thus providing a target interval for accurate location.

[0048] Step 2: Disconnect the grounding at the injection point.

[0049] Select a signal injection point on one side of the identified defective branch and disconnect the grounding connection at that point. The purpose of disconnecting the grounding here is to provide an injection port for the alternating excitation signal, allowing the alternating current to form a path along the metal sleeve and the grounding loop, ensuring a stable current distribution of the excitation signal within the defective branch. The disconnection operation only involves a temporary disconnection of the grounding terminal and does not involve damage to the cable body structure; it can be restored immediately after the inspection is completed.

[0050] Step 3: Signal Source Input and Excitation Output

[0051] Connect the output terminal of the alternating signal source between the metal sleeve at the injection point and the grounding terminal to output an alternating excitation signal to the grounded circuit under test. The signal source adopts DDS direct digital frequency synthesis technology, with an output frequency range of 133Hz, 640Hz, or 1280Hz and a power range of 0~5W, all of which are continuously adjustable.

[0052] The selection of signal frequency needs to comprehensively consider cable length, outer sheath dielectric characteristics, and on-site interference: higher frequencies result in lower capacitive reactance of the coupling capacitor and higher detection sensitivity, but also faster signal attenuation along the loop and shorter detection distance; lower frequencies have the opposite effect. For scenarios requiring short distances and high positioning accuracy, higher frequencies should be selected. The signal source output is equipped with an overvoltage protection circuit and impedance matching network to withstand power frequency induced voltage surges, ensuring equipment and personnel safety.

[0053] Step 4: Thin Film Electrode Installation

[0054] Multiple thin-film electrodes are sequentially attached to the outer sheath of the cable corresponding to the defective branch, along the cable route. The thin-film electrodes are made of flexible conductive film material with an insulating adhesive layer on the back. They can be directly wrapped around or partially wrapped around the outer surface of the cable sheath without any pretreatment.

[0055] Each thin-film electrode forms a coupling capacitor with the cable's metal sheath through the outer sheath insulation layer. The capacitance of this coupling capacitor is determined by the dielectric constant and thickness of the cable's outer sheath, as well as the electrode area. Taking a common 110kV cable outer sheath (approximately 3mm thick, with a relative dielectric constant of approximately 2.5) as an example, using a 100mm × 200mm thin-film electrode, the coupling capacitance of a single electrode is approximately 150pF, which meets the detection sensitivity requirements.

[0056] Step 5: Coupling Voltage Detection and Defect Judgment

[0057] refer to Figure 3 and Figure 4 The coupling voltage detection unit is connected sequentially to each thin-film electrode to measure the coupling response voltage amplitude at each electrode. The detection unit uses a high input impedance preamplifier (input impedance not less than 100MΩ) to reduce the load effect on the coupling voltage divider circuit; the subsequent stage is equipped with a bandpass filter with the same frequency as the excitation signal to effectively suppress power frequency and its harmonic interference, as well as spatial electromagnetic interference; finally, the voltage amplitude data is output through the RMS value detection circuit.

[0058] Defect Judgment Principle: When the grounding loop resistance is uniformly distributed along the cable, the alternating excitation current decays uniformly along the loop, and the voltage amplitude coupled to each electrode also shows a monotonically smooth decay trend, with the voltage ratio between adjacent electrodes being a stable value. When a contact resistance defect exists at a certain location in the loop (such as poor lead sealing or loose terminals), an additional voltage drop will occur at that point, causing a sudden change in the voltage gradient on both sides of the defect point. That is, the voltage amplitude on the side closer to the signal source is higher, and the voltage amplitude on the side farther from the signal source is lower, and the ratio between the two deviates from the normal decay ratio.

[0059] By comparing the ratio of the coupling voltage amplitude measured between adjacent electrodes, if the ratio deviates from the normal threshold (which can be determined by the standard attenuation coefficient of the cable model), a defect is identified between the two electrodes. This initial inspection revealed the abnormal region.

[0060] Detection methods for cross-connection systems: (See reference) Figure 3For cross-connected grounding systems, the detector continuously attaches electrodes along the cable route according to the cross-connection transposition method and performs testing. Within each transposition segment, thin-film electrodes are sequentially attached to the corresponding positions on the outer sheath of the three-phase cables, and the coupling voltage distribution is tested phase by phase and segment by segment. Since lead-sealing defects in cross-connected systems mainly occur at the joints (i.e., transposition nodes), the voltage changes on both sides of each joint can be focused on. By comparing the consistency of the three-phase voltage distribution within the same transposition segment, the abnormal lead-sealing location can be quickly located.

