CN114167221B - Epoxy resin insulation aging discrimination and test method under different voltage frequencies - Google Patents
Epoxy resin insulation aging discrimination and test method under different voltage frequencies Download PDFInfo
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Abstract
The invention relates to the technical field of fault diagnosis, in particular to a method for judging and checking insulation aging of epoxy resin under different voltage frequencies, which comprises the following steps: s1, obtaining an epoxy resin sample, respectively performing withstand voltage tests at different frequencies, and further obtaining an aging sample; s2, measuring an evaluation parameter related to the aging state of the epoxy resin sample, and classifying by using a class I SVM; s3, classifying the classification result in the S2 by using the first I type SVM again, and finishing the training of the evaluation parameters of the model; s4, testing the model input test data, and outputting a final result after verifying the model aging discrimination effect. The invention pointedly reflects the insulation state of the insulating material epoxy resin, can accurately reflect the aging state of the epoxy resin from multiple aspects, further reflects the insulation performance state of the electrical equipment, and has certain guiding significance for the operation state of the evaluation equipment.
Description
Technical Field
The invention relates to the technical field of fault diagnosis, in particular to a method for judging and checking insulation aging of epoxy resin under different voltage frequencies.
Background
With the increase of national economy in China, the electric energy demand becomes stronger, and in an electric power system, various links such as the production, transformation, transportation, distribution and the like of electric energy are closely dependent on various electric equipment. The dry-type electrical equipment has the advantages of low operation loss, low noise, good insulating property, good fireproof property, small volume and the like, and is widely applied to important occasions such as offshore oil platforms.
Meanwhile, in recent years, the increasingly-enhanced living standard of people has increased requirements on safe and stable operation of an electric power network, and current harmonic distortion is serious in the electric power system due to the increase of nonlinear loads, and the electric power harmonic is used as one of environmental pollution hazards of the electric power network, so that the safe operation of electric equipment can be influenced. In addition, the loss of the electrical equipment can be increased along with the deepening of the distortion degree of the harmonic waveform, the aging speed of the insulating medium is further increased, the service life of the insulating medium is shortened, and the safety problem of the whole power system is seriously threatened.
The epoxy resin is used as an important insulating material, and the insulating performance of the epoxy resin directly determines the working performance of electrical equipment. Therefore, the analysis of various performance indexes of the epoxy resin can monitor and evaluate the insulation state of the epoxy resin in real time, and further reflect the insulation condition of the electrical equipment so as to reduce the equipment fault probability, improve the maintenance quality, reduce the maintenance cost and prolong the service life of the equipment, which has become a main melody of the maintenance development of the electrical equipment.
Disclosure of Invention
Aiming at the defects of the prior art, the invention discloses a method for judging and checking the insulation aging of epoxy resin under different voltage frequencies, which is used for reflecting the actual condition of the insulation aging of the epoxy resin.
The invention is realized by the following technical scheme:
the invention provides a method for judging and checking insulation aging of epoxy resin under different voltage frequencies, which comprises the following steps:
s1, obtaining an epoxy resin sample, respectively performing withstand voltage tests at different frequencies, and further obtaining an aging sample;
s2, measuring an evaluation parameter related to the aging state of the epoxy resin sample, and classifying by using a class-II SVM;
s3, classifying the classification result in the S2 by using a class-II SVM again, and ending the evaluation parameter training of the model;
s4, testing the model input test data, and outputting a final result after verifying the model aging discrimination effect.
Further, in the method, the degree of aging of the epoxy resin is measured by the repeated discharge rate of the partial discharge, the degree of aging of the epoxy resin is measured by the roughness, the degree of aging of the epoxy resin is measured by the activation energy, or the degree of aging of the epoxy resin is measured by the porosity of the material.
Further, in the method, the evaluation parameters related to the aging state of the epoxy resin include: dielectric loss, discharge repetition rate of partial discharge, roughness, activation energy, porosity
Further, in the method, when the aging degree of the epoxy resin is measured by using the repeated discharge rate of partial discharge, the characteristic parameter is extracted from the change of tan delta to evaluate the aging state of the insulating paperboard, and then the dielectric loss factor tan delta at the characteristic frequency f The data corresponding to the corresponding aging time satisfies the exponential relationship:
DP＝A×exp(-tanδ f /B)+C
wherein the DP aging state, tan delta is the dielectric loss factor at the characteristic frequency, A, B, C is the fitting parameter, and each parameter and the fitting goodness are shown in the following table. The exponential relationship fitting degree of the dielectric loss factor and the aging state under the characteristic frequency is higher, and the frequency can be used for evaluating the aging state.
| Frequency of | Fitting formula | Goodness of fit |
| 10-3Hz | DP＝7773exp(-tanδ f /0.3394)+627.5 | 0.99 |
| 10-2Hz | DP＝1758exp(-tanδ f /0.1087)+583.2 | 0.99 |
。
Further, in the method, U is used for measuring the aging degree of the epoxy resin by using the repeated discharge rate of partial discharge CB C is the withstand voltage of the insulating air gap b 、C c 、ε rc 、ε bc Where d, delta are parameters of the insulating medium and the insulating air gap contained in the insulating material, the partial discharge repetition rate N of the epoxy resin can be expressed as:
the repeated discharge rate of partial discharge shows a trend from slow to burst to gentle along with the aging time, and the relation between the repeated discharge rate and the aging is represented by a burst to gentle curve segment.
