A method and system for monitoring the capacitance of a flexible HVDC converter station bushing

Abstract

The application discloses a kind of capacitive capacity monitoring method and system of flexible direct current converter station bushing, it is related to the field of flexible direct current transmission equipment on-line monitoring and electrical parameter identification technique, including in the bushing of flexible direct current converter station bushing end screen and ground setting capacitor voltage divider and constructing series capacitor measurement structure, acquisition bushing primary voltage signal and end screen current.Primary voltage signal and end screen current are carried out synchronous signal preprocessing, using wavelet transform and filtering strategy to remove noise and extract frequency domain features.Capacitive capacity coupling relationship of bushing structure parameter is calculated based on frequency domain features, and abnormal point is judged by establishing capacitive capacity change identification model and combining temperature and humidity data.The method described in the application effectively overcomes the problems of static analysis lag, single variable misjudgment and insufficient frequency spectrum resolution, realizes real-time monitoring of flexible direct current bushing capacitive capacity, abnormal dynamic early warning and system improvement of model adaptability, and significantly enhances the safety operation guarantee capability of equipment throughout its life cycle.

Description

Technical Field

[0001] This invention relates to the field of online monitoring and electrical parameter identification technology for flexible DC transmission equipment, specifically to a method and system for monitoring the electrical capacity of through-wall bushings in flexible DC converter stations. Background Technology

[0002] Flexible DC transmission technology, as an important form of next-generation high-voltage DC transmission, is gradually being widely used in long-distance power transmission and renewable energy grid connection due to its advantages such as strong converter controllability and good adaptability. In flexible DC converter systems, wall bushings serve as the connection channel between AC and DC systems, and their insulation performance and operational stability are crucial to the safe operation of the system. In recent years, with the increasing harmonic pollution and the continuous improvement of system voltage levels, the health status monitoring of wall bushings has gradually shifted from offline detection to online monitoring. Related research focuses on how to accurately obtain key operating parameters such as bushing capacitance to achieve dynamic identification and early warning control of insulation aging trends.

[0003] Although some literature has attempted to introduce fiber optic electric field sensors and harmonic analysis methods for bushing condition monitoring, several limitations remain in practical engineering scenarios. First, most existing capacitance detection methods rely on offline measurement or periodic calibration, failing to capture real-time capacitance change trends and thus failing to meet the requirements of flexible DC converter systems for rapid response to high-frequency transient anomalies. Second, in high-frequency current disturbance environments, traditional capacitance estimation methods lack sufficient anti-interference capability against harmonic components, especially struggling to accurately separate weak local variation signals under power frequency backgrounds. Furthermore, existing monitoring systems lack a fusion modeling mechanism for multi-source signals (such as structural parameters, ambient temperature and humidity, and frequency domain energy characteristics), leading to significant model prediction bias and insufficient reliability of early warning results. More critically, traditional capacitance judgment methods often rely on static threshold settings, unable to adaptively adjust to environmental changes, easily resulting in misjudgments or omissions, limiting the ability to early identify potential insulation degradation in actual operation. Summary of the Invention

[0004] In view of the above-mentioned problems, the present invention is proposed.

[0005] Therefore, the technical problem solved by this invention is that existing methods for monitoring the capacitance of through-wall bushings have the following drawbacks: they cannot achieve online capacitance estimation, lack an efficient mechanism for extracting frequency domain features, are difficult to cope with dynamic interference from environmental factors, and there are problems with how to achieve dynamic identification and abnormal early warning of the capacitance of through-wall bushings based on structural modeling and frequency domain feature fusion.

[0006] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for monitoring the capacitance of a through-wall bushing in a flexible DC converter station, comprising setting a capacitor voltage divider between the end screen of the through-wall bushing and ground and constructing a series capacitor measurement structure to collect the primary voltage signal of the bushing and the current of the end screen.

[0007] The primary voltage signal and the final screen current are preprocessed to synchronize the signal. Wavelet transform and filtering strategies are used to remove noise and extract frequency domain features.

[0008] Based on frequency domain characteristics, the coupling relationship between bushing structural parameters and capacitance is calculated, a capacitance change identification model is established, and anomalies are identified by combining temperature and humidity data.

[0009] The calculation of the coupling relationship between bushing structural parameters and capacitance based on frequency domain features includes taking the length, inner diameter, and dielectric constant of the through-wall bushing as structural parameter inputs, constructing a capacitance estimation function based on the capacitance coupling model in combination with frequency domain features, importing the model through a lookup table, using the spectral energy ratio and the rate of change of the dominant frequency in the frequency domain features as independent variables, and using the capacitance change trend per unit length as the output result, and performing standardization and normalization processing in combination with historical data to form a standard coupling curve for subsequent anomaly point comparison.