[0061] Testing methods for single-ended grounding systems: (Refer to...) Figure 4 For single-ended grounding systems, bidirectional detection is achieved by changing the signal source injection location. First, a signal is injected at the cable's beginning, and the coupling voltage distribution at each electrode is measured along the cable. Then, the signal source is moved to the cable's end, and the signal is injected again and measured. By comparing the voltage amplitude and attenuation trend at each location in the two tests, cross-validation of the bidirectional detection results eliminates systematic errors introduced by factors such as uneven cable structure and differences in outer sheath thickness, thus improving positioning accuracy.

[0062] To verify the feasibility of this invention in practical applications, a field test was conducted on a 110kV high-voltage cable cross-interconnected grounding section. This section of cable is approximately 1.2km long and uses a three-section cross-interconnected grounding method. During operation, it was found that the resistance of the B-phase grounding loop was too high.

[0063] Step 1: Coarse Location Using a Constant Current Source. Inside the first cross-connection grounding box, a 3A DC current source was used to inject constant current into the AB, AC, and BC sections respectively. A DC current clamp meter was used to measure the three-phase current, and a system of equations was established to solve for the resistance of each section. The results showed that the resistance of the first section of phase B (RB1) was 0.85Ω, far exceeding the normal value of less than 0.1Ω for cables of the same grade. The defect was determined to be located in the first section of phase B, specifically within the interval between the lead seal of the first end cap and the small-sized side lead seal of the first intermediate joint.

[0064] Step 2: Precise Positioning Preparation. Disconnect the ground at the beginning of phase B, connect an alternating signal source, and set the output frequency to 640Hz and the output amplitude to 10V. Attach a thin-film electrode to the outer sheath of each of the two adjacent cable sections that are cross-connected in phase B.

[0065] Step 3: Coupling voltage detection. The coupling voltage amplitude at the two electrode positions was measured sequentially. The data showed that the voltage amplitude decrease rate between electrode 1 and electrode 2 increased significantly, from the normal attenuation rate of about 5% to about 83%, deviating from the normal threshold.

[0066] Step 4: Precise Location. Analysis revealed the defect to be located at the lead seal of the small side tailpipe of the intermediate joint. Upon peeling it off, a weak solder joint was confirmed inside the lead seal, which matched the location result.

[0067] Field application results show that this method can accurately locate specific defects from branch identification to the point of failure while the cable is energized, without damaging the cable structure. It has high detection efficiency and accurate results, meeting the needs of on-site operation and maintenance.

[0068] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A non-destructive and precise method for locating grounding loop resistance defects, characterized in that, Includes the following steps: S1. Auxiliary constant current source coarse positioning: Inject a constant DC current into the grounding circuit under test, measure the current of each branch and the voltage of the circuit, and determine the defective branch with abnormal resistance by calculating the resistance value of each section of the circuit, and lock the defect in the interval between the lead-sealed connection points on both sides of the branch. S2, Grounding disconnection at injection point: Select a signal injection point on one side of the defective branch and disconnect the grounding connection at that injection point; S3, Signal Source Access and Excitation Output: Connect the alternating signal source between the metal sleeve of the injection point and the ground, and output an alternating excitation signal with a set frequency and amplitude to the grounding circuit under test; S4. Thin film electrode installation: On the surface of the outer sheath of the cable in the defective branch, multiple thin film electrodes are sequentially attached along the cable route. Each electrode and the cable metal sheath form a coupling capacitance through the outer sheath insulation layer, serving as a non-intrusive voltage sensing unit. S5. Coupling voltage detection and defect judgment: Measure the coupling response voltage amplitude at each thin film electrode in sequence and compare the voltage amplitude change pattern between adjacent electrodes; when the ratio of coupling voltage amplitude between the electrodes on both sides of a certain position changes abruptly, the position is determined to be a loop resistance defect point.

2. The method for non-destructive and precise location of grounding loop resistance defects according to claim 1, characterized in that, The auxiliary constant current source positioning method described in step S1 is the 3A DC power supply test method: inject DC current between the two phase copper busbars of the cross-interconnected grounding box with a 3A constant current source, measure the DC current distribution on the three-phase metal sleeve with a high-precision DC current clamp meter, solve the resistance of each loop segment by establishing the Kirchhoff current and voltage equations, and determine the defective branch by comparing it with the theoretical value.

