CN117169788B - Method for analyzing moisture state of middle joint of crosslinked polyethylene insulated power cable - Google Patents
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Abstract
The invention discloses a method for analyzing the moisture state of an intermediate joint of a crosslinked polyethylene insulated power cable, which relates to the technical field of moisture analysis of power cables and comprises the following steps: s1, selecting a plurality of middle joints of the crosslinked polyethylene insulated power cable as a damp test sample; s2, respectively placing the damp test samples in different damp scenes for damp test, and sequentially measuring dielectric spectrum curves of each damp test sample; s3, simulating the equivalent circuit model by using simulation software, adjusting parameters of the equivalent circuit model, and recording pulse waveform images under different parameters of the equivalent circuit model; s4, injecting pulse signals into an actual middle joint testing end, measuring and recording actual measurement pulse waveform images, and matching with a pulse waveform library. The invention combines the equivalent circuit model to simulate, establishes the pulse waveform library, realizes the analysis of the damp state, and effectively detects and analyzes the damp state of the middle joint of the crosslinked polyethylene insulated power cable.
Description
Technical Field
The invention relates to the technical field of power cable wetting analysis, in particular to a method for analyzing a wetting state of an intermediate joint of a crosslinked polyethylene insulated power cable.
Background
Crosslinked polyethylene (XLPE) insulated power cable is a type of cable commonly used for power transmission and distribution, and the main insulation material of XLPE cable is crosslinked polyethylene, which is made by treating polyethylene under high temperature and high pressure conditions, and has excellent electrical properties and can withstand high voltage. Meanwhile, XLPE insulation has excellent electrical characteristics including low resistance, low dielectric loss and high insulation resistance, which makes XLPE cables suitable for power transmission and distribution of electric energy, can operate at high voltage, and has good stability. The crosslinked polyethylene insulated power cable also has excellent thermal stability, can operate at higher temperatures without failure, and is important for long-term operation in power transmission and distribution systems.
XLPE cables have found increasing use in electrical power systems in recent years due to their good electrical and mechanical properties. In order to connect two sections of cross-linked polyethylene (XLPE) insulated power cables, it is often necessary to use an intermediate connector, which is a cable connection device that allows the insulated portions of the two cables to be connected together to ensure continuity and reliability of the power transmission.
However, as the application scale increases, the failure rate of XLPE cables and their intermediate connectors also increases dramatically, and statistics of related cable and intermediate connector failures indicate that environmental problems are a major factor in causing cable insulation failure. The most common environmental problem is the humidity factor, which is typically 95% and sometimes even up to 100% in overcast and rainy weather. In such wet weather, when the cable joint is made, moisture in the air easily enters the inside of the cable through the joint, resulting in deterioration of insulation performance of the cable. In addition, the common 10kVXLPE cable adopts cable pit to lay and directly buries and lays, and the outside operational environment of cable is very abominable, often has a large amount of sewage silts up in the cable pit, and the cable of in operation directly soaks in sewage, and directly buries the cable of laying and directly contacts with moist soil, and moisture invade the cable inside through the oversheath damage easily, causes insulation degradation, finally causes cable insulation failure.
Therefore, timely detection of the moisture defect of the cable and the intermediate joint is of great significance for evaluating the insulation health level of the cable line and formulating a targeted maintenance strategy.
For the problems in the related art, no effective solution has been proposed at present.
Disclosure of Invention
Aiming at the problems in the related art, the invention provides a method for analyzing the moisture state of an intermediate joint of a crosslinked polyethylene insulated power cable, which aims to overcome the technical problems in the prior art.
For this purpose, the invention adopts the following specific technical scheme:
the method for analyzing the moisture state of the intermediate joint of the crosslinked polyethylene insulated power cable comprises the following steps:
s1, selecting a plurality of middle joints of the crosslinked polyethylene insulated power cable as a damp test sample;
s2, respectively placing the damp test samples in different damp scenes for damp test, sequentially measuring dielectric spectrum curves of each damp test sample, and constructing corresponding equivalent circuit models;
s3, simulating the equivalent circuit model by using simulation software, adjusting parameters of the equivalent circuit model, and recording pulse waveform images under different parameters of the equivalent circuit model to form a pulse waveform library;
s4, injecting pulse signals into the testing end of the actual intermediate joint, measuring and recording actual measurement pulse waveform images, matching with a pulse waveform library, and analyzing the damp state of the actual intermediate joint.
Further, respectively placing the damped test samples in different damped scenes for damped test, sequentially measuring dielectric spectrum curves of each damped test sample, and constructing a corresponding equivalent circuit model, wherein the method comprises the following steps:
s21, setting a humidifying scene formed by different humid environments and different humidifying time periods in a closed test environment, so that each humidifying test sample reaches respective preset humidifying degree;
s22, naming numerical intervals of the degree of wetting into different levels of wetting states according to ascending order;
s23, measuring a dielectric spectrum curve of each damp test sample by using a frequency domain dielectric spectrum technology;
s24, constructing an equivalent circuit model corresponding to each damp test sample according to the structural characteristics of the middle joint of the crosslinked polyethylene insulated power cable and the dielectric parameters of the dielectric spectrum curve;
s25, extracting dielectric fingerprints in a dielectric spectrum curve, building a vector machine model by fitting the fingerprints, and building an association relation between the moisture degree and the equivalent resistance R.
