A method and system for locating cable defects by integrating reflection coefficient and impedance spectrum

Abstract

This invention discloses a method and system for locating cable defects by fusing reflection coefficient and impedance spectrum, relating to the field of insulation condition diagnosis and assessment technology for power equipment. The method includes: acquiring reflection coefficient spectrum data and impedance spectrum data from the cable's head end; extracting the imaginary part of the reflection coefficient spectrum and the amplitude information of the impedance spectrum and fusing them to obtain fused spectrum data; performing localization processing on the reflection coefficient spectrum, impedance spectrum, and fused spectrum based on windowed Fourier transform to construct a local defect diagnosis function; and analyzing the diagnosis curve to determine the defect location and severity. This invention significantly improves the identification accuracy of the location pulse by coherently enhancing defect information through spectrum fusion, suppressing background fluctuations at non-defect locations. It has advantages such as a location error of less than 0.3%, strong anti-interference ability, and low misjudgment rate, making it suitable for efficient on-site fault detection of power cables.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment insulation condition diagnosis and assessment technology, specifically to a cable defect location method and system that integrates reflection coefficient and impedance spectrum. Background Technology

[0002] Power cables are crucial equipment for transmitting and distributing electrical energy in power systems. They offer advantages such as convenient installation, small footprint, stable power transmission, long service life, low maintenance workload, and high safety, and are widely used in all aspects of power generation, transmission, and distribution. Power cables mainly consist of a conductor core, cross-linked polyethylene (XLPE) main insulation, a metallic shield, and sealing materials, primarily serving as electrical insulation and mechanical support. However, the XLPE main insulation and metallic shield are the weakest points in the cable's insulation. Firstly, during cable manufacturing, defects such as micropores, impurities, and protrusions in the semi-conductive shield layer may exist in the main insulation. After operation, under heat and electrical stress, these defects can lead to localized defects such as water trees and electrical trees. Secondly, during cable laying and operation, non-standard power cable channels make the metallic shield and main insulation susceptible to damage from external forces. When the cable is energized, damaged metallic shields and main insulation are prone to aging under the influence of heat, moisture, and microorganisms, forming localized defects and causing insulation failure. Localized defects are potential faults that precede cable line outages and directly affect the service life of power cables. Therefore, conducting research on cable defect location is of great significance for timely detection of potential hazards in cable lines and ensuring the safe and reliable operation of cables.

[0003] Currently, frequency domain reflection is one of the mainstream technologies for diagnosing local defects in cables. Its core principle is to inject a sinusoidal sweep signal with a specific frequency range into the cable head. When the signal propagates in the cable, it will be reflected at the impedance mismatch point where the defect is formed. By receiving the reflected signal, a frequency domain reflection coefficient spectrum and a broadband impedance spectrum containing defect information can be constructed. Then, the defect location can be achieved through a spectrum transformation algorithm (such as a Fourier transform algorithm).

[0004] However, in existing frequency domain reflectance methods, the frequency domain reflectance coefficient spectrum and broadband impedance spectrum are used independently, failing to achieve spectral-level fusion. This results in inherent and insurmountable defects in the technology. Specifically, while the reflectance coefficient spectrum has high sensitivity to defects, its noise immunity is weak, and it is prone to large fluctuations in non-defect areas, leading to chaotic positioning curves. The broadband impedance spectrum has strong noise immunity, but its response signal to weak defects is extremely weak, making it difficult to effectively identify early-stage, minute defects. These defects directly result in large fluctuation amplitudes in the positioning curve obtained from a single spectrum, easily leading to misjudgments. It fails to balance the sensitivity and noise immunity of defect detection, making it difficult to meet the high-precision defect positioning requirements in engineering.

[0005] Therefore, there is an urgent need to propose a high-precision method for locating local defects in power cables, in order to solve the technical problems of large fluctuations in the positioning curve, easy misjudgment, and inability to balance defect detection sensitivity and noise resistance in the existing technology. Summary of the Invention

[0006] The technical problem to be solved by this invention is that the accuracy of existing methods for diagnosing local defects in cables is insufficient when relying solely on reflection coefficient spectrum or impedance spectrum for localization.

