Damp state evaluation method and device based on oil paper insulation nonlinear characteristics, equipment, medium and product

Abstract

The invention discloses a damping state evaluation method, device and equipment based on oil paper insulation nonlinear characteristics, a medium and a product, and relates to the field of insulation state detection, and the method comprises the steps: obtaining a third harmonic component proportion of a response current of to-be-detected oil paper under a preset excitation signal; acquiring a third harmonic component proportion of response current of the dry paperboard under a preset excitation signal, and performing per-unit value processing on the third harmonic component proportion of the response current of the to-be-detected oiled paper under the preset excitation signal, wherein the size parameters and the material parameters of the dry paperboard are the same as those of the to-be-detected oiled paper; obtaining the third harmonic per unit value of the response current of the oil paper to be detected under the preset excitation signal; according to the third harmonic per unit value of the response current of the to-be-measured oil paper under the preset excitation signal, the water content of the to-be-measured oil paper is calculated through the function relation. According to the invention, the damp state of the insulation in the transformer is sensitively and accurately evaluated.

Description

Technical Field

[0001] The present application relates to the field of insulation status detection, and in particular to a method, device, equipment, medium and product for evaluating the moisture status based on the nonlinear characteristics of oil-paper insulation. Background Art

[0002] The state of oil-paper insulation determines the operating safety of oil-immersed power transformers, and moisture is the most important factor that causes the degradation of its insulation performance. More than 90% of the moisture in the oil-paper insulation system exists in the solid insulation paper. Limited by the sealed insulation structure of the transformer, it is difficult to take paper samples for direct testing of its moisture content in engineering. Traditional methods for evaluating moisture include testing the moisture content of the oil and estimating the moisture content of the paper based on the equilibrium curve, as well as indirect estimation methods using the transformer insulation resistance and power frequency dielectric loss values. However, practice has shown that these methods are not sensitive to moisture in solid insulation, and further methods that can sensitively and accurately evaluate moisture in transformer insulation have always been a research hotspot in this field. Summary of the invention

[0003] The purpose of this application is to provide a method, device, equipment, medium and product for evaluating the moisture state of insulation based on the nonlinear characteristics of oil-paper insulation, which can realize sensitive and accurate evaluation of the moisture state of insulation in the transformer.

[0004] To achieve the above objectives, this application provides the following solutions:

[0005] In a first aspect, the present application provides a method for evaluating the moisture state of oil-paper insulation based on nonlinear characteristics, comprising:

[0006] Obtain the proportion of the third harmonic component of the response current of the oil-paper to be tested under the preset excitation signal;

[0007] Obtaining the proportion of the third harmonic component of the response current of the dry paperboard having the same size parameters and material parameters as the oil paper to be tested under a preset excitation signal;

[0008] Based on the proportion of the third harmonic component of the response current of the dry paperboard under the preset excitation signal, the proportion of the third harmonic component of the response current of the oil paper to be tested under the preset excitation signal is processed in per unit value to obtain the third harmonic per unit value of the response current of the oil paper to be tested under the preset excitation signal;

[0009] According to the third harmonic standard value of the response current of the oil paper to be tested under the preset excitation signal, the moisture content of the oil paper to be tested is calculated using a functional relationship; the functional relationship represents the relationship between the third harmonic standard value of the response current of the oil paper to be tested under the preset excitation signal and the moisture content, and the moisture content represents the moisture state of the oil paper to be tested.

[0010] Optionally, the formula for per-unit value processing is:

[0011]

[0012] in, is the third harmonic per unit value of the response current of the oil-paper to be tested under the preset excitation signal, β3 is the proportion of the third harmonic component of the response current of the oil-paper to be tested under the preset excitation signal, β 3-Dry It is the proportion of the third harmonic component of the response current of the dry paperboard under the preset excitation signal.

[0013] Optionally, the functional relationship is:

[0014]

[0015] in, is the third harmonic per unit value of the response current of the oil-paper to be tested under the preset excitation signal, mc is the moisture content of the oil-paper to be tested, and M and N are fitting parameters.

[0016] Optionally, the functional relationship is:

[0017]

[0018] in, is the third harmonic per unit value of the response current of the oil-paper to be tested under the preset excitation signal, and mc is the moisture content of the oil-paper to be tested.

[0019] In a second aspect, the present application provides a device for evaluating the moisture state of oil-paper insulation nonlinear characteristics, comprising: a signal generator, a voltage amplification module, a current amplification module, a signal acquisition module and a host computer;

[0020] The host computer is connected to the control end of the signal generator, the signal generator is connected to the voltage amplifier, the voltage amplifier is connected to the oil paper to be tested, and the host computer is used to control the signal generator to send a preset excitation signal;

[0021] The current amplification module is connected to the oil paper to be tested, and the current amplification module is also connected to the signal acquisition module, and the signal acquisition module is connected to the host computer;

[0022] The host computer is used to calculate the moisture content of the oil-paper to be tested according to the response current of the oil-paper to be tested under the preset excitation signal collected by the signal acquisition module and using the above-mentioned moisture state evaluation method based on the nonlinear characteristics of oil-paper insulation.

