A cable metallic sheath ground fault non-intrusive detection system and method

Abstract

This application discloses a non-invasive detection system and method for grounding faults in the metallic sheath of cables. The system includes a dual-frequency excitation host, at least one wireless synchronous acquisition substation, and a monitoring intelligent processing terminal. The dual-frequency excitation host is connected to an excitation coil and is used to send ultra-low frequency excitation signals and power frequency odd harmonic excitation signals to the excitation coil. The wireless synchronous acquisition substation includes a fixture and a current / voltage sensor. The monitoring intelligent processing terminal is communicatively connected to the wireless synchronous acquisition substation, receives the acquired data from the wireless synchronous acquisition substation, and calculates the impedance in the grounding loop of the cable's metallic sheath. This application achieves live, non-invasive, rapid, and accurate grounding fault detection through active dual-frequency excitation, multi-node synchronous acquisition, and impedance decoupling analysis. It can simultaneously identify latent faults such as loose grounding and intermittent connections, as well as explicit faults such as open circuits and breakdowns.

Description

Technical Field

[0001] This application relates to the field of cable construction technology, and in particular to a non-invasive detection system and method for grounding faults in the metallic sheath of cables. Background Technology

[0002] Currently, my country's urban power grid construction and upgrading are in a phase of rapid development. Cable tunnels, as the core carrier for power cable laying, directly impact the stability and reliability of urban power supply through their construction quality and operational safety. With cable tunnels developing towards longer distances, larger cross-sections, and multiple voltage levels, the difficulty of quality control in the construction of cable metal sheath grounding systems has increased significantly, and safety hazards caused by grounding faults are becoming increasingly prominent. The grounding treatment of the cable metal sheath (including armor, shielding layer, and metal sleeve) is a crucial protective structure for cables. It is a key aspect of ensuring safe cable operation, preventing electric shock, suppressing electromagnetic interference, and resisting overvoltage surges. It is also a core control point for cable tunnel engineering supervision, acceptance, and quality inspection.

[0003] Cable metal sheath grounding faults are often related to a variety of factors, including construction techniques, material quality, and environmental conditions. During cable tunnel construction, defects such as loose welding of grounding down conductors, inadequate bolt tightening, and improper grounding electrode installation can easily lead to excessive contact resistance at the grounding point. Humid environments and corrosive gases within the tunnel can accelerate the corrosion and oxidation of grounding components, causing latent grounding faults. Mechanical damage during cable laying can lead to insulation damage in the sheath, subsequently inducing visible faults such as grounding short circuits. Grounding faults have multiple impacts on cable operation and engineering construction: minor latent grounding faults (such as excessive contact resistance) accelerate cable sheath aging, reduce cable lifespan, and increase subsequent maintenance costs; severe visible grounding faults (such as grounding wire breaks or sheath breakdown) can cause the cable metal sheath to carry dangerously high voltages, leading to electric shock, equipment burnout, or even fires, power outages, and disruption of urban production and daily life. Furthermore, grounding faults can also generate electromagnetic interference, affecting the normal operation of surrounding communication, signal, and control lines. Therefore, timely, accurate, and efficient detection of grounding faults in the metal sheath of cables and investigation of potential construction quality hazards are of great significance for ensuring the construction quality of cable tunnel projects and the safe and stable operation of power systems.

[0004] Detection of grounding faults in the metal sheath of cables is one of the core contents of cable tunnel engineering supervision. Supervision units need to use various methods such as process supervision, parallel sampling inspection, and final acceptance to control the construction quality of the grounding system throughout the process to ensure that it meets the relevant standard requirements. Existing grounding fault detection technologies mainly include DC resistance method, sheath circulation current detection method, online monitoring system, etc. These technologies can achieve preliminary detection of grounding faults to a certain extent. However, after years of engineering practice, it has been shown that their application reliability in cable tunnel supervision scenarios still needs to be improved. The main problems include: (1) Existing detection technologies are mostly designed for the power grid operation and maintenance stage and do not fully adapt to the core needs of supervision and acceptance, batch sampling inspection, and mobile supervision. Most of them require power outage and wire disconnection operations, which not only have high coordination costs but also affect the progress of engineering construction. Moreover, they cannot complete real-time detection in a live state; (2) There is strong power frequency electromagnetic interference in the tunnel. The data accuracy of traditional portable detection equipment is low and the error is large. The results cannot be used as the legal basis for supervision and acceptance, and manual interpretation of data is difficult and inefficient, and is prone to misjudgment and omission; (3) Existing technology can only identify obvious faults such as grounding break and sheath breakdown, but cannot detect hidden faults such as loose bolts, poor welding connection, and excessive contact resistance caused by corrosion and oxidation. Such hidden faults are the most common quality defects in cable tunnel grounding construction, and their long-term existence can easily lead to serious safety accidents; (4) Existing detection methods cannot distinguish whether the fault occurs in the cable sheath body, grounding down conductor, grounding point contact section or grounding grid, which makes it impossible for the supervision unit to accurately define the construction responsibility subject, and the issuance of rectification notices lacks clear closed-loop basis, making it difficult to achieve full-process closed-loop quality control.

