A method for locating a fault in a buried cable under frozen ground

Abstract

The present application relates to the technical field of power cable fault location, and discloses a buried cable fault location method under frozen soil, comprising the following steps: obtaining temperature distribution data of frozen soil along the buried cable; determining the equivalent dielectric constant of frozen soil at each position along the cable based on the temperature distribution data; temperature compensation correction is made to the propagation speed of the traveling wave signal in the cable according to the equivalent dielectric constant to obtain the corrected propagation speed; a test signal is injected into the cable, the time difference between the transmitted signal and the fault point reflection signal is collected, and the fault point distance is calculated in combination with the corrected propagation speed. The present application explicitly proposes the concept of deep frozen soil correction factor and its calculation formula, automatically triggers secondary wave speed correction when the monitored freezing depth exceeds the preset threshold of 1.5 meters, considers the change effect of large-scale deep freezing on the electromagnetic boundary conditions around the cable, and makes up for the deficiency of correction only relying on single-point temperature of cable burial depth.

Description

Technical Field

[0001] This invention relates to the field of power cable fault location technology, specifically to a method for locating faults in buried cables under frozen soil. Background Technology

[0002] The accuracy of cable fault location directly affects power supply reliability and repair efficiency. Time-domain reflectometry (TDR), a classic cable fault location method, calculates the fault distance by injecting test pulses into the cable and measuring the time difference between the emitted and reflected pulses. However, the location accuracy of the TDR method is highly dependent on the accuracy of the traveling wave propagation speed in the cable, which is affected by the dielectric constant of the surrounding medium.

[0003] In permafrost environments, the dielectric constant of soil exhibits significant nonlinear characteristics with temperature changes. When the temperature drops below freezing, the unfrozen water content in the soil decreases and the proportion of ice phase increases, leading to a substantial change in the equivalent dielectric constant. Existing cable fault location technologies, such as the "TDR Power Cable Global Fault Location Method Based on Multi-Frequency Cooperative Excitation and Environmental Adaptive Correction" disclosed in patent document CN121069107A, although incorporating environmental parameter sensing and wave velocity correction mechanisms, primarily design their environmental models for conventional temperature and humidity conditions. They do not consider the dynamic impact of the unique ice-water phase transition process of permafrost on the dielectric constant, nor do they address the additional disturbance effect of freezing depth on electromagnetic field boundary conditions. This results in a significant increase in location errors under permafrost conditions, making it difficult to meet the actual engineering requirements for location accuracy.

[0004] Especially for low-voltage power cables of 380V and below, due to manufacturing standards and cost limitations, a metallic shielding layer is usually not installed. When using the time-domain reflectometry (TD-RS) method for fault location, the electromagnetic field carried by the traveling wave pulse injected into the cable penetrates the insulation sheath and diffuses outward, directly coupling with the permafrost medium surrounding the cable. In this case, the return path of the traveling wave signal depends on the surrounding soil, and the cable and permafrost constitute a composite transmission environment. The equivalent propagation speed of the traveling wave is simultaneously affected by both the cable insulation material and the dielectric properties of the surrounding permafrost. Changes in permafrost temperature cause changes in the unfrozen water content and the proportion of ice phase, resulting in a significant drift in the equivalent dielectric constant of the permafrost, directly causing a deviation in the traveling wave velocity and severely reducing fault location accuracy. This physical mechanism is particularly prominent in unshielded low-voltage cables and remains a technical challenge that current technology has not yet solved.

[0005] Therefore, there is an urgent need for a cable fault location method that can accurately characterize the quantitative relationship between the dielectric properties of frozen soil and temperature and freezing depth. Summary of the Invention

[0006] The present invention aims to solve the above-mentioned problems in the prior art and provide a cable fault location method that can accurately characterize the quantitative relationship between the dielectric properties of frozen soil and temperature and freezing depth, and dynamically and non-uniformly correct the traveling wave velocity.

[0007] This invention is achieved through the following technical solution:

[0008] A method for locating faults in buried cables under frozen soil includes the following steps:

[0009] Obtain temperature distribution data of frozen soil along the buried cable route;

[0010] Based on the temperature distribution data, the equivalent dielectric constant of the frozen soil at various locations along the cable route is determined;

[0011] Based on the equivalent dielectric constant, the propagation speed of the traveling wave signal in the cable is corrected by temperature compensation to obtain the corrected propagation speed.

[0012] A test signal is injected into the cable, the time difference between the transmitted signal and the reflected signal from the fault point is collected, and the distance to the fault point is calculated by combining the corrected propagation speed.