[0023] In a third aspect, the present application provides a computer device, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-mentioned method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation.

[0024] In a fourth aspect, the present application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-mentioned method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation.

[0025] In a fifth aspect, the present application provides a computer program product, including a computer program, which, when executed by a processor, implements the above-mentioned method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation.

[0026] According to the specific embodiments provided in this application, this application discloses the following technical effects:

[0027] The present application provides a method, device, equipment, medium and product for evaluating the moisture state of oil-paper insulation based on the nonlinear characteristics of oil-paper insulation. The method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation includes: obtaining the proportion of the third harmonic component of the response current of the oil-paper to be tested under a preset excitation signal; obtaining the proportion of the third harmonic component of the response current of the dry paperboard with the same size parameters and material parameters as the oil-paper to be tested under the preset excitation signal; performing per-unit value processing on the proportion of the third harmonic component of the response current of the oil-paper to be tested under the preset excitation signal based on the proportion of the third harmonic component of the response current of the dry paperboard under the preset excitation signal, and obtaining the per-unit value of the third harmonic of the response current of the oil-paper to be tested under the preset excitation signal; according to the per-unit value of the third harmonic of the response current of the oil-paper to be tested under the preset excitation signal, using a functional relationship, the moisture content of the oil-paper to be tested is calculated. The present application utilizes the nonlinear harmonic characteristics of the response current of oil-paper insulation, proposes a method for evaluating the moisture state of oil-paper insulation using the per-unit value of the third harmonic proportion as a characteristic parameter, and realizes sensitive and accurate evaluation of the moisture state of insulation in the transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0029] Figure 1 A schematic flow chart of a method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation provided in one embodiment of the present application;

[0030] Figure 2 A working flow chart of a device for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation provided in one embodiment of the present application;

[0031] Figure 3The waveform diagram of the excitation voltage u(t) and the response current i(t) of samples with different moisture contents provided in one embodiment of the present application;

[0032] Figure 4 The response current waveform of the sample under different f0 provided in an embodiment of the present application (mc = 3.02%, E m =2000V / mm) diagram;

[0033] Figure 5 Different E provided in one embodiment of the present application m The response current waveform of the sample below (mc = 3.02%, f0 = 0.01Hz);

[0034] Figure 6 The damp-proof insulating paperboard β provided in one embodiment of the present application k Schematic diagram of the changing pattern;

[0035] Figure 7 Schematic diagram of different insulation structure samples provided in one embodiment of the present application;

[0036] Figure 8 A schematic diagram of the proportion of each harmonic of different insulation structure samples provided in one embodiment of the present application;

[0037] Fig. 9 The moisture content mc and β provided in one embodiment of the present application * Schematic diagram of the fitting relationship between the three;

[0038] Fig.10 A flow chart for diagnosing the moisture status of oil-paper insulation equipment provided in one embodiment of the present application;

[0039] Fig.11 A schematic diagram of a transformer main insulation equivalent model provided in one embodiment of the present application;

[0040] Fig.12 A schematic diagram showing a comparison between the measured value and the estimated value of the moisture content mc provided in one embodiment of the present application;

[0041] Fig.13 A schematic diagram of a packaged moisture state assessment device provided in one embodiment of the present application;

[0042] Fig.14 A schematic diagram of an amplification and filtering circuit provided in one embodiment of the present application;

[0043] Fig.15 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0044] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0045] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0046] In an exemplary embodiment, Figure 1 As shown, a method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation is provided, comprising the following steps 101 to 104. Among them:

[0047] Step 101, obtaining the proportion of the third harmonic component of the response current of the oil-paper to be tested under a preset excitation signal.

[0048] Step 102, obtaining the proportion of the third harmonic component of the response current of the dry paperboard having the same size parameters and material parameters as the oil paper to be tested under a preset excitation signal.

[0049] Step 103, based on the proportion of the third harmonic component of the response current of the dry paperboard under the preset excitation signal, the proportion of the third harmonic component of the response current of the oil paper to be tested under the preset excitation signal is processed in per unit value to obtain the third harmonic per unit value of the response current of the oil paper to be tested under the preset excitation signal.

[0050] Step 104, according to the third harmonic standard value of the response current of the oil paper to be tested under the preset excitation signal, the moisture content of the oil paper to be tested is calculated using a functional relationship; the functional relationship represents the relationship between the third harmonic standard value of the response current of the oil paper to be tested under the preset excitation signal and the moisture content, and the moisture content represents the moisture state of the oil paper to be tested.

[0051] By implementing the above steps 101 to 104, and utilizing the nonlinear harmonic characteristics of the oil-paper insulation response current, a method for evaluating the moisture state of the oil-paper insulation is proposed using the third harmonic proportion per unit value as a characteristic parameter, thereby realizing sensitive and accurate evaluation of the moisture state of the insulation in the transformer.

