A method and system for evaluating the insulation aging state of a cable shielding layer

Abstract

The present application relates to the technical field of cable state monitoring, and particularly relates to a cable shielding layer insulation aging state evaluation method and system. The method comprises the following steps: synchronously collecting an initial current sequence and an initial temperature sequence through a high-frequency current transformer and an optical fiber temperature sensor; determining a maximum correlation translation step to perform hysteresis compensation to obtain an aligned temperature sequence; calculating an exponential change rule of a difference value to reconstruct a dynamic health current baseline; calculating an absolute difference value and combining a variation rate at an adjacent time to extract a true aging characteristic value; performing logarithmic conversion and recursive accumulation on a value exceeding a preset tolerance lower limit to obtain an evaluation index, so that a circuit breaker control execution mechanism performs closed-loop removal control. The present application strips normal impedance drift interference, accurately locks essential leakage components, and significantly improves the accuracy of equipment protection.

Description

Technical Field

[0001] This invention relates to the field of cable condition monitoring technology, and in particular to a method and system for assessing the aging condition of cable shield insulation. Background Technology

[0002] Existing 110kV and above high-voltage cables typically employ a single-core structure. To prevent the massive induced circulating current generated by multiple grounding points in the metallic shielding layer, which could burn out the cable, an outer sheath, or shielding insulation, must be wrapped around the metallic shielding layer to isolate it from the ground. Therefore, monitoring the aging condition of the shielding insulation is crucial for ensuring the safe operation of power grid equipment. Current methods for monitoring cable shielding insulation aging usually involve directly setting a fixed leakage current alarm threshold on the grounding lead of the shielding layer for condition assessment.

[0003] However, under actual industrial operating conditions with varying loads, the current-carrying capacity of the cable fluctuates drastically. The Joule heat generated within the cable core undergoes a radial heat conduction process from the inside out, ultimately transferring to the external shielding insulation. Under this thermoelectric coupling, the impedance parameters of the shielding insulation material decrease significantly with increasing temperature. This objective physical phenomenon inevitably causes the shielding grounding current to fluctuate considerably with temperature changes.

[0004] Current methods rely solely on fixed current thresholds for status determination, completely neglecting the objective impact of cable heating on the insulation dielectric impedance characteristics. Under heavy load or frequent load fluctuations, the normal leakage current of the shielding layer increases significantly with rising temperature due to severe cable heating. In this situation, a fixed threshold cannot effectively distinguish between normal current fluctuations caused by temperature increases and abnormal leakage currents caused by actual insulation material degradation. This flaw in the monitoring logic leads to existing technologies easily misinterpreting high current phenomena caused by normal equipment heating as insulation faults under complex operating conditions, resulting in frequent false alarms; or, to avoid false alarms, the threshold may be artificially set too high, leading to missed alarms by completely masking early aging hazards. Summary of the Invention

[0005] To address the problem that existing technologies using fixed static thresholds cannot handle temperature drift interference under variable load conditions, leading to normal heating fluctuations being misjudged as insulation aging, this invention provides a method and system for assessing the insulation aging status of cable shielding layers.

[0006] In a first aspect, the present invention provides a method for evaluating the aging state of cable shielding insulation, employing the following technical solution:

[0007] A method for assessing the aging condition of cable shield insulation includes the following steps:

[0008] The initial current sequence is acquired by a through-hole high-frequency current transformer on the grounding lead of the shielded layer, and the initial temperature sequence is acquired synchronously by a fiber optic temperature sensor.

[0009] Based on the initial current sequence and the initial temperature sequence, determine the translation step size that maximizes the correlation between the downsampled initial current sequence and the translated initial temperature sequence, and obtain the aligned temperature sequence;

[0010] Based on the alignment temperature sequence, the exponent of the difference between the alignment temperature sequence and the reference temperature is calculated, and combined with a preset characteristic coefficient, the dynamic health current baseline is obtained.

[0011] Based on the initial current sequence and the dynamic healthy current baseline, the absolute difference between the initial current sequence and the dynamic healthy current baseline is calculated, and combined with the rate of change of the initial current sequence at adjacent times, the true aging characteristic value is obtained.

[0012] Based on the true aging characteristic values, logarithmic transformation and recursive accumulation are performed on the values ​​that exceed the preset residual tolerance limit to obtain the shielding layer insulation aging state assessment index, so as to realize the insulation layer aging state assessment.

[0013] This invention separates the normal impedance amplitude drift component affected by temperature changes from the total measured current by calculating the dynamic health current baseline and the true aging characteristic value. This enables the evaluation system to effectively distinguish between normal physical thermal fluctuations and true insulation aging characteristics under variable load conditions, reducing the false alarm rate caused by normal equipment heating.

