High-voltage cable sheath fault diagnosis method, device, equipment and medium

Abstract

The embodiment of the invention provides a high-voltage cable sheath fault diagnosis method and device, equipment and a medium. The method comprises the following steps: firstly, acquiring sheath voltage-to-ground time sequence data and sheath ring current time sequence data under a dynamic working condition that a load current of a main cable changes; then, constructing a sheath voltage frequency domain parameter according to the sheath voltage-to-ground time sequence data; secondly, constructing sheath ring current time domain parameters according to the sheath ring current time sequence data; and finally, matching the sheath voltage frequency domain parameter and the sheath ring current time domain parameter with fault mode characteristics in a preset fault mode library to obtain a fault diagnosis result of the sheath. According to the method, the influence of the load absolute value on the steady-state measurement value is avoided, and the accuracy of the fault diagnosis result is improved.

Description

Technical Field

[0001] This application relates to the field of power equipment condition monitoring technology, and in particular to a method, device, equipment and medium for diagnosing faults in the sheath of high-voltage cables. Background Technology

[0002] High-voltage cables are core transmission equipment in power systems, widely used in urban power grids, industrial power supply, and long-distance power transmission. As a crucial component of the cable structure, the grounding status of the cable sheath directly affects the safety and stability of cable operation. Sheath grounding faults can lead to localized overheating, accelerated insulation aging, and even cable breakdown, seriously threatening power grid safety. In power system operation and maintenance, real-time monitoring and fault diagnosis of high-voltage cable sheaths are necessary to provide early warnings of potential risks. Therefore, there is an urgent need for a multi-dimensional feature analysis method based on sheath response characteristics during dynamic load changes to achieve high-precision, interference-resistant sheath fault diagnosis and ensure the reliable operation of the power system.

[0003] Existing fault diagnosis methods for high-voltage cable sheaths are mainly based on the voltage-current amplitude relationship under steady-state conditions. Specifically, by collecting the sheath-to-ground voltage and circulating current signals under stable cable load conditions, calculating the voltage-to-current amplitude ratio or phase difference, and comparing it with a preset threshold, it is determined whether a grounding fault exists in the sheath.

[0004] However, existing solutions are insufficient in terms of accuracy and reliability. Summary of the Invention

[0005] This application provides a method, apparatus, equipment, and medium for diagnosing faults in the sheath of high-voltage cables, in order to solve the problems of insufficient accuracy and reliability in the prior art.

[0006] In a first aspect, embodiments of this application provide a method for diagnosing faults in the sheath of a high-voltage cable, including:

[0007] Under dynamic operating conditions of varying load current in the main cable, collect timing data of sheath-to-ground voltage and sheath circulating current.

[0008] Construct the sheath voltage frequency domain parameters based on the sheath-to-ground voltage time series data;

[0009] Construct the time-domain parameters of the sheath circulation based on the sheath circulation time-series data;

[0010] The sheath voltage frequency domain parameters and the sheath circulating current time domain parameters are matched with the fault mode features in the preset fault mode library to obtain the fault diagnosis results of the sheath.

[0011] In one possible implementation, the acquisition of sheath-to-ground voltage and sheath circulating current timing data under dynamic operating conditions of varying main cable load current includes:

[0012] Monitor the change process of the load current of the main cable and calculate the second derivative of the load current of the main cable;

[0013] Identify the inflection point where the sign of the second derivative reverses;

[0014] The data collection operation is triggered within a preset delay period after the inflection point.

[0015] In one possible implementation, constructing the sheath voltage frequency domain parameters based on the sheath-to-ground voltage time-series data includes:

[0016] The phase information of at least two frequency components near the resonant frequency is extracted by performing frequency domain transformation on the timing data of the sheath to ground voltage.

[0017] Calculate the phase angle relationship between the phase information and construct a phase angle sequence;

[0018] The phase angle sequence is reconstructed in phase space to obtain the trajectory, and the Lyapunov exponent of the trajectory and the sample entropy of the phase angle sequence are calculated.

[0019] The Lyapunov exponent and the sample entropy are used as vector components to form the frequency domain parameters of the sheath voltage.

[0020] In one possible implementation, constructing the sheath circulation time-domain parameters based on the sheath circulation time-series data includes:

[0021] The time series data of the protective layer circulation is decomposed into fast-scale components and slow-scale components.

[0022] The fast-scale component and the slow-scale component are subjected to analytical signal processing respectively, the cross-correlation coefficient is calculated and the fusion weight is determined;

[0023] The fast-scale component and the slow-scale component are fused according to the fusion weight to obtain the instantaneous envelope;

[0024] The instantaneous envelope is fitted to the theoretical response model, and the deviation is extracted as the time-domain parameter of the sheath circulation. The theoretical response model is established based on the material conductivity of the sheath, the geometric dimensions of the sheath, and the equivalent capacitance between the sheath and the ground.

[0025] In one possible implementation, after constructing the sheath circulation time-domain parameters, the method further includes:

[0026] Obtain the sheath circulation timing data of a reference cable arranged adjacent to the main cable;

[0027] The reference cable sheath circulating current timing data is analyzed and processed to obtain the reference instantaneous envelope;

[0028] The morphological matching degree between the instantaneous envelope of the main cable and the reference instantaneous envelope is calculated and used as a reference parameter for the main cable.

[0029] In one possible implementation, before matching the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with fault mode features in a preset fault mode library, the method further includes:

[0030] Based on the Lyapunov exponent and the sample entropy in the frequency domain parameters of the sheath voltage, the complex value of the equivalent impedance of the sheath grounding loop at the resonant frequency is inversely calculated.

[0031] Based on the deviation in the time-domain parameters of the sheath circulation current, the equivalent impedance time-domain response of the sheath grounding loop is inferred.

[0032] The time-domain equivalent impedance response is obtained by performing an inverse transformation on the complex value of the equivalent impedance.

[0033] The degree of consistency between the time-domain equivalent impedance response and the time-domain equivalent impedance response is used as a consistency parameter for the sheath.

[0034] In one possible implementation, matching the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with fault mode features in a preset fault mode library includes:

[0035] The frequency domain parameters of the sheath voltage, the time domain parameters of the sheath circulation current, the spatial distribution parameters, the thermal coupling parameters, the comparison parameters, and the consistency parameters are constructed into a multi-dimensional feature vector;

[0036] Calculate the spatial distance between the multidimensional feature vector and the features of each fault mode in the preset fault mode library in the preset parameter space;

[0037] The fault type corresponding to the fault mode feature with the smallest spatial distance is selected as the preliminary diagnostic result;

[0038] Obtain the multidimensional feature vectors of the protective layer at multiple past diagnostic times to form a trajectory;

[0039] Analyze the movement direction of the trajectory and the positional relationship between the features of each fault mode in the preset fault mode library and the preset parameter space to determine the fault evolution information;

[0040] The preliminary diagnostic results and fault evolution information are output as the fault diagnosis results.

[0041] Secondly, embodiments of this application provide a high-voltage cable sheath fault diagnosis device, comprising:

[0042] The acquisition module is used to acquire sheath-to-ground voltage timing data and sheath circulating current timing data under dynamic operating conditions of changing main cable load current;

[0043] The first construction module is used to construct the sheath voltage frequency domain parameters based on the sheath-to-ground voltage time-series data.

[0044] The second construction module is used to construct the sheath circulation time-domain parameters based on the sheath circulation time-series data.

[0045] The matching module is used to match the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with the fault mode characteristics in the preset fault mode library to obtain the fault diagnosis results of the sheath.

[0046] In one possible implementation, the acquisition module is specifically used for:

[0047] Monitor the change process of the load current of the main cable and calculate the second derivative of the load current of the main cable;

[0048] Identify the inflection point where the sign of the second derivative reverses;

[0049] The data collection operation is triggered within a preset delay period after the inflection point.

[0050] In one possible implementation, the first building module is specifically used for:

[0051] The phase information of at least two frequency components near the resonant frequency is extracted by performing frequency domain transformation on the timing data of the sheath to ground voltage.

[0052] Calculate the phase angle relationship between the phase information and construct a phase angle sequence;

[0053] The phase angle sequence is reconstructed in phase space to obtain the trajectory, and the Lyapunov exponent of the trajectory and the sample entropy of the phase angle sequence are calculated.

[0054] The Lyapunov exponent and the sample entropy are used as vector components to form the frequency domain parameters of the sheath voltage.

[0055] In one possible implementation, the second building module is specifically used for:

[0056] The time series data of the protective layer circulation is decomposed into fast-scale components and slow-scale components.

[0057] The fast-scale component and the slow-scale component are subjected to analytical signal processing respectively, the cross-correlation coefficient is calculated and the fusion weight is determined;

[0058] The fast-scale component and the slow-scale component are fused according to the fusion weight to obtain the instantaneous envelope;

[0059] The instantaneous envelope is fitted to the theoretical response model, and the deviation is extracted as the time-domain parameter of the sheath circulation. The theoretical response model is established based on the material conductivity of the sheath, the geometric dimensions of the sheath, and the equivalent capacitance between the sheath and the ground.

