Cable defect and joint positioning method and device

Abstract

The invention discloses a cable defect and joint positioning method and device. The device comprises a self-adaptive coaxial structure recovery sleeve installed outside a cable terminal; the test clamp is used for connecting the vector network analyzer and the cable; and the vector network analyzer applies a high-frequency excitation signal of a preset frequency band to the to-be-detected cable through a high-frequency signal generation module, and synchronously acquires broadband impedance spectrum data of the cable transmission link through a broadband response acquisition unit. The broadband impedance spectrum comprises characteristic information of a cable body, a joint and a defect position; and the upper computer is used for processing the broadband impedance spectrum data acquired by the vector network analyzer. And the vector network analyzer obtains broadband impedance spectrum data, extracts a positioning spectrogram by using Keyser window windowing processing and CZT conversion, and accurately identifies an abnormal reflection peak to position a defect or a joint position. The method can effectively eliminate the influence of the mismatching of the cable terminal structure on the test result in the field FDR test, thereby improving the accuracy and reliability of cable defect and joint positioning.

Description

Technical Field

[0001] The present invention relates to the technical field of cable defect detection, and in particular to a method and device for locating cable defects and joints by restoring a terminal coaxial structure. Background Art

[0002] In practical applications, cables serve as a critical transmission medium in power and communication systems, and their operational safety directly impacts the stability of the entire system. However, due to the long-term exposure to harsh conditions such as underground burial or complex environments, cables are susceptible to external forces, environmental corrosion, and insulation aging, leading to various defects, particularly shield damage and insulation degradation. Furthermore, cable joints, as crucial structures connecting multiple cable segments, have complex internal structures and numerous connection points. Under harsh conditions such as humidity, high temperatures, or high voltages, they are highly susceptible to faults such as electrical breakdown, poor contact, and partial discharge. Therefore, in addition to detecting cable defects, accurately locating cable joints is equally important. These defects can significantly increase cable signal reflections and transmission losses. If not detected and addressed promptly, they can lead to power or communication outages, which can severely impact the stability and safety of the entire system. Therefore, developing reliable cable defect detection and joint location methods is of great engineering value in ensuring safe system operation.

[0003] Currently, cable defect detection technologies primarily include time domain reflectometry (TDR) and frequency domain reflectometry (FDR). TDR locates defects by analyzing the temporal characteristics of a broadband impedance spectrum. This method can visually display fault locations within cables and is widely used for cable defect detection. However, TDR has limitations when dealing with long cables and complex environments. In particular, signal attenuation and distortion can reduce detection accuracy in the presence of high noise levels, complex cable layouts, and environmental interference.

[0004] Compared to TDR, frequency domain reflectometry (FDR) technology locates defects by analyzing the frequency characteristics of a cable's broadband impedance spectrum. FDR technology introduces more high-frequency components. High-frequency signals have short wavelengths and high spatial resolution, making them more sensitive to local impedance variations within the cable, thereby improving the accuracy and sensitivity of defect location. Therefore, FDR offers enhanced defect detection capabilities and improved anti-interference performance in cable defect detection, and holds broad application prospects. However, despite the significant advantages of FDR technology in detection accuracy and sensitivity, impedance discontinuities in cable terminal structures remain a key factor influencing detection accuracy in practical applications. Impedance discontinuities in cable terminal structures primarily manifest as impedance mismatches caused by differences in geometry, material properties, and connection methods. These differences significantly impact the transmission and reflection of detection signals. Components in the terminal structure, such as the splice box, stress cone, and composite sleeve, differ significantly from the geometry of the cable itself. These abrupt cross-sectional changes can easily cause signal reflection and scattering. Furthermore, the dielectric constants of dielectric materials such as the insulating oil, composite sleeve, and mechanical connector within the terminal differ from those of the cable itself, leading to fluctuations in the impedance spectrum response during high-frequency signal transmission. Furthermore, terminal fixtures are typically made of metal. These highly conductive components create impedance discontinuities, further increasing the reflected signal amplitude and causing phase shifts, thus affecting detection accuracy. Existing terminal impedance matching typically uses fixed-size metal sleeves or load resistors, which are difficult to adapt to varying cable diameters and cannot dynamically conform to the cable terminal surface, resulting in limited effectiveness in suppressing high-frequency signal reflections.