Further, the equivalent circuit model comprises an equivalent resistor R, an equivalent capacitor C1, an equivalent capacitor C2, an equivalent capacitor C3, an equivalent inductor L1, an equivalent inductor L2, an equivalent inductor L3, an equivalent inductor L4 and a wave impedance Z;
the equivalent resistor R is the equivalent resistor of water and conductive silica gel, the equivalent capacitor C1 is the equivalent capacitor of the crosslinked polyethylene insulated power cable and the crosslinked polyethylene insulated power cable of the wire core, the equivalent capacitor C2 is the equivalent capacitor of the conductive silica gel between the crosslinked polyethylene insulated power cable and the crosslinked polyethylene insulated power cable of the wire core, the equivalent capacitor C3 is the equivalent capacitor symmetrical to the equivalent capacitor C1, the equivalent inductor L1 and the equivalent inductor L2 are the equivalent inductors of the wire core and the conductive silica gel at one side of the middle joint respectively, and the equivalent inductor L3 and the equivalent inductor L4 are the equivalent inductors of the wire core and the conductive silica gel at the other side of the middle joint respectively;
one end of the equivalent inductor L1 is respectively connected with one end of the equivalent inductor L2 and one end of the equivalent capacitor C1, the other end of the equivalent inductor L2 is respectively connected with one end of the equivalent capacitor C2, one end of the equivalent resistor R and one end of the equivalent inductor L3, the other end of the equivalent inductor L3 is respectively connected with one end of the equivalent inductor L4 and one end of the equivalent capacitor C3, the other ends of the equivalent inductor L1 and the equivalent inductor L4 are respectively connected with the wave impedance Z, and the other ends of the equivalent capacitor C1, the equivalent capacitor C2, the equivalent resistor R and the equivalent capacitor C3 are all kept connected and grounded.
Further, the method for extracting dielectric fingerprints in dielectric spectrum curves and fitting fingerprints to build a vector machine model and building an association relationship between the humidity degree and the equivalent resistance R comprises the following steps:
s251, extracting dielectric fingerprints in a dielectric spectrum curve corresponding to the damp test sample;
s252, expanding the dielectric fingerprint by using a fitting analysis algorithm of the expansion source data to construct a training data set for building a vector machine model;
s253, training the vector machine model by using the training data set, and establishing the vector machine model for realizing the associated prediction between the damp degree and the equivalent resistance R.
Further, the step of extracting dielectric fingerprints in dielectric spectrum curves corresponding to the damp test samples comprises the following steps:
s2511 extracting a dielectric spectrum curvetanδA curve;
s2512, selecttanδIntegral values in four characteristic ranges of a high frequency band in the curve are extracted, four groups of dielectric fingerprints are extracted, and the extraction expression of the dielectric fingerprints is as follows:
；
in the method, in the process of the invention,D 1 、D 2 、D 3 andD 4 Respectively representing four groups of dielectric fingerprints;frepresentation oftanδThe frequency of the curve;
s2513, extracting conductivity of conductive silica gel in the middle joint of the crosslinked polyethylene insulated power cable as auxiliary dielectric fingerprints, and combining the conductivity with four groups of dielectric fingerprints to form five groups of dielectric fingerprints.
Further, the dielectric fingerprint is expanded by using a fitting analysis algorithm of the expansion source data, and the construction of the training data set for building the vector machine model comprises the following steps:
s2521, the dielectric constant of the damp test sample is used as an independent variableXThe value of the degree of wetting is taken as an independent variableYDielectric fingerprint values are respectively used as dependent variablesZ i And (2) andi∈（1，5）；
s2522 to be known as an argumentXIndependent variableYDependent variableZ i Substituting the parameters into a fitting analysis model, and solving the parameters of the fitting analysis model by fitting calculation to obtain a fitting analysis model with determined parameters;
s2523, setting the change step length of the independent variable X and the independent variable Y to 0.5 and 1 respectively, and grouping the independent variable numbersX，Y) Substituting the training data set into a fitting analysis model to obtain an extended training data set.
Further, the known independent variablesXIndependent variableYDependent variableZ i Substituting the parameters into a fitting analysis model, and solving the parameters of the fitting analysis model by fitting calculation to obtain the fitting analysis model with determined parameters, wherein the fitting analysis model comprises the following steps of:
s25221, constructing a polynomial fitting equation of a fitting analysis model, wherein the polynomial fitting equation of the fitting analysis model has the expression:
；
in the method, in the process of the invention,β 0 -β 9 all represent fitting analysis model parameters of the fitting analysis model;
s25222 to give a known argumentXIndependent variableYDependent variableZ i Substituting the values into a fitting analysis model, and calculating the values of the fitting analysis model parameters by using a least square method.
