Cable Fault Location Method and Device Based on Broadband Impedance Spectrum Peak Attenuation Compensation

Abstract

This invention relates to a cable fault location method and apparatus based on broadband impedance spectrum peak attenuation compensation. The method includes: acquiring a broadband impedance spectrum signal from the faulty cable; performing a discrete Fourier transform on the broadband impedance spectrum signal, and then normalizing it using the maximum reflection peak as the standard to obtain a location amplitude spectrum containing defect characteristics; processing the location amplitude spectrum using wavelet filtering, determining the coordinates of the fundamental frequency, second harmonic, and third harmonic of the faulty cable in the filtered location amplitude spectrum, and fitting it to obtain a compensation curve; performing difference processing on the location amplitude spectrum and the compensation curve to obtain a compensated location amplitude spectrum; and determining the fault location of the cable based on the peak characteristics of the compensated location amplitude spectrum. Compared with the prior art, this invention can locate various cable faults, has higher resolution, fewer interference peaks in the location spectrum, and low data redundancy.

Description

Technical Field

[0001] This invention relates to the field of cable fault location technology, and in particular to a cable fault location method and apparatus based on broadband impedance spectrum peak attenuation compensation. Background Technology

[0002] In recent years, rapid urbanization has led to a severe shortage of urban land, while the safety and environmental concerns surrounding overhead lines have spurred the widespread adoption of power cables. Compared to overhead lines, cables offer advantages such as smaller footprint, higher power supply reliability, and larger transmission capacity. However, with the increasing number of cables laid and their service life, cable failures and aging have become key concerns. In actual operation, thermal effects, moisture, outer sheath damage, and manufacturing defects can all cause cable aging, leading to cable failures. Since most cables are laid underground, the inability to quickly and accurately locate the fault location increases repair time and costs, and can even cause power outages, resulting in significant economic losses. Therefore, monitoring and diagnosing the operating status of cables to ensure their safe and stable operation is extremely important.

[0003] The commonly used defect location method is partial discharge (PD) method; however, the complex electromagnetic environment in the field can easily affect its detection sensitivity. Time-domain reflectometry (TDR) is one of the most widely used methods for locating local defects in cables. It injects a narrow pulse signal, which attenuates rapidly during propagation in the time domain, resulting in poor detection of weak defects. Frequency-domain reflectometry (FDR), due to its higher sensitivity, has become an effective method for cable diagnosis and fault location. FDR injects a swept-frequency signal into the cable under test and analyzes the characteristics of the reflected signal generated at the fault point to detect and locate cable defects. FDR has a significant advantage over traditional TDR in detecting weak cable defects.

[0004] Wideband impedance spectroscopy (WIS) is one of the non-destructive testing (FDR) methods for cable defect detection. Based on transmission line theory, WIS calculates and analyzes cable impedance (amplitude and phase) as a function of a signal applied across a wide frequency band. By monitoring and locating changes in cable impedance, it enables condition monitoring and fault location of the cable.

[0005] The choice of time-frequency conversion method in FDR is the key to achieving high-precision cable positioning. Existing research has a variety of methods to achieve the conversion from the frequency domain to the time domain, such as inverse Fourier transform and integral transform using different integral kernel functions. Although traditional FDR can achieve cable fault location, the fault location function has low resolution and high data redundancy, which can easily lead to misjudgment or omission of fault points. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the prior art by providing a cable fault location method and device based on broadband impedance spectrum peak attenuation compensation, thereby improving the accuracy and sensitivity of the FDR method in identifying local cable faults and facilitating the accurate identification of weak fault locations.

[0007] The objective of this invention can be achieved through the following technical solutions: A cable fault location method based on broadband impedance spectrum peak attenuation compensation includes the following steps: Acquire broadband impedance spectrum signals from faulty cables; The broadband impedance spectrum signal is subjected to discrete Fourier transform, and then normalized using the maximum reflection peak value as the standard to obtain a location amplitude spectrum containing defect characteristics. Wavelet filtering is used to process the location amplitude spectrum. The coordinates of the fundamental frequency, second harmonic, and third harmonic of the faulty cable are determined from the filtered location amplitude spectrum, and a compensation curve is obtained by fitting. The positioning amplitude spectrum and the compensation curve are subjected to difference processing to obtain the positioning amplitude spectrum after attenuation compensation; The location of the cable fault is determined based on the peak value of the compensated location amplitude spectrum.

[0008] Furthermore, the process of setting the horizontal axis of the positioning amplitude spectrum is as follows: the fault distance is converted into a time dimension by the wave velocity factor to obtain the horizontal axis in the time domain; the vertical axis of the positioning amplitude spectrum is the amplitude of the broadband impedance spectrum.