[0014] Preferably, obtaining the aligned temperature sequence includes:

[0015]

[0016]

[0017] In the formula, Represents the total number of sampling points within the time window; The index representing the time step of the translation; Represents the first time window Initial current sequence values ​​at each local analysis time point; The mean of the initial current sequence values ​​within the time window; Represents the first time window Initial temperature sequence values ​​at each local analysis time point; The mean of the initial temperature sequence values ​​within the time window; This represents the optimal number of physical thermal delay steps; Representing the The initial temperature sequence values ​​at each time point; Representing the The aligned temperature sequence values ​​at each time point are obtained; all aligned temperature sequence values ​​are arranged in chronological order to obtain the aligned temperature sequence.

[0018] This invention achieves the alignment of the initial current sequence and the initial temperature sequence on the data time axis by determining the translation step size to compensate for the hysteresis of the data sequence, thus compensating for the physical time delay caused by the radial heat conduction process of the cable and providing an accurate data source for subsequent reconstruction of the current baseline.

[0019] Preferably, the specific formula for calculating the exponent of the difference between the aligned temperature sequence and the reference temperature based on the aligned temperature sequence, and combining it with preset characteristic coefficients, is as follows:

[0020]

[0021] In the formula, Represents the sampling time index; For the first Aligned temperature sequence values ​​at each time point; Representing the The dynamic health current baseline value at each moment; This represents the reference temperature. , as well as All represent preset characteristic coefficients, and the dynamic health current baseline values ​​at all times are used to form the dynamic health current baseline.

[0022] This invention utilizes the exponential relationship of the difference calculated by aligning temperature sequences to quantify the physical law of the nonlinear change of the shielding layer insulation impedance with temperature, and constructs a dynamic healthy current baseline that is dynamically adjusted with operating temperature, thereby improving the adaptability of the baseline to dynamic operating conditions.

[0023] Preferably, the method for obtaining the preset feature coefficients includes:

[0024] Under the condition that the cable shielding layer is intact and brand new and manufactured, load currents of different gradients are applied by a frequency converter. After the cable is thermally balanced, the actual grounding current of the shielding layer at each gradient stable temperature point is recorded. Based on the obtained sample data of multiple sets of temperature and current, the least squares method is used to fit the curve, thereby solving the preset characteristic coefficients of the corresponding cable model.

[0025] Preferably, the absolute difference between the initial current sequence and the dynamic healthy current baseline is calculated based on the initial current sequence and the dynamic healthy current baseline. This difference, combined with the rate of change of the initial current sequence at adjacent times, yields the true aging characteristic value. The specific relationship is as follows:

[0026]

[0027] In the formula, Represents the sampling time index; For the first time collected The initial current sequence values ​​at each time point; For the first time collected The initial current sequence values ​​at each time point; For the first The dynamic health current baseline value at each moment; Representing the True aging characteristic values ​​at a given moment; Represents the sampling time interval; Represents the sensitivity coefficient to high-frequency burrs; This represents a tiny constant to prevent the denominator from being zero.

[0028] This invention highlights high-frequency current mutations caused by localized micro-discharges in the early stages of insulation aging by calculating the absolute difference and integrating the rate of change at adjacent times, while suppressing low-frequency thermal drift interference and improving the sensitivity of early aging feature extraction.

[0029] Preferably, the method for obtaining the high-frequency burr sensitivity coefficient includes:

[0030] In a test environment, partial discharge simulation tests were performed on the shielding insulation of old and aged cables of the same type. A high-frequency oscilloscope was used to collect and calculate the average current change rate of a large number of typical discharge pulses. The reciprocal of the average current change rate was extracted and multiplied by a preset safety margin multiple to determine the high-frequency glitch sensitivity coefficient.

[0031] Preferably, based on the true aging characteristic values, the values ​​exceeding the preset residual tolerance limit are logarithmically transformed and recursively accumulated to obtain the shielding layer insulation aging state evaluation index, with the specific relationship being:

[0032]

[0033] In the formula, Represents the sampling time index; Represents the current number The evaluation index of the aging state of the shielding layer insulation at each moment; Representing the The evaluation index of the aging state of the shielding layer insulation at each moment; Representing the The true aging characteristic values ​​at each moment; This represents the preset residual tolerance lower limit; This represents the material degradation rate constant.

[0034] This invention simulates the physical process of irreversible damage accumulation in shielding insulation materials through logarithmic transformation and recursive accumulation operations, reducing the interference of single transient data fluctuations on the overall evaluation results, and making the final output shielding insulation aging status evaluation index more stable.