[0052] Frequency Domain Dielectric Spectrum (FDS) technology is generally believed to be able to sensitively reflect the moisture status of the insulation in the transformer, and has the characteristics of non-destructive testing without the need for hanging cover sampling. Its basic principle is to use the change in the response current characteristics of the insulation to sinusoidal excitation voltages of different frequencies after moisture, and use the frequency domain characteristic curve tanδ-f of the dielectric loss tangent as the evaluation basis to extract various characteristic parameters and establish a quantitative relationship between them and the moisture content in the insulation. Based on this, the principle of step 101 in the above embodiment is:

[0053] From the perspective of dielectric theory, for linear solid materials, the relationship between the volume current density J, the electric field intensity E and the conductivity σ is shown in formula (1):

[0054] J=E·σ (1)

[0055] For polymer materials, due to the nonlinear conductivity process of different fillers and matrix structures inside, the process is not dominated by a single mechanism, but by the combined action of multiple conductive mechanisms. Relevant studies have shown that when damp oil-paper insulation is subjected to an external electric field, the Poole-Frenkel effect will occur, and its conductivity and electric field strength show a nonlinear relationship, characterized by ln(σ) and E 1 / 2 In this case, the relationship between the oil-paper insulation conductivity σ and the electric field strength E can be described by formula (2):

[0056]

[0057] When the sinusoidal excitation voltage U = Asin(ωt), equation (3) can be introduced to describe the nonlinear characteristics of oil-paper insulation, and its UI characteristic relationship is as follows:

[0058]

[0059] By analyzing formula (2), we can find that when the domain is x∈(-∞,+∞), f(ωt) is an odd function with a period of 2π. By performing Fourier series expansion on it and using the function properties of f(ωt), we can obtain:

[0060]

[0061] When n = 2k, bn can be rewritten as:

[0062]

[0063] Therefore, when n is an even number (n = 2, 4, ...), b n =0, that is, there are only odd-order terms in equation (6). Combining equations (4) to (7), the Fourier series expansion of equation (3) can be rewritten as equation (8):

[0064]

[0065] In summary, f(ωt) contains only the odd-order terms of sin(ωt), sin(3ωt), …. As n increases, b n The third harmonic is dominant among the harmonics. Therefore, the moisture content of oil-paper insulation can be evaluated based on its nonlinear characteristics after being damp.

[0066] Represented by the US MEGGER Company and Austrian OMICRON Company, commercial insulation diagnostic analyzers have been developed to realize the evaluation of the moisture content of insulation in transformers on site. However, the insulation structure in the transformer is complex, and the composite insulation structure such as oil channels and barriers has a great influence on the tanδ-f curve. The on-site test needs to use the XY model to convert the test data into equivalent results of a single-layer insulation cardboard, so that it can be compared with the database established by the laboratory based on the test results of a single-layer cardboard to obtain the moisture results. However, the values ​​of X and Y have a great influence on the evaluation results, and in most cases it is difficult to determine the accurate values ​​of X and Y of the transformer insulation structure, which makes the evaluation results of this method have great uncertainty. Existing studies regard oil-paper insulation as a linear system, focusing on the phase difference between the voltage and current fundamental waves, but not considering the voltage-variable and frequency-variable characteristics of the response current waveform. Studies have shown that oil-paper insulation will exhibit nonlinear characteristics under certain conditions, and the response current under sinusoidal excitation has odd harmonic components and no longer presents a standard sinusoidal waveform. Therefore, further searching for new characteristic parameters that are not limited by the complex insulation structure of the transformer and that can sensitively reflect the moisture state of the internal insulation in combination with the nonlinear characteristics of the oil-paper insulation is the key to promoting the application of this technology in engineering. The embodiment of this application uses the per-unit value processing method to solve this problem, as follows.

[0067] In this embodiment, oil-impregnated paper samples with different moisture contents were prepared. The insulating paperboard used was Weidmann 1mm thick cellulose insulating paperboard, and the insulating oil was 25# Karamay mineral oil. The preparation process was as follows: the insulating paperboard and the insulating oil were placed in a vacuum environment of 90℃ / 50Pa and dried for 48 hours, and then the insulating paperboard was impregnated with oil and placed in a vacuum drying oven for 48 hours to obtain a dry oil-paper insulation sample. The initial moisture content of the dry paperboard was measured by Karl Fischer titration, and the initial weight of the dry paperboard was weighed by weighing, and the expected weight of the paperboard after moisture absorption was calculated. Then the paperboard was placed in the air, and after natural moisture absorption for different times, the expected weight was reached by combining weighing and Karl Fischer titration. Then, the insulating paperboard was put back into the insulating oil and left for 48 hours to balance the moisture between the oil and paper. Finally, insulating paperboard samples with moisture contents mc of 1.04%, 2.03%, 3.02%, and 4.06% were prepared.

[0068] Combination Figure 2 The structure of the three electrodes is connected, and a voltage of U is applied to the high voltage electrode end of the insulating paper sample. m , the sinusoidal excitation voltage u(t) = U m sin(2πf0t), corresponding to the electric field strength E m , the total response current flowing through the sample in the detection measuring electrode is i(t).

[0069] This section will discuss the moisture content, excitation signal frequency f0 and electric field strength E m Three factors affect the oil-paper insulation response current waveform.

