Method, system, device and medium for assessing moisture status of cable joint interface

Abstract

The present application relates to the technical field of power equipment state monitoring and fault diagnosis, and discloses a cable joint interface damp state evaluation method, system, device and medium, the method comprises the following steps: selecting and optimizing excitation signal waveform according to the frequency domain characteristics of multiple ultrasonic excitation signals; applying the preferred excitation signal waveform of different frequencies to the pre-constructed dry composite interface and collecting the echo signal, and determining the preferred signal frequency from the echo signal; constructing a multi-damp state composite interface of the cable joint, collecting the echo signal of the excitation signal of the preferred excitation signal waveform and the preferred signal frequency in the multi-damp state composite interface; calculating the time-frequency domain characteristic parameters of the echo signal, and constructing a damp state evaluation rule according to the time-frequency domain characteristic parameters; using the damp state evaluation rule to evaluate the real-time echo signal of the cable joint to be detected. The present application can provide more accurate and comprehensive decision basis for damp state evaluation.

Description

Technical Field

[0001] This invention relates to the field of power equipment condition monitoring and fault diagnosis technology, specifically to a method, system, device, and medium for assessing the moisture status of cable joint interfaces. Background Technology

[0002] Power cable lines are widely used in power systems due to their advantages such as good concealment, small footprint, and strong anti-interference capabilities. However, the large-scale application of power cables also significantly increases the probability of faults. Although the failure probability of cable systems is much lower than that of overhead transmission lines, the enclosed and compact structure of power cables and accessories, often located in urban core areas, makes fault location difficult, repair time-consuming, and complex, resulting in losses far greater than those of overhead lines. Cable lines consist of cables and their accessories (intermediate joints and terminal joints). Therefore, power cable accessories, as key connecting components in the power transmission and distribution network, directly affect the safety of the entire power grid. One of the core causes of cable joint failures is moisture absorption at the interface insulation. During joint fabrication, improper interface treatment, residual impurities, and installation stress can lead to microscopic defects or loose bonding at the interface between the cable joint and the main cable insulation. During long-term operation, due to the breathing effect, external moisture penetration, or seal failure, moisture from the environment gradually intrudes into these microscopic interfaces. Moisture intrusion can lead to a series of serious consequences. For example, moisture can significantly reduce the dielectric strength of interfacial insulating materials, making them more prone to breakdown under overvoltage. At the same time, moisture can promote the hydrolytic aging of polymer insulating materials (such as silicone rubber), reducing their mechanical and electrical properties.

[0003] Currently, assessing the condition of in-operation cable accessories faces significant challenges. Mainstream methods for assessing cable joint condition, such as traditional electrical methods, partial discharge detection, and optical imaging, all have significant limitations when addressing the specific issue of interface moisture. Furthermore, these methods are all offline, unable to provide direct, non-destructive online monitoring of cable joints. Traditional electrical methods (such as insulation resistance) reflect the overall condition of the insulation system; moisture infestation often occurs in its later stages, lacking early warning capabilities. While partial discharge detection is sensitive to interface defects, partial discharge is usually a result of insulation defects developing to a certain stage, making it extremely insensitive to the "latent" state of early moisture infestation, thus hindering early detection. Therefore, a new detection method is urgently needed to accurately detect the moisture condition of composite interfaces in cable accessories online. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to perform a non-destructive and quantitative assessment of the moisture state of the composite interface inside a cable joint.

[0005] The present invention solves the above-mentioned technical problems through the following technical means:

[0006] Multiple ultrasonic excitation signals are acquired for assessing the moisture status, and a preferred excitation signal waveform is selected based on the frequency domain characteristics of each ultrasonic excitation signal; The preferred excitation signal waveforms of different frequencies are applied to the pre-constructed dry composite interface, and the preferred signal frequency is determined based on the multi-frequency echo signal after application. Construct a composite interface of multiple moisture-affected states for a cable joint, and collect the waveform of the preferred excitation signal and the echo signal of the excitation signal with the preferred signal frequency at the composite interface of multiple moisture-affected states. Calculate the time-frequency domain characteristic parameters of the echo signal, and construct a moisture status assessment rule based on the time-frequency domain characteristic parameters; The moisture condition assessment rule is used to assess the moisture condition of the cable joint under test using the real-time echo signal.

[0007] Optionally, the step of selecting the preferred excitation signal waveform based on the frequency domain characteristics of each of the ultrasonic excitation signals includes: Perform a fast Fourier transform on each of the ultrasonic excitation signals to obtain the spectral signal; Harmonic component analysis is performed on the spectral signal to obtain harmonic component information corresponding to each ultrasonic excitation signal; A preferred excitation signal waveform is selected from the ultrasonic excitation signals based on the harmonic component information.

[0008] Optionally, determining the preferred signal frequency based on the applied multi-frequency echo signal includes: Calculate the echo amplitude values ​​of the multi-frequency echo signal at different frequencies; The preferred signal frequency is selected based on the echo amplitude value.

