Wideband impedance spectroscopy cable defect positioning method and system based on improved Z transformation

Abstract

The invention discloses a broadband impedance spectroscopy cable defect positioning method and system based on improved Z transformation, and the method comprises the steps: enabling the input impedance of each section of a cable to serve as the load impedance of a previous section according to an equivalent distribution parameter circuit of a defective cable, and carrying out the forward deduction from the tail end of the cable section by section, and finally obtaining the head end input broadband impedance spectrum of the defective cable. And carrying out improved Z transformation considering spectrum leakage suppression on the head-end input broadband impedance spectrum of the defective cable, converting the head-end input broadband impedance spectrum of the defective cable from a frequency domain to a time domain, and positioning the cable defect through a wave crest in the time domain. According to the method, spectrum leakage suppression processing is carried out on a traditional Z transformation method in broadband impedance spectrum analysis, and the accuracy of cable defect positioning can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of cable defect location, and relates to a broadband impedance spectroscopy cable defect location method and system based on an improved Chirp-Z Transform (ICZT). Background Art

[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 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 issues, which can lead to localized electrical parameter anomalies and defects. These defects gradually worsen under the influence of electric fields, causing faults such as open circuits, short circuits, and high- or low-resistance ground faults, shortening the cable life and, in severe cases, even causing widespread power outages and significant economic losses.

[0003] In recent years, domestic and foreign scholars have explored a variety of cable fault diagnosis methods, and quickly identifying defects and locating faults has become the current research focus.

[0004] Currently, the traveling wave method is the most commonly used method for locating local defects in cables. Depending on the analysis domain, it can be divided into time domain reflectometry (TDR) and frequency domain reflectometry (FDR). The TDR method locates defects by calculating the time delay difference between the incident pulse signal and the reflected pulse signal. This method is simple to operate and has a certain degree of anti-interference ability. However, since the Gaussian pulse signal injected by the TDR method has fewer high-frequency components and the signal propagates in the time domain, it will experience severe attenuation and dispersion, resulting in low sensitivity for defect location. The FDR method, on the other hand, injects a swept frequency signal containing a large number of high-frequency components at the beginning of the cable, making the defect location results of this method extremely accurate, and has gradually become a research hotspot in recent years.

[0005] The existing FDR method collects the wideband impedance spectrum of the front end and performs time-frequency domain conversion to realize accurate positioning of defects. In order to convert the information in the frequency domain into the information in the time domain, the collected impedance spectrum data is usually analyzed by using fast Fourier transform, but this method has some limitations in engineering practical application on the basis of theoretical simulation. On the one hand, the fast Fourier transform algorithm requires that the number of data points in the time domain and the frequency domain is consistent, and the converted data is uniformly distributed in the entire time domain or frequency domain, so that a large amount of redundant time domain information is obtained by this method, which is irrelevant to the defect positioning result of the cable, and may introduce interference peaks, affecting the judgment of the defect positioning result; on the other hand, when the number of test points of the wideband impedance spectrum is relatively limited, the amount of time domain data that can be obtained is also reduced due to the consistency requirement of the data amount in the fast Fourier transform algorithm. This not only reduces the resolution of the time domain data curve, but also further reduces the resolution of the defect positioning function, which is prone to fence effect and difficult to accurately position the cable defects. SUMMARY

[0006] In order to solve the problems in the prior art, the present application provides a wideband impedance spectrum cable defect positioning method and system based on improved Z transform, which realizes accurate positioning of cable defects in the power grid based on the cable frequency spectrum impedance characteristics obtained from the wideband impedance spectrum and the improved Z transform method.

[0007] The application adopts the following technical solutions.

[0008] The first aspect of the application provides a wideband impedance spectrum cable defect positioning method based on improved Z transform, comprising: Step 1: According to the equivalent distributed parameter circuit of the cable with defects, the input impedance of each section of the cable is regarded as the load impedance of the previous section, and the input wideband impedance spectrum of the cable with defects is obtained by deducing from the end of the cable to the front end. Step 2: The improved Z transform considering frequency spectrum leakage suppression is performed on the input wideband impedance spectrum of the cable with defects to convert the input wideband impedance spectrum of the cable with defects from the frequency domain to the time domain, and the cable defects are positioned by peak positioning in the time domain.