[0035] Preferably, the method for obtaining the material degradation rate constant includes: taking samples of the same batch of cables and conducting accelerated thermal aging destructive experiments on the shielding insulation, continuously recording the evolution process of the true aging characteristic values ​​until the shielding insulation is completely broken down, extracting the slope of the curve of the avalanche-like growth stage of the characteristic values ​​before the breakdown, and extracting the fitting coefficient by performing logarithmic fitting on the attenuation curve to determine the material degradation rate constant.

[0036] Preferably, the reference temperature is set to 20 degrees Celsius.

[0037] Secondly, this invention provides a cable shield insulation aging condition assessment system, which adopts the following technical solution:

[0038] A cable shield insulation aging condition assessment system includes a processor and a memory, wherein the memory stores computer program instructions, and when the computer program instructions are executed by the processor, the above-mentioned cable shield insulation aging condition assessment method is implemented.

[0039] By adopting the above technical solution, a computer program is generated from the above-mentioned method for evaluating the aging state of cable shield insulation, and stored in a memory for loading and execution by a processor. Terminal devices are then manufactured based on the memory and processor for convenient use.

[0040] The present invention has the following technical effects:

[0041] Existing technologies use fixed static thresholds for status determination. Under high-temperature and heavy-load conditions, this can easily lead to misinterpreting normal impedance drops in insulation materials caused by temperature rise as fault leaks. To address this, this invention introduces a dynamic healthy current baseline to dynamically adjust the current reference value according to the actual temperature. This design precisely eliminates the absolute amplitude drift caused by normal thermal fluctuations, avoiding the risk of false alarms from the monitoring system under wide temperature range disturbances.

[0042] Furthermore, genuine early-stage micro-air gap discharges often manifest as extremely weak high-frequency spikes, which are easily swallowed up by the low-frequency fluctuations of a large background current. Therefore, this invention introduces relative deviation ratios and high-frequency time variation rates when extracting true aging characteristic values. This design not only eliminates the swallowing effect of a large current base through normalization but also provides targeted nonlinear amplification of the instantaneous spikes caused by micro-discharges, achieving high sensitivity to early insulation defects even under significant heating background noise.

[0043] Furthermore, the aging of high-voltage cable insulation is essentially an irreversible process of material damage accumulation. Conventional alarm methods based on single transient exceedances are easily triggered by occasional electromagnetic disturbances in the field, resulting in false tripping. Therefore, this invention utilizes a preset residual tolerance lower limit calibrated based on the field environment to filter out ineffective background noise, and outputs a shield insulation aging status assessment index through recursive accumulation in the time domain. This design perfectly aligns with the physical laws of fatigue damage in polymer materials, objectively reproducing the true lifespan loss trajectory of the equipment while minimizing false judgments caused by isolated transient spikes. Attached Figure Description

[0044] Figure 1 This is a flowchart of a method for evaluating the aging state of cable shield insulation provided in an embodiment of the present invention;

[0045] Figure 2 Baseline tracking comparison chart provided for embodiments of the present invention;

[0046] Figure 3 This is a comparison diagram of the peeling of true aging features provided in an embodiment of the present invention;

[0047] Figure 4 A comparative diagram of aging damage evolution provided for embodiments of the present invention. Detailed Implementation

[0048] This invention discloses a method for assessing the aging state of cable shielding insulation, referring to... Figure 1 This includes steps S1-S5:

[0049] S1: The initial current sequence is acquired through a through-hole high-frequency current transformer on the grounding lead of the shielded layer, and the initial temperature sequence is acquired synchronously through an optical fiber temperature sensor.

[0050] Preferably, as an example, the initial current sequence is acquired through a through-hole high-frequency current transformer on the shielded grounding lead, and the initial temperature sequence is simultaneously acquired through a fiber optic temperature sensor, including:

[0051] First, the original analog signal is obtained by using a through-type high-frequency current transformer sleeved outside the grounding lead of the cable shield and an optical fiber temperature sensor close to the surface of the cable outer sheath. Then, hardware low-pass anti-aliasing filtering preprocessing is performed to obtain the anti-aliasing analog signal.

[0052] Next, using a unified system clock pulse as a reference, the anti-aliasing analog signal is synchronously discretized and sampled using an analog-to-digital converter to extract the dual-channel discrete instantaneous values.

[0053] Subsequently, the dual-channel discrete instantaneous values ​​are arranged in time-axis order to output the initial current sequence and the initial temperature sequence.

[0054] S2: Based on the initial current sequence and the initial temperature sequence, determine the translation step size that maximizes the correlation between the downsampled initial current sequence and the translated initial temperature sequence, and obtain the aligned temperature sequence.

[0055] It should be noted that there is a significant physical time delay in the conduction of heat from the internal cable core to the external shielding insulation. This means that the initial current sequence and the initial temperature sequence acquired in the above steps are out of sync. Timing alignment is necessary to facilitate subsequent analysis.