[0007] This invention solves the above-mentioned technical problems through the following technical means: a cable defect location method that integrates reflection coefficient and impedance spectrum, comprising: S1. Obtain the reflection coefficient spectrum data and impedance spectrum data of the cable head end, and perform cable traveling wave analysis to derive the mathematical expressions for the reflection coefficient spectrum and impedance spectrum. S2. Extract the imaginary part information of the reflection coefficient spectrum and the amplitude information of the impedance spectrum, and obtain fused spectrum data through fusion processing; S3. Based on the windowed Fourier transform, the reflection coefficient spectrum, impedance spectrum and fused spectrum data are respectively processed to locate the defect and construct a local defect diagnosis function. S4. Analyze the diagnostic curve corresponding to the local defect diagnostic function to determine the location and severity of the local defects in the cable.

[0008] Furthermore, the impedance spectrum in step S1 is constructed in the following manner: Establish a cable traveling wave propagation model, taking the load at the cable tail end as... The origin of the voltage vector points positively towards the cable's beginning; the voltage and current at any point on the cable contain both incident and reflected waves, therefore the voltage vector... With current vector The expression is:

[0009] In the formula, , These represent the cable traveling wave propagation constant and characteristic impedance, respectively. , These represent the incident voltage and the reflected voltage, respectively. According to the voltage vector With current vector The ratio is used to calculate the input impedance at a distance x from the origin. :

[0010] In the formula, The reflection coefficient at the cable end; when hour, The total length of the cable, and the input impedance spectrum of the intact cable head. : .

[0011] Furthermore, the reflection coefficient spectrum in step S1 is constructed in the following manner: The intensity of reflection and refraction when a signal encounters impedance mismatch during transmission on a transmission line is defined as the ratio of the reflected voltage wave to the incident voltage wave or the ratio of the reflected current wave to the incident current wave, and the reflection coefficient at a distance from the origin. The calculation formula is:

[0012] when At that time, the reflection coefficient of the intact cable head end :

[0013] In the formula, This is the end load.

[0014] Furthermore, the fused spectrum data includes: Using Euler's formula to analyze the input impedance spectrum at the beginning of the cable and the reflection coefficient at the cable end Decompose:

[0015]

[0016] In the formula, , These are the attenuation coefficient, which characterizes the amplitude decay of the traveling wave, and the phase coefficient, which characterizes the phase change of the traveling wave; Pick Amplitude:

[0017] Pick Virtual part:

[0018] Fusion spectrum data The calculation formula is: .

[0019] Furthermore, the calculation formula for the local defect diagnosis function is as follows:

[0020] In the formula, and These are the lower and upper limits of the measurement frequency range, respectively. It can measure the reflection coefficient spectrum, impedance spectrum, or fused spectrum data of the cable head end. This is the frequency domain form of the window function. For frequency, This is the distance from the defect to the beginning of the cable. This represents the propagation speed of the traveling wave.

[0021] Furthermore, it also includes a positioning error assessment step: The formula for calculating positioning error is:

[0022] In the formula, The calculated value for cable defects. This represents the actual value of the cable defect. The total length of the cable to be tested is given.

[0023] Furthermore, it also includes a noise immunity performance evaluation step: Transform the logarithmic form of the local defect diagnosis curve into a linear form. The peak-to-peak value, mean, maximum deviation, variance, and standard deviation of the amplitude signal in the non-defect area are calculated to quantify the amplitude fluctuation level in the non-defect area. The calculation formula is as follows:

[0024]

[0025]

[0026]

[0027] In the formula, , , , , , These represent the extracted amplitude signals. Peak-to-peak value, mean, maximum deviation, variance, and signal length, th indivual value.

[0028] The present invention also provides a cable defect location system that integrates reflection coefficient and impedance spectrum, comprising: The spectrum data acquisition module is used to acquire the reflection coefficient spectrum data and impedance spectrum data of the cable head end, and to perform cable traveling wave analysis to derive the mathematical expressions for the reflection coefficient spectrum and impedance spectrum. The spectrum fusion diagnostic module is used to extract the imaginary part information of the reflection coefficient spectrum and the amplitude information of the impedance spectrum, and obtain fused spectrum data through fusion processing; The diagnostic function construction module is used to perform localization processing on the reflection coefficient spectrum, impedance spectrum and fused spectrum data based on windowed Fourier transform, and construct a local defect diagnostic function. The defect analysis output module is used to analyze the diagnostic curves corresponding to the local defect diagnosis function to determine the location and severity of local defects in the cable.