Further, the simulation software is utilized to simulate the equivalent circuit model, parameters of the equivalent circuit model are adjusted, pulse waveforms under different parameters of the equivalent circuit model are recorded, and the step of forming a pulse waveform library comprises the following steps:
s31, inputting an equivalent circuit model into simulation software, adjusting parameters of each component in the circuit to equivalent circuit model parameters corresponding to a damp scene, injecting a simulation pulse signal into the equivalent circuit model, and measuring a reflected waveform at the head end of the equivalent circuit model to obtain an initial pulse waveform image;
s32, adjusting parameters of the equivalent circuit model in simulation software, setting adjustment periods and parameter intervals, sequentially measuring pulse waveforms and pulse waveform images of the equivalent circuit model under different parameters of the equivalent circuit model, and combining all pulse waveform images to form a pulse waveform library.
Further, injecting a pulse signal into a testing end of the actual intermediate joint, measuring and recording an actually measured pulse waveform image, matching with a pulse waveform library, and analyzing the wetting state of the actual intermediate joint, wherein the method comprises the following steps of:
s41, positioning the position of an actual middle joint to be detected, detecting a partial discharge signal of the actual middle joint by adopting a pulse current method, and acquiring an actual measurement pulse waveform image after injecting a pulse signal;
s42, extracting characteristic parameters of the actually measured pulse waveform image, realizing the matching between the actually measured pulse waveform image and a pulse waveform library, and searching for an optimal matching result;
s43, determining dielectric spectrum curves and equivalent circuit model parameters corresponding to the actual intermediate joint according to the optimal matching result, predicting the wetting degree of the actual intermediate joint by using a vector machine model, and finally determining the wetting state of the actual intermediate joint according to the wetting degree value.
Further, extracting characteristic parameters of the actually measured pulse waveform image to realize the matching between the actually measured pulse waveform image and the pulse waveform library, and searching the optimal matching result comprises the following steps:
s421, denoising, filtering and normalizing the actually measured pulse waveform image;
s422, setting a fixed window and a similar tolerance threshold, calculating the mutual approximation entropy of the actually measured pulse waveform image by using a mutual approximation entropy algorithm, and reflecting the complexity and regularity of the actually measured pulse waveform image;
s423, comparing the mutual approximation entropy value of the actually measured pulse waveform image with the mutual approximation entropy value in the pulse waveform library by utilizing a minimum distance matching algorithm, and calculating a distance score between the waveform images;
s424, the pulse waveform images in the pulse waveform library are arranged in an ascending order according to the distance scores, and the pulse waveform image with the highest distance score is selected as the optimal matching result.
The beneficial effects of the invention are as follows:
1. by setting a damped test sample and combining an equivalent circuit model for simulation, a pulse waveform library is established, dielectric spectrum curves of cable intermediate connectors in different damped states are associated with pulse waveforms, so that the damped state analysis is realized, the damped state of the crosslinked polyethylene insulated power cable intermediate connectors can be effectively detected and analyzed, different damped conditions can be accurately identified by comparing actual test pulse waveforms with waveforms in the library, the reliability and safety of a cable insulation system are improved, timely maintenance and insulation repair measures are facilitated, and potential fault risks are reduced.
2. By simulating scenes of different wetting degrees and measuring dielectric spectrum curves, an equivalent circuit model of the crosslinked polyethylene insulated power cable intermediate connector in different wetting states is constructed, and an association relation between the wetting degrees and an equivalent resistor R is established, so that the electric characteristics of the cable intermediate connector in different wetting conditions can be accurately simulated, more accurate prediction of the wetting degrees and monitoring of the state of the insulation system are realized, timely maintenance measures are facilitated, potential fault risks are reduced, and the reliability and safety of the power system are improved.
3. By constructing a pulse waveform library, the pulse waveform of the actual intermediate connector is allowed to be compared with waveforms in the library, so that the wetting state of the actual intermediate connector is determined, the non-invasive monitoring of the wetting state of the cable intermediate connector is realized, the need of damaging or interfering with a cable is avoided, a highly accurate analysis method is provided, the wetting condition can be timely identified, and the potential fault risk of a cable insulation system is reduced; the prediction and state division of the damp degree are realized through the vector machine model, and timely maintenance measures are facilitated.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
FIG. 1 is a flow chart of a method for analyzing the moisture status of an intermediate joint of a crosslinked polyethylene insulated power cable according to an embodiment of the invention;
fig. 2 is a schematic circuit diagram of an equivalent circuit model in a method for analyzing a wet state of an intermediate joint of a crosslinked polyethylene insulated power cable according to an embodiment of the present invention.
Detailed Description
According to the embodiment of the invention, a method for analyzing the moisture state of the middle joint of the crosslinked polyethylene insulated power cable is provided.
The invention will now be further described with reference to the accompanying drawings and detailed description, as shown in fig. 1, a method for analyzing a moisture state of an intermediate joint of a crosslinked polyethylene insulated power cable according to an embodiment of the invention, the method comprising the steps of:
s1, selecting a plurality of cross-linked polyethylene insulated power cable intermediate connectors as a damp test sample.
S2, respectively placing the damped test samples in different damped scenes for damped test, sequentially measuring dielectric spectrum curves of each damped test sample, and constructing corresponding equivalent circuit models.