[0009] Furthermore, the fundamental frequency of the faulty cable is determined from the filtered amplitude spectrum, and the corresponding calculation expression is: In the formula, The fundamental frequency of the faulty cable is the fundamental frequency of a pseudo-periodic function generated by the reflection of a broadband signal wave at a distance d from the end of the cable. The relative phase velocity of the electrical signal in the cable. The speed of light in a vacuum.

[0010] Furthermore, relative phase velocity The calculation expression is: In the formula, For cable length, The k-th resonant peak frequency is It is the (k+1)th resonant peak frequency.

[0011] Furthermore, the resonant peak frequency and Obtained from the filtered location amplitude spectrum.

[0012] Furthermore, by finding the second and third harmonic positions in the filtered amplitude spectrum, the coordinates of the second and third harmonics of the faulty cable can be determined.

[0013] Furthermore, the coordinates of the fundamental frequency, second harmonic, and third harmonic of the faulty cable are fitted using the least squares method to obtain the compensation curve.

[0014] Furthermore, the compensation curve is subtracted from the filtered positioning amplitude spectrum to obtain the attenuation-compensated positioning amplitude spectrum.

[0015] Furthermore, the compensated positioning amplitude spectrum is displayed using data visualization technology to assist users in determining the location of cable faults based on the peak values ​​of the spectrum.

[0016] The present invention also provides a cable fault location device based on broadband impedance spectrum peak attenuation compensation, including a memory and a processor. The memory stores a computer program, and the processor calls the computer program to execute the steps of the method described above.

[0017] Compared with the prior art, the present invention has the following advantages: (1) Compared with the traditional broadband impedance spectrum localization method, this invention utilizes the peak attenuation compensation method. By subtracting the localization amplitude spectrum containing defect features from the corresponding compensation curve, the attenuation-compensated localization amplitude spectrum is obtained. The compensation curve is mainly based on the coordinate points of the fundamental frequency, second harmonic, and third harmonic of the cable under test, which can accurately bind the physical / electrical laws of the cable itself and strengthen important peak features. The resulting attenuation-compensated localization amplitude spectrum can locate various cable faults. This method has higher resolution and fewer interference peaks in the localization spectrum, resulting in low data redundancy. In addition, this invention also uses peak detection and wavelet filtering to denoise the transformation results, which effectively eliminates noise in the reflection coefficient spectrum and preserves the characteristics of the original signal as much as possible, thereby significantly improving the fault localization effect.

[0018] (2) The present invention uses wavelet filtering to process the fault location spectrum. Through wavelet transform, the location of the fault peak can be determined more clearly, and some noise interference is eliminated, but the waveform at the fault location is not enhanced.

[0019] (3) This invention combines the coordinates of the fundamental frequency, second harmonic and third harmonic of the cable under test to fit and obtain a compensation curve to perform difference processing on the positioning spectrum. The fundamental frequency corresponds to the basic oscillation mode of the cable and directly reflects the basic impedance characteristics of the conductor and insulation. The second and third harmonics are strongly correlated with the cable insulation aging, local defects and other "ideal states". The compensation curve obtained through the above feature points can accurately bind the compensation process to the physical / electrical laws of the cable itself, avoid irrelevant signals from interfering with the compensation logic, and ensure that the compensation direction is highly consistent with the repair of the real impedance characteristics. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating a cable fault location method based on broadband impedance spectrum peak attenuation compensation provided in an embodiment of the present invention. Figure 2 This invention provides a schematic diagram of the positions of two adjacent resonant frequencies in a broadband impedance spectrum. The horizontal axis represents frequency, and the vertical axis represents the magnitude of impedance, with the unit being ohms. Detailed Implementation

[0021] 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 with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0022] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0023] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0024] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of this invention is usually placed during use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0025] It should be noted that the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0026] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," not that the structure must be completely horizontal, but can be slightly tilted.

[0027] Example 1 The theoretical analysis process of this improved scheme will be introduced below: FDR (Fault-Redirect Line) is based on transmission line theory. A transmission line is part of a circuit, serving as a connection between a generator and a load. The performance of a transmission line depends on the ratio of its length to the wavelength λ of the electrical signal entering it. Wavelength is defined as: (1) Where v is the velocity of the electrical signal in the conductor (also known as the phase velocity), and f is the frequency of the signal.

[0028] When the transmission line length is much shorter than the wavelength, such as when the cable is short (a few meters) and the signal frequency is low (a few kilohertz), the line has no effect on the behavior of the circuit. Therefore, from the power supply side, the circuit impedance (Z) is always equal to the load impedance.

