Cable defect detection method and device based on time-frequency domain reflection method

Abstract

The application discloses a cable defect detection method and device based on a time-frequency domain reflection method, and the method comprises the following steps: obtaining the characteristic impedance of a cable under high frequency; establishing a cable transmission model containing a defect section, and calculating a cable transfer function based on the cable transmission model and the characteristic impedance of the cable; detecting the defect position of the cable based on a reference signal and the cable transfer function, wherein the reference signal is a preset Gaussian envelope linear adjustable frequency signal; and detecting the defect type of the cable based on the polarity change corresponding to the envelope region center of the envelope line. The cable defect detection method and device based on the time-frequency domain reflection method can detect the positioning of the cable defect and the type of the cable defect, thereby facilitating the investigation of the cable defect and reducing the difficulty of processing the cable defect.

Description

Technical Field

[0001] This invention relates to the field of cable defect detection technology, and in particular to a cable defect detection method and apparatus based on time-frequency domain reflection. Background Technology

[0002] The laying environment of submarine cables is complex and variable. Therefore, submarine cables are susceptible to failures caused by factors such as seabed structure, natural disasters, marine life, and ship anchors. Furthermore, submarine cables are located in a marine environment with high water pressure, high humidity, and high salinity. As the service life increases, defects may occur in local areas of submarine cables, such as deformation, external damage, water trees, or moisture in the joints. This leads to a decrease in the overall insulation of the submarine cable. If these defects are not detected and dealt with in time, they will gradually develop into failures, and in severe cases, they may even cause breakdown accidents.

[0003] Currently, cable defect detection is mostly based on time-domain reflectometry or frequency-domain reflectometry. However, cable defect detection based on time-domain reflectometry or frequency-domain reflectometry can only locate the defect, but cannot detect or identify the type of defect. This brings great inconvenience to the investigation of cable defects and also increases the difficulty of handling cable defects. Summary of the Invention

[0004] The purpose of this invention is to provide a cable defect detection method and apparatus based on the time-frequency domain reflection method, which can locate and detect cable defects and detect the type of cable defects, thereby facilitating the investigation of cable defects and reducing the difficulty of handling cable defects.

[0005] To achieve the above objectives, in a first aspect, the present invention provides a cable defect detection method based on time-frequency domain reflection, comprising:

[0006] To obtain the characteristic impedance of the cable at high frequencies;

[0007] A cable transmission model containing defective sections is established, and the cable transfer function is calculated based on the cable transmission model and the characteristic impedance of the cable.

[0008] Based on the reference signal and the cable transfer function, the defect location of the cable is detected. The reference signal is a preset Gaussian envelope linear tunable frequency signal.

[0009] The defect type of the cable is detected based on the polarity change corresponding to the center of the envelope region.

[0010] In a preferred embodiment of the present invention, obtaining the characteristic impedance of the cable at high frequencies includes:

[0011] Based on the equivalent distributed parameter circuit model of the cable, the characteristic impedance of the cable at high frequencies is calculated.

[0012] In a preferred embodiment of the present invention, the step of establishing a cable transmission model containing defective sections, and calculating the cable transfer function based on the cable transmission model and the characteristic impedance of the cable, includes:

[0013] Establish a cable transmission model containing defective sections;

[0014] Based on the cable transmission model and the characteristic impedance of the cable, the transfer functions at multiple reflection locations in the cable transmission model are calculated respectively.

[0015] The cable transfer function is calculated based on the transfer functions of the multiple reflection locations.

[0016] In a preferred embodiment of the present invention, the step of establishing a cable transmission model containing defective sections, and calculating the cable transfer function based on the cable transmission model and the characteristic impedance of the cable, includes:

[0017] Establish a cable transmission model containing defective sections;

[0018] The traveling wave method was used to locate defects in the cable transmission model, and the defect location results were obtained.

[0019] Based on the defect location results, the cable transmission model, and the characteristic impedance of the cable, the cable transfer function is calculated.

[0020] In a preferred embodiment of the present invention, before detecting the defect location of the cable based on the reference signal and the cable transfer function, the method further includes:

[0021] A Gaussian envelope linearly adjustable frequency signal is selected as a reference signal, and the corresponding parameters in the reference signal are adjusted according to the parameter information of the cable.

[0022] In a preferred embodiment of the present invention, detecting the defect location of the cable based on the reference signal and the cable transfer function includes:

[0023] Based on the reference signal and the cable transfer function, the corresponding envelope is obtained;

[0024] The location of defects in the cable can be detected using the envelope in the time domain.

[0025] In a preferred embodiment of the present invention, obtaining the corresponding envelope based on the reference signal and the cable transfer function includes:

[0026] Using the reference signal as the incident signal and the cable transfer function, the incident and reflected superimposed signal is calculated.

[0027] The corresponding envelope is obtained based on the incident and reflected superimposed signals.

[0028] In a preferred embodiment of the present invention, the step of calculating the incident and reflected superimposed signal using a reference signal as the incident signal and the cable transfer function includes:

[0029] The reflected signal is calculated using the reference signal as the incident signal and the cable transfer function.