[0013] As an optimization, the temperature distribution data includes soil temperature values ​​at at least two depth layers to determine the freezing depth along the cable route; when the freezing depth exceeds a preset threshold, a depth correction factor is introduced to correct the propagation speed a second time.

[0014] As an optimization, the equivalent dielectric constant of the frozen soil satisfy:

[0015] ;

[0016] in, , , , The relative permittivity of soil particles, ice, unfrozen water, and air are respectively. , , , These are the volume fractions of the corresponding components; To account for the dielectric constant correction term in the dynamic process of the ice-water phase transition in permafrost, let be the permafrost temperature. With volumetric moisture content A function that satisfies: ; These are empirical correction coefficients; For temperature The volume content of unfrozen water under the given conditions was determined by the characteristic curve of unfrozen water content-temperature in frozen soil. This represents the volumetric water content of the frozen soil.

[0017] As an optimization, the model that performs temperature compensation correction on the propagation speed satisfies:

[0018] ;

[0019] in, The corrected traveling wave propagation velocity at position z along the cable axis. The speed of light in a vacuum Let f be a function of the equivalent relative permittivity of frozen soil. Let be the frozen soil temperature distribution function along the cable route. Let be the volumetric water content distribution function of frozen soil. For cable burial depth, This is the temperature compensation factor function.

[0020] As an optimization, the depth correction factor is a freeze depth correction coefficient. ,satisfy:

[0021] ;

[0022] in, This refers to the depth of permafrost freezing. For reference burial depth, The depth influence coefficient is used; the preset threshold is 1.5 meters.

[0023] As an optimization, the test signal is a multi-frequency test signal, including simultaneously injected high-frequency narrow pulses and low-frequency wide pulses. The high-frequency narrow pulses are used to improve the resolution of short-distance faults, and the low-frequency wide pulses are used to enhance the penetration capability and reflected signal strength of high-resistivity fault points.

[0024] As an optimization, it also includes: performing wavelet threshold denoising preprocessing on the acquired reflection signals, and using a deep learning model based on convolutional neural networks to perform fusion analysis on the multi-frequency pulse reflection features in order to identify the differences in reflection waveforms of different types of faults.

[0025] As an optimization, the methods for obtaining permafrost temperature distribution data include at least one of the following: distributed optical fiber temperature sensors deployed along the cable path, temperature probe arrays pre-embedded at different depths along the cable, and permafrost temperature prediction models based on the coupling of remote sensing data and ground temperature.

[0026] As part of the optimization, the following measures are also taken: establishing a database linking permafrost temperature and fault location accuracy; periodically collecting temperature distribution data and measured location data of known fault points during seasonal changes in permafrost; and adaptively optimizing the temperature compensation correction model and depth correction factor.

[0027] As an optimization, the buried cable is a low-voltage power cable with a rated voltage of 380V or below and no metal shielding layer, and the frozen soil type includes at least one of perennial frozen soil, seasonal frozen soil and island frozen soil.

[0028] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0029] This invention introduces a frozen soil temperature-dielectric constant correlation model and a temperature compensation factor to perform real-time, continuous, and non-uniform correction of traveling wave propagation velocity, effectively eliminating wave velocity offset errors caused by frozen soil temperature changes and significantly improving positioning accuracy. Simultaneously, when the freezing depth exceeds a preset threshold, a depth frozen soil correction factor is introduced for secondary correction, further compensating for the influence of deep freezing on electromagnetic field distribution. This invention is particularly suitable for low-voltage buried cables of 380V and below without metallic shielding.

[0030] This invention, based on the theory of multiphase component mixing in frozen soil, constructs a dielectric constant calculation model incorporating contributions from soil particles, ice, unfrozen water, and air, and adds a dielectric constant correction term reflecting the dynamic process of the ice-water phase transition. This model can accurately simulate the nonlinear evolution of the dielectric constant of frozen soil during freezing and thawing, providing a solid physical basis for wave velocity correction and filling the theoretical and engineering application gap in cable fault location in frozen soil environments. Furthermore, this invention fully considers the physical mechanism of electromagnetic field coupling between unshielded cables and frozen soil, solving the location problem caused by wave velocity variations with frozen soil conditions.