[0009] Preferably, step 1 specifically comprises: In the equivalent distributed parameter circuit of the cable with defects, the position of the cable front end is denoted as x =0, the local defect is located at a distance of l 1 l 2 from the cable front end, l 0 l 1 and l 2 The cable end is treated as an open circuit to make the reflection coefficient at l 0 C l= 1, the characteristic impedance of the normal section cable Z 0 and the propagation coefficient of the normal section cable c 0 to obtain the impedance of the cable from l to l 2 at l 2 Z l2 , the characteristic impedance of the defective section cable Z d obtained l 2, the reflection coefficient at C l2 According to C l2 , Z d and the propagation coefficient of the defective section cable c d obtained the impedance Z l1 of the cable at l 1, and equivalent Z l1 to the load impedance of the cable from l 0 to l 1, obtained the reflection coefficient at C 1 l1 According to C l1 , Z 0 and c 0, obtained the input broadband impedance of the defective cable Z d , and further obtained Z d the graph of the input broadband impedance of the defective cable as a function of frequency. Preferably, the characteristic impedance of the normal section cable Z 0 and the propagation coefficient of the normal section cable c 0 to obtain the impedance of the cable from l to l 2 at l 2 Z l2 , in particular as follows: (13) the characteristic impedance of the defective section cable Z d obtained l 2, the reflection coefficient at C l2 , in particular as follows: (14).

[0010] Preferably, the characteristic impedance of the normal section cable C ​l2 、 Z d and the propagation coefficient of the defective cable c d Find the cable l Impedance Z at 1 l1 , as follows: (15) The Z l1 Equivalent to 0 to l The load impedance of a cable section is obtained l The reflection coefficient at point 1 is C l1 , as follows: (16).

[0011] Preferably, the C l1 、 Z 0 and c 0 Obtain the broadband impedance of the first end of the defective cable Z d , as follows: (17).

[0012] Preferably, the propagation coefficient of the defective cable segment is c d , characteristic impedance of the defective section of the cable Z d The details are as follows: (18) in, R d 、 L d 、 G d and C d They are the distributed resistance, distributed inductance, distributed conductance and distributed capacitance at the defect; oh is the angular frequency of the input signal from the beginning of the cable to the end of the cable.

[0013] Preferably, the improved Z-transform considering spectrum leakage suppression is performed on the broadband impedance spectrum of the defective cable head end input, specifically: (30) Where, * Indicates that the data is conjugated; Improved Z transform result considering spectrum leakage suppression; X=2n-1, Δ=2k-1, X is the length of the window function; Δ is the shape parameter of the window function, and k is the serial number of the sampling point; y ( n ) is the frequency domain data of the broadband impedance spectrum input at the head end of the defective cable; n for y ( n ) count variable; A 0 is the starting sampling point on the spiral line z The length of the vector radius is 0; i 0 is the starting sampling point on the spiral line during Z transformation z Phase angle of 0; f 0 is the sampling phase difference on the spiral line during Z transformation; W 0 is the stretching rate of the helix during the Z transformation; N is the number of data points of the discrete data signal processed by the Z transform.

[0014] Preferably, the starting sampling point on the spiral line during Z transformation z Phase angle of 0 i 0. Sampling phase difference on the spiral line during Z transform f 0. Starting sampling point on the spiral line z 0 vector radius length A 0. The stretch rate of the helix during Z transformation W 0Specific details are as follows: (25) (26) (27) (28) Where, M is the kth sampling point during Z transform z k The number of data points; x max 、 x min , Δ x are the maximum value, minimum value and resolution of the defect positioning interval respectively; Floor means round down; f s is the sampling frequency of the Z transform; v is the propagation speed of electromagnetic waves in the cable; N is the number of data points of the discrete data signal processed by the Z transform.

[0015] The second aspect of the present invention provides a broadband impedance spectroscopy cable defect location system based on an improved Z-transform, comprising: The impedance spectrum acquisition module is used to treat the input impedance of each cable segment as the load impedance of the previous segment based on the equivalent distributed parameter circuit of the defective cable, and deduce the impedance of each segment forward from the end of the cable to finally obtain the broadband impedance spectrum of the input of the defective cable head end; The defect location module is used to perform an improved Z-transform on the broadband impedance spectrum input at the head end of the defective cable, taking into account spectrum leakage suppression. The broadband impedance spectrum input at the head end of the defective cable is converted from the frequency domain to the time domain, and the cable defects are located by peaks in the time domain.