[0056] Preferably, as an example, based on the initial current sequence and the initial temperature sequence, determining the translation step size that maximizes the correlation between the downsampled initial current sequence and the translated initial temperature sequence to obtain the aligned temperature sequence includes:

[0057]

[0058]

[0059] Specifically, continuous data points of a preset length prior to the current moment are extracted from the initial current sequence and the initial temperature sequence as a local time window. Represents the index of continuous sampling time; Represents the index of a local sampling moment within a time window; This represents the total number of sampling points within the time window. The index representing the time step of the translation; Represents the first within the time window The initial current sequence at each local analysis moment is in milliamperes; The mean of the initial current sequence is represented by milliamperes. Represents the first time window The initial temperature sequence values ​​at each local analysis time point, in degrees Celsius; The mean of the initial temperature sequence is expressed in degrees Celsius. This represents the optimal physical thermal delay step number, which is dimensionless. Representing the The aligned temperature sequence values ​​at each time point, in degrees Celsius. Representing the The initial temperature sequence values ​​at each time point, in degrees Celsius. This represents the time step of the translation when the maximum value is obtained. .

[0060] The aligned temperature sequence is obtained by arranging all aligned temperature sequence values ​​in chronological order.

[0061] Understandably, suppose that the high-voltage power supply cable of an industrial park experiences a sudden surge in load from the nighttime off-peak to full load at the start of the morning shift. Although the incoming core heats up instantly, due to the radial thermal resistance of the cable insulation layer, the actual temperature measured by the fiber optic sensor on the outer surface often shows a significant increase only after a lag of nearly 20 minutes. In this case, through correlation analysis in the above formula, the true physical thermal delay step can be accurately calculated. This allows for sequence alignment using physical thermal delay steps, thus preventing misalignment from affecting subsequent analysis.

[0062] S3: Based on the alignment temperature sequence, calculate the exponent of the difference between the alignment temperature sequence and the reference temperature, and combine it with a preset characteristic coefficient to obtain the dynamic health current baseline.

[0063] It should be noted that, under healthy cable conditions, the equivalent impedance of the shielding insulation material exhibits a significant non-linear decrease as the operating temperature rises. This physical characteristic means that even without actual insulation aging, normal grounding leakage current will show exponential amplitude drift with temperature fluctuations. Using conventional fixed static threshold methods can easily lead to equipment misinterpreting normal thermal fluctuations as insulation faults during high-temperature, heavy-load operation, resulting in false alarms. Therefore, the core objective of this step is to utilize the mapping relationship between temperature and impedance to calculate a dynamic healthy current baseline that can adaptively adjust to temperature fluctuations.

[0064] Preferably, as an example, based on the aligned temperature sequence, the exponent of the difference between the aligned temperature sequence and the reference temperature is calculated, and combined with a preset characteristic coefficient, a dynamic health current baseline is obtained, including:

[0065] First, obtain the reference temperature in the storage cell.

[0066] Next, the dynamic health current baseline is calculated based on the reference temperature and alignment temperature sequence, specifically satisfying the following relationship:

[0067]

[0068] In the formula, Represents the sampling time index; For the first Aligned temperature sequence values ​​at each time point; Representing the The baseline value of the dynamic health current at each moment is given in milliamperes. This represents the reference temperature, which is in degrees Celsius. For example, Take 20 degrees Celsius; , as well as All represent preset characteristic coefficients, among which The unit is milliampere (mA). The unit is the reciprocal of Celsius. The unit is milliampere, and the dynamic health current baseline is formed by the dynamic health current baseline at all times.

[0069] Understandably, suppose that the high-voltage power supply cable of an industrial park experiences a sudden surge in load from the nighttime low to the full load of the morning shift in the early morning. Because the cable has been under low load for an extended period, the surface temperature of the outer sheath is extremely low. Subsequently, the sudden increase in load causes the conductor to heat up, resulting in a rapid increase in the surface temperature of the outer sheath. Under this specific condition, due to the sharp decrease in the equivalent impedance of the insulation material, the actual grounding current measured by the sensor will inevitably undergo a non-linear amplitude amplification following the temperature change. At this point, in the relationship... It will quickly turn from negative to positive and continue to increase, thus in the exponential function Under the influence of nonlinear mapping, the final calculated dynamic health current baseline is obtained. It can perfectly describe the current leakage pattern, thereby preventing false detection of insulation faults caused by normal current fluctuations.

[0070] It should be noted that the method for obtaining the preset feature coefficients includes:

[0071] First, with the same model of cable brand new and the cable shield insulation intact, multiple load currents of different gradients are applied to the cable core through a frequency converter.

[0072] Next, after the cables at each gradient reach thermal equilibrium, the surface temperature of the outer sheath and the grounding current of the shielding layer are simultaneously collected at this state to obtain... The calibration temperature sample data and calibration current sample data are corresponding to each group.