[0029] The present invention also provides a processing device, including at least one processor and at least one memory communicatively connected to the processor, wherein: the memory stores program instructions executable by the processor, and the processor can execute the above-described method steps by calling the program instructions.

[0030] The present invention also provides a computer-readable storage medium storing computer instructions that cause the computer to perform the above-described method steps.

[0031] The advantages of this invention are: This invention derives formulas for cable reflection coefficient spectrum and impedance spectrum, analyzes the dimensional relationship between the two spectra, and multiplies the imaginary part of the reflection coefficient spectrum as a coefficient with the amplitude of the impedance spectrum to achieve fusion. By comparing the differences between the fused spectrum and the single-spectrum diagnostic curve, the superiority of the fused spectrum localization method is demonstrated, overcoming the shortcomings of existing frequency domain detection methods in terms of poor localization effect and improving the accuracy of cable fault detection. Compared with broadband impedance spectrum localization methods, this invention has a higher localization amplitude for local defects such as local damage and thermal aging, and can control the localization error within 0.3%. Compared with frequency domain reflection coefficient spectrum localization methods, this invention has stronger noise resistance, reducing fluctuations at non-defect locations by approximately 47% to 73% and standard deviation by more than 50%, significantly reducing the misjudgment rate of local defects in cables. Furthermore, this method is applicable to various cable types such as high-voltage cables and coaxial cables, has a clear process, is easy to integrate into existing testing equipment, and has outstanding engineering practicality. Attached Figure Description

[0032] Figure 1 This is a flowchart of a cable defect location method that integrates reflection coefficient and impedance spectrum according to Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the test platform according to Embodiment 1 of the present invention; Figure 3 The cable diagnostic curves are shown in three methods for applying Embodiment 1 of the present invention to power cables. Figure 4The present invention is applied to the cable diagnostic curve of a power cable under noise interference in Embodiment 1. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1 like Figure 1 As shown, a cable defect location method that integrates reflection coefficient and impedance spectrum includes: S1. Obtain the reflection coefficient spectrum data and impedance spectrum data of the cable head end, and perform cable traveling wave analysis to derive the mathematical expressions for the reflection coefficient spectrum and impedance spectrum.

[0035] Specifically, cable traveling wave analysis: Before analyzing the reflection coefficient spectrum and impedance spectrum at the cable's beginning, it is necessary to analyze the propagation law of the cable traveling wave. On the one hand, when the traveling wave propagates in the cable, it will be reflected at the impedance mismatch (local defect), affecting the mathematical formulas of the reflection coefficient spectrum and impedance spectrum. On the other hand, before obtaining the expressions for the reflection coefficient spectrum and impedance spectrum at the beginning, there is an inherent connection between the two, which is related to the propagation law of the traveling wave. The traveling wave analysis process is as follows: Based on transmission line theory, the load point at the cable tail end is considered as... The origin of the voltage vector points positively towards the cable end. Voltage and current at any point on the cable contain both incident and reflected waves, which propagate in opposite directions: the incident wave travels positively towards the load, and the reflected wave travels negatively towards the power source. Therefore, the voltage vector... With current vector The expression is:

[0036] In the formula, , These represent the cable traveling wave propagation constant and characteristic impedance, respectively. , These represent the incident voltage and the reflected voltage, respectively.

[0037] Voltage vector With current vector The ratio is the input impedance at the distance from the origin. :

[0038] In the formula, This is the reflection coefficient at the cable end, which is set to 1 when the cable end is open-circuited.

[0039] when hour, The total length of the cable, and the input impedance spectrum of the intact cable head. :

[0040] On a transmission line, the degree of reflection and refraction of a signal when it encounters an impedance mismatch during transmission is represented by the cable reflection coefficient, which is the ratio of the distance between the reflected voltage (current) wave and the incident voltage (current) wave from the origin. The reflection coefficient at that location is for:

[0041] when At that time, the reflection coefficient of the intact cable head end :

[0042] S2. Extract the imaginary part information of the reflection coefficient spectrum and the amplitude information of the impedance spectrum, and obtain fused spectrum data through fusion processing.