[0016] A third aspect of the present invention provides a terminal, comprising a processor and a storage medium; the storage medium is used to store instructions; and the processor is used to operate according to the instructions to execute the steps of the method.

[0017] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the method when executed by a processor.

[0018] Compared with the prior art, the beneficial effects of the present invention include at least: In the broadband impedance spectrum analysis, the present invention proposes to perform spectrum leakage processing on the basis of traditional Z transform to achieve Z transform improvement. By adopting the idea of ​​windowing design, the spectrum is limited to the range of [-1, 1] through cosine and acrcos transforms. This can effectively suppress the spectrum 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is the cable equivalent distributed parameter circuit; Figure 2 This is a flow chart of the broadband impedance spectroscopy cable defect location method based on improved Z transform; Figure 3 is the equivalent distributed parameter circuit of the defective cable; Figure 4 is the cable impedance spectrum; Figure 5 Simulation results for cable defect location. DETAILED DESCRIPTION

[0020] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. The embodiments described in this application are only part of the embodiments of the present invention, not all of them. Based on the spirit of the present invention, other embodiments obtained by ordinary technicians in this field without making creative efforts are all within the scope of protection of the present invention.

[0021] Embodiment 1 of the present invention provides a broadband impedance spectrum cable defect location method based on an improved Z transform, which locates cable defects based on the cable spectrum impedance characteristics obtained from the broadband impedance spectrum and the improved Z transform method, thereby achieving accurate location of cable defects in the power grid. Figure 2 As shown, the method includes the following steps: Step 1: Based on the equivalent distributed parameter circuit of the defective cable, the input impedance of each cable segment is regarded as the load impedance of the previous segment, and the impedance spectrum of each segment is deduced from the end of the cable forward to obtain the broadband impedance spectrum of the cable head end. Further preferably, the cable distributed parameter model and the first-end input impedance spectrum are specifically as follows: (1) Cable distributed parameter model According to the transmission line theory, under high frequency conditions, the 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 are the distributed resistance, distributed inductance, distributed capacitance and distributed conductance of the cable per unit length, d x Indicates a small unit of cable.

[0022] Under high frequency conditions, the distribution values ​​of the cable can be calculated based on the actual material, structure, size and other relevant parameters of the cable. R 0. L 0 can be approximated as: (1) (2) Where: oh is the angular frequency of the input signal, ω= 2π f ; m 0 is the vacuum permeability; r c and r s are the cable core radius and the inner radius of the metal shielding layer respectively; r c and rs are the conductivity of the cable core and the conductivity of the metal shielding layer, respectively.

[0023] Cable length per unit C 0. G 0 is (3) (4) Where: e is the dielectric constant of the insulation layer; s is the electrical conductivity of the insulation layer.

[0024] In total length l In the cable, the signal input end is set as the starting end (i.e. the origin), the load end is the end (i.e. the end point), and at any position away from the cable starting end x Voltage at U ( x ) and current I ( x ) can be expressed as (5) (6) Where: U i 、 U r are the incident voltage and the reflected voltage respectively; c 0 is the cable propagation coefficient; Z 0 is the characteristic impedance of the cable.

[0025] The propagation coefficient and characteristic impedance of the cable are determined by the type and structure of the cable and can be obtained by the following formula: (7) (8) (9) Where: α is the attenuation constant, which represents the attenuation characteristics of the wave; β is the phase constant, which represents the phase shift characteristics of the wave; v is the propagation speed of electromagnetic waves in the cable; f is the frequency of the incident signal; l is the wavelength of the electromagnetic wave in the cable.

[0026] (2) Input impedance spectrum at the cable head end In actual engineering, the amplitude of the wave in the cable will decay exponentially along the propagation direction. The electromagnetic wave transmitted in the cable can be decomposed into the incident wave transmitted in the forward direction and the reflected wave transmitted 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 , cable head reflection coefficient C L may be expressed as: (10) where: Z L is the cable end load impedance, when the cable end is open ( Z L =∞), the reflection coefficient C L =1; while the end short circuit ( Z L =0), then C L =- 1.

