A cable overheat online positioning method and system based on broadband impedance spectrum

Abstract

The application discloses a kind of cable overheat online positioning method and system based on wideband impedance spectrum, belong to power system equipment state monitoring and fault location technical field.The method of the present application is by in the first end of the cable to be measured through protection device access measurement / excitation device, wideband frequency sweep excitation is applied and the input impedance spectrum of cable first end is synchronously collected;After the impedance spectrum is handled by window function to suppress spectrum leakage, inverse fourier transform is carried out to obtain time domain reflection response, and combined with signal propagation speed, it is mapped into distance positioning curve along cable;By comparing with the reference positioning curve under the normal operation state of cable, local abnormal index is constructed, and the determination and accurate positioning of local overheat fault are realized.The present application can realize early sensitive detection and high-precision positioning of local overheat defect under the condition that cable is not powered on, has the advantages of low false alarm rate and strong engineering adaptability, and can effectively improve the safety and efficiency of power cable operation and maintenance.

Description

Technical Field

[0001] This invention belongs to the field of power system equipment condition monitoring and fault location technology, specifically relating to an online cable overheating location method and system based on broadband impedance spectrum. Background Technology

[0002] With the continuous advancement of new power system construction, power cables, with their advantages of high power supply reliability, small footprint, and strong environmental adaptability, have seen a continuous increase in their application in urban power distribution networks, industrial parks, underground utility tunnels, and other scenarios, becoming a core device for power transmission. During long-term operation, power cables are prone to localized overheating due to problems such as poor core crimping, excessive joint contact resistance, external heat source intrusion, and installation defects. Localized overheating accelerates the thermal aging and decomposition of the cable insulation material, significantly shortening the cable's lifespan. In severe cases, it can lead to insulation breakdown, cable trench fires, causing large-scale power outages, equipment damage, and even casualties, posing a significant threat to the safe and stable operation of the power grid.

[0003] Currently, the industry commonly employs passive fire prevention measures to control cable overheating risks, such as fire-resistant sand filling, fire-resistant cable tray covering, and flame-retardant coating. These measures can only suppress the spread of flames after a fire has occurred and cannot achieve early identification and warning of overheating defects. Furthermore, passive protection structures severely hinder normal heat dissipation from the cable, exacerbating localized overheating and masking defects in the cable itself, significantly hindering routine maintenance and repair. Existing cable condition inspection methods mostly rely on offline detection and infrared thermography after power outages. These methods not only require coordinating complex power outage plans, significantly reducing power supply reliability, but also suffer from long detection cycles, inability to detect intermittent overheating defects, and insufficient detection capability for hidden overheated sections within the cable. They fail to meet the core maintenance requirements of the power grid for real-time cable condition awareness and early risk prevention. Therefore, developing an online detection technology capable of early, sensitive, and accurate location of localized overheating defects while the cable is operating without power interruption has become a critical technical problem urgently needing to be solved in the industry.

[0004] Currently, the traveling wave method is the most widely used technique in the industry for locating and detecting cable defects. According to the different signal analysis domains, it can be divided into two main categories: time domain reflection (TDR) and frequency domain reflection (FDR).

[0005] TDR (Time Delay Detection) calculates the defect location by injecting a narrow Gaussian pulse into the cable end and comparing the time delay difference between the incident pulse and the reflected pulse at the defect location. It boasts advantages such as simple operation and mature principles, and has found some application in offline fault detection. However, in practical engineering applications, TDR technology suffers from the following insurmountable technical shortcomings: First, the sensitivity of early defect detection is severely insufficient. The narrow pulse signal injected by TDR has limited effective high-frequency components, which can only identify obvious faults such as severe insulation deterioration and large impedance changes. However, early local overheating of the cable will only cause small changes in the local distributed parameters of the cable, and the corresponding impedance change is extremely small. TDR technology cannot capture such early defect signals at all and cannot achieve early warning of overheating risk. Second, the long-distance positioning accuracy is poor, and the ability to identify small defect segments is weak. When the pulse signal of TDR propagates in the cable, the high-frequency components will undergo significant attenuation and dispersion, causing the pulse signal to continuously broaden as it propagates along the cable. This not only greatly increases the positioning error of long-distance cables, but also completely drowns out the reflected signal of shorter local overheated segments (such as defect segments ranging from centimeters to meters), making it impossible to accurately locate local overheated defects. Third, it cannot be adapted to live-line testing scenarios. During the operation of the power grid, there are a large number of power frequency harmonics, transient interference from switching operations, corona discharge and other electromagnetic noise. The narrow pulse signal of the TDR is easily overwhelmed by strong electromagnetic interference, resulting in an extremely low signal-to-noise ratio during live measurement. Stable and effective measurement data cannot be obtained, and offline testing can only be performed when the cable is de-energized, which cannot meet the operation and maintenance requirements of real-time online monitoring.