[0031] This invention explicitly proposes the concept and calculation formula of a deep permafrost correction factor. When a preset threshold such as a freezing depth exceeding 1.5 meters is detected, a secondary wave velocity correction is automatically triggered. This takes into account the effect of large-scale deep freezing on the electromagnetic boundary conditions around the cable, compensating for the shortcomings of relying solely on single-point temperature at the cable burial depth for correction. Examples show that under extreme conditions where the freezing depth exceeds 2 meters, introducing this correction factor can correct positioning errors from tens of meters to the meter level, ensuring that this method maintains excellent positioning performance in permafrost regions and extremely cold climates.

[0032] This invention employs a collaborative testing strategy that simultaneously injects high-frequency narrow pulses and low-frequency wide pulses: the high-frequency component ensures high-resolution localization of near-end and low-resistivity faults, while the low-frequency component, with its strong penetrating power, effectively captures the weak reflection signals of high-resistivity faults. Based on this, wavelet threshold denoising and convolutional neural networks are used to fuse and analyze the multi-frequency reflection features, automatically distinguishing the waveform differences between high-resistivity faults, open-circuit faults, and short-circuit faults. This solves the problem of complex impedance characteristics at fault points and low signal-to-noise ratio of reflected signals caused by water freezing in permafrost environments, making accurate interpretation difficult. This improves the accuracy and automation level of fault type identification.

[0033] This invention establishes a database linking frozen soil temperature and fault location accuracy. During seasonal freeze-thaw cycles, the model is periodically self-calibrated using known location points (such as cable joints), and relevant parameters in the temperature compensation factor function are dynamically optimized. This closed-loop adaptive optimization mechanism enables the wave velocity correction model to continuously approximate the true physical response under specific regional and soil conditions. With the accumulation of operational data, the location accuracy will be continuously improved, effectively extending the applicability and accuracy of this technical solution throughout its entire lifecycle. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention and should not be considered as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort. In the drawings:

[0035] Figure 1 This is a schematic diagram of the overall process of a method for locating faults in buried cables under frozen soil according to the present invention.

[0036] Figure 2 This is a schematic diagram of the structure of the multiphase component mixing model of frozen soil in this invention;

[0037] Figure 3 This is a characteristic curve of the change of unfrozen water content in frozen soil with temperature in an embodiment of the present invention;

[0038] Figure 4 The temperature compensation factor function in this invention A schematic diagram of the curve;

[0039] Figure 5 The deep permafrost correction factor in this invention With freezing depth Relationship curve diagram;

[0040] Figure 6 This is a schematic diagram of the multi-frequency test signal injection and fault point reflection waveform in an embodiment of the present invention;

[0041] Figure 7 This is a schematic diagram of the temperature distribution of frozen soil along the cable and the segmented wave velocity calculation in an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of the present invention are only used to explain the present invention and are not intended to limit the present invention.

[0043] Example 1 discloses a method for locating faults in buried cables under frozen soil, such as... Figure 1 As shown, the following is a detailed description of each step of the technical solution of the present invention.

[0044] S1. Obtain temperature distribution data of frozen soil along the buried cable route.

[0045] First, obtain the temperature distribution data of the frozen soil along the route of the buried cable to be tested. The temperature distribution data includes soil temperature values ​​at at least two depth layers to determine the freezing depth along the cable route.

[0046] Specifically, the methods for obtaining temperature distribution data include at least one of the following: distributed optical fiber temperature sensors deployed along the cable path, temperature probe arrays pre-embedded at different depths along the cable, and permafrost temperature prediction models based on the coupling of remote sensing data and ground temperature.

[0047] In this embodiment, during cable laying, temperature-sensing optical fibers are simultaneously deployed along the cable laying path and connected to a distributed optical fiber temperature measurement system. This system, based on the Raman scattering principle, can acquire temperature data at real-time intervals per meter along the cable. Simultaneously, temperature probe array shafts are installed at regular intervals along the cable, with multiple temperature sensors at different depths installed in each shaft. For example, sensors are installed at depths of 0.5m, 1.0m, 1.5m, and the cable burial depth to obtain soil temperature values ​​at different depths.

[0048] The above method was used to obtain data on the distribution of frozen soil temperature at various locations and depths along the cable route.

[0049] S2. Based on the temperature distribution data, determine the equivalent dielectric constant of the frozen soil at each location along the cable.

[0050] Because low-voltage cables lack a metallic shielding layer, the traveling wave electromagnetic field leaks out and couples with the surrounding frozen soil medium. The equivalent dielectric constant of the cable-frozen soil system is directly affected by changes in the frozen soil composition and temperature. Therefore, by obtaining the equivalent dielectric constant of the frozen soil at various points along the cable route using a frozen soil temperature-dielectric constant correlation model, the traveling wave propagation velocity can be corrected in real-time in sync with the frozen soil condition, effectively eliminating positioning errors caused by changes in the dielectric properties of the frozen soil.