[0010] As a preferred embodiment of the capacitance monitoring method for the through-wall bushing of the flexible DC converter station described in this invention, the method of setting up a capacitor voltage divider includes connecting two capacitors in series between the end screen and ground to form a voltage divider measurement circuit. The two capacitors are a main capacitor and a detection capacitor, respectively. The detection capacitor is connected to a voltage acquisition node to measure the voltage change across the main capacitor, thereby obtaining the potential difference change curve between the end screen of the through-wall bushing and ground, and realizing the indirect derivation of the capacitance value.

[0011] As a preferred embodiment of the capacitance monitoring method for the through-wall bushing of the flexible DC converter station described in this invention, the construction of the series capacitance measurement structure includes: arranging multiple broadband current sensors and high-voltage end voltage leads in a ring around the outer shell of the through-wall bushing; the high-voltage end voltage is led out through an insulated cable and connected to a voltage sampling circuit; the end-screen current is measured through a Rogowski coil and acquired synchronously with the voltage signal; and a minimum threshold for the sampling frequency is set.

[0012] As a preferred embodiment of the capacitance monitoring method for through-wall bushings in flexible DC converter stations described in this invention, the preprocessing of the primary voltage signal and the final screen current for synchronization includes: digital denoising of the voltage and current signals; removing power frequency interference components from the voltage signal using a bandpass filter based on band filtering; and extracting transient spectral components from the current signal using wavelet transform. After denoising, time-domain alignment of the voltage and current signals is achieved using timestamp marking.

[0013] As a preferred embodiment of the capacity monitoring method for through-wall bushings of flexible DC converter stations described in this invention, the step of removing noise and extracting frequency domain features using wavelet transform and filtering strategies includes: performing a six-level decomposition using the Daubechies wavelet function to extract high-frequency harmonic components; obtaining a spectral distribution map through power spectral density analysis; and extracting feature point parameters within the target frequency band as input features for the subsequent capacity coupling model based on the set frequency band weights. The energy proportion of each frequency band is used as an important dimension of the model feature vector to participate in the subsequent coupling relationship modeling.

[0014] As a preferred embodiment of the capacitance monitoring method for through-wall bushings in flexible DC converter stations described in this invention, the extraction of feature points within the target frequency band includes dividing the frequency range from 1kHz to 10MHz into five sub-bands. Within each sub-band, the dominant harmonic peak frequency, total band energy, maximum band amplitude, and transient slope are selected as feature point parameters. After energy normalization, each band forms a 20-dimensional feature vector describing the energy distribution characteristics of high-frequency harmonics throughout the frequency domain. Before inputting the feature vector into the capacitance coupling model, a principal component analysis is performed to reduce the modeling dimensionality while retaining key spectral change information.

[0015] As a preferred embodiment of the capacitance monitoring method for through-wall bushings in flexible DC converter stations according to the present invention, the step of calculating the coupling relationship between bushing structural parameters and capacitance based on frequency domain features includes: acquiring the structural parameters of the through-wall bushing, including the bushing length, internal diameter, and dielectric properties of the material, and establishing a reference capacitance value per unit length based on the physical structure of the through-wall bushing. Based on the high-frequency energy ratio and main frequency variation obtained in the frequency domain feature extraction, a feature index describing the change in electrical behavior is constructed, and the feature index and structural parameters are combined and input into a preset estimation function. The estimation function is trained using historical operating data to obtain a set of weight parameters adapted to different types of bushings, and outputs the estimated capacitance value per unit length at the current moment. The estimated capacitance change trend is compared with the standard coupling curve recorded in the healthy state during historical operation, and all data are uniformly standardized. During the comparison process, if there is a continuous deviation between the estimated curve and the standard coupling curve, and the deviation exceeds the set judgment threshold, then the capacitance characteristics of the current bushing have changed abnormally. The time point and segment corresponding to the deviation are marked.

[0016] As a preferred embodiment of the capacitance monitoring method for through-wall bushings of flexible DC converter stations described in this invention, the step of establishing a capacitance change identification model and judging abnormal points by combining temperature and humidity data includes: calculating the difference between the standard coupling curve recorded in the healthy state during historical operation and the current measured curve; setting temperature and humidity correction coefficients to dynamically adjust the difference threshold; real-time acquisition of temperature and humidity from on-site environmental sensors; and calculation of the correction factor through regression analysis. If the difference exceeds the correction threshold, it is considered an abnormal capacitance change. The abnormal section is located, and the start and end positions of the abnormal section, the capacitance change rate, and the corresponding timestamp are output.

