Method and system for locating defects in a cable based on improved z-transform broadband impedance spectroscopy

Abstract

The application discloses a wide-frequency impedance spectrum cable defect positioning method and system based on improved Z transform, and the method comprises the following steps: according to an equivalent distributed parameter circuit of a cable with defects, input impedance of each section of the cable is regarded as load impedance of a previous section, and the input impedance is deduced from the end of the cable to the front section by section, and finally, input wide-frequency impedance spectrum of the first end of the cable with defects is obtained; the input wide-frequency impedance spectrum of the first end of the cable with defects is subjected to improved Z transform considering spectrum leakage suppression, the input wide-frequency impedance spectrum of the first end of the cable with defects is converted from the frequency domain to the time domain, and cable defects are positioned through wave peak positioning in the time domain. In the wide-frequency impedance spectrum analysis, the traditional Z transform method is subjected to spectrum leakage suppression processing, and the accuracy of cable defect positioning can be significantly improved.

Description

Technical Field

[0001] This invention belongs to the field of cable defect location technology, and relates to a broadband impedance spectrum cable defect location method and system based on the improved chirp-z transform (ICZT). Background Technology

[0002] With the continuous development of power transmission and distribution lines and the increasing number of cables in operation, power outages caused by internal faults in cross-linked polyethylene (XLPE) cables are becoming increasingly common. Although XLPE cables can have a service life of up to 30 years under ideal conditions, they are susceptible to various factors in actual operation, such as harsh laying environments, external damage, corrosion of the protective layer, and cable quality problems, leading to abnormal local electrical parameters and defects. These defects gradually worsen under the influence of an electric field, causing faults such as open circuits, short circuits, and high-resistance or low-resistance grounding, shortening the cable's lifespan, and in severe cases, even causing large-scale power outages and significant economic losses.

[0003] In recent years, scholars at home and abroad have explored various methods for diagnosing cable faults, and quickly identifying defects and locating faults has become the focus of current research.

[0004] Currently, the traveling wave method is the most commonly used method for locating local defects in cables. Based on the different analysis domains, it can be divided into time-domain reflectometry (TDR) and frequency-domain reflectometry (FDR). TDR locates defects by calculating the time delay difference between the incident and reflected pulse signals. This method is simple to operate and has a certain degree of anti-interference capability. However, because the Gaussian pulse signal injected in TDR has few high-frequency components, and the signal undergoes severe attenuation and dispersion during propagation in the time domain, the sensitivity of defect location is relatively low. In contrast, FDR injects a swept-frequency signal containing a large number of high-frequency components at the cable end, resulting in extremely high accuracy in defect location and gradually becoming a research hotspot in recent years.

[0005] Existing FDR methods acquire broadband impedance spectra at the cable's origin and perform time-frequency domain transformation to achieve precise defect location. To convert frequency-domain information into time-domain information, Fast Fourier Transform (FFT) is typically used to analyze the acquired impedance spectrum data. However, while this method performs well in theoretical simulations, it still has limitations in practical engineering applications. Firstly, the FFT algorithm requires the number of data points in both the time and frequency domains to be consistent, and the converted data must be evenly distributed across either domain. Therefore, this method yields a large amount of useless redundant time-domain information. This redundant information is not only irrelevant to the cable defect location results but may also introduce interference peaks, affecting the judgment of defect location. Secondly, when the number of test points for the broadband impedance spectrum is relatively limited, the amount of time-domain data that can be acquired is correspondingly reduced due to the consistency requirement of the FFT algorithm. This not only reduces the resolution of the time-domain data curve but also further reduces the resolution of the defect location function, easily leading to the picket fence effect and making it difficult to accurately locate cable defects. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a broadband impedance spectrum cable defect location method and system based on an improved Z-transform. Based on the cable spectral impedance characteristics obtained from the broadband impedance spectrum, combined with the improved Z-transform method, accurate location of cable defects in the power grid can be achieved.

[0007] The present invention adopts the following technical solution.