[0030] The incident and reflected signals are summed to obtain the superimposed incident and reflected signals.

[0031] In a preferred embodiment of the present invention, obtaining the corresponding envelope based on the incident and reflected superimposed signals includes:

[0032] The Hilbert transform of the incident and reflected superimposed signals is obtained, and the corresponding magnitude is calculated to obtain the corresponding envelope.

[0033] Secondly, the present invention provides a cable defect detection device based on the time-frequency domain reflection method, comprising:

[0034] The acquisition module is used to obtain the characteristic impedance of the cable at high frequencies;

[0035] The model processing module is used to establish a cable transmission model containing defective sections, and to calculate the cable transfer function based on the cable transmission model and the characteristic impedance of the cable.

[0036] The defect location detection module is used to detect the defect location of the cable based on a reference signal and the cable transfer function, wherein the reference signal is a preset Gaussian envelope linear tunable frequency signal.

[0037] The defect type detection module is used to detect the defect type of the cable based on the polarity change corresponding to the center of the envelope region.

[0038] Compared with existing technologies, the cable defect detection method and apparatus based on time-frequency domain reflection of this invention have the following advantages:

[0039] This invention relates to a cable defect detection method and apparatus based on the time-frequency domain reflection method. By establishing a cable transmission model containing the defective section and obtaining the characteristic impedance of the cable, the cable transfer function is calculated. Using a preset Gaussian envelope linear tunable frequency signal as a reference signal, the location of the cable defect is detected based on the reference signal and the cable transfer function. Furthermore, based on the polarity change corresponding to the center of the envelope region, the type of cable defect is detected. This invention effectively realizes the location detection of cable defects and the detection of cable defect types, thereby facilitating the investigation of cable defects and reducing the difficulty of handling cable defects. Attached Figure Description

[0040] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments of the present invention will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 This is a flowchart illustrating the cable defect detection method based on the time-frequency domain reflection method provided in an embodiment of the present invention.

[0042] Figure 2 This is a schematic diagram of the cable equivalent distributed parameter circuit model provided in an embodiment of the present invention;

[0043] Figure 3 This is a schematic diagram of traveling wave reflection of a cable transmission model with a defective section provided in an embodiment of the present invention;

[0044] Figure 4 This is a schematic diagram of a Gaussian envelope linearly adjustable frequency signal provided in an embodiment of the present invention;

[0045] Figure 5 This is a schematic diagram illustrating the influence of different center frequencies on the time-domain waveform provided in an embodiment of the present invention;

[0046] Figure 6 This is a schematic diagram illustrating the effect of different pulse widths on time-domain waveforms provided in an embodiment of the present invention;

[0047] Figure 7 This is a schematic diagram illustrating the influence of different bandwidths on time-domain waveforms provided in an embodiment of the present invention;

[0048] Figure 8a This is a simulation location and identification result diagram corresponding to the increase in local characteristic impedance of a cable in simulation verification, provided by an embodiment of the present invention;

[0049] Figure 8bThis is a simulation location and identification result diagram corresponding to the reduction of local characteristic impedance of the cable in simulation verification, provided by an embodiment of the present invention;

[0050] Figure 8c This is a simulation location and identification result diagram corresponding to the cable over-resistance grounding in simulation verification provided by an embodiment of the present invention;

[0051] Figure 8d This is a simulation location and identification result diagram corresponding to a cable short circuit in simulation verification provided by an embodiment of the present invention;

[0052] Figure 8e This is a simulation positioning and identification result diagram corresponding to cable open circuit in simulation verification provided by an embodiment of the present invention;

[0053] Figure 9 This is a time-domain test waveform diagram of a 32000m submarine cable without noise reduction during experimental verification, provided by an embodiment of the present invention.

[0054] Figure 10 This is a time-domain test waveform diagram of a 32000m submarine cable after wavelet denoising in experimental verification, provided by an embodiment of the present invention.

[0055] Figure 11 This is a schematic diagram of the time-domain envelope results of a 32,000m submarine cable in experimental verification provided by an embodiment of the present invention;

[0056] Figure 12 This is a schematic diagram of the envelope positioning results of a 32,000m submarine cable in experimental verification provided by an embodiment of the present invention;

[0057] Figure 13 This is a structural block diagram of a cable defect detection device based on the time-frequency domain reflection method provided in an embodiment of the present invention. Detailed Implementation

[0058] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0059] Currently, cable defect detection is mostly based on time-domain reflectometry or frequency-domain reflectometry. However, cable defect detection based on time-domain reflectometry or frequency-domain reflectometry can only locate the defect, but cannot detect or identify the type of defect. This brings great inconvenience to the investigation of cable defects and also increases the difficulty of handling cable defects.

[0060] To address the problems in the prior art, this invention provides a cable defect detection method and apparatus based on time-frequency domain reflection, which can locate and detect cable defects and detect the type of cable defect, thereby facilitating the investigation of cable defects and reducing the difficulty of handling cable defects.

[0061] See Figure 1 , Figure 1 This is a schematic flowchart of the cable defect detection method based on the time-frequency domain reflection method provided in the embodiment of the present invention.