[0017] As a preferred embodiment of the capacitance monitoring method for through-wall bushings in flexible DC converter stations according to the present invention, the regression analysis method includes: selecting multiple sets of environmental temperature and humidity variation curve difference samples under the same load conditions from the bushing's historical operating data; and using the least squares method to perform multivariate linear fitting on the temperature sensitivity coefficient and humidity sensitivity coefficient to obtain a regression equation. The temperature sensitivity coefficient represents the correction ratio of the difference amplitude caused by each 1°C change, and the humidity sensitivity coefficient represents the error tolerance variation amplitude caused by each 1%RH change.

[0018] Another objective of this invention is to provide a capacitance monitoring system for through-wall bushings in flexible DC converter stations. This system uses a capacitance identification and judgment module to calculate the coupling relationship between bushing structural parameters and capacitance based on frequency domain features, establish a capacitance change identification model, and combine temperature and humidity data to identify anomalies. This solves the problems of existing through-wall bushing capacitance monitoring methods, such as the inability to achieve online capacitance estimation, the lack of an efficient extraction mechanism for frequency domain features, the difficulty in dealing with dynamic interference from environmental factors, and the lack of a dynamic identification and anomaly warning system for through-wall bushing capacitance based on structural modeling and frequency domain feature fusion.

[0019] As a preferred embodiment of the capacitance monitoring system for the through-wall bushing of the flexible DC converter station described in this invention, it includes a signal acquisition module, a frequency domain preprocessing and extraction module, and a capacitance identification and judgment module.

[0020] The signal acquisition module is used to set up a capacitor voltage divider and construct a series capacitor measurement structure between the end screen of the bushing of the flexible DC converter station and the ground to acquire the primary voltage signal of the bushing and the current of the end screen.

[0021] The frequency domain preprocessing extraction module is used to perform synchronous signal preprocessing on the primary voltage signal and the final screen current, and uses wavelet transform and filtering strategies to remove noise and extract frequency domain features.

[0022] The capacitance identification and judgment module is used to calculate the coupling relationship between the bushing structure parameters and capacitance based on frequency domain features, establish a capacitance change identification model, and judge abnormal points by combining temperature and humidity data.

[0023] The calculation of the coupling relationship between bushing structural parameters and capacitance based on frequency domain features includes taking the length, inner diameter, and dielectric constant of the through-wall bushing as structural parameter inputs, constructing a capacitance estimation function based on the capacitance coupling model in combination with frequency domain features, importing the model through a lookup table, using the spectral energy ratio and the rate of change of the dominant frequency in the frequency domain features as independent variables, and using the capacitance change trend per unit length as the output result, and performing standardization and normalization processing in combination with historical data to form a standard coupling curve for subsequent anomaly point comparison.

[0024] A computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of a method for monitoring the capacitance of through-wall bushings in a flexible DC converter station.

[0025] A computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, implements the steps of a method for monitoring the capacitance of a through-wall bushing in a flexible DC converter station.

[0026] The beneficial effects of this invention are as follows: The capacitance monitoring method for through-wall bushings in flexible DC converter stations provided by this invention, by setting a capacitive voltage divider between the end screen of the through-wall bushing and ground, and constructing a series capacitor measurement structure, collects the primary voltage signal and the end screen current, achieving high-fidelity acquisition of electrical signals under high-frequency harmonic coverage. This provides a stable and accurate foundational signal support for subsequent frequency domain analysis and modeling.

[0027] The collected voltage and current signals are filtered, decomposed by wavelet, and analyzed by spectrum to extract frequency domain features and construct normalized feature vectors for subsequent modeling input. This achieves the beneficial effect of effectively transforming complex frequency domain changes into structurally recognizable inputs, thereby improving the model's discrimination accuracy and robustness.

[0028] A capacitance estimation model is constructed based on structural parameters and frequency domain characteristics. Combined with temperature and humidity data, dynamic correction and regression analysis are used to achieve capacitance anomaly identification and early warning. This achieves a high-resolution identification capability for minute capacitance fluctuations and an environmentally adaptive anomaly early warning mechanism, providing a beneficial basis for early intervention decisions in system operation and maintenance. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1The first embodiment of the present invention provides an overall flowchart of a method for monitoring the capacitance of a flexible DC converter station through-wall bushing.

[0031] Figure 2 This is an overall schematic diagram of a capacity monitoring system for a flexible DC converter station through-wall bushing, provided in the second embodiment of the present invention. Detailed Implementation

[0032] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of the present invention.

[0033] Example 1, referring to Figure 1 As an embodiment of the present invention, a method for monitoring the capacitance of a through-wall bushing in a flexible DC converter station is provided, comprising:

[0034] S1: Install a capacitor voltage divider between the end screen of the bushing and ground in the flexible DC converter station and construct a series capacitor measurement structure to collect the primary voltage signal of the bushing and the current of the end screen.