[0006] FDR (Frequency Directional Reduction) acquires the broadband impedance spectrum of the cable head by injecting a broadband sweep signal into the cable head. Through frequency-to-time domain transformation, it obtains the impedance distribution characteristics along the cable, indirectly reflecting changes in local cable parameters. Compared to TDR (Time-Dependent Reduction) technology, it offers higher positioning accuracy and has become a research hotspot in the field of cable condition monitoring in recent years. However, existing FDR technology still suffers from the following key technical bottlenecks, failing to meet the core requirements of engineering-based online applications: First, it cannot achieve true online live-line testing. Most existing FDR (Fault-Responder) solutions are designed only for offline laboratory testing scenarios, without considering the high-voltage surges and strong electromagnetic interference in live power grid operation scenarios. They lack supporting high-voltage isolation, energy-limiting lightning protection, and anti-interference protection circuits. Directly connecting to live cables can lead to breakdown and damage to the measuring equipment, or even cause grounding faults in the power grid, seriously threatening the safety of equipment and power grid operation. Therefore, it is impossible to achieve long-term stable online operation in engineering sites. Second, the problem of spectral leakage is serious, making it difficult to balance positioning accuracy and detection sensitivity. Most existing FDR technologies directly perform inverse Fourier transform on the acquired impedance spectrum data without optimizing for finite-length spectral data, inevitably leading to serious spectral leakage. Excessive sidelobes can completely mask the weak reflection signals of localized minor overheating defects, resulting in missed defect detection. Furthermore, conventional fixed window function processing methods cannot achieve a flexible balance between time-domain positioning resolution and sidelobe suppression performance, making it difficult to simultaneously meet the dual requirements of large-area detection of long cables and high-precision positioning of localized defects. Third, the robustness of anomaly identification is poor, and the false alarm rate is high in engineering applications. Most existing FDR technologies only judge defects by the absolute change of impedance amplitude, without establishing standardized quantitative indicators for local anomalies. They are easily affected by factors such as fluctuations in cable load current, changes in ambient temperature, and differences in cable length. In actual engineering scenarios, the false alarm and missed alarm rates are high, and stable and reliable overheating defect identification cannot be achieved. Fourth, poor engineering adaptability and scalability. Most existing FDR technologies are laboratory prototypes for principle verification, with hardware architectures that are not modularized or standardized. They cannot adapt to the installation and deployment requirements of complex field environments such as substations and cable corridors, nor can they be seamlessly integrated with existing power grid online monitoring systems and operation and maintenance management platforms, making it difficult to achieve large-scale engineering applications.

[0007] In summary, existing cable overheating detection technologies cannot simultaneously meet the core requirements of "uninterrupted online operation, sensitive early defect identification, accurate overheating location, and stable engineering application," which severely restricts the ability to prevent and control cable overheating risks in advance. There is an urgent need to develop a cable local overheating online location technology solution that can adapt to the live operation scenario of the power grid, has high sensitivity, high positioning accuracy, and high engineering applicability. Summary of the Invention

[0008] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a cable overheating online location method and system based on broadband impedance spectrum. This method and system can realize early online detection and location of local overheating in operating cables, and has high sensitivity, low false alarm rate, adaptability to long cables, and good engineering feasibility. It is used to solve the technical problems that existing cable overheating detection technologies cannot simultaneously meet the requirements of uninterrupted online operation, sensitive early identification of minor defects, high-precision location of long cables, and engineering anti-interference.

[0009] The present invention adopts the following technical solution: A method for online location of cable overheating based on broadband impedance spectrum includes the following steps: S1. Connect the measuring / excitation device to the first end of the cable under test via a protection device; S2. The measurement / excitation device applies a sweep frequency signal to the cable under test within a preset sweep frequency range, and simultaneously acquires the input impedance at the beginning of the cable to obtain the input impedance spectrum. S3. Apply a window function to the input impedance spectrum to suppress spectral leakage; S4. Perform an inverse Fourier transform on the input impedance spectrum after window function processing to obtain the time-domain reflection response curve; S5. Based on the propagation speed of the swept frequency signal in the cable under test, map the time-domain coordinates of the time-domain reflection response curve to the spatial position coordinates along the cable length direction. This yields the distance positioning curve; S6. Compare the distance positioning curve with the reference distance positioning curve under normal operating conditions of the cable under test to obtain local anomaly indicators distributed along the spatial coordinates. ; S7, when the local abnormal indicators When the preset threshold is exceeded, it is determined that the cable under test has a local overheating fault, and the corresponding fault location coordinates are output.

[0010] Preferably, in step S2, the preset frequency sweep range is from 10kHz to 50MHz.

[0011] Preferably, in step S3, the window function is a Kaiser window, and the Kaiser window includes parameters. β By adjusting the parameters β It can balance temporal resolution and sidelobe suppression performance.

[0012] Preferably, in step S4, the inverse Fourier transform is a discrete inverse Fourier transform, specifically:

[0013] in, f ( t ) is the spectral density function F ( ω The time-domain function in the time domain. Angular frequency, The imaginary unit, This represents the time value corresponding to the time-domain sampling point output by the inverse Fourier transform.

[0014] Preferably, in step S5, the spatial location coordinates The mapping calculation method is as follows:

[0015] in, t This represents the time value corresponding to the time-domain sampling point output by the inverse Fourier transform. This represents the propagation speed of the swept frequency signal.

[0016] Preferably, the propagation speed of the swept frequency signal in the cable under test is... v =2.0×10 8 m / s.

[0017] Preferably, in step S6, the local anomaly index The calculation method is as follows:

[0018] in, This is the distance location curve for a localized overheating fault. This is the reference distance positioning curve for the cable under test during normal operation.

[0019] Preferably, in step S2, the number of frequency points of the sweep signal is set to 4096.

[0020] Preferably, in step S6, the reference distance positioning curve of the cable under test under normal operating conditions is obtained by processing the input impedance spectrum of the cable under test under normal operating conditions through window function and IFFT transformation.

[0021] Secondly, embodiments of the present invention provide an online cable overheating location system based on a broadband impedance spectrum, comprising: The signal generation module is used to generate a sweep frequency signal within a preset sweep frequency range; The signal acquisition module is used to acquire the input impedance signal at the beginning of the cable under test and perform digital processing. The synchronization and clock module is used to provide a synchronous clock reference with nanosecond-level time alignment accuracy for the signal generation module and the signal acquisition module; The protection / isolation device is equipped with lightning protection and isolation circuits to ensure safe access protection between the system and the live cable under test; The background analysis and storage unit is used to perform window function processing, inverse Fourier transform, local anomaly index calculation, fault judgment and location result output, and storage of measurement data and reference distance positioning curves on the collected input impedance spectrum.