[0073] Subsequently, using the difference between the calibrated temperature sample data and the reference temperature as the independent variable and the calibrated current sample data as the dependent variable, a least-squares fitting residual sum of squares objective function is constructed, with the specific relationship as follows:

[0074]

[0075]

[0076] In the formula, The index representing the serial number of the calibrated sample; This represents the total number of sample groups obtained. Representing the The calibration current sample data of the group is in milliamperes; Representing the The calibration temperature sample data of the group are in degrees Celsius. This represents the reference temperature, and its unit is degrees Celsius. This represents the objective function of the sum of squared residuals, and its unit is square milliamperes. This represents the preset feature coefficient corresponding to the minimum value. Preset characteristic coefficients and preset characteristic coefficients The value of .

[0077] Finally, a nonlinear optimization algorithm is used to iteratively solve the objective function to find the minimum point. The three optimal parameter solutions that minimize the objective function are directly determined as the preset characteristic coefficients. The preset characteristic coefficients and the preset characteristic coefficients .

[0078] S4: Based on the initial current sequence and the dynamic healthy current baseline, calculate the absolute difference between the initial current sequence and the dynamic healthy current baseline, and combine it with the rate of change of the initial current sequence at adjacent times to obtain the true aging characteristic value.

[0079] It should be noted that the early stages of true shielding insulation aging are usually accompanied by minute partial discharges. This physical phenomenon superimposes high-frequency spikes onto the normal leakage current. The physical characteristic of these spikes is that their absolute amplitude is extremely small, but their instantaneous time variation rate is extremely large. If the judgment is based solely on the absolute difference between the actual current and the healthy baseline, these minute early aging characteristics are easily masked by the low-frequency fluctuations of the overall current, leading to the underreporting of early potential problems. Therefore, the core objective of this step is to integrate the absolute difference and the high-frequency time variation rate to extract true aging characteristic values ​​that are highly sensitive to early partial discharges.

[0080] Preferably, as an example, based on the initial current sequence and the dynamic healthy current baseline, the absolute difference between the initial current sequence and the dynamic healthy current baseline is calculated, and combined with the rate of change of the initial current sequence at adjacent time points, the true aging characteristic value is obtained, including:

[0081]

[0082] In the formula, Represents the sampling time index; For the first time collected The initial current sequence values ​​at each time point are given, with the unit being milliamperes; For the first time collected The initial current sequence values ​​at each time point are given, with the unit being milliamperes; For the first The baseline value of the dynamic health current at each moment is given in milliamperes. Representing the The true aging characteristic value at a given moment, with dimensionless units; This represents the sampling time interval, measured in seconds. For example... Pick Second; This represents the high-frequency glitch sensitivity coefficient, and its unit is milliampere per second. This represents a tiny constant to prevent the denominator from being zero, and its unit is seconds.

[0083] Understandably, when the cable is subjected to continuous high-temperature thermal stress under heavy early-shift loads, the pre-existing micro-air gaps within its insulation layer will be activated by the thermal stress, leading to intermittent internal micro-discharges. At this time, although the overall grounding current appears normal due to the baseline rise, the micro-discharges will cause a large number of high-frequency current spikes to be generated locally. (The division structure on the left...) As a basic deviation stripping term, it ensures that small discharge increments are not swallowed up by large background current bases by removing the healthy current baseline value; the structure on the right As a high-frequency characteristic amplification term, its function is to specifically capture the instantaneous and drastic jumps caused by discharge spikes using the first-order time difference. When only low-frequency thermal fluctuations exist, the amplification term on the right approaches a constant. At this point, only the basic relative deviation is output; however, once the high-frequency jump of the micro-discharge is captured, the amplification term on the right side will increase sharply, acting as a multiplier factor to perform a highly targeted nonlinear multiplication of the relative deviation ratio on the left side. Thus, by stripping away the dual mathematical mapping of the base and the amplified high frequency, the microscopic physical discharge characteristics of early insulation aging are accurately captured.

[0084] It should be noted that the method for obtaining the high-frequency burr sensitivity coefficient includes:

[0085] In a test environment, partial discharge simulation tests were performed on the shielding insulation of old and aged cables of the same type. A high-frequency oscilloscope was used to collect and calculate the average current change rate of a large number of typical discharge pulses. The reciprocal of the average current change rate was extracted and multiplied by a preset safety margin multiple to determine the high-frequency glitch sensitivity coefficient.

[0086] S5: Based on the true aging characteristic value, logarithmic transformation and recursive accumulation are performed on the values ​​that exceed the preset residual tolerance limit to obtain the shielding layer insulation aging state evaluation index, so as to realize the insulation layer aging state evaluation.