[0035] In the capacitance monitoring process of the bushings passing through the wall in a flexible DC converter station, the first step is to complete signal acquisition and construct the measurement structure. To this end, a capacitive voltage divider structure is installed between the end screen of the bushing and ground to accurately capture electrical signals and indirectly derive capacitance. The capacitive voltage divider forms a measurement circuit by connecting two capacitors in series between the end screen and ground. One capacitor is the main capacitor, carrying the majority of the voltage. The other is a detection capacitor, with one end connected to the end screen of the bushing and the other end led out to the voltage acquisition node. The voltage across the detection capacitor is acquired in real time by the measurement circuit and, in conjunction with the known parameters of the main capacitor, indirectly calculates the potential difference change between the entire end screen and ground, thus providing a basic input for subsequent capacitance estimation.

[0036] To further improve the spatial resolution and current monitoring integrity of the acquired data, several broadband current sensors are evenly distributed around the circumference of the bushing casing. These sensors are fixed in a ring structure to ensure that they can comprehensively acquire induced current signals around the bushing from multiple angles. The current sensors are either capacitively coupled or Rogowski coil type, with a detection range covering a wide frequency range from power frequency to several megahertz. Simultaneously, a primary voltage signal is led out from the high-voltage end of the bushing through an insulated lead wire and connected to a voltage sampling circuit via a dedicated voltage lead-out structure, achieving safe isolation and effective acquisition of the high-voltage signal.

[0037] To ensure the synchronization and sampling accuracy of voltage and current signals in the time domain, all acquisition channels are equipped with a unified clock trigger control. The signal acquisition frequency is set to a sampling rate of no less than 10 megabits per second, ensuring that complete waveform characteristics can still be captured even under harmonic conditions containing high-frequency components. This acquisition frequency parameter is preset according to the rated operating voltage level of the converter station and the target monitoring frequency bandwidth, and has a fixed lower limit, not lower than the minimum bandwidth multiple of the monitoring requirements.

[0038] Through the above structural arrangement and sampling logic control, step S1 completes the synchronous high-fidelity acquisition of the primary voltage signal of the through-wall bushing and the current signal of the end screen, and provides a highly complete and computable signal foundation for subsequent preprocessing and coupling calculation.

[0039] S2: Perform synchronization signal preprocessing on the primary voltage signal and the final screen current, and use wavelet transform and filtering strategies to remove noise and extract frequency domain features.

[0040] Digital denoising is performed on both voltage and current signals. For the voltage signal, a bandpass filter based on band filtering is used to remove power frequency interference components. For the current signal, transient spectral components are extracted using wavelet transform. After denoising, time-domain alignment of the voltage and current signals is achieved using timestamps.

[0041] Furthermore, to remove power frequency interference from the voltage signal, the bandpass filter response function is defined as follows:

[0042] ,

[0043] in, Indicates frequency as The transfer function value of the bandpass filter. Indicates the first element in the input signal Each frequency component. This indicates the lower cutoff frequency of the bandpass filter. This indicates the upper limit frequency of the bandpass filter, setting a range to exclude 50Hz power frequency interference and retain high-frequency harmonic components.

[0044] The Daubechies wavelet function is used to perform a six-level decomposition to extract high-frequency harmonic components. The spectrum distribution is obtained through power spectral density analysis. Based on the set frequency band weights, feature point parameters within the target frequency band are extracted as input features for the subsequent capacitance coupling model. The energy proportion of each frequency band is used as an important dimension of the model feature vector to participate in the subsequent coupling relationship modeling.

[0045] Furthermore, the wavelet decomposition coefficients are calculated as follows:

[0046] ,

[0047] in, Indicates the first Layer scale, time point The wavelet decomposition coefficients. Indicates the first Wavelet scale of the layer (corresponding frequency band). Indicates the first element in the original signal Each sampling channel in time The value. Describes the Daubechies wavelet basis functions, at scale The first The response function of each channel. This indicates the total number of channels.

[0048] The extraction of feature points within the target frequency band involves dividing the 1kHz to 10MHz frequency range into five sub-bands. Within each sub-band, the dominant harmonic peak frequency, total band energy, maximum band amplitude, and transient slope are selected as feature point parameters. After energy normalization, each band forms a 20-dimensional feature vector that describes the energy distribution characteristics of high-frequency harmonics across the entire frequency domain.

[0049] Furthermore, the frequency band normalized energy vector calculation is expressed as:

[0050] ,

[0051] in, Indicates the first The normalized energy value of each frequency band. Indicates the first The total original energy value within each frequency band. The total energy of all five frequency bands. and This indicates the frequency band number subscript.

[0052] Before the feature vectors are input into the capacitance coupling model, a principal component analysis is performed to reduce the dimensionality of the model while retaining key spectral change information.