Further, in the method, when the aging degree of the epoxy resin is measured by using the roughness, an x-axis and a y-axis are established along the edge of the image, a z-axis is established by using gray values, interpolation is added, modeling is performed by using MATLAB, discrete points are sampled on the x-axis and the y-axis, the number of the discrete points is M and N respectively, the average value of the gray values of the absolute value of the offset distance is set to be mu,
the epoxy roughness can be calculated using the three-dimensional arithmetic mean deviation S a Characterized by:
converting the picture into a matrix by utilizing MATLAB, wherein the numerical value represents a gray value, changing the picture pixel into m multiplied by n, namely, the matrix is m multiplied by n, calculating a gray median along the X direction, establishing an X-Z relation curve, and displaying the surface roughness, wherein the abscissa is the pixel in the X direction, the ordinate is the gray value median on the pixel point, and the horizontal comparison shows that the epoxy damaged depths with different ageing degrees are shown.
Furthermore, in the method, when the aging degree of the epoxy resin is measured by using the activation energy, the frequency and the temperature of a certain point in the frequency domain dielectric spectrum of the dielectric loss before and after translation satisfy the Arrhenius equation,
wherein Ea represents the activation energy of the epoxy resin of the insulating material; t is the thermodynamic temperature; f is the frequency corresponding to a certain point on the frequency domain dielectric spectrum of dielectric loss at the temperature T before translation; k is Boltzmann constant, k=1.23×10 -23 J/K；
Secondly, confirming an AFT value under the activation energy according to the relation between the activation energy and the accelerated aging factor;
t in 0 Is the normal working temperature of the material; t is the laboratory accelerated heat aging temperature.
Finally, according to the ageing conditions in the laboratory and the AFT value thereof, the ageing age of the actual dry-type electrical equipment at the working temperature is equivalently calculated by virtue of the ageing time at the temperature. The calculation formula is shown as follows:
t is in 0 The time of a certain corresponding state point at the normal working temperature of the epoxy resin; t is the temperature pair at accelerated heat agingThe time of the same status point should be taken.
Furthermore, in the method, when the aging degree of the epoxy resin is measured by using the porosity of the material, the porosity is used for representing the damaged depth of the epoxy resin with different aging degrees, and then the calculation formula for calculating the porosity of the material is as follows:
wherein xi is the porosity, S b Represents the pore area and S represents the cross-sectional area.
Furthermore, in the method, the collected evaluation parameters are classified by using a class-two SVM, and the initial two types of aging states of the epoxy resin insulating material are divided, specifically as follows:
for a given sample point, it is mapped non-linearly
R→H, the estimated function y is obtained as:
wherein: omega is a weight vector; b is a bias vector, and the normal state and the good state of the epoxy resin insulating material are regarded as the first aging state, and the general state and the aging state are regarded as the first aging state; assigning y a label +1 in the ageing state of the class and assigning y a label-1 in the ageing state of the class;
defining the distance between the sample point and the optimal classification surface as J (omega, zeta) to maximize the classification interval of the sample, and describing the problem of solving the optimal classification surface as solving a constraint problem shown in the following formula:
constructing Lagrange function by constraint conditions and objective function
Solving a quadratic programming problem, wherein formula beta i Is a Lagrangian operator; solving the Lagrange function, and solving the bias derivative of each variable to obtain omega 1 And b 1 。
Further, in the method, the evaluation parameters after classification of the class-two SVM are classified into a normal state, a good state, a general state and an aging state by the class-two SVM, and the method comprises the following steps:
for one of two kinds of evaluation parameters classified by the class I SVM, nonlinear mapping is carried out
R→H, the estimated function y is obtained as:
wherein: omega is a weight vector; b is a bias vector, a +1 label is given to y in a normal state in a first aging state of the epoxy resin insulating material, and a-1 label is given to y in a good state in the first aging state of the epoxy resin insulating material;
defining the distance between the sample point and the optimal classification surface as J (omega, zeta) to maximize the classification interval of the sample, and describing the problem of solving the optimal classification surface as solving a constraint problem shown in the following formula:
constructing Lagrange function by constraint conditions and objective function
Solving a quadratic programming problem, wherein formula beta i Solving the Lagrange function to obtain the omega by solving the Lagrange function and solving the bias derivative of each variable 2 And b 2 Likewise, ω is solved by a Lagrange function 3 And b 3 。
And for the other evaluation parameter of the two evaluation parameters after the class I SVM classification, a +1 label is given to y in a general state in the class I aging state of the epoxy resin insulating material, and a-1 label is given to y in the aging state in the class I aging state of the epoxy resin insulating material.