[0009] Optionally, the composite interface for constructing the cable joint under multiple moisture conditions includes: The composite interfacial pressure of an actual cable joint is applied to the interfacial sample of the cable joint using a pre-constructed pressure loading device. While applying pressure to the composite interface, the position of the droplets between the interface samples is fixed; At the specified location, droplets are applied at a certain liquid volume gradient using a precise droplet application device to simulate different degrees of moisture absorption at the composite interface, thereby obtaining a composite interface with multiple moisture states.

[0010] Optionally, calculating the time-frequency domain characteristic parameters of the echo signal includes: The echo signal is preprocessed to obtain an effective noise-reduced signal; Calculate the dimensionless and dimensional characteristics of the effective noise-reduced signal at the preferred signal frequency; Perform a Fast Fourier Transform on the effective noise-reduced signal to obtain the signal spectrum, and calculate the frequency domain feature parameters based on the signal spectrum; By combining the dimensionless features, the dimensional features, and the frequency domain feature parameters, the time-frequency domain feature parameters of the echo signal are obtained.

[0011] Optionally, the step of preprocessing the echo signal to obtain an effective noise-reduced signal includes: The echo signal is subjected to data denoising processing to obtain a denoised signal; Extract the effective noise reduction signal from the noise reduction signal.

[0012] Optionally, the step of constructing the moisture state assessment rule based on the time-frequency domain feature parameters includes: Calculate the drying reference characteristic parameters of the preferred excitation signal at the drying composite interface; The drying reference characteristic parameters are calculated by calculating the center frequency relative downshift rate and amplitude relative attenuation rate of the mid-frequency domain characteristic parameters in the time-frequency domain. Moisture state assessment rules are generated based on the relative downward shift rate of the center frequency, the relative attenuation rate of the amplitude, and the dimensionless and dimensional features in the time-frequency domain feature parameters.

[0013] To address the aforementioned problems, this invention also proposes a moisture condition assessment system for cable joint interfaces, the system comprising: An ultrasonic excitation signal waveform optimization module is used to acquire multiple ultrasonic excitation signals for moisture status assessment and to select the optimal excitation signal waveform based on the frequency domain characteristics of each ultrasonic excitation signal. A frequency optimization module is used to apply the preferred excitation signal waveforms of different frequencies to the pre-constructed dry composite interface, and to determine the preferred signal frequency based on the multi-frequency echo signal after application. The echo signal acquisition module is used to construct a composite interface of multiple moisture-affected states of the cable joint, and to acquire the echo signal of the preferred excitation signal waveform and the excitation signal of the preferred signal frequency at the composite interface of multiple moisture-affected states. A moisture condition assessment rule construction module is used to calculate the time-frequency domain characteristic parameters of the echo signal and construct moisture condition assessment rules based on the time-frequency domain characteristic parameters. The moisture condition assessment module is used to assess the moisture condition of the cable joint under test using the real-time echo signal of the aforementioned moisture condition assessment rules.

[0014] The present invention also provides a processing device, characterized in that it includes at least one processor and at least one memory communicatively connected to the processor, wherein: the memory stores program instructions executable by the processor, and the processor can execute the above-mentioned method for assessing the moisture status of the cable joint interface by calling the program instructions.

[0015] The present invention also provides a computer-readable storage medium, characterized in that the computer-readable storage medium stores computer instructions that cause the computer to perform the above-described method for assessing the moisture condition of the cable joint interface.

[0016] The advantages of this invention are: This invention analyzes the propagation characteristics of ultrasound at composite interfaces, demonstrating that the presence of moisture at the interface affects the primary echo. It also shows the theoretical feasibility of using time-domain and frequency-domain analysis of the primary echo to determine the degree of moisture absorption at the composite interface. Furthermore, it clarifies the propagation characteristics of ultrasonic excitation signals with different waveforms and frequencies at the composite interface. By performing time-domain and frequency-domain analysis on the echo, a suitable ultrasonic characteristic signal is selected. This selected excitation signal effectively satisfies the advantages of low attenuation and concentrated spectrum, providing a more accurate and comprehensive decision-making basis for assessing the moisture state. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating a method for assessing the moisture status of a cable joint interface according to an embodiment of the present invention. Figure 2 This is a spectrum diagram of the echo signal under a sinusoidal pulse train in one embodiment of the present invention; Figure 3 This is a spectrum diagram of the echo signal under the modulation signal in one embodiment of the present invention; Figure 4 This is a graph showing the variation of echo signal amplitude values ​​at different frequencies in one embodiment of the present invention; Figure 5 This is a schematic diagram of ultrasonic propagation corresponding to a preferred excitation signal on a composite interface with multiple moisture states in one embodiment of the present invention; Figure 6 This is a time-domain waveform diagram of the echo signal of the composite interface under water and waterless conditions in one embodiment of the present invention; Figure 7 This is a frequency domain waveform diagram of the echo signal of the composite interface under water and waterless conditions in one embodiment of the present invention; Figure 8 This is a functional module diagram of a cable joint interface moisture condition assessment system provided in one embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] Reference Figure 1 The diagram shown is a flowchart illustrating a method for assessing the moisture state of a cable joint interface according to an embodiment of the present invention. In this embodiment, the method for assessing the moisture state of the cable joint interface includes: S1. Acquire multiple ultrasonic excitation signals for moisture condition assessment, and select the preferred excitation signal waveform based on the frequency domain characteristics of each ultrasonic excitation signal.