[0070] ①Influence of moisture content

[0071] Figure 3 Given E m =2000V / mm, f0 = 0.01Hz sinusoidal excitation u(t), the total response current i(t) waveform of oil-paper insulation samples with different moisture contents, and the fundamental component i is extracted by FFT (Fast Fourier Transform) of the response current fund (t), Figure 3 (a), (b), (c), and (d) are the voltage u(t), total response current i(t), and response current fundamental wave i(t) when mc=1.04%, mc=2.03%, mc=3.02%, and mc=4.06%, respectively. fund (t) waveform diagram.

[0072] It can be seen that when the moisture content is low, the total response current waveform is similar to a standard sine wave, and the current fundamental component basically coincides with the total current waveform; as the moisture content increases, the response current waveform gradually becomes distorted, and at a moisture content of 4.06%, the waveform has become severely distorted.

[0073] ②Influence of excitation signal frequency f0

[0074] Set the electric field strength E m =2000V / mm, test the response current of different frequencies f0 of damp oil-paper insulation. Taking 3.02% moisture content insulation paperboard as an example, the waveforms of voltage, total response current and fundamental wave of response current under different frequencies f0 excitation are as follows: Figure 4 As shown, Figure 4 (a), (b), (c), and (d) are the voltage u(t), total response current i(t), and response current fundamental wave i(t) when f0 = 0.01 Hz, f0 = 0.1 Hz, f0 = 1 Hz, and f0 = 10 Hz, respectively. fund (t) waveform diagram.

[0075] Depend on Figure 4 It can be seen that when the frequency is high, the response current waveform of the sample to be tested is not distorted, and the extracted response current fundamental wave basically coincides with the response current; while under low-frequency excitation, the time domain waveform of the response current will produce obvious distortion, that is, the lower the frequency of the excitation signal, the more serious the distortion of the response current waveform.

[0076] ③Electric field strength amplitude E m Impact

[0077] Set the excitation signal frequency f0 = 0.01Hz, and test the different electric field strengths E of damp oil-paper insulation m Taking 3.02% moisture content insulation paperboard as an example, the different electric field strengths E m The waveforms of the voltage, total response current and fundamental wave of the response current are as follows: Figure 5 As shown, Figure 5 (a), (b), (c), and (d) are E m =200V / mm, E m =800V / mm, E m =1600V / mm, E m = Voltage u(t), total response current i(t), response current fundamental wave i when 2000V / mm fund (t) waveform diagram.

[0078] Depend on Figure 5 It can be seen that under different electric field strengths, the response current waveform of the sample to be tested is distorted to a certain extent, and as the electric field strength increases, the distortion of the time domain waveform of the response current becomes more obvious.

[0079] From the above test results, it can be seen that when the oil-paper insulation is seriously damp, the response current of the sample will be distorted, and as the moisture content increases, the applied electric field strength increases, and the frequency decreases, the distortion of the response current waveform will also increase. The following will further analyze the harmonic components of the response current and explore its correlation with the dampness of the oil-paper insulation sample.

[0080] ④ Characteristic parameters of the damp state of oil-paper insulation

[0081] Figure 6 The proportion of each harmonic component of the response current of the insulation samples with different moisture levels at frequency f0 = 0.01Hz and different electric field strengths is β k , Figure 6 (a), (b), (c), and (d) are the β values ​​of damp insulation paperboard with mc = 1.04%, mc = 2.03%, mc = 3.02%, and mc = 4.06%, respectively. kSchematic diagram of the change rule. It can be seen that when the moisture content is low, that is, when mc = 1.04%, the proportion of each harmonic is very small, below 0.3%. When the moisture content increases, the content of each harmonic increases, and the more obvious harmonic current components are odd harmonics, among which the third harmonic β3 accounts for the highest proportion. Even at low electric field strength, the β3 of the mc = 2.03% sample is higher than 0.5%. It can also be seen that when the moisture content increases, the amplitude of the electric field strength has a significant effect on the nonlinear characteristics of oil-paper insulation.

[0082] From the above analysis, it can be seen that moisture is the main factor causing the oil-paper insulation to exhibit nonlinear characteristics. When the oil-paper insulation exhibits nonlinear characteristics due to moisture, the electric field strength E m The frequency f0 will strengthen the nonlinear characteristics of oil-paper insulation. At the same time, although the electric field strength and sample moisture content have a certain influence on each harmonic component, β3 shows an obvious positive correlation.

[0083] The actual transformer main insulation structure is more complex than the single-layer oil-paper insulation, and is composed of partitions, stays, oil channels, etc. In order to study the quantitative relationship between the degree of moisture in oil-paper insulation and the current harmonic characteristics, the influence of the field strength difference caused by different dielectric thickness on the β3 parameter is considered, and equation (9) is used for per-unit value processing.

[0084]

[0085] In the formula, β 3-Dry is the third harmonic proportion of the drying paperboard, β * 3 is the per-unit value of the third harmonic.