[0053] Furthermore, the dimensionality reduction representation of principal component analysis features is as follows:

[0054] ,

[0055] in, Represents the principal component vector. Each dimension. Indicates from the normalized energy dimension Projected to principal component dimension The weighting coefficients. The first normalized energy vector represents the first normalized energy vector. Each component. This indicates the dimensionality number of the principal components after dimensionality reduction. This indicates the frequency band energy dimension number before dimensionality reduction. This represents the dimension of the original feature vector (20 in this invention).

[0056] It should be noted that step S2 of this invention achieves accurate extraction of high-frequency harmonics and fusion of structural features by constructing a multi-stage frequency domain signal processing chain. First, by combining bandpass filtering and wavelet six-level decomposition, power frequency interference is effectively eliminated and transient high-frequency characteristics are captured. Second, a multi-dimensional feature vector based on frequency band energy ratio, dominant frequency, etc., is designed, and normalization and principal component dimensionality reduction operations are introduced to ensure that the model input retains key information while reducing dimensional complexity. This step overcomes the problems of low resolution and simple feature structure in existing technologies, achieving a unified approach to robust high-frequency noise extraction and structural coupling modeling, thus improving the sensitivity and engineering adaptability of through-wall bushing capacitance monitoring.

[0057] S3: Calculate the coupling relationship between bushing structural parameters and capacitance based on frequency domain characteristics, establish a capacitance change identification model, and combine temperature and humidity data to identify anomalies.

[0058] The structural parameters of the through-wall bushing are obtained, including its length, internal diameter, and dielectric properties. A reference capacitance value per unit length is established based on the physical structure of the bushing. Based on the high-frequency energy proportion and main frequency variation obtained from frequency domain feature extraction, feature indices describing changes in electrical behavior are constructed. These feature indices are then combined with the structural parameters and input into a pre-defined estimation function.

[0059] Furthermore, the capacitance per unit length estimation function is expressed as:

[0060] ,

[0061] in, Indicates time The estimated capacitance per unit length at any given time. This indicates the actual length of the through-wall sleeve. This indicates the internal diameter of the through-wall sleeve. This represents the relative permittivity of the bushing material. This indicates the proportion of high-frequency energy at the current moment. This represents the rate of change of the dominant frequency compared to the historical curve. , , , and This represents the weight coefficients obtained during model training, used to adjust the ratio for different inputs. This represents the bias constant term.

[0062] The estimation function is trained using historical operating data to obtain a set of weight parameters suitable for different types of bushings, and outputs an estimated value of the capacitance per unit length at the current moment. The estimated capacitance change trend is compared with the standard coupling curve recorded during historical operation under healthy conditions, and all data are standardized. During the comparison, if there is a persistent deviation between the estimated curve and the standard coupling curve, and the deviation exceeds a set judgment threshold, then the capacitance characteristics of the current bushing have changed abnormally. The time points and segments corresponding to the deviation are marked.

[0063] Furthermore, the standardized interpolation is expressed as:

[0064] ,

[0065] in, Indicates the current time The normalized difference. This represents the currently estimated capacitance per unit length. This represents the standard capacitance change curve value under historical healthy conditions. The numerator represents the capacitance deviation, and the denominator is the standard reference, which is the proportion of deviation between the overall measurement estimate and the standard reference.

[0066] The difference between the standard coupling curve recorded during historical operation and the current measured curve is calculated, and temperature and humidity correction coefficients are set to dynamically adjust the difference threshold. Temperature and humidity are collected in real time from the field environmental sensors, and the correction factor is calculated by regression analysis.

[0067] Furthermore, the dynamic temperature and humidity correction threshold is calculated and expressed as follows:

[0068] ,

[0069] in, Indicates the current time The dynamic judgment threshold is adjusted accordingly. This represents a fixed threshold value used for static difference determination. This represents the temperature correction sensitivity coefficient, indicating the percentage effect of each 1°C temperature change on the threshold. This indicates the actual ambient temperature at the current time. This represents the humidity correction sensitivity coefficient, indicating the percentage change in threshold value for every 1% RH humidity change. This indicates the actual ambient humidity at the current point in time.

[0070] If the difference exceeds the correction threshold, it is considered an abnormal change in capacitance. The abnormal section is located, and the start and end positions of the abnormal section, the capacitance change rate, and the corresponding timestamp are output. The regression analysis method involves selecting multiple sets of environmental temperature and humidity difference curves under the same load conditions from the bushing's historical operating data. The least squares method is used to perform multiple linear fitting on the temperature and humidity sensitivity coefficients to obtain the regression equation.