[0005] In recent years, various equipment and methods for detecting grounding faults in cable metal sheaths have emerged. Some equipment can accurately identify visible grounding faults, but in actual tunnel supervision and inspection, many bottlenecks remain: the detection operation is cumbersome, requiring multiple professional technicians to work together, and its adaptability is poor; non-invasive detection technology is immature, and most detection methods require stripping the cable sheath or modifying the original grounding circuit, which can easily cause secondary damage to the cable; the detection data lacks comparison with engineering design benchmarks, making it difficult to use for supervision and acceptance judgments; online monitoring systems are costly, require pre-installation, cannot meet the actual needs of supervision units for batch sampling and mobile testing, and are difficult to maintain later. In order to ensure that the detection process does not affect the construction progress of cable tunnels, improve the efficiency of supervision and inspection, reduce detection costs, accurately identify visible and hidden grounding faults, clarify the definition of construction responsibilities, and ensure the impartiality and traceability of detection data to meet the requirements of supervision archiving, it is urgent to invent a new grounding fault detection method and system adapted to the cable tunnel supervision scenario. With the rise of automation and intelligent technologies, many new technologies in the field of power equipment testing have been proposed, providing technical support for non-invasive, precise, and portable testing of grounding faults in cable metal sheaths.

[0006] Chinese patent application number CN202511475293.3 discloses a method, device, and electronic equipment for diagnosing grounding faults in high-voltage cable sheaths. The diagnostic method provided by this patent specifically includes: first, acquiring multi-source state parameters, which are used to accurately characterize the real-time operating status of the sheath grounding system corresponding to the high-voltage cable sheath; second, performing multi-source heterogeneous data processing on the acquired multi-source state parameters to extract the fundamental and harmonic components of the sheath current, as well as the vibration energy value of the cable joint; subsequently, combining the multi-source state parameters themselves with the processed fundamental, harmonic, and vibration energy values, comprehensively determining the current fault type of the high-voltage cable sheath grounding; next, based on the multi-source state parameters and the power topology diagram of the high-voltage cable sheath, locating and determining the specific location information of the fault segment; finally, generating a complete fault diagnosis result based on the determined current fault type and the located fault segment location information, providing a basis for subsequent fault handling.

[0007] Chinese patent application number CN202511472426.1 discloses a method and system for diagnosing defects in the sheath grounding system under resonant withstand voltage of power transmission cables, belonging to the field of power transmission cable testing technology. The diagnostic method provided by this patent includes the following steps: First, deploy and install a sheath grounding current acquisition system to ensure precise connection between the acquisition system and the grounding terminal of the metal sheath of the transmission cable, thus ensuring the accuracy of current signal acquisition. Second, conduct main insulation resonant withstand voltage tests on the three-phase lines of the transmission cable in sequence. During the withstand voltage test of each phase, a preset current acquisition system is used to synchronously acquire and record the grounding current waveform of the metal sheath, achieving synchronous linkage between the withstand voltage test and current acquisition. Subsequently, a dedicated signal processing algorithm is used to perform noise reduction and analysis on the acquired grounding current waveform, accurately extracting the resonant component in the grounding current and eliminating the influence of interference signals on defect diagnosis. Finally, a defect diagnosis matrix is ​​constructed based on the extracted resonant component, and the deviation value between the defect diagnosis matrix and the preset standard matrix is ​​calculated. This deviation value is used as the defect characterization index of the cable sheath grounding system. Based on this characterization index, the defect diagnosis conclusion of the sheath grounding system under the resonant withstand voltage condition of the transmission cable is finally obtained. This patent, by simultaneously acquiring and analyzing the grounding current waveform of the metal sheath during the resonant withstand voltage test of the main insulation of a three-phase cable, accurately extracts the resonant component, and uses the deviation calculation of the defect diagnosis matrix to achieve accurate identification of grounding system defects. This effectively improves the detection sensitivity and diagnostic reliability of latent defects in the sheath grounding system before cable commissioning, providing technical support for the safe commissioning of cables.

[0008] Chinese patent application number CN202422751917.7 discloses a handheld cable grounding fault detection device, belonging to the field of cable testing technology. The detection device provided by this patent specifically includes: a device housing with wiring holes, a control circuit board integrated into the housing cavity, and an LCD screen and an illuminated touch button module embedded in the housing surface. The control circuit board integrates a power supply module, an inverter, a residual current transformer, a control module, and a relay. The circuit connections of each component are as follows: the output terminal of the power supply module is electrically connected to the input terminal of the inverter, providing a stable power supply to the inverter; the relay is connected in series in the output circuit of the inverter to control the on / off state of the inverter output circuit; both the residual current transformer and the relay are signal-connected to the control module, with the residual current transformer specifically used to detect the residual current signal on the inverter output circuit and transmit the detected signal to the control module in real time; the LCD screen and the illuminated touch button module are also electrically connected to the control module, with the LCD screen used to display detection data and fault information in real time, and the illuminated touch button module used to perform operations such as starting / stopping the device and adjusting parameters. The detection device provided by this patent has a simple structure, low manufacturing cost, small size, and is easy to carry. It can realize rapid and accurate detection of cable grounding faults and is suitable for the basic needs of on-site mobile detection.