[0043] Specifically, the fusion analysis of the reflection coefficient spectrum and impedance spectrum at the cable head end includes the following steps: Analysis of the two spectrum fusion principles: Using Euler's formula to analyze the input impedance spectrum at the beginning of the cable and the reflection coefficient at the cable end Decompose:

[0044]

[0045] In the formula, , These are the attenuation coefficient, which characterizes the amplitude decay of the traveling wave, and the phase coefficient, which characterizes the phase change of the traveling wave, respectively.

[0046] Depend on Therefore, the frequency Treating it as the independent variable, the equivalent frequency is... When the cable is When a defect occurs, the spectral function will produce an equivalent frequency. Therefore, after estimating the frequency values ​​of the trigonometric functions, it is possible to... Determine the location of the defect.

[0047] Both single reflection coefficient spectrum and impedance spectrum have advantages in locating cable faults. To combine the advantages of the two spectra, Euler's formula is used to analyze the input impedance spectrum at the cable head. and the reflection coefficient at the cable end The data is decomposed, and the amplitude values ​​commonly used for positioning are extracted from the reflection coefficient spectrum of the cable head end. Phase , real part and the virtual part The amplitude commonly used for positioning in the input impedance spectrum Phase , real part and the virtual part The functional expressions for the four spectrums are shown in Table 1, with the cable end open-circuited.

[0048] Table 1 Summary of expressions for the two types of spectra

[0049] The obtained spectra are processed using a Fast Fourier Transform algorithm to simulate the location results of the reflection coefficient spectrum and the input impedance spectrum, taking into account the real part, imaginary part, phase, and amplitude spectra. These results are shown in Tables 2 and 3. The simulated cable length is 100m, the defect location is between 49.8 and 50.0 meters, and the defect capacitance is 1.5C0.

[0050] Table 2 shows that all four spectral localization results of the impedance spectrum can locate defects at 50 meters. The imaginary part of the impedance spectrum has the highest localization amplitude (0.268), but distortion points appear at non-defect locations, affecting defect localization and identification. The real part and amplitude spectrum of the impedance spectrum show relatively small peak values ​​for defect localization, while the real part spectrum exhibits small distortion points at non-defect locations. Therefore, the amplitude and phase spectra without distortion points in the impedance spectrum are selected as one of the fusion objects.

[0051] Table 2. Results of impedance spectral localization for four different spectrum types.

[0052] Table 3 shows that the phase spectrum failed to locate the defect, while the other three spectral localization curves all achieved defect localization at 50 meters. Furthermore, the phase spectrum of the reflection coefficient spectrum exhibits significant distortion points at non-defect locations, affecting defect localization and identification. The real and imaginary parts of the reflection coefficient spectrum have the highest localization amplitudes, both at 0.26, while the amplitude spectrum's localization amplitude is much smaller than the other three. Therefore, the imaginary and real parts of the reflection coefficient spectrum provide better localization results and can be used as one of the fusion methods.

[0053] Table 3. Results of four spectral localization methods for the reflection coefficient spectrum.

[0054] According to the convolution theorem, the imaginary or real part of the reflection coefficient spectrum, which provides better positioning, is multiplied and fused with the phase or amplitude of the impedance spectrum. This results in a time-domain convolution operation between the two spectra, leading to coherent enhancement of the defect pulses in both spectra, amplifying the defect information and thus achieving better positioning. The formulas for the fused impedance phase-reflection real part and impedance phase-reflection imaginary part are... , This will lead to the frequency When taken as the independent variable, the equivalent frequency of the Fourier transform is determined by... Become When impedance mismatch (defect) occurs in a cable, two distortion points appear. The main difference between the fusion formulas for the imaginary part of the reflection and the impedance amplitude, and the real part of the reflection and the impedance amplitude, lies in the different trigonometric functions. Simplifying these two fused spectra, we can obtain similar results. and The former has a larger value, which is more advantageous when identifying defect pulses through time-frequency domain conversion. The corresponding simulation results are shown in Table 4 for the localization results of different fusion spectrum methods. Two spectra with better localization effects were then selected for fusion: the imaginary part spectrum of the reflection coefficient spectrum and the amplitude spectrum of the impedance spectrum.