[0022] Thirdly, a computer device includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described online cable overheating location method based on broadband impedance spectrum.

[0023] Fourthly, embodiments of the present invention provide a computer-readable storage medium including a computer program, which, when executed by a processor, implements the steps of the above-described online cable overheating location method based on broadband impedance spectrum.

[0024] Fifthly, a chip includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the steps of the above-described online cable overheating location method based on broadband impedance spectrum.

[0025] In a sixth aspect, embodiments of the present invention provide an electronic device, including a computer program, which, when executed by the electronic device, implements the steps of the above-described online cable overheating location method based on broadband impedance spectrum.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects: A method for online cable overheating location based on broadband impedance spectrum is proposed. This method utilizes a non-invasive protection device at the cable's head end, enabling detection without cable cutting or power outages, thus truly adapting to live-line operation scenarios. By employing a complete signal processing chain—including broadband impedance spectrum acquisition at the cable's head end, Kaiser window function spectrum optimization, fast inverse Fourier transform time-domain conversion, and time-domain coordinate to spatial coordinate mapping—it accurately captures minute impedance changes in the cable caused by localized overheating, solving the problem of missed detection of early overheating defects in existing technologies. Furthermore, by comparing the location curve with a baseline distance under normal cable operation, a local anomaly index is constructed, forming a standardized fault judgment logic. This provides a complete technical framework for subsequent parameter optimization, fundamentally solving the core challenge of existing technologies simultaneously achieving online detection, early identification, and precise location.

[0027] Furthermore, the preferred range for the preset sweep frequency is 10kHz to 50MHz, which is the core parameter ensuring high sensitivity and long-distance detection in this invention. The lower frequency limit of 10kHz ensures the propagation capability of the sweep signal in long cables, effectively avoiding excessive attenuation of high-frequency signals during cable propagation, and adapting to the detection needs of long-distance power distribution cables spanning several kilometers; the upper frequency limit of 50MHz ensures sufficient spatial positioning resolution, capable of capturing localized micro-overheating defects at the centimeter to meter level, solving the problem of poor positioning accuracy caused by insufficient high-frequency components in TDR technology, effectively avoiding the main frequency bands of power grid harmonics and transient interference from switching operations, and improving the signal-to-noise ratio in live detection scenarios; at the same time, it perfectly balances signal propagation distance and positioning accuracy.

[0028] Furthermore, the Kaiser window, as an adjustable window function, flexibly controls the main lobe width and side lobe attenuation by adjusting the β parameter, perfectly solving the problem that fixed window functions cannot balance resolution and anti-interference. This solution can be flexibly adapted to field conditions. In scenarios involving long cables and large-scale inspection, the β value can be reduced to improve time-domain resolution, while in scenarios involving short cables and high-precision inspection, the β value can be increased to enhance side lobe suppression, effectively preventing weak reflection signals from being masked and significantly improving the ability to identify early, minor overheating defects.

[0029] Furthermore, the inverse Fourier transform is the core bridge connecting the frequency domain impedance spectrum and the time domain reflection response. Only through precise transformation calculations can the frequency domain impedance characteristics collected at the cable head end be converted into a time domain reflection signal that reflects the impedance distribution along the cable, ultimately achieving defect location. This perfectly adapts to the rapid calculation requirements of hardware platforms such as FPGAs, ensuring the efficiency and accuracy of signal processing, providing reliable intermediate data support for subsequent coordinate mapping and location calculations, and improving the feasibility and stability of the technical solution.

[0030] Furthermore, the sweep frequency signal is emitted from the cable head end, reflected at the defect, and returns to the head end. The total distance the signal propagates is twice the round trip distance from the cable head end to the defect. Therefore, by calculating the propagation speed × time ÷ 2, the conversion from time-domain coordinates to the cable's spatial position can be accurately realized, perfectly matching the physical laws of electromagnetic wave propagation in the cable. This fundamentally eliminates systematic errors in positioning calculations and ensures the accuracy of the positioning results. At the same time, it provides a unified execution standard for positioning calculations, ensuring consistency and repeatability of positioning results under different cable models and different working conditions, and avoiding positioning deviations caused by fuzzy calculation logic.

[0031] Furthermore, the optimal value for the propagation speed was clarified, providing a fixed benchmark parameter for coordinate mapping calculations and avoiding positioning errors caused by ambiguous speed values. This value was verified by experiments in the embodiments, achieving a positioning result of 39.9m in the detection of defects at 40m on a 61m cable, with an absolute error of only 0.1m and a relative positioning accuracy of up to 0.25%. At the same time, this value is compatible with most commonly used cable models in engineering, eliminating the need for repeated on-site calibration for different cables and significantly reducing the workload of on-site deployment.

[0032] Furthermore, by adopting a relative amplitude ratio quantification method, compared with absolute difference calculation, baseline drift caused by factors such as differences in cable impedance distribution, load current fluctuations, and changes in ambient temperature can be effectively eliminated, fundamentally reducing the false alarm rate in engineering sites. At the same time, by processing absolute values, the quantification dimension of impedance changes is unified, which can accurately capture minute impedance changes caused by local overheating, greatly improving the sensitivity of early defect identification, providing a unified standard for quantifying the severity of overheating defects, and facilitating the setting of early warning thresholds and the classification of fault levels.