[0027] For the cable with full length l , the impedance x from the cable transmission line at any position Z x to the cable end is: (11) Taking x =0, the expression of the whole cable head input impedance spectrum Z l can be obtained: (12) The impedance spectrum of the cable refers to the input impedance Z l of the cable as a function of frequency. As can be seen from equation (11), for a cable with a certain load, its input impedance is determined by the propagation coefficient c 0 and the characteristic impedance Z 0, and the propagation coefficient c 0 and the characteristic impedance Z0 are determined by the distribution parameters of the cable ( R 0, L 0, C 0, G 0), which are determined by the geometric structure, conductor material properties, and insulation material properties of the cable, reflecting the insulation state of the cable. Therefore, the input impedance of the cable can reflect the insulation state of the cable.

[0028] (3) Input impedance spectrum of cable with defects at the head 1) When a local defect occurs in the cable, the corresponding electrical parameters of the defect section will change, thereby causing changes in the propagation coefficient and characteristic impedance of the section. Figure 3 is the equivalent circuit diagram of the distribution parameters of the cable with defects, at a distance of x =0 l 1from the cable headl There are local defects in 2 places, 0~ l 1 and l 2~ l The section can be regarded as a normal section of cable. Assume that the propagation coefficient and characteristic impedance of the defective section of cable are c d and Z d .

[0029] The input impedance of each section is regarded as the load impedance of the previous section, and it can be deduced from the end of the cable layer by layer to the front, and finally the input impedance spectrum of the defective section is obtained.

[0030] 2) Usually, the end of the cable is open circuit, so in the model l Reflection coefficient at C l =1, from l arrive l 2 This part of the cable is intact l The impedance at point 2 is Z l2 , which can be expressed as: (13) Therefore, we can obtain l Reflection coefficient at 2 locations C l2 : (14) 3) Then find the cable l Impedance Z at 1 l1 : (15) Will l Impedance Z at 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 : (16) 4) Finally, the impedance of the cable at point 0 can be obtained, which is also the input impedance of the entire cable head end with local defects. Z d : (17) The propagation coefficient of the cable with defect is the same as that of the intact section. c d and characteristic impedance Z d It is derived from the following formula: (18) If there is a defect in the local insulation of the cable, the distribution parameters at the defect will change. In order to conveniently describe the change of the distribution parameters at the defect, the defect coefficient is defined k 1, k 2, k 3 and k 4, respectively represent the distributed resistance at the defect R d , distributed inductance L d , distributed conductivity G d and distributed capacitance C d The change rate of the corresponding distribution parameters of the intact cable can be expressed as: (19) The defect coefficient of normal cable segments is 1; When the cable is damaged or deformed significantly, the structure is destroyed. k 1 will change and is usually greater than 1; Affected by the self-inductance and mutual inductance between the conductor and the shield, k The degree of change of 2 is relatively k 4 smaller; Affected by the weakening of the capacitive effect, k 3 and k 4 are all less than 1.

[0031] When the cable is locally overheated, the dielectric constant of the insulation material will increase. k 4 is greater than 1, k 3 is much greater than 1.

[0032] Step 2: Perform an improved Z-transform that considers spectrum leakage suppression on the broadband impedance spectrum of the defective cable headend. Convert the broadband impedance spectrum of the defective cable headend from the frequency domain to the time domain, and locate the cable defect by the peak in the time domain.

[0033] Further preferably, the traditional Z transform method is subjected to spectrum leakage suppression processing, an improved Z transform method is proposed, and 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 input at the head end of the defective cable is converted from the frequency domain to the time domain based on the improved Z transform method, and the cable defects are located according to the peaks in the time domain.

[0034] The broadband impedance spectroscopy cable defect location based on the improved Z transform is as follows: 1) Z Transformation principle The Z-transform can uniformly sample the spiral line in the Z-plane at different start and end time positions, and thus obtain the data transform result in a specific time region. For a discrete data signal y ( n ), its Z-transform result Y ( z ) can be expressed as: (20) wherein, N is the data point number of y ( n ); n is the count variable of the discrete data signal y ( n ).