[0055] As shown in Table 4, the defect localization pulse at 50 meters is very small in phase with the impedance, and distortion points appear at 25 meters and 75 meters. This is consistent with the presence of [something] in the fused formula. , The difference is related to the double-angle formula. Both the real and imaginary parts of the reflection, along with the impedance amplitude, can achieve defect location at 50 meters without any distortion. However, the defect location pulse amplitude of the reflection imaginary part minus the impedance amplitude (0.289) is greater than that of the reflection real part minus the impedance amplitude (0.138). Therefore, the superiority of the reflection imaginary part minus impedance amplitude fusion method in this invention can be demonstrated.

[0056] Table 4 Localization results of different fusion spectrum methods

[0057] Pick Amplitude:

[0058] Pick Virtual part:

[0059] The fusion function is denoted as The calculation formula is as follows:

[0060] Trigonometric functions included in the formula and characteristic impedance It is a key parameter for achieving precise positioning and improving noise immunity by fusing spectrum.

[0061] S3. Based on the windowed Fourier transform, the reflection coefficient spectrum, impedance spectrum and fused spectrum data are respectively processed to locate the defect and construct a local defect diagnosis function.

[0062] Specifically, local defect diagnosis function The location of the individual reflection coefficient spectrum, impedance spectrum, and fused spectrum is achieved through windowed Fourier transform. The diagnostic function calculation formula is as follows:

[0063] In the formula, and These are the lower and upper limits of the measurement frequency range, respectively. It can measure the reflection coefficient spectrum, impedance spectrum, or fused spectrum of the cable head end. For the frequency domain form of the window function, the Chebyshev window is selected.

[0064] S4. Analyze the diagnostic curves corresponding to the local defect diagnostic function to determine the location and severity of local defects in the cable.

[0065] Comparative analysis of diagnostic curves between fused spectrum and single spectrum: The different trigonometric periodic functions included in the expressions for the reflection coefficient spectrum and impedance spectrum at the cable's head end can lead to differences in the local defect diagnosis function, resulting in varying local defect location effectiveness. Each spectrum has its own advantages and disadvantages in local defect location. A local defect diagnosis function that integrates spectral data retains the advantages of both spectra, achieving better location results. This is achieved by analyzing the width of the location pulse. and defect location error This demonstrates the reliability of the fusion spectrum method.

[0066] The formula for calculating positioning error is:

[0067] In the formula, The calculated value for cable defects. This represents the actual value of the cable defect. The total length of the cable to be tested is given.

[0068] To analyze the amplitude fluctuations at non-defect locations, the logarithmic form of the positioning curve is transformed into a linear form, and... By calculating a segment of signal at a non-defect location. The peak-to-peak value, maximum deviation, variance, and standard deviation of the fluctuation are used to quantify the amplitude fluctuation at non-defect locations.

[0069]

[0070]

[0071]

[0072]

[0073] In the formula, , , , , , These represent the extracted amplitude signals. Peak-to-peak value, mean, maximum deviation, variance, and signal length, th indivual value.

[0074] The reflection coefficient spectrum and impedance spectrum of the cable head end were measured as follows: Based on the principle of fusing the frequency domain reflection coefficient spectrum and impedance spectrum, a sinusoidal sweep signal is injected into the cable head end, and the reflected signal is received to obtain the imaginary part of the reflection coefficient spectrum and the amplitude data of the impedance spectrum at the cable head end. The obtained reflection coefficient spectrum and impedance spectrum data are input and stored in the computer, and then the two spectra are fused to obtain the fused spectrum. Finally, the reflection coefficient spectrum, impedance spectrum, and fused spectrum are successively substituted into the local defect diagnosis function to obtain the cable defect diagnosis curves for each spectrum. A schematic diagram of the test platform is shown below. Figure 2 As shown, the swept frequency signal is generated by a signal generator and connected to a computer (PC) via a double-headed arrow to enable bidirectional data and command transmission. The other end is connected to the cable head via a cable for transmitting incident signals and receiving reflected signals. The swept frequency sinusoidal signal has a frequency band of 100kHz to 200MHz.

[0075] The test used YJV-8.7 / 15kV 1*120mm type wire. 2 The parameters of the power cable are shown in Table 5. Among them, defect 1 of the power cable is localized thermal aging of the cable insulation, and defect 2 is localized damage to the copper shield of the cable, but the electrical connection is still maintained.

[0076] Table 5 Test Cable Parameters

[0077] Substituting the reflection coefficient spectrum, impedance spectrum, and fused spectrum of the power cable's head end into the local defect diagnosis function, three local defect diagnosis curves are obtained. The location curves represented by their logarithmic amplitudes are shown below. Figure 3 As shown.