[0033] Furthermore, the number of sweep points directly determines the frequency domain sampling resolution. A higher number of sweep points results in a higher time domain resolution after IFFT transformation, leading to better spatial positioning accuracy. However, this also increases the complexity of hardware computation and reduces the real-time performance of detection. A sweep point count of 4096 points, a power of 2, perfectly matches the Fast Fourier Transform algorithm on hardware platforms such as FPGAs, significantly improving signal processing speed and ensuring real-time performance of online detection. Simultaneously, this number of sweep points is compatible with a sweep range of 10kHz-50MHz, enabling centimeter-level spatial resolution and precise capture of short-distance localized overheating defects.

[0034] Furthermore, the source and processing standards of the baseline curve were clarified, ensuring the consistency of the two comparison curves and fundamentally avoiding misjudgments caused by systematic errors. At the same time, the baseline curve was limited to the normal operating state of the cable under test, rather than a general standard curve, which perfectly adapts to cables of different lengths, models, and laying environments, eliminating detection errors caused by individual cable differences and greatly improving the accuracy and robustness of anomaly identification.

[0035] It is understood that the beneficial effects of the second to sixth aspects mentioned above can be found in the relevant descriptions in the first aspect mentioned above, and will not be repeated here.

[0036] In summary, this invention achieves highly sensitive online detection of localized cable overheating through wideband frequency sweeping and Kaiser window optimization; it solves the problems of large dispersion and high false alarm rate in long cables by utilizing time-domain-space mapping and difference algorithms. The system's integrated protection and isolation design combines engineering safety with practicality, significantly improving the intelligence level of power grid operation and maintenance.

[0037] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0038] Figure 1 This is a flowchart of the method of the present invention; Figure 2 Diagram of an online positioning test platform for locally overheated sections of power cables; Figure 3 This is a diagram showing the online location results of a locally overheated section of a power cable. Figure 4 A schematic diagram of a computer device provided in an embodiment of the present invention; Figure 5 This is a block diagram of a chip provided according to an embodiment of the present invention.

[0039] Among them, 1. Distribution box; 2. Single-phase voltage regulator; 3. Local overheating online positioning device; 4. Computer; 60. Computer equipment; 61. Processor; 62. Memory; 63. Computer program; 600. Electronic equipment; 610. Processing unit; 620. Storage unit; 6201. Random access memory unit; 6202. Cache memory unit; 6203. Read-only memory unit; 6204. Program / utility; 6205. Program module; 630. Bus; 640. Display unit; 650. Input / output interface; 660. Network adapter; 700. External device. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0042] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0043] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations. For example, A and / or B can represent three cases: A alone, A and B simultaneously, and B alone. Additionally, the character " / " in this invention generally indicates that the preceding and following objects have an "or" relationship.

[0044] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0045] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0046] The accompanying drawings illustrate various structural schematic diagrams according to embodiments disclosed in this invention. These drawings are not to scale, and some details have been enlarged for clarity, and some details may have been omitted. The shapes of the various regions and layers shown in the drawings, as well as their relative sizes and positional relationships, are merely exemplary and may deviate from reality due to manufacturing tolerances or technical limitations. Furthermore, those skilled in the art can design regions / layers with different shapes, sizes, and relative positions as needed.

[0047] This invention provides an online cable overheating location method based on broadband impedance spectrum. A broadband sweep excitation is applied to the cable end via a protection device to measure the amplitude and phase spectra of the input impedance. The frequency domain data is processed using a window function and subjected to inverse Fourier transform to obtain the time-domain reflection response, which is then mapped to spatial location using the propagation velocity. By comparing the results with the normal state, local anomaly indicators are calculated and judged to achieve sensitive detection and accurate location of local overheating. The device includes signal generation, acquisition, protection isolation, and background analysis units, supporting online, real-time positioning and data storage, suitable for engineering deployment and expansion integration. By injecting a swept-frequency signal at the cable end to obtain the wideband impedance spectrum at the cable end, and combining window function optimization and IFFT time-domain mapping, it can detect minute impedance changes caused by local overheating earlier and more sensitively and achieve high-precision positioning without cutting the cable core and under online operation conditions. At the same time, a protection device is introduced to achieve high-voltage isolation and energy-limiting protection, ensuring the safety and reliability of the equipment. The hardware adopts a modular digital-to-analog converter (DAC) / analog-to-digital converter (ADC) + field-programmable gate array (FPGA), which facilitates engineering deployment, expansion, and integration with other sensing systems, thereby significantly improving the reliability and operation and maintenance efficiency of online monitoring.

[0048] Please see Figure 1 This invention discloses an online cable overheating location method based on broadband impedance spectrum, comprising the following steps: S1, Protection Access The measurement / excitation device is connected to the cable head end via a protection device; the protection device is used to isolate the measurement channel and provide overvoltage / overcurrent protection, ensuring the safety of connection and measurement stability under online operating conditions.

[0049] S2, Frequency Sweep Excitation and Impedance Acquisition The measurement / excitation device applies a sweep frequency signal to the cable under test within a preset sweep frequency range and simultaneously acquires the input impedance at the cable end to obtain the input impedance spectrum.

[0050] In one embodiment, a frequency sweep excitation is applied within a frequency range of [10kHz, 50MHz] and the input impedance is measured, with the number of frequency points set to 4096. In an alternative embodiment, the frequency sweep method is either a linear sweep or a logarithmic sweep.

[0051] S3, Window Function Processing The input impedance spectrum is processed using a window function to suppress spectral leakage.

[0052] In one embodiment, a Kaiser window is employed, with adjustable Kaiser window parameter β, to balance temporal resolution and sidelobe suppression performance.

[0053] S4. Obtain the time-domain reflection response using IFFT transformation. In one embodiment, an inverse Fourier transform (IFFT) is performed on the input impedance spectrum after processing by a window function to obtain the time-domain reflection response curve.

[0054] The inverse Fourier transform is:

[0055] in, f ( t ) is the spectral density function F ( ω The time-domain function in the time domain.