[0020] In this embodiment of the invention, the multiple ultrasonic excitation signals can be three commonly used ultrasonic excitation signals: sinusoidal pulse trains, modulation signals, and square wave pulse trains. For frequency domain analysis of ultrasonic detection of moisture conditions at cable joint interfaces, two aspects need to be considered: firstly, the waveform quality itself (whether the spectrum is concentrated and has few harmonic components); secondly, the echo quality (spectral concentration) of the excitation waveform after reflection through the composite interface. Therefore, frequency domain analysis of the above three ultrasonic excitation signals is required to exclude excitation signals containing many harmonic components and to preferentially select excitation waveforms that do not contain harmonic components, in order to prevent frequency domain changes caused by moisture at the composite interface during the moisture condition assessment process.

[0021] Specifically, the step of selecting the preferred excitation signal waveform based on the frequency domain characteristics of each of the ultrasonic excitation signals includes: Perform a fast Fourier transform on each of the ultrasonic excitation signals to obtain the spectral signal; Harmonic component analysis is performed on the spectral signal to obtain harmonic component information corresponding to each ultrasonic excitation signal; A preferred excitation signal waveform is selected from the ultrasonic excitation signals based on the harmonic component information.

[0022] In this embodiment of the invention, for sinusoidal pulse trains, a fast Fourier transform can be performed using the sinc function convolution to obtain the frequency spectrum signal. For modulated signals and square wave pulse trains, a fast Fourier transform can be performed using preset transform parameters to obtain the corresponding frequency spectrum signal.

[0023] Furthermore, the harmonic components of the spectral signal can be identified by locating the harmonic frequencies. For example, for a fundamental frequency of f0, the nth harmonic frequency is fn=n. f0, where n=2, 3, 4, ... The total harmonic distortion (THD) is then calculated to quantitatively analyze the harmonics of each ultrasonic excitation signal, thereby generating harmonic component information corresponding to the ultrasonic excitation signal.

[0024] For example, when performing excitation spectrum analysis on three commonly used ultrasonic excitation signals—sinusoidal pulse trains, modulated signals, and square wave pulse trains—the signal frequencies in the spectra of sinusoidal pulse trains and modulated signals are relatively concentrated. However, compared to each other, the energy of the modulated signal is more concentrated, which can inject more energy into the object being measured. As for the excitation signal, the square wave pulse train, its spectrum itself already contains rich odd harmonics (fundamental, 3rd, 5th, 7th, etc.) with non-negligible amplitude, and the spectrum is not very concentrated.

[0025] Among them, see Figure 2 as well as Figure 3 The figure shows the echo signal spectrum under different ultrasonic excitation signals, representing the echo spectrum of the sinusoidal pulse train and the modulated signal. The horizontal axis represents frequency, and the vertical axis represents amplitude. Figure 2 This represents the echo spectrum of a sinusoidal pulse train. Figure 3 This represents the echo spectrum of the modulated signal. From... Figure 2 It can be seen that when the excitation signal is a sinusoidal pulse train, the echo spectrum is not concentrated enough and there is also a lot of noise. However, for the modulated signal, the echo spectrum is more concentrated, and there are no other harmonic components to interfere except for the second harmonic. Therefore, using the modulated signal as the excitation waveform is more appropriate.

[0026] Specifically, in the harmonic component information corresponding to the ultrasonic excitation signal, the sinusoidal pulse train has no harmonic components under ideal conditions, but is easily affected by spectral leakage; the modulation signal has no harmonic components; the square wave pulse train itself is a harmonic source, so it contains a large number of harmonic components. In summary, the present invention can select the signal waveform of the modulation signal, for example, selecting the Gaussian modulation signal as the preferred excitation signal waveform.

[0027] S2. Apply the preferred excitation signal waveforms of different frequencies to the pre-constructed dry composite interface, and determine the preferred signal frequency based on the multi-frequency echo signal after application.

[0028] In this embodiment of the invention, the ultrasonic waves generated by the preferred excitation signal waveform are generally injected from silicone rubber, then propagate within the silicone rubber and are reflected at the composite interface. Since silicone rubber is a high-attenuation material, two main considerations are taken into account when analyzing the interface echo: 1. Silicone rubber itself is a high-attenuation material, and the amplitude will significantly decrease when the composite interface is damp. Therefore, it is necessary to select a signal frequency with a larger echo amplitude under dry interface conditions to amplify the impact of moisture on the echo amplitude. 2. With a larger echo amplitude, it is easier to extract the echo time-frequency domain characteristic parameters.

[0029] Among them, the dry composite interface is the composite interface of the cable joint in a dry state, which is formed by the contact of the silicone rubber surface and the cross-linked polyethylene surface through rough surfaces.