[0062] The cable defect detection method based on time-frequency domain reflection described in the embodiments of the present invention is applicable to the defect detection of conventional cables, and is also applicable to, and especially applicable to, the defect detection of submarine cables. It can also be applied to computer equipment.

[0063] Understandably, when performing cable defect detection, if a defect in the cable has developed into a fault, then the cable defect detection at that location can also be regarded as cable fault detection. Accordingly, the location of the cable defect at that location is the cable fault location, and the type of cable defect at that location is the cable fault type.

[0064] In one embodiment, the present invention provides a cable defect detection method based on time-frequency domain reflection, comprising the following steps:

[0065] Step S110: Obtain the characteristic impedance of the cable at high frequency.

[0066] In one embodiment, when a computer device obtains the characteristic impedance of a cable at high frequencies, it can do so based on the characteristic impedance of the cable at high frequencies input by the operator.

[0067] In one embodiment, when obtaining the characteristic impedance of a cable at high frequencies, the computer device can, according to, such as Figure 2 The equivalent distributed parameter circuit model of the cable shown is used to calculate the characteristic impedance of the cable at high frequencies.

[0068] Specifically, a cable is a typical transmission line. Based on transmission line theory, the transmission characteristics of signals in a power cable can be explained using this theory. When the cable length is much greater than the signal wavelength, the cable is used in a manner similar to... Figure 2 The distributed parameter circuit model shown indicates that, due to the skin effect and proximity effect, the resistance R (Ω / m) and inductance L (H / m) per unit length Δl of the cable can be approximated as:

[0069]

[0070]

[0071] The conductance G (S / m) and capacitance C (F / m) per unit length Δl of the cable can be expressed as:

[0072]

[0073] Where ω is the angular frequency, r c r s These are the cable core radius and the inner radius of the shielding layer, respectively, ρ c ρ s σ and ε represent the resistivity of the cable core and the resistivity of the shielding layer, respectively; μ0 is the permeability of vacuum; and σ and ε are the conductivity and dielectric constant of the dielectric, respectively.

[0074] According to Kirchhoff's laws... Figure 2 Analysis of the distributed parameter circuit model shown yields the following results:

[0075]

[0076] By solving the above differential equation, we can obtain the expressions for the voltage U and current I of the cable at a distance l from the beginning:

[0077]

[0078] Among them, U + e -γl U - e γl These represent the positive and negative directions of voltage wave propagation, respectively; γ is the propagation constant of the cable itself; and Z0 is the characteristic impedance of the cable, also known as the characteristic impedance.

[0079]

[0080]

[0081] At high frequencies, the characteristic impedance of a cable can be considered as the ratio of inductance L to capacitance C, and it is a constant value, i.e.:

[0082]

[0083] The propagation constant γ of the cable itself can be further expressed by the cable's attenuation constant α, phase constant β, and the fixed wave velocity v of the electromagnetic wave propagating in the cable as follows:

[0084]

[0085] In a uniform transmission line under high-frequency conditions, the expression for the wave velocity v of the cable is:

[0086]

[0087] Where, c0 = 3 × 10 8 m / s, where μ is the speed of electromagnetic wave propagation in a vacuum. r ε r These are the relative permeability and relative permittivity of the insulating material, respectively. It can be seen that under high-frequency conditions, the cable wave velocity is almost a unique constant value, mainly determined by the material properties of the cable itself.

[0088] Step S120: Establish a cable transmission model containing defective sections, and calculate the cable transfer function based on the cable transmission model and the characteristic impedance of the cable.

[0089] In one embodiment, when a computer device calculates the cable transfer function based on a cable transmission model and the characteristic impedance of the cable, the cable transfer function is calculated by analyzing the traveling wave propagation process based on the cable transmission model and the characteristic impedance of the cable.

[0090] Understandably, when there are no defective sections in the cable, the traveling wave is reflected only once at the cable end. Let the end reflection coefficient be ρ, then we have:

[0091]

[0092] Among them, Z L This represents the load impedance of the cable.

[0093] When the cable end is open-circuited (i.e., Z) L =∞), at which point ρ=1, total internal reflection will occur; correspondingly, the reflection coefficient Γ(ω) at the cable end or the cable transfer function H(ω) is:

[0094]

[0095] When a cable has a local defect, it will form an impedance discontinuity. According to the traveling wave theory, the traveling wave will undergo a series of reflections when it propagates in the cable, and the reflection coefficient at the beginning of the cable will also change accordingly.

[0096] In one embodiment, the established cable transmission model containing defective sections is as follows: Figure 3 As shown, Figure 3 The cable transmission model shown with defective sections is a single-defect cable transmission model with a length of l.

[0097] When calculating the cable transfer function based on the cable transmission model and the characteristic impedance of the cable, the traveling wave method can be used to locate defects in the cable transmission model and obtain the defect location results; based on the defect location results, the cable transmission model and the characteristic impedance of the cable, the cable transfer function is calculated.