[0035] In the Z-plane, the sampling points with equal interval angle are arranged on a segment of spiral line, and the sampling point Z k is obtained as shown in equation (21). z

[0036] (21) wherein, M is the data point number of z k ; A is the characteristic complex number of the start sampling point z 0 on the spiral line; W is the characteristic complex number of the sampling path on the spiral line; k is the count variable of z k .

[0037] A and W can be respectively expressed as: (22) (23) wherein, A 0 is the vector radius length of the start sampling point z 0 on the spiral line; i 0 is the phase angle of the start sampling point z 0 on the spiral line; f 0 is the sampling phase difference on the spiral line, when f 0>0, the spiral line rotates counterclockwise, and when f 0<0, the spiral line rotates clockwise; W 0 is the stretch rate of the spiral line, when W 0>1, the spiral line is in a state of internal shrinkage, and when​W When 0<1, the spiral is in an outward extension state. W When 0=1, the spiral appears as an arc of equal radius.

[0038] Combining equations (22) and (23), we can obtain: (twenty four) in, is the time domain data after Z transformation.

[0039] Compared with 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 time data.

[0040] 2) Z Confirmation of transformation parameters When using Z transform to analyze broadband impedance spectrum data, it is necessary to determine the cable length range 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 above parameters can be freely selected based on the test results. A 0, generally take A 0=1 is more convenient.

[0041] In total length l The corresponding time delay in the time domain data of the reflected wave at the end of the cable is 2 l / v , therefore, for x min and x max For the time domain data, the corresponding delays are 2 x min / v , 2 x max / v , the range of the time domain data to be converted is [2 x min / v , 2 x max / v According to the time domain data range, the parameters in the CTZ transformation can be determined as follows: (25) (26) (27) (28) floor means down rounding; f s is the sampling frequency of the discrete data signal y ( n ).

[0042] In practice, x max , x min , Δ x is automatically set according to the cable length, l 1, l 2 belongs to the range of x min , x max ].

[0043] Further, in the conversion process of time domain data and frequency domain data, the truncation effect of data will cause the problem of spectrum leakage, which will cause the sidelobe noise of defects to cover the reflection signal of small defects, and bring errors to the positioning analysis of defects. In view of this phenomenon, the present application improves the transformation, so as to improve the positioning sensitivity. Z

[0044] The improved Z transformation expression is: (29) In the formula, X =2n-1;Δ=2k-1;X is the length of the window function; Δ is the shape parameter of the adjusting window function, and k is the serial number of the sampling point.

[0045] Therefore, the complete defect positioning function can be obtained as: (30) In the formula, * indicates that the conjugate processing is performed on the data, and the frequency domain is converted into the time domain by performing the conjugate processing on the frequency domain data y(n); is the improved Z transformation result considering the spectrum leakage suppression, that is, the defect positioning function, and the wave peak is the cable defect position; y ( n ) is the discrete data signal processed by the Z transformation, and indicates the frequency domain data of the input wideband impedance spectrum of the head end of the cable with defects.

[0046] In order to verify the reliability of the method of the present application, a 100m cable model is built on the Matlab platform with 10kV XLPE cable as the research object, and the basic parameters are shown in Table 1. The lower limit of frequency is set to 10kHz, the upper limit of frequency is set to 60MHZ, and the cable end is open circuit processed, and the obtained​ Figure 4 The impedance spectrum is shown.

[0047] Table 1 Basic simulation parameters of cables

[0048] Then a local heating defect is set at 70m, with a defect length of 0.1m. The specific parameters are shown in Table 2. The defect position is simulated by the traditional fast Fourier transform method and the method proposed in this invention. The results are as follows: Figure 5 shown.

[0049] Table 2 Simulation defect parameter settings

[0050] The simulation results show that the positioning result of the method proposed in the present invention is 69.6999 m. In the traditional positioning method, in addition to the peaks at 69.3007 m at the defect site and 99.991 m of the total cable length, obvious peaks appear at 129.691 m, 169.292 m, 198.992 m, and 229.682 m. These peaks are redundant interference peaks, which seriously interfere with the judgment of the accurate location of the defect. In the traditional method, because the number of data points before and after the fast Fourier transform is consistent, there will be a large amount of invalid data in the defect positioning result of the traditional method, resulting in a large number of interfering characteristic peaks in the final defect positioning function, making it difficult to determine the true cable defect characteristic peak. The method proposed in the present invention only has two peaks, namely the fault point and the cable end point, which greatly reduces the redundancy of the data and improves the accuracy of the judgment of the cable defect characteristic peak.