[0060] In one possible implementation, the apparatus further includes a processing module, which, after constructing the sheath circulation time-domain parameters, is configured to:

[0061] Obtain the sheath circulation timing data of a reference cable arranged adjacent to the main cable;

[0062] The reference cable sheath circulating current timing data is analyzed and processed to obtain the reference instantaneous envelope;

[0063] The morphological matching degree between the instantaneous envelope of the main cable and the reference instantaneous envelope is calculated and used as a reference parameter for the main cable.

[0064] In one possible implementation, before matching the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with fault mode features in a preset fault mode library, the processing module is further configured to:

[0065] Based on the Lyapunov exponent and the sample entropy in the frequency domain parameters of the sheath voltage, the complex value of the equivalent impedance of the sheath grounding loop at the resonant frequency is inversely calculated.

[0066] Based on the deviation in the time-domain parameters of the sheath circulation current, the equivalent impedance time-domain response of the sheath grounding loop is inferred.

[0067] The time-domain equivalent impedance response is obtained by performing an inverse transformation on the complex value of the equivalent impedance.

[0068] The degree of consistency between the time-domain equivalent impedance response and the time-domain equivalent impedance response is used as a consistency parameter for the sheath.

[0069] In one possible implementation, the matching module is specifically used for:

[0070] The frequency domain parameters of the sheath voltage, the time domain parameters of the sheath circulation current, the spatial distribution parameters, the thermal coupling parameters, the comparison parameters, and the consistency parameters are constructed into a multi-dimensional feature vector;

[0071] Calculate the spatial distance between the multidimensional feature vector and the features of each fault mode in the preset fault mode library in the preset parameter space;

[0072] The fault type corresponding to the fault mode feature with the smallest spatial distance is selected as the preliminary diagnostic result;

[0073] Obtain the multidimensional feature vectors of the protective layer at multiple past diagnostic times to form a trajectory;

[0074] Analyze the movement direction of the trajectory and the positional relationship between the features of each fault mode in the preset fault mode library and the preset parameter space to determine the fault evolution information;

[0075] The preliminary diagnostic results and fault evolution information are output as the fault diagnosis results.

[0076] Thirdly, embodiments of this application provide an electronic device, including: a memory and a processor;

[0077] The memory stores computer-executed instructions;

[0078] The processor executes computer execution instructions stored in the memory, causing the processor to perform the first aspect and / or various possible implementations of the first aspect as described above.

[0079] Fourthly, embodiments of this application provide a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, are used to implement the first aspect and / or various possible implementations of the first aspect.

[0080] The high-voltage cable sheath fault diagnosis method, apparatus, equipment, and medium provided in this application first collect time-series data of the sheath-to-ground voltage and sheath circulating current for dynamic operating conditions where the main cable load current changes. By introducing load changes as an excitation source, the electromagnetic response of the sheath grounding loop is fully excited, thereby obtaining dynamic response information reflecting the intrinsic characteristics of the sheath grounding state. Subsequently, frequency domain analysis is performed on the sheath-to-ground voltage time-series data, transforming it from the time domain to the frequency domain. The phase relationship between different frequency components is extracted, and a frequency domain parameter of the sheath voltage is constructed accordingly. This parameter can characterize the phase response characteristics of the equivalent loop formed by the sheath and the ground in the frequency dimension, avoiding reliance solely on electrical... The voltage amplitude is affected by changes in load size. Next, the sheath circulating current time-series data is processed using time-domain analysis to characterize its establishment, evolution, and attenuation patterns over time, constructing sheath circulating current time-domain parameters. These parameters reflect the transient response characteristics of the sheath grounding loop under load disturbances and its deviation from the ideal grounding state. Finally, the sheath voltage frequency-domain parameters and sheath circulating current time-domain parameters are fused and matched with the characteristic patterns corresponding to various sheath faults in a preset fault mode library. Based on the matching results, fault diagnosis conclusions for the sheath are output, thereby achieving accurate identification of the sheath grounding state and fault type determination under dynamic load conditions, improving the reliability and adaptability of sheath fault diagnosis. Attached Figure Description

[0081] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0082] Figure 1 This is an application environment diagram of the high-voltage cable sheath fault diagnosis method provided in the embodiments of this application;

[0083] Figure 2 A flowchart illustrating the high-voltage cable sheath fault diagnosis method provided in this application embodiment. Figure 1 ;

[0084] Figure 3 A flowchart illustrating the high-voltage cable sheath fault diagnosis method provided in this application embodiment. Figure 2 ;

[0085] Figure 4 This is a schematic diagram of the high-voltage cable sheath fault diagnosis device provided in the embodiments of this application;

[0086] Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.

[0087] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0088] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0089] High-voltage cables are core transmission equipment in power systems, widely used in urban power grids, industrial power supply, and long-distance power transmission. As a crucial component of the cable structure, the grounding status of the cable sheath directly affects the safety and stability of cable operation. Sheath grounding faults can lead to localized overheating, accelerated insulation aging, and even cable breakdown, seriously threatening power grid safety. In power system operation and maintenance, real-time monitoring and fault diagnosis of high-voltage cable sheaths are necessary to provide early warnings of potential risks. Therefore, there is an urgent need for a multi-dimensional feature analysis method based on sheath response characteristics during dynamic load changes to achieve high-precision, interference-resistant sheath fault diagnosis and ensure the reliable operation of the power system.

[0090] Existing fault diagnosis methods for high-voltage cable sheaths are mainly based on the voltage-current amplitude relationship under steady-state conditions. Specifically, by collecting the sheath-to-ground voltage and circulating current signals under stable cable load conditions, calculating the voltage-to-current amplitude ratio or phase difference, and comparing it with a preset threshold, it is determined whether a grounding fault exists in the sheath.

[0091] However, in existing technologies, the voltage and current signals of the sheath are easily affected by load fluctuations and environmental noise. Signals acquired under a single steady-state condition often contain a significant amount of interference. Furthermore, existing methods primarily rely on voltage and current amplitude information for judgment, ignoring the dynamic characteristics of the signals in the frequency and time domains. This makes the existing methods insufficient in distinguishing between different types of faults. Additionally, existing methods generally use fixed thresholds or simple ratio calculations to determine fault types, lacking in-depth analysis of the physical characteristics of the sheath grounding loop.

[0092] Based on this, this application proposes a fault diagnosis method for high-voltage cable sheaths. Addressing the shortcomings of existing high-voltage cable sheath fault diagnosis technologies, which primarily rely on steady-state voltage and current amplitudes for judgment, are susceptible to load fluctuations, and struggle to distinguish different fault types, the inventors no longer focus on the absolute magnitude of measured quantities under steady-state conditions. Instead, they utilize the change in the main cable load current as an external excitation, collecting sheath-to-ground voltage and sheath circulating current time-series data under dynamic conditions to characterize the intrinsic characteristics of the sheath grounding loop from the perspective of system response. In specific implementation, frequency domain analysis is performed on the sheath-to-ground voltage time-series data to extract the phase relationship between different frequency components and construct sheath voltage frequency domain parameters to reflect the phase response characteristics of the grounding loop in the frequency dimension. Simultaneously, time domain analysis is performed on the sheath circulating current time-series data to extract response features during the establishment and evolution of the circulating current and construct sheath circulating current time-domain parameters to characterize the transient response behavior of the grounding loop. Finally, the aforementioned frequency domain parameters and time domain parameters are matched with features in a preset fault mode library to obtain the fault diagnosis result for the sheath. This technical solution transforms the dynamic response characteristics under load disturbances into stable and comparable diagnostic parameters, enabling the diagnostic results to directly reflect the intrinsic physical properties of the sheath grounding state. This effectively reduces the impact of load size and operating condition changes on the diagnostic results, improving the accuracy, distinguishability, and reliability of sheath fault identification in engineering applications.

[0093] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0094] Figure 1 This is an application environment diagram of the high-voltage cable sheath fault diagnosis method provided in the embodiments of this application; the high-voltage cable sheath fault diagnosis method provided in the embodiments of this application can be applied to, for example... Figure 1 In the application environment shown, monitoring terminal 101 communicates with server 102 via a network. A data storage system can store the data that server 102 needs to process. The data storage system can be integrated onto server 102, or it can be located in the cloud or on other network servers. Monitoring terminal 101 can be, but is not limited to, an independent monitoring device installed at a cable joint, an embedded monitoring device installed in a sheath grounding box, or a sheath monitoring module integrated into a power distribution terminal. Server 102 can be a standalone physical server, a server cluster or distributed system composed of multiple physical servers, or a cloud server providing cloud computing services. Server 102 can be deployed in the local monitoring center of a substation or in the remote dispatch center of a power company.

[0095] Figure 2 A flowchart illustrating the high-voltage cable sheath fault diagnosis method provided in this application embodiment. Figure 1 ;like Figure 2 As shown, the method includes:

[0096] S201. Collect sheath-to-ground voltage timing data and sheath circulating current timing data under dynamic operating conditions of changing main cable load current.