3. The method for non-destructive and precise location of grounding loop resistance defects according to claim 1, characterized in that, The thin-film electrode mentioned in step S4 is a flexible conductive thin film, which is attached to the outer surface of the cable outer sheath in a wrap-around or semi-wrap-around manner. The coupling capacitance between the electrode and the metal sheath is determined by the dielectric constant, thickness and electrode area of ​​the cable outer sheath, and the coupling capacitance value is not less than 100pF.

4. The method for non-destructive and precise location of grounding loop resistance defects according to claim 1, characterized in that, The specific method for defect judgment in step S5 is as follows: For a uniformly distributed loop resistance, the coupling voltage at each electrode shows a monotonically decreasing trend along the cable direction; when there is a contact resistance defect in the loop, the voltage gradient on both sides of the defect point changes abruptly. By comparing the ratio of the coupling voltage amplitude measured by adjacent electrodes, when the ratio deviates from the normal attenuation ratio threshold, it is determined that there is a defect point between the two electrodes.

5. The method for non-destructive and precise location of grounding loop resistance defects according to claim 1, characterized in that, For cross-interconnected grounding systems, the detector continuously attaches electrodes along the cable route according to the cross-interconnection transposition method and performs detection. It compares the coupling voltage distribution pattern in each transposition segment to determine the location of defects at the lead seal or connection terminal.

6. The method for non-destructive and precise location of grounding loop resistance defects according to claim 1, characterized in that, For single-ended grounding systems, by changing the signal source injection position, alternating excitation signals are injected alternately at both ends of the cable. The magnitude and attenuation trend of the coupling voltage at each detection point before and after the signal source position change are compared. Combined with the bidirectional detection results for cross-verification, the precise location of loop resistance defects can be achieved.

7. The method for non-destructive and precise location of grounding loop resistance defects according to claim 1, characterized in that, The output frequency range of the alternating excitation signal in step S3 is 133Hz, 640Hz or 1280Hz, and the power range is 0~5W. The signal frequency and amplitude are adaptively adjusted according to the cable length, outer sheath material and on-site interference conditions to ensure the signal-to-noise ratio of the coupling voltage detection.

8. A system for precisely locating grounding loop resistance defects using the method described in any one of claims 1-7, characterized in that, It includes an auxiliary constant current source positioning module, a non-invasive precision positioning module, and a handheld control terminal module; The auxiliary constant current source positioning module is electrically connected to the grounding circuit under test. It is used to inject a constant DC current into the grounding circuit and measure the current distribution of each branch, calculate the resistance of each section of the circuit, and determine the defective branch. The non-invasive precision positioning module includes an alternating signal source unit, a thin film electrode group, and a coupling voltage detection unit. The alternating signal source unit is used to inject an alternating excitation signal into the grounding circuit under test. The thin film electrode group is attached to the surface of the cable outer sheath to form a coupling capacitor voltage divider. The coupling voltage detection unit is used to collect the coupling response voltage at each electrode and analyze the defect location. The handheld control terminal module communicates wirelessly with the auxiliary constant current source positioning module and the non-invasive precision positioning module, respectively, and is used to issue detection commands, receive detection data and output positioning results.

9. The non-destructive and precise positioning system for grounding loop resistance defects according to claim 8, characterized in that, The auxiliary constant current source positioning module includes a 3A constant DC current source, a high-precision DC current clamp meter, and a processing unit. The output of the DC current source is connected to two-phase copper busbars in the cross-interconnected grounding box. The DC current clamp meter is clamped to the outside of the three-phase grounding cable. The processing unit establishes a set of equations based on the measured current and voltage data and solves for the resistance values ​​of each circuit segment.

10. The non-destructive precision positioning system for grounding loop resistance defects according to claim 8, characterized in that, The alternating signal source unit has a built-in DDS direct digital frequency synthesis circuit and a power amplifier circuit, outputting a sinusoidal alternating signal with a frequency range of 133Hz, 640Hz, or 1280Hz and a power range of 0~5W adjustable. The output terminal is equipped with overvoltage protection and an impedance matching network. The thin film electrode group consists of multiple flexible conductive thin film electrodes, with an insulating adhesive layer on the back of the electrodes. Each detection segment has no less than one electrode. The coupling voltage detection unit includes a high input impedance preamplifier circuit, a bandpass filter circuit, and an RMS detection circuit. The input impedance of the preamplifier circuit is not less than 100MΩ.

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