In the description of the invention, the method for respectively placing the damp test samples in different damp scenes for damp test, sequentially measuring the dielectric spectrum curve of each damp test sample, and constructing the corresponding equivalent circuit model comprises the following steps:
s21, setting a humidifying scene formed by different humid environments and different humidifying time periods in a closed test environment, so that each humidifying test sample reaches the respective preset humidifying degree.
First, the determination of the conditions of the tide to be simulated is crucial for determining the preset degree of tide, which is clearly required to simulate different tide scenarios, including different humidity levels, temperatures and times. A closed test environment is created to control humidity and temperature by using a laboratory or control room, an airtight container, a humidity control system, and a temperature control system. According to the humidity scene to be simulated, the humidity in the test environment is ensured to reach the target value by injecting humid air and using a humidity controller and a humidity sensor. In addition, the time that each test sample needs to be exposed in the damped scene is determined, so that the samples are placed in the test environment according to the preset damped degree and time period.
Humidity and temperature sensors are used to monitor the humidity and temperature of the test environment throughout the test to ensure that they remain within target ranges.
S22, naming the numerical intervals of the degree of wetting as the states of different levels according to ascending order.
In the description of the present invention, the damp state can be classified into different levels according to actual scenes, and each level of the damp state is assigned with a respective damp degree range, and the following damp states are exemplified:
1. dry state (Dry): this is the lowest level of wet condition, indicating that the cable intermediate connector is not affected by moisture. The corresponding range of moisture level values may be set to 0% -5%.
2. Weak Moisture (light Moisture): indicating that the cable intermediate joint is slightly affected by moisture but not to a sufficient extent to cause serious problems. The corresponding range of moisture level values may be set to 6% -15%.
3. Mild Moisture (Mild Moisture): the cable intermediate joint is slightly moisture affected and of moderate extent may cause slight expansion or damage to some of the insulation. The corresponding range of moisture regain values may be set to 16% -30%.
4. Moderate moisture (Moderate Moisture): indicating that the cable intermediate joint is affected by moderate moisture to a greater extent, it may cause swelling, decomposition or damage to the insulation. The corresponding range of moisture regain values may be set to 31% -50%.
5. Significant wetting (Significant Moisture): this level indicates that the cable intermediate joint is subjected to significant moisture or flooding, which may cause significant insulation expansion, decomposition or damage. The corresponding range of moisture regain values may be set to 51% -75%.
6. Severe damp (Severe moistures): this is the highest level of moisture condition, meaning that the cable intermediate connector is severely wet or soaked, potentially leading to severe insulation damage and cable failure. The corresponding range of moisture regain values may be set to 76% -100%.
S23, measuring the dielectric spectrum curve of each damp test sample by using a frequency domain dielectric spectrum technology.
Frequency domain dielectric spectroscopy is a method for measuring dielectric properties of materials, including dielectric constants and dielectric losses. In the analysis of the wet state, it can be used to detect the degree of wetting of the cable intermediate connector. A frequency domain dielectric spectrum analyzer, an instrument specifically used for measuring dielectric properties, needs to be used to ensure that the probe and electrodes of the instrument are clean during the measurement process to avoid interfering with the measurement results. The measuring range of the instrument is set, including a frequency range and a voltage range, to adapt to the tested sample. While the damp test specimens are properly prepared, including ensuring that the specimen surface is clean to eliminate the effects of any possible contaminants. Depending on the size and shape of the sample, the appropriate electrode is chosen to ensure good electrode contact.
The frequency domain dielectric spectrum analyzer is activated and the measurement is started, the instrument will measure the dielectric constant and dielectric loss of the dielectric at different frequencies. The result of the measurement will generate a dielectric spectrum curve, typically with frequency on the abscissa and dielectric constant and dielectric loss on the ordinate.
S24, constructing an equivalent circuit model corresponding to each damp test sample according to the structural characteristics of the middle joint of the crosslinked polyethylene insulated power cable and the dielectric parameters of the dielectric spectrum curve.
In the description of the present invention, as shown in fig. 2, the equivalent circuit model includes an equivalent resistor R, an equivalent capacitor C1, an equivalent capacitor C2, an equivalent capacitor C3, an equivalent inductor L1, an equivalent inductor L2, an equivalent inductor L3, an equivalent inductor L4, and a wave impedance Z.
The equivalent resistor R is the equivalent resistor of water and conductive silica gel, the equivalent capacitor C1 is the equivalent capacitor of the crosslinked polyethylene insulated power cable and the crosslinked polyethylene insulated power cable of the wire core, the equivalent capacitor C2 is the equivalent capacitor of the conductive silica gel between the crosslinked polyethylene insulated power cable and the crosslinked polyethylene insulated power cable of the wire core, the equivalent capacitor C3 is the equivalent capacitor symmetrical to the equivalent capacitor C1, the equivalent inductor L1 and the equivalent inductor L2 are the equivalent inductors of the wire core and the conductive silica gel on one side of the middle joint respectively, and the equivalent inductor L3 and the equivalent inductor L4 are the equivalent inductors of the wire core and the conductive silica gel on the other side of the middle joint respectively.