[0097] In one possible approach, the change process of the main cable load current is first monitored, and the second derivative of the main cable load current is calculated; then, the inflection point when the sign of the second derivative reverses is identified; finally, within a preset delay time after the inflection point, the acquisition operation is triggered.

[0098] It should be understood that the monitoring terminal first continuously monitors the load current of the main cable, collecting the current value in real time and forming a time-series data of the load current changing over time. Based on this, the second derivative of the load current time-series data is calculated to obtain the second derivative sequence of the main cable load current. When the load current changes from accelerating to decelerating or vice versa, the corresponding second derivative will reverse sign. Therefore, by traversing the second derivative sequence and detecting its sign change, the time point when the second derivative reverses sign is identified and determined as the inflection point of the load current change trend. Subsequently, data acquisition is triggered within a preset delay period after the inflection point, thereby capturing the complete response process of the sheath-to-ground voltage and sheath circulating current transitioning from the initial state to a new equilibrium state.

[0099] The second derivative is used to characterize the rate of change of the load current, and the preset delay time is used to wait for the electromagnetic response of the sheath to the load change to be fully established. Its value can be set according to parameters such as the length of the main cable line, the sheath grounding method, and the conductivity of the sheath material.

[0100] For example, when the main cable length is 5 km, 10 km, or 15 km, the preset delay time can be set to 0.5 seconds, 1 second, or 1.5 seconds, respectively. By starting the acquisition operation within the preset delay time after the inflection point, the sheath-to-ground voltage is collected to form sheath-to-ground voltage timing data, and the sheath circulating current is collected to form sheath circulating current timing data. This allows us to obtain the complete dynamic response process of the sheath grounding loop transitioning from the original state to a new equilibrium state under load change excitation.

[0101] Understandably, compared to the traditional method of collecting data after the load current reaches a steady state, this method avoids the incomparability problem caused by the linear change of the measured sheath-to-ground voltage and sheath circulating current with the absolute value of the load current. For example, if the sheath-to-ground voltage is measured to be 8V when the main cable load current is 100A and 16V when the main cable load current is 200A, although the voltage values ​​are different, the grounding state they reflect may be the same, which can lead to misjudgment by the method based on absolute values. This makes the time series data on which the subsequent analysis is based mainly reflect the dynamic response characteristics of the sheath grounding state itself, providing a stable and physically consistent input data foundation for the construction of subsequent frequency domain parameters and time domain parameters.

[0102] It should also be noted that, in this embodiment, collecting the sheath-to-ground voltage timing data includes simultaneously collecting the sheath-to-ground voltage at at least three spatial locations along the length of the sheath, to form multiple voltage timing data sets with a unified time reference and the same sampling frequency. These spatial locations can be set at the beginning, middle, and end of the sheath, or they can be evenly distributed along the length of the sheath, or the corresponding key measurement locations can be selected according to the sheath grounding method. For example, for a 12-kilometer-long high-voltage cable sheath, spatial locations can be set at 0 km, 6 km, and 12 km, or at 0 km, 4 km, 8 km, and 12 km.

[0103] Subsequently, any one of the multiple voltage time series data is selected as the voltage time series data for subsequent frequency domain analysis and feature extraction processing. At the same time, the waveform consistency between multiple voltage time series data is calculated. By calculating the cross-correlation coefficient, phase difference or waveform matching degree between voltage time series data pairwise, and statistically processing the calculation results, spatial distribution parameters reflecting the spatial distribution characteristics of the sheath-to-ground voltage are obtained. When the voltage time series waveforms at different spatial locations are highly consistent, the spatial distribution parameters have higher values, while when there is phase shift or waveform distortion, the spatial distribution parameters decrease accordingly.

[0104] As can be seen, the above method not only acquires voltage time-series data for subsequent analysis but also simultaneously obtains spatial distribution parameters reflecting the spatial consistency of sheath voltage, thus avoiding the problem that single-point measurements cannot cover the entire length of the sheath. At the same time, sheath circulating current is simultaneously acquired within the same dynamic acquisition window, forming sheath circulating current time-series data. This ensures strict alignment of sheath-to-ground voltage time-series data and sheath circulating current time-series data on the time axis, providing a consistent data foundation for subsequent joint analysis based on voltage frequency domain characteristics and circulating current time domain characteristics. By simultaneously acquiring data at multiple spatial locations and introducing spatial distribution parameters, the spatial non-uniformity of the sheath grounding state can be effectively identified, preventing missed detections due to faults such as local insulation breakdown and multi-point grounding. This provides more comprehensive and reliable input data for subsequent sheath fault diagnosis.

[0105] Furthermore, the sheath circulating current is continuously sampled by a current sensor arranged in the sheath circuit to form circulating current time-series data of the sheath circulating current changing over time; at the same time, the sheath surface temperature is collected synchronously during the acquisition of sheath circulating current time-series data to form temperature time-series data of the sheath surface temperature changing over time, and the sheath surface temperature can be acquired by a thermocouple temperature sensor, an infrared temperature sensor or a fiber optic temperature sensor arranged on the sheath surface.

[0106] Subsequently, time-series analysis was performed on the temperature data to identify the point in time when the temperature transitioned from a stable state to a continuously rising state, and this point was determined as the temperature initiation time. Simultaneously, time-series analysis was performed on the sheath circulation data to identify the point in time when the circulation transitioned from a stable state to a continuously rising state, and this point was determined as the circulation initiation time. Further, the time interval between the temperature initiation time and the circulation initiation time was calculated, and this time interval was used as a thermal coupling parameter for the sheath, characterizing the temporal relationship between the sheath circulation establishment process and the sheath temperature response process. By simultaneously acquiring sheath circulation time-series data and sheath temperature time-series data within the same dynamic acquisition window, and introducing the thermal coupling parameter as an auxiliary feature, the response characteristics of the sheath grounding loop under load variation excitation can be characterized from the perspective of electro-thermal coupling.

[0107] Under normal grounding conditions, the thermal resistance between the sheath and the ground is small, heat is easily conducted, and the thermal coupling parameter is relatively large. However, under fault conditions such as poor grounding, loose connection, or insulation breakdown, the thermal resistance between the sheath and the ground increases, heat accumulates in the sheath, and the thermal coupling parameter decreases accordingly.

[0108] The sheath circulating current timing data and thermal coupling parameters obtained through the above methods can not only reflect the transient current response characteristics of the sheath grounding loop, but also introduce information in the thermal field dimension. This effectively avoids the problem of being affected by load current fluctuations due to relying solely on the sheath-to-ground voltage or the amplitude of the sheath circulating current, and provides a more stable and physically consistent input data basis for subsequent sheath fault diagnosis.

[0109] S202. Construct the frequency domain parameters of the sheath voltage based on the time series data of the sheath voltage to ground.

[0110] In one feasible approach, firstly, the time-series data of the sheath voltage to ground is transformed in the frequency domain to extract the phase information of at least two frequency components near the resonant frequency; then, the phase angle relationship between the phase information is calculated to construct a phase angle sequence; next, the phase space of the phase angle sequence is reconstructed to obtain the trajectory, and the Lyapunov exponent of the trajectory and the sample entropy of the phase angle sequence are calculated; finally, the Lyapunov exponent and the sample entropy are used as vector components to constitute the frequency domain parameters of the sheath voltage.

[0111] It should be noted that after obtaining the voltage timing data, it is also necessary to establish a distributed parameter equivalent circuit model of the sheath and the ground based on the main cable length and the sheath grounding method, and calculate the resonant frequency corresponding to this equivalent circuit. The distributed parameter equivalent circuit is an equivalent circuit model composed of distributed capacitance, distributed inductance, and distributed resistance formed between the sheath and the ground, and the resonant frequency is the frequency at which this equivalent circuit resonates under the influence of an electromagnetic field.

[0112] It is understandable that the resonant frequency of the equivalent circuit of distributed parameters formed by the sheath and the ground is directly related to the length of the main cable line. The longer the line length, the greater the equivalent inductance, and the lower the resonant frequency. The grounding method of the sheath also affects the resonant frequency; the resonant frequency under single-point grounding differs from that under two-end grounding. The sheath can be grounded at a single point, at both ends, or in a cross-connection grounding configuration. Single-point grounding means the sheath is grounded at only one end, while the other end is insulated; two-end grounding means the sheath is grounded at both ends; and cross-connection grounding means the sheath is grounded in sections through a cross-connection box.

[0113] It is not difficult to understand that by obtaining the line length parameters of the main cable and the grounding method parameters of the sheath, and using the circuit theory of the equivalent circuit of distributed parameters, the resonant frequency of the equivalent circuit formed by the sheath and the ground is calculated using the transmission line resonant frequency calculation formula. The specific value of the resonant frequency is calculated from parameters such as the line length of the main cable, the conductivity of the sheath material, and the equivalent capacitance between the sheath and the ground using circuit theory formulas. Those skilled in the art can calculate it based on the actual cable parameters.