[0008] The first aspect of this invention proposes a method for locating defects in broadband impedance spectra cables based on an improved Z-transform, comprising:

[0009] Step 1: Based on the equivalent distributed parameter circuit of the defective cable, the input impedance of each segment of the cable is regarded as the load impedance of the previous segment. The impedance is derived segment by segment from the end of the cable to obtain the input broadband impedance spectrum of the beginning of the defective cable.

[0010] Step 2: Perform an improved Z-transform on the wideband impedance spectrum of the defective cable head end, taking into account spectral leakage suppression, to transform the wideband impedance spectrum of the defective cable head end from the frequency domain to the time domain, and locate the cable defect by wave peak in the time domain.

[0011] Preferably, step 1 specifically includes:

[0012] In the equivalent distributed parameter circuit of a defective cable, record the position of the cable start-up. x =0, local defect located at a distance from the cable start end l 1~ l 2 locations, 0~ l 1 and l 2~ l This is a normal section of cable;

[0013] Open the cable end to make l Reflectance at location C l =1, combined with the characteristic impedance of a normal section of cable Z 0 and normal section cable propagation coefficient c 0 was obtained from l arrive l 2 cable sections l impedance at point 2 Z l2 Combined with the characteristic impedance of the defective section of the cable Z d Seeking l Reflectance at point 2 C l2 ;

[0014] according to C l2 , Z d and the propagation coefficient of the defective cable segment c d Find the cable at l The impedance Z at point 1 l1 and Z l1 Equivalent to from 0 to l The load impedance of a cable segment is calculated. l The reflection coefficient at point 1 is C l1 ;

[0015] according to C l1 , Z 0 and c 0. Calculate the input broadband impedance at the beginning of the defective cable. Z d And thus obtain Z d The spectrum as a function of frequency serves as the input broadband impedance spectrum of the defective cable's head end.

[0016] Preferably, the characteristic impedance of the combined normal section cable Z 0 and normal section cable propagation coefficient c 0 was obtained from l arrive l 2 cable sections l impedance at point 2 Z l2 The details are as follows:

[0017] (13)

[0018] The characteristic impedance of the combined defective section cable Z d Seeking lReflectance at point 2 C l2 The details are as follows:

[0019] (14).

[0020] Preferably, the according to C l2 , Z d and the propagation coefficient of the defective cable segment c d Find the cable at l The impedance Z at point 1 l1 The details are as follows:

[0021] (15)

[0022] The Z l1 Equivalent to from 0 to l The load impedance of a cable segment is calculated. l The reflection coefficient at point 1 is C l1 The details are as follows:

[0023] (16).

[0024] Preferably, the according to C l1 , Z 0 and c 0. Calculate the input broadband impedance at the beginning of the defective cable. Z d The details are as follows:

[0025] (17).

[0026] Preferably, the propagation coefficient of the defective section of the cable is... c d Characteristic impedance of defective cable sections Z d Specifically as follows:

[0027] (18)

[0028] in, R d , L d , G d and C d These represent the distributed resistance, distributed inductance, distributed conductance, and distributed capacitance at the defect location, respectively. oh This refers to the angular frequency of the signal input from the beginning to the end of the cable.

[0029] Preferably, the improved Z-transform of the input broadband impedance spectrum at the defective cable end, considering spectral leakage suppression, specifically involves:

[0030] (30)

[0031] In the formula, * This indicates that the data is being processed using conjugate;

[0032] Improved Z-transform results considering spectral leakage suppression;

[0033] X =2n-1, Δ=2k-1, X is the length of the window function; Δ is the shape parameter of the adjustment window function, and k is the index of the sampling point;

[0034] y ( n (This refers to the frequency domain data of the broadband impedance spectrum input at the head end of a defective cable.)

[0035] n for y ( n The counting variable;

[0036] A 0 is the starting sampling point on the spiral. z The length of the vector radius of 0;

[0037] i 0 is the starting sampling point on the spiral line during Z-transform. z Phase angle of 0;

[0038] f 0 represents the sampling phase difference on the spiral line during Z-transformation;

[0039] W 0 is the elongation of the helix during the Z-transform;

[0040] N It is the number of data points of the discrete data signal processed by the Z-transform.