[0071] Furthermore, the temperature and humidity correction factor regression model is expressed as follows:

[0072] ,

[0073] in, Indicates the first historical sample Standardized difference of groups. This indicates the ambient temperature corresponding to this group of samples. This indicates the ambient humidity corresponding to this group of samples. This represents the intercept constant of the regression equation. Indicates the first The residual term of the group of samples represents the regression error.

[0074] The temperature sensitivity coefficient represents the correction ratio of the difference caused by a 1°C change, while the humidity sensitivity coefficient represents the error tolerance range caused by a 1%RH change.

[0075] It should be noted that step S3 of this invention constructs a capacitance estimation model by fusing structural parameters and frequency domain features, thereby achieving dynamic estimation and anomaly identification of the capacitance per unit length of the through-wall bushing. A multi-dimensional feature input function is used to model the capacitance change trend, and a standardized curve comparison mechanism is introduced to ensure consistency between the estimation results and historical health status. Furthermore, a dynamic threshold adjustment method based on temperature and humidity factors is proposed, utilizing regression analysis to adaptively correct the judgment criteria, thus effectively avoiding false alarms caused by environmental fluctuations. This step overcomes the limitations of existing technologies that rely solely on static thresholds or single indicators for judgment, achieving high-precision anomaly detection capabilities through multi-parameter coupling and electrical-environmental synergy.

[0076] Example 2, refer to Figure 2 As an embodiment of the present invention, a capacitance monitoring system for through-wall bushings of flexible DC converter stations is provided, including a signal acquisition module 100, a frequency domain preprocessing extraction module 200, and a capacitance identification and judgment module 300.

[0077] S4: Signal acquisition module 100 is used to set up a capacitor voltage divider and construct a series capacitor measurement structure between the end screen of the bushing of the flexible DC converter station and the ground to acquire the primary voltage signal of the bushing and the current of the end screen.

[0078] It includes a capacitor divider deployment submodule 101 and a high-frequency electrical signal acquisition submodule 102.

[0079] Furthermore, the capacitor divider deployment submodule 101 is used to configure a high-voltage adapter capacitor between the end screen of the through-wall bushing of the flexible DC converter station and ground, and to construct a series capacitor measurement channel to extract the high-voltage side signal to reduce the amplitude for easier sampling. The high-frequency electrical signal acquisition submodule 102 is used to synchronously acquire the primary side voltage signal of the through-wall bushing and the grounding current of the end screen, and uses a wideband current transformer to achieve full-band response to high-frequency components.

[0080] It should be noted that the capacitor divider deployment submodule 101 provides a safe high-voltage signal access method for the entire signal acquisition module, which is the foundation for the non-intrusive capacitance monitoring of this system. The high-frequency electrical signal acquisition submodule 102 ensures the consistency and bandwidth integrity of voltage and current signal acquisition, providing raw data support for subsequent frequency domain feature extraction.

[0081] It should also be noted that the signal acquisition module 100 is a prerequisite for frequency domain modeling and state analysis in this system, and the quality of the acquired signal has a direct impact on the subsequent identification results.

[0082] S5: Frequency domain preprocessing extraction module 200 is used to perform synchronous signal preprocessing on the primary voltage signal and the final screen current, and uses wavelet transform and filtering strategies to remove noise and extract frequency domain features.

[0083] It includes a signal filtering and normalization submodule 201 and a frequency domain feature extraction submodule 202.

[0084] Furthermore, the signal filtering and normalization submodule 201 is used to perform bandpass filtering on the acquired voltage and current signals to suppress power frequency interference and low-frequency noise, and to unify the amplitude range using a normalization algorithm. The frequency domain feature extraction submodule 202 is used to perform multi-level wavelet decomposition and Fourier analysis to extract frequency domain features such as harmonic energy and dominant frequency drift, and to construct a multi-dimensional feature vector as subsequent input.

[0085] It should be noted that the signal filtering and normalization submodule 201 provides a clean and standardized input signal, improving the accuracy and comparability of feature calculation. The frequency domain feature extraction submodule 202 is the core of the recognition model input construction, and the extracted spectral distribution indicators are highly correlated with capacitance changes.

[0086] It should also be noted that the frequency domain preprocessing extraction module 200 is an intermediate link connecting the acquisition and recognition stages, and its output features directly determine the resolution and response speed of the modeling results.

[0087] S6: Capacitance identification and judgment module 300 is used to calculate the coupling relationship between bushing structure parameters and capacitance based on frequency domain characteristics, establish a capacitance change identification model, and judge abnormal points in combination with temperature and humidity data.

[0088] It includes a capacity estimation modeling submodule 301 and an environmental factor correction judgment submodule 302.