Further, in the method, after model training is finished, an expression of a female model for dividing the first type state and the first type state is obtained, test data is introduced, a female model test is firstly carried out, and the first type state or the first type state is judged and obtained through the obtained label value y; secondly, according to different sub-models corresponding to the first type state and the first type state, performing a test, and judging to obtain a normal state, a good state, a general state and an aging state corresponding to the first type state according to the obtained tag value y; and finally, verifying the aging discrimination effect of the model.
The beneficial effects of the invention are as follows:
the invention establishes an epoxy resin aging state evaluation method under different voltage frequencies based on dielectric loss, partial discharge repeated discharge rate, roughness, activation energy and porosity indexes of the epoxy resin, and the method can accurately reflect the aging state of the epoxy resin from multiple aspects so as to reflect the insulating performance state of electrical equipment, thereby having certain guiding significance for evaluating the running state of the equipment.
The measuring equipment required by the parameters related by the invention is simpler, the equipment is required to be simple and convenient, the test method is simple and easy to understand, and the corresponding relation between the frequency and the aging state can be established by utilizing the parameters of dielectric loss, repeated discharge rate of partial discharge, roughness, activation energy and porosity.
Drawings
In order to more clearly illustrate the embodiments of the invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only some embodiments of the invention, and that 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 discriminating and inspecting insulation aging of epoxy resin;
FIG. 2 is a black and white view of an internal bond cross section of an epoxy according to an embodiment of the present invention;
FIG. 3 is a three-dimensional model of the surface roughness of an epoxy resin according to an embodiment of the present invention;
FIG. 4 is a view showing a cross section of the surface of an epoxy resin according to an embodiment of the present invention;
FIG. 5 is a graph of surface roughness of an epoxy resin according to an embodiment of the present invention;
FIG. 6 is a black and white view of an internal bond cross section of an epoxy in accordance with an embodiment of the present invention;
FIG. 7 is a gray level histogram of an epoxy image according to an embodiment of the present invention;
fig. 8 is a block diagram of an embodiment of the SVM of the present invention.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Example 1
Referring to fig. 1, the embodiment provides a method for judging and inspecting insulation aging of epoxy resin of dry-type electrical equipment, which comprises the following steps:
s1: and (3) selecting an epoxy resin sample, and performing withstand voltage tests on the epoxy resin sample under different frequencies to obtain an ageing sample of the epoxy resin insulating material under different voltage frequencies.
S2: and measuring an evaluation parameter related to the aging state of the epoxy resin sample. A total of 100 sample data including normal operation data and failure data are randomly extracted as test samples.
S3: and classifying the collected evaluation parameters by using a class-II SVM, and dividing the initial aging states of the epoxy resin insulating material into two classes.
S4: and classifying the evaluation parameters classified by the class-III SVM by using the class-III SVM, and dividing the aging states of the specific four classes of the epoxy resin insulating material.
S5: after the model evaluation parameter training is finished, test data are introduced to test, and the model aging discrimination effect is verified.
As an implementation of this embodiment, the preparation method of the epoxy resin insulation material for the dry electrical equipment under different voltage frequencies of this embodiment specifically includes: taking an epoxy resin insulating material of new dry-type electrical equipment, and carrying out degassing and drying treatment for 46-50 hours at the temperature of 70-90 ℃ and the pressure of 40-60 Pa; and performing withstand voltage tests on the epoxy resin at different frequencies to obtain dry type electrical equipment insulating material samples at different voltage frequencies.
The epoxy resin insulation material obtained in this example was subjected to a deaeration drying treatment at 80℃under 50Pa for 48 hours. The present invention is not particularly limited in the source of the epoxy resin insulation material of the new dry type electric device, and is obtained by cutting the outer insulation layer using the dry type electric device known to those skilled in the art.
The purpose of the degassing and drying treatment in this embodiment is to eliminate the factors that interfere with the test results, such as thermal stress generated in the preparation process of the sample, moisture adsorbed on the surface, etc.; it is possible to carry out the process by using a vacuum drying oven well known to those skilled in the art.
In the embodiment, the epoxy resin sample is subjected to withstand voltage test under the frequencies of fundamental frequency, frequency tripling, frequency quintupling and frequency seven doubling. When the discharge amount was more than 10pC, it was considered that a discharge phenomenon occurred, and the voltage was kept constant at this time, and a withstand voltage test was performed for 15 hours. Thus, aging samples of the epoxy resin insulating material at different frequencies are obtained, and the parts of the epoxy resin sample at different frequencies are not less than 10 parts per group.
The present example uses dielectric loss to determine the degree of aging of the epoxy resin. The voltage frequency has a great influence on the dielectric loss of the epoxy resin insulating material, and the dielectric loss of the epoxy resin insulating material under the frequency doubling voltage is far greater than the power frequency. The aging-aggravated change of the epoxy resin insulating material in the low-frequency region is obvious, so that the characteristic parameters are extracted from the change to evaluate the aging state of the epoxy resin. With the increase of voltage and frequency, the dielectric loss value of the epoxy resin is in an increasing trend, and when the voltage and frequency are larger and the development of partial discharge is serious, the dielectric loss value is obviously slowed down, and the epoxy resin has a certain saturation trend.