[0041] Preferably, the initial sampling point on the spiral line during Z-transformation z Phase angle of 0 i 0, Sampling phase difference on the spiral during Z-transform f 0. Starting sampling point on the spiral line z 0 vector radius length A 0, the elongation of the spiral during Z-transformation W 0 Specifically as follows:

[0042] (25)

[0043] (26)

[0044] (27)

[0045] (28)

[0046] In the formula, M It is the kth sampling point during Z-transformation. z k Number of data points;

[0047] x max , x min Δ x These represent the maximum value, minimum value, and resolution of the defect location range, respectively.

[0048] floor indicates rounding down to the nearest integer;

[0049] f s The sampling frequency of the Z-transform;

[0050] v The speed at which electromagnetic waves propagate in a cable;

[0051] N It is the number of data points of the discrete data signal processed by the Z-transform.

[0052] A second aspect of this invention proposes a broadband impedance spectrum cable defect location system based on an improved Z-transform, comprising:

[0053] The impedance spectrum acquisition module is used to treat the input impedance of each segment of the cable as the load impedance of the previous segment based on the equivalent distributed parameter circuit of the defective cable, and derive it segment by segment from the end of the cable forward to finally obtain the input broadband impedance spectrum of the beginning of the defective cable.

[0054] The defect location module is used to perform an improved Z-transform on the wideband impedance spectrum of the defective cable head end, taking into account spectral leakage suppression. This transforms the wideband impedance spectrum of the defective cable head end from the frequency domain to the time domain, and locates the cable defect in the time domain by wave crest.

[0055] A third aspect of the present invention provides a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0056] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0057] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0058] This invention proposes to improve the Z-transform by performing spectral leakage processing on the basis of traditional Z-transform in broadband impedance spectrum analysis. By adopting a windowing design approach and using cosine and acrcosine transformations, the spectrum is limited to the range of [-1, 1]. This can effectively suppress the spectral leakage problem when the broadband impedance spectrum is converted from the frequency domain to the time domain, avoid data redundancy and useless data accumulation, and significantly improve the accuracy of cable defect location. Attached Figure Description

[0059] Figure 1 This is the equivalent distributed parameter circuit for the cable;

[0060] Figure 2 The flowchart shows a broadband impedance spectrum cable defect location method based on improved Z-transform.

[0061] Figure 3 This is the equivalent distributed parameter circuit for a defective cable.

[0062] Figure 4 The impedance spectrum of the cable;

[0063] Figure 5 Simulation results for locating cable defects. Detailed Implementation

[0064] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of this invention. The embodiments described in this application are merely some embodiments of this invention, and not all embodiments. Based on the spirit of this invention, other embodiments obtained by those skilled in the art without creative effort are all within the protection scope of this invention.

[0065] Embodiment 1 of this invention provides a broadband impedance spectrum cable defect location method based on an improved Z-transform. Based on the cable spectral impedance characteristics obtained from the broadband impedance spectrum, and combined with the improved Z-transform method, cable defect location is achieved, enabling accurate location of cable defects in the power grid. Figure 2 As shown, the method includes the following steps:

[0066] Step 1: Based on the equivalent distributed parameter circuit of the defective cable, the input impedance of each segment of the cable is regarded as the load impedance of the previous segment. The impedance is derived segment by segment from the end of the cable to obtain the input broadband impedance spectrum of the beginning of the defective cable.

[0067] More preferably, the cable distributed parameter model and the input impedance spectrum at the first end are as follows:

[0068] (1) Cable distributed parameter model

[0069] According to transmission line theory, under high-frequency conditions, a cable should be equivalent to a distributed parameter model, and its distributed parameter equivalent circuit is as follows: Figure 1 As shown in the figure, R 0、 L 0、 C 0、 G 0 represents the distributed resistance, distributed inductance, distributed capacitance, and distributed conductance per unit length of the cable. d x A tiny unit representing a cable.

[0070] At high frequencies, the various distribution values ​​of a cable can be calculated from relevant parameters such as the cable's actual material, structure, and dimensions. (The last part, "unit length of cable," appears to be incomplete and unrelated to the preceding text.) R 0、 L 0 can be approximated as:

[0071] (1)

[0072] (2)

[0073] In the formula: oh The angular frequency of the input signal. ω= 2π f ; m 0 represents the permeability of free space; r c and r s These are the cable core radius and the inner radius of the metal shielding layer, respectively. r c and r s These are the conductivity of the cable core and the conductivity of the metal shielding layer, respectively.