[0009] Chinese patent application number CN202210180056.4 discloses a method, system, device, and storage medium for detecting grounding faults in AC cables. The detection method provided by this patent specifically includes: first, acquiring the first neutral current and the first phase current of each phase line on the AC cable near the transformer end; second, performing vector calculations on the acquired first neutral current and the first phase currents of each phase; if the vector sum is not equal to zero, responding to a first synchronous measurement command, further acquiring the first current of the first phase near the transformer end and the second current of the first phase near the load end of the AC cable; subsequently, performing vector calculations on the first and second currents; if the vector sum is still not equal to zero, determining that a grounding fault exists in the cable segment between the two current measurement points. The corresponding detection system includes a first acquisition module, a first judgment module, a second acquisition module, a second judgment module, and a fault detection module, with each module working together to achieve the complete execution of the above detection method. By adopting the detection method and system in this patent, grounding faults in AC cables can be detected in a timely and accurate manner, effectively avoiding the risk of fault escalation and improving the operational safety performance of the power system.

[0010] Chinese Patent Application No. CN201010211445.6 discloses a method for detecting cable grounding faults. The method includes: connecting one end of the faulty cable to the output of a DC regulated power supply, and short-circuiting the other end to any other intact cable of any phase; connecting the output of the DC regulated power supply to the other end of the intact cable of that phase; turning on the DC regulated power supply and stabilizing the output current at 5-10A; using a DC voltmeter to measure the voltage values ​​V1 and V2 at both ends of the faulty cable to the cable tray, respectively, to calculate the approximate location of the cable fault; disconnecting the DC regulated power supply, setting a multimeter to the resistance setting, with one end connected to the faulty cable and the other end grounded; using an insulating rope to loop around the faulty cable near the approximate measurement location and moving it; when the multimeter resistance reading reaches its maximum value, the location of the insulating rope is the fault location.

[0011] Analysis of the existing technologies reveals that current detection technologies focus on fault identification, location, or portable detection, but none are specifically designed for the core application scenario of cable tunnel construction supervision, resulting in significant technical deficiencies in practical engineering applications.

[0012] The main drawback of existing technologies is that they cannot simultaneously achieve accurate detection of both latent and overt faults in cable metal sheath grounding systems without power interruption, intrusion, or alteration of the original wiring. Since most existing detection methods rely on power outage tests, wire disconnection measurements, or passive current sampling, they struggle to effectively identify common latent defects encountered during construction, such as excessive contact resistance, loose welds, and loose bolts. Judgments can only be made after the fault has progressed to serious overt faults like grounding failure or sheath breakdown, failing to meet the core need of supervisors to identify potential quality issues early during the construction and acceptance phase.

[0013] The inability of existing technologies to detect latent faults in a non-invasive, energized state results in insufficient accuracy and poor data stability in the strong electromagnetic interference environment of cable tunnels, making it difficult to use the test results as a legal basis for supervision and acceptance. Furthermore, most existing methods can only determine the presence of a fault, but cannot perform impedance decoupling analysis on components such as the sheath, grounding down conductor, contact resistance, and grounding grid in the grounding circuit. This makes it impossible to distinguish the specific location and responsible link of the fault, hindering the supervision unit from accurately locating and assigning responsibility for construction quality issues. In addition, while some testing devices are portable, their functions are limited, their anti-interference capabilities are weak, they cannot be combined with engineering design parameters to form acceptance standards, and they lack the ability to automatically generate supervision and inspection reports. Meanwhile, some high-precision testing systems rely on prior installation and are costly, failing to meet the requirements of flexible spot checks and rapid testing on-site. The overall testing process is cumbersome and inefficient, making it difficult to truly meet the actual needs of quality control throughout the entire cable tunnel construction process. Summary of the Invention

[0014] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide a non-invasive detection system and method for grounding faults in the metallic sheath of cables. Through active dual-frequency excitation, multi-node synchronous acquisition, and impedance decoupling analysis, it achieves live, non-invasive, rapid, and accurate grounding fault detection. It can simultaneously identify latent faults such as loose grounding and poor connections, as well as overt faults such as open circuits and breakdowns. Furthermore, it can distinguish the fault location and the responsible party, improving the accuracy and reliability of cable tunnel supervision and inspection, reducing on-site operational difficulty and testing costs, and providing stable, efficient, and traceable technical support for the quality acceptance and safety management of cable tunnel construction.

[0015] The technical solution of this application is as follows: On the one hand, this application provides a non-invasive detection system for grounding faults in the metallic sheath of cables, comprising: A dual-frequency excitation host, wherein the dual-frequency excitation host is connected to an excitation coil, and the dual-frequency excitation host is used to send an ultra-low frequency excitation signal and a power frequency odd harmonic excitation signal to the excitation coil; At least one wireless synchronous acquisition substation, the wireless synchronous acquisition substation including a fixture and a current / voltage sensor, the wireless synchronous acquisition substation being used to acquire the current / voltage signal in the grounding circuit of the metal sheath of the cable under test; And a smart supervision processing terminal, which is communicatively connected to a wireless synchronous acquisition substation, receives the data collected by the wireless synchronous acquisition substation, and calculates the impedance in the grounding circuit of the cable metal sheath.