[0005] Therefore, in practical applications, effectively solving the impedance mismatch problem caused by the specific structure of cable terminals has become an important research direction for improving the accuracy of cable defect detection. Although existing detection technologies can detect cable defects to a certain extent, in practical applications, especially in complex environments and long-distance cable detection, the anti-interference and detection accuracy of traditional methods are still limited. To address the detection difficulties caused by the impedance discontinuity of the specific structure of cable terminals, it is urgent to propose a cable defect location method that can restore the terminal coaxial structure and improve signal integrity and impedance continuity to cope with detection under complex working conditions. Summary of the Invention

[0006] The present invention proposes a cable defect and joint locating method and device, which can effectively eliminate the influence of cable terminal structure mismatch on test results during on-site FDR testing, and achieve this through signal processing technology, thereby improving the accuracy and reliability of cable defect and joint locating.

[0007] The technical solution adopted by the present invention is:

[0008] A cable defect and joint locating device, comprising:

[0009] An adaptive coaxial structure recovery sleeve is installed outside the cable terminal, and the adaptive coaxial structure recovery sleeve matches the cable body and is coaxial;

[0010] Test fixture for electrical connection between vector network analyzer and cable;

[0011] As a key signal processing device, the vector network analyzer (VNA) applies a high-frequency excitation signal of a preset frequency band to the cable under test through a high-frequency signal generation module. The broadband response acquisition unit then simultaneously acquires broadband impedance spectrum data from the cable transmission link. This broadband impedance spectrum contains characteristic information about the cable itself, its connectors, and the location of defects. This spectrum constructs a stimulus-response signal model, providing raw data support for defect location.

[0012] As the core unit for data processing and analysis, the host computer performs in-depth processing on the broadband impedance spectrum data collected by the vector network analyzer.

[0013] The adaptive coaxial structure recovery sleeve includes: an inner layer made of highly conductive copper mesh woven material, which utilizes the excellent conductivity and flexibility of copper to fit tightly to the cable terminal, quickly restore the coaxial structure of the cable, and ensure the integrity of high-frequency signal transmission; an outer layer made of polymer composite insulating material, which forms a high-efficiency electromagnetic shielding layer through a special material formula and molding process, which can effectively isolate external electromagnetic interference and ensure the purity of the detection environment.

[0014] The adaptive coaxial structure recovery sleeve is equipped with a fastening mechanism and a locking structure to adjust the tightness of the sleeve and the cable, achieving a tight and stable fit with the cable terminal. The sleeve's pulley snap-on fastening mechanism and axial snap-on adaptive locking structure automatically adjust the tightness to within ±5mm of the cable terminal diameter, achieving a tight and stable fit. This effectively suppresses relative vertical displacement and provides a reliable physical and electrical foundation for subsequent testing.

[0015] Tightly connect the inner layer of the adaptive coaxial structure recovery sleeve with the shielding layer extending from the cable, buckle the locking structure of the recovery sleeve and adjust the fastening mechanism to lock the cable under test, ensuring that the recovery sleeve has good contact with the shielding layer extending from the cable.

[0016] The test fixture and ground shielding module form a signal transmission guarantee unit. The ground shielding module isolates external electromagnetic noise and ensures stable signal transmission. This module, internal to the vector network analyzer, includes a metal shielding housing and a multi-layer filter circuit. The metal shielding housing provides electromagnetic shielding, while the filter circuit suppresses signal interference. This effectively isolates external electromagnetic noise, ensuring stable and accurate signal transmission.