[0056] S5. Mapping from time-domain coordinates to spatial coordinates Based on the propagation speed of the swept frequency signal in the cable under test, the time-domain coordinates of the time-domain reflection response curve are mapped to the spatial position coordinates along the length of the cable under test. This yields the distance positioning curve.

[0057] In one embodiment, time-domain coordinates are mapped to spatial locations. x The method is as follows:

[0058] in, t The time values ​​corresponding to the time-domain sampling points output by the IFFT. This represents the propagation speed of the swept frequency signal.

[0059] In a specific example, v =2.0×10 8 m / s.

[0060] S6. Construction of Abnormal Indicators Local anomaly indicators are obtained by comparing the positioning curve with the positioning curve during normal operation. .

[0061] In one implementation, local anomaly indicators for:

[0062] in, This is the distance location curve for a localized overheating fault. This is the reference distance positioning curve for the cable under test during normal operation.

[0063] The reference positioning curve can be pre-collected and stored by the cable under test under normal operating conditions.

[0064] S7, Fault Determination and Location Output When local abnormal indicators When the preset judgment conditions are met, it is determined that there is a local overheating fault in the cable, and the corresponding fault location is output.

[0065] In one embodiment, the preset determination condition is: when When a local overheating fault occurs at that location, the corresponding spatial coordinates are output. As a location result.

[0066] In another embodiment of the present invention, a cable overheating online location system based on broadband impedance spectrum is provided. This system can be used to implement the above-mentioned cable overheating online location method based on broadband impedance spectrum. Specifically, the cable overheating online location system based on broadband impedance spectrum includes a signal generation module, a signal acquisition module, a synchronization and clock module, a protection / isolation device, and a background analysis and storage unit.

[0067] The signal generation module is used to generate a sweep frequency signal within a preset sweep frequency range. The signal generation module includes a high-speed DAC (1 GSPS / 16 bit) and an FPGA, used to generate excitation signals with programmable frequency, amplitude, and timing.

[0068] The signal acquisition module is used to acquire the input impedance signal at the beginning of the cable under test and perform digital processing. The signal acquisition module includes a high-speed ADC (250 MSPS / 14 bit), an FPGA, and a local DDR cache. The FPGA implements digital filtering, triggering, denoising, and Ethernet framing. A synchronization module is used for multi-channel time / phase synchronization to provide nanosecond-level time alignment accuracy.

[0069] The synchronization and clock module is used to provide a synchronous clock reference with nanosecond-level time alignment accuracy for the signal generation module and the signal acquisition module; The protection / isolation device is equipped with lightning protection and isolation circuits to ensure safe access protection between the system and the live cable under test; The background analysis and storage unit is used to perform window function processing, inverse Fourier transform, local anomaly index calculation, fault judgment and location result output, and storage of measurement data and reference distance positioning curves on the collected input impedance spectrum.

[0070] An online cable overheating location system based on broadband impedance spectrum, comprising: Distribution box, The RG58 coaxial cable is connected to the distribution box via a switch and forms a single-phase circuit with the load. The heating band uses a temperature controller and thermocouples to monitor and control the cable surface temperature in real time, and is wrapped around the cable surface to simulate real cable overheating. The cable overheating online positioning device is connected to the cable head end via a protection device.

[0071] This invention provides a terminal device comprising a processor and a memory. The memory stores a computer program, which includes program instructions. The processor executes the program instructions stored in the computer storage medium. The processor may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. It is the computing and control core of the terminal, suitable for implementing one or more instructions, specifically suitable for loading and executing one or more instructions to achieve a corresponding method flow or function. The processor described in this embodiment can be used in the operation of a cable overheating online location method based on a broadband impedance spectrum, including: A measurement / excitation device is connected to the cable under test via a protection device at the cable end. The measurement / excitation device applies a sweep frequency signal to the cable under test within a preset sweep frequency range and simultaneously acquires the input impedance at the cable end to obtain the input impedance spectrum. The input impedance spectrum is processed by a window function to suppress spectral leakage. An inverse Fourier transform is performed on the windowed input impedance spectrum to obtain the time-domain reflection response curve. Based on the propagation speed of the sweep frequency signal in the cable under test, the time-domain coordinates of the time-domain reflection response curve are mapped to the spatial position coordinates along the length of the cable under test. The distance positioning curve is obtained; the distance positioning curve is compared with the reference distance positioning curve under normal operating conditions of the cable under test to obtain local anomaly indicators distributed along the spatial coordinates. When the local abnormal indicators When the preset threshold is exceeded, it is determined that there is a local overheating fault in the cable, and the corresponding fault location coordinates are output.

[0072] Please see Figure 4The terminal device is a computer device. In this embodiment, the computer device 60 includes a processor 61, a memory 62, and a computer program 63 stored in the memory 62 and executable on the processor 61. When executed by the processor 61, the computer program 63 implements the online cable overheating location method based on broadband impedance spectrum in this embodiment. To avoid repetition, details are omitted here. Alternatively, when executed by the processor 61, the computer program 63 implements the functions of each model / unit in the online cable overheating location system based on broadband impedance spectrum in this embodiment. To avoid repetition, details are omitted here.

[0073] Computer device 60 can be a desktop computer, laptop, handheld computer, cloud server, or other computing device. Computer device 60 may include, but is not limited to, a processor 61 and a memory 62. Those skilled in the art will understand that... Figure 4 This is merely an example of computer device 60 and does not constitute a limitation on computer device 60. It may include more or fewer components than shown, or combine certain components, or different components. For example, computer device may also include input / output devices, network access devices, buses, etc.

[0074] The processor 61 may be a Central Processing Unit (CPU), or other general-purpose processors, graphics processing units (GPUs), tensor processing units (TPUs), digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor.