[0051] After obtaining the temperature distribution data, the equivalent dielectric constant of the frozen soil at various locations along the cable is determined based on this data.

[0052] Specifically, this step employs a dielectric constant calculation model based on the multiphase component mixing theory of frozen soil. Frozen soil is considered a multiphase composite medium composed of soil particles, ice, unfrozen water, and air, and its equivalent relative dielectric constant is determined by... Satisfy the following formula:

[0053] ;

[0054] in, , , , The relative permittivity of soil particles, ice, unfrozen water, and air are respectively. , , , These are the volume fractions of the corresponding components; To account for the dielectric constant correction term in the dynamic process of the ice-water phase transition in permafrost, let be the permafrost temperature. With volumetric moisture content A function that satisfies: ; This is an empirical correction factor, with a value ranging from 0.05 to 0.15; For temperature The volume content of unfrozen water under the given conditions was determined by the characteristic curve of unfrozen water content-temperature in frozen soil. The volumetric water content of frozen soil, and the dynamic process of ice-water phase transition, as follows: Figure 2 As shown, Figure 3 The unfrozen water content of frozen soil A schematic diagram showing the change with temperature T.

[0055] Based on the temperature distribution data obtained from S1, and combined with geological parameters such as soil type and volumetric water content in the area, the volume content of unfrozen water under the current temperature conditions is queried or calculated to determine the volume fraction of each component. Finally, the equivalent relative permittivity of the frozen soil at various locations along the cable route is calculated using the above formula.

[0056] S3. Based on the equivalent dielectric constant, the propagation speed of the traveling wave signal in the cable is corrected by temperature compensation to obtain the corrected propagation speed.

[0057] After obtaining the equivalent dielectric constant of the frozen soil, the propagation speed of the traveling wave signal in the cable is corrected by temperature compensation based on the equivalent dielectric constant to obtain the corrected propagation speed.

[0058] Specifically, the traveling wave velocity correction model used in this step satisfies the following formula:

[0059] ;

[0060] in, The corrected traveling wave propagation velocity at position z along the cable axis. The speed of light in a vacuum Let f be a function of the equivalent relative permittivity of frozen soil. Let be the frozen soil temperature distribution function along the cable route. Let be the volumetric water content distribution function of frozen soil. For cable burial depth, This is the temperature compensation factor function. Figure 4 Temperature compensation factor A schematic diagram showing the relationship between temperature T and temperature.

[0061] The temperature compensation factor function The following formula must be satisfied (when temperature T ≤ freezing temperature). hour):

[0062] ;

[0063] in: This is the temperature sensitivity coefficient, with a value ranging from 0.005 to 0.02. This refers to the freezing temperature of permafrost. For reference temperature, when At that time, the permafrost was in an unfrozen state. That is, no temperature compensation correction is performed.

[0064] Based on the equivalent dielectric constant of the frozen soil calculated by S2 and the temperature distribution data obtained by S1, the corrected traveling wave propagation velocity is calculated by substituting them into the above formula.

[0065] S4. Inject a test signal into the cable, collect the time difference between the transmitted signal (i.e., the injected test signal) and the reflected signal from the fault point, and calculate the distance to the fault point in conjunction with the corrected propagation speed.

[0066] After obtaining the corrected propagation speed, a test signal is injected into the buried cable under test, the time difference between the transmitted signal and the reflected signal at the fault point is collected, and the distance to the fault point is calculated in combination with the corrected propagation speed.

[0067] Specifically, the test signal mentioned in this step is a multi-frequency test signal, including simultaneously injected high-frequency narrow pulses and low-frequency wide pulses. Among them, the high-frequency narrow pulse (frequency of 1MHz to 5MHz) is used to improve the resolution of short-distance faults, and the low-frequency wide pulse (frequency of 50kHz to 100kHz) is used to enhance the penetration capability and reflected signal strength of high-resistivity fault points.

[0068] At the cable end, a time-domain reflectometer capable of generating multi-frequency coordinated signals is used to simultaneously inject high-frequency narrow pulses and low-frequency wide pulses into the cable. The reflected waveforms are then acquired using an oscilloscope or other acquisition equipment.

[0069] To improve signal quality and accurately identify fault types, this step also includes preprocessing the acquired reflected signals with wavelet threshold denoising and using a deep learning model based on convolutional neural networks to fuse and analyze the multi-frequency pulse reflection features, so as to automatically distinguish the differences in reflected waveforms between high-resistance faults, open-circuit faults and short-circuit faults.