[0051] Embodiment 2 of the present invention provides a broadband impedance spectroscopy cable defect location system based on an improved Z transform, comprising: The impedance spectrum acquisition module is used to treat the input impedance of each cable segment as the load impedance of the previous segment based on the equivalent distributed parameter circuit of the defective cable, and deduce the impedance of each segment forward from the end of the cable to finally obtain the broadband impedance spectrum of the input of the defective cable head end; The defect location module is used to perform an improved Z-transform on the broadband impedance spectrum input at the head end of the defective cable, taking into account spectrum leakage suppression. The broadband impedance spectrum input at the head end of the defective cable is converted from the frequency domain to the time domain, and the cable defects are located by peaks in the time domain.

[0052] 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 operate according to the instructions to execute the steps of the method.

[0053] Embodiment 4 of the present invention provides a computer-readable storage medium having a computer program stored thereon, which implements the steps of the method when executed by a processor.

[0054] Compared with the prior art, the beneficial effects of the present invention include at least: The present invention proposes to perform spectrum leakage processing on the basis of traditional Z transform in broadband impedance spectrum analysis, realizes Z transform improvement, and can effectively suppress the spectrum leakage problem when the broadband impedance spectrum is converted from frequency domain to time domain, thereby significantly improving the accuracy of cable defect location.

[0055] The present disclosure may be a system, method and / or computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present disclosure.

[0056] A computer-readable storage medium can be a tangible device that can hold and store instructions for use by an instruction execution device. A computer-readable storage medium can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punched card or raised structure in a groove on which instructions are stored, and any suitable combination thereof. As used herein, a computer-readable storage medium is not to be construed as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse passing through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0057] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0058] Computer readable program instructions for carrying out operations of the present disclosure can be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine dependent instructions, microcode, firmware instructions, state-setting data, or either source code or object code written in any combination of one or more programming languages, including an object oriented programming language such as Smalltalk, C++ or the like, and conventional procedural programming languages such as the "C" programming language or similar programming languages. The computer readable program instructions can execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection can be made to an external computer (for example, through the Internet using an Internet Service Provider). In some embodiments, electronic circuitry including, for example, programmable logic circuitry, field-programmable gate array (FPGA), or programmable logic array (PLA) can execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry, in order to perform aspects of the present disclosure.

[0059] Finally, it should be noted that the above-mentioned embodiments are merely used to illustrate the technical solutions of the present application, but not to limit it. Although the present application has been described in detail with reference to the above-mentioned embodiments, those skilled in the art should understand that the specific embodiments of the present application can be modified or replaced, and any modification or replacement without departing from the spirit and scope of the present application should be covered in the protection scope of the claims of the present application.

Claims

1. A broadband impedance spectroscopy cable defect location method based on improved Z transform, characterized in that: include: Step 1: Based on the equivalent distributed parameter circuit of the defective cable, the input impedance of each cable segment is regarded as the load impedance of the previous segment. The impedance spectrum of each segment is deduced from the end of the cable forward, and finally the broadband impedance spectrum of the cable head end is obtained. Step 2: Perform an improved Z-transform that takes spectrum leakage suppression into account on the broadband impedance spectrum of the defective cable headend. Convert the broadband impedance spectrum from the frequency domain to the time domain, and locate the cable defect by the peak in the time domain. The improved Z-transform considering spectrum leakage suppression is performed on the broadband impedance spectrum of the defective cable head end input, specifically: (30) Where, * Indicates that the data is conjugated; Improved Z transform result considering spectrum leakage suppression; X =2n-1, Δ=2k-1, X is the length of the window function; Δ is the shape parameter of the window function, and k is the serial number of the sampling point; y ( n ) is the frequency domain data of the broadband impedance spectrum input at the head end of the defective cable; n for y ( n ) count variable; A 0 is the starting sampling point on the spiral z The length of the vector radius is 0; θ 0 is the starting sampling point on the spiral line during Z transformation z A phase angle of 0; φ 0 is the sampling phase difference on the spiral line during Z transformation; W 0 is the stretching rate of the helix during the Z transformation; N is the number of data points of the discrete data signal processed by the Z transform; The starting sampling point on the spiral line during Z transform z Phase angle of 0 θ 0. Sampling phase difference on the spiral line during Z transform φ 0. Starting sampling point on the spiral line z 0 vector radius length A 0. The stretch rate of the helix during Z transformation W 0Specific details are as follows: (25) (26) (27) (28) Where, M is the kth sampling point during Z transform z k The number of data points; x max 、 x min , Δ x They are the maximum value, minimum value and resolution of the defect positioning interval respectively; floor means rounding down; f s is the sampling frequency of the Z transform; v is the propagation speed of electromagnetic waves in the cable; N is the number of data points of the discrete data signal processed by the Z transform.