[0029] However, if the line length is greater than the signal wavelength (l≥λ), the line characteristics play an important role, and the circuit impedance seen from the power supply side is mismatched with the load, except in some very special cases.

[0030] The voltage V and current I on the cable are determined by the following differential equations, which are called the telegraph equations: (2) (3) Where ω is the signal angular frequency, R is the conductor resistance, L is the inductance, C is the capacitance, and G is the insulation conductivity, all of which are related to the cable length unit.

[0031] When a high-frequency signal passes through a cable, these four parameters can fully describe the cable's characteristics. In transmission line theory, the behavior of a transmission line is usually described as a function of two complex numbers.

[0032] The first is the propagation function: (4) Normally written as: (5) In the formula, the real part α is the line attenuation constant, and the imaginary part β is the propagation constant, which is related to the phase velocity v, angular frequency ω, and wavelength λ. (6) The second parameter is the characteristic impedance: (7) Using equations (4) and (7), solving differential equations (2) and (3) yields the line impedance of the cable at a distance d from the end: (8) in For generalized reflection coefficient: (9) Load reflection coefficient: (10) ZL is the load impedance connected at the end of the line.

[0033] It is easy to see from equations (8), (9), and (10) that when the load matches the characteristic impedance, Γ_d = Γ_L = 0, and then Zd = Z0 = ZL for any length and frequency. In all other cases, the line impedance is a complex variable controlled by equation (8).

[0034] Existing methods based on transmission line theory (time-domain reflectometry) attempt to locate local cable faults by measuring V (Equation (2)) as a function of time and assessing the time delay from the incident wave to the reflected wave. Line attenuation and ambient noise in real-world environments limit their sensitivity, preventing the possibility of detecting attenuation at an early stage, especially for cables exceeding several kilometers in length. Furthermore, a global cable condition assessment is not possible, which is crucial for estimating the remaining cable life in harsh environments.

[0035] like Figure 1 As shown in the figure, this embodiment provides a cable fault location method based on broadband impedance spectrum peak attenuation compensation. Compared with the traditional broadband impedance spectrum location method, the peak attenuation compensation method can locate various cable faults. This method has higher resolution, fewer interference peaks in the location spectrum, and low data redundancy.

[0036] Specifically, the following steps are included: S1: Acquire broadband impedance spectrum signal from the faulty cable; The input impedance amplitude and phase spectrum Z(f) at the beginning of the cable can be measured using a vector network analyzer. S2: Perform Discrete Fourier Transform (DFT) on the broadband impedance spectrum signal, and then normalize it using the maximum reflection peak as the standard to obtain the location amplitude spectrum containing defect characteristics. Performing a Directed Fourier Transform (DFT) on the imaginary part of the amplitude spectrum reveals numerous impedance abrupt changes. This is due to multiple reflections and refractions of the signal within the cable. The maximum reflection peak represents the cable's end location. Normalizing the amplitude spectrum using the cable end reflection peak as a standard yields a location amplitude spectrum incorporating defect characteristics. The location amplitude spectrum obtained after DFT transformation of the cable impedance spectrum gradually increases in amplitude from the beginning to the end, reaching a peak at the end. Small changes in cable distributed parameters caused by latent defects are often difficult to observe in the spectrum, potentially leading to misjudgments.

[0037] Preferably, the process of setting the horizontal coordinate of the location amplitude spectrum is as follows: the fault distance is converted into a time dimension by the wave velocity factor to obtain the horizontal coordinate in the time domain.

[0038] That is, the horizontal axis can be determined according to the set wave velocity factor. (0 < <1, generally between 0.4 and 0.7, which is related to material properties) is converted into distance, which is referred to here as time domain t'.

[0039] S3: Use wavelet filtering to process the location amplitude spectrum, determine the coordinates of the fundamental frequency, second harmonic and third harmonic of the faulty cable in the filtered location amplitude spectrum, and fit it to obtain the compensation curve. Wavelet transform can more clearly determine the location of the fault peak and eliminate some noise interference, but the waveform at the fault location is not enhanced.

[0040] The process of determining the coordinates of the fundamental frequency, second harmonic, and third harmonic of the faulty cable in the filtered amplitude spectrum is as follows: Calculate the frequency f' in the time domain t', where f' is the fundamental frequency of the pseudo-periodic function generated by the reflection of the broadband signal wave at a distance d from the end of the cable, and is calculated using the following formula: in, It is the speed of light in a vacuum. It is the relative phase velocity of the electrical signal in the cable; It can be calculated using the following formula: Where L represents the cable length. Represents the speed of light in a vacuum. The k-th resonant peak frequency. This refers to the (k+1)th resonant peak frequency. In a broadband impedance spectrum, two adjacent resonant frequencies are easily found, such as... Figure 2 As shown.