[0070] The time difference between the transmitted pulse and the reflected pulse at the fault point is accurately read from the processed reflected waveform. Then, the distance to the fault point is calculated based on the propagation speed v(z) calibrated by S3.

[0071] Considering that the wave velocity at different locations along the cable may vary due to uneven temperature distribution, the cable is divided into several segments. The corrected traveling wave velocity of the i-th segment is... The time difference of the round-trip propagation of the multi-frequency test signal in the i-th cable segment is The distance from the fault point to the test end Satisfy the following formula:

[0072] ;

[0073] n is the number of segments along the cable. When the temperature distribution along the cable is uniform, the above formula simplifies to: .like Figure 7 The diagram shown is a schematic diagram of the temperature distribution of frozen soil along the cable route and the calculation of segmented wave velocity.

[0074] S5. A deep permafrost correction factor is introduced for secondary correction.

[0075] The temperature distribution data obtained in S1 includes soil temperature values ​​at at least two depth layers, which can be used to determine the freezing depth along the cable route. When the freezing depth exceeds a preset threshold, a depth correction factor is introduced to perform a secondary correction on the propagation velocity obtained in step three.

[0076] Specifically, the preset threshold is 1.5 meters. When the freezing depth... When the depth exceeds 1.5 meters, a secondary correction of the deep permafrost is triggered.

[0077] The depth correction factor is the freeze depth correction coefficient. It satisfies the following formula:

[0078] ;

[0079] in, This refers to the depth of permafrost freezing. For reference burial depth, a value of 1.0 meter is used. The depth of influence coefficient ranges from 0.03 to 0.08. Figure 5 Depth correction factor (Also known as the deep permafrost correction factor) and freezing depth A diagram illustrating the relationship between the two.

[0080] Final propagation speed after second correction Substituting the corrected speed into the fault distance calculation formula in step four yields a more accurate positioning result.

[0081] To further improve the long-term applicability and accuracy of this method, this embodiment also includes: S6, an adaptive optimization step.

[0082] Specifically, a database linking permafrost temperature and fault location accuracy should be established. During seasonal changes in permafrost (e.g., the winter permafrost development period), data on the distribution of permafrost temperature along the cable route and measured location data of known fault points or known locations (e.g., cable joints) should be collected regularly.

[0083] The temperature compensation correction model was self-calibrated using the above data. The deviations between the positioning results and the actual positions at different temperatures and freezing depths were recorded, and the temperature compensation factor function was updated and fine-tuned accordingly. Temperature sensitivity coefficient in Depth influence coefficient of depth correction factor Through this closed-loop adaptive optimization mechanism, the model parameters continuously approximate the actual physical properties under specific soil conditions in the region.

[0084] In some embodiments, the method of the present invention is particularly applicable to low-voltage power cables with a rated voltage of 380V and below and no metallic shielding. The frozen soil temperature distribution data includes soil temperature values ​​at four depths: 0.5m, 1.0m, 1.5m below ground level, and at the cable burial depth, wherein the cable burial depth is 0.8m to 2.5m. Because this type of cable lacks a metallic shielding layer, the traveling wave electromagnetic field penetrates the insulating sheath and couples directly with the surrounding frozen soil medium. The cable and frozen soil constitute a composite transmission environment, and the traveling wave velocity is simultaneously affected by both the cable insulation material and the dielectric properties of the surrounding frozen soil. The temperature compensation correction and depth secondary correction mechanism of the present invention can effectively solve this technical problem.

[0085] Furthermore, this invention is applicable to various types of permafrost, including at least one of perennial permafrost, seasonal permafrost, and island permafrost.

[0086] The invention will now be illustrated through specific examples.

[0087] Case 1: Typical Implementation Process for Cable Fault Location in Seasonally Frozen Soil Areas

[0088] This embodiment describes the specific process of fault location for a 380V cross-linked polyethylene (XLPE) insulated unshielded low-voltage power cable buried at a depth of 0.8 meters in a seasonally frozen soil region.

[0089] Step S1: Obtain frozen soil temperature distribution data.

[0090] During cable laying, a temperature-sensing optical fiber is laid synchronously along the cable path and connected to a distributed optical fiber temperature measurement system. This system, based on the Raman scattering principle, can acquire temperature data at real-time intervals per meter along the cable. In this embodiment, the temperature-sensing optical fiber is laid in a bundled manner close to the cable's outer sheath, directly acquiring the soil temperature at the cable's burial depth.