[0087] It is important to note that the aging of high-voltage cable shielding insulation is essentially an irreversible, cumulative physical process of material damage, rather than a single, instantaneous failure. This means that the actual insulation lifespan degradation must undergo a long-term characteristic evolution. However, in real-world engineering environments, occasional strong electromagnetic disturbances or measurement noise can often trigger isolated transient spikes in characteristic values. If conventional methods of triggering alarms based on single data exceeding limits are used, these occasional disturbances without substantial damage are easily misjudged as insulation breakdown, thus triggering unplanned shutdowns. Therefore, to objectively reconstruct the true lifespan degradation process, the core objective of this step is to filter out invalid transient noise and achieve accurate insulation fault detection.

[0088] Preferably, as an example, based on the true aging characteristic value, the values ​​exceeding the preset residual tolerance lower limit are logarithmically transformed and recursively accumulated to obtain the shielding layer insulation aging state assessment index, so as to realize the insulation layer aging state assessment, including:

[0089]

[0090] In the formula, Represents the sampling time index; Represents the current number The shielding insulation aging status assessment index at each moment is dimensionless. Representing the The shielding insulation aging status assessment index at each moment is dimensionless. Representing the The true aging characteristic value at each moment, which has no dimensionless unit; This represents the preset residual tolerance lower limit, which has a dimensionless unit. It represents the material degradation rate constant, and it has no dimensionless unit.

[0091] Understandably, as this heavy-load operation continues throughout the morning shift, the aforementioned tiny air gap expands continuously under sustained high temperature and electrical stress, with real discharge energy continuously and violently bombarding the insulating medium. At this point, the true aging characteristic value substituted into the formula... This will exceed the background noise threshold at high frequencies for extended periods. , The function will be continuously activated. This will then accumulate in historical values. Based on this, the final calculated evaluation index The irreversible monotonous increase, through this continuous deduction, intuitively describes the phenomenon of irreversible cumulative damage to insulating materials during long-term operation.

[0092] It should be noted that the lower limit of residual tolerance The methods for obtaining it include:

[0093] With the target cable's shield insulation in good condition, and maintaining the normal electromagnetic background interference environment of the industrial site where the cable is located, the background current sequence and the corresponding background temperature sequence are continuously collected within a preset time period using a sensor module.

[0094] Next, based on the acquired background current sequence and background temperature sequence, the true aging characteristic values ​​of the insulation layer at several moments under fault-free conditions are calculated.

[0095] Subsequently, Gaussian normal statistics are used to statistically analyze the true aging eigenvalues ​​at all times to obtain the mean and standard deviation of the true aging eigenvalues. Three times the standard deviation of the true aging eigenvalues ​​is calculated and summed with the mean of the true aging eigenvalues ​​to obtain the base fluctuation limit boundary. Then, the base fluctuation limit boundary is multiplied by a preset disturbance tolerance coefficient to obtain the preset residual tolerance lower limit.

[0096] It should also be noted that the method for obtaining the material degradation rate constant includes:

[0097] First, samples of cables from the same batch were taken and subjected to accelerated thermal aging destructive tests on the shielding insulation in a laboratory environment, while simultaneously acquiring high-frequency current and temperature data throughout the process.

[0098] Next, the true aging characteristic values ​​are calculated and cached in real time at each moment throughout the entire life cycle from the start of the experiment until the cable shield insulation completely breaks down physically.

[0099] Subsequently, a full-scale threshold for physical damage assessment representing complete failure of the insulation material is preset. It represents the end of life, for example. Take 100.

[0100] Finally, the material degradation rate constant is calculated:

[0101]

[0102] In the formula, This represents the material degradation rate constant, which is dimensionless. Represents the preset full-scale threshold for physical damage assessment, and its unit is dimensionless; An index representing the sampling time points throughout the entire accelerated aging experiment cycle; This represents the total number of sampling steps at the moment of breakdown; Representing the The true aging characteristic value at each moment, which has no dimensionless unit; This represents the preset residual tolerance lower limit, which has a dimensionless unit.

[0103] It is understandable that the total cumulative damage a cable insulation layer can withstand from a brand-new, intact state to complete physical breakdown is an objective, fixed value, corresponding to the full-scale threshold in the numerator of the equation. The denominator of this equation is a complete record and accumulation of all the true aging characteristic value increments released by the cable before breakdown, achieved through high-frequency monitoring. Since insulation breakdown is the inevitable result of the continuous accumulation of each tiny discharge, dividing the numerator (representing the total damage tolerance limit) by the denominator (representing the sum of all discharge characteristics) allows for a precise engineering calculation of how much insulation life is consumed for each unit of characteristic increment generated by the insulation material. This calculation directly utilizes objective experimental data from the ultimate failure state to inversely calibrate the degradation rate constant specific to this material.