[0030] Specifically, the excitation signals, consisting of a series of preferred excitation signal waveforms at different frequencies, are injected into the silicone rubber interface of the dry composite interface model. This is done by scanning the frequency at a fixed step size within a preset frequency band, using a preferred center frequency as a reference, to obtain excitation signals of different frequencies. For each applied specific frequency excitation, the first echo signal reflected back from the composite interface is simultaneously acquired.

[0031] Specifically, determining the preferred signal frequency based on the applied multi-frequency echo signal includes: Calculate the echo amplitude values ​​of the multi-frequency echo signal at different frequencies; The preferred signal frequency is selected based on the echo amplitude value.

[0032] In this embodiment of the invention, the peak amplitude of the echo signal at different frequencies, i.e. the echo amplitude value, is calculated. The sharp attenuation of the echo amplitude value directly indicates that silicone rubber, as a high attenuation material, and the presence of the interface cause severe scattering and absorption attenuation of ultrasonic waves. Therefore, it is necessary to select the ultrasonic excitation frequency with high echo energy as the preferred signal frequency.

[0033] For example, the magnitudes of echo amplitudes at different frequencies are shown in Table 1: Table 1

[0034] See Figure 4 As shown, the curves represent the variation of echo signal amplitude values ​​at different frequencies. Figure 4 It can be seen that as the frequency increases, the amplitude of the echo reflected from the interface changes to a certain extent, and the amplitude value is larger at 2~2.5MHz, indicating that the energy of the echo is stronger (the degree of attenuation is smaller) at this frequency. Therefore, the present invention can select 2~2.5MHz as the preferred signal frequency.

[0035] In this embodiment of the invention, the frequency of the modulation signal is optimized by changing different frequencies of the modulation signal, and the final optimized signal frequency is applied to the simulation and experimental analysis of the actual composite interface to ensure the high quality of the echo signal received in the actual process.

[0036] S3. Construct a composite interface of multiple moisture-affected states for the cable joint, and collect the waveform of the preferred excitation signal and the echo signal of the excitation signal with the preferred signal frequency at the composite interface of multiple moisture-affected states.

[0037] In this embodiment of the invention, the composite interface of the cable connector is an SIR-XLPE composite interface constructed from silicone rubber (SIR) and cross-linked polyethylene (XLPE), with the silicone rubber and XLPE in contact through a rough surface. The multi-moisture composite interface is obtained by applying liquid to the composite interface to simulate different degrees of moisture absorption.

[0038] Specifically, the composite interface for constructing the cable joint under multiple moisture conditions includes: The composite interfacial pressure of an actual cable joint is applied to the interfacial sample of the cable joint using a pre-constructed pressure loading device. While applying pressure to the composite interface, the position of the droplets between the interface samples is fixed; At the specified location, droplets are applied at a certain liquid volume gradient using a precise droplet application device to simulate different degrees of moisture absorption at the composite interface, thereby obtaining a composite interface with multiple moisture states.

[0039] In detail, two samples of different materials were used to form the composite interface: one was silicone rubber (SIR), and the other was cross-linked polyethylene (XLPE). A pressure loading device was used to apply the composite interface pressure of an actual cable joint to the two samples. Simultaneously, a precise droplet application device was used to apply liquid at a specific volume gradient between the two samples to simulate different degrees of moisture absorption at the composite interface. Specifically, the positions of the droplets applied by the precise droplet application device between the two samples and the position of the ultrasonic probe on the silicone rubber surface were fixed. After applying moisture to the composite interface, the pressure was maintained and the sample was allowed to stand for a period of time, allowing the moisture to redistribute within the interface through capillary action and pressure, ensuring complete moisture absorption and obtaining multiple composite interfaces under moist conditions.

[0040] In this embodiment of the invention, the pressure loading device precisely controls the interface pressure through a bolt-nut or spring system, so that the SIR and XLPE samples are fully bonded, eliminating air gaps and simulating the interface contact in the actual installation state; the precise droplet application device precisely controls the degree of moisture absorption at the composite interface according to a certain liquid volume gradient, simulating the water intrusion after the cable joint seal fails.

[0041] Furthermore, by mounting an ultrasonic probe on the surface of the silicone rubber, an excitation signal with a preferred waveform and preferred frequency is applied above the multi-moisture composite interface, as described in [reference]. Figure 5 The diagram shown illustrates the ultrasonic propagation corresponding to the excitation signal on a composite interface with multiple moisture conditions.

[0042] in, Figure 5 In the diagram, 1 represents the pressure applied to the silicone rubber surface 5 and the cross-linked polyethylene (XLPE) surface 6, 3 represents the incident wave of the excitation signal, 2 represents the reflected wave, 4 represents the transmitted wave, and 7 represents the rough surface contact between the silicone rubber surface 5 and the cross-linked polyethylene (XLPE) surface 6.

[0043] In this embodiment of the invention, for each applied preferred excitation signal waveform and preferred excitation signal frequency, the first echo signal reflected back from the composite interface is simultaneously acquired to obtain the echo signal.