[0086] For different oil-paper insulation structures, the following are usually used: Figure 7 The XY model shown is for the partition ( Figure 7 (a) in), gasket ( Figure 7 (b)) and oil passages (insulating oil, Figure 7 In which, X represents the ratio of the total thickness of the partition to the thickness of the main insulation, and Y represents the ratio of the total width of the stay to the average circumference between the windings (usually X and Y parameters are taken as 0.1 to 0.5). Figure 7 (d), (e), (f), and (g) are XY models when X=1, Y=0, X=0.5, Y=0.5, X=0.5, Y=0.22, and X=0.33, Y=0.22, respectively.

[0087] The expressions of X and Y parameters are shown in equations (10) and (11):

[0088]

[0089] In the formula, d1 represents the total thickness of the circular insulating paperboard (equivalent to the partition part), d2 represents the total thickness of the annular insulating paperboard (equivalent to the strut part), r1 represents the outer diameter of the annular insulating paperboard in contact with the measuring electrode, and r2 represents the inner diameter of the annular insulating paperboard. By changing the number of strut layers and the inner diameter, the main insulation model with different X and Y values ​​can be obtained.

[0090] Four insulating structure samples with different X and Y values ​​were prepared in the laboratory, structures A to D, and their harmonic characteristics of the response current were tested, such as Fig.12 The four different insulation structures are simulated by changing the number of layers and inner diameter of the paperboard to simulate the main insulation model with different X and Y values. The moisture content of the samples is shown in Table 1.

[0091] Table 1 Water content in paper of different insulation structure samples (%)

[0092] Model mc1 mc2 mc3 mc4 A 1.04 2.03 3.02 4.06 B 1.05 2.05 3.03 4.12 C 1.02 2.06 3.05 4.03 D 1.09 2.05 3.08 4.17

[0093] For four different insulation structure samples, the total response current i(t) is obtained under the sinusoidal excitation with a voltage amplitude of 2000V and a moisture content of mc1, mc2, mc3, and mc4, and the proportion of the 2nd to 10th harmonics is calculated, as shown in the figure. Figure 8 As shown, Figure 8 (a), (b), (c), and (d) are schematic diagrams of the proportion of each harmonic of the insulation structure samples A, B, C, and D. It is found that the harmonic components are mainly odd harmonics, and the proportion of the third harmonic component β3 is particularly prominent, which is positively correlated with the moisture content mc.

[0094] Combined with formula (9), β3 is normalized to per unit value, and the relationship between moisture content mc and β is fitted by formula (12). * 3, the fitting curve results are as follows Fig. 9 shown.

[0095]

[0096] Where M and N are fitting parameters.

[0097] observe Fig. 9 It can be found that the characteristic quantity β * There is an obvious power function relationship between 3 and mc. At the same time, when the moisture level of the samples is close, the β between different structural insulation systems * 3 The difference is small, β * 3 changes with mc and is basically the same as that of single-layer paperboard (Model a). * The functional relationship between 3 is shown in (13).

[0098]

[0099] The implementation principle of the evaluation method described in step 104 is as follows.

[0100] The diagnostic process of the damp state of oil-paper insulation is as follows: Fig.10 First, an AC voltage excitation with a frequency of 0.01 Hz and an amplitude of 2000 V is applied to the oil-paper insulation to test its dielectric response current, and the fundamental waveform of the response current and the characteristic quantity β are extracted through FFT transformation. * 3. Then calculate the specific moisture content according to the fitting relationship between characteristic parameters and moisture content, β * Substitute the value of 3 into formula (13) to calculate the specific water content.

[0101] The above embodiment proposes the mc and β of different insulating oil papers. * 3, this application will further prepare a transformer main insulation equivalent model with a cylindrical complex structure, such as Fig.11 As shown, Fig.11 (a) is the front view of the transformer main insulation equivalent model. Fig.11 (b) is a top view of the transformer main insulation equivalent model, which is intended to further verify the β * 3. The correlation law between the moisture degree of oil-paper insulation and the actual insulation structure. Among them, the main insulation equivalent model shell, high-voltage electrode, test electrode and shielding electrode are all made of stainless steel. During the test, vacuum-dried insulating oil is injected, and the high and low voltage windings and insulating paperboard are fully immersed.

[0102] Oil-paper insulation samples with moisture contents of 1.56%, 2.53%, 3.61% and 4.52% were prepared. By changing the number of partitions and stays, three transformer equivalent models with different insulation structures were obtained, namely structures I, II and III, as shown in Table 2.

[0103] Table 2 Transformer main insulation equivalent model structural parameters

[0104]

[0105]

[0106] A sinusoidal excitation with a voltage amplitude of 2000 V and a frequency of 0.01 Hz was applied to the above samples to obtain the harmonic characteristics of the response current i(t). The sample moisture content evaluation results calculated using formula (13) were compared with the actual values. Fig.12 Although there are some differences between the evaluation results of moisture content and the measured results, the overall law is consistent with the above experimental phenomenon, which further proves the feasibility of the evaluation method proposed in the present invention.

[0107] Based on the same inventive concept, the embodiment of the present application also provides a device for evaluating the moisture state of oil-paper insulation based on nonlinear characteristics. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiments of one or more devices for evaluating the moisture state of oil-paper insulation based on nonlinear characteristics provided below can refer to the limitations of the method for evaluating the moisture state based on nonlinear characteristics of oil-paper insulation above, and will not be repeated here.