[0114] It should be understood that the frequency domain response of the sheath to ground voltage during load changes is most sensitive near the resonant frequency, and different grounding fault modes exhibit significant differences in their frequency response characteristics near the resonant frequency. Under normal single-point grounding conditions, the phase relationship of the frequency components near the resonant frequency is stable, while multi-point grounding or insulation breakdown faults cause the phase relationship of the frequency components near the resonant frequency to become disordered. Therefore, extracting at least two frequency components within a preset frequency band near the resonant frequency can capture the response characteristics of the sheath grounding loop in the sensitive frequency band.

[0115] Subsequently, a frequency domain transformation (including any one of Fast Fourier Transform, Wavelet Transform, or Hilbert-Huang Transform) is performed on the voltage time series to obtain spectral data containing the amplitude and phase of each frequency component. Within the spectral data, a preset frequency band is set centered on the resonant frequency, and at least two target frequency components with large amplitudes are identified within this band. Further, the voltage time series is divided into N time windows in chronological order, where the window length can be set according to the sampling frequency and analysis frequency resolution. Adjacent time windows may or may not overlap. A frequency domain transformation is performed on each time window, and the phase information of the target frequency components is extracted within each time window. Finally, the phase angle relationship between the phase information in each time window is calculated, and the phase angle relationship is expressed as a phase difference. The phase differences of each time window are arranged in chronological order to form a phase angle sequence. Based on this, phase space reconstruction is performed on the phase angle sequence to obtain the phase space trajectory. The phase space reconstruction adopts a delayed embedding method and sets the embedding dimension and time delay to construct a phase space point sequence. The phase space point sequence is then connected in time order to form the trajectory. The maximum Lyapunov exponent is calculated based on the trajectory, and the sample entropy is calculated based on the phase angle sequence. The Lyapunov exponent is used to characterize the divergence or convergence characteristics of the phase space trajectory, and the sample entropy is used to characterize the complexity and irregularity of the phase angle sequence. Finally, the maximum Lyapunov exponent and the sample entropy are used as vector components to construct the frequency domain parameters of the sheath voltage, and the dynamic response characteristics of the sheath grounding loop in the resonant sensitive frequency band are characterized from the perspective of frequency domain phase coupling and its temporal evolution.

[0116] Since the frequency domain parameters of the sheath voltage are derived from the dynamic characteristics and complexity of the phase angle sequence, the dependence on the absolute magnitude of the voltage amplitude is avoided, thereby reducing the impact of load changes on characteristic quantities. Furthermore, the normal grounding state and fault grounding states such as multi-point grounding and insulation breakdown exhibit distinguishable response differences in the parameter space, improving the accuracy of grounding state identification and fault diagnosis.

[0117] S203. Construct the time-domain parameters of the sheath circulation based on the sheath circulation time-series data.

[0118] In one feasible approach, the sheath circulation time series data is first decomposed into fast-scale and slow-scale components. Then, the fast-scale and slow-scale components are subjected to analytical signal processing to calculate the cross-correlation coefficients and determine the fusion weights. Next, the fast-scale and slow-scale components are fused according to the fusion weights to obtain the instantaneous envelope. Finally, the instantaneous envelope is fitted with the theoretical response model, and the deviation is extracted as the sheath circulation time-domain parameter.

[0119] The theoretical response model is based on the material conductivity of the sheath, its geometric dimensions, and the equivalent capacitance between the sheath and the ground. Multi-scale decomposition is a signal processing method that decomposes the first circulating current time series into multiple components according to different time scales. The fast-scale component is the high-frequency component with a faster rate of change in the first circulating current time series, and the slow-scale component is the low-frequency component with a slower rate of change in the first circulating current time series. The criteria for distinguishing between the fast-scale and slow-scale components can be determined based on the ratio of the component frequency to the characteristic frequency of the sheath grounding loop, the instantaneous frequency statistical characteristics of the component, or by those skilled in the art based on the frequency distribution characteristics of the actual sheath circulating current signal.

[0120] Understandably, multi-scale decomposition methods can be empirical mode decomposition, wavelet decomposition, or variational mode decomposition. The first circulation time series is processed using a multi-scale decomposition method, decomposing it into components at different time scales. Based on the frequency characteristics of each component, higher-frequency components are classified as fast-scale components, and lower-frequency components are classified as slow-scale components.

[0121] It should be noted that the sheath circulating current contains both fast-response and slow-response components during load changes. The fast-response component reflects the high-frequency transient characteristics of the sheath grounding loop, while the slow-response component reflects the low-frequency establishment process of the sheath grounding loop. Different grounding fault modes exhibit different combinations of characteristics in fast and slow responses, and using either the fast-scale component or the slow-scale component alone may miss some fault characteristic information.

[0122] Subsequently, a Hilbert transform is performed on the fast-scale component to obtain the corresponding analytic signal. The analytic signal is in complex form, and its magnitude is calculated to obtain the fast-scale envelope. Similarly, a Hilbert transform is performed on the slow-scale component to obtain the corresponding analytic signal, and its magnitude is calculated to obtain the slow-scale envelope.

[0123] The fast-scale envelope reflects the variation of the amplitude of the fast-scale component over time, while the slow-scale envelope reflects the variation of the amplitude of the slow-scale component over time. The fast-scale and slow-scale envelopes characterize the response process of the sheath circulation at different time scales.

[0124] It is not difficult to understand that, let the fast-scale component be... ,right Perform Hilbert transform to obtain ,in Indicates time, Indicates time The amplitude of the fast-scale component, Indicates time The fast-scale component Hilbert transform results are used to construct an analytic signal. ,in The imaginary unit, For the analytic signal corresponding to the fast-scale component, calculate To obtain the fast-scale envelope ,in Indicates time The fast-scale envelope amplitude. Similarly, for the slow-scale component... Processing is performed to obtain the slow-scale envelope. ,in This represents the amplitude of the slow-scale component at time t. This represents the slow-scale envelope amplitude at time t.

[0125] Furthermore, regarding the fast-scale envelope and slow-scale envelope Perform cross-correlation calculations to determine the Pearson correlation coefficient between the two envelope sequences, thus obtaining the cross-correlation number. cross-relationship number The calculation formula is:

[0126] ;

[0127] in, The length of the envelope sequence, The mean of the fast-scale envelope. This represents the mean of the slow-scale envelope. This represents the cross-correlation coefficient between the fast-scale envelope and the slow-scale envelope.

[0128] The fusion weight is a weighting coefficient used to determine the proportion of the fast-scale envelope and the slow-scale envelope in the fusion process. The fusion weight is determined based on the cross-correlation coefficient. When the cross-correlation coefficient is close to 1, it indicates that the fast-scale envelope and the slow-scale envelope are highly consistent, and they can be assigned similar fusion weights. When the cross-correlation coefficient is small, it indicates that the fast-scale envelope and the slow-scale envelope contain different information, and the fusion weight needs to be determined based on the energy or variance of their respective envelopes.

[0129] It is not difficult to understand that the determination of the fusion weights can be based on a linear mapping relationship of cross-correlation coefficients, a comprehensive calculation relationship between cross-correlation coefficients and envelope energy, or it can be set by those skilled in the art based on the energy distribution characteristics of the actual fast-scale and slow-scale envelopes. Let the fusion weights of the fast-scale envelope be... The fusion weights of the slow-scale envelope are The fusion weights satisfy the normalization condition. ,in This represents the weighting coefficient of the fast-scale envelope in the fusion process. This represents the weighting coefficient of the slow-scale envelope in the fusion process.

[0130] It is easy to understand that the shape of the instantaneous envelope reflects the comprehensive response characteristics of the sheath grounding loop to load changes. There are differences between normal grounding and fault grounding states in terms of the rise rate, peak position, and decline trend of the instantaneous envelope. The sheath material conductivity is a conductivity performance parameter reflecting the sheath material's ability to conduct current. The sheath's geometric dimensions include its length, cross-sectional area, and thickness. The equivalent capacitance between the sheath and the ground is the equivalent lumped parameter of the distributed capacitance formed between the sheath and the ground.

[0131] It is understandable that the theoretical response model is a theoretical calculation model of the circulating current establishment process based on the circuit parameters of the sheath grounding loop. This model describes the theoretical curve of the sheath circulating current establishing over time under ideal normal grounding conditions. The theoretical response model can be an exponential response model based on a first-order RC circuit, an oscillating response model based on a second-order RLC circuit, or a wave response model based on distributed parameter transmission line theory.

[0132] It is not difficult to understand that the electrical conductivity parameter of the protective layer is denoted as... The geometric parameters of the protective layer include the protective layer length. Cross-sectional area of ​​protective layer Protective layer thickness The equivalent capacitance between the protective layer and the ground is denoted as ,in Indicates the electrical conductivity of the protective coating material. Indicates the length of the protective layer. This represents the cross-sectional area of ​​the protective layer. Indicates the thickness of the protective layer. This represents the equivalent capacitance between the sheath and the ground. Based on the resistance R of the sheath grounding loop, the equivalent capacitance between the sheath and the ground... An RC charging model is established as the theoretical response model, where R represents the equivalent resistance of the sheath grounding loop. The expression for the theoretical response model is:

[0133]

[0134] in Indicates time The amplitude of the circulation envelope predicted by the theoretical response model. This is the theoretical steady-state circulation amplitude. It is a time constant. is the base of the natural logarithm.