[0044] S4. Calculate the time-frequency domain characteristic parameters of the echo signal, and construct a moisture status assessment rule based on the time-frequency domain characteristic parameters.

[0045] In this embodiment of the invention, for a preferred excitation signal incident perpendicularly to the composite interface of two media, the formula for calculating the reflection coefficient R is:

[0046] in, The acoustic impedance of the first medium is... The acoustic impedance of the second medium.

[0047] Furthermore, the acoustic impedance of water lies between that of silicone rubber and cross-linked polyethylene. When the interface between the silicone rubber and cross-linked polyethylene changes from dry to wet, reflection decreases significantly while transmission increases, leading to a decrease in the echo amplitude. The echo amplitude can directly reflect the moisture state of the interface. However, as the moisture level of the composite interface increases, the tiny air gaps in the interface are continuously filled by moisture, and the composite interface evolves from SIR-air-XLPE to SIR-air, moisture-XLPE. This has a corresponding impact on the time-frequency domain parameters of the echo. Therefore, it is necessary to evaluate the moisture state by calculating the time-frequency domain characteristic parameters.

[0048] Among them, the time-frequency domain characteristic parameters include dimensional features such as absolute mean, root mean square, standard deviation, skewness, kurtosis, and peak-to-peak value; as well as dimensionless features such as peak factor, impulse factor, waveform factor, and margin factor; the time-frequency domain characteristic parameters also include the frequency domain characteristic parameters formed by the relative downshift rate of the center frequency and the relative attenuation rate of the amplitude in the frequency domain.

[0049] Specifically, the calculation of the time-frequency domain characteristic parameters of the echo signal includes: The echo signal is preprocessed to obtain an effective noise-reduced signal; Calculate the dimensionless and dimensional characteristics of the effective noise-reduced signal at the preferred signal frequency; Perform a Fast Fourier Transform on the effective noise-reduced signal to obtain the signal spectrum, and calculate the frequency domain feature parameters based on the signal spectrum; By combining the dimensionless features, the dimensional features, and the frequency domain feature parameters, the time-frequency domain feature parameters of the echo signal are obtained.

[0050] In this embodiment of the invention, the step of preprocessing the echo signal to obtain an effective noise-reduced signal includes: The echo signal is subjected to data denoising processing to obtain a denoised signal; Extract the effective noise reduction signal from the noise reduction signal.

[0051] In detail, data denoising can involve processing the acquired raw echo signal (filtering, smoothing, DC removal, etc.). Simultaneously, a valid first echo segment is selected as the effective denoised signal, eliminating noise segments and multiple reflections to ensure a clean, interference-free standard echo, guaranteeing accurate subsequent frequency domain calculations. This can be achieved by utilizing the difference in arrival time between the first echo, noise, and multiple reflections, and by setting a time window to extract the effective denoised signal.

[0052] Furthermore, a Fast Fourier Transform is performed on the effectively denoised signal to obtain spectral data. The amplitude of the signal at each frequency point is obtained to form a frequency-amplitude curve, which is the effectively denoised signal in the frequency domain.

[0053] In another embodiment of the present invention, the method for calculating dimensional features is shown in Table 2: Table 2

[0054] in, The total number of data points representing the effective noise reduction signal. For effective noise reduction of the signal, the first Data points Indicates the mean of data points in the effective noise-reduced signal, It represents the standard deviation of data points in the effective noise-reduced signal.

[0055] The dimensionless characteristics are calculated as shown in Table 3 below: Table 3

[0056] in, This represents the peak value of the effective noise-reduced signal. This represents the root mean square of the signal points in the effective noise reduction signal. This represents the absolute mean of the signal.

[0057] In this embodiment of the invention, skewness in the time-frequency domain characteristic parameters can be used to measure the asymmetry of the probability distribution of a random variable; kurtosis can measure the steepness of the probability distribution of a random variable; the spurious factor is the ratio of the signal peak value to the root mean square value, representing the extreme values ​​of signal fluctuations; and the impulse factor is the ratio of the signal peak value to the absolute mean value. The ratio of waveform factor to waveform frequency is used to detect whether there is an impact on the signal; waveform factor can reflect the sharpness of the signal waveform.

[0058] Furthermore, water, as a viscous medium, absorbs and scatters high-frequency components much more effectively than low-frequency components. This may lead to severe attenuation of high-frequency components in the received echo signal, resulting in a decrease in the overall center frequency. Correspondingly, in the frequency domain, this means a decrease in the center frequency amplitude and a reduction in the main frequency points. Therefore, the center frequency and center frequency amplitude of the signal spectrum are calculated as frequency domain characteristic parameters to establish the relationship between the time-frequency domain characteristic parameters and the degree of moisture absorption at the composite interface.

[0059] In this embodiment of the invention, constructing the moisture state assessment rule based on the time-frequency domain feature parameters includes: Calculate the drying reference characteristic parameters of the preferred excitation signal at the drying composite interface; The drying reference characteristic parameters are calculated by calculating the center frequency relative downshift rate and amplitude relative attenuation rate of the mid-frequency domain characteristic parameters in the time-frequency domain. Moisture state assessment rules are generated based on the relative downward shift rate of the center frequency, the relative attenuation rate of the amplitude, and the dimensionless and dimensional features in the time-frequency domain feature parameters.