[0108] In an exemplary embodiment, Fig.13 As shown, a device for evaluating the moisture state of oil-paper insulation nonlinear characteristics is provided, which includes: a signal generator, a voltage amplification module, a current amplification module, a signal acquisition module and a host computer.

[0109] The device for evaluating the moisture state of oil-paper insulation nonlinear characteristics in this embodiment has the function of emitting variable frequency, variable voltage sinusoidal excitation voltage and collecting current, so a signal generation module and a signal collection module are required. Considering that the test object is capacitive, the impedance value is large under low frequency excitation, and the response current signal is weak, the test platform adds a voltage amplification module and a current amplification module.

[0110] The signal generation module mainly includes a signal generator. The signal generator is Keysight 33500B, which can generate a custom sine signal with an amplitude of 0 to ±10V and a frequency of 1μHz to 1MHz. Since the impedance of the actual oil-paper insulation is very large, even reaching more than 10GΩ under low-frequency excitation, and the voltage amplitude output from the signal generator is only a few volts, the amplitude of the measured response current is usually weak and easily interfered by the surrounding environmental noise.

[0111] In order to ensure that the response current and excitation voltage flowing through the sample can be effectively measured, it is also necessary to add a voltage amplifier module to linearly amplify the excitation voltage and then apply it to the insulation to be tested. The voltage amplifier module selects the Trek-Model-2220 power amplifier, which has the function of amplifying the voltage input signal by 200 times, and also has high-voltage amplification and monitoring functions. The maximum bias voltage does not exceed 1V, and the voltage ripple does not exceed 50mV. Altai's PXI-8512B is selected as the signal collector, which can monitor the voltage signal amplified by the amplifier and synchronously collect the current signal. The independently developed and designed current amplifier module consists of two parts: the current amplifier circuit and the filter circuit. The use of relays can realize the flexible switching of multi-gear amplification factors. In addition, the module uses multiple sets of filter capacitors and sampling resistors to form a filter circuit that can meet the requirements of different cut-off frequencies.

[0112] The working process of the device for evaluating the moisture state of oil-paper insulation nonlinear characteristics is as follows: Fig.13As shown: First, the voltage amplitude and frequency required for the test are set on the host computer, and the host computer controls the signal generator to emit standard sinusoidal voltages of different frequencies and amplitudes in turn. The sinusoidal voltage amplitude at this time is 0~±10V, and then it is amplified 200 times by the high-voltage amplifier module. One end of the amplified excitation voltage is applied to the high-voltage electrode of the sample under test, and the other end flows through the monitoring circuit of the high-voltage amplifier module itself, and the amplified monitoring voltage data is collected by the signal acquisition module. The measurement signal output by the three-electrode measurement end also needs to pass through the current amplifier module. First, the relay switches the gear to match the sampling resistors of different resistance values, converts the response current signal into a voltage signal, and then the current amplifier module amplifies it to the range that the signal acquisition module can collect. Since the test site cannot avoid the existence of external interference signals, after the measurement signal is amplified, it needs to be filtered by the filter circuit, and then the measurement signal is digitized by the signal acquisition module and sent to the host computer, and finally the complete current time domain waveform can be obtained. This hardware test system can output a voltage range of 0 to ±2000V, a frequency range of 1mHz to 7.5kHz, and can collect a response current amplitude range of ±5pA to ±5mA.

[0113] In order to facilitate the replacement of the test site and transportation to the site for testing, the present application encapsulates the hardware structure of the dielectric response current test system to improve the integration of the test system. Fig.13 As shown in the figure, since there is usually complex electromagnetic interference in the on-site test environment, the packaging shell of the test system is made of aluminum alloy and equipped with grounding contacts to maintain good grounding during the test and play a role in electrostatic shielding.

[0114] The specific selection of hardware for the moisture state evaluation device of oil-paper insulation nonlinear characteristics is as follows:

[0115] (1) Signal generation module

[0116] The signal generation module uses the 33500B waveform generator manufactured by Keysight, which can generate a variety of waveforms, including sine waves, square waves, pulse waves, triangle waves, etc. The Trueform signal generation technology used by Keysight 33500B has more advantages than traditional direct digital synthesis technology, including low jitter, fast edge time, high fidelity, etc. It has more advantages than traditional DDS generators in functionality, fidelity and flexibility. In this experiment, it can stably output a standard sine waveform adjustable within 0 to 10V to ensure the quality of the excitation signal without affecting the response current test results.