[0078] Cut Figure 3The positioning curve segment at 60-80 meters was analyzed, and the amplitude fluctuation of the positioning curve at non-defect locations was examined. The calculation results of each parameter are shown in Table 6. Figure 3 As can be seen, the peak-to-peak value of the fused spectrum at the non-defect location of the power cable is 0.095, which is 47.1% lower than that of the single reflection coefficient spectrum and 72.6% lower than that of the single impedance spectrum. Maximum deviation, variance, and standard deviation can all be used to describe the degree to which the waveform amplitude deviates from the mean, and their magnitudes can also characterize the oscillation of the waveform at the non-defect location. Table 6 shows that the maximum deviation, variance, and standard deviation of the fused spectrum are the smallest compared to the single reflection coefficient spectrum and impedance spectrum. Taking the standard deviation as an example, the standard deviation of the fused spectrum at the non-defect location is 0.025, which is 49.1% and 70.6% lower than that of the single reflection coefficient spectrum and impedance spectrum, respectively. This indicates that the fused spectrum method can significantly reduce the amplitude fluctuation of the location curve at the non-defect location and reduce the misjudgment rate of cable defect location.

[0079] Table 6. Calculation results of relevant parameters for amplitude fluctuation of the location curve at non-defect locations.

[0080] Further comparative analysis of the differences in pulse correlation parameters at the defect location under the three methods is shown in Table 7. It can be seen that, taking defect 1 as an example, the pulse width at the defect location under the fused spectrum is smaller than that of the reflection coefficient spectrum and the impedance spectrum, and the positioning error is less than 0.3%, which is between the reflection coefficient spectrum and the impedance spectrum. This indicates that the fused frequency domain can also achieve excellent local defect positioning effect in cables.

[0081] Table 7 Calculation results of pulse correlation parameters for local defect location.

[0082] When measuring cable spectrum in the field, interference from the surrounding environment is unavoidable, introducing noise into the measuring instrument. To further compare the impact of noise on the cable defect location effect of the three methods, Gaussian white noise with an amplitude of 0.05 was added to the measured spectrum signal. The cable diagnostic curves for the three methods are shown below. Figure 4 As shown in Table 8, the signal amplitude fluctuation parameters at non-defect locations are as follows.

[0083] contrast Figure 3 and Figure 4As can be seen, all three methods can successfully locate local defects after adding noise interference, but the amplitude fluctuations at non-defect locations differ significantly. Table 8 shows that after adding noise interference, the peak-to-peak value, maximum deviation, variance, and standard deviation of the fused spectrum remain the smallest. Compared to the single reflection coefficient spectrum and impedance spectrum, the peak-to-peak value of the fused spectrum decreased by 46.9% and 37.7%, respectively; the standard deviation of the fused spectrum decreased by 53.3% and 55.6%, respectively. This demonstrates that even under complex noise interference, the fused spectrum method can significantly reduce the amplitude fluctuations at non-defect locations on the localization curve, exhibiting the best performance among the three methods.

[0084] Table 8. Calculation results of relevant parameters for amplitude fluctuation of the location curve at non-defect locations under noise interference.

[0085] In summary, the fused spectrum method demonstrates superior localization performance at coaxial cable defects. Compared to single reflection coefficient and impedance spectra, the pulse width at the defect location using the fused spectrum is smaller, resulting in a localization error of less than 0.3%, falling between the reflection coefficient and impedance spectra. At non-defect locations, the fused spectrum method exhibits stronger noise immunity than the single reflection coefficient spectrum. After adding noise interference, the peak-to-peak value and standard deviation of the amplitude fluctuations in the fused spectrum are reduced by 46.9% and 53.3%, respectively.

[0086] Example 2 Based on Embodiment 1, Embodiment 2 of the present invention further provides a cable defect location system that integrates reflection coefficient and impedance spectrum, comprising: The spectrum data acquisition module is used to acquire the reflection coefficient spectrum data and impedance spectrum data of the cable head end, and to perform cable traveling wave analysis to derive the mathematical expressions for the reflection coefficient spectrum and impedance spectrum.