[0016] Furthermore, the dual-frequency excitation host is equipped with an ultra-low frequency signal generator and a power frequency harmonic dual-frequency signal generator, which are used to generate an ultra-low frequency excitation signal of 0.1Hz-1Hz and a power frequency odd harmonic excitation signal of 150Hz / 250Hz, respectively. The ultra-low frequency signal generator and the power frequency harmonic dual-frequency signal generator are coupled through dual independent phase-locked loop circuits, and the two signals share a unified clock reference.

[0017] Furthermore, the dual-frequency excitation host is equipped with a miniature interference acquisition coil, which is used to pick up the 50Hz power frequency magnetic field and environmental electromagnetic interference signal at the tunnel site. The compensation component with the same amplitude but opposite phase as the interference signal is generated by the feedforward adaptive cancellation circuit, and the compensation component is superimposed on the main excitation signal in real time and output.

[0018] Furthermore, the dual-frequency excitation host is equipped with a host interface, and the excitation coil is connected to the host interface via a connecting wire; The excitation coil is a flexible structure with an opening for fitting into the grounding circuit of the cable's metal sheath. A magnetic flux closed-loop detection unit is installed at the coil opening to monitor in real time the coupling degree between the coil and the grounding lead, the magnetic circuit closure state, and the signal transmission efficiency. The dual-frequency excitation host dynamically adjusts the output impedance, excitation power, and driving voltage based on the real-time monitoring results to achieve the set coupling matching degree between the coil and the grounding lead. Furthermore, the fixture includes two clamps, each equipped with a magnetic attraction device, and a complementary induction coil is installed inside the clamp.

[0019] Furthermore, the wireless synchronization acquisition substation is also equipped with: UWB / BeiDou fusion positioning unit, used for positioning and time synchronization; The main control and wireless communication unit is used to communicate with the intelligent processing terminal for supervision.

[0020] Furthermore, the intelligent supervision processing terminal includes: The digital twin modeling module is used to construct a digital twin model of the grounding circuit of the metal sheath of the cable to be tested; The dual-frequency impedance joint decoupling algorithm module is used to calculate the impedance in the grounding loop of the cable metal sheath based on the data collected by the wireless synchronous acquisition substation, and decompose the grounding loop impedance into four independent components: sheath body resistance, down conductor resistance, grounding point contact resistance, and grounding electrode resistance. The fault classification and responsibility determination module, based on impedance decoupling results and digital twin model, completes fault type identification and level classification in accordance with the power engineering construction quality acceptance specifications, and automatically determines the responsible party and construction link based on the impedance component where the fault is located.

[0021] Furthermore, the intelligent supervision processing terminal also includes an automatic acceptance report generation module, which is used to generate a supervision acceptance report based on the results of the digital twin model and the fault classification module.

[0022] On the other hand, this application provides a non-invasive detection method for grounding faults in the metallic sheath of cables, which is implemented using the system described above and includes the following steps: S1: Develop a testing plan based on the tunnel length and the number of grounding points; S2: According to the testing plan, a dual-frequency excitation host and several wireless synchronous acquisition substations are installed in the grounding circuit of the cable's metal sheath. S3: The dual-frequency excitation host injects ultra-low frequency excitation signal and power frequency odd harmonic excitation signal into the excitation coil, and the wireless synchronous acquisition substation collects ultra-low frequency response data and harmonic response data at its location. S4: Deploy intelligent processing terminals for supervision and construct a digital twin benchmark model of the cable metal sheath grounding circuit based on the testing plan; S5: The intelligent processing terminal for supervision receives and processes the acquisition signals from several wireless synchronous acquisition substations, determines the fault type and location, and generates a supervision acceptance report.

[0023] In summary, the beneficial effects of this application are as follows: 1. This invention provides a non-invasive detection device and method for grounding faults in the metal sheath of cables, suitable for cable tunnel engineering supervision and acceptance scenarios. It can achieve uninterrupted and non-destructive testing of cables with different voltage levels and different grounding methods, accurately meeting the core needs of supervision spot checks, on-site monitoring, etc.

[0024] 2. This invention adopts a dual-frequency excitation collaborative detection mode, injecting two complementary signals, 0.1Hz~1Hz ultra-low frequency and 150Hz / 250Hz power frequency odd harmonics, through a portable dual-frequency excitation host, to accurately capture latent faults (excessive contact resistance) and obvious faults (grounding break, sheath breakdown, etc.), achieving full coverage detection of fault types.

[0025] 3. The wireless synchronous acquisition substation of the present invention integrates a UWB / BeiDou fusion positioning unit and a magnetically detachable flexible sensor, which can be directly magnetically fixed to the grounding lead or cable sheath joint without binding or disconnection, and can achieve microsecond-level time synchronization and precise positioning, ensuring the accuracy of data acquisition and fault location.