[0135] It should be noted that the theoretical response model describes the establishment process of the sheath circulating current under ideal normal grounding conditions. When a fault occurs in the sheath grounding loop, the actual sheath circulating current response process will deviate from the theoretical response model. For example, a loose connection fault will cause the grounding loop resistance to increase, slowing down the circulating current establishment speed, and the actual response curve will lag behind the theoretical response model; multiple grounding faults will cause the circulating current response process to exhibit oscillations or multi-peak characteristics, and the actual response curve will show morphological distortion compared to the theoretical response model. Therefore, by comparing the difference between the actual instantaneous envelope and the theoretical response model, it is possible to identify whether a fault exists in the sheath grounding loop.

[0136] Finally, the instantaneous envelope Compared with theoretical response models Curve fitting is performed, and the parameters in the theoretical response model are adjusted using the least squares method or other curve fitting methods. and This minimizes the fitting error between the theoretical response model curve and the instantaneous envelope curve. The deviation is a quantitative indicator of the deviation of the instantaneous envelope from the theoretical response model. The deviation can be the root mean square error between the instantaneous envelope and the theoretical response model, the normalized correlation distance between them, or the amplitude difference between the instantaneous envelope and the theoretical response model at characteristic moments.

[0137] It is not difficult to understand that calculating the instantaneous envelope With the fitted theoretical response model The root mean square error between them is taken as the deviation and denoted as the time-domain parameter of the protective layer circulation. The larger the deviation, the greater the deviation of the instantaneous envelope from the theoretical response model, and the more likely there is a fault in the sheath grounding loop.

[0138] It should be noted that traditional methods typically use the peak or average value of the sheath circulating current as the basis for judgment. These parameters are also affected by the load size and cannot exclude the interference of load changes on the diagnostic results. The deviation of the instantaneous envelope from the theoretical response model, however, is a normalized deviation index that reflects the morphological difference between the actual and theoretical response processes, independent of the absolute magnitude of the circulating current amplitude. Under normal grounding conditions, the actual response process closely matches the theoretical response process with a small deviation. However, under fault grounding conditions, the actual response process deviates significantly from the theoretical response process. By extracting the deviation as a time-domain parameter of the sheath circulating current, time-domain characteristics related only to the grounding state can be obtained, thus eliminating the interference of load changes on the diagnostic results.

[0139] S204. Match the sheath voltage frequency domain parameters and sheath circulating current time domain parameters with the fault mode characteristics in the preset fault mode library to obtain the fault diagnosis results of the sheath.

[0140] Understandably, by matching the sheath voltage frequency domain parameters and sheath circulating current time domain parameters with the characteristics of various fault modes in a preset fault mode library, the sheath grounding state can be quantitatively determined within a unified parameter space. This allows for the comparison and analysis of the frequency domain phase response characteristics and time domain transient response characteristics of the current sheath under dynamic load changes with the typical response characteristics corresponding to different grounding fault modes, thereby accurately identifying the fault type to which the sheath grounding state belongs. Since the sheath voltage frequency domain parameters mainly reflect the phase coupling and dynamic characteristics of the grounding loop in the resonant frequency band, and the sheath circulating current time domain parameters reflect the transient establishment and evolution behavior of the grounding loop, both characterize the intrinsic physical properties of the sheath grounding loop from the frequency domain and time domain, respectively. Through joint matching, the influence of load size, operating condition fluctuations, and environmental interference can be effectively avoided by relying solely on voltage or current amplitude. This enables reliable differentiation of different fault modes such as normal grounding, multi-point grounding, loose connection, and insulation breakdown, thereby improving the accuracy, stability, and engineering applicability of sheath fault diagnosis.

[0141] The high-voltage cable sheath fault diagnosis method provided in this application first collects time-series data of sheath-to-ground voltage and sheath circulating current for dynamic operating conditions where the main cable load current changes. By introducing load change as an excitation source, the electromagnetic response of the sheath grounding loop is fully excited, thereby obtaining dynamic response information reflecting the intrinsic characteristics of the sheath grounding state. Subsequently, frequency domain analysis is performed on the sheath-to-ground voltage time-series data, transforming it from the time domain to the frequency domain. The phase relationship between different frequency components is extracted, and a frequency domain parameter of the sheath voltage is constructed accordingly. This parameter can characterize the phase response characteristics of the equivalent loop formed by the sheath and the ground in the frequency dimension, avoiding reliance solely on voltage amplitude. Affected by changes in load size, the sheath circulating current time-series data is then processed using time-domain analysis. The establishment, evolution, and attenuation patterns of the circulating current over time are characterized, and sheath circulating current time-domain parameters are constructed. These parameters reflect the transient response characteristics of the sheath grounding loop under load disturbances and its deviation from the ideal grounding state. Finally, the sheath voltage frequency-domain parameters and the sheath circulating current time-domain parameters are fused and matched with the characteristic patterns corresponding to various sheath faults in a preset fault mode library. Based on the matching results, fault diagnosis conclusions for the sheath are output, thereby achieving accurate identification of the sheath grounding state and fault type determination under dynamic load conditions, improving the reliability and adaptability of sheath fault diagnosis.

[0142] It should be noted that, since the time-domain fluctuations of the main cable sheath circulating current simultaneously incorporate common components such as load changes, electromagnetic coupling, and environmental disturbances, it is difficult to distinguish the characteristic deviations caused by sheath anomalies based solely on its own time-series characteristics. Therefore, it is necessary to introduce the sheath circulating current of an adjacent reference cable as a benchmark to achieve suppression of common-mode effects and relative quantification of anomalous characteristics. Specifically:

[0143] First, the sheath circulating current timing data of the reference cable arranged adjacent to the main cable is obtained; then, the sheath circulating current timing data of the reference cable is subjected to analytical signal processing to obtain the reference instantaneous envelope; finally, the morphological matching degree between the instantaneous envelope of the main cable and the instantaneous envelope of the reference cable is calculated as a reference parameter for the main cable.

[0144] It should be understood that, to further improve the reliability of the determination of the sheath circulating current time-domain characteristics, a reference cable arranged adjacent to the main cable needs to be introduced as a comparison object. The reference cable is an adjacent cable laid in the same power line as the main cable, physically adjacent to it, usually located in the same cable trench or cable tunnel, thus operating in the same environment and experiencing similar load changes. The selection of the reference cable meets the requirements of having the same or similar model and specifications, consistent load change conditions, and a known normal sheath grounding state.

[0145] By collecting sheath circulating current measurement data of the reference cable within the same time period as the main cable, a sheath circulating current time series for the reference cable is formed. This reference sheath circulating current time series has the same time base and sampling frequency as the first circulating current time series of the main cable. Subsequently, the sheath circulating current time series of the reference cable is processed using the same analytical signal processing procedure as the main cable. Fast-scale and slow-scale components are obtained through multi-scale decomposition. Analytical signal processing is then performed on the fast-scale and slow-scale components to obtain their corresponding envelopes. The fusion weight is determined based on the correlation between the fast-scale and slow-scale envelopes. The two types of envelopes are then fused to obtain a reference instantaneous envelope. This reference instantaneous envelope is used to characterize the typical time-domain response characteristics of the sheath circulating current under normal grounding conditions during load changes. After obtaining the instantaneous envelopes of the main cable and the reference instantaneous envelope of the reference cable, amplitude normalization is performed on the two envelope curves, and the similarity between them in shape is calculated to obtain the shape matching degree. Furthermore, the morphological matching degree can be characterized by the correlation coefficient, the reciprocal of the dynamic time-normalized distance, or the reciprocal of the normalized Euclidean distance, and this morphological matching degree can be used as a reference parameter for the main cable.

[0146] If the instantaneous envelope of the main cable is denoted as The reference instantaneous envelope of the reference cable is denoted as ,in Indicates the time of the main cable The instantaneous envelope amplitude, Indicates the reference cable at time The reference instantaneous envelope amplitude is obtained. The instantaneous envelopes of the main cable and the reference instantaneous envelope of the reference cable are normalized separately. The Pearson correlation coefficient between the two normalized curves is calculated to obtain the shape matching degree. ,in This indicates the morphological matching degree between the instantaneous envelope of the main cable and the reference instantaneous envelope of the reference cable.

[0147] It's easy to understand that the closer the shape matching degree is to 1, the more similar the instantaneous envelope of the main cable is to the reference instantaneous envelope of the reference cable, and the closer the grounding state of the main cable is to a normal state. Conversely, the smaller the shape matching degree, the greater the difference between the instantaneous envelope of the main cable and the reference instantaneous envelope of the reference cable, and the more likely there is an abnormality in the grounding state of the main cable. The shape matching degree... Used as a reference parameter for the main cable.