[0087] Specifically, a cable traveling wave propagation model is established, taking the load at the cable tail end as... The origin of the voltage vector points positively towards the cable's beginning; the voltage and current at any point on the cable contain both incident and reflected waves, therefore the voltage vector... With current vector The expression is:

[0088] In the formula, , These represent the cable traveling wave propagation constant and characteristic impedance, respectively. , These represent the incident voltage and the reflected voltage, respectively.

[0089] According to the voltage vector With current vector The ratio is used to calculate the input impedance at a distance x from the origin. :

[0090] In the formula, This is the reflection coefficient at the end of the cable.

[0091] when hour, The total length of the cable, and the input impedance spectrum of the intact cable head. :

[0092] The intensity of reflection and refraction when a signal encounters impedance mismatch during transmission on a transmission line is defined as the ratio of the reflected voltage wave to the incident voltage wave or the ratio of the reflected current wave to the incident current wave, and the reflection coefficient at a distance from the origin. The calculation formula is:

[0093] when At that time, the reflection coefficient of the intact cable head end :

[0094] In the formula, This is the end load.

[0095] The spectrum fusion diagnostic module is used to extract the imaginary part information of the reflection coefficient spectrum and the amplitude information of the impedance spectrum, and obtain fused spectrum data through fusion processing.

[0096] Specifically, the Euler formula is used to analyze the input impedance spectrum at the cable's beginning. and the reflection coefficient at the cable end Decompose:

[0097]

[0098] In the formula, , These are the attenuation coefficient, which characterizes the amplitude decay of the traveling wave, and the phase coefficient, which characterizes the phase change of the traveling wave, respectively.

[0099] Pick Amplitude:

[0100] Pick Virtual part:

[0101] fusion function The calculation formula is: .

[0102] The diagnostic function construction module is used to locate and process the reflection coefficient spectrum, impedance spectrum and fused spectrum data based on windowed Fourier transform, and construct local defect diagnostic functions.

[0103] Specifically, the formula for calculating the local defect diagnosis function is as follows:

[0104] In the formula, and These are the lower and upper limits of the measurement frequency range, respectively. It can measure the reflection coefficient spectrum, impedance spectrum, or fused spectrum data of the cable head end. This is the frequency domain form of the window function. For frequency, This is the distance from the defect to the beginning of the cable. This represents the propagation speed of the traveling wave.

[0105] The defect analysis output module is used to analyze the diagnostic curves corresponding to the local defect diagnosis function to determine the location and severity of local defects in the cable.

[0106] Specifically, the formula for calculating positioning error is:

[0107] In the formula, The calculated value for cable defects. This represents the actual value of the cable defect. The total length of the cable to be tested is given.

[0108] The noise immunity assessment unit is used to convert the logarithmic form of the local defect diagnosis curve into a linear form. The peak-to-peak value, mean, maximum deviation, variance, and standard deviation of the amplitude signal in the non-defect area are calculated to quantify the amplitude fluctuation level in the non-defect area.

[0109] The calculation formula is as follows:

[0110]

[0111]

[0112]

[0113] In the formula, , , , , , These represent the extracted amplitude signals. Peak-to-peak value, mean, maximum deviation, variance, and signal length, th indivual value.

[0114] Example 3 Based on Embodiment 1, Embodiment 3 of the present invention also provides a processing device, including at least one processor and at least one memory communicatively connected to the processor, wherein: the memory stores program instructions executable by the processor, and the processor can execute the method steps of Embodiment 1 by calling the program instructions.

[0115] Example 4 Based on Embodiment 1, Embodiment 4 of the present invention also provides a computer-readable storage medium storing computer instructions that cause the computer to perform the steps of the method described in Embodiment 1.

[0116] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for locating cable defects by integrating reflection coefficient and impedance spectrum, characterized in that, include: S1. Obtain the reflection coefficient spectrum data and impedance spectrum data of the cable head end, and perform cable traveling wave analysis to derive the mathematical expressions for the reflection coefficient spectrum and impedance spectrum. S2. Extract the imaginary part information of the reflection coefficient spectrum and the amplitude information of the impedance spectrum, and obtain fused spectrum data through fusion processing; S3. Based on the windowed Fourier transform, the reflection coefficient spectrum, impedance spectrum and fused spectrum data are respectively processed to locate the defect and construct a local defect diagnosis function. S4. Analyze the diagnostic curve corresponding to the local defect diagnostic function to determine the location and severity of the local defects in the cable.