One end of the equivalent inductor L1 is respectively connected with one end of the equivalent inductor L2 and one end of the equivalent capacitor C1, the other end of the equivalent inductor L2 is respectively connected with one end of the equivalent capacitor C2, one end of the equivalent resistor R and one end of the equivalent inductor L3, the other end of the equivalent inductor L3 is respectively connected with one end of the equivalent inductor L4 and one end of the equivalent capacitor C3, the other ends of the equivalent inductor L1 and the equivalent inductor L4 are respectively connected with the wave impedance Z, and the other ends of the equivalent capacitor C1, the equivalent capacitor C2, the equivalent resistor R and the equivalent capacitor C3 are all kept connected and grounded.
S25, extracting dielectric fingerprints in a dielectric spectrum curve, building a vector machine model by fitting the fingerprints, and building an association relation between the moisture degree and the equivalent resistance R.
In the description of the invention, the vector machine model is built by extracting dielectric fingerprints in dielectric spectrum curves and fitting fingerprints, and the establishment of the association relation between the moisture degree and the equivalent resistance R comprises the following steps:
s251, extracting dielectric fingerprints in a dielectric spectrum curve corresponding to the damp test sample.
Where dielectric fingerprints refer to electrical characteristics of a material or system in frequency domain dielectric spectroscopy, these characteristics can be represented by dielectric spectral curves. Dielectric fingerprints provide detailed information about the electrical properties of a material or system, especially about its dielectric constant and dielectric loss as a function of frequency.
In the description of the present invention, the extraction of dielectric fingerprints in dielectric spectrum curves corresponding to a damped test sample comprises the following steps:
s2511 extracting a dielectric spectrum curvetanδA curve.
S2512, selecttanδIntegral values in four characteristic ranges of a high frequency band in the curve are extracted, four groups of dielectric fingerprints are extracted, and the extraction expression of the dielectric fingerprints is as follows:
。
in the method, in the process of the invention,D 1 、D 2 、D 3 andD 4 Representing four sets of dielectric fingerprints, respectively.
fRepresentation oftanδThe frequency of the curve.
S2513, extracting conductivity of conductive silica gel in the middle joint of the crosslinked polyethylene insulated power cable as auxiliary dielectric fingerprints, and combining the conductivity with four groups of dielectric fingerprints to form five groups of dielectric fingerprints.
And S252, expanding the dielectric fingerprint by using a fitting analysis algorithm of the expansion source data, and constructing a training data set for building a vector machine model.
In the description of the present invention, the dielectric fingerprint is extended by using a fitting analysis algorithm of extended source data, and constructing a training data set for constructing a vector machine model includes the following steps:
s2521, the dielectric constant of the damp test sample is used as an independent variableXThe value of the degree of wetting is taken as an independent variableYDielectric fingerprint values are respectively used as dependent variablesZ i And (2) andi∈（1，5）。
s2522 to be known as an argumentXIndependent variableYDependent variableZ i Substituting the parameters into a fitting analysis model, and solving the parameters of the fitting analysis model by fitting calculation to obtain the fitting analysis model with determined parameters.
The fitting analysis model is a mathematical model, which is generally used to describe and predict trends, relationships and patterns of data. These models create an appropriate mathematical function by fitting known data points that can estimate the value of the dependent variable at a given independent variable.
In the description of the present invention, the known argument will beXIndependent variableYDependent variableZ i Substituting the parameters into a fitting analysis model, and solving the parameters of the fitting analysis model by fitting calculation to obtain the fitting analysis model with determined parameters, wherein the fitting analysis model comprises the following steps of:
s25221, constructing a polynomial fitting equation of a fitting analysis model, wherein the polynomial fitting equation of the fitting analysis model has the expression:
。
in the method, in the process of the invention,β 0 -β 9 all represent fitting analytical model parameters of the fitting analytical model.
S25222 to give a known argumentXIndependent variableYDependent variableZ i Substituting the values into a fitting analysis model, and calculating the values of the fitting analysis model parameters by using a least square method.
The least squares method is an optimization method whose goal is to minimize the sum of fitting errors. Namely, by adjusting model parameters #β 0 -β 9 ) The sum of the fitting errors is minimized by summing the fitting errors and differentiating the parameters.
S2523, setting the change step length of the independent variable X and the independent variable Y to 0.5 and 1 respectively, and grouping the independent variable numbersX，Y) Substituting the training data set into a fitting analysis model to obtain an extended training data set.
S253, training the vector machine model by using the training data set, and establishing the vector machine model for realizing the associated prediction between the damp degree and the equivalent resistance R.
S3, simulating the equivalent circuit model by using simulation software, adjusting parameters of the equivalent circuit model, and recording pulse waveform images under different parameters of the equivalent circuit model to form a pulse waveform library.
In the description of the invention, the simulation software is utilized to simulate the equivalent circuit model, the parameters of the equivalent circuit model are regulated, the pulse waveforms under the parameters of different equivalent circuit models are recorded, and the formation of the pulse waveform library comprises the following steps:
s31, inputting the equivalent circuit model into simulation software, adjusting parameters of each component in the circuit to equivalent circuit model parameters corresponding to the damp scene, injecting a simulation pulse signal into the equivalent circuit model, and measuring a reflected waveform at the head end of the equivalent circuit model to obtain an initial pulse waveform image.