[0060] In this embodiment of the invention, the multi-moisture composite interface includes the composite interface where no droplets are applied by the precise droplet application device, including but not limited to the dry composite interface pre-constructed in S2. The time-frequency domain feature parameters of the preferred excitation signal under the dry composite interface are collected, and the time-frequency domain feature parameters under the dry composite interface are used as the drying reference feature parameters.

[0061] Furthermore, the relative downward shift rate of the center frequency and the relative attenuation rate of the spectral amplitude of the time-domain state parameters and the dry baseline characteristic parameters were calculated for each moisture-affected composite interface. Based on the degree of attenuation of the frequency domain characteristics, the moisture-affected state of the cable joint interface insulation was quantitatively assessed. The higher the degree of moisture, the stronger the absorption and scattering of high-frequency ultrasonic components by moisture, the lower the center frequency, the smaller the spectral amplitude, and the more significant the high-frequency attenuation.

[0062] Meanwhile, the intrusion of moisture causes changes in the acoustic impedance of the composite interface, leading to variations in various parameters. This invention achieves a quantitative classification assessment of the moisture state by utilizing the relative change rate of characteristic parameters in the time-frequency domain of ultrasonic echoes. Using the characteristic parameters of the dry interface as a benchmark, the normalized change amplitude characterizes the degree of interface insulation damage. The specific rules for assessing the moisture state are as follows: 1. Core Methods of Quantitative Evaluation Using the characteristic parameters under dry conditions as a benchmark, calculate the relative attenuation rate of each characteristic parameter: Wherein, relative attenuation rate = (drying reference value) (Measured moisture content) / Dryness baseline value × 100% The higher the relative attenuation rate, the more significant the distortion of the ultrasonic signal caused by moisture at the interface, and the more severe the insulation damage.

[0063] 2. Quantitative determination of dimensional features: Peak-to-peak value Relative attenuation rate <10%: interface is dry and insulation is in good condition; Relative attenuation rate 10%~30%: slight moisture at the interface, mild damage to insulation; Relative attenuation rate 30%–60%: Moderate moisture absorption at the interface, with significant insulation damage; Relative attenuation rate > 60%: The interface is severely damp, and the insulation deteriorates significantly.

[0064] Skewness The greater the skewness approaches 0, the higher the signal symmetry and the more severe the moisture absorption.

[0065] A relative attenuation rate with an absolute value of skewness greater than 40% can be considered as moderate or higher degree of moisture absorption.

[0066] Kudo The smaller the decrease in kurtosis, the less damp it is; the larger the decrease, the more damp it is.

[0067] A kurtosis relative decay rate > 50% can be considered as severe moisture absorption.

[0068] 3. Quantitative Determination of Dimensionless Features The four dimensionsless characteristics show similar trends. The comprehensive relative attenuation rate, which is the sum of the four dimensionsless characteristics, is used for evaluation. The comprehensive attenuation rate is divided into four ranges (comprehensive attenuation rate <15%; comprehensive attenuation rate 15%–40%; comprehensive attenuation rate 40%–70%; comprehensive attenuation rate >70%), corresponding to the four moisture states of the composite interface (normal insulation, slightly damp, moderately damp, and severely damp). 4. Frequency domain feature quantization determination Further calculate the relative downshift rate of the center frequency: Relative downshift rate of center frequency = (Center frequency value of echo signal under dry composite interface) (Center frequency of echo signal under damp composite interface) / (Center frequency of echo signal under dry composite interface) × 100% The relative downshift rate of the center frequency and the relative attenuation rate of the amplitude of each characteristic parameter are used as characteristic parameter attenuation rates to determine four moisture states (normal insulation, slight moisture, moderate moisture, and severe moisture).

[0069] Specifically, the rules for assessing moisture conditions include calculating the corresponding levels for different moisture conditions: Level 1 (Normal): The attenuation rate of all characteristic parameters is <15%, and there is no obvious moisture on the interface; Level 2 (Slightly Moisturized): Characteristic parameter attenuation rate of 15% to 40% for single / multiple characteristic parameters, and trace amounts of moisture are present at the interface; Level 3 (moderate moisture): The attenuation rate of multiple characteristic parameters is 40% to 70%, a continuous water film has been formed at the interface, and the insulation performance has decreased significantly. Level 4 (Severely Moisturized): The attenuation rate of multiple characteristic parameters is >70%, the interface is completely filled with water, and there is a risk of insulation breakdown.

[0070] This invention establishes a correlation between changes in various characteristic parameters and the degree of moisture absorption of the composite interface through the above quantitative evaluation rules, thereby achieving a comprehensive evaluation of the moisture absorption state of the composite interface.

[0071] The study systematically investigates the changes in echoes at composite interfaces under humid conditions. By preparing composite interfaces with different degrees of moisture, the acoustic response of ultrasound waves after passing through the composite interfaces is observed to explore the correlation between primary echo parameters and the degree of moisture at the composite interfaces.