2. The cable defect location method based on the fusion of reflection coefficient and impedance spectrum according to claim 1, characterized in that, The impedance spectrum in step S1 is constructed in the following manner: Establish a cable traveling wave propagation model, taking the load at the cable tail end as... The origin of the voltage vector points positively towards the cable's beginning; the voltage and current at any point on the cable contain both incident and reflected waves, therefore the voltage vector... With current vector The expression is: In the formula, , These represent the cable traveling wave propagation constant and characteristic impedance, respectively. , These represent the incident voltage and the reflected voltage, respectively. According to the voltage vector With current vector The ratio is used to calculate the input impedance at a distance x from the origin. : In the formula, The reflection coefficient at the cable end; when hour, The total length of the cable, and the input impedance spectrum of the intact cable head. : 。 3. The cable defect location method based on the fusion of reflection coefficient and impedance spectrum according to claim 1, characterized in that, The reflection coefficient spectrum in step S1 is constructed in the following way: The intensity of reflection and refraction when a signal encounters impedance mismatch during transmission on a transmission line is defined as the ratio of the reflected voltage wave to the incident voltage wave or the ratio of the reflected current wave to the incident current wave, and the reflection coefficient at a distance from the origin. The calculation formula is: when At that time, the reflection coefficient of the intact cable head end : In the formula, This is the end load.

4. The cable defect location method based on the fusion of reflection coefficient and impedance spectrum according to claim 1, characterized in that, The fused spectrum data includes: Using Euler's formula to analyze the input impedance spectrum at the beginning of the cable and the reflection coefficient at the cable end Decompose: In the formula, , These are the attenuation coefficient, which characterizes the amplitude decay of the traveling wave, and the phase coefficient, which characterizes the phase change of the traveling wave; Pick Amplitude: Pick Virtual part: Fusion spectrum data The calculation formula is: 。 5. The cable defect location method based on the fusion of reflection coefficient and impedance spectrum according to claim 1, characterized in that, The formula for calculating the local defect diagnosis function is as follows: In the formula, and These are the lower and upper limits of the measurement frequency range, respectively. It can measure the reflection coefficient spectrum, impedance spectrum, or fused spectrum data of the cable head end. This is the frequency domain form of the window function. For frequency, This is the distance from the defect to the beginning of the cable. This represents the propagation speed of the traveling wave.

6. The cable defect location method based on the fusion of reflection coefficient and impedance spectrum according to claim 1, characterized in that, It also includes a positioning error assessment step: The formula for calculating positioning error is: In the formula, The calculated value for cable defects. This represents the actual value of the cable defect. The total length of the cable to be tested is given.

7. The cable defect location method based on the fusion of reflection coefficient and impedance spectrum according to claim 1, characterized in that, It also includes a noise immunity assessment step: Transform the logarithmic form of the local defect diagnosis curve into a linear form. The peak-to-peak value, mean, maximum deviation, variance, and standard deviation of the amplitude signal in the non-defect area are calculated to quantify the amplitude fluctuation level in the non-defect area. The calculation formula is as follows: In the formula, , , , , , These represent the extracted amplitude signals. Peak-to-peak value, mean, maximum deviation, variance, and signal length, th indivual value.

8. A cable defect location system integrating reflection coefficient and impedance spectrum, characterized in that, include: The spectrum data acquisition module is used to acquire the reflection coefficient spectrum data and impedance spectrum data of the cable head end, and to perform cable traveling wave analysis to derive the mathematical expressions for the reflection coefficient spectrum and impedance spectrum. The spectrum fusion diagnostic module is used to extract the imaginary part information of the reflection coefficient spectrum and the amplitude information of the impedance spectrum, and obtain fused spectrum data through fusion processing; The diagnostic function construction module is used to perform localization processing on the reflection coefficient spectrum, impedance spectrum and fused spectrum data based on windowed Fourier transform, and construct a local defect diagnostic function. The defect analysis output module is used to analyze the diagnostic curves corresponding to the local defect diagnosis function to determine the location and severity of local defects in the cable.

9. A processing device, characterized in that, The method includes at least one processor and at least one memory communicatively connected to the processor, wherein the memory stores program instructions executable by the processor, and the processor can execute the method as described in any one of claims 1 to 7 by invoking the program instructions.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions that cause the computer to perform the method as described in any one of claims 1 to 7.

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