The embodiment is at 10 -3 To 10 -1 In the Hz range, is sensitive to insulation aging reactions. Preferred choice 10 -3 Hz，10 -2 And the Hz is used as the characteristic frequency of the aging state evaluation of the epoxy resin insulating material, and the aging degree of the epoxy resin insulating material is judged according to the index relation that the dielectric loss factor at the characteristic frequency and corresponding aging time corresponding data are met.
In this example, the degree of aging of the epoxy resin was measured by using the repeated discharge rate of partial discharge. Along with the increase of the externally applied voltage of the insulating material, the electric fields born by the electrodes and the inside of the epoxy resin of the insulating material can also be increased, the energy of electrons or ions of partial discharge impacting the insulating material is increased, the repeated discharge rate of the partial discharge is increased along with the increase of the externally applied voltage, and the failure process of the epoxy resin of the insulating material is shortened.
In this example, the discharge repetition rate of partial discharge increases with increasing voltage and frequency in the later stage of the test, and it is considered that the aging degree is further increased.
The present example uses roughness to determine the degree of aging of the epoxy resin. In the early stage of the test, the surface of the epoxy resin sample is smooth and flat, and the picture is dark.
In the middle test period, along with the increase of frequency and the increase of aging time, the surface of the epoxy resin sample is provided with 'sharp protrusions', the picture mainly takes dark color as a main part, a small number of bright spots are distributed, and the surface smoothness of the sample is good.
In the middle and later stages of the test, the sharp protrusions on the surface of the epoxy resin sample are increased, the surface of the sample is fluctuant like a continuous mountain peak, the colors of pictures are bright and dark alternately, and the surface smoothness is poor; in the later stage of the test, the 'continuous mountain peak' on the surface of the epoxy resin sample is basically disappeared, the picture is almost completely lightened, and the surface is rougher.
The surface roughness of the epoxy insulating material is further increased with increasing frequency and aging time in this embodiment. The roughness can thus be used to characterize the depth to which epoxy resins of varying degrees of aging are destroyed.
The present example uses the activation energy to determine the degree of aging of the epoxy resin. With the increase of frequency and aging time, the percentage of activated molecules of the epoxy resin material sample is increased, the number of effective collisions is increased, and the reaction rate is accelerated. The "binding force" between atoms within the molecule is broken, resulting in destruction of the reactant molecules, a decrease in the activation energy of the epoxy resin sample, and a reduction in the life of the dry electrical device. The roughness can thus be used to characterize the depth to which epoxy resins of varying degrees of aging are destroyed.
The present example uses the porosity of the material to determine the degree of aging of the epoxy resin. In the early stage of the experiment, the epoxy resin is tightly combined, obvious pores are not seen, and the fracture phenomenon is avoided; in the middle of the experiment, as the aging time is prolonged, the bonding compactness between epoxy resin molecules is reduced, gaps are gradually formed, and the arrangement is loose; in the later stage of the experiment, the porosity of the epoxy resin shows a slow rising trend along with the deepening of the aging degree. The porosity can thus be used to characterize the depth to which epoxy resins of varying degrees of aging are destroyed.
In the embodiment, various ageing indexes of the epoxy resin are measured, and the insulation state of the epoxy resin is comprehensively judged by utilizing a multi-classification-based SVM method, so that the ageing state evaluation of the epoxy resin is realized.
Example 2
In a specific implementation aspect, the embodiment provides a method for measuring an evaluation parameter related to an aging state of an epoxy resin sample, wherein 200 sample data including normal operation data and fault data are randomly extracted as test samples. And 5 state evaluation parameters corresponding to each frequency are selected under 4 frequencies, and 10 groups of data are included under each evaluation parameter. 8 sets of data in each evaluation parameter were used as training data and 2 sets of data were used as test data.
As a specific implementation of the present invention, the epoxy resin aging state evaluation parameters include dielectric loss, partial discharge repetition discharge rate, roughness, activation energy, and porosity.
In the embodiment, the aging degree of the epoxy resin is measured by using the dielectric loss of the material, the dielectric loss of the epoxy resin insulating material is greatly influenced by the voltage frequency, and the dielectric loss of the epoxy resin insulating material under the frequency doubling voltage is far greater than the power frequency.
In the embodiment, the conducting dielectric loss tan delta is implemented according to a DL/T47.3-2018 field insulation test, and the test adopts a high-voltage dielectric loss tester to measure the dielectric loss.
In this embodiment, the epoxy insulating material gradually develops with increasing frequency, and the dielectric loss value gradually changes under the influence of the frequency. With the increase of voltage and frequency, the dielectric loss value of the epoxy resin is in an increasing trend, and when the voltage and frequency are larger and the development of partial discharge is serious, the dielectric loss value is obviously slowed down, and the epoxy resin has a certain saturation trend.