[0148] Understandably, by introducing a reference cable arranged adjacent to the main cable as a benchmark and comparing the sheath circulation current response process of the main cable and the reference cable under the same environmental and load conditions, the influence of common-mode interference factors such as changes in ambient temperature and drift in material parameters on the diagnostic results can be effectively eliminated. This allows the reference parameters to more accurately reflect the degree of deviation of the grounding state of the main cable sheath from the normal state, thereby further improving the accuracy and reliability of fault diagnosis.

[0149] Figure 3 A flowchart illustrating the high-voltage cable sheath fault diagnosis method provided in this application embodiment. Figure 2 ,like Figure 3 As shown, in this embodiment... Figure 2 Based on the embodiments, the process of fault mode feature matching is described in detail. The method includes:

[0150] S301. Construct a multi-dimensional feature vector from the sheath voltage frequency domain parameters, sheath circulation time domain parameters, spatial distribution parameters, thermal coupling parameters, comparison parameters, and consistency parameters.

[0151] It should be understood that, in this embodiment, a multi-dimensional feature vector for fault diagnosis is constructed based on the unified organization and vectorization of the above-mentioned multiple parameters. Specifically, the sheath voltage frequency domain parameter consists of two components: the Lyapunov exponent and the sample entropy, used to characterize the dynamic characteristics and complexity of the sheath-to-ground voltage phase relationship; the sheath circulating current time domain parameter is the deviation of the instantaneous envelope of the sheath circulating current from the theoretical response model, used to characterize the transient response characteristics of the sheath grounding loop; the spatial distribution parameter is used to characterize the consistency of the sheath-to-ground voltage waveform at different spatial locations; the thermal coupling parameter is the time interval between the temperature initiation time and the circulating current initiation time, used to characterize the electro-thermal coupling response characteristics of the sheath; the reference parameter is the morphological matching degree between the instantaneous envelope of the main cable sheath circulating current and the corresponding envelope of the reference cable; the consistency parameter is used to characterize the consistency between the time-domain equivalent impedance response obtained by back-derived from the frequency domain parameters and the time-domain equivalent impedance response obtained by back-derived from the circulating current time domain parameters.

[0152] Understandably, the above parameters are arranged in a preset order, with the sheath voltage frequency domain parameter providing two vector components and the remaining parameters each providing one vector component, thus forming a multidimensional feature vector containing seven components. During the construction of this multidimensional feature vector, each component can be normalized to eliminate the influence of differences in dimensions and numerical ranges between different physical quantities. This allows the multidimensional feature vector to comprehensively characterize the sheath grounding state in multiple dimensions, including frequency domain, time domain, spatial distribution, electro-thermal coupling, comparison characteristics, and physical consistency, within a unified parameter space. This provides a unified and stable data representation for subsequent fault mode matching and diagnostic judgment based on the feature space.

[0153] S302. Calculate the spatial distance between the multidimensional feature vector and the features of each fault mode in the preset fault mode library in the preset parameter space.

[0154] It should be understood that, in this embodiment, based on the multi-dimensional feature vector constructed in step S301, distance calculation is performed between the multi-dimensional feature vector and the fault mode features in the preset fault mode library within the preset parameter space, in order to quantify the degree of difference between the current sheath grounding state and each known fault mode. The preset fault mode library is a pre-established feature database, which stores fault mode features corresponding to various sheath grounding states. Each fault mode feature is represented in the form of a feature vector, and its vector dimension is consistent with the dimension of the multi-dimensional feature vector. The fault modes in the preset fault mode library include at least the normal single-point grounding mode, multi-point grounding mode, virtual connection mode, and insulation breakdown mode. The preset parameter space is a high-dimensional feature space spanned by the components of the multi-dimensional feature vector, and its spatial dimension is the same as the dimension of the multi-dimensional feature vector. Different sheath grounding states correspond to different distribution locations or regions in this parameter space. Furthermore, using a preset distance metric, the spatial distance between the multidimensional feature vector and each fault mode feature in the preset fault mode library is calculated in the preset parameter space. The spatial distance is used to characterize the similarity between the multidimensional feature vector and the corresponding fault mode feature. The spatial distance can be any one of Euclidean distance, Mahalanobis distance, or Manhattan distance.

[0155] It is understandable that by traversing the preset fault mode library, the spatial distance between the multidimensional feature vector and each fault mode feature is calculated one by one, and the corresponding distance set is obtained. The smaller the spatial distance value, the closer the position of the multidimensional feature vector and the fault mode feature in the parameter space is, and the higher the degree of matching between the current sheath grounding state and the fault mode, thus providing a quantitative basis for subsequent fault mode determination.

[0156] S303. Select the fault type corresponding to the fault mode feature with the minimum spatial distance as the preliminary diagnostic result.

[0157] It should be understood that, in this embodiment, after calculating the spatial distance between the multidimensional feature vector and each fault mode feature in the preset fault mode library, the resulting distance set is compared and analyzed. The fault mode feature with the smallest spatial distance value is selected, and the fault type corresponding to this fault mode feature is determined as the preliminary diagnostic result of the current sheath grounding state. Since spatial distance is used to quantify the similarity between the multidimensional feature vector and each fault mode feature in the preset parameter space, the smallest spatial distance indicates that the current sheath grounding state has the highest degree of matching with the corresponding fault mode in multiple physical feature dimensions. Therefore, this fault mode can most directly reflect the actual situation of the sheath grounding state at the current moment. The preliminary diagnostic result is given based on the multidimensional feature vector at the current diagnostic moment, which is used to characterize the fault type that is closest to the sheath grounding state at that moment. The fault type can be any grounding state such as normal single-point grounding, multi-point grounding, loose connection, or insulation breakdown.

[0158] It should be noted that the preliminary diagnostic results only reflect the current state matching relationship and have not yet incorporated the evolution information of the sheath grounding state in the time dimension, so as to provide a basis for subsequent fault evolution analysis and result correction by combining the feature vectors of multiple historical diagnostic moments.

[0159] S304. Obtain the multidimensional feature vectors of the protective layer at multiple past diagnostic times to form a trajectory.

[0160] It should be understood that, in this embodiment, to analyze the evolution characteristics of the sheath grounding state over time, multi-dimensional feature vectors corresponding to multiple past diagnostic moments of the sheath are retrieved from the historical data storage system. These past diagnostic moments are historical moments when the sheath state diagnosis was completed before the current diagnostic moment. Multiple past diagnostic moments can be selected from the most recent several days or weeks, or they can cover all diagnostic moments since the sheath was put into operation. Each past diagnostic moment corresponds to a multi-dimensional feature vector constructed according to step S301. The multi-dimensional feature vectors of multiple past diagnostic moments are arranged in chronological order to form a temporal feature sequence reflecting the changes in the sheath grounding state.

[0161] Furthermore, the multidimensional feature vectors from multiple past diagnostic moments and the current diagnostic moment are mapped into a preset parameter space. The positions corresponding to each multidimensional feature vector are then connected sequentially according to time to form a feature trajectory. The starting point of the trajectory corresponds to the earliest past diagnostic moment, and the ending point corresponds to the current diagnostic moment. This feature trajectory describes the temporal evolution path of the sheath grounding state in the preset parameter space. Its overall shape and direction reflect the changing trend of the sheath grounding state over time. When the feature trajectory remains near a certain fault mode characteristic region for a long period, it indicates that the sheath grounding state remains relatively stable. When the feature trajectory gradually deviates from its original region and moves towards other fault mode characteristic regions, it indicates that the sheath grounding state is evolving or deteriorating. By constructing and analyzing this feature trajectory, a temporal basis is provided for subsequent fault evolution determination and diagnostic result correction.

[0162] S305. Analyze the movement direction of the trajectory and the positional relationship between the characteristics of each fault mode in the preset fault mode library and the preset parameter space to determine the fault evolution information.

[0163] It should be understood that, in this embodiment, after obtaining the characteristic trajectory of the sheath grounding state in the preset parameter space, the movement direction of the trajectory is analyzed, and the fault evolution information of the sheath grounding state is determined by combining the distribution positions of the fault mode features in the preset fault mode library in the preset parameter space. Specifically, by selecting the multi-dimensional feature vector positions corresponding to the trajectory at several recent diagnostic times, the displacement vector between adjacent times is calculated, thereby obtaining the overall movement direction and change trend of the trajectory in the preset parameter space; or the path of the trajectory within a preset time window is fitted to determine the extension direction of the trajectory, which is used to characterize the movement direction of the sheath grounding state.

[0164] Subsequently, the trajectory's movement direction is compared and analyzed with the location of each fault mode characteristic area in the preset fault mode library. This determines whether the trajectory is moving towards the characteristic area of ​​a normal single-point grounding mode, or towards the characteristic area of ​​a fault mode such as multi-point grounding, loose connection, or insulation breakdown, thereby determining the evolution trend of the sheath grounding state. When the trajectory's movement direction points to the characteristic area of ​​a normal single-point grounding mode, it indicates that the sheath grounding state is showing an improving trend; when the trajectory's movement direction points to the characteristic area of ​​a certain fault mode, it indicates that the sheath grounding state is evolving towards the corresponding fault state.