[0017] The test fixture adopts an elastic crimping structure. The main body is composed of a metal clamp with an integrated elastic crimping mechanism and red and black wires. The structural diagram is shown in the figure. Figure 5 As shown. The metal chuck has a built-in elastic arm, and its contact surface is specially plated to reduce contact resistance. The red and black wires correspond to the signal terminal and ground terminal of the vector network analyzer respectively. When connected, the ends of the red and black wires are connected to the signal output part and the ground part of the vector network analyzer port to build an electrical path for the instrument; the metal chuck clamps the conductor and shielding layer of the cable to be tested through elastic crimping action, establishes an electrical connection with the cable to be tested, and realizes the injection of test signals and the return of reflected signals. The mechanical stability of its elastic crimping and the low resistance characteristics of the plating ensure the reliability of the electrical connection. The test fixture adopts an elastic crimping structure and the contact surface is specially plated to significantly reduce the contact resistance. Ensure that the electrical connection between the vector network analyzer and the cable is stable and reliable.

[0018] The conductor of the cable under test passes through the red wire of the test fixture to establish a signal transmission link with the signal output / input port of the vector network analyzer; the shielding layer passes through the black wire of the test fixture to build a reference ground loop with the reference ground port of the vector network analyzer.

[0019] The vector network analyzer acquires broadband impedance spectrum data, and uses Kaiser window processing and CZT transformation to extract positioning spectra, accurately identifying abnormal reflection peaks to locate defects or joint positions.

[0020] Strip off the outer sheath, shielding layer and insulation layer at the end of the cable, remove the outer sheath and shielding layer about 1m long and the insulation layer 0.8m long at the end of the cable, exposing the 0.8m long copper conductor part, and then use insulating material to reconstruct the insulation layer of the exposed copper conductor part to form a cable terminal.

[0021] The cable defect and joint location method includes the following steps:

[0022] Step 1: Build a cable defect and joint detection platform and a host computer analysis platform, and restore the coaxial structure of the cable terminal to be tested;

[0023] Step 2: Select a sweep frequency band that matches the cable characteristics as the operating frequency band of the vector network analyzer for measurement, and transmit the broadband impedance spectrum data to the host computer;

[0024] Step 3: Perform windowing and CZT transformation on the acquired broadband impedance spectrum data to generate a positioning spectrum, and extract the location information of the cable joints and defects through peak detection.

[0025] The step 1 comprises the following steps:

[0026] Step 1.1: Install an adaptive coaxial structure recovery sleeve on the outside of the cable terminal to restore the coaxial structure. Use a radially adjustable fastening mechanism to ensure a tight fit with the cable, so that the terminal forms a coaxial structure.

[0027] Step 1.2: Connect the high-frequency signal generation module, vector network analyzer, and impedance matching test fixture in sequence to establish a complete detection path, and implement electromagnetic shielding on all connected components.

[0028] The step 2 comprises the following steps:

[0029] Step 2.1: Configure the frequency domain sampling parameters of the vector network analyzer according to the cable transmission characteristics. The test step length Δf (Hz) is given by equation (1):

[0030]

[0031] In formula (1), v is the propagation velocity of electromagnetic waves in the cable, unit: m / s; l is the actual length of the measured cable, unit: m; Δf is the frequency domain measurement step;

[0032] According to the step size parameter determined by formula (1), a suitable measurement frequency band is selected as the working frequency band of the vector network analyzer for measurement to balance the test resolution and signal-to-noise ratio;

[0033] Step 2.2: Transmit the broadband impedance spectrum data collected by the vector network analyzer to the host computer through a standard communication interface. The data includes the complex impedance spectrum (real part + imaginary part) and phase information, which serves as the data input source for subsequent cable defect and joint location.

[0034] The step 3 comprises the following steps:

[0035] Step 3.1: Perform windowing on the broadband impedance spectrum data Z0(f) measured by the vector network analyzer. Use the Kaiser Window function to optimize the spectrum characteristics. The Kaiser Window formula is:

[0036]

[0037] In formula (2), I0 is the zero-order modified Bessel function; β is the window function control parameter (controls the main lobe width and side lobe attenuation); M is the number of samples; n is the index of the current sample point (0≤n≤M-1);

[0038] Obtain the windowed impedance spectrum data Z w (f) = Z0(f)*w(n), windowing processing is performed to improve the signal-to-noise ratio.