[0074] cable per unit length C 0、 G 0 is

[0075] (3)

[0076] (4)

[0077] In the formula: e The dielectric constant of the insulating layer; s The conductivity of the insulating layer.

[0078] With a total length of l In a cable, the end where the signal input is located is designated as the beginning (origin), and the load end is designated as the end (terminus). The cable can be positioned at any point from the beginning. x voltage at U ( x ) and currentI ( x ) can be represented as

[0079] (5)

[0080] (6)

[0081] In the formula: U i , U r These are the incident voltage and the reflected voltage, respectively. c 0 represents the cable propagation coefficient; Z 0 represents the characteristic impedance of the cable.

[0082] The propagation coefficient and characteristic impedance of a cable are determined by its type and structure, and can be obtained by the following formula.

[0083] (7)

[0084] (8)

[0085] (9)

[0086] In the formula: α is the attenuation constant, representing the attenuation characteristics of the wave; β is the phase constant, representing the phase shift characteristics of the wave; v The speed at which electromagnetic waves propagate in a cable; f The frequency of the incident signal; l The wavelength of the electromagnetic wave in the cable.

[0087] (2) Input impedance spectrum at the beginning of the cable

[0088] In practical engineering, the amplitude of waves in cables decays exponentially along the propagation direction. Electromagnetic waves propagating in cables can be decomposed into incident waves propagating in the forward direction and reflected waves propagating in the reverse direction. The ratio of the reflected voltage (current) wave to the incident voltage (current) wave is defined as the reflection coefficient. C Reflection coefficient at the cable end C L It can be represented as:

[0089] (10)

[0090] In the formula: Z L The load impedance at the cable end is the impedance when the cable end is open ( Z L When (=∞), the reflection coefficient C L =1; while terminal short circuit (Z L When =0), then C L =- 1.

[0091] For a total length of l The cable, from any position on the cable transmission line x Impedance at the end of the cable Z x for:

[0092] (11)

[0093] Pick x =0 will give the input impedance spectrum at the beginning of the entire cable. Z l The expression:

[0094] (12)

[0095] The impedance spectrum of a cable refers to its input impedance. Z l The spectrum of frequency variation. From equation (11), it can be seen that for a cable with a fixed load, its input impedance is determined by the cable's propagation coefficient. c 0 and characteristic impedance Z 0 determines the propagation coefficient. c 0 and characteristic impedance Z0 are determined by the distributed parameters of the cable ( R 0、 L 0、 C 0、 G 0) The distributed parameters of a cable are determined by its geometry, conductor material properties, and insulation material properties, reflecting the insulation state of the cable. Therefore, the input impedance of a cable can reflect its insulation state.

[0096] (3) Input impedance spectrum of the defective cable head

[0097] 1) When a local defect occurs in a cable, the corresponding electrical parameters of the defective section will change, which in turn will cause changes in the propagation coefficient and characteristic impedance of that section. Figure 3 The equivalent circuit diagram of the distributed parameters of a defective cable is shown, at a distance from the cable head ( x =0) l 1~ l There are 2 local defects, 0~ l 1 and l 2~ l The defective section of the cable can be considered a normal section. Let the propagation coefficient and characteristic impedance of the defective section be respectively... c d and Z d .

[0098] By treating the input impedance of each segment as the load impedance of the previous segment, we can proceed layer by layer from the end of the cable to obtain the input impedance spectrum of the defective segment.