[0075] The memory 62 can be an internal storage unit of the computer device 60, such as a hard disk or memory of the computer device 60. The memory 62 can also be an external storage device of the computer device 60, such as a plug-in hard disk, smart media card (SMC), secure digital (SD) card, flash card, etc. equipped on the computer device 60.

[0076] Furthermore, the memory 62 may include both internal storage units of the computer device 60 and external storage devices. The memory 62 is used to store computer programs and other programs and data required by the computer device. The memory 62 can also be used to temporarily store data that has been output or will be output.

[0077] Please see Figure 5 The terminal device is an electronic device 600, which is manifested in the form of a general-purpose computing device. The components of the electronic device may include, but are not limited to: at least one processing unit 610, at least one storage unit 620, a bus 630 connecting different platform components (including storage unit 620 and processing unit 610), a display unit 640, etc.

[0078] The storage unit stores program code, which can be executed by the processing unit 610 to perform the steps described in the method section of this specification according to various exemplary embodiments of the present invention. For example, the processing unit 610 can perform actions such as... Figure 1 The steps are shown in the figure.

[0079] Storage unit 620 may include readable media in the form of volatile storage units, such as random access memory (RAM) 6201 and / or cache memory 6202, and may further include read-only memory (ROM) 6203.

[0080] Storage unit 620 may also include a program / utility 6204 having a set (at least one) program module 6205, such program module 6205 including but not limited to: operating system, one or more application programs, other program modules and program data, each or some combination of these examples may include an implementation of a network environment.

[0081] Bus 630 can represent one or more of several types of bus structures, including a memory cell bus or memory cell controller, a peripheral bus, a graphics acceleration port, a processing unit, or a local bus using any of the multiple bus structures.

[0082] Electronic device 600 can also communicate with one or more external devices 700 (e.g., keyboard, pointing device, Bluetooth device, etc.), and with one or more devices that enable a user to interact with electronic device 600, and / or with any device that enables electronic device 600 to communicate with one or more other computing devices (e.g., router, modem). This communication can be performed via input / output interface 650. Furthermore, electronic device 600 can also communicate with one or more networks (e.g., local area network, wide area network, and / or public network, such as the Internet) via network adapter 660. Network adapter 660 can communicate with other modules of electronic device 600 via bus 630. It should be understood that, although not shown in the figures, other hardware and / or software modules can be used in conjunction with electronic device 600, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, RAID systems, tape drives, and data backup storage platforms.

[0083] This invention also provides a storage medium, specifically a computer-readable storage medium, which is a memory device in a terminal device for storing programs and data. It is understood that the computer-readable storage medium here can include both built-in storage media in the terminal device and extended storage media supported by the terminal device; it can be any tangible medium containing or storing a program that can be used by or in conjunction with an instruction execution system, apparatus, or device. The computer-readable storage medium provides storage space that stores the terminal's operating system. Furthermore, the storage space also stores one or more instructions suitable for loading and execution by a processor, which can be one or more computer programs (including program code). More specific examples of the computer-readable storage medium include: an electrical connection with one or more wires, a portable disk, a hard disk, random access memory, read-only memory, erasable programmable read-only memory, optical fiber, portable compact disk read-only memory, optical storage device, magnetic storage device, or any suitable combination thereof.

[0084] Computer-readable storage media also include data signals propagated in baseband or as part of a carrier wave, carrying readable program code. Such propagated data signals can take various forms, including but not limited to electromagnetic signals, optical signals, or any suitable combination thereof. A readable storage medium can also be any readable medium other than a readable storage medium that can send, propagate, or transmit a program for use by or in connection with an instruction execution system, apparatus, or device. The program code contained on the readable storage medium can be transmitted using any suitable medium, including but not limited to wireless, wired, optical fiber, radio frequency, etc., or any suitable combination thereof.

[0085] Program code for performing the operations of this invention can be written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Java and C++, and conventional procedural programming languages ​​such as C or similar languages. The program code can execute entirely on the user's computing device, partially on the user's device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server. In cases involving remote computing devices, the remote computing device can be connected to the user's computing device via any type of network, including a local area network (LAN) or a wide area network (WAN), or it can be connected to an external computing device (e.g., via the Internet using an Internet service provider).

[0086] One or more instructions stored in a computer-readable storage medium can be loaded and executed by a processor to implement the corresponding steps of the online cable overheating location method based on broadband impedance spectrum in the above embodiments; one or more instructions in the computer-readable storage medium are loaded and executed by the processor to perform the following steps: A measurement / excitation device is connected to the cable under test via a protection device at the cable end. The measurement / excitation device applies a sweep frequency signal to the cable under test within a preset sweep frequency range and simultaneously acquires the input impedance at the cable end to obtain the input impedance spectrum. The input impedance spectrum is processed by a window function to suppress spectral leakage. An inverse Fourier transform is performed on the windowed input impedance spectrum to obtain the time-domain reflection response curve. Based on the propagation speed of the sweep frequency signal in the cable under test, the time-domain coordinates of the time-domain reflection response curve are mapped to the spatial position coordinates along the length of the cable under test. The distance positioning curve is obtained; the distance positioning curve is compared with the reference distance positioning curve under normal operating conditions of the cable under test to obtain local anomaly indicators distributed along the spatial coordinates. When the local abnormal indicators When the preset threshold is exceeded, it is determined that there is a local overheating fault in the cable, and the corresponding fault location coordinates are output.

[0087] The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0088] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0089] Example 1 For online location of local overheating in power cables, the cable overheating online location device is connected to the cable head end through a protection device. This invention uses RG58 coaxial cable as an example. Due to the structure of the coaxial cable, the loop composed of the cable's metal core and metal shielding layer is selected as the signal transmission line.