[0098] Specifically, when using the traveling wave method for... Figure 3When locating the defective cable transmission model shown, only the result of a single reflection of the signal is needed to obtain the defect location result; in order to simplify the calculation, this embodiment only derives the single reflection process;

[0099] like Figure 3 As shown, the cable is analyzed in three segments, where l is the total length of the cable, l-l2 is the length of the first segment, l2-l1 is the length of the second segment, and l1 is the length of the third segment. The reflection coefficients at l1, l2, and l are ρ1, ρ2, and ρ, respectively. The formulas for calculating ρ1 and ρ2 are as follows:

[0100]

[0101]

[0102] Where Z1 is the characteristic impedance at the cable defect. As can be seen from the above calculation formula, ρ2 = -ρ1. Therefore, -ρ1 is used instead of ρ2 in subsequent calculations.

[0103] According to the formula for calculating ρ1, when the characteristic impedance at this location is greater than the characteristic impedance of the cable body, ρ1 is greater than 0, and a reflected signal with the same polarity as the incident signal will be generated at this location, that is, a positive polarity reflected wave will be generated; similarly, when the characteristic impedance at this location becomes smaller, ρ1 is less than 0, and a reflected signal with the opposite polarity to the incident signal will be generated at this location, that is, a negative polarity reflected wave will be generated.

[0104] In this embodiment, optionally, when calculating the cable transfer function based on the cable transmission model and the characteristic impedance of the cable, the transfer functions of multiple reflection positions in the cable transmission model can be calculated separately based on the cable transmission model and the characteristic impedance of the cable; and the cable transfer function can be calculated based on the transfer functions of the multiple reflection positions.

[0105] Furthermore, in this embodiment, the cable transfer function under the single-defect condition can be expressed as:

[0106]

[0107]

[0108]

[0109] H(ω)=H1(ω)+H2(ω)+H3(ω)

[0110] Where H1(ω) is the transfer function considering only the end reflection, H2(ω) is the transfer function considering only the reflection at the end l2 of the defect, H3(ω) is the transfer function considering only the reflection at the beginning l1 of the defect, and H(ω) is the overall transfer function.

[0111] In this embodiment, H1(ω), H2(ω), and H3(ω) are the transfer functions of multiple reflection positions in the cable transmission model, and H(ω) is the cable transfer function. The cable transfer function is calculated by summing the transfer functions of multiple reflection positions.

[0112] In one embodiment, by analyzing the traveling wave propagation process, the traveling wave method is used to locate the defects in the cable transmission model containing defective sections. This facilitates the calculation of the cable transfer function and makes the calculated cable transfer function more accurate. In turn, it is beneficial to locate and detect cable defects and detect the types of cable defects.

[0113] Furthermore, by calculating the transfer functions of multiple reflection locations in the cable transmission model, and then calculating the cable transfer function based on the transfer functions of multiple reflection locations, the method fully considers multiple different reflection locations in the cable, which makes the calculated cable transfer function more accurate. This, in turn, makes the location detection of cable defects and the detection of cable defect types more precise.

[0114] Step S130: Based on the reference signal and the cable transfer function, the defect location of the cable is detected. The reference signal is a preset Gaussian envelope linear tunable frequency signal.

[0115] In one embodiment, prior to step S130, the cable defect detection method based on time-frequency domain reflection of the present invention may further include the following steps:

[0116] The Gaussian envelope linearly tunable frequency signal used in the time-frequency domain reflection method is selected as the reference signal, and the corresponding parameters in the reference signal are adjusted according to the cable parameter information.

[0117] Understandably, the adjusted Gaussian envelope linearly adjustable frequency signal is the same as the Gaussian envelope linearly adjustable frequency signal.

[0118] In this embodiment, a Gaussian envelope linearly adjustable frequency signal is selected as the reference signal. The corresponding parameters in the reference signal can be adjusted according to the cable parameter information using a signal generator and an oscilloscope.

[0119] In this embodiment, the selected Gaussian envelope linearly tunable frequency signal can be as follows: Figure 4 As shown, its frequency band range can be arbitrarily adjusted, and its mathematical expression is:

[0120]

[0121] Where α determines the width of the reference signal, and α is inversely proportional to the pulse width, that is, the larger α is, the narrower the pulse width; β determines the frequency bandwidth of the reference signal, and β is linearly related to the bandwidth, that is, the larger β is, the wider the bandwidth, which can be regarded as the slope of the time-frequency distribution; ω0 is the center angular frequency, and its relationship with the center frequency f0 is ω0=2πf0; t0 is the center time of the adjustable frequency reference signal, and t is the time variable;

[0122] The time center t of the reference signal in the time domain s and the duration T of the pulse width s The calculation formula is as follows:

[0123]

[0124] The formulas for calculating the frequency center ωs and bandwidth bs of the reference signal in the frequency domain are as follows:

[0125]

[0126] Where S(ω) is the time-domain reference signal s(t) obtained by taking its Fourier transform, and its expression is:

[0127]

[0128] When selecting a reference signal, the center frequency f0 of the waveform and the pulse width T of the signal are determined based on the characteristics of the cable, such as its length and material. s bandwidth b s Adjustments can be made to account for the effects of different center frequencies, pulse widths, and bandwidths on the reference signal, as shown below. Figure 5 As shown in Figure 7, the parameters α and β of the reference signal s(t) can be calculated using the above formulas.