[0117] The specific technical parameters are as follows:

[0118] ① High sampling rate: The sampling rate is as high as 250MSa / s, which can provide arbitrary waveforms with higher time resolution;

[0119] ② High resolution: The output voltage has a 16-bit resolution, and the minimum output voltage amplitude can be as low as 1mV;

[0120] ③ High bandwidth: The output voltage frequency range is wide, with an upper limit of up to 30MHz and a lower limit of 1μHz, and an accuracy of up to 15pHz. Within the entire bandwidth range, the system supports internal modulation to generate complex signal outputs;

[0121] ④Low distortion: extremely low total harmonic distortion characteristics, the value is less than 0.04%, can output stable standard waveform, high fidelity can eliminate the interference of external noise on test results;

[0122] ⑤ Low jitter: With an edge jitter characteristic of less than 40μs, this advantage ensures the high accuracy of the output waveform in terms of edge and triggering, thereby enhancing the accuracy and stability of the output waveform;

[0123] ⑥ Connectivity: It is easier and more convenient to connect to a PC or network, and it has multiple interfaces including USB, LAN (LXI-C), and GPIB standard interfaces.

[0124] (2) Voltage amplifier module

[0125] The voltage amplifier module uses the model-2220 high-voltage power amplifier produced by Trek, which has a power of 40W and can output a sinusoidal voltage with a maximum amplitude of 2000V. In this experiment, it can linearly amplify the excitation voltage within 10V emitted by the signal generation module by 200 times. This device has high cost performance and higher performance, with advantages such as high stability, wide bandwidth, small voltage ripple, and fast boost speed.

[0126] The specific technical parameters are as follows:

[0127] ① High stability: Temperature changes will affect the accuracy of the amplifier output value. The temperature drift of Trek model-2220 during operation is less than 180ppm / ℃, and the time drift is less than 300ppm / hr. High stability can ensure that this test platform can maintain a stable operating state even in different test environments or long-term continuous working conditions, ensuring that the output waveform quality is not affected in any way;

[0128] ② Wideband: DC to 7.5kHz wideband output, can meet the frequency requirements of the test;

[0129] ③ Small voltage ripple: the output voltage range is 0-2000V, the error is less than 1V, the DC bias is less than 0.05%, and the output noise is less than 50mV;

[0130] ④Fast boost speed: The output voltage boost speed of Trek model-2220 is greater than 100V / μs, and the response time is extremely fast. The efficient boost speed and extremely short response time can ensure the accuracy of the output waveform and have little impact on the measurement results.

[0131] (3) Current Amplification Module

[0132] Since the actual response current is small, when the response current is lower than the minimum resolution of the acquisition circuit, the response current waveform cannot be effectively acquired. Therefore, the main function of the current amplifier module is to convert the response current into a voltage signal and amplify it to an amplitude that the acquisition circuit can recognize in order to perform effective data acquisition. At the same time, under low-frequency conditions, the response current is often small, and when the on-site interference noise is too large, the effective signal is easily submerged by the noise. Therefore, in order to avoid the interference caused by various noises during on-site testing and to ensure that the signal collected by the signal collector is the response current passing through the tested insulation sample, a filter circuit must be added to the current amplifier module to filter the current signal.

[0133] The filter circuit uses a first-order RC low-pass filter circuit, whose main function is to remove high-frequency noise from the input signal and smooth the signal. The filtering principle and the amplifier circuit principle are as follows: Fig.14 As shown. During the platform construction process, the filtering effect of using a cutoff frequency that is more than 10 times the signal frequency is not ideal. However, considering that the closer the filter circuit cutoff frequency is to the signal frequency, the easier it is for the filtered signal to attenuate, the cutoff frequency of the RC filter circuit is selected to be 10 times the signal frequency based on the actual test results. In the hardware circuit, the low-pass filter cutoff frequency fcutoff is jointly determined by R1 and C1, as shown in formula (14). Interference noise signals higher than the cutoff frequency will be effectively filtered out, while the collected response current signal frequency can pass without distortion because it is lower than the cutoff frequency. The resistance value of the sampling resistor R1 is determined according to the size of the response current to realize the conversion of the current signal into a voltage form, which is then amplified in two stages and finally transmitted to the signal acquisition module. The gear position of the filter capacitor C1 is then determined according to the size of the cutoff frequency.

[0134]

[0135] In the actual test process, it is usually necessary to apply voltage excitations of different amplitudes and frequencies. The impedance of the oil-paper insulation is different at different frequencies, and the response current will differ by orders of magnitude. Therefore, it is necessary to use relays to achieve automatic gear switching to match amplifier circuits with different amplification factors. At the same time, the filter circuit also needs to select filter circuits of different gears according to different excitations, that is, select R1 and C1 with different values.

[0136] This application designs a current amplification module with nine amplification levels, with a minimum amplification factor of 10 2 , the maximum magnification is 10 10 Among them, the upper circuit board is equipped with nine sampling resistors and relays to realize the switching of nine-speed amplification factors, and uses six filter capacitors with different capacitance values ​​and relays to cooperate to achieve the adjustment of different amplification factors.

[0137] (4) Signal acquisition module

[0138] The voltage excitation output by the voltage amplifier and the response current flowing through the insulation sample under test are both analog signals. In order to display the time domain waveforms and data of voltage and current on the host computer for further analysis of the response current, it is necessary to use a signal acquisition module to convert the voltage excitation or response current from analog signals to digital signals.