[0089] The calculation of the coupling relationship between bushing structural parameters and capacitance based on frequency domain features includes taking the length, inner diameter, and dielectric constant of the through-wall bushing as structural parameter inputs, constructing a capacitance estimation function based on the capacitance coupling model by combining frequency domain features, importing the model through a lookup table, and using the spectral energy ratio and the rate of change of the dominant frequency in the frequency domain features as independent variables, and the capacitance change trend per unit length as the output result. The data is then standardized and normalized based on historical data to form a standard coupling curve for subsequent anomaly point comparison.

[0090] Furthermore, the capacitance estimation modeling submodule 301 is used to construct a unit length capacitance estimation function by combining the structural parameters of the through-wall bushing and the frequency domain feature vector, and to train a regression model using historical operating data to obtain the curve of the estimated value changing over time. The environmental factor correction judgment submodule 302 is used to combine data collected by on-site temperature and humidity sensors, calculate the temperature and humidity sensitivity coefficient based on regression analysis, dynamically correct the judgment threshold, and determine the anomaly of capacitance changes.

[0091] It should be noted that the capacitance estimation modeling submodule 301 constructs a coupling channel between electrical signal changes and physical parameters, ensuring that the recognition results have physical interpretability and scene adaptability. The environmental factor correction judgment submodule 302 effectively eliminates the disturbance effect of external environmental changes on the judgment threshold, improving the stability and accuracy of the judgment.

[0092] It should also be noted that the capacitance identification and judgment module 300 is a key component of this system to achieve intelligent early warning and anomaly location. The output results can be directly used for operation and maintenance strategy optimization and fault intervention response.

Claims

1. A method for monitoring the capacitance of through-wall bushings in a flexible DC converter station, characterized in that, include: A capacitor voltage divider is installed between the end screen of the through-wall bushing of the flexible DC converter station and the ground, and a series capacitor measurement structure is constructed to collect the primary voltage signal of the bushing and the current of the end screen. The primary voltage signal and the final screen current are preprocessed to synchronize the signal, and wavelet transform and filtering strategies are used to remove noise and extract frequency domain features. Based on frequency domain features, the coupling relationship between bushing structural parameters and capacitance is calculated, a capacitance change identification model is established, and abnormal points are judged by combining temperature and humidity data. The calculation of the coupling relationship between bushing structural parameters and capacitance based on frequency domain features includes taking the length, inner diameter, and dielectric constant of the through-wall bushing as structural parameter inputs, constructing a capacitance estimation function based on the capacitance coupling model in combination with frequency domain features, importing the model through a lookup table, using the spectral energy ratio and the rate of change of the dominant frequency in the frequency domain features as independent variables, and using the capacitance change trend per unit length as the output result, and performing standardization and normalization processing in combination with historical data to form a standard coupling curve for subsequent anomaly point comparison.

2. The method for monitoring the capacitance of through-wall bushings in flexible DC converter stations as described in claim 1, characterized in that: The capacitor voltage divider includes... Two capacitors are connected in series between the end screen and ground to form a voltage divider measurement circuit. The two capacitors are the main capacitor and the detection capacitor. The detection capacitor is connected to the voltage acquisition node. The voltage change across the main capacitor is measured to obtain the potential difference change curve between the end screen of the wall bushing and ground, thus realizing the indirect derivation of the capacitance value.

3. The method for monitoring the capacitance of through-wall bushings in flexible DC converter stations as described in claim 1 or 2, characterized in that: The construction of the series capacitance measurement structure includes: Multiple broadband current sensors and high-voltage lead wires are arranged in a ring around the outer casing of the wall bushing. The high-voltage lead wire is led out through an insulated cable and connected to the voltage sampling circuit. The current of the end screen is measured by a Rogowski coil and is collected synchronously with the voltage signal. A minimum threshold for the sampling frequency is set.

4. The method for monitoring the capacitance of through-wall bushings in flexible DC converter stations as described in claim 3, characterized in that: The synchronization signal preprocessing for the primary voltage signal and the final screen current includes... Digital denoising processing is performed on voltage and current signals. The voltage signal is filtered by a bandpass filter based on frequency band filtering to remove power frequency interference components, and the transient spectrum components of the current signal are extracted by wavelet transform. After the noise reduction process is completed, the voltage and current signals are aligned in the time domain by using timestamp marking.

5. The method for monitoring the capacitance of through-wall bushings in flexible DC converter stations as described in claim 4, characterized in that: The method of using wavelet transform and filtering strategies to remove noise and extract frequency domain features includes... The Daubechies wavelet function is used to perform a six-level decomposition to extract high-frequency harmonic components. The spectrum distribution is obtained through power spectral density analysis. Based on the set frequency band weights, feature point parameters within the target frequency band are extracted as input features for the subsequent capacitance coupling model. The energy proportion of each frequency band is used as an important dimension of the model feature vector to participate in the subsequent coupling relationship modeling.