S32, adjusting parameters of the equivalent circuit model in simulation software, setting adjustment periods and parameter intervals, sequentially measuring pulse waveforms and pulse waveform images of the equivalent circuit model under different parameters of the equivalent circuit model, and combining all pulse waveform images to form a pulse waveform library.
S4, injecting pulse signals into the testing end of the actual intermediate joint, measuring and recording actual measurement pulse waveform images, matching with a pulse waveform library, and analyzing the damp state of the actual intermediate joint.
In the description of the invention, pulse signals are injected into the testing end of the actual intermediate joint, the actual measured pulse waveform image is measured and recorded and matched with a pulse waveform library, and the analysis of the wetting state of the actual intermediate joint comprises the following steps:
s41, positioning the position of the actual intermediate joint to be detected, detecting the partial discharge signal of the actual intermediate joint by adopting a pulse current method, and acquiring an actual measurement pulse waveform image after injecting the pulse signal.
S42, extracting characteristic parameters of the actually measured pulse waveform image, realizing the matching between the actually measured pulse waveform image and the pulse waveform library, and searching for an optimal matching result.
In the description of the invention, the characteristic parameters of the actually measured pulse waveform image are extracted to realize the matching between the actually measured pulse waveform image and the pulse waveform library, and the searching of the optimal matching result comprises the following steps:
s421, denoising, filtering and normalizing the actually measured pulse waveform image.
The measured pulse waveform image is preprocessed, including denoising (reducing the influence of noise), filtering (smoothing signals to remove high-frequency noise or burst noise), normalization (scaling waveform values to a standard range), and the like, so as to ensure the quality of data.
S422, setting a fixed window and a similar tolerance threshold, and calculating the mutual approximation entropy of the actually measured pulse waveform image by using a mutual approximation entropy algorithm to reflect the complexity and regularity of the actually measured pulse waveform image.
The fixed window is the window size of the mutual approximation entropy calculation, which is used to divide the waveform into different segments to calculate the mutual approximation entropy. The choice of the appropriate window size is critical because it affects the calculation of the mutual approximation entropy. Typically, the window size should be adjusted according to the characteristics and requirements of the waveform. Smaller windows may capture local features of the waveform more finely, while larger windows may consider the waveform's integrity more fully.
A similarity tolerance threshold is used to determine similarity between waveform segments. Two waveform segments are considered similar if their mutual approximation entropy values are less than a similar tolerance threshold. This threshold typically needs to be set according to the particular problem. Smaller similarity tolerance thresholds will screen out similar fragments more tightly, while larger thresholds will allow more variation. Typically, the selection of similar tolerance thresholds is based on experience or experimentation.
Where the window size and the similarity tolerance threshold have been determined, the mutual approximation entropy of the waveforms is calculated. The mutual approximation entropy is a non-linear measure used to evaluate the similarity and complexity between two waveform segments. And calculating the mutual approximate entropy value between different segments in the waveform. For each segment, it is compared with other segments one by one, and a mutual approximation entropy value is calculated. For the calculated mutual approximation entropy values, segments with mutual approximation entropy smaller than a similar tolerance threshold are screened out, and the segments are considered to be similar.
S423, comparing the mutual approximation entropy value of the actually measured pulse waveform image with the mutual approximation entropy value in the pulse waveform library by utilizing a minimum distance matching algorithm, and calculating the distance score between the waveform images.
S424, the pulse waveform images in the pulse waveform library are arranged in an ascending order according to the distance scores, and the pulse waveform image with the highest distance score is selected as the optimal matching result.
S43, determining dielectric spectrum curves and equivalent circuit model parameters corresponding to the actual intermediate joint according to the optimal matching result, predicting the wetting degree of the actual intermediate joint by using a vector machine model, and finally determining the wetting state of the actual intermediate joint according to the wetting degree value.