The low frequency region 10 of the present embodiment -3 To 10 -1 The change of tan delta along with aging aggravation in the Hz range is obvious, so that the aging state of the insulating paperboard can be estimated by extracting characteristic parameters from the change of tan delta.
In this embodiment 10 is selected -3 Hz，10 -2 Hz is used as characteristic frequency of the aging state evaluation of the epoxy resin insulating material, and dielectric loss factor tan delta at the characteristic frequency f The data corresponding to the corresponding aging time satisfies the exponential relationship:
DP＝A×exp(-tanδ f /B)+C
wherein DP aging state, tan δ is dielectric loss factor at characteristic frequency (f=10 -3 、10 -2 ) A, B, C are fitting parameters, and the respective parameters and goodness of fit are shown in the following table. The exponential relationship fitting degree of the dielectric loss factor and the aging state under the characteristic frequency is higher, and the frequency can be used for evaluating the aging state.
| Frequency of | Fitting formula | Goodness of fit |
| 10-3Hz | DP＝7773exp(-tanδ f /0.3394)+627.5 | 0.99 |
| 10-2Hz | DP＝1758exp(-tanδ f /0.1087)+583.2 | 0.99 |
In this example, the degree of aging of the epoxy resin was measured by using the partial discharge repetition discharge rate. Along with the increase of the externally applied voltage of the insulating material, the electric fields born by the electrodes and the epoxy resin insulating material can also be increased, the energy of electrons or ions of partial discharge impacting the insulating material is increased, the repeated discharge rate of the partial discharge is increased along with the increase of the externally applied voltage, and the failure process of the epoxy resin of the insulating material is shortened.
The repeated discharge rate of the partial discharge in the embodiment is one of important factors of insulation aging and is also an important characterization parameter of insulation aging.
In the embodiment, UCB is the withstand voltage of an insulating air gap in a partial discharge test experiment according to the related standard in the DL417-2006 electric equipment partial discharge field measurement guide rule, C b 、C c 、ε rc 、ε bc D, delta are parameters of the insulating medium in the insulating material and contained within the insulating air gap. The partial discharge repetition rate N of the epoxy resin can be expressed as:
the invention adopts a curve section from burst to gentle to represent the relation between the repeated discharge rate and aging.
In this embodiment, the degree of aging of the epoxy resin is measured by using roughness, as shown in fig. 2, the surface of the epoxy resin is smooth and flat under the action of no electric stress, and the picture is dark.
In the middle test period, along with the increase of frequency and the increase of aging time, the surface of the epoxy resin sample is provided with 'sharp protrusions', the picture mainly takes dark color as a main part, a small number of bright spots are distributed, and the surface smoothness of the sample is good.
In the middle and later stages of the test, the sharp protrusions on the surface of the epoxy resin sample are increased, the surface of the sample is fluctuated like a continuous mountain peak, the colors of pictures are bright and dark alternately, and the surface smoothness is poor.
In the later test period, the 'continuous mountain peak' on the surface of the epoxy resin sample is basically disappeared, the picture is almost completely lightened, and the surface is rougher. When the epoxy resin is subjected to the effects of frequency multiplication and electric stress, the phenomena of epoxy falling off, hollowness and the like appear on the surface, and the roughness is obviously increased.
The SEM image of the surface of the epoxy resin in this embodiment is a gray image, the gray value of which depends on the distance between the particles and the light source, and the higher the gray value, the closer to the light source, and vice versa.
In this embodiment, to build a three-dimensional model of its surface roughness, x and y axes are built along the image edges, and a z axis is built with gray values, to ensure that the model is relatively smooth, interpolation is added, modeling is performed using MATLAB, and the result is shown in fig. 3.
when this embodiment is further implemented, the portion of the gray scale value in the Y direction in fig. 4 with relatively uniform value is taken for further analysis.
In the embodiment, MATLAB is utilized to convert the picture into a matrix, the numerical value represents a gray value, the picture pixel is changed into an m×n matrix, namely the matrix is an m×n matrix, a gray median is calculated along the X direction, an X-Z relation curve is established, and the surface roughness is displayed in a more visual mode.
In this embodiment, as shown in fig. 5, the abscissa is a pixel in the X direction, the ordinate is the median of the gray values on the pixel, and the horizontal comparison can be used to represent the damaged depths of the epoxy with different aging degrees. The transverse line is the average height of the interface of the section.
The present example uses the activation energy to determine the degree of aging of the epoxy resin. The degree of aging of the epoxy resin was measured using the activation energy. With the increase of frequency, the percentage of activated molecules of the epoxy resin sample is increased, the number of effective collisions is increased, and the reaction rate is accelerated. The "binding force" between atoms within the molecule is broken, resulting in the destruction of the reactant molecules.