[0026] 4. This invention constructs a digital twin benchmark model of the cable grounding system through a smart processing terminal for supervision. Combined with an impedance decoupling algorithm, the total impedance of the grounding circuit is decomposed into four independent components, which can accurately identify the fault type, locate the fault point, and clarify the responsible party for the fault, thus solving the pain point of difficulty in defining supervisory responsibilities.

[0027] 5. This invention realizes a closed loop for the entire testing process, and can automatically generate a special testing report for supervision with electronic signatures, timestamps, location information, etc., without the need for manual processing. It can be directly included in the project completion archive, greatly improving the efficiency of supervision and testing, and meeting the legal requirements for the impartiality and traceability of supervision data.

[0028] 6. This invention adopts a modular and portable design, requiring no pre-installation. A single supervisor can complete the deployment and operation. After the test is completed, it can be quickly disassembled, stored, and reused. It is suitable for the flexible testing needs of cable tunnels with narrow spaces and multiple grounding points, and has no extra exposed parts, making it easy to transport and use on site. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the dual-frequency excitation host in one embodiment of this application; Figure 2 This is a schematic diagram of the overall structure of a wireless synchronization acquisition substation in one embodiment of this application; Figure 3This is a schematic diagram illustrating the principle of a non-invasive detection method for grounding faults in the metal sheath of cables in one embodiment of this application.

[0030] In the diagram: 1. Main unit interface; 2. Main unit charging port; 3. Insulated handle; 4. Display screen; 5. Adjustment button for the dual-frequency signal generator of ultra-low frequency and power frequency harmonics; 6. Main unit power switch; 7. Connecting cable; 8. Excitation coil; 21. Fixture; 22. Current / voltage sensor; 23. UWB / BeiDou fusion positioning unit; 24. Insulated connector; 25. Power and signal adjustment button; 26. Main control and wireless communication unit. Detailed Implementation

[0031] The specific embodiments of this application are described in detail below with reference to the accompanying drawings.

[0032] One specific embodiment of this application provides a non-intrusive detection system for grounding faults in the metal sheath of cables, including a dual-frequency excitation host, at least one wireless synchronous acquisition substation, and a smart processing terminal for supervision.

[0033] The dual-frequency excitation host is connected to an excitation coil, and the dual-frequency excitation host is used to send ultra-low frequency excitation signals and power frequency odd harmonic excitation signals to the excitation coil. For example... Figure 1 As shown, the dual-frequency excitation host is equipped with a host interface 1, and the excitation coil 8 is connected to the host interface 1 via a connecting wire 7. The excitation coil 8 is a flexible structure with an opening for fitting into the grounding circuit of the cable's metal sheath. The top of the dual-frequency excitation host is equipped with a host charging port 2 and an insulated handle 3. The front of the dual-frequency excitation host is equipped with a display screen 4, an adjustment button 5 for the ultra-low frequency and power frequency harmonic dual-frequency signal generator, and a host power switch 6.

[0034] The portable dual-frequency excitation host serves as the signal excitation core of this system. It integrates a dual-frequency signal generator for both ultra-low frequency and power frequency harmonics, paired with a flexible, openable excitation coil. Employing a non-invasive design, it requires no power outages, no stripping of cable sheaths, and no alteration of the original grounding circuit. Supervisors simply need to place the flexible excitation coil directly onto the grounding lead of the cable terminal or the grounding lead of the cross-connection box to complete the deployment; no disconnection is required, effectively preventing secondary damage to the cable. The host utilizes dual-frequency independent phase-locked loop synchronous excitation technology. Two independent phase-locked loop circuits perform phase locking and frequency reference calibration on the ultra-low frequency excitation signal and the power frequency odd harmonic excitation signal, respectively. The two signals share a unified clock reference, enabling parallel synchronous injection within the same excitation coil. The signal phases are strictly decoupled and do not crosstalk, allowing for dual-frequency excitation output without time-division switching, significantly shortening the detection cycle. Simultaneously, it ensures the synchronization and consistency of response signal acquisition, providing a stable and reliable excitation foundation for subsequent impedance decoupling calculations and accurate fault diagnosis. The host can stably output two complementary excitation signals: an ultra-low frequency excitation signal of 0.1Hz~1Hz and a power frequency odd harmonic excitation signal of 150Hz / 250Hz. The ultra-low frequency excitation signal can ignore the inductive and capacitive reactance components of the grounding loop and is only sensitive to the pure resistive component. It is used to accurately detect latent faults such as loose grounding bolts and poor welding leading to excessive contact resistance. The power frequency odd harmonic excitation signal can avoid the mainstream 50Hz power frequency interference in the tunnel. Combined with phase-locked loop amplification technology, it can completely filter out the strong electromagnetic interference brought by the load current. At the same time, it is sensitive to the amplitude frequency and phase frequency characteristics of the loop impedance. It is used to accurately identify obvious faults such as grounding disconnection, sheath insulation breakdown, and grounding electrode failure. The two signals work together to achieve comprehensive coverage detection of fault types.