In summary, by means of the technical scheme, the damping test sample is set, the simulation is carried out by combining the equivalent circuit model, the pulse waveform library is established, the dielectric spectrum curves of the cable intermediate connectors in different damping states are associated with the pulse waveforms, and the damping state analysis is realized, so that the damping state of the crosslinked polyethylene insulated power cable intermediate connectors can be effectively detected and analyzed, different damping conditions can be accurately identified by comparing the actual test pulse waveforms with waveforms in the library, the reliability and the safety of the cable insulation system are improved, timely maintenance and insulation repair measures are facilitated, and potential fault risks are reduced. By simulating scenes of different wetting degrees and measuring dielectric spectrum curves, an equivalent circuit model of the crosslinked polyethylene insulated power cable intermediate connector in different wetting states is constructed, and an association relation between the wetting degrees and an equivalent resistor R is established, so that the electric characteristics of the cable intermediate connector in different wetting conditions can be accurately simulated, more accurate prediction of the wetting degrees and monitoring of the state of the insulation system are realized, timely maintenance measures are facilitated, potential fault risks are reduced, and the reliability and safety of the power system are improved. By constructing a pulse waveform library, the pulse waveform of the actual intermediate connector is allowed to be compared with waveforms in the library, so that the wetting state of the actual intermediate connector is determined, the non-invasive monitoring of the wetting state of the cable intermediate connector is realized, the need of damaging or interfering with a cable is avoided, a highly accurate analysis method is provided, the wetting condition can be timely identified, and the potential fault risk of a cable insulation system is reduced; the prediction and state division of the damp degree are realized through the vector machine model, and timely maintenance measures are facilitated.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (8)
1. The method for analyzing the moisture state of the intermediate joint of the crosslinked polyethylene insulated power cable is characterized by comprising the following steps of:
s1, selecting a plurality of middle joints of the crosslinked polyethylene insulated power cable as a damp test sample;
s2, respectively placing the damped test samples in different damped scenes for damped test, sequentially measuring dielectric spectrum curves of each damped test sample, and constructing corresponding equivalent circuit models;
s3, simulating the equivalent circuit model by using simulation software, adjusting parameters of the equivalent circuit model, and recording pulse waveform images under different parameters of the equivalent circuit model to form a pulse waveform library;
s4, injecting pulse signals into the testing end of the actual intermediate joint, measuring and recording actual measurement pulse waveform images, matching with the pulse waveform library, and analyzing the wetting state of the actual intermediate joint;
the method comprises the steps of respectively placing the damped test samples in different damped scenes for damped test, sequentially measuring dielectric spectrum curves of each damped test sample, and constructing corresponding equivalent circuit models, wherein the method comprises the following steps of:
s21, setting a humidifying scene formed by different humid environments and different humidifying time periods in a closed test environment, so that each humidifying test sample reaches respective preset humidifying degree;
s22, naming numerical intervals of the degree of wetting into different levels of wetting states according to ascending order;
s23, measuring a dielectric spectrum curve of each damp test sample by using a frequency domain dielectric spectrum technology;
s24, constructing an equivalent circuit model corresponding to each damp test sample according to the structural characteristics of the middle joint of the crosslinked polyethylene insulated power cable and the dielectric parameters of the dielectric spectrum curve;
s25, extracting dielectric fingerprints in the dielectric spectrum curve and fitting fingerprints to build a vector machine model, and building an association relation between the moisture degree and the equivalent resistance R;
the method for extracting the dielectric fingerprints in the dielectric spectrum curve and building a vector machine model by fitting the fingerprints, and building the association relation between the moisture degree and the equivalent resistance R comprises the following steps:
s251, extracting dielectric fingerprints in the dielectric spectrum curves corresponding to the damp test samples;
s252, expanding the dielectric fingerprint by using a fitting analysis algorithm of the expansion source data to construct a training data set for building a vector machine model;
s253, training the vector machine model by using the training data set, and establishing a vector machine model for realizing the associated prediction between the damp degree and the equivalent resistance R;
the equivalent resistance R is the equivalent resistance of water and conductive silica gel.
2. The method for analyzing the moisture state of the middle joint of the crosslinked polyethylene insulated power cable according to claim 1, wherein the equivalent circuit model comprises an equivalent resistor R, an equivalent capacitor C1, an equivalent capacitor C2, an equivalent capacitor C3, an equivalent inductor L1, an equivalent inductor L2, an equivalent inductor L3, an equivalent inductor L4 and a wave impedance Z;
the equivalent resistor R is an equivalent resistor of water and conductive silica gel, the equivalent capacitor C1 is an equivalent capacitor of a crosslinked polyethylene insulated power cable and a core crosslinked polyethylene insulated power cable, the equivalent capacitor C2 is an equivalent capacitor of the conductive silica gel between the crosslinked polyethylene insulated power cable and the core crosslinked polyethylene insulated power cable, the equivalent capacitor C3 is an equivalent capacitor symmetrical to the equivalent capacitor C1, the equivalent inductor L1 and the equivalent inductor L2 are equivalent inductors of a core and the conductive silica gel at one side of the middle joint respectively, and the equivalent inductor L3 and the equivalent inductor L4 are equivalent inductors of a core and the conductive silica gel at the other side of the middle joint respectively;
one end of the equivalent inductor L1 is connected with one end of the equivalent inductor L2 and one end of the equivalent capacitor C1 respectively, the other end of the equivalent inductor L2 is connected with one end of the equivalent capacitor C2, one end of the equivalent resistor R and one end of the equivalent inductor L3 respectively, the other end of the equivalent inductor L3 is connected with one end of the equivalent inductor L4 and one end of the equivalent capacitor C3 respectively, the other end of the equivalent inductor L1 and the other end of the equivalent inductor L4 are connected with the wave impedance Z respectively, and the other end of the equivalent capacitor C1, the other end of the equivalent capacitor C2, the other end of the equivalent resistor R and the other end of the equivalent capacitor C3 are all kept connected and grounded.