[0165] Furthermore, by calculating the displacement of the trajectory per unit time in the preset parameter space, the trajectory's movement rate is obtained, which characterizes the rate of change in the sheath grounding state. A larger movement rate indicates a faster evolution of the sheath grounding state, while a smaller movement rate indicates a slower change. By combining the trajectory's movement direction and movement rate, fault evolution information containing both fault evolution trends and speeds is formed. This introduces a time-dimensional evolution criterion based on the preliminary diagnostic results, providing a more comprehensive and forward-looking basis for trend judgment, risk assessment, and operation and maintenance decisions regarding the sheath grounding state.

[0166] S306. Output the preliminary diagnosis results and fault evolution information as the fault diagnosis results.

[0167] It should be understood that, in this embodiment, after obtaining the preliminary diagnostic results of the sheath grounding state and the corresponding fault evolution information, the two are integrated to form the final fault diagnosis result and output it. The preliminary diagnostic results characterize the grounding state type closest to the sheath at the current diagnostic moment, while the fault evolution information characterizes the evolution trend and speed of the sheath grounding state over time. By combining the preliminary diagnostic results with the fault evolution information, the resulting fault diagnosis result not only reflects the current grounding state classification of the sheath but also indicates whether the grounding state is stabilizing, gradually improving, or continuously deteriorating, thus providing a comprehensive diagnostic conclusion combining static judgment and dynamic prediction for the sheath's operating status. The fault diagnosis result can be output in the form of text description, graphical display, or structured report. The output content includes at least the current grounding state type of the sheath, the evolution trend of the grounding state, and the risk level information corresponding to the evolution trend. It can also provide corresponding maintenance prompts or handling suggestions based on the severity of the diagnostic results.

[0168] Through the above methods, the multi-dimensional feature vector constructed based on the sheath voltage frequency domain parameters, sheath circulating current time domain parameters, spatial distribution parameters, thermal coupling parameters, comparison parameters, and consistency parameters, along with the matching results of the preset fault mode library and the evolution analysis of the feature trajectory, are uniformly integrated into the final diagnostic output. This achieves accurate identification, reliable classification, and trend judgment of sheath grounding faults, effectively overcoming the shortcomings of traditional methods that rely on single or a few feature parameters and are easily affected by noise and operating condition fluctuations. Furthermore, by introducing time-series evolution analysis capabilities, fault diagnosis is upgraded from single-moment judgment to a comprehensive diagnostic result with trend prediction and early warning capabilities, thereby improving the safety and reliability of power system operation and maintenance.

[0169] It should be noted that before matching the fault mode characteristics with those in the preset fault mode library, since the impact of sheath faults on externally observable voltage and current characteristics is often indirectly reflected through changes in the equivalent impedance of the sheath grounding loop, and single time-domain or frequency-domain characteristics are insufficient to fully characterize the true dynamic behavior of this equivalent impedance, it is necessary to perform consistency verification and fusion characterization on the equivalent impedance of the sheath grounding loop obtained from different feature domains. Specifically:

[0170] First, based on the Lyapunov exponent and sample entropy in the frequency domain parameters of the sheath voltage, the complex value of the equivalent impedance of the sheath grounding loop at the resonant frequency is inversely calculated. Then, based on the deviation in the time domain parameters of the sheath circulating current, the time domain response of the equivalent impedance of the sheath grounding loop is inversely calculated. Next, the complex value of the equivalent impedance is inversely transformed to obtain the time domain equivalent impedance response. Finally, the degree of consistency between the time domain equivalent impedance response and the time domain equivalent impedance response is compared and used as the consistency parameter of the sheath.

[0171] It should be understood that, in order to cross-validate the reliability of the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters, before performing fault mode matching, a mapping relationship between the sheath voltage frequency domain parameters and the impedance characteristics of the sheath grounding loop is first established based on the Lyapunov exponent and sample entropy in the sheath voltage frequency domain parameters. Based on this, the complex value of the equivalent impedance of the sheath grounding loop at the resonant frequency is inversely calculated. This complex value of the equivalent impedance is used to characterize the resistance and reactance characteristics of the sheath grounding loop under frequency domain conditions. Subsequently, based on the deviation in the sheath circulating current time domain parameters, combined with the transient response model of the sheath grounding loop, the time domain response of the equivalent impedance of the sheath grounding loop during load changes is inversely calculated. This time domain response of the equivalent impedance is used to describe the dynamic evolution of the equivalent impedance of the sheath grounding loop over time.

[0172] Furthermore, an inverse transformation is performed on the complex value of the equivalent impedance to convert the impedance characteristics represented in the frequency domain into the corresponding time-domain equivalent impedance response, thus obtaining the time-domain impedance response curve derived from the frequency domain characteristic parameters. Finally, the time-domain equivalent impedance response obtained by inverse transformation from the frequency domain is compared and analyzed with the time-domain equivalent impedance response derived from the time-domain characteristic parameters. The similarity between the two in the time domain is calculated, and this similarity is used as the sheath consistency parameter. The consistency parameter is used to characterize the consistency between the sheath grounding loop impedance characteristics derived from two different physical perspectives: frequency domain characteristics and time domain characteristics. When the consistency parameter is high, it indicates that the frequency domain parameters of the sheath voltage and the time domain parameters of the sheath circulating current are physically consistent, and the reliability of the characteristic parameters is high. When the consistency parameter is low, it indicates that there may be measurement anomalies or external disturbances in the frequency domain or time domain characteristics. By introducing the consistency parameter, self-consistency verification of the sheath characteristic parameters is achieved, providing reliability constraints for subsequent multi-dimensional feature vector construction and fault diagnosis, thereby improving the robustness and reliability of the overall diagnostic results.

[0173] Figure 4 This is a schematic diagram of the high-voltage cable sheath fault diagnosis device provided in the embodiments of this application; as shown below. Figure 4 As shown, the device includes:

[0174] The acquisition module 401 is used to acquire the sheath-to-ground voltage timing data and sheath circulating current timing data under dynamic operating conditions of changing load current of the main cable.

[0175] The first construction module 402 is used to construct the sheath voltage frequency domain parameters based on the sheath-to-ground voltage time series data;

[0176] The second construction module 403 is used to construct the time-domain parameters of the sheath circulation based on the sheath circulation time-series data;

[0177] The matching module 404 is used to match the sheath voltage frequency domain parameters and sheath circulating current time domain parameters with the fault mode characteristics in the preset fault mode library to obtain the fault diagnosis results of the sheath.

[0178] In one possible implementation, the acquisition module 401 is specifically used for:

[0179] Monitor the change process of the load current of the main cable and calculate the second derivative of the load current of the main cable;

[0180] Identify the inflection point where the sign of the second derivative reverses;

[0181] The data collection operation is triggered within a preset delay period after the inflection point.

[0182] In one possible implementation, the first building module 402 is specifically used for:

[0183] The phase information of at least two frequency components near the resonant frequency is extracted by performing frequency domain transformation on the time series data of the sheath to ground voltage.

[0184] Calculate the phase angle relationship between phase information and construct a phase angle sequence;

[0185] The phase space is reconstructed from the phase angle sequence to obtain the trajectory, and the Lyapunov exponent of the trajectory and the sample entropy of the phase angle sequence are calculated.

[0186] The Lyapunov exponent and sample entropy are used as vector components to construct the frequency domain parameters of the sheath voltage.

[0187] In one possible implementation, the second building module 403 is specifically used for:

[0188] Multi-scale decomposition was performed on the time series data of the protective layer circulation to obtain fast-scale and slow-scale components.

[0189] Analytical signal processing is performed on the fast-scale component and the slow-scale component respectively to calculate the cross-correlation coefficient and determine the fusion weight;

[0190] The fast-scale components and slow-scale components are fused according to the fusion weights to obtain the instantaneous envelope;

[0191] The instantaneous envelope was fitted to the theoretical response model, and the deviation was extracted as the time-domain parameter of the sheath circulation. The theoretical response model was established based on the material conductivity of the sheath, the geometric dimensions of the sheath, and the equivalent capacitance between the sheath and the ground.

[0192] In one possible implementation, the apparatus further includes a processing module, which, after constructing the time-domain parameters of the protective layer circulation, is used to:

[0193] Obtain the sheath circulation timing data of a reference cable arranged adjacent to the main cable;

[0194] The reference cable sheath circulating current timing data is analyzed and processed to obtain the reference instantaneous envelope;

[0195] The morphological matching degree between the instantaneous envelope of the main cable and the reference instantaneous envelope is calculated and used as a reference parameter for the main cable.

[0196] In one possible implementation, before matching the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with fault mode characteristics in a preset fault mode library, the processing module is further configured to:

[0197] Based on the Lyapunov exponent and sample entropy in the frequency domain parameters of the sheath voltage, the complex value of the equivalent impedance of the sheath grounding loop at the resonant frequency is inversely calculated.