[0104] To demonstrate the effectiveness of the solution, relevant experiments were conducted. Below are the images obtained from the experiments:

[0105] Figure 2 This is a baseline tracking comparison chart. The thin solid line represents the initial current sequence, the horizontal dotted line represents the traditional static over-limit threshold set in the industry, and the thick dashed line represents the dynamic healthy current baseline.

[0106] As can be seen from the image, the thin solid line representing the initial current sequence exhibits a large peak due to temperature influence, directly breaking through the horizontal dotted line. This means that if a traditional static threshold is used, the device will generate a serious false alarm at this point. In contrast, the thick dashed line representing the dynamic healthy current baseline follows the low-frequency macroscopic fluctuations of the initial current sequence, successfully fitting the normal current fluctuations caused by temperature, effectively eliminating the potential for false alarms caused by operating condition interference.

[0107] Figure 3 This is a comparison chart of the stripping of true aging features. The dashed lines in the chart represent the traditional fixed baseline stripping features extracted using the industry-standard fixed baseline method. The thick solid lines represent the true aging features of this invention.

[0108] In the initial health phase of equipment operation, the dashed line, lacking a dynamic baseline adjustment mechanism, equates normal fluctuations caused by temperature rise to damage components, presenting highly misleading false characteristic peaks. In contrast, the thick solid line of this invention, thanks to the real-time compensation of the dynamic baseline, effectively suppresses its characteristic values ​​and converges them within an extremely low noise floor range. Although it retains minor fluctuations in measurement white noise, it effectively eliminates macroscopic trend misjudgments caused by temperature rise during operation, achieving a substantial improvement in anti-interference capability. In the latter half, where there are real weak aging pulses, the characteristic amplitude extracted by the dashed line approaches the baseline due to the overall current base decreasing, easily leading to missed detections. The thick solid line, however, effectively amplifies hidden fault components with its highly sensitive differential operator, presenting a significant high-frequency characteristic pulse sequence with a high signal-to-noise ratio on the graph.

[0109] Figure 4 This is a comparison chart of aging damage evolution. The thick dotted line in the chart represents the traditional cumulative damage assessment value output based on the conventional over-limit accumulation mechanism. The smooth solid line represents the shielding insulation aging status assessment index output by this invention.

[0110] As can be seen from the curve evolution trend, the thick dotted line, in the first half when the equipment is in a fully healthy state, is misled by thermal drift, exhibiting a large-scale accumulation of pseudo-damage, causing its evaluation benchmark to completely fail. In contrast, the continuous solid line of this invention successfully filters out background noise using the tolerance lower limit, maintaining absolute numerical silence during the healthy phase; only when a real high-frequency discharge pulse is captured in the latter half of the time series does it exhibit a step-like increase highly synchronized with the discharge frequency, effectively demonstrating the anti-interference quantification accuracy of this invention under complex operating conditions.

[0111] This invention also discloses a cable shield insulation aging condition assessment system, including a processor and a memory. The memory stores computer program instructions, which, when executed by the processor, implement a cable shield insulation aging condition assessment method according to the present invention.

[0112] The system also includes other components well known to those skilled in the art, such as communication buses and communication interfaces, the settings and functions of which are known in the art and will not be described in detail here.

[0113] In this invention, the aforementioned memory can be any tangible medium containing or storing a program that can be used or combined with an instruction execution system, apparatus, or device. For example, a computer-readable storage medium can be any suitable magnetic or magneto-optical storage medium, such as resistive random access memory (DRAM), dynamic random access memory (DRAM), static random access memory (SRAM), enhanced dynamic random access memory (DRAM), high-bandwidth memory, hybrid memory cube, etc., or any other medium that can be used to store desired information and can be accessed by an application, module, or both. Any such computer storage medium can be part of a device or accessible to or connected to a device.

Claims

1. A method for assessing the aging condition of cable shielding insulation, characterized in that, Including the following steps: The initial current sequence is acquired by a through-hole high-frequency current transformer on the grounding lead of the shielded layer, and the initial temperature sequence is acquired synchronously by a fiber optic temperature sensor. Based on the initial current sequence and the initial temperature sequence, determine the translation step size that maximizes the correlation between the downsampled initial current sequence and the translated initial temperature sequence, and obtain the aligned temperature sequence; Based on the alignment temperature sequence, the exponent of the difference between the alignment temperature sequence and the reference temperature is calculated, and combined with a preset characteristic coefficient, the dynamic health current baseline is obtained. Based on the initial current sequence and the dynamic healthy current baseline, the absolute difference between the initial current sequence and the dynamic healthy current baseline is calculated, and combined with the rate of change of the initial current sequence at adjacent times, the true aging characteristic value is obtained. Based on the true aging characteristic values, logarithmic transformation and recursive accumulation are performed on the values ​​that exceed the preset residual tolerance limit to obtain the shielding layer insulation aging state assessment index, so as to realize the insulation layer aging state assessment.