[0035] The host also integrates an adaptive tunnel electromagnetic interference cancellation excitation function. It uses a built-in miniature interference acquisition coil to pick up the 50Hz power frequency magnetic field and environmental electromagnetic interference signals in the tunnel in real time. The feedforward adaptive cancellation circuit generates a compensation component with the same amplitude but opposite phase as the interference signal. This component is then superimposed on the main excitation signal in real time and output. This suppresses the influence of strong electromagnetic interference on the signal amplitude and phase from the excitation source, keeping the excitation output stability at an extremely high level. This effectively solves the problems of traditional excitation devices being susceptible to interference, signal drift, and decreased detection accuracy in the complex electromagnetic environment of tunnels, and further improves the detection capability of latent faults and weak fault signals.

[0036] The accompanying flexible open coil non-inductive coupling excitation control technology allows the openable flexible excitation coil to adopt a non-inductive layered winding process. A magnetic flux closed-loop detection unit is set at the coil opening, which can monitor the coupling degree between the coil and the grounding lead, the magnetic circuit closure state, and the signal transmission efficiency in real time. The host dynamically adjusts the output impedance, excitation power, and driving voltage based on the real-time monitoring results, automatically achieving non-invasive optimal coupling matching. There is no need to manually adjust the coil position or fix the angle. Even under different wire diameters, different installation postures, and different spatial positions, the excitation signal coupling remains stable and attenuated, completely improving the defects of unstable coupling and poor signal consistency of traditional open coils, and further enhancing the convenience and reliability of non-invasive detection.

[0037] The system comprises several wireless synchronous acquisition substations, each including a fixture and a current / voltage sensor. These substations are used to acquire current / voltage signals in the grounding loop of the metallic sheath of the cable under test. (Reference) Figure 2 The fixture 21 is a magnetically pleasing, openable flexible fixture; the fixture 21 includes two clamps, which can be opened and closed by external force. Magnetic suction devices are provided on the clamps. The wireless synchronous acquisition substation also includes a UWB / BeiDou fusion positioning unit 23 and a main control and wireless communication unit 26. The UWB / BeiDou fusion positioning unit is used for positioning and time synchronization; the main control and wireless communication unit is used for communication with the intelligent processing terminal for supervision. The main control and wireless communication unit is connected to the fixture via an insulating connector 24, and the main control and wireless communication unit is equipped with power and signal adjustment buttons 25.

[0038] Multiple wireless synchronous acquisition substations can be deployed independently according to detection needs, which can flexibly adapt to complex scenarios such as different cable tunnel laying lengths, different grounding points, and multi-circuit parallel detection. Each substation uses a magnetically pleasing flexible fixer as its core installation structure. The fixer adopts a symmetrical double-clamp design, with complementary induction coils built into both sides of the clamp. During use, there is no need for rigid full closure. It can form a stable magnetic circuit simply by relying on magnetic attraction to fasten to the outside of the grounding down conductor or cable sheath joint. Structurally, it solves the problem of unstable sampling caused by the small operating space in the tunnel and the difficulty of the coil to close in place. The substation integrates a UWB / BeiDou fusion positioning unit and a magnetically detachable flexible current / voltage sensor. The entire unit features a fully enclosed, non-intrusive design, allowing direct magnetic attachment to the grounding lead or cable sheath joint. This eliminates the need for binding, insulation stripping, or alteration of existing wiring, enabling stable acquisition of current and voltage response data and precise self-positioning. The fusion positioning accuracy reaches ±1cm. It can real-time analyze and report the tunnel chainage, cable loop number, and grounding point number, perfectly adapting to the flexible deployment needs of random on-site inspections, mobile monitoring, and multi-point synchronous testing. The substation incorporates built-in magnetic coupling automatic compensation technology, which monitors coil coupling status and signal attenuation in real time. It automatically compensates for signal gain and phase based on coil opening deviations, installation distance changes, and grounding lead posture differences, ensuring consistent sampling accuracy under different installation conditions and lead postures, effectively eliminating detection errors caused by installation factors. Meanwhile, the substations support autonomous synchronous networking technology, enabling multiple substations to automatically establish wireless collaborative links. This achieves microsecond-level wireless time synchronization without relying on upper-level terminals. Combined with UWB / BeiDou fusion timing, it can fully adapt to complex obstructed environments in tunnels without GPS signals. This ensures that all deployed substations on-site can collect current and voltage response data corresponding to dual-frequency excitation signals at exactly the same time and simultaneously upload accurate location information. This completely eliminates impedance calculation errors caused by signal transmission delays and sampling timing deviations, comprehensively guaranteeing the synchronization and accuracy of data acquisition and fault location. The collected response data, location information, and sampling timestamps are transmitted to the supervisor's intelligent processing terminal via encrypted wireless communication. The data is encrypted, verified, and tamper-proof throughout the process. All records are traceable and cannot be manually modified, strictly meeting the legal requirements for the impartiality and traceability of engineering supervision and testing data. This provides reliable data support for subsequent fault identification, precise location, responsibility allocation, and supervisor acceptance judgment.