[0039] Step 3.2: Calculate the broadband impedance spectrum Z after windowing w(f) Perform CZT transformation. CZT is used to optimize the signal data quality. The spectrum calculation formula of the broadband impedance spectrum after CZT transformation is as follows:

[0040]

[0041] Among them, X(k) is the spectrum data after CZT transformation; Z w (f) is the windowed impedance spectrum data; n is the discrete time series index of the input signal, ranging from 0 to N-1; W N =e -j2π / N is the rotation factor, N is the number of sampling points, and k is the target frequency point for CZT calculation.

[0042] The broadband impedance spectrum Z after windowing by CZT w (f) Perform spectrum analysis to further optimize signal quality and obtain a positioning spectrum.

[0043] Step 3.3: By analyzing the location of the abnormal peak in the positioning spectrum obtained after spectrum analysis, the cable joint and defect can be located.

[0044] The present invention provides a method and device for locating cable defects and joints, and the technical effects are as follows:

[0045] 1) The present invention solves the problems of strong reflection and signal distortion caused by terminal impedance mismatch by restoring the coaxial structure of the cable terminal in a field environment, significantly improving the accuracy and reliability of defect and joint positioning.

[0046] 2) The present invention designs an adaptive coaxial structure recovery sleeve with a snap-on double-layer structure, including an inner copper mesh structure layer with good conductivity and an outer polymer composite insulation layer, which has electromagnetic shielding and external interference suppression capabilities. The coaxial recovery sleeve is provided with a pulley buckle on the surface, and an adaptive locking structure is arranged axially in the middle, which can be adjusted within the range of ±5mm according to the actual diameter of the cable terminal to ensure a close fit and avoid displacement in the vertical direction. This structure not only effectively restores the coaxial structure of the cable terminal, improves impedance continuity, and significantly improves the positioning accuracy of defects and joints, but also has engineering advantages such as easy installation, strong structural compatibility, and excellent anti-interference performance. It is suitable for different types of cables and a variety of complex test environments, and significantly improves the stability and repeatability of system detection.

[0047] 3) The method of this invention is applicable to a variety of complex cable environments, especially in environments with multiple connectors and high noise levels, demonstrating excellent detection stability and applicability. This method not only improves the sensitivity and anti-interference capabilities of defect detection, but also provides a solid theoretical basis and engineering guidance for the practical application of FDR technology in complex field environments, greatly expanding its scope of application and practical value. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be further described below with reference to the accompanying drawings and examples:

[0049] Figure 1 Schematic diagram of the patented cable defect location system designed for this invention.

[0050] Figure 2 Flowchart for defect and joint location testing.

[0051] Figure 3 This is a structural diagram of the coaxial structure of the restored cable terminal.

[0052] Figure 4 Schematic diagram of the structure of the adaptive coaxial structure recovery sleeve.

[0053] Figure 5 Schematic diagram of the test fixture.

[0054] Figure 6 The figure shows the joint and defect location spectrum of an 85m cable without an adaptive coaxial structure recovery sleeve.

[0055] Figure 7 The connector and defect location spectrum of an 85m cable with an adaptive coaxial structure recovery sleeve.

[0056] Figure 8 The figure shows the joint and defect location spectrum of a 200m cable without the adaptive coaxial structure recovery sleeve.

[0057] Figure 9 The joint and defect location spectrum of a 200m cable with an adaptive coaxial structure recovery sleeve.

[0058] In the figure, 1. conductor, 2. shielding layer, 3. insulation layer, 4. outer sheath, 5. adaptive coaxial structure recovery sleeve, 6. inner layer, 7. outer layer, 8. fastening mechanism, 9. locking structure. DETAILED DESCRIPTION

[0059] The present invention provides a method and device for locating cable defects and joints. First, an adaptive coaxial structure recovery sleeve is installed on the exterior of the cable terminal, creating a coaxial structure that matches the cable itself. This addresses signal distortion and reflection enhancement caused by impedance discontinuities at the terminal. A vector network analyzer (VNA) is then used to acquire broadband impedance spectrum data. The localization spectrum is extracted using a Kaiser window and CZT transform, accurately identifying abnormal reflection peaks to pinpoint defects or joints. Experimental results demonstrate that this method significantly improves defect detection resolution, anti-interference capabilities, and positioning accuracy. It is suitable for defect detection in power cables, radio frequency cables, and high-frequency transmission cables of various lengths and in complex environments.