When the embodiment is implemented, the frequency and the temperature of a certain point in the frequency domain dielectric spectrum of the dielectric loss before and after translation satisfy the Arrhenius equation, namely
Wherein Ea represents the activation energy of the epoxy resin of the insulating material; t is the thermodynamic temperature; f is the frequency corresponding to a certain point on the frequency domain dielectric spectrum of dielectric loss at the temperature T before translation; k is Boltzmann constant, k=1.23×10 -23 J/K。
Secondly, confirming an AFT value under the activation energy according to the relation between the activation energy and the accelerated aging factor;
t in 0 Is the normal working temperature of the material; t is the laboratory accelerated heat aging temperature.
Finally, according to the ageing conditions in the laboratory and the AFT value thereof, the ageing age of the actual dry-type electrical equipment at the working temperature is equivalently calculated by virtue of the ageing time at the temperature. The calculation formula is shown as follows:
t is in 0 The time of a certain corresponding state point at the normal working temperature of the epoxy resin; t is the time corresponding to the same state point at the accelerated heat aging temperature.
The present example determines the activation energy of an epoxy insulating material based on the time the epoxy reaches a standard mass loss rate and determines the value of the activation energy at that time. Then confirming the AFT value under the activation energy according to the relation between the activation energy and the accelerated aging factor; finally, according to the ageing conditions in the laboratory and the AFT value thereof, the ageing years of the actual dry-type electrical equipment at the working temperature are equivalently calculated according to the ageing time at the temperature.
The present example uses the porosity of the material to determine the degree of aging of the epoxy resin. In the early stage of the experiment, the epoxy resin is tightly combined, no obvious pores are seen, and no fracture phenomenon exists.
In the middle of the experiment in this example, the compactness of the bonding between the epoxy resin molecules is reduced, gaps are gradually formed, and the arrangement is loose as the aging time is prolonged.
In the later stage of the experiment of the embodiment, the porosity of the epoxy resin shows a slow rising trend along with the deepening of the aging degree. The porosity can thus be used to characterize the depth to which epoxy resins of varying degrees of aging are destroyed.
wherein xi is the porosity, S b Represents the pore area and S represents the cross-sectional area. Specifically, the contrast and color saturation of the picture are adjusted to make the color boundary between the aperture and the epoxy clearer (fig. 6), and an image gray level histogram is drawn by using an imhist function (fig. 7).
In this embodiment, the closer the image and the gray histogram thereof are to black, the closer the pixel gray is to 0, the fewer the number of pixels, the more the number of pixels is to break and turn points are observed in the histogram, and the image is binarized and converted into a black-and-white image by taking the gray value as a threshold value, so that the holes are separated from the epoxy resin, the holes are represented as black, the epoxy is white, and the black-and-white colors are interchanged for convenient observation, thereby further calculating the white area ratio, that is, the ratio of the pixels with gray of 0 to the total number of pixels is the porosity.
Example 3
In a specific implementation, the present embodiment provides a method for classifying the collected evaluation parameters by using a second type SVM, and dividing the initial two types of aging states of the epoxy resin insulation material on the basis of embodiment 2, and a flowchart is shown in fig. 8.
The present embodiment is non-linearly mapped for a given sample point
R→H, the estimated function y is obtained as:
wherein: omega is a weight vector; b is the bias vector. The normal state and the good state of the epoxy resin insulating material are regarded as the first aging state, and the general state and the aging state are regarded as the first aging state.
In the embodiment, y is given a label +1 in the aging state of type i, and y is given a label-1 in the aging state of type i.
In this embodiment, the distance from the sample point to the optimal classification surface is defined as J (ω, ζ), so that the classification interval of the sample is maximized, and as an optimal choice in this embodiment, the problem of solving the optimal classification surface is described as solving a constraint problem represented by the following formula:
in the embodiment, the Lagrange function is constructed through constraint conditions and an objective function
The present embodiment solves the quadratic programming problem, where formula β i Is a lagrangian.
Finally, the embodiment solves the Lagrangian function of the above type, and solves various variablesObtaining omega by deviation 1 And b 1 。
Example 4
In a specific implementation aspect, the embodiment provides, based on embodiment 3, that the evaluation parameters after classification of the class i SVM use class i SVM classification to divide the aging states of the specific four classes of the epoxy resin insulating material into a normal state, a good state, a general state and an aging state.
In the embodiment, one of two kinds of evaluation parameters after classification of the first class SVM is subjected to nonlinear mapping
R→H, the estimated function y is obtained as:
wherein: omega is a weight vector; b is the bias vector.
In the embodiment, a +1 label is given to y in the normal state of the first type of aging state of the epoxy resin insulation material, and a-1 label is given to y in the good state of the first type of aging state of the epoxy resin insulation material.