[0099] 2) Normally, the cable ends are left open, so in the model... l Reflectance at location C l =1, from l arrive l 2. This part of the cable is intact. l The impedance at point 2 is Z l2 , can be represented as:

[0100] (13)

[0101] Therefore, we can obtain... l Reflectance at 2 locations C l2 :

[0102] (14)

[0103] 3) Then calculate the cable at... l The impedance Z at point 1 l1 :

[0104] (15)

[0105] Will l The impedance Z at point 1 l1 Equivalent to a good cable 0 to l The load impedance of region 1 can be obtained. l The reflection coefficient at point 1 is C l1 :

[0106] (16)

[0107] 4) Finally, the impedance of the cable at point 0 can be obtained, which is also the input impedance of the entire cable including the local defect at the beginning. Z d :

[0108] (17)

[0109] Similar to intact sections, the propagation coefficient of cables containing defects is... c d and characteristic impedance Z d The following formula is used to derive:

[0110] (18)

[0111] If there is a defect in the local insulation of the cable, the distributed parameters at the defect location will change. To facilitate the description of the change in distributed parameters at the defect location, a defect coefficient is defined. k 1, k 2, k 3 and k 4, representing the distributed resistance at the defect location. R d Distributed inductance L d Distributed conductivity G d and distributed capacitance C d The rate of change of the corresponding distributed parameters at the defect location relative to the intact cable can be expressed as:

[0112] (19)

[0113] The defect coefficient for a normal cable section is 1.

[0114] When a cable is damaged or undergoes significant deformation, its structure is destroyed. k The value 1 can change and is usually greater than 1;

[0115] Influenced by the self-inductance and mutual inductance between the conductor and the shielding layer, k The degree of change of 2 is relatively k 4 is relatively small;

[0116] Affected by the weakening of the capacitive effect, k 3 and k 4 are all less than 1.

[0117] When a cable experiences localized overheating, the dielectric constant of the insulation material increases. k 4 is greater than 1. k 3 is much greater than 1.

[0118] Step 2: Perform an improved Z-transform on the wideband impedance spectrum of the defective cable head end, taking into account spectral leakage suppression, to transform the wideband impedance spectrum of the defective cable head end from the frequency domain to the time domain, and locate the cable defect by wave peak in the time domain.

[0119] More preferably, the traditional Z-transform method is subjected to spectral leakage suppression processing, and an improved Z-transform method is proposed. The improved Z-transform parameters are determined according to the maximum value, minimum value and resolution of the set defect location interval. The broadband impedance spectrum of the defective cable head end is converted from the frequency domain to the time domain based on the improved Z-transform method, and the cable defect is located according to the peak in the time domain.

[0120] The specific method for broadband impedance spectrum cable defect localization based on the improved Z-transform is as follows:

[0121] 1) Z Transformation Principle

[0122] The Z-transform can uniformly sample along a spiral at different start and end times in the Z-plane, thus obtaining the data transformation result within a specific time region. For discrete data signals... y ( n Regarding the Z-transform result, Y ( z This can be represented as:

[0123] (20)

[0124] In the formula, N yes y ( n The number of data points; n Discrete data signals y ( n The counting variable is ).

[0125] exist Z Sampling points are obtained by setting equally spaced angular sampling points along a segment of a spiral in a plane. z k As shown in equation (21).

[0126] (twenty one)

[0127] In the formula: M yes z k Number of data points; A It is the starting sampling point on the spiral. z Characteristic complex numbers of 0; W It is the characteristic complex number of the sampling path on the spiral; k yes z k The counting variable.

[0128] A and W They can be represented as:

[0129] (twenty two)

[0130] (twenty three)

[0131] In the formula: A 0 is the starting sampling point on the spiral. z The length of the vector radius of 0;

[0132] i0 is the starting sampling point on the spiral. z Phase angle of 0;

[0133] f 0 represents the sampling phase difference on the spiral line, when f When 0 > 0, the spiral rotates counterclockwise. f When 0 < 0, the spiral rotates clockwise;

[0134] W 0 is the elongation of the spiral, when W When 0 > 1, the spiral is in a contracted state. W When 0 < 1, the spiral is in an outward-extending state. W When 0=1, the spiral appears as a circular arc with equal radius.

[0135] Combining equations (22) and (23), we can obtain:

[0136] (twenty four)

[0137] in, This is the time-domain data after Z-transformation.

[0138] Compared to the traditional Fast Fourier Transform, the Z-transform can convert known frequency domain data into time data of any range and improve the resolution of the time data.