[0060] The two cables to be tested used in the present invention are both SYV-50-3 model coaxial cables to simulate power cables, with total lengths of 85m and 200m respectively, and the test instrument used is Dingyang SHA8645A vector network analyzer.

[0061] The overall structure of the device of the present invention is as follows Figure 1 As shown: The data acquisition and control unit includes a host computer analysis and display platform and a vector network analyzer. The vector network analyzer is connected to the conductor 1 and shielding layer 2 of the cable under test through a test fixture. In addition, the structural diagram of the coaxial structure recovery at the end of the cable is shown in Figure 3 As shown, the structural diagram of the adaptive coaxial structure recovery sleeve 5 is as follows Figure 4 shown.

[0062] Example 1:

[0063] This embodiment is an experiment to locate four joints and one shielding layer defect of an 85m RF coaxial cable, wherein the joint and defect locations are: 1# joint at 18.25m, 2# joint at 36.00m, shielding layer defect at 46.42m, 3# joint at 54.62m, and 2# joint at 69.25m.

[0064] Dingyang SHA8645A vector network analyzer is set with a sweep frequency lower limit of 0.1MHz, a frequency upper limit of 59.9MHz, and a sampling point number of 1601. This embodiment performs joint and defect location experiments on the tested cable without terminal coaxial structure restoration and the tested cable after terminal coaxial structure restoration. The test flow chart is shown in the figure below. Figure 2 As shown, the following steps are included:

[0065] S1.1: Build a cable defect and joint detection platform and a host computer analysis platform. Connect the signal source, vector network analyzer and test fixture in sequence to establish a complete detection path. The structural diagram is as follows: Figure 1 As shown, the vector network analyzer should be calibrated, zeroed, and grounded and shielded.

[0066] S1.2: Select an 85m long SYV-50-3 coaxial cable. Use professional tools to strip the outer jacket 4, copper shielding layer, and insulation layer 3 at the end of the cable. Remove approximately 1m of the outer jacket 4 and copper shielding layer, and 0.8m of the insulation layer 3 at the end of the cable, exposing a 0.8m long copper conductor portion. Then, use insulating material to reconstruct the insulation layer of the exposed copper conductor portion, forming a "cable terminal" similar to that in actual working conditions.

[0067] S1.3: Connect the copper core conductor and shield of an 85-meter-long coaxial cable to the test fixture on the vector network analyzer. After ensuring the connections are correct, select a test frequency range of 0.1 MHz to 59.9 MHz and 1601 test points. Test the cable to obtain its broadband impedance spectrum data, Z0(f1).

[0068] S1.4: The measured broadband impedance spectrum data Z0(f1) is transmitted to the host computer. First, the measured broadband impedance spectrum data Z0(f1) is windowed, β=6, to improve its signal-to-noise ratio, and the windowed impedance spectrum data Z0(f1) is obtained. w (f1), after adding window data Z w (f1) Perform CZT transformation to obtain the positioning spectrum, the result is as follows Figure 6 shown. Figure 6 It is difficult to see the abnormal peaks caused by joints and defects because the unrestored coaxial structure makes the impedance at the simulated terminal discontinuous, which seriously affects the reflected signal. The positioning spectrum is interfered by the abnormal peaks, making it impossible to distinguish and locate the specific positions of the joints and defects.

[0069] To further verify this method, the coaxial structure restoration process is performed on the cable end based on the above. The specific method is:

[0070] S2.1: Restore the coaxial structure of the "cable terminal" in the simulated actual working condition, and use the adaptive coaxial structure recovery set 5 to reconstruct the coaxial structure of the simulated cable terminal. The structural diagram is as follows: Figure 3 As shown, the structural diagram of the adaptive coaxial structure recovery sleeve 5 is as shown Figure 4 As shown, the inner layer 6 in the adaptive coaxial structure recovery sleeve 5 is tightly connected to the shielding layer 2 extending from the cable under test, and the locking structure 9 of the coaxial recovery sleeve is buckled while adjusting the fastening mechanism 8 to lock the cable under test to ensure that the coaxial structure recovery sleeve has good contact with the shielding layer extending from the cable.