2. The method for locating cable defects using broadband impedance spectroscopy based on improved Z-transform according to claim 1, characterized in that: Step 1 specifically includes: In the equivalent distributed parameter circuit containing defective cables, the position of the cable head end is recorded as x =0, the local defect is located at a distance from the cable head end l 1~ l 2 places, 0~ l 1 and l 2~ l The section is the normal cable; Make the cable end 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 is obtained from l arrive l 2 sections of cable l Impedance at 2 Z l2 , combined with the characteristic impedance of the defective cable Z d Obtain l Reflection coefficient at 2 Γ l2 ; according to Γ l2 、 Z d and the propagation coefficient of the defective cable γ d Find the cable l Impedance Z at 1 l1 , and Z l1 Equivalent to 0 to l The load impedance of a cable section is obtained l The reflection coefficient at point 1 is Γ l1 ; according to Γ l1 、 Z 0 and γ 0 Obtain the broadband impedance of the first end of the defective cable Z d , and then get Z d The spectrum that changes with frequency is used as the broadband impedance spectrum of the first end of the defective cable.

3. The method for locating cable defects using broadband impedance spectroscopy based on improved Z-transform according to claim 2, characterized in that: The characteristic impedance of the normal section cable Z 0 and the propagation coefficient of the normal section cable γ 0 is obtained from l arrive l 2 sections of cable l Impedance at 2 Z l2 , as follows: (13) The characteristic impedance of the cable with defective section Z d Obtain l Reflection coefficient at 2 Γ l2 , as follows: (14)。 4. The method for locating cable defects using broadband impedance spectroscopy based on improved Z-transform according to claim 2, characterized in that: The basis Γ l2 、 Z d and the propagation coefficient of the defective cable γ d Find the cable l Impedance Z at 1 l1 , as follows: (15) The Z l1 Equivalent to 0 to l The load impedance of a cable section is obtained l The reflection coefficient at point 1 is Γ l1 , as follows: (16)。 5. The method for locating cable defects using broadband impedance spectroscopy based on improved Z-transform according to claim 2, characterized in that: The basis Γ l1 、 Z 0 and γ 0 Obtain the broadband impedance of the first end of the defective cable Z d , as follows: (17)。 6. The method for locating cable defects using broadband impedance spectroscopy based on improved Z-transform according to claim 2, characterized in that: The propagation coefficient of the defective cable γ d , characteristic impedance of the defective section of the cable Z d The details are as follows: (18) in, R d 、 L d 、 G d and C d They are the distributed resistance, distributed inductance, distributed conductance and distributed capacitance at the defect; ω is the angular frequency of the input signal from the beginning of the cable to the end of the cable.

7. A broadband impedance spectroscopy cable defect location system based on improved Z transform, used to execute the method according to any one of claims 1 to 6, characterized in that: The system comprises: The impedance spectrum acquisition module is used to treat the input impedance of each cable segment as the load impedance of the previous segment based on the equivalent distributed parameter circuit of the defective cable, and deduce the impedance of each segment forward from the end of the cable to finally obtain the broadband impedance spectrum of the input of the defective cable head end; The defect location module is used to perform an improved Z-transform on the broadband impedance spectrum input at the head end of the defective cable, taking into account spectrum leakage suppression. The broadband impedance spectrum input at the head end of the defective cable is converted from the frequency domain to the time domain, and the cable defects are located by peaks 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 configured to operate according to the instructions to execute the steps of the method according to any one of claims 1 to 6.

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

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