[0091] During cable laying, a temperature-sensing optical fiber is laid synchronously along the cable path and connected to a distributed optical fiber temperature measurement system. This system, based on the Raman scattering principle, can acquire temperature data at real-time intervals per meter along the cable. In this embodiment, the temperature-sensing optical fiber is laid in a bundled manner close to the cable's outer sheath, directly acquiring the soil temperature at the cable's burial depth.

[0092] Meanwhile, in order to obtain temperature profiles at different depths, a temperature probe array shaft was installed every 500 meters along the cable route. Each shaft was equipped with four platinum resistance temperature sensors (accuracy ±0.1℃) at depths of 0.5m, 1.0m, 1.5m underground, and at the cable burial depth (1.2m).

[0093] At the detection time in this embodiment, the average temperature along the cable was measured to be -5.2℃ using a distributed fiber optic temperature measurement system. The temperature distribution at each layer obtained by the temperature probe array was: -2.1℃ at 0.5m, -4.5℃ at 1.0m, -5.2℃ at 1.2m, and -4.8℃ at 1.5m. This data indicates that the cable line was frozen and that seasonal permafrost existed.

[0094] Step S2: Calculate the equivalent relative permittivity of frozen soil.

[0095] Based on the dielectric constant model of the multiphase component mixing theory of frozen soil, the equivalent relative dielectric constant of frozen soil at various locations along the cable route is calculated. In this embodiment, the soil type along the cable route is silty clay, and its saturated volumetric water content is... The relative permittivity of soil particles is approximately 0.35. Take 4.5 as the relative permittivity of ice. Take 3.2 as the relative permittivity of unfrozen water. Take 82 (at -5°C) as the relative permittivity of air. Take 1.0.

[0096] Based on the measured temperature Query the unfrozen water content-temperature characteristic curve of the silty clay to determine the current unfrozen water volume content. It is approximately 0.08. At this point, the volume fraction of ice is... It was calculated from the phase transition.

[0097] Calculate the volume fraction:

[0098] (Converted from soil dry density);

[0099] ;

[0100] ;

[0101] (Calculated by subtracting the volume of water and ice from the porosity).

[0102] Substitute into the formula to calculate Base value:

[0103] .

[0104] Calculate the correction term according to the formula. :

[0105] Take the empirical correction coefficient ,but .

[0106] Finally, the equivalent relative permittivity of the frozen soil was obtained. .

[0107] Step S3: Construct and apply the traveling wave velocity correction model.

[0108] First, calculate the base wave velocity. If permafrost temperature correction is not considered, the traditional method would directly take... .

[0109] However, this invention introduces a temperature compensation factor. .for Take the freezing temperature Reference temperature Temperature sensitivity coefficient Calculate according to the formula:

[0110] .

[0111] Therefore, the corrected traveling wave propagation speed .

[0112] Step S4: Multi-frequency test signal injection and fault distance calculation.

[0113] At the cable end, a time-domain reflectometer (TDR) capable of generating multi-frequency coordinated signals is used to inject test signals into the cable. In this embodiment, a 1MHz high-frequency narrow pulse (pulse width 1μs) and an 80kHz low-frequency wide pulse (pulse width...) are injected simultaneously. ).

[0114] like Figure 6 As shown, the oscilloscope acquired the reflected waveform, which, after wavelet threshold denoising preprocessing, was fed into a pre-trained convolutional neural network model for feature fusion analysis. The model automatically identified a high-resistivity fault feature (water ingress and freezing at the joint) approximately 580 meters from the test end. Since this cable lacks a metallic shielding layer, the traveling wave signal loop relies on the surrounding soil, and the wave velocity shift effect caused by changes in frozen soil temperature is significant. After correction using this method, the positioning accuracy is greatly improved.

[0115] Accurately read the time difference between the transmitted pulse and the reflected pulse at the fault point from the high-frequency pulse reflection waveform: .

[0116] Based on the wave velocity calibrated in step S3 Considering that the soil temperature along the cable route is basically uniform, the entire cable is treated as one section. Perform the calculation:

[0117] .

[0118] On-site excavation verified that the actual fault point was located 579.8 meters from the test end, with a positioning error of only 0.3 meters and a relative error of less than 0.05%. However, if the traditional fixed wave velocity method were used (assuming an unfrozen soil dielectric constant of approximately 15 and a wave velocity of approximately 77.5), the error would be significantly lower. The calculated fault distance is 516.2 meters, with an error exceeding 60 meters, which will greatly increase the cost of excavation and emergency repair.