[0039] The intelligent processing terminal for supervision maintains a stable communication connection with the wireless synchronous acquisition substation, receiving in real time the acquired data, location information, timestamps, and coupling status information uploaded by each substation. Based on the dual-frequency excitation response data, it performs accurate calculations and in-depth analysis of the cable's metallic sheath grounding loop impedance. The intelligent processing terminal includes a digital twin modeling module, a dual-frequency impedance joint decoupling algorithm module, a fault classification and responsibility determination module, a visual fault location module, a health assessment and trend prediction module, an adaptive matching module for supervision acceptance thresholds, a retest closed-loop management module, an encrypted evidence storage and electronic archiving module, an offline synchronization module, and an automatic acceptance report generation module.

[0040] The digital twin modeling module can import engineering design parameters, tunnel structure information, and grounding loop topology to automatically construct a high-precision digital twin reference model of the grounding loop of the cable's metal sheath under test. It also supports synchronous model correction based on the real-time position, attitude, and coupling status transmitted from the acquisition substations, achieving real-time mapping and matching between the on-site conditions and the virtual model. The impedance decoupling algorithm module employs a dual-frequency impedance joint decoupling algorithm. Based on dual-path response data of ultra-low frequency and power frequency odd harmonics, it performs cross-verification and collaborative calculation, accurately decomposing the total impedance of the grounding loop into four independent components: sheath body resistance, down conductor resistance, grounding point contact resistance, and grounding electrode resistance. Simultaneously, it combines a multi-substation data collaborative fusion calculation mechanism to eliminate single-point acquisition errors, significantly improving impedance calculation accuracy and fault identification capabilities. The fault classification and responsibility determination module, based on the impedance decoupling results and the digital twin model, completes fault type identification and classification according to the power engineering construction quality acceptance specifications. It automatically determines the responsible party and construction link based on the impedance component where the fault is located, providing a clear basis for supervision and rectification instructions. The visualized fault location and 3D annotation module uses a digital twin scenario to intuitively highlight fault points, linking tunnel station numbers, spatial coordinates, and grounding point numbers for 3D annotation, facilitating rapid on-site location and troubleshooting. The health assessment and trend prediction module scores the grounding system's health based on calculated data, identifies deterioration trends, and provides potential risk predictions, extending from post-event detection to pre-event warning. The adaptive matching module for supervision and acceptance thresholds automatically retrieves corresponding national and industry standard thresholds based on cable voltage level, laying length, and grounding method, eliminating the need for manual configuration and ensuring consistent and compliant acceptance criteria. The retesting comparison and rectification closed-loop management module supports automatic data retention and comparative analysis throughout the initial inspection, rectification, and retesting processes, forming a complete "inspection-rectification-retesting-confirmation" supervision closed loop. The offline detection and automatic online synchronization module allows terminals to independently complete data storage and calculation in tunnel environments without communication, automatically uploading and supplementing data after communication is restored, ensuring uninterrupted detection and no data loss.

[0041] The intelligent processing terminal for supervision is the core of this system for data processing, fault identification, and report generation. It supports real-time on-site results, significantly improving supervision and inspection efficiency and reducing the barriers to manual operation and data interpretation. The digital twin modeling module allows supervisors to directly import cable engineering design drawings and concealed works records, automatically generating a digital twin benchmark model of the grounding system of the tested cable. It outputs a standard impedance characteristic library for each component of the grounding system at different frequencies, serving as a legal benchmark for acceptance comparison, thus solving the core pain point of supervision and inspection lacking historical maintenance data for comparison. The impedance decoupling algorithm module can decouple and calculate the dual-frequency data and location information transmitted by the wireless synchronous acquisition substation, decomposing the grounding loop impedance into four independent components: sheath body resistance, down conductor resistance, grounding point contact resistance, and grounding electrode resistance. Combined with the digital twin benchmark model and the accurate location information reported by the substation, it achieves... The system enables precise identification of fault types, accurate location of fault points, and clear definition of the responsible parties. The fault classification module perfectly aligns with the supervision workflow, classifying faults into four levels according to the "Power Engineering Construction Quality Acceptance Specification": Level I Major Faults, Level II Serious Quality Defects, Level III General Quality Defects, and Qualified Items. This provides a clear basis for the supervisor to issue rectification notices. The automatic acceptance report generation module automatically generates a dedicated inspection report for the supervisor, complete with electronic signatures, timestamps, location information, design benchmark values, measured values, fault location, and rectification suggestions. This report can be directly included in the project completion archives without manual processing by the supervisor, achieving a closed-loop management system encompassing inspection, rectification, re-inspection, and archiving.

[0042] Another specific embodiment of this application provides a non-intrusive detection method for grounding faults in the metallic sheath of cables, executed using the system described above, with reference to... Figure 3 It includes the following steps: S1: Develop a testing plan based on the tunnel length and the number of grounding points; S2: According to the testing plan, a dual-frequency excitation host and several wireless synchronous acquisition substations are installed in the grounding circuit of the cable's metal sheath. S3: The dual-frequency excitation host injects ultra-low frequency excitation signal and power frequency odd harmonic excitation signal into the excitation coil, and the wireless synchronous acquisition substation collects ultra-low frequency response data and harmonic response data at its location. S4: Deploy intelligent processing terminals for supervision and construct a digital twin benchmark model of the cable metal sheath grounding circuit based on the testing plan; S5: The intelligent processing terminal for supervision receives and processes the acquisition signals from several wireless synchronous acquisition substations, determines the fault type and location, and generates a supervision acceptance report.