[0139] 2) Z Transformation parameter confirmation

[0140] When analyzing broadband impedance spectrum data using Z-transform, it is necessary to determine the length range of the cable to be analyzed. Therefore, the maximum value, minimum value, and resolution of the defect location interval are set as follows: x max , x min Δ x In actual testing, the aforementioned parameters can be freely selected based on the test results. For A For 0, it is generally taken as A 0=1 is more convenient.

[0141] With a total length of l The time delay corresponding to the reflected wave at the end of the cable in the time domain is 2. l / v Therefore, for x min and x max In terms of time domain data, the corresponding latency is 2. x min / v 2 xmax / v The range of the time-domain data to be converted is [2]. x min / v ,2 x max / v Based on this time-domain data range, the parameters in the CTZ transform can be determined as follows:

[0142] (25)

[0143] (26)

[0144] (27)

[0145] (28)

[0146] In the formula, floor represents rounding down; f s Discrete data signals y ( n The sampling frequency.

[0147] In practice, x max , x min Δ x The settings can be customized based on the cable length. l 1. l 2 belongs to [ x min , x max Within the range.

[0148] Furthermore, during the conversion between time-domain and frequency-domain data, data truncation can cause spectral leakage, leading to sidelobe noise from defects masking the reflection signals of minute defects and introducing errors into defect localization analysis. To address this phenomenon, this invention... Z The transformation is improved to enhance positioning sensitivity.

[0149] The improved Z-transform expression is:

[0150] (29)

[0151] In the formula, X =2n-1; Δ=2k-1; X is the length of the window function; Δ is the shape parameter of the adjustment window function; k is the index of the sampling point.

[0152] Therefore, the complete defect location function can be obtained as follows:

[0153] (30)

[0154] In the formula, * This indicates that the data is conjugate processed, which converts the frequency domain to the time domain by performing conjugate processing on the frequency domain data y(n);

[0155] The improved Z-transform result, which takes into account spectral leakage suppression, i.e. the defect location function, has its peak as the location of the cable defect.

[0156] y ( n ) is the discrete data signal processed by the Z-transform, representing the frequency domain data of the wideband impedance spectrum input at the head end of the defective cable.

[0157] To verify the reliability of the method proposed in this invention, a 10kV XLPE cable was used as the research object. A cable model with a total length of 100m was built on the Matlab platform, and its basic parameters are shown in Table 1. The lower frequency limit was set to 10kHz, the upper frequency limit to 60MHz, and the cable end was left open-circuited. The following results were obtained: Figure 4 The impedance spectrum is shown.

[0158] Table 1 Basic simulation parameters of the cable

[0159]

[0160] Subsequently, a localized heating defect with a length of 0.1m was set at a distance of 70m. Specific parameters are shown in Table 2. The defect location was simulated using both the traditional Fast Fourier Transform method and the method proposed in this invention. The results are as follows: Figure 5 As shown.

[0161] Table 2 Simulation Defect Parameter Settings

[0162]

[0163] Simulation results show that the proposed method achieves a location of 69.6999 m. In contrast, traditional methods show peaks at 69.3007 m at the defect location and at the total cable length of 99.991 m, with significant peaks also appearing at 129.691 m, 169.292 m, 198.992 m, and 229.682 m. These peaks are redundant interference peaks, severely hindering the accurate determination of the defect location. Because the number of data points before and after the Fast Fourier Transform is consistent, traditional methods result in a large amount of invalid data in the defect location results, leading to numerous interfering characteristic peaks in the final defect location function, making it difficult to identify the true cable defect characteristic peaks. The proposed method, however, only has two peaks: the fault point and the cable end point, significantly reducing data redundancy and improving the accuracy of identifying cable defect characteristic peaks.

[0164] Embodiment 2 of the present invention provides a broadband impedance spectrum cable defect location system based on improved Z-transform, comprising:

[0165] The impedance spectrum acquisition module is used to treat the input impedance of each segment of the cable as the load impedance of the previous segment based on the equivalent distributed parameter circuit of the defective cable, and derive it segment by segment from the end of the cable forward to finally obtain the input broadband impedance spectrum of the beginning of the defective cable.