[0129]

[0130] The following explains the changes in the time-domain waveform of the reference signal in the time-frequency domain reflection method when different parameters of the reference signal are selected, and the waveform parameters that should be selected for the local defect location detection of cables. The parameter settings of the reference signal are mainly related to the length, material and attenuation factor of the cable. During detection, it is necessary to ensure the best time-frequency resolution for defect identification, so as to completely reflect the location information of the local defect and avoid waveform aliasing. At the same time, the attenuation loss of the reference signal in the cable should be minimized.

[0131] When the cable length is short, the center frequency f0 of the reference signal should be set higher to avoid waveform aliasing during signal propagation, thus ensuring complete defect differentiation. Conversely, when the cable length is long, the high-frequency components of the signal attenuate significantly during propagation. Using a reference signal with a high center frequency will result in extremely low energy reflection at the end. If the defect is far from the detection point, it may be undetectable due to energy loss. Therefore, for long-distance cables, a lower center frequency should be selected to minimize the impact of high-frequency signal loss and ensure detection of the entire cable.

[0132] Although higher center frequencies experience greater attenuation during propagation in cables, higher frequencies mean that the pulse width of the reference signal can be as small as possible, avoiding waveform aliasing. This results in higher spatial resolution of the waveform, allowing for better identification of subtle local defects in the cable. Therefore, in actual testing, the waveform parameters of the reference signal can be adjusted according to the specific conditions of the cable. Figure 5 ;

[0133] The center frequency also has a certain impact on the pulse width of the reference signal. When a fixed center frequency is selected, the larger the signal pulse width, the more oscillations the waveform will have. Conversely, when the signal pulse width is small, the number of waveform oscillations will decrease, and it may even cause distortion of the reference signal waveform. This is evident from the above. Figure 6 ;

[0134] The bandwidth of the reference signal is affected by both the signal pulse width and the center frequency. A larger bandwidth will cause frequency variations in the waveform in the time domain, meaning that the frequencies of the left and right halves of the waveform will change. This can be seen from... Figure 7 ;

[0135] To better locate and detect local defects in cables, the waveform of the reference signal should be kept as symmetrical as possible. As can be seen from the time-domain waveforms under different parameter settings, the center frequency needs to meet a certain frequency requirement and the signal pulse width needs to meet a certain time width requirement in order for the reference signal waveform to meet the requirements of good time-domain resolution of details. At the same time, the frequency bandwidth should not be too large, otherwise it will lead to waveform distortion.

[0136] In one embodiment, by adjusting the Gaussian envelope linearly tunable frequency signal, the detection and testing effect can be improved, so that the detection and testing effect can be optimized.

[0137] In one embodiment, when a computer device detects the location of a cable defect based on a reference signal and a cable transfer function, the corresponding envelope can be obtained based on the reference signal and the cable transfer function; the location of the cable defect can then be detected in the time domain using the envelope.

[0138] In this embodiment, optionally, when the computer device obtains the corresponding envelope based on the reference signal and the cable transfer function, the reference signal can be the incident signal and the cable transfer function, and the incident and reflected superimposed signal can be calculated; the corresponding envelope can be obtained based on the incident and reflected superimposed signal.

[0139] Furthermore, when calculating the incident and reflected superimposed signal using the reference signal as the incident signal and the cable transfer function, the reflected signal can be calculated using the reference signal as the incident signal and the cable transfer function; the incident and reflected superimposed signal can be calculated using the sum of the incident signal and the reflected signal; when obtaining the corresponding envelope based on the incident and reflected superimposed signal, the Hilbert transform of the incident and reflected superimposed signal can be applied, and the corresponding magnitude can be obtained to obtain the corresponding envelope.

[0140] Specifically, based on the cable transfer function described above, the reflected signal of the entire cable segment when the incident signal is the reference signal s(t) can be expressed as:

[0141] r(t) = IFFT[H(ω)·FFT(s(t))]

[0142] That is, the incident signal s(t) is transformed to the frequency domain by Fourier transform and multiplied with the cable transfer function H(ω), and then the whole is transformed by inverse Fourier transform to obtain the reflected signal r(t) in the time domain;

[0143] The incident and reflected superimposed signal is y(t) = s(t) + r(t). By taking the Hilbert transform of the incident and reflected superimposed signal y(t) and obtaining the corresponding magnitude, the envelope of the incident and reflected superimposed signal can be obtained. The formula for obtaining the envelope is as follows:

[0144] y up (t) = abs[Hilbert(y(t))]

[0145] y down (t) = -abs[Hilbert(y(t))]

[0146] Where abs represents modulo, y up (t) represents the upper envelope, y down (t) represents the lower envelope.

[0147] In one embodiment, when the defect location of a cable is detected using an envelope in the time domain, the peak value of the envelope is the defect location of the cable.

[0148] In one embodiment, the corresponding envelope can be obtained with great accuracy through the above method, and then the defect location of the cable can be detected with great accuracy in the time domain using the envelope, greatly improving the positioning and detection effect of cable defects.