[0041] Frequency f' can be defined as the fundamental frequency, given the relative phase velocity. In the positioning spectrum, it is easy to find the t' domain point representing the end of the cable by using the local extreme value position.

[0042] Expand the scope of investigation and continue to search for the positions of 2 times the fundamental frequency and 3 times the fundamental frequency in the positioning spectrum, which represent the second and third harmonics of frequency f', respectively.

[0043] The fundamental frequency and its second and third harmonics can form three coordinate points on the positioning spectrum: (t1, P1), (t2, P2), and (t3, P3). Applying the least squares method to these three points yields the formula for the compensation line.

[0044] S4: Perform difference processing on the positioning amplitude spectrum and the compensation curve to obtain the compensated positioning amplitude spectrum; That is, the compensation curve is subtracted from the filtered positioning amplitude spectrum to obtain the compensated positioning amplitude spectrum. S5: Determine the fault location of the cable based on the peak value of the compensated location amplitude spectrum.

[0045] Optionally, the compensated location amplitude spectrum can be displayed using data visualization technology to help users determine the location of cable faults based on the peak values ​​of the spectrum.

[0046] That is, after the fault location spectrum is processed, the processing results are saved and output for further processing and display by external devices or computers. The results can be displayed through data visualization technology to help users determine the location of cable faults based on the peak values ​​of the spectrum.

[0047] Example 2 This embodiment provides a cable fault location device based on broadband impedance spectrum peak attenuation compensation, including a memory and a processor. The memory stores a computer program, and the processor calls the computer program to execute the steps of the cable fault location method based on broadband impedance spectrum peak attenuation compensation as described in Embodiment 1.

[0048] The computer program code used to implement the methods of the present invention can be written in any combination of one or more programming languages. This computer program code can be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the computer program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The computer program code can be executed entirely on the machine, partially on the machine, as a standalone software package partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0049] The preferred embodiments of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. A cable fault location method based on wideband impedance spectrum peak value attenuation compensation, characterized in that, Includes the following steps: Acquire broadband impedance spectrum signals from faulty cables; The broadband impedance spectrum signal is subjected to discrete Fourier transform, and then normalized using the maximum reflection peak value as the standard to obtain a location amplitude spectrum containing defect characteristics. Wavelet filtering is used to process the location amplitude spectrum. The coordinates of the fundamental frequency, second harmonic, and third harmonic of the faulty cable are determined from the filtered location amplitude spectrum, and a compensation curve is obtained by fitting. The positioning amplitude spectrum and the compensation curve are subjected to difference processing to obtain the positioning amplitude spectrum after attenuation compensation; The location of the cable fault is determined based on the peak value of the compensated location amplitude spectrum.

2. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 1, characterized in that, The process of setting the horizontal axis of the location amplitude spectrum is as follows: the fault distance is converted into a time dimension by the wave velocity factor to obtain the horizontal axis in the time domain; the vertical axis of the location amplitude spectrum is the amplitude of the broadband impedance spectrum.

3. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 1, characterized in that, The fundamental frequency of the faulty cable is determined from the filtered amplitude spectrum, and the corresponding calculation expression is: In the formula, The fundamental frequency of the faulty cable is the fundamental frequency of a pseudo-periodic function generated by the reflection of a broadband signal wave at a distance d from the end of the cable. The relative phase velocity of the electrical signal in the cable. The speed of light in a vacuum.

4. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 3, characterized in that, relative phase velocity The calculation expression is: In the formula, For cable length, The k-th resonant peak frequency is It is the (k+1)th resonant peak frequency.

5. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 4, characterized in that, resonant peak frequency and Obtained from the filtered location amplitude spectrum.

6. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 1, characterized in that, By finding the second and third harmonic positions in the filtered amplitude spectrum, the coordinates of the second and third harmonics of the faulty cable can be determined.

7. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 1, characterized in that, The least squares method was used to fit the coordinates of the fundamental frequency, second harmonic, and third harmonic of the faulty cable to obtain the compensation curve.

8. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 1, characterized in that, Subtract the compensation curve from the filtered positioning amplitude spectrum to obtain the attenuation-compensated positioning amplitude spectrum.

9. The cable fault location method based on broadband impedance spectrum peak attenuation compensation according to claim 1, characterized in that, The compensated location amplitude spectrum is displayed using data visualization technology to help users determine the location of cable faults based on the peak values ​​of the spectrum.

10. A cable fault location device based on broadband impedance spectrum peak attenuation compensation, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor calling the computer program to perform the steps of the method as described in any one of claims 1 to 9.

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