[0072] For details, please refer to [link / reference]. Figure 6 The figure shows the waveforms of the echo signal in the time domain under water and dry conditions. Figure 7 The waveform of the echo signal in the frequency domain is shown in the presence and absence of water. When the ultrasonic wave passes through the SIR-XLPE composite interface, the echo time domain waveform changes significantly depending on whether the interface is wet or dry. The two more intuitive parameters, echo amplitude and echo time, both change, which is consistent with the theoretical analysis and demonstrates the feasibility of using ultrasonic waves to detect the moisture state of the composite interface.

[0073] In summary, the optimized ultrasonic excitation signal effectively satisfies the advantages of low attenuation and concentrated spectrum, providing a more accurate and comprehensive decision-making basis for subsequent ultrasonic testing. It also demonstrates the feasibility of ultrasonic testing for the moisture state of composite interfaces. Further systematic analysis of the primary echo parameters can be conducted to achieve a non-destructive assessment of the moisture state of the composite interface insulation.

[0074] S5. The moisture condition of the cable joint to be tested is assessed using the real-time echo signal of the aforementioned moisture condition assessment rules.

[0075] In this embodiment of the invention, the terminal joint of the cable joint to be tested, which requires moisture condition assessment, is quantitatively assessed in real time according to the moisture condition assessment rules.

[0076] Specifically, the step of assessing the moisture status of the cable joint under test using the moisture status assessment rules includes: The preferred excitation signal is collected as a real-time echo signal at the cable joint to be tested. Calculate the real-time relative attenuation rate between the real-time characteristic parameters of the real-time echo signal and the pre-constructed dry reference characteristic parameters; The moisture condition assessment is performed based on the real-time relative attenuation rate to obtain the moisture condition level of the cable joint to be tested.

[0077] In detail, a preferred excitation signal is injected into the SIR-XLPE composite interface of the cable joint to be tested, and the echo signal returned from the SIR-XLPE composite interface of the cable joint to be tested is collected to obtain the real-time echo signal. The time-frequency domain characteristic parameters of the real-time echo signal are calculated as real-time characteristic parameters.

[0078] Furthermore, the relative downward shift rate of the center frequency and the relative attenuation rate of the amplitude between the real-time characteristic parameters and the dry reference characteristic parameters under the dry composite interface are calculated to obtain the real-time relative attenuation rate. The moisture status level corresponding to the real-time relative attenuation rate is determined by the moisture status assessment rules, so as to realize the moisture status assessment of the SIR-XLPE composite interface of the cable joint to be tested.

[0079] In this embodiment of the invention, the optimized excitation signal effectively satisfies the advantages of low attenuation and concentrated spectrum, providing a more accurate and comprehensive decision-making basis for moisture condition assessment. This also demonstrates the feasibility of ultrasonic detection of the moisture condition of composite interfaces. Subsequent systematic analysis of the primary echo parameters can achieve non-destructive assessment of the moisture condition of the composite interface insulation.

[0080] like Figure 8 The diagram shown is a functional block diagram of a cable joint interface moisture condition assessment system provided in an embodiment of the present invention.

[0081] The cable joint interface moisture condition assessment system 100 of the present invention can be installed in a processing device. Depending on the functions implemented, the cable joint interface moisture condition assessment system 100 may include an ultrasonic excitation signal waveform optimization module 101, a frequency optimization module 102, an echo signal acquisition module 103, a moisture condition assessment rule construction module 104, and a moisture condition assessment module 105. The module described in this invention can also be referred to as a unit, which refers to a series of computer program segments that can be executed by an electronic device processor and perform a fixed function, stored in the memory of the electronic device.

[0082] In this embodiment, the functions of each module / unit are as follows: The ultrasonic excitation signal waveform optimization module 101 is used to acquire multiple ultrasonic excitation signals for moisture status assessment, and to select the optimal excitation signal waveform based on the frequency domain characteristics of each ultrasonic excitation signal. The frequency optimization module 102 is used to apply the preferred excitation signal waveforms of different frequencies to the pre-constructed dry composite interface, and determine the preferred signal frequency based on the multi-frequency echo signal after application. The echo signal acquisition module 103 is used to construct a composite interface of multiple moisture-affected states of the cable joint, and to acquire the echo signal of the preferred excitation signal waveform and the excitation signal of the preferred signal frequency at the composite interface of multiple moisture-affected states. The moisture state assessment rule construction module 104 is used to calculate the time-frequency domain characteristic parameters of the echo signal and construct moisture state assessment rules based on the time-frequency domain characteristic parameters. The moisture condition assessment module 105 is used to assess the moisture condition of the cable joint under test using the moisture condition assessment rules and the real-time echo signal.

[0083] The specific execution methods for the steps in each of the above modules are the same as the corresponding execution steps in the above method for assessing the moisture status of cable joint interfaces.

[0084] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example.