In this embodiment, the distance from the sample point to the optimal classification surface is defined as J (ω, ζ), so that the classification interval of the sample is maximized, and the problem of solving the optimal classification surface is described as solving a constraint problem represented by the following formula:
in the embodiment, the Lagrange function is constructed through constraint conditions and an objective function
In the embodiment, the Lagrange function is solved, and the bias derivative is solved for each variable to obtain omega 2 And b 2 。
When the embodiment is implemented, for the other evaluation parameter of the two evaluation parameters after class I and class I SVM classification, a +1 label is given to y in a general state in class I aging state of the epoxy resin insulating material, and a-1 label is given to y in an aging state in class I aging state of the epoxy resin insulating material.
When the embodiment is circularly implemented, the omega is solved by the Lagrangian function in other steps 3 And b3.
Example 5
In a specific implementation aspect, the present embodiment provides a result verification method based on embodiments 3 and 4, where test data is introduced after the training of the evaluation parameters of the model is finished, and a test is performed to verify the aging discrimination effect of the model.
After the model training of the embodiment is finished, an expression for dividing the first type state and the female model of the first type state is obtained
In the embodiment, the expression of the sub-model for dividing the normal state and the good state in the class i model is as follows:
in this embodiment, the expression of the sub-model of the general state and the aging state is divided in the class i model:
in this embodiment, test data is finally introduced, and first, a female model test is performed, and the type i state or the type i state is determined and obtained through the obtained tag value y.
In a further implementation, according to the embodiment, the test is performed according to different sub-models corresponding to the type i state and the type i state, and the normal state, the good state, the general state and the aging state corresponding to the type i state are obtained through judging according to the obtained tag value y; and finally, verifying the aging discrimination effect of the model.
Example 6
The present embodiment discloses an electronic device including a processor and a memory storing execution instructions, wherein when the processor executes the execution instructions stored in the memory, the processor executes the method described in embodiments 1 to 5.
In summary, the invention establishes an epoxy resin aging state evaluation method under different voltage frequencies based on dielectric loss, repeated discharge rate of partial discharge, roughness, activation energy and porosity indexes of the epoxy resin, and the method can accurately reflect the aging state of the epoxy resin from multiple aspects so as to reflect the insulating performance state of electrical equipment, thereby having certain guiding significance for evaluating the running state of the equipment.
The measuring equipment required by the parameters related by the invention is simpler, the equipment is required to be simple and convenient, the test method is simple and easy to understand, and the corresponding relation between the frequency and the aging state can be established by utilizing the parameters of dielectric loss, repeated discharge rate of partial discharge, roughness, activation energy and porosity.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (7)
1. The epoxy resin insulation aging discrimination and test method under different voltage frequencies is characterized by comprising the following steps:
s1, obtaining an epoxy resin sample, respectively performing withstand voltage tests at different frequencies, and further obtaining an aging sample;
s2, measuring an evaluation parameter related to the aging state of the epoxy resin sample, and classifying by using a class I SVM;
s3, classifying the classification result in the S2 by using the first I type SVM again, and finishing the training of the evaluation parameters of the model;
s4, testing the model input test data, and outputting a final result after verifying the model aging discrimination effect;
in the method, the aging degree of the epoxy resin is measured by using the repeated discharge rate of partial discharge, the aging degree of the epoxy resin is measured by using roughness, the aging degree of the epoxy resin is measured by using dielectric loss, the aging degree of the epoxy resin is measured by using activation energy, and the aging degree of the epoxy resin is measured by using material porosity;
in the method, when the aging degree of the epoxy resin is measured by utilizing the repeated discharge rate of partial discharge, the characteristic parameter is extracted from the change of tan delta to evaluate the aging state of the insulating paperboard, and then the dielectric loss factor tan delta at the characteristic frequency is calculated f The data corresponding to the corresponding aging time satisfies the exponential relationship:
DP＝A×exp(-tanδ f /B)+C
wherein DP is an aging state, tan delta f Is the dielectric loss factor at the characteristic frequency, A, B, C is the fitting parameter;
in the method, U is used for measuring the aging degree of the epoxy resin by utilizing the repeated discharge rate of partial discharge CB C is the withstand voltage of the insulating air gap b 、C c 、ε rc 、ε bc D, delta are parameters of the insulating medium and the insulating air gap contained in the insulating material, the partial discharge repetition rate N of the epoxy resin can be calculatedExpressed as:
the repeated discharge rate of partial discharge shows a trend from slow to burst to gentle along with the aging time, and the relation between the repeated discharge rate and the aging is represented by a burst to gentle curve segment.
2. The method for judging and inspecting the insulation aging of the epoxy resin under different voltage frequencies according to claim 1, wherein in the method, when the aging degree of the epoxy resin is measured by utilizing roughness, an x-axis and a y-axis are established along the edge of an image, a z-axis is established by gray values, interpolation is added, modeling is performed by utilizing MATLAB, discrete points are sampled on the x-axis and the y-axis, the number of the discrete points is M and N respectively, the average value of the gray values of the absolute value of offset is mu,
the epoxy roughness can be calculated using the three-dimensional arithmetic mean deviation S a Characterized by:
converting the picture into a matrix by utilizing MATLAB, wherein the numerical value represents a gray value, setting the image pixel as m multiplied by n, namely, setting the matrix as m multiplied by n, calculating a gray median along the X direction, establishing an X-Z relation curve, and displaying surface roughness, wherein the abscissa is the pixel in the X direction, the ordinate is the gray value median on the pixel point, and the horizontal comparison shows that the epoxy damaged depths with different ageing degrees are shown.