2. The method for evaluating the aging state of cable shield insulation according to claim 1, characterized in that, The process of obtaining the aligned temperature sequence includes: In the formula, Represents the total number of sampling points within the time window; The index representing the time step of the translation; Represents the first time window Initial current sequence values ​​at each local analysis time point; The mean of the initial current sequence values ​​within the time window; Represents the first time window Initial temperature sequence values ​​at each local analysis time point; The mean of the initial temperature sequence values ​​within the time window; This represents the optimal number of physical thermal delay steps; Representing the The initial temperature sequence values ​​at each time point; Representing the The aligned temperature sequence values ​​at each time point are obtained; all aligned temperature sequence values ​​are arranged in chronological order to obtain the aligned temperature sequence.

3. The method for evaluating the aging state of cable shield insulation according to claim 1, characterized in that, Based on the aligned temperature sequence, the exponent of the difference between the aligned temperature sequence and the reference temperature is calculated, and combined with a preset characteristic coefficient, the specific relationship of the dynamic health current baseline is obtained as follows: In the formula, Represents the sampling time index; For the first Aligned temperature sequence values ​​at each time point; Representing the The dynamic health current baseline value at each moment; This represents the reference temperature. , as well as All represent preset characteristic coefficients, and the dynamic health current baseline values ​​at all times are used to form the dynamic health current baseline.

4. The method for evaluating the aging state of cable shield insulation according to claim 3, characterized in that, The methods for obtaining the preset feature coefficients include: Under the condition that the cable shielding layer is intact and brand new and manufactured, load currents of different gradients are applied by a frequency converter. After the cable is thermally balanced, the actual grounding current of the shielding layer at each gradient stable temperature point is recorded. Based on the obtained sample data of multiple sets of temperature and current, the least squares method is used to fit the curve, thereby solving the preset characteristic coefficients of the corresponding cable model.

5. The method for evaluating the aging state of cable shield insulation according to claim 1, characterized in that, The method involves calculating the absolute difference between the initial current sequence and the dynamic healthy current baseline, and combining this with the rate of change of the initial current sequence at adjacent times to obtain the true aging characteristic value. The specific relationship is as follows: In the formula, Represents the sampling time index; For the first time collected The initial current sequence values ​​at each time point; For the first time collected The initial current sequence values ​​at each time point; For the first The dynamic health current baseline value at each moment; Representing the True aging characteristic values ​​at a given moment; Represents the sampling time interval; Represents the sensitivity coefficient to high-frequency burrs; This represents a tiny constant to prevent the denominator from being zero.

6. The method for evaluating the aging state of cable shield insulation according to claim 5, characterized in that, The method for obtaining the high-frequency burr sensitivity coefficient includes: In a test environment, partial discharge simulation tests were performed on the shielding insulation of old and aged cables of the same type. A high-frequency oscilloscope was used to collect and calculate the average current change rate of a large number of typical discharge pulses. The reciprocal of the average current change rate was extracted and multiplied by a preset safety margin multiple to determine the high-frequency glitch sensitivity coefficient.

7. The method for evaluating the aging state of cable shield insulation according to claim 1, characterized in that, Based on the true aging characteristic values, logarithmic transformation and recursive accumulation are performed on the values ​​exceeding the preset residual tolerance limit to obtain the shielding layer insulation aging state evaluation index. The specific relationship is as follows: In the formula, Represents the sampling time index; Represents the current number The evaluation index of the aging state of the shielding layer insulation at each moment; Representing the The evaluation index of the aging state of the shielding layer insulation at each moment; Representing the The true aging characteristic values ​​at each moment; This represents the preset residual tolerance lower limit; This represents the material degradation rate constant.

8. The method for evaluating the aging state of cable shield insulation according to claim 7, characterized in that, The method for obtaining the material degradation rate constant includes: taking samples of the same batch of cables and conducting accelerated thermal aging destructive experiments on the shielding insulation, continuously recording the evolution process of the true aging characteristic values ​​until the shielding insulation is completely broken down, extracting the slope of the curve of the avalanche growth stage of the characteristic values ​​before the breakdown, and extracting the fitting coefficient by performing logarithmic fitting on the attenuation curve to determine the material degradation rate constant.

9. The method for evaluating the aging state of cable shield insulation according to claim 1, characterized in that, The reference temperature is set at 20 degrees Celsius.

10. A cable shield insulation aging condition assessment system, characterized in that, include: A processor and a memory, the memory storing computer program instructions that, when executed by the processor, implement a method for assessing the aging state of cable shield insulation according to any one of claims 1-9.

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