[0090] Step 1, Hardware Configuration Signal generation: A DAC+FPGA is used to generate a sweep frequency excitation (frequency band set to 10kHz~50MHz); Signal acquisition: ADC (set to 250MSPS / 14bit) + FPGA real-time buffer and preprocessing; Control and storage: The embedded ARM (running Linux) is responsible for control, parameter management, and communication with the background. Local storage is used to save event data.

[0091] Step 2, Measure parameters Frequency range: f _low=10kHz, f _high=50MHz; Number of frequency points: N=4096; Window function: Kaiser window, β =6; Sweep signal propagation speed (approximate): v =2.0×10 8 m / s.

[0092] Step 3: Connect the positioning device to the beginning of the cable via the protection device. The protection device provides high-voltage isolation, energy limiting and lightning protection to ensure the safe operation of the positioning equipment when it is energized.

[0093] Step 4, build as follows Figure 2The experimental platform for online location of localized overheating sections of a power cable, as shown, consists of a distribution box 1 outputting 220V power, which is regulated by a single-phase voltage regulator 2 and then connected to the cable circuit under test. A localized overheating online location device 3 is connected in series to the cable's beginning and connected to a computer 4 via a communication line to achieve signal acquisition, data transmission, and location analysis. The total cable length is set to 61m. The localized overheating section is generated by a uniformly wound heating strip (20cm wide) located 40m from the cable's beginning. A temperature controller and thermocouples are used to monitor and control the cable surface temperature in real time, with the temperature set at 110℃.

[0094] Step 5, to obtain as follows Figure 3 The online positioning results of the locally overheated section of the power cable shown are as follows: the online positioning accuracy of the locally overheated section is as high as 0.25%. This indicates that the local overheating online positioning device based on broadband impedance spectrum can not only achieve online positioning without interrupting power supply, but also maintain excellent detection sensitivity.

[0095] Based on the experimental platform of Example 1, four sets of control verification experiments were added to further verify the technical advantages of the present invention through quantitative data, as follows: The test circuit of Example 1 is used: a 61m long RG58 coaxial cable is connected to a 220V distribution box and a resistive load via a switch to form a single-phase circuit; a heating tape is wrapped around the cable at 40m to simulate a local overheating defect with a defect width of 20cm, and the temperature is precisely controlled by a temperature controller and a thermocouple. The positioning device of this invention is connected to the beginning of the cable via a protection device. The measurement parameters are set as follows: frequency sweep range 10kHz-50MHz, number of frequency points 4096, Kaiser window β=6, and signal propagation speed. v =2.0×10 8 m / s.

[0096] Comparison of positioning performance between the present invention and the traditional TDR method The control group used the industry-standard traditional TDR detection scheme, injecting a 50ns Gaussian narrow pulse with a center frequency of 10MHz. Under the same experimental conditions as the method of this invention, the overheating defect at 110℃ at 40m was detected, and the positioning performance of the two schemes was compared.

[0097] Compared with traditional TDR technology, the positioning accuracy of the method of this invention is improved by nearly 8 times. It completely solves the core pain points of traditional TDR, such as insufficient high-frequency components, insufficient early micro-defect recognition ability caused by signal attenuation and dispersion, and poor long-distance positioning accuracy. It can reliably identify early overheating defects that traditional methods cannot capture at all.

[0098] Detection sensitivity verification experiment at different overheating temperatures The defect location was fixed at 40m and the defect width was 20cm. The cable surface temperature was set at 40℃, 60℃, 80℃, 110℃ and 130℃ respectively (corresponding to temperature differences of 15℃, 35℃, 55℃, 85℃ and 105℃ from ambient temperature). The method of this invention was used to detect and record the peak value of the local anomaly index Δ(x) and the identification effect.

[0099] The method of this invention can identify early minor overheating defects with temperature differences as low as 15°C, and has excellent early warning capabilities. It can capture overheating risks before irreversible deterioration of cable insulation occurs, and completely solves the industry problem that existing technologies can only identify obvious faults with severe insulation deterioration and cannot achieve early warning.

[0100] Detection capability verification experiment for different defect lengths With a fixed defect location of 40m and an overheating temperature of 110℃, overheating defects with widths of 5cm, 10cm, 20cm, 50cm, and 100cm were set up respectively. The method of this invention was used to detect and verify the ability to identify small defects of different lengths.

[0101] The method of this invention can reliably identify local overheating defects at ultra-short distances of 5cm, with extremely high spatial resolution. It can accurately locate minute overheating defects in key parts such as cable joints and wire core crimping, perfectly adapting to various defect scenarios in engineering sites and solving the problem of high missed detection rate of short-distance minute defects in existing technologies.

[0102] Consistency verification experiment of online and offline charging detection The defect location was fixed at 40m, the defect width at 20cm, and the overheating temperature at 110℃. The method of this invention was used to detect the defect in both the online state with the cable energized at 220V and carrying a 10A load and the offline state after power failure. The consistency of the two sets of test results was compared.

[0103] The method of this invention effectively avoids power grid frequency and load interference by using protective isolation devices and selecting the optimal wideband frequency. The results of live online detection and offline detection are completely consistent, truly realizing high-precision online positioning of cables without power interruption. This solves the core pain point of existing FDR technology, which can only detect offline and cannot adapt to power grid operation scenarios.