[0149] Step S140: Based on the polarity change corresponding to the center of the envelope region, the defect type of the cable is detected.

[0150] In one embodiment, the cable defect / fault types include increased local characteristic impedance, decreased local characteristic impedance, transition resistance grounding, short circuit, and open circuit. The increased local characteristic impedance and decreased local characteristic impedance are cable defect types; the transition resistance grounding, short circuit, and open circuit are cable fault types. This is because when cable defect detection is performed, the defect in the cable has already developed into a fault, and therefore the detected type is the cable fault type.

[0151] In one embodiment, the polarity change corresponding to the center of the envelope region is the waveform corresponding to the cable defect / fault type. The waveforms corresponding to different cable defect / fault types are as follows: when the local characteristic impedance increases, the corresponding waveform is "left positive and right negative"; when the local characteristic impedance decreases, the corresponding waveform is "left negative and right positive"; when grounded through a transition resistor, the corresponding waveform is a unipolar negative peak; the waveform corresponding to a short circuit is a unipolar negative peak; and the waveform corresponding to an open circuit is a unipolar positive peak.

[0152] In one embodiment, the method of detecting the cable defect type by the polarity change corresponding to the center of the envelope region can accurately detect the cable defect / fault type.

[0153] The cable defect detection method based on the time-frequency domain reflection method of this invention has been verified by simulation. The following is a simulation verification example to illustrate the cable defect detection method based on the time-frequency domain reflection method of this invention.

[0154] This invention relates to a cable defect detection method based on the time-frequency domain reflection method. A 500m long 500kV oil-filled submarine cable with a single defect is used as the modeling and simulation object. Cable samples (numbered 1-5) in different states are set at a location of 200m, and numerical simulations are performed. The parameters are shown in the table below:

[0155]

[0156] It should be noted that when the location of a cable defect is detected, it means that the defect location is an impedance discontinuity point, and the type of impedance discontinuity point is the cable defect / fault type.

[0157] The parameters of the reference signal s(t) are set according to the above calculation formula, and the signal pulse width T is... s =8×10 -8 s, bandwidth b s =1MHz, center frequency f0 = 10MHz, center time t0 = 0.5μs, sampling frequency f s =200MHz;

[0158] To obtain the reflected signal in the simulated cable transmission model, the cable transfer function, i.e., the reflection coefficient at the cable's head end, is used for calculation. First, the fast Fourier transform of the input signal s(t) is obtained and convolved with the cable transfer function H(ω). Then, the result of the convolution is calculated using an inverse fast Fourier transform to obtain the time-domain waveform of the reflected signal r(t). The Hilbert transform of the incident and reflected superimposed signal y(t) is then obtained, and its magnitude is calculated to obtain the upper and lower envelopes y of the incident and reflected superimposed signal. up (t) and y down (t), and then the time-domain envelope result and envelope localization result of the reflected superimposed signal of cable models 1-5 are obtained, such as Figures 8a-8e As shown;

[0159] By combining the time-frequency domain reflection method with the envelope, the reflection characteristics of local defects can be defined. Since the maximum peak of the envelope corresponds to the time center of the reference signal, the judgment can be made based on the peaks and valleys on both sides of the axisymmetric line of the envelope and the envelope itself.

[0160] When the local capacitance decreases, the local characteristic impedance of the corresponding region increases, such as... Figure 8a As shown, a positive peak appears to the left of the envelope axis of symmetry and a negative peak appears to the right, i.e., "positive first and then negative";

[0161] When the local capacitance increases, the corresponding local characteristic impedance decreases, such as... Figure 8b As shown, a negative peak appears to the left of the envelope axis of symmetry and a positive peak appears to the right, i.e., "negative first, then positive";

[0162] When grounded through a transition resistor, such as Figure 8c As shown, a negative peak appears at the time center of the reflected wave at the center of the envelope, i.e., at the defect location;

[0163] When a short circuit fault occurs, such as Figure 8d As shown, a negative peak appears at the center of the envelope;

[0164] When an open circuit fault occurs, such as Figure 8e As shown, a positive peak appears at the center of the envelope, which is consistent with the reflection characteristics of the cable in the open circuit state at the beginning and end.

[0165] To experimentally verify this invention, the cable defect detection method based on the time-frequency domain reflection method was experimentally verified. A 500kV oil-filled submarine cable with a total length of 32,000m was used as the detection object. In actual engineering testing, the time-domain waveforms collected were as follows: Figure 9 As shown, after processing with the adaptive wavelet threshold denoising algorithm, the result is as follows: Figure 10 The time-domain waveform is shown; correspondingly, the time-domain envelope result obtained by applying the cable defect detection method based on the time-frequency domain reflection method of this invention is as follows. Figure 11 As shown, the corresponding envelope localization results are as follows: Figure 12 As shown;

[0166] Depend on Figure 11 The time-domain envelope results show that, since there are no defects in the middle of the submarine cable, only the characteristics of the cable's end are assessed. During the inspection, the oil-filled submarine cable was in a broken state, therefore the end was in an open-circuit state. Figure 11 The positive polarity at the mid-terminus is corroborated by the simulation results.