[0166] The defect location module is used to perform an improved Z-transform on the wideband impedance spectrum of the defective cable head end, taking into account spectral leakage suppression. This transforms the wideband impedance spectrum of the defective cable head end from the frequency domain to the time domain, and locates the cable defect in the time domain by wave crest.

[0167] Embodiment 3 of the present invention provides a terminal, including a processor and a storage medium; the storage medium is used to store instructions; the processor is used to perform operations according to the instructions to execute the steps of the method.

[0168] Embodiment 4 of the present invention provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the steps of the method.

[0169] Compared with the prior art, the beneficial effects of the present invention include at least the following:

[0170] This invention proposes to improve the Z-transform by performing spectral leakage processing on the basis of traditional Z-transform in broadband impedance spectrum analysis. This can effectively suppress the spectral leakage problem when the broadband impedance spectrum is converted from the frequency domain to the time domain, and significantly improve the accuracy of cable defect location.

[0171] This disclosure can be a system, method, and / or computer program product. A computer program product may include a computer-readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of this disclosure.

[0172] Computer-readable storage media can be tangible devices capable of holding and storing instructions for use by an instruction execution device. Computer-readable storage media can be, for example—but not limited to—electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of computer-readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination of the foregoing. The computer-readable storage media used herein are not to be construed as transient signals themselves, such as radio waves or other freely propagating electromagnetic waves, electromagnetic waves propagating through waveguides or other transmission media (e.g., light pulses through fiber optic cables), or electrical signals transmitted through wires.

[0173] The computer-readable program instructions described herein can be downloaded from computer-readable storage media to various computing / processing devices, or downloaded via a network, such as the Internet, local area network, wide area network, and / or wireless network, to an external computer or external storage device. The network may include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. A network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards them to the computer-readable storage media in the respective computing / processing device.

[0174] Computer program instructions used to perform the operations of this disclosure may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, status setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, etc., and conventional procedural programming languages ​​such as the "C" language or similar programming languages. The computer-readable program instructions may execute entirely on the user's computer, partially on the user's computer, as a standalone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In cases involving a remote computer, the remote computer may be connected to the user's computer via any type of network—including a local area network (LAN) or a wide area network (WAN)—or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, electronic circuitry, such as programmable logic circuitry, field-programmable gate arrays (FPGAs), or programmable logic arrays (PLAs), is personalized by utilizing the status information of the computer-readable program instructions to implement various aspects of this disclosure.

[0175] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for cable defect location based on improved Z-transform broadband impedance spectroscopy, characterized in that, Comprising: Step 1: according to the equivalent distributed parameter circuit of the defective cable, the input impedance of each section of the cable is regarded as the load impedance of the previous section, and the input broadband impedance spectrum of the defective cable is finally obtained by deducing from the end of the cable to the front; Step 2: the improved Z transform considering spectrum leakage suppression is performed on the input broadband impedance spectrum of the defective cable, and the input broadband impedance spectrum of the defective cable is converted from the frequency domain to the time domain, and the cable defect is located by peak positioning in the time domain. The improved Z transform considering spectrum leakage suppression on the input broadband impedance spectrum of the defective cable is specifically: (30) wherein * represents conjugate processing of data; is the improved Z-transform result considering the spectrum leakage suppression; X =2n-1, Δ=2k-1, X is the length of window function; Δ is the shape parameter of adjusting window function, k is the serial number of sampling point; y n is the frequency domain data of broadband impedance spectrum of the input end of the defective cable; n y is the count variable of n ; A 0 is the vector radius length of the starting sampling point on the helix z 0; θ 0 is the phase angle of the starting sampling point on the helix z 0 in Z transform; φ 0 is the sampling phase difference of the helix in Z transform; W 0 is the stretch rate of the helix in Z transform; N is the data point number of the discrete data signal processed by Z transform;​​ The initial sampling point on the spiral during Z-transformation z Phase angle of 0 θ 0, Sampling phase difference on the spiral during Z-transform φ 0. Starting sampling point on the spiral line z 0 vector radius length A 0, the elongation of the spiral during Z-transformation W 0 Specifically as follows: (25) (26) (27) (28) wherein, M is the kth sample point of the Z-transform z k the number of data points; x max , x min , Δ x are the maximum, minimum and resolution of the defect localization interval, respectively; floor denotes the floor function; f s is the sampling frequency of the Z-transform; v is the propagation speed of the electromagnetic wave in the cable; N is the number of data points of the discrete data signal processed by the Z-transform.