[0119] Step S5: Secondary correction of the deep permafrost correction factor.

[0120] In this embodiment, the measured maximum freezing depth is approximately 1.2 meters, which does not exceed the preset threshold of 1.5 meters. Therefore, the secondary correction of the depth-permafrost correction factor is not triggered. However, in another measurement scenario, the freezing depth... Reaching 1.8 meters, reference burial depth Depth of influence coefficient Then, based on the calculated correction coefficient... At this point, the wave speed in step S3... It needs to be multiplied by this correction factor, that is This is to compensate for the combined effects of deep permafrost on the distribution of electromagnetic fields.

[0121] Step S6: Adaptive optimization of the model.

[0122] During the winter permafrost development period, this method is periodically (once a week) self-verified using cable joints at known locations (as known "fault points"). The deviations between the positioning results and the actual locations at different temperatures and freezing depths are recorded, and the temperature sensitivity coefficient in the temperature compensation factor function is updated and fine-tuned. and depth of influence coefficient This constructs a database linking frozen soil temperature and fault location accuracy, enabling model parameters to continuously approximate the true physical properties of the soil in the region, thus achieving adaptive optimization.

[0123] It should be noted that, since the fault location of 380V low-voltage cables still needs to be accurately located after the coarse measurement, after the fault distance is output in step S4, this invention can be used in conjunction with the step voltage method or the acoustic-magnetic synchronization method: the TDR coarse measurement result is used to narrow the search range, and then the step voltage method or the acoustic-magnetic synchronization method is used to accurately capture the fault point, forming a complete closed loop for low-voltage cable fault location.

[0124] Case 2: A process for locating high-resistivity faults in permafrost regions.

[0125] This embodiment describes the high-resistance fault location of a 380V unshielded low-voltage buried cable with a burial depth of 1.5 meters and a total length of 800 meters in a permafrost region of the Qinghai-Tibet Plateau.

[0126] Step S1 Supplement: Since there are no permanent temperature monitoring devices in this area, a permafrost temperature prediction model based on the coupling of remote sensing data and ground temperature is adopted. Inputting recent land surface temperature remote sensing inversion data (LST), snow depth data, and historical borehole ground temperature data, the model predicts an average temperature of -2.8℃ along the cable route and outputs the permafrost temperature distribution function along the route. .

[0127] Step S2 Supplement: According to geological survey data along the route, this area is permafrost soil with high ice content and gravel. When using the model for calculation, the unfrozen water content is extremely low (approximately 2%), and the dielectric constant is mainly contributed by ice and soil particles. The calculated values ​​are... It is approximately 6.5, significantly lower than that of seasonally frozen soil areas.

[0128] Step S4 Supplement: The fault type is a high-resistance fault, and its reflected pulse is very weak. This invention uses an 80kHz low-frequency wide pulse injection. Due to the long wavelength of the low-frequency signal, it has strong penetrating power and can pass through the high-resistance fault point (such as a partial conductor breakage caused by frost heave but not complete separation) to generate effective reflection. At the same time, a convolutional neural network is used to fuse and analyze the weak disturbances in the high-frequency channel and the wide and gentle reflection peaks in the low-frequency channel to accurately identify the fault reflection wave. The final calculated fault distance is 12.34km. After line inspection, it was found that the cable was damaged by frost heave at 12.15km, and the conductor was partially broken. The positioning accuracy is about 40% higher than the existing low-frequency pulse method. This result verifies the effectiveness of the method of this invention on unshielded low-voltage cables: the change in the dielectric properties of frozen soil affects the traveling wave speed through the cable-frozen soil composite transmission environment. The temperature compensation and multi-frequency fusion identification performed by this invention can significantly improve the fault location effect of low-voltage cables in frozen soil environments.

[0129] Case 3: Specific application scenarios of deep permafrost correction factor.

[0130] In a certain area of ​​Northeast China, a cable buried at a depth of 0.9 meters experienced an intermittent fault that was difficult to locate. The measurement was taken in January, when the temperature was extremely low, causing the frozen soil to freeze to a depth of 2.1 meters.

[0131] At this point, even though the cable is buried at a depth of only 0.9 meters, the soil beneath it is completely frozen, creating a unique structure where the cable is frozen from top to bottom. This structure has a far greater impact on the boundary conditions of the electromagnetic field than if only the surface layer is frozen. Therefore, although the cable's burial depth remains unchanged, a depth-based frozen soil correction factor must be introduced.