[0071] S2.2: Make good use of the detection platform built in the above experiment, connect the restored test fixtures in sequence, establish a complete detection path, and select the same test frequency band and measurement points as the above experimental points to test the cable under test, and obtain its broadband impedance spectrum data Z0(f2). Perform the same data processing as the broadband impedance spectrum data Z0(f1) tested above to obtain Z w (f2), thus obtaining the positioning spectrum, the result is as follows Figure 7 shown. Figure 7 It can be clearly seen that the abnormal peaks are located at 18.07m, 35.73m, 46.18m, 54.40m, 69.08m, and Figure 6In sharp contrast, the adaptive coaxial structure recovery sleeve 5 greatly improves the positioning accuracy of joints and defects.

[0072] Example 2:

[0073] This embodiment further verifies the reliability of the method of the present invention on the basis of Example 1, and selects a SYV-50-3 coaxial cable of the same model as Example 1 and with a length of 200m to simulate the cable terminal and restore its coaxial structure, and conducts experiments on locating two joints and two shielding layer defects on the cable, wherein the joint and defect positions are respectively 1# shielding layer defect at 23.70m, 1# joint at 79.75m, 2# shielding layer defect at 130.70m, and 2# joint at 145.60m. The lower limit of the sweep frequency set by the Dingyang SHA8645A vector network analyzer is 0.1MHz, the upper limit of the frequency is 300MHz, and the number of sampling points is 1601. This embodiment conducts joint and defect location experiments on the cable under test without the end coaxial structure and the cable under test after the end coaxial structure is restored, including the following steps:

[0074] S3.1: Make good use of Example 1 to build a detection platform, and perform the same structural treatment on the 200m coaxial cable as that of forming the "cable terminal" in Example 1. After the treatment, the "terminal" copper core conductor and the shielding layer of the 200m long unrestored "terminal" coaxial structure coaxial cable are connected to the test fixture on the vector network analyzer in turn. After ensuring that the connection is correct, the cable under test is tested to obtain its broadband impedance spectrum data Z0 (f3).

[0075] S3.3: The measured broadband impedance spectrum data Z0(f3) is transmitted to the host computer. First, the measured broadband impedance spectrum data Z0(f3) is subjected to windowing processing. Due to the increase in cable length in Example 2, in order to improve the long-distance signal resolution, the size of the window function is increased, and β=100 is set. By increasing the sidelobe suppression ratio, the signal-to-noise ratio is better improved, and the windowed impedance spectrum data Z0(f3) is obtained. w (f3), after adding window, all data Z w (f3) Perform CZT transformation to obtain the positioning spectrum, the result is as follows Figure 8 shown. Figure 8 Since the unrestored coaxial structure makes the impedance at the simulated terminal discontinuous, the reflected signal is seriously affected, making it difficult to see the positions of the abnormal peaks caused by the connector and shielding layer defects.

[0076] To further verify this method, the coaxial structure of the cable end is restored based on the above. The specific method is:

[0077] S4.1: Use the adaptive coaxial structure recovery sleeve to restore the coaxial structure of the "terminal" of the 200m coaxial test cable as in Example 1, and fit the adaptive coaxial structure recovery sleeve and the terminal tightly to ensure the accuracy of the test. S4.2: Transmit the tested broadband impedance spectrum data Z0 (f4) to the host computer, test the cable to obtain its broadband impedance spectrum data Z0 (f4) and perform the same data processing as the broadband impedance spectrum data Z0 (f3) tested above to obtain Z w (f4), thus obtaining the localization spectrum, the result is as follows Figure 9 shown. Figure 9 It can be clearly seen that the abnormal peaks are located at 23.35m, 79.32m, 130.33m, 144.27m, and Figure 8 In sharp contrast, the installation of the adaptive coaxial structure recovery sleeve greatly improved the positioning accuracy of joints and defects.