6. The method for monitoring the capacitance of through-wall bushings in a flexible DC converter station as described in claim 5, characterized in that: The extraction of feature points within the target frequency band includes, Based on frequency band division, the frequency range of 1kHz to 10MHz is divided into five sub-bands. Within each sub-band, the main peak frequency of harmonics, the total energy of the frequency band, the maximum amplitude of the frequency band, and the transient slope are selected as characteristic point parameters. After the energy of each frequency band is normalized, a 20-dimensional feature vector is formed to describe the energy distribution characteristics of high-frequency harmonics in the entire frequency domain. Before the feature vectors are input into the capacitance coupling model, a principal component analysis is performed to reduce the dimensionality of the model while retaining key spectral change information.

7. The method for monitoring the capacitance of through-wall bushings in a flexible DC converter station as described in claim 6, characterized in that: The calculation of the coupling relationship between bushing structural parameters and capacitance based on frequency domain characteristics includes... Obtain the structural parameters of the through-wall bushing, including the bushing's length, internal diameter, and dielectric properties of the material, and establish a reference capacitance value per unit length based on the physical structure of the through-wall bushing. Based on the high-frequency energy ratio and main frequency variation obtained from frequency domain feature extraction, feature indicators describing changes in electrical behavior are constructed, and the feature indicators are combined with structural parameters and input into a preset estimation function. The estimation function is trained using historical operating data to obtain a set of weight parameters that are suitable for different types of bushings, and outputs the estimated value of the capacitance per unit length at the current moment. The estimated capacitance change trend is compared with the standard coupling curve recorded under the health state during historical operation, and all data are uniformly standardized. During the comparison process, if there is a persistent deviation between the estimated curve and the standard coupling curve, and the deviation exceeds the set judgment threshold, then the current capacitance characteristics of the bushing have changed abnormally. Mark the time points and segments corresponding to the deviations.

8. The method for monitoring the capacitance of through-wall bushings in a flexible DC converter station as described in claim 7, characterized in that: The establishment of a capacitance change identification model and the determination of anomalies based on temperature and humidity data include, The difference between the standard coupling curve recorded during the historical operation and the current measured curve is calculated, and temperature and humidity correction coefficients are set to dynamically adjust the difference threshold. Temperature and humidity are collected in real time from the field environmental sensors. The correction factor is calculated by regression analysis. If the difference exceeds the correction threshold, it is considered as an abnormal change in capacitance. The abnormal section is located, and the start and end positions of the abnormal section, the capacitance change rate and the corresponding timestamp are output.

9. The method for monitoring the capacitance of through-wall bushings in a flexible DC converter station as described in claim 8, characterized in that: The regression analysis method includes, Multiple sets of environmental temperature and humidity and capacitance change curve difference samples were selected from the historical data of bushing operation under the same load conditions. The least squares method was used to perform multiple linear fitting on the temperature sensitivity coefficient and humidity sensitivity coefficient to obtain the regression equation. The temperature sensitivity coefficient represents the correction ratio of the difference caused by a 1°C change, while the humidity sensitivity coefficient represents the error tolerance range caused by a 1%RH change.

10. A capacitance monitoring system for through-wall bushings in a flexible DC converter station, characterized in that: It includes a signal acquisition module (100), a frequency domain preprocessing extraction module (200), and a capacitance identification and judgment module (300). The signal acquisition module (100) is used to set up a capacitor voltage divider and construct a series capacitor measurement structure between the end screen of the through-wall bushing of the flexible DC converter station and the ground to acquire the primary voltage signal of the bushing and the current of the end screen. The frequency domain preprocessing extraction module (200) is used to perform synchronous signal preprocessing on the primary voltage signal and the final screen current, and to remove noise and extract frequency domain features by using wavelet transform and filtering strategies. The capacitance identification and judgment module (300) is used to calculate the coupling relationship between the bushing structure parameters and capacitance based on frequency domain features, establish a capacitance change identification model, and judge abnormal points in combination with temperature and humidity data; The calculation of the coupling relationship between bushing structural parameters and capacitance based on frequency domain features includes taking the length, inner diameter, and dielectric constant of the through-wall bushing as structural parameter inputs, constructing a capacitance estimation function based on the capacitance coupling model in combination with frequency domain features, importing the model through a lookup table, using the spectral energy ratio and the rate of change of the dominant frequency in the frequency domain features as independent variables, and using the capacitance change trend per unit length as the output result, and performing standardization and normalization processing in combination with historical data to form a standard coupling curve for subsequent anomaly point comparison.

11. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method for monitoring the capacitance of the through-wall bushing of the flexible DC converter station as described in any one of claims 1 to 9.

12. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the method for monitoring the capacitance of the through-wall bushing of the flexible DC converter station as described in any one of claims 1 to 9.

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