[0104] In summary, this invention provides an online cable overheating location method and system based on a wideband impedance spectrum. Through 10kHz-50MHz wideband sweep excitation and Kaiser window optimization, it effectively suppresses spectral leakage and accurately captures minute impedance changes caused by localized overheating. It achieves an ultra-high location accuracy of 0.25% for overheating defects as small as 20cm wide, significantly improving early defect identification capabilities. The protective isolation device enables safe access to the cable while it is energized, allowing real-time monitoring without power outages and effectively ensuring power supply reliability. The use of relative amplitude ratio local anomaly indicators effectively eliminates interference from load fluctuations and ambient temperature changes, significantly reducing false alarm rates in engineering projects. The modular hardware architecture is adaptable to complex engineering scenarios such as power distribution rooms and cable tunnels, and can be seamlessly integrated into existing power grid operation and maintenance systems, significantly improving the ability to prevent and control cable overheating risks in advance, and effectively reducing safety accidents and economic losses caused by cable faults.

[0105] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the above-described division of functional units and modules is merely an example. In practical applications, the above functions can be assigned to different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiments can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit. Furthermore, the specific names of the functional units and modules are only for easy differentiation and are not intended to limit the scope of protection of this application. The specific working process of the units and modules in the above system can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0106] In the above embodiments, the descriptions of each embodiment have different focuses. For parts that are not described in detail or recorded in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0107] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed in this invention can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0108] In the embodiments provided by this invention, it should be understood that the disclosed devices / terminals and methods can be implemented in other ways. For example, the device / terminal embodiments described above are merely illustrative. For instance, the division of modules or units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.

[0109] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0110] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0111] If the integrated module / unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, all or part of the processes in the methods of the above embodiments of the present invention can also be implemented by a computer program instructing related hardware. The computer program can be stored in a computer-readable storage medium, and when executed by a processor, it can implement the steps of the various method embodiments described above. The computer program includes computer program code, which can be in the form of source code, object code, executable files, or certain intermediate forms. The computer-readable medium can include: any entity or device capable of carrying the computer program code, a recording medium, a USB flash drive, a portable hard drive, a magnetic disk, an optical disk, a computer memory, a read-only memory (ROM), a random-access memory (RAM), an electrical carrier signal, a telecommunication signal, and a software distribution medium, etc.

[0112] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus, and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart... Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0113] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0114] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0115] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for online location of cable overheating based on broadband impedance spectrum, characterized in that, Includes the following steps: S1. Connect the measuring / excitation device to the first end of the cable under test via a protection device; S2. The measurement / excitation device applies a sweep frequency signal to the cable under test within a preset sweep frequency range, and simultaneously acquires the input impedance at the beginning of the cable to obtain the input impedance spectrum. S3. Apply a window function to the input impedance spectrum to suppress spectral leakage; S4. Perform an inverse Fourier transform on the input impedance spectrum after window function processing to obtain the time-domain reflection response curve; S5. Based on the propagation speed of the swept frequency signal in the cable under test, map the time-domain coordinates of the time-domain reflection response curve to the spatial position coordinates along the length of the cable under test. This yields the distance positioning curve; S6. Compare the distance positioning curve with the reference distance positioning curve under normal operating conditions of the cable under test to obtain local anomaly indicators distributed along the spatial coordinates. ; S7, when the local abnormal indicators When the preset threshold is exceeded, it is determined that the cable under test has a local overheating fault, and the corresponding fault location coordinates are output.

2. The online cable overheating location method based on broadband impedance spectrum according to claim 1, characterized in that, In step S2, the preset frequency sweep range is from 10kHz to 50MHz.

3. The online cable overheating location method based on broadband impedance spectrum according to claim 1, characterized in that, In step S3, the window function is a Kaiser window, and the Kaiser window contains parameters. β By adjusting the parameters β It can balance temporal resolution and sidelobe suppression performance.

4. The online cable overheating location method based on broadband impedance spectrum according to claim 1, characterized in that, In step S4, the inverse Fourier transform is a discrete inverse Fourier transform, specifically: in, f ( t ) is the spectral density function F ( ω The time-domain function in the time domain. Angular frequency, The imaginary unit, This represents the time value corresponding to the time-domain sampling point output by the inverse Fourier transform.

5. The online cable overheating location method based on broadband impedance spectrum according to claim 1, characterized in that, In step S5, the spatial location coordinates The mapping calculation method is as follows: in, t This represents the time value corresponding to the time-domain sampling point output by the inverse Fourier transform. This represents the propagation speed of the swept frequency signal.

6. The online cable overheating location method based on broadband impedance spectrum according to claim 5, characterized in that, The propagation speed of the frequency sweep signal in the cable under test v =2.0×10 8 m / s.

7. The online cable overheating location method based on broadband impedance spectrum according to claim 1, characterized in that, In step S6, the local anomaly index The calculation method is as follows: in, This is the distance location curve for a localized overheating fault. This is the reference distance positioning curve for the cable under test during normal operation.

8. The online cable overheating location method based on broadband impedance spectrum according to claim 1, characterized in that, In step S2, the number of frequency points of the sweep signal is set to 4096.

9. The online cable overheating location method based on broadband impedance spectrum according to claim 1, characterized in that, In step S6, the reference distance positioning curve of the cable under test under normal operating conditions is obtained by processing the input impedance spectrum of the cable under test under normal operating conditions through window function and inverse Fourier transform.

10. A cable overheating online positioning system based on broadband impedance spectrum, characterized in that, include: The signal generation module is used to generate a sweep frequency signal within a preset sweep frequency range; The signal acquisition module is used to acquire the input impedance signal at the beginning of the cable under test and perform digital processing. The synchronization and clock module is used to provide a synchronous clock reference with nanosecond-level time alignment accuracy for the signal generation module and the signal acquisition module; The protection / isolation device is equipped with lightning protection and isolation circuits to ensure safe access protection between the system and the live cable under test; The background analysis and storage unit is used to perform window function processing, inverse Fourier transform, local anomaly index calculation, fault judgment and location result output, and storage of measurement data and reference distance positioning curves on the collected input impedance spectrum.

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