[0167] The aforementioned cable defect detection method based on time-frequency domain reflection is particularly suitable for defect detection in submarine cables. It calculates the cable transfer function by establishing a cable transmission model containing the defective section and obtaining the characteristic impedance of the cable. Using a preset Gaussian envelope linear tunable frequency signal as a reference signal, the method detects the location of the cable defect based on the reference signal and the cable transfer function. Furthermore, it detects the type of cable defect based on the polarity change corresponding to the center of the envelope region. This method effectively realizes the location detection of cable defects and the detection of cable defect types, thereby facilitating the investigation of cable defects and reducing the difficulty of handling cable defects.

[0168] In order to implement the methods corresponding to the above embodiments and achieve the corresponding functions and technical effects, a cable defect detection device based on the time-frequency domain reflection method is provided below.

[0169] See Figure 13 , Figure 13 This is a structural block diagram of a cable defect detection device based on the time-frequency domain reflection method provided in an embodiment of the present invention.

[0170] In one embodiment, the cable defect detection device based on the time-frequency domain reflection method of the present invention includes:

[0171] The acquisition module 210 is used to obtain the characteristic impedance of the cable at high frequencies;

[0172] The model processing module 220 is used to establish a cable transmission model containing defective sections, and to calculate the cable transfer function based on the cable transmission model and the characteristic impedance of the cable.

[0173] The defect location detection module 230 is used to detect the defect location of the cable based on a reference signal and the cable transfer function. The reference signal is a preset Gaussian envelope linear tunable frequency signal.

[0174] The defect type detection module 240 is used to detect the defect type of the cable based on the polarity change corresponding to the center of the envelope region.

[0175] The aforementioned cable defect detection device based on the time-frequency domain reflection method is particularly suitable for defect detection in submarine cables. It calculates the cable transfer function by establishing a cable transmission model containing the defective section and obtaining the characteristic impedance of the cable. Using a preset Gaussian envelope linear tunable frequency signal as a reference signal, it detects the location of the cable defect based on the reference signal and the cable transfer function. Furthermore, it detects the type of cable defect based on the polarity change corresponding to the center of the envelope region. This device effectively realizes the location detection of cable defects and the detection of cable defect types, thereby facilitating the investigation of cable defects and reducing the difficulty of handling cable defects.

[0176] In one embodiment, the acquisition module 210 may be specifically used for:

[0177] Based on the equivalent distributed parameter circuit model of the cable, the characteristic impedance of the cable at high frequencies is calculated.

[0178] In one embodiment, the model processing module 220 may be specifically used for:

[0179] Establish a cable transmission model containing defective sections;

[0180] Based on the cable transmission model and the characteristic impedance of the cable, the transfer functions at multiple reflection locations in the cable transmission model are calculated respectively.

[0181] The cable transfer function is calculated based on the transfer functions at multiple reflection locations.

[0182] In one embodiment, the model processing module 220 may be specifically used for:

[0183] Establish a cable transmission model containing defective sections;

[0184] The traveling wave method was used to locate defects in the cable transmission model, and the defect location results were obtained.

[0185] Based on the defect location results, cable transmission model, and characteristic impedance of the cable, the cable transfer function is calculated.

[0186] In one embodiment, the cable defect detection device based on the time-frequency domain reflection method of the present invention may further include:

[0187] The signal selection module is used to select a Gaussian envelope linear tunable frequency signal as a reference signal and adjust the corresponding parameters in the reference signal according to the cable parameter information.

[0188] In one embodiment, the defect location detection module 230 may be specifically used for:

[0189] Based on the reference signal and the cable transfer function, the corresponding envelope is obtained;

[0190] The location of cable defects can be detected using the envelope in the time domain.

[0191] In this embodiment, when the defect location detection module 230 obtains the corresponding envelope based on the reference signal and the cable transfer function, it can:

[0192] Using the reference signal as the incident signal and the cable transfer function, the superimposed incident and reflected signal is calculated.

[0193] The corresponding envelope is obtained based on the incident and reflected superimposed signals.

[0194] Optionally, when the defect location detection module 230 calculates the incident and reflected superimposed signal using the reference signal as the incident signal and the cable transfer function, it can:

[0195] The reflected signal is calculated using the reference signal as the incident signal and the cable transfer function.

[0196] The superimposed incident and reflected signals are calculated by summing the incident and reflected signals.

[0197] Optionally, when the defect location detection module 230 obtains the corresponding envelope based on the incident and reflected superimposed signals, it can:

[0198] Calculate the Hilbert transform of the incident and reflected superimposed signals, and obtain the corresponding magnitude to get the corresponding envelope.

[0199] The cable defect detection device based on the time-frequency domain reflection method described above can implement the cable defect detection method based on the time-frequency domain reflection method described above. For specific limitations and other details of the embodiments of the cable defect detection device based on the time-frequency domain reflection method described above, please refer to the content of the cable defect detection method based on the time-frequency domain reflection method described above; further details will not be repeated in the embodiments.