[0198] Based on the deviation in the time-domain parameters of the sheath circulation current, the equivalent impedance time-domain response of the sheath grounding loop is inferred.

[0199] The time-domain equivalent impedance response is obtained by performing an inverse transformation on the complex value of the equivalent impedance.

[0200] The degree of consistency between the time-domain equivalent impedance response and the time-domain equivalent impedance response is used as a consistency parameter for the sheath.

[0201] In one possible implementation, the matching module 404 is specifically used for:

[0202] The frequency domain parameters of the sheath voltage, the time domain parameters of the sheath circulation current, the spatial distribution parameters, the thermal coupling parameters, the comparison parameters, and the consistency parameters are constructed into a multi-dimensional feature vector;

[0203] Calculate the spatial distance between the multidimensional feature vector and the features of each fault mode in the preset fault mode library in the preset parameter space;

[0204] The fault type corresponding to the fault mode feature with the smallest spatial distance is selected as the preliminary diagnostic result;

[0205] Obtain the multidimensional feature vectors of the protective layer at multiple past diagnostic times to form a trajectory;

[0206] The fault evolution information is determined by analyzing the relationship between the movement direction of the trajectory and the position of each fault mode feature in the preset fault mode library in the preset parameter space.

[0207] The preliminary diagnostic results and fault evolution information are output as the fault diagnosis results.

[0208] The high-voltage cable sheath fault diagnosis device provided in this application embodiment can execute the method provided in the above method embodiment. Its implementation principle and technical effect are similar, and will not be described in detail here.

[0209] Figure 5 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application. Figure 5 As shown, the electronic device 50 provided in this embodiment includes at least one processor 501 and a memory 502. Optionally, the device 50 further includes a communication component 503. The processor 501, memory 502, and communication component 503 are connected via a bus 504.

[0210] In a specific implementation, at least one processor 501 executes computer execution instructions stored in memory 502, causing at least one processor 501 to perform the above-described method.

[0211] The specific implementation process of processor 501 can be found in the above method embodiments, and its implementation principle and technical effect are similar. It will not be repeated here.

[0212] In the above embodiments, it should be understood that the processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), etc. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the method disclosed in this invention can be directly implemented by a hardware processor, or implemented by a combination of hardware and software modules within the processor.

[0213] The memory may include random access memory (RAM) and may also include non-volatile memory (NVM), such as at least one disk storage device.

[0214] The bus can be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, or an Extended Industry Standard Architecture (EISA) bus, etc. Buses can be categorized as address buses, data buses, control buses, etc. For ease of illustration, the buses shown in the accompanying drawings are not limited to a single bus or a single type of bus.

[0215] This application also provides a computer-readable storage medium storing computer-executable instructions, which, when executed by a processor, implement the above-described method.

[0216] The aforementioned readable storage medium can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (SRAM), electrically erasable programmable read-only memory (EEPROM), erasable programmable read-only memory (EPROM), programmable read-only memory (PROM), read-only memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk. The readable storage medium can be any available medium accessible to a general-purpose or special-purpose computer.

[0217] An exemplary readable storage medium is coupled to a processor, enabling the processor to read information from and write information to the readable storage medium. Of course, the readable storage medium can also be a component of the processor. The processor and the readable storage medium can reside in an Application Specific Integrated Circuit (ASIC). Alternatively, the processor and the readable storage medium can exist as discrete components in the device.

[0218] The division of units is merely a logical functional division; 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 indirect coupling or communication connection through some interfaces, devices, or units, and may be electrical, mechanical, or other forms.

[0219] 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.

[0220] In addition, 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.

[0221] If a function 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, the technical solution of this invention, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0222] Those skilled in the art will understand that all or part of the steps of the above-described method embodiments can be implemented by hardware related to program instructions. The aforementioned program can be stored in a computer-readable storage medium. When executed, the program performs the steps of the above-described method embodiments; and the aforementioned storage medium includes various media capable of storing program code, such as ROM, RAM, magnetic disks, or optical disks.

[0223] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for diagnosing faults in the sheath of high-voltage cables, characterized in that, include: Under dynamic operating conditions of varying load current in the main cable, collect timing data of sheath-to-ground voltage and sheath circulating current. Construct the sheath voltage frequency domain parameters based on the sheath-to-ground voltage time series data; Construct the time-domain parameters of the sheath circulation based on the sheath circulation time-series data; The sheath voltage frequency domain parameters and the sheath circulating current time domain parameters are matched with the fault mode features in the preset fault mode library to obtain the fault diagnosis results of the sheath.

2. The method according to claim 1, characterized in that, The acquisition of sheath-to-ground voltage and sheath circulating current timing data under dynamic operating conditions of varying main cable load current includes: Monitor the change process of the load current of the main cable and calculate the second derivative of the load current of the main cable; Identify the inflection point where the sign of the second derivative reverses; The data collection operation is triggered within a preset delay period after the inflection point.

3. The method according to claim 1, characterized in that, The step of constructing the sheath voltage frequency domain parameters based on the sheath-to-ground voltage time series data includes: The phase information of at least two frequency components near the resonant frequency is extracted by performing frequency domain transformation on the timing data of the sheath to ground voltage. Calculate the phase angle relationship between the phase information and construct a phase angle sequence; The phase angle sequence is reconstructed in phase space to obtain the trajectory, and the Lyapunov exponent of the trajectory and the sample entropy of the phase angle sequence are calculated. The Lyapunov exponent and the sample entropy are used as vector components to form the frequency domain parameters of the sheath voltage.

4. The method according to claim 1, characterized in that, The step of constructing the time-domain parameters of the sheath circulation based on the sheath circulation time-series data includes: The time series data of the protective layer circulation is decomposed into fast-scale components and slow-scale components. The fast-scale component and the slow-scale component are subjected to analytical signal processing respectively, the cross-correlation coefficient is calculated and the fusion weight is determined; The fast-scale component and the slow-scale component are fused according to the fusion weight to obtain the instantaneous envelope; The instantaneous envelope is fitted to the theoretical response model, and the deviation is extracted as the time-domain parameter of the sheath circulation. The theoretical response model is established based on the material conductivity of the sheath, the geometric dimensions of the sheath, and the equivalent capacitance between the sheath and the ground.

5. The method according to claim 4, characterized in that, After constructing the time-domain parameters of the sheath circulation, the method further includes: Obtain the sheath circulation timing data of a reference cable arranged adjacent to the main cable; The reference cable sheath circulating current timing data is analyzed and processed to obtain the reference instantaneous envelope; The morphological matching degree between the instantaneous envelope of the main cable and the reference instantaneous envelope is calculated and used as a reference parameter for the main cable.

6. The method according to claim 3, characterized in that, Before matching the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with fault mode features in a preset fault mode library, the method further includes: Based on the Lyapunov exponent and the sample entropy in the frequency domain parameters of the sheath voltage, the complex value of the equivalent impedance of the sheath grounding loop at the resonant frequency is inversely calculated. Based on the deviation in the time-domain parameters of the sheath circulation current, the equivalent impedance time-domain response of the sheath grounding loop is inferred. The time-domain equivalent impedance response is obtained by performing an inverse transformation on the complex value of the equivalent impedance. The degree of consistency between the time-domain equivalent impedance response and the time-domain equivalent impedance response is used as a consistency parameter for the sheath.

7. The method according to claim 1, characterized in that, The step of matching the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with fault mode features in a preset fault mode library includes: The frequency domain parameters of the sheath voltage, the time domain parameters of the sheath circulation current, the spatial distribution parameters, the thermal coupling parameters, the comparison parameters, and the consistency parameters are constructed into a multi-dimensional feature vector; Calculate the spatial distance between the multidimensional feature vector and the features of each fault mode in the preset fault mode library in the preset parameter space; The fault type corresponding to the fault mode feature with the smallest spatial distance is selected as the preliminary diagnostic result; Obtain the multidimensional feature vectors of the protective layer at multiple past diagnostic times to form a trajectory; Analyze the movement direction of the trajectory and the positional relationship between the features of each fault mode in the preset fault mode library and the preset parameter space to determine the fault evolution information; The preliminary diagnostic results and fault evolution information are output as the fault diagnosis results.

8. A fault diagnosis device for high-voltage cable sheaths, characterized in that, include: The acquisition module is used to acquire sheath-to-ground voltage timing data and sheath circulating current timing data under dynamic operating conditions of changing main cable load current; The first construction module is used to construct the sheath voltage frequency domain parameters based on the sheath-to-ground voltage time-series data. The second construction module is used to construct the sheath circulation time-domain parameters based on the sheath circulation time-series data. The processing module is used to match the sheath voltage frequency domain parameters and the sheath circulating current time domain parameters with the fault mode characteristics in the preset fault mode library to obtain the fault diagnosis results of the sheath.

9. An electronic device, characterized in that, include: Memory, processor; The memory stores computer-executed instructions; The processor executes computer execution instructions stored in the memory, causing the processor to perform the method as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer-executable instructions, which, when executed by a processor, are used to implement the method as described in any one of claims 1-7.

Images