3. The method for analyzing the moisture status of the intermediate connector of a crosslinked polyethylene insulated power cable according to claim 2, wherein the step of extracting the dielectric fingerprint in the dielectric spectrum curve corresponding to the moisture test sample comprises the steps of:
s2511 extracting the dielectric spectrum curvetanδA curve;
s2512, selecting thetanδIntegral values in four characteristic ranges of a high frequency band in the curve are extracted, four groups of dielectric fingerprints are extracted, and the extraction expression of the dielectric fingerprints is as follows:
；
in the method, in the process of the invention,D 1 、D 2 、D 3 andD 4 Respectively representing four groups of dielectric fingerprints;
frepresentation oftanδThe frequency of the curve;
s2513, extracting conductivity of conductive silica gel in the middle joint of the crosslinked polyethylene insulated power cable as auxiliary dielectric fingerprints, and combining the conductivity with four groups of dielectric fingerprints to form five groups of dielectric fingerprints.
4. A method for analyzing the moisture status of an intermediate joint of a crosslinked polyethylene insulated power cable according to claim 3, wherein the fitting analysis algorithm using the extended source data extends the dielectric fingerprint, and constructing a training data set for constructing a vector machine model comprises the following steps:
s2521, using the dielectric constant of the damped test sample as an independent variableXThe value of the degree of wetting is taken as an independent variableYDielectric fingerprint values are respectively used as dependent variablesZ i And (2) andi∈（1，5）；
s2522 to be known the argumentXIndependent variableYDependent variableZ i Substituting the parameters into a fitting analysis model, and solving the parameters of the fitting analysis model by fitting calculation to obtain a fitting analysis model with determined parameters;
s2523, setting the change step length of the independent variable X and the independent variable Y to 0.5 and 1 respectively, and grouping the independent variable numbersX，Y) Substituting the fitting analysis model to obtain an extended training data set.
5. The method for analyzing the moisture status of an intermediate joint of a crosslinked polyethylene insulated power cable according to claim 4, wherein said independent variables are knownXIndependent variableYDependent variableZ i Substituting the parameters into a fitting analysis model, and solving the parameters of the fitting analysis model by fitting calculation to obtain the fitting analysis model with determined parameters, wherein the fitting analysis model comprises the following steps of:
s25221, constructing a polynomial fitting equation of a fitting analysis model, wherein the polynomial fitting equation of the fitting analysis model has the expression:
；
in the method, in the process of the invention,β 0 -β 9 all represent fitting analysis model parameters of the fitting analysis model;
s25222 the argument to be knownXIndependent variableYDependent variableZ i Substituting the fitting analysis model by least squaresThe method calculates the numerical value of the fitting analysis model parameter.
6. The method for analyzing the moisture state of the intermediate joint of the crosslinked polyethylene insulated power cable according to claim 2, wherein the simulating the equivalent circuit model by using simulation software, adjusting the parameters of the equivalent circuit model, and recording pulse waveforms under different parameters of the equivalent circuit model, and forming a pulse waveform library comprises the following steps:
s31, inputting the equivalent circuit model into simulation software, adjusting parameters of each component in a circuit to equivalent circuit model parameters corresponding to the damped scene, injecting a simulation pulse signal into the equivalent circuit model, and measuring a reflected waveform at the head end of the equivalent circuit model to obtain an initial pulse waveform image;
s32, adjusting parameters of the equivalent circuit model in the simulation software, setting adjustment periods and parameter intervals, sequentially measuring pulse waveforms of the equivalent circuit model and pulse waveform images thereof under different parameters of the equivalent circuit model, and combining all the pulse waveform images to form a pulse waveform library.
7. The method for analyzing the damping state of the middle joint of the crosslinked polyethylene insulated power cable according to claim 6, wherein the step of injecting pulse signals into the test end of the actual middle joint, measuring and recording the actual measured pulse waveform image, matching the pulse waveform image with the pulse waveform library, and analyzing the damping state of the actual middle joint comprises the following steps:
s41, positioning the position of an actual middle joint to be detected, detecting a partial discharge signal of the actual middle joint by adopting a pulse current method, and acquiring an actual measurement pulse waveform image after injecting a pulse signal;
s42, extracting characteristic parameters of the actually measured pulse waveform image, realizing the matching between the actually measured pulse waveform image and the pulse waveform library, and searching an optimal matching result;
s43, determining dielectric spectrum curves and equivalent circuit model parameters thereof corresponding to the actual intermediate joint according to the optimal matching result, predicting the wetting degree of the actual intermediate joint by using the vector machine model, and finally determining the wetting state of the actual intermediate joint according to the wetting degree value.
8. The method for analyzing the moisture state of the intermediate joint of the crosslinked polyethylene insulated power cable according to claim 7, wherein the step of extracting the characteristic parameters of the actually measured pulse waveform image to match the actually measured pulse waveform image with the pulse waveform library and searching for an optimal matching result comprises the following steps:
s421, denoising, filtering and normalizing the actually measured pulse waveform image;
s422, setting a fixed window and a similar tolerance threshold, and calculating the mutual approximation entropy of the actually measured pulse waveform image by using a mutual approximation entropy algorithm to embody the complexity and regularity of the actually measured pulse waveform image;
s423, comparing the mutual approximation entropy value of the actually measured pulse waveform image with the mutual approximation entropy value in the pulse waveform library by utilizing a minimum distance matching algorithm, and calculating a distance score between the waveform images;
s424, arranging the pulse waveform images in the pulse waveform library in an ascending order according to the distance scores, and selecting the pulse waveform image with the highest distance score as the optimal matching result.
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