2. The broadband impedance spectrum cable defect positioning method based on the improved Z transform according to claim 1, characterized in that: Step 1 specifically includes: In the equivalent distributed parameter circuit of a defective cable, let the cable head position x =0, the local defect is located at a distance of cable head l 1~ l 2 place, 0~ l 1 and l 2~ l place is a normal section of cable; The cable end is treated as an open circuit l The reflection coefficient at Γ l = 1, combined with the characteristic impedance of the normal section cable Z 0 and the propagation coefficient of the normal section cable γ 0 to obtain the impedance of the cable from l to l 2 at l 2 Z l2 , combined with the characteristic impedance of the defective section cable Z d The reflection coefficient at l 2 is obtained Γ l2 ; according to Γ l2 , Z d and the propagation coefficient of the defective cable segment γ d Find the cable at l The impedance Z at point 1 l1 and Z l1 Equivalent to from 0 to l The load impedance of a cable segment is calculated. l The reflection coefficient at point 1 is Γ l1 ; According to Γ l1 , Z 0 and γ 0 to obtain the input broadband impedance of the defective cable head end Z d , and then Z d the graph as a function of frequency, as the input broadband impedance spectrum of the defective cable head end.

3. The broadband impedance spectrum cable defect positioning method based on the improved Z transform according to claim 2, characterized in that: The characteristic impedance of the normal segment cable Z 0 and the propagation coefficient of the normal segment cable γ 0 is obtained from l to l 2 segment cable at l 2 Z l2 , as follows: (13) The characteristic impedance of the defective segment of the cable Z d Obtained l Reflection coefficient at 2 Γ l2 In particular as follows: (14)。 4. The broadband impedance spectrum cable defect positioning method based on the improved Z transform according to claim 2, characterized in that: According to Γ l2 , Z d and the propagation coefficient of the defective cable segment γ d Find the cable at l The impedance Z at point 1 l1 The details are as follows: (15) The Z l1 is equivalent to from 0 to l The load impedance of the 1st cable is obtained l The reflection coefficient at 1 is Γ l1 In particular as follows: (16)。 5. The broadband impedance spectrum cable defect positioning method based on the improved Z transform according to claim 2, characterized in that: The according to Γ l1 , Z 0 and γ 0 to obtain the input broadband impedance of the defective cable head end Z d , as follows: (17)。 6. The broadband impedance spectrum cable defect positioning method based on the improved Z transform according to claim 2, characterized in that: Propagation coefficient of the defective cable γ d Characteristic impedance of the defective cable Z d In detail, (18) wherein R d , L d , G d and C d are the distributed resistance, distributed inductance, distributed conductance and distributed capacitance at the defect, respectively; ω is the angular frequency of the input signal from the cable head end to the cable end.

7. A broadband impedance spectroscopy cable defect location system based on modified Z-transform for performing the method of any one of claims 1 to 6, characterized in that, The system comprises: An impedance spectrum acquisition module for obtaining the input broadband impedance spectrum of the defective cable by regarding the input impedance of each section of the cable as the load impedance of the previous section according to the equivalent distributed parameter circuit of the defective cable, and finally deducing from the end of the cable to the front; A defect positioning module for performing the improved Z transform considering spectrum leakage suppression on the input broadband impedance spectrum of the defective cable, converting the input broadband impedance spectrum of the defective cable from the frequency domain to the time domain, and locating the cable defect by peak positioning in the time domain.

8. A terminal comprising a processor and a storage medium; characterized in that: The storage medium is used to store instructions; The processor is used to operate according to the instructions to perform the steps of the method according to any one of claims 1-6.

9. A computer readable storage medium having stored thereon a computer program, characterized in that, The program is executed by the processor to realize the steps of the method according to any one of claims 1-6.

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