[0200] In the several embodiments provided by this invention, it should be understood that the disclosed apparatus and methods can also be implemented in other ways. The apparatus embodiments described above are merely illustrative; for example, the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods, and computer program products according to various embodiments of the invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in a block diagram and / or flowchart, and combinations of blocks in block diagrams and / or flowcharts, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0201] In addition, the functional modules in the various embodiments of the present invention can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0202] If the aforementioned functions are implemented as software functional modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0203] The above description is merely an embodiment of the present invention and is not intended to limit the scope of protection of the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. It should be noted that similar reference numerals 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.

[0204] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0205] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A cable defect detection method based on time-frequency domain reflection, characterized in that, include: To obtain the characteristic impedance of the cable at high frequencies; A cable transmission model containing defective sections is established, and the cable transfer function is calculated based on the cable transmission model and the characteristic impedance of the cable. Based on the reference signal and the cable transfer function, the defect location of the cable is detected. The reference signal is a preset Gaussian envelope linear tunable frequency signal. The step of detecting the defect location of the cable based on the reference signal and the cable transfer function includes: Based on the reference signal and the cable transfer function, the corresponding envelope is obtained; The location of defects in the cable can be detected using the envelope in the time domain. Obtaining the corresponding envelope based on the reference signal and the cable transfer function includes: Using the reference signal as the incident signal and the cable transfer function, the incident and reflected superimposed signal is calculated. The corresponding envelope is obtained based on the incident and reflected superimposed signals. The calculation of the incident and reflected superimposed signal using the reference signal as the incident signal and the cable transfer function includes: The reflected signal is calculated using the reference signal as the incident signal and the cable transfer function. The incident and reflected signals are summed to obtain the superimposed incident and reflected signals; The step of obtaining the corresponding envelope based on the incident and reflected superimposed signals includes: The Hilbert transform of the incident and reflected superimposed signals is obtained, and the corresponding magnitude is calculated to obtain the corresponding envelope. The defect type of the cable is detected based on the polarity change corresponding to the center of the envelope region.

2. The cable defect detection method based on time-frequency domain reflection method according to claim 1, characterized in that, Obtaining the characteristic impedance of the cable at high frequencies includes: Based on the equivalent distributed parameter circuit model of the cable, the characteristic impedance of the cable at high frequencies is calculated.

3. The cable defect detection method based on time-frequency domain reflection method according to claim 1, characterized in that, The process of establishing a cable transmission model containing defective sections, and calculating the cable transfer function based on the cable transmission model and the characteristic impedance of the cable, includes: Establish a cable transmission model containing defective sections; Based on the cable transmission model and the characteristic impedance of the cable, the transfer functions at multiple reflection locations in the cable transmission model are calculated respectively. The cable transfer function is calculated based on the transfer functions of the multiple reflection locations.

4. The cable defect detection method based on time-frequency domain reflection method according to claim 1, characterized in that, The process of establishing a cable transmission model containing defective sections, and calculating the cable transfer function based on the cable transmission model and the characteristic impedance of the cable, includes: Establish a cable transmission model containing defective sections; The traveling wave method was used to locate defects in the cable transmission model, and the defect location results were obtained. Based on the defect location results, the cable transmission model, and the characteristic impedance of the cable, the cable transfer function is calculated.

5. The cable defect detection method based on time-frequency domain reflection method according to claim 1, characterized in that, Before detecting the defect location of the cable based on the reference signal and the cable transfer function, the method further includes: A Gaussian envelope linearly adjustable frequency signal is selected as a reference signal, and the corresponding parameters in the reference signal are adjusted according to the parameter information of the cable.

6. A cable defect detection device based on the time-frequency domain reflection method, characterized in that, include: The acquisition module is used to obtain the characteristic impedance of the cable at high frequencies; The model processing module is used to establish a cable transmission model containing defective sections, and to calculate the cable transfer function based on the cable transmission model and the characteristic impedance of the cable. The defect location detection module is used to detect the defect location of the cable based on a reference signal and the cable transfer function, wherein the reference signal is a preset Gaussian envelope linear tunable frequency signal. The step of detecting the defect location of the cable based on the reference signal and the cable transfer function includes: Based on the reference signal and the cable transfer function, the corresponding envelope is obtained; The location of defects in the cable can be detected using the envelope in the time domain. Obtaining the corresponding envelope based on the reference signal and the cable transfer function includes: Using the reference signal as the incident signal and the cable transfer function, the incident and reflected superimposed signal is calculated. The corresponding envelope is obtained based on the incident and reflected superimposed signals. The calculation of the incident and reflected superimposed signal using the reference signal as the incident signal and the cable transfer function includes: The reflected signal is calculated using the reference signal as the incident signal and the cable transfer function. The incident and reflected signals are summed to obtain the superimposed incident and reflected signals; The step of obtaining the corresponding envelope based on the incident and reflected superimposed signals includes: The Hilbert transform of the incident and reflected superimposed signals is obtained, and the corresponding magnitude is calculated to obtain the corresponding envelope. The defect type detection module is used to detect the defect type of the cable based on the polarity change corresponding to the center of the envelope region.

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