[0132] , ,Pick .

[0133] calculate .

[0134] After applying this factor, the wave velocity decreased from the initially corrected 85.5. Adjusted to 85.5 × 1.068 = 91.3 The final positioning distance was 405 meters. During on-site excavation, a cable insulation deformation fault caused by frozen soil compression was discovered at 403 meters. Without this secondary correction, the positioning result would be at 379 meters, a deviation of 26 meters, which would have led to excavation failure and subsequent blind, large-scale excavation.

[0135] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. 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.

Claims

1. A method for locating faults in buried cables under frozen soil, characterized in that, Includes the following steps: Obtain temperature distribution data of frozen soil along the buried cable route; Based on the temperature distribution data, the equivalent dielectric constant of the frozen soil at various locations along the cable route is determined; Based on the equivalent dielectric constant, the propagation speed of the traveling wave signal in the cable is corrected by temperature compensation to obtain the corrected propagation speed. A test signal is injected into the cable, the time difference between the transmitted signal and the reflected signal from the fault point is collected, and the distance to the fault point is calculated by combining the corrected propagation speed.

2. The method for locating faults in buried cables under frozen soil according to claim 1, characterized in that, The temperature distribution data includes soil temperature values ​​at at least two depth layers to determine the freezing depth along the cable route; when the freezing depth exceeds a preset threshold, a depth correction factor is introduced to correct the propagation speed.

3. The method for locating faults in buried cables under frozen soil according to claim 1, characterized in that, The equivalent dielectric constant of the frozen soil satisfy: ； in, , , , The relative permittivity of soil particles, ice, unfrozen water, and air are respectively. , , , These are the volume fractions of the corresponding components; To account for the dielectric constant correction term in the dynamic process of the ice-water phase transition in permafrost, let be the permafrost temperature. With volumetric moisture content A function that satisfies: ; These are empirical correction coefficients; For temperature The volume content of unfrozen water under the given conditions was determined by the characteristic curve of unfrozen water content-temperature in frozen soil. This represents the volumetric water content of the frozen soil.

4. The method for locating faults in buried cables under frozen soil according to claim 1, characterized in that, The model that performs temperature compensation correction on the propagation velocity satisfies: ； in, The corrected traveling wave propagation velocity at position z along the cable axis. The speed of light in a vacuum Let f be a function of the equivalent relative permittivity of frozen soil. Let be the frozen soil temperature distribution function along the cable route. Let be the volumetric water content distribution function of frozen soil. For cable burial depth, This is the temperature compensation factor function.

5. A method for locating faults in buried cables under frozen soil according to claim 2, characterized in that, The depth correction factor is the freeze depth correction coefficient. ,satisfy: ； in, This refers to the depth of permafrost freezing. For reference burial depth, The depth influence coefficient is used; the preset threshold is 1.5 meters.

6. The method for locating faults in buried cables under frozen soil according to claim 1, characterized in that, The test signal is a multi-frequency test signal, including simultaneously injected high-frequency narrow pulses and low-frequency wide pulses. The high-frequency narrow pulses are used to improve the resolution of short-distance faults, and the low-frequency wide pulses are used to enhance the penetration capability and reflected signal strength of high-resistivity fault points.

7. A method for locating faults in buried cables under frozen soil according to claim 6, characterized in that, It also includes: performing wavelet threshold denoising preprocessing on the collected reflection signals, and using a deep learning model based on convolutional neural networks to perform fusion analysis on the reflection features of multi-frequency pulses in order to identify the differences in reflection waveforms of different types of faults.

8. The method for locating faults in buried cables under frozen soil according to claim 1, characterized in that, The methods for obtaining permafrost temperature distribution data include at least one of the following: distributed optical fiber temperature sensors deployed along the cable path, temperature probe arrays pre-buried at different depths along the cable, and permafrost temperature prediction models based on the coupling of remote sensing data and ground temperature.

9. A method for locating faults in buried cables under frozen soil according to claim 1, characterized in that, It also includes: establishing a correlation database between permafrost temperature and fault location accuracy; periodically collecting temperature distribution data and measured location data of known fault points during the seasonal changes of permafrost; and adaptively optimizing the temperature compensation correction model and depth correction factor.

10. A method for locating faults in buried cables under frozen soil according to any one of claims 1-9, characterized in that, The buried cable is a low-voltage power cable with a rated voltage of 380V or below and no metal shielding layer, and the frozen soil type includes at least one of perennial frozen soil, seasonal frozen soil and island frozen soil.

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