[0078] By comparing and analyzing the four result graphs, the experimental results show that the coaxial structure is not restored. Figure 6 and Figure 8 In the process, the joint defect positioning error is large, false alarm signals occur frequently, interference signals and defect signals are difficult to effectively distinguish, and the joint defect position is difficult to accurately identify; after the coaxial structure is restored Figure 7 and Figure 9 The positioning effect is significantly improved, the positioning abnormal peaks of joints and defects are effectively enhanced, the false alarms are significantly reduced, and the precise positioning of the defect position is achieved, verifying the improvement of the signal focusing effect by restoring the coaxial structure. Figure 7 The corresponding embodiment 1 Figure 9 The cable used is 2.4 times longer, indicating that the method of the present invention can show high accuracy and stability in locating joints and defects on cables of different lengths.

[0079] Tables 1 and 2 provide the location results and error analysis for connector and shield defects on two test cables in Examples 1 and 2, respectively. The absolute error is defined as the difference between the actual location and the located location of each connector and shield defect, while the relative error is defined as the ratio of the absolute error to the total length of the test cable.

[0080] As shown in Table 1, the absolute error in locating defects in each connector and shield layer does not exceed 0.27m, and the relative error does not exceed 0.32%. As shown in Table 2, the absolute error in locating defects in each connector and shield layer does not exceed 0.43m, and the relative error does not exceed 0.22%. In summary, the experimental results fully demonstrate that restoring the coaxial structure of the cable terminal not only effectively suppresses interference signals and improves the signal-to-noise ratio, but also significantly enhances defect location accuracy and system detection consistency.

[0081] Table 1 Positioning results and error analysis of Example 1

[0082]

[0083] Table 2 Positioning results and error analysis of Example 2

[0084]

[0085] The method of the present invention can be applied not only to power cables, but also to defect detection and assessment of radio frequency cables and high-frequency transmission cables. Especially in complex field environments, it can quickly and accurately locate cable defects and reduce on-site detection time and costs.

Claims

1. A cable defect and joint locating device, characterized in that The device includes: An adaptive coaxial structure recovery sleeve (5) is installed outside the cable terminal, and the adaptive coaxial structure recovery sleeve (5) matches the cable body and is coaxial; Test fixture, used to connect the vector network analyzer and the cable; The vector network analyzer applies a high-frequency excitation signal of a preset frequency band to the cable to be tested through a high-frequency signal generation module, and then synchronously obtains broadband impedance spectrum data of the cable transmission link through a broadband response acquisition unit. The broadband impedance spectrum contains characteristic information of the cable body, joints, and defect locations. The host computer processes the broadband impedance spectrum data collected by the vector network analyzer.

2. A cable defect and joint locating device according to claim 1, characterized in that: The self-adaptive coaxial structure recovery sleeve (5) comprises an inner layer (6) made of a high-conductivity copper mesh braided material and an outer layer (7) made of a polymer composite insulating material.

3. A cable defect and joint locating device according to claim 2, characterized in that: The adaptive coaxial structure recovery sleeve (5) is provided with a fastening mechanism (8) and a locking structure (9) for adjusting the tightness of the recovery sleeve and the cable to achieve a tight and stable fit with the cable terminal.

4. A cable defect and joint locating device according to claim 3, characterized in that: The inner layer (6) of the adaptive coaxial structure recovery sleeve (5) is tightly connected to the shielding layer (2) extending from the cable, and the locking structure (9) of the recovery sleeve is fastened while adjusting the fastening mechanism (8) to lock the tested cable, ensuring that the recovery sleeve has good contact with the shielding layer (2) extending from the cable.

5. The cable defect and joint locating device according to claim 1, characterized in that: The test fixture adopts an elastic crimping structure, and the main body includes a metal clamp with an integrated elastic crimping mechanism, and red and black wires; The metal chuck has a built-in elastic arm, and its contact surface is specially plated to reduce contact resistance; The red and black wires correspond to the signal terminal and ground terminal of the vector network analyzer respectively. When connecting, the ends of the red and black wires are connected to the signal output part and ground part of the vector network analyzer port to build the electrical path of the instrument; The metal clamp clamps the conductor (1) and the shielding layer (2) of the cable to be tested through an elastic crimping action, thereby establishing an electrical connection with the cable to be tested and achieving injection of a test signal and return of a reflected signal.