[0085] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0086] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for assessing the moisture condition of a cable joint interface, characterized in that, include: Multiple ultrasonic excitation signals are acquired for assessing the moisture status, and a preferred excitation signal waveform is selected based on the frequency domain characteristics of each ultrasonic excitation signal; The preferred excitation signal waveforms of different frequencies are applied to the pre-constructed dry composite interface, and the preferred signal frequency is determined based on the multi-frequency echo signal after application. Construct a composite interface of multiple moisture-affected states for a cable joint, and collect the waveform of the preferred excitation signal and the echo signal of the excitation signal with the preferred signal frequency at the composite interface of multiple moisture-affected states. Calculate the time-frequency domain characteristic parameters of the echo signal, and construct a moisture status assessment rule based on the time-frequency domain characteristic parameters; The moisture condition assessment rule is used to assess the moisture condition of the cable joint under test using the real-time echo signal.

2. The method for assessing the moisture status of cable joint interfaces as described in claim 1, characterized in that, The step of selecting the preferred excitation signal waveform based on the frequency domain characteristics of each ultrasonic excitation signal includes: Perform a fast Fourier transform on each of the ultrasonic excitation signals to obtain the spectral signal; Harmonic component analysis is performed on the spectral signal to obtain harmonic component information corresponding to each ultrasonic excitation signal; A preferred excitation signal waveform is selected from the ultrasonic excitation signals based on the harmonic component information.

3. The method for assessing the moisture status of cable joint interfaces as described in claim 1, characterized in that, The step of determining the preferred signal frequency based on the applied multi-frequency echo signal includes: Calculate the echo amplitude values ​​of the multi-frequency echo signal at different frequencies; The preferred signal frequency is selected based on the echo amplitude value.

4. The method for assessing the moisture status of cable joint interfaces as described in claim 1, characterized in that, The composite interface for constructing a cable joint under multiple moisture conditions includes: The composite interfacial pressure of an actual cable joint is applied to the interfacial sample of the cable joint using a pre-constructed pressure loading device. While applying pressure to the composite interface, the position of the droplets between the interface samples is fixed; At the specified location, droplets are applied at a certain liquid volume gradient using a precise droplet application device to simulate different degrees of moisture absorption at the composite interface, thereby obtaining a composite interface with multiple moisture states.

5. The method for assessing the moisture status of cable joint interfaces as described in claim 1, characterized in that, The calculation of the time-frequency domain characteristic parameters of the echo signal includes: The echo signal is preprocessed to obtain an effective noise-reduced signal; Calculate the dimensionless and dimensional characteristics of the effective noise-reduced signal at the preferred signal frequency; Perform a Fast Fourier Transform on the effective noise-reduced signal to obtain the signal spectrum, and calculate the frequency domain feature parameters based on the signal spectrum; By combining the dimensionless features, the dimensional features, and the frequency domain feature parameters, the time-frequency domain feature parameters of the echo signal are obtained.

6. The method for assessing the moisture status of cable joint interfaces as described in claim 5, characterized in that, The step of preprocessing the echo signal to obtain an effective noise-reduced signal includes: The echo signal is subjected to data denoising processing to obtain a denoised signal; Extract the effective noise reduction signal from the noise reduction signal.

7. The method for assessing the moisture status of cable joint interfaces as described in claim 1, characterized in that, The step of constructing a moisture state assessment rule based on the time-frequency domain feature parameters includes: Calculate the drying reference characteristic parameters of the preferred excitation signal at the drying composite interface; The drying reference characteristic parameters are calculated by calculating the center frequency relative downshift rate and amplitude relative attenuation rate of the mid-frequency domain characteristic parameters in the time-frequency domain. Moisture state assessment rules are generated based on the relative downward shift rate of the center frequency, the relative attenuation rate of the amplitude, and the dimensionless and dimensional features in the time-frequency domain feature parameters.

8. A system for assessing the moisture condition of a cable joint interface, characterized in that, include: An ultrasonic excitation signal waveform optimization module is used to acquire multiple ultrasonic excitation signals for moisture status assessment and to select the optimal excitation signal waveform based on the frequency domain characteristics of each ultrasonic excitation signal. A frequency optimization module is used to apply the preferred excitation signal waveforms of different frequencies to the pre-constructed dry composite interface, and to determine the preferred signal frequency based on the multi-frequency echo signal after application. The echo signal acquisition module is used to construct a composite interface of multiple moisture-affected states of the cable joint, and to acquire the echo signal of the preferred excitation signal waveform and the excitation signal of the preferred signal frequency at the composite interface of multiple moisture-affected states. A moisture condition assessment rule construction module is used to calculate the time-frequency domain characteristic parameters of the echo signal and construct moisture condition assessment rules based on the time-frequency domain characteristic parameters. The moisture condition assessment module is used to assess the moisture condition of the cable joint under test using the real-time echo signal of the aforementioned moisture condition assessment rules.

9. A processing device, characterized in that, It includes at least one processor and at least one memory communicatively connected to the processor, wherein: the memory stores program instructions executable by the processor, and the processor can execute the method as described in any one of claims 1-7 by invoking the program instructions.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores computer instructions that cause the computer to perform the method as described in any one of claims 1-7.

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