3. The method for judging and inspecting the insulation aging of the epoxy resin under different voltage frequencies according to claim 1, wherein in the method, when the aging degree of the epoxy resin is firstly measured by utilizing the activation energy, the frequency and the temperature of a certain point in a frequency domain dielectric spectrum of dielectric loss before and after translation satisfy the Arrhenius equation,
wherein Ea represents the activation energy of the epoxy resin of the insulating material; t is the thermodynamic temperature; f is the frequency corresponding to a certain point on the frequency domain dielectric spectrum of dielectric loss at the temperature T before translation; k is Boltzmann constant, k=1.23×10 -23 J/K；
Secondly, confirming an AFT value under the activation energy according to the relation between the activation energy and the accelerated aging factor;
t in 0 Is the normal working temperature of the material; t is the accelerated thermal ageing temperature in the laboratory;
finally, according to the ageing conditions in a laboratory and the AFT value thereof, equivalently calculating the ageing years of the actual dry-type electrical equipment at the working temperature by virtue of the ageing time at the temperature; which is a kind of
The calculation formula is as follows:
t is in 0 The time of a certain corresponding state point at the normal working temperature of the epoxy resin; t is the time corresponding to the same state point at the accelerated heat aging temperature.
4. The method for judging and testing the insulation aging of the epoxy resin under different voltage frequencies according to claim 1, wherein when the aging degree of the epoxy resin is tested by using the porosity of the material, the porosity is used for representing the damaged depth of the epoxy resin with different aging degrees, and the calculation formula for calculating the porosity of the material is as follows:
wherein xi is the porosity, S b Represents the pore area and S represents the cross-sectional area.
5. The method for judging and checking the insulation aging of the epoxy resin under different voltage frequencies according to claim 1, wherein the method is characterized in that the collected evaluation parameters are classified by using a first class SVM, and the initial two classes of aging states of the epoxy resin insulation material are divided as follows:
for a given sample point, it is mapped non-linearly
The estimated function y is obtained as:
wherein: omega is a weight vector; b is a bias vector, and the normal state and the good state of the epoxy resin insulating material are regarded as the first aging state, and the general state and the aging state are regarded as the first aging state; giving y a label +1 in the aging state of the first type, and giving y a label-1 in the aging state of the first type;
defining the distance between the sample point and the optimal classification surface as J (omega, zeta) to maximize the classification interval of the sample, and describing the problem of solving the optimal classification surface as solving a constraint problem shown in the following formula:
constructing Lagrange function by constraint conditions and objective function
Solving a quadratic programming problem, wherein formula beta i Is a Lagrangian operator; solving the Lagrange function, and solving the bias derivative of each variable to obtain omega 1 And b 1 。
6. The method for judging and testing the insulation aging of the epoxy resin under different voltage frequencies according to claim 1, wherein the method is characterized in that the evaluation parameters after classification of the class I SVM are classified into a normal state, a good state, a general state and an aging state by using the class I SVM, and the method is specifically as follows:
for one of two kinds of evaluation parameters classified by the class I SVM, nonlinear mapping is carried out
The estimated function y is obtained as:
wherein: omega is a weight vector; b is a bias vector, a +1 label is given to y in a normal state in a first aging state of the epoxy resin insulating material, and a-1 label is given to y in a good state in the first aging state of the epoxy resin insulating material;
defining the distance between the sample point and the optimal classification surface as J (omega, zeta) to maximize the classification interval of the sample, and describing the problem of solving the optimal classification surface as solving a constraint problem shown in the following formula:
constructing Lagrange function by constraint conditions and objective function
Solving a quadratic programming problem, wherein formula beta i Solving the Lagrange function to obtain the omega by solving the Lagrange function and solving the bias derivative of each variable 2 And b 2 Likewise, ω is solved by a Lagrange function 3 And b 3 ；
And for the other evaluation parameter of the two evaluation parameters after the class I SVM classification, a +1 label is given to y in a general state in the class I aging state of the epoxy resin insulating material, and a-1 label is given to y in the aging state in the class I aging state of the epoxy resin insulating material.
7. The method for judging and checking the insulation aging of the epoxy resin under different voltage frequencies according to claim 1, wherein after the model training is finished, an expression of a female model for dividing a first type state and a first type state is obtained, test data are introduced, a female model test is firstly carried out, and the first type state or the first type state is judged and obtained through the obtained label value y; secondly, according to different sub-models corresponding to the first type state and the first type state, performing a test, and judging to obtain a normal state, a good state, a general state and an aging state corresponding to the first type state according to the obtained tag value y; and finally, verifying the aging discrimination effect of the model.
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