6. The cable defect and joint locating device according to claim 1, characterized in that: The conductor (1) of the cable to be tested is connected to the signal output / input port of the vector network analyzer through the red wire of the test fixture to establish a signal transmission link; the shielding layer (2) is connected to the reference ground port of the vector network analyzer through the black wire of the test fixture to establish a reference ground loop.

7. A method for locating cable defects and joints using the device of any one of claims 1 to 6, characterized in that The following steps are involved: Step 1: Build a cable defect and joint detection platform and a host computer analysis platform, and restore the coaxial structure of the cable terminal to be tested; Step 2: Select a sweep frequency band that matches the cable characteristics as the operating frequency band of the vector network analyzer for measurement, and transmit the broadband impedance spectrum data to the host computer; Step 3: Perform windowing and CZT transformation on the acquired broadband impedance spectrum data to generate a positioning spectrum, and extract the location information of the cable joints and defects through peak detection.

8. The cable defect and joint locating method according to claim 7, characterized in that: The step 1 comprises the following steps: Step 1.1: Install an adaptive coaxial structure recovery sleeve (5) for recovering the coaxial structure on the outside of the cable terminal, and ensure that it fits tightly with the cable through a radially adjustable fastening mechanism (8) to form a coaxial structure at the terminal; Step 1.2: Connect the high-frequency signal generation module, vector network analyzer, and impedance matching test fixture in sequence to establish a complete detection path, and implement electromagnetic shielding on all connected components.

9. The cable defect and joint locating method according to claim 7, characterized in that: The step 2 comprises the following steps: Step 2.1: Configure the frequency domain sampling parameters of the vector network analyzer according to the cable transmission characteristics. The test step length Δf (Hz) is given by equation (1): In formula (1), v is the propagation velocity of electromagnetic waves in the cable, unit: m / s; l is the actual length of the measured cable, unit: m; Δf is the frequency domain measurement step; According to the step size parameter determined by formula (1), a suitable measurement frequency band is selected as the working frequency band of the vector network analyzer for measurement to balance the test resolution and signal-to-noise ratio; Step 2.2: Transmit the broadband impedance spectrum data collected by the vector network analyzer to the host computer through a standard communication interface. The data includes complex impedance spectrum and phase information, which serves as the data input source for subsequent cable defect and joint location.

10. The cable defect and joint locating method according to claim 7, characterized in that: The step 3 comprises the following steps: Step 3.1: Perform windowing on the broadband impedance spectrum data Z0(f) measured by the vector network analyzer. Use the Kaiser window function to optimize the spectrum characteristics. The Kaiser window formula is: In formula (2), I0 is the zero-order modified Bessel function; β is the window function control parameter, which controls the main lobe width and side lobe attenuation; M is the number of samples; n is the index of the current sample point, 0≤n≤M-1; Obtain the windowed impedance spectrum data Z w (f) = Z0(f)*w(n), windowing processing to improve the signal-to-noise ratio; Step 3.2: Calculate the broadband impedance spectrum Z after windowing w (f) Perform CZT transformation; optimize signal data quality through CZT; the spectrum calculation formula of the broadband impedance spectrum after CZT transformation is as follows: Among them, X(k) is the spectrum data after CZT transformation; Z w (f) is the windowed impedance spectrum data; n is the discrete time series index of the input signal, ranging from 0 to N-1; W N =e -j2π / N is the rotation factor, N is the number of sampling points, and k is the target frequency point for CZT calculation; The broadband impedance spectrum Z after windowing by CZT w (f) performing spectrum analysis to further optimize signal quality and obtain a positioning spectrum; Step 3.3: By analyzing the location of the abnormal peak in the positioning spectrum obtained after spectrum analysis, the cable joint and defect can be located.

Images