[0043] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept of this application, and these all fall within the protection scope of this application.

Claims

1. A non-invasive detection system for grounding faults in the metallic sheath of cables, characterized in that, include: A dual-frequency excitation host, wherein the dual-frequency excitation host is connected to an excitation coil, and the dual-frequency excitation host is used to send an ultra-low frequency excitation signal and a power frequency odd harmonic excitation signal to the excitation coil; At least one wireless synchronous acquisition substation, the wireless synchronous acquisition substation including a fixture and a current / voltage sensor, the wireless synchronous acquisition substation being used to acquire the current / voltage signal in the grounding circuit of the metal sheath of the cable under test; And a smart supervision processing terminal, which is communicatively connected to a wireless synchronous acquisition substation, receives the data collected by the wireless synchronous acquisition substation, and calculates the impedance in the grounding circuit of the cable metal sheath.

2. The non-invasive cable metal sheath grounding fault detection system according to claim 1, characterized in that, The dual-frequency excitation host is equipped with an ultra-low frequency signal generator and a power frequency harmonic dual-frequency signal generator, which are used to generate ultra-low frequency excitation signals of 0.1Hz-1Hz and power frequency odd harmonic excitation signals of 150Hz / 250Hz, respectively. The ultra-low frequency signal generator and the power frequency harmonic dual-frequency signal generator are coupled through dual independent phase-locked loop circuits, and the two signals share a unified clock reference.

3. The non-invasive cable metal sheath grounding fault detection system according to claim 2, characterized in that, The dual-frequency excitation host is equipped with a miniature interference acquisition coil, which is used to pick up the 50Hz power frequency magnetic field and environmental electromagnetic interference signal at the tunnel site. The compensation component with the same amplitude but opposite phase as the interference signal is generated by the feedforward adaptive cancellation circuit, and the compensation component is superimposed on the main excitation signal in real time and output.

4. The non-invasive cable metal sheath grounding fault detection system according to claim 2, characterized in that, The dual-frequency excitation host is equipped with a host interface, and the excitation coil is connected to the host interface through a connecting wire. The excitation coil is a flexible structure with an opening for fitting into the grounding circuit of the cable's metal sheath. A magnetic flux closed-loop detection unit is installed at the coil opening to monitor the coupling degree between the coil and the grounding lead, the magnetic circuit closure state, and the signal transmission efficiency in real time. The dual-frequency excitation host dynamically adjusts the output impedance, excitation power, and driving voltage based on the real-time monitoring results to achieve the set coupling matching degree between the coil and the grounding lead.

5. The non-invasive detection system for grounding faults in the metallic sheath of cables according to claim 1, characterized in that, The fixture includes two clamps, each equipped with a magnetic attraction device and a complementary induction coil inside the clamp.

6. The non-invasive cable metal sheath grounding fault detection system according to claim 4, characterized in that, The wireless synchronization acquisition substation is also equipped with: UWB / BeiDou fusion positioning unit, used for positioning and time synchronization; The main control and wireless communication unit is used to communicate with the intelligent processing terminal for supervision.

7. The non-invasive detection system for grounding faults in the metallic sheath of cables according to claim 1, characterized in that, The intelligent supervision processing terminal includes: The digital twin modeling module is used to construct a digital twin model of the grounding circuit of the metal sheath of the cable to be tested; The dual-frequency impedance joint decoupling algorithm module is used to calculate the impedance in the grounding loop of the cable metal sheath based on the data collected by the wireless synchronous acquisition substation, and decompose the grounding loop impedance into four independent components: sheath body resistance, down conductor resistance, grounding point contact resistance, and grounding electrode resistance. The fault classification and responsibility determination module, based on impedance decoupling results and digital twin model, completes fault type identification and level classification in accordance with the power engineering construction quality acceptance specifications, and automatically determines the responsible party and construction link based on the impedance component where the fault is located.

8. The non-invasive detection system for grounding faults in the metallic sheath of cables according to claim 1, characterized in that, The intelligent processing terminal for supervision also includes an automatic acceptance report generation module, which is used to generate a supervision acceptance report based on the results of the digital twin model and the fault classification module.

9. A non-invasive detection method for grounding faults in the metallic sheath of cables, characterized in that, The system described in any one of claims 1-8 is used for execution, comprising the following steps: S1: Develop a testing plan based on the tunnel length and the number of grounding points; S2: According to the testing plan, a dual-frequency excitation host and several wireless synchronous acquisition substations are installed in the grounding circuit of the cable's metal sheath. S3: The dual-frequency excitation host injects ultra-low frequency excitation signal and power frequency odd harmonic excitation signal into the excitation coil, and the wireless synchronous acquisition substation collects ultra-low frequency response data and harmonic response data at its location. S4: Deploy intelligent processing terminals for supervision and construct a digital twin benchmark model of the cable metal sheath grounding circuit based on the testing plan; S5: The intelligent processing terminal for supervision receives and processes the acquisition signals from several wireless synchronous acquisition substations, determines the fault type and location, and generates a supervision acceptance report.

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