[0139] The analog-to-digital converter is the core part of the data acquisition card. It converts analog signals into digital signals. Its accuracy and speed depend on parameters such as resolution, sampling rate and conversion time. The sampling rate refers to the number of samples extracted from a continuous signal and converted into a discrete signal per unit time (1 second). Generally speaking, the higher the resolution of the signal acquisition card, the faster the sampling rate, and the shorter the conversion time, the higher its accuracy and speed. In order to ensure the authenticity and integrity of the signal, the signal acquisition card used should have a higher resolution and sampling rate, as well as a shorter response time. The embodiment of the present application uses PXI-8512B under Altai as a signal acquisition card, which can monitor the voltage signal amplified by the amplifier and synchronously collect current signals. The acquisition range of the current signal is ±5pA~±5mA, and the error is less than 2%.

[0140] The specific technical parameters are as follows:

[0141] ① Sampling rate: The maximum sampling rate is 80Ms / s, which can ensure high-speed and high-precision acquisition of signals;

[0142] ② Resolution: The resolution of PXI-8512B is 12 bits, which can distinguish the slight change of 2mV;

[0143] ③Response time: The shorter the response time, the smaller the impact on data acquisition. The response time of PXI-8512B does not exceed 10μs, and the impact on the test results can be ignored;

[0144] ④Analog bandwidth: The larger the range of signal frequency variation, the wider the required signal bandwidth. The analog bandwidth of PXI-8512B is up to 40MHz, which can meet the requirements of all test frequencies in this experiment.

[0145] ⑤Number of channels: 4 channels, which can realize synchronous acquisition of multiple signals.

[0146] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Fig.15 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. The processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store moisture state assessment method data. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a moisture state assessment method based on the nonlinear characteristics of oil-paper insulation is implemented.

[0147] Those skilled in the art will understand that Fig.15 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components. In an exemplary embodiment, a computer device is provided, including a memory and a processor, wherein a computer program is stored in the memory, and the processor implements the steps in the above-mentioned method embodiments when executing the computer program.

[0148] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0149] In an exemplary embodiment, a computer program product is provided, including a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0150] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0151] Those of ordinary skill in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM).

[0152] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0153] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0154] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for evaluating the moisture state of oil-paper insulation based on nonlinear characteristics, characterized in that: include: Obtain the proportion of the third harmonic component of the response current of the oil-paper to be tested under the preset excitation signal; Obtaining the proportion of the third harmonic component of the response current of the dry paperboard having the same size parameters and material parameters as the oil paper to be tested under a preset excitation signal; Based on the proportion of the third harmonic component of the response current of the dry paperboard under the preset excitation signal, the proportion of the third harmonic component of the response current of the oil paper to be tested under the preset excitation signal is processed in per unit value to obtain the third harmonic per unit value of the response current of the oil paper to be tested under the preset excitation signal; According to the third harmonic standard value of the response current of the oil paper to be tested under the preset excitation signal, the moisture content of the oil paper to be tested is calculated using a functional relationship; the functional relationship represents the relationship between the third harmonic standard value of the response current of the oil paper to be tested under the preset excitation signal and the moisture content, and the moisture content represents the moisture state of the oil paper to be tested.

2. The method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation according to claim 1 is characterized in that: The formula for per-unit value processing is: in, is the third harmonic per unit value of the response current of the oil-paper to be tested under the preset excitation signal, β3 is the proportion of the third harmonic component of the response current of the oil-paper to be tested under the preset excitation signal, β 3-Dry It is the proportion of the third harmonic component of the response current of the dry paperboard under the preset excitation signal.

3. The method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation according to claim 1 is characterized in that: The functional relationship is: in, is the third harmonic per unit value of the response current of the oil-paper to be tested under the preset excitation signal, mc is the moisture content of the oil-paper to be tested, and M and N are fitting parameters.

4. The method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation according to claim 1 or 3, characterized in that: The functional relationship is: in, is the third harmonic per unit value of the response current of the oil-paper to be tested under the preset excitation signal, and mc is the moisture content of the oil-paper to be tested.

5. A device for evaluating the moisture state of oil-paper insulation nonlinear characteristics, characterized in that: include: Signal generator, voltage amplification module, current amplification module, signal acquisition module and host computer; The host computer is connected to the control end of the signal generator, the signal generator is connected to the voltage amplifier, the voltage amplifier is connected to the oil paper to be tested, and the host computer is used to control the signal generator to send a preset excitation signal; The current amplification module is connected to the oil paper to be tested, and the current amplification module is also connected to the signal acquisition module, and the signal acquisition module is connected to the host computer; The host computer is used to calculate the moisture content of the oil-paper to be tested according to the response current of the oil-paper to be tested under the preset excitation signal collected by the signal acquisition module, using the moisture state assessment method based on the nonlinear characteristics of oil-paper insulation as described in any one of claims 1-4.

6. A computer device comprising: A memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the moisture state assessment method based on the nonlinear characteristics of oil-paper insulation as described in any one of claims 1 to 4.

7. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation described in any one of claims 1 to 4 is implemented.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method for evaluating the moisture state based on the nonlinear characteristics of oil-paper insulation described in any one of